Autism: A Unique Type of Mercury Poisoning

Sallie Bernard (sbernard@nac.net)
Albert Enayati, B.S., Ch.E., M.S.M.E.**
Teresa Binstock
Heidi Roger
Lyn Redwood, R.N., M.S.N., C.R.N.P.
Woody McGinnis, M.D.

April 3, 2000
Revision of April 21, 2000

Abstract

Autism is a syndrome characterized by impairments in social relatedness, language and communication, a need for routine and sameness, abnormal movements, and sensory dysfunction. Mercury (Hg) is a toxic metal that can exist as a pure element or in a variety of inorganic and organic forms and can cause immune, sensory, neurological, motor, and behavioral dysfunctions similar to traits defining or associated with autism. Thimerosal, a preservative frequently added to childhood vaccines, has become a major source of Hg in human infants and toddlers. According to the FDA and the American Academy of Pediatricians, fully vaccinated children now receive, within their first two years, Hg levels that exceed safety limits established by the FDA and other supervisory agencies. A thorough review of medical literature and U.S. government data indicates (i) that many and perhaps most cases of idiopathic autism, in which an extended period of developmental normalcy is followed by an emergence of symptoms, are induced by early exposure to Hg; (ii) that this type of autism represents a unique form of Hg poisoning (HgP); (iii) that excessive Hg exposure from thimerosal in vaccine injections is an etiological mechanism for causing the traits of autism; (iv) that certain genetic and non-genetic factors establish a predisposition whereby thimerosal's adverse effects occur only in some children; and (v) that vaccinal Hg in thimerosal is causing a heretofore unrecognized mercurial syndrome.

Synopsis

A review of medical literature indicates that the characteristics of autism and of mercury poisoning (HgP) are strikingly similar. Traits defining or associated with both disorders are summarized in Table A immediately following the Table of Contents and are discussed and cited in the body of this document. The parallels between the two diseases are so thorough as to suggest, based on total Hg injected into U.S. children, that many cases of autism are a form of mercury poisoning.

For these children, the exposure route is childhood vaccines, most of which contain thimerosal, a preservative which is 49.6% ethylmercury by weight. The amount of mercury a typical child under two years receives from vaccinations equates to 237.5 micrograms, or 3.53 x 1017 molecules (353,000,000,000,000,000 molecules). Most such vaccinal Hg may not be excreted and instead migrates to the brain.

The total amount injected into infants and toddlers (i) is known to exceed Federal safety standards, (ii) is officially considered to be a “low” level; whereby (iii) only a small percentage of exposed individuals exhibit symptoms of toxicity. In fact, children who develop Hg-related autism are likely to have had a predisposition derived from genetic and non-genetic factors.

Importantly, the timings of vaccinal Hg-exposure and its latency period coincide with the emergence of autistic-symptoms in specific children. Moreover, excessive mercury has been detected in urine, hair, and blood samples from autistic children; and parental reports, though limited at this date, indicate significant improvement in symptoms subsequent to heavy-metal chelation therapy.

The HgP phenotype is diverse and depends upon a number of factors - including type of Hg, route of entry into the body, rate and level of dose, individual genotype, and the age and immune status of the patient. Historically, variation among these factors has caused slightly different manifestations of mercurialism; Mad Hatter’s disease, Minamata disease, acrodynia, and industrial exposures provide examples.

The pathology arising from the mercury-related variables involved in autism - intermittent bolus doses of ethylmercury injected into susceptible infants and toddlers - is heretofore undescribed in medical literature. Therefore, in accord with existing HgP data and HgP’s ability to induce virtually all the traits defining or associated with autism spectrum disorders, we hypothesize that many and perhaps most cases of autism represent a unique form of mercury poisoning.

This conclusion and its supporting data have important implications for the affected population of autistic individuals and their families, for other unexplained disorders with symptoms similar to those of heavy metal intoxication, for vaccine content, and for childhood vaccination programs. Due to its high potential for neurotoxicity, thimerosal should be removed immediately from all vaccine products designated for infants and toddlers.

Abstract & Synopsis
Table of Contents
Autism-Mercurialism Comparisons

Introduction
Autism
Mercury
Diagnosing Mercury Poisoning in Autism

I. Symptom Comparison
a. Affect/Psychological Presentation
b. Language & Hearing
c. Sensory Perception
d. Movement/Motor Function
e. Cognition/Mental Function
f. Behaviors
g. Vision
h. Physical Presentations
j. Gastrointestinal Function

II. Comparison of Biological Abnormalities
a. Biochemistry
b. Immune System
c. CNS Structure
d. Neurons & Neurochemicals
e. EEG Activity/Epilepsy

III. Mechanisms, Sources & Epidemiology of Exposure
a. Exposure Mechanism
b. Population Susceptibility
c. Sex Ratio
d. Exposure Levels & Autism Prevalence
e. Genetic Factors
f. Course of Disease
g. Thimerosal Interaction with Vaccines

IV. Detection of Mercury in Autistic Children
Case Studies
Discussion

Discussion

Diagnostic Criteria Are Met
Unique Form Would be Expected, Implicates Vaccinal Thimerosal
Historical Precedent Exists
Barriers Preventing Earlier Discovery Are Removed

Medical & Societal Implications

Affected Population
Other Disorders
Vaccination Programs

References

Table A:
Summary Comparison of Characteristics
of Autism & Mercury Poisoning < tr> < tr>

Mercury Poisoning	Autism
*Psychiatric Disturbances*
Social deficits, shyness, social withdrawal	Social deficits, social withdrawal, shyness
Depression, mood swings; mask face	Depressive traits, mood swings; flat affect
Anxiety	Anxiety
Schizoid tendencies, OCD traits	Schizophrenic & OCD traits; repetitiveness
Lacks eye contact, hesitant to engage others	Lack of eye contact, avoids conversation
Irrational fears	Irrational fears
Irritability, aggression, temper tantrums	Irritability, aggression, temper tantrums
Impaired face recognition	Impaired face recognition
Speech, Language & Hearing Deficits
Loss of speech, failure to develop speech	Delayed language, failure to develop speech
Dysarthria; articulation problems	Dysarthria; articulation problems
Speech comprehension deficits	Speech comprehension deficits
Verbalizing & word retrieval problems	Echolalia; word use & pragmatic errors
Sound sensitivity	Sound sensitivity
Hearing loss; deafness in very high doses	Mild to profound hearing loss
Poor performance on language IQ tests	Poor performance on verbal IQ tests
*Sensory Abnormalities*
Abnormal sensation in mouth & extremities	Abnormal sensation in mouth & extremities
Sound sensitivity	Sound sensitivity
Abnormal touch sensations; touch aversion	Abnormal touch sensations; touch aversion
Vestibular abnormalities	Vestibular abnormalities
Motor Disorders
Involuntary jerking movements - arm flapping, ankle jerks, myoclonal jerks, choreiform movements, circling, rocking	Stereotyped movements - arm flapping, jumping, circling, spinning, rocking; myoclonal jerks; choreiform movements
Deficits in eye-hand coordination; limb apraxia; intention tremors	Poor eye-hand coordination; limb apraxia; problems with intentional movements
Gait impairment; ataxia - from incoordination & clumsiness to inability to walk, stand, or sit; loss of motor control	Abnormal gait and posture, clumsiness and incoordination; difficulties sitting, lying, crawling, and walking
Difficulty in chewing or swallowing	Difficulty chewing or swallowing
Unusual postures; toe walking	Unusual postures; toe walking
*Cognitive Impairments*
Borderline intelligence, mental retardation - some cases reversible	Borderline intelligence, mental retardation - sometimes "recovered"
Poor concentration, attention, response inhibition	Poor concentration, attention, shifting attention
Uneven performance on IQ subtests	Uneven performance on IQ subtests
Verbal IQ higher than performance IQ	Verbal IQ higher than performance IQ
Poor short term, verbal, & auditory memory	Poor short term, auditory & verbal memory
Poor visual and perceptual motor skills, impairment in simple reaction time	Poor visual and perceptual motor skills, lower performance on timed tests
Difficulty carrying out complex commands	Difficulty carrying out multiple commands
Word-comprehension difficulties	Word-comprehension difficulties
Deficits in understanding abstract ideas & symbolism; degeneration of higher mental powers	Deficits in abstract thinking & symbolism, understanding other’s mental states, sequencing, planning & organizing
*Unusual Behaviors*
Stereotyped sniffing (rats)	Stereotyped, repetitive behaviors
ADHD traits	ADHD traits
Agitation, unprovoked crying, grimacing, staring spells	Agitation, unprovoked crying, grimacing, staring spells
Sleep difficulties	Sleep difficulties
Eating disorders, feeding problems	Eating disorders, feeding problems
Self injurious behavior, e.g. head banging	Self injurious behavior, e.g. head banging
Visual Impairments
Poor eye contact, impaired visual fixation	Poor eye contact, problems in joint attention
“Visual impairments,” blindness, near-sightedness, decreased visual acuity	“Visual impairments”; inaccurate/slow saccades; decreased rod functioning
Light sensitivity, photophobia	Over-sensitivity to light
Blurred or hazy vision	Blurred vision
Constricted visual fields	Not described
*Physical Disturbances*
Increase in cerebral palsy; hyper- or hypo-tonia; abnormal reflexes; decreased muscle strength, especially upper body; incontinence; problems chewing, swallowing, salivating	Increase in cerebral palsy; hyper- or hypotonia; decreased muscle strength, especially upper body; incontinence; problems chewing and swallowing
Rashes, dermatitis/dry skin, itching; burning	Rashes, dermatitis, eczema, itching
Autonomic disturbance: excessive sweating, poor circulation, elevated heart rate	Autonomic disturbance: unusual sweating, poor circulation, elevated heart rate
*Gastro-intestinal Disturbances*
Gastroenteritis, diarrhea; abdominal pain, constipation, “colitis”	Diarrhea, constipation, gaseousness, abdominal discomfort, colitis
Anorexia, weight loss, nausea, poor appetite	Anorexia; feeding problems/vomiting
Lesions of ileum & colon; increased gut permeability	Leaky gut syndrome
Inhibits dipeptidyl peptidase IV, which cleaves casomorphin	Inadequate endopeptidase enzymes needed for breakdown of casein & gluten
*Abnormal Biochemistry*
Binds -SH groups; blocks sulfate transporter in intestines, kidneys	Low sulfate levels
Has special affinity for purines & pyrimidines	Purine & pyrimidine metabolism errors lead to autistic features
Reduces availability of glutathione, needed in neurons, cells & liver to detoxify heavy metals	Low levels of glutathione; decreased ability of liver to detoxify heavy metals
Causes significant reduction in glutathione peroxidase and glutathione reductase	Abnormal glutathione peroxidase activities in erythrocytes
Disrupts mitochondrial activities, especially in brain	Mitochondrial dysfunction, especially in brain
*Immune Dysfunction*
Sensitivity due to allergic or autoimmune reactions; sensitive individuals more likely to have allergies, asthma, autoimmune-like symptoms, especially rheumatoid-like ones	More likely to have allergies and asthma; familial presence of autoimmune diseases, especially rheumatoid arthritis; IgA deficiencies
Can produce an immune response in CNS	On-going immune response in CNS
Causes brain/MBP autoantibodies	Brain/MBP autoantibodies present
Causes overproduction of Th2 subset; kills/inhibits lymphocytes, T-cells, and monocytes; decreases NK T-cell activity; induces or suppresses IFNg & IL-2	Skewed immune-cell subset in the Th2 direction; decreased responses to T-cell mitogens; reduced NK T-cell function; increased IFNg & IL-12
*CNS Structural Pathology*
Selectively targets brain areas unable to detoxify or reduce Hg-induced oxidative stress	Specific areas of brain pathology; many functions spared
Damage to Purkinje and granular cells	Damage to Purkinje and granular cells
Accummulates in amygdala and hippocampus	Pathology in amygdala and hippocampus
Causes abnormal neuronal cytoarchitecture; disrupts neuronal migration & cell division; reduces NCAMs	Neuronal disorganization; increased neuronal cell replication, increased glial cells; depressed expression of NCAMs
Progressive microcephaly	Progressive microcephaly and macrocephaly
Brain stem defects in some cases	Brain stem defects in some cases
*Abnormalities in Neuro-chemistry*
Prevents presynaptic serotonin release & inhibits serotonin transport; causes calcium disruptions	Decreased serotonin synthesis in children; abnormal calcium metabolism
Alters dopamine systems; peroxidine deficiency in rats resembles mercurialism in humans	Possibly high or low dopamine levels; positive response to peroxidine (lowers dopamine levels)
Elevates epinephrine & norepinephrine levels by blocking enzyme that degrades epinephrine	Elevated norepinephrine and epinephrine
Elevates glutamate	Elevated glutamate and aspartate
Leads to cortical acetylcholine deficiency; increases muscarinic receptor density in hippocampus & cerebellum	Cortical acetylcholine deficiency; reduced muscarinic receptor binding in hippocampus
Causes demyelinating neuropathy	Demyelination in brain
*EEG Abnormalities / Epilepsy*
Causes abnormal EEGs, epileptiform activity	Abnormal EEGs, epileptiform activity
Causes seizures, convulsions	Seizures; epilepsy
Causes subtle, low amplitude seizure activity	Subtle, low amplitude seizure activities
*Population Characteristics*
Effects more males than females	Male:female ratio estimated at 4:1
At low doses, only affects those geneticially susceptible	High heritability - concordance for MZ twins is 90%
First added to childhood vaccines in 1930s	First "discovered" among children born in 1930s
Exposure levels steadily increased since 1930s with rate of vaccination, number of vaccines	Prevalence of autism has steadily increased from 1 in 2000 (pre1970) to 1 in 500 (early 1990s), higher in 2000.
Exposure occurs at 0 - 15 months; clinical silent stage means symptom emergence delayed; symptoms emerge gradually, starting with movement & sensation	Symptoms emerge from 4 months to 2 years old; symptoms emerge gradually, starting with movement & sensation

Introduction

Autism

Autism, or Autistic Spectrum Disorder (ASD), is considered a neurodevelopmental syndrome, emerging early in life and exhibiting a constellation of seemingly unrelated features and a wide variation in symptom expression and level of severity by individual (Filipek et al, 1999; Bailey et al, 1996). The diagnostic criteria for autism are qualitative impairments in social relatedness, deficits in verbal and nonverbal communication, and the presence of repetitive and restricted behaviors or interests (APA, 1994). As will be cited below, other traits associated with autism are movement disorder, sensory dysfunction, and cognitive impairments as well as gastrointestinal difficulties and immune abnormalities (Gillberg & Coleman, 1992; Warren et al, 1990; Horvath et al, 1999). Onset must occur before age 36 months (APA, 1994); although in some instances deficits are apparent at birth, in the great majority of cases there are at least several months of normal development followed by clear regression or failure to progress normally (Gillberg & Coleman, 1992; Filipek et al, 1999; Bailey et al, 1996). Formerly regarded as a rare disease, autism is now said to affect one in 500 children (Bristol et al, 1996), with some estimates suggesting one in 100 for a broader phenotype often labeled as the "autism-spectrum" of disorders and which includes both higher and lower functioning individuals (Arvidsson et al, 1997; Wing, 1996).

Autism and autistic symptoms can arise from a number of known disorders, most notably tuberous sclerosis, Rhett syndrome, Landau-Kleffner syndrome, Fragile X, Phenylketonuria, purine autism, and other purine metabolic diseases such as PRPP synthetase defects and 5'-nucleotidase superactivity. The etiology and pathogenesis of the vast majority of autism cases - 70% - 90% (Gillberg and Coleman, 1992; Bailey et al, 1996) - remain unexplained, however, despite ASD being "one of the most extensively studied disorders in child psychiatry today" (Malhotra and Gupta, 1999). Nevertheless, there is general agreement that most cases of autism arise "from the interaction of an early environmental insult and a genetic predisposition" (Trottier et al, 1999; Bristol et al, 1996).

Mercury

A heavy metal, mercury (Hg) is widely considered one of the most toxic substances on earth (Clarkson, 1997). Instances of Hg poisoning or "mercurialism" have been described since Roman times. The Mad Hatter in Alice in Wonderland was a victim of occupational exposure to mercury vapor, referred to as "Mad Hatter's Disease." Further human data has been derived from instances of widespread poisonings during the 20th Century. These misfortunes include an outbreak in Minamata, Japan, caused by consumption of contaminated fish and resulting in "Minamata Disease;" outbreaks in Iraq, Guatemala and Russia due to ingestion of contaminated seed grains; and, in the first half of the century, poisoning of infants and toddlers by mercury in teething powders, leading to acrodynia or Pink Disease. Besides these epidemics, numerous instances of individual or small group cases of Hg intoxication and subsequent phenotype are described in the literature.

The constellation of mercury-induced symptoms varies enormously from individual to individual. The diversity of disease manifestations derives from a number of interacting variables which are summarized in Table I. The variables which affect phenotype include an individual's age, the total dosage, dose rate, duration of exposure, type of mercury, routes of exposure such as inhaled, subcutaneous, oral, or intramuscular, and, most importantly, by individual sensitivity arising from immune and genetic factors (Dales, 1972; Koos and Longo, 1976; Matheson et al, 1980; Eto et al, 1999; Feldman, 1982; Warkany and Hubbard, 1953).

Table I: Summary of Mercury Exposure Variables
Leading to Diverse & Non-Specific Symptomatology

Variable	Level of Variable
Exposure Amount	Ranges from high doses, leading to death or near death with severe impairments, to low "safe" doses, leading to subtle neurological and other physical impairments
Duration of exposure	One time vs. multiple times over the course of weeks, months, or years
Dose rate	Bolus dose, daily dose
Individual sensitivity	A function of (a) the age at which exposure occurs, that is, prenatal, infant, child, adolescent, or adult, (b) genetically determined reactivity to mercury, and (c) gender
Common types of mercury	The organic alkyl forms - methylmercury and ethylmercury; and inorganic forms - metallic mercury, elemental (liquid) mercury, and ionic mercury/mercuric salt
Primary routes of exposure	Inhalation of mercury vapors, orally through the intestinal tract, subcutaneous and intramuscular injections, topically through ear drops, teething powders, skin creams and ointments, and intravenously during medical treatments

While these variations in exposure, individual status, and genotype give rise to a diverse clinical phenotype, there are nevertheless obvious commonalities across all mercury-caused disorders. Thus, for example, victims will almost always develop a movement disorder, but in some individuals this may manifest as mere clumsiness, while others will develop severe involuntary jerking movements. Likewise, psychological disturbances are usually present, but in some individuals these might manifest as anxiety while in others it might present as aggression or irritability.

Diagnosing Mercury Poisoning in Autism

Mercury poisoning can be difficult to diagnose and is often interpreted by clinicians as a psychiatric disorder, especially if exposure is not suspected (Diner and Brenner, 1998; Frackelton and Christensen, 1998). The difficulty in diagnosis derives primarily from two notable characteristics of this heavy metal. First, there can be a long latent period between time of exposure and onset of overt symptoms, so that the connection between the two events is often overlooked. The latency period is discussed in more detail below. Second, the diverse manifestations of the disease make it difficult for the clinician to find a precise match of his particular patient's symptoms with those described in other case reports (Adams et al, 1983, Kark et al, 1971; Florentine and Sanfilippo, 1991; Matheson et al, 1980; Frackelton and Christensen, 1998; Warkany & Hubbard, 1953).

Due to the difficulty of diagnosing mercurialism based on presentation of non-specific symptoms alone, clinicians have come to rely on the following criteria (Warkany & Hubbard, 1953; Vroom and Greer, 1972).

Observation of impairments in many but not all of the following domains: (a) movement/motor disorder, (b) sensory abnormalities, (c) psychological and behavioral disturbances, (d) neurological and cognitive deficits, (e) impairments in language, hearing, and vision, and (f) miscellaneous physical presentations such as rashes or unusual reflexes (Adams et al, 1983; Snyder, 1972; Vroom & Greer, 1972).
Known exposure to Hg (a) at a level that has been documenting as causing impairment in similar individuals under similar circumstances, and (b) at approximately the same time as the symptoms emerge, with allowances given for the latency period (Ross et al, 1977; Amin-Zaki et al, 1978). It should be noted that the dose which is considered "toxic" vs. "safe" is unresolved among toxicologists; some researchers feel that any amount of exposure is "unsafe" (see EPA, 1997, pp.6-47 to 6-59, for dose discussion).
Detectable levels of mercury in urine, blood, or hair (Florentine and Sanfilippo, 1991; Frackelton and Christensen, 1998; EPA, 1997, p.ES-2). Importantly, because mercury can clear from biologic samples before the patient feels symptoms or is tested, the lack of detectable mercury is not cause for ruling out mercury poisoning; and conversely, detectable levels have been observed in unaffected individuals (Adams et al, 1983; Warkany & Hubbard, 1953; Cloarec, 1995).
Improvement in symptoms after chelation. While many patients' symptoms resolve with chelation, some clearly poisoned individuals do not improve. Other exposed subjects have also been known to improve without intervention (Vroom & Greer, 1972; Warkany & Hubbard, 1953).

Thus, none of these criteria is sufficient on its own for a certain diagnosis. Rather, observed effects within two or three domains are generally required. This paper, which reviews and compares the extensive literature available on both ASD and mercury, provides citations documenting that, based on these four diagnostic criteria, many if not most cases of autism meet the requirements for mercury poisoning. In fact, this review and its citations (i) delineate a single mechanism for inducing all of the primary domains of impairment and biological abnormalities in autism, including its genetic component, prevalence levels, and sex ratios; and (ii) identify that mechanism as arising from the "environmental insult" of early childhood exposure to mercury. Furthermore, the route of exposure is thimerosal, which is 50% ethylmercury by weight and which is a preservative used in many childhood vaccines.

We are not suggesting that the previous reports of mercurialism described in the literature are in fact cases of autism; rather, we claim that autism represents its own unique form of Hg poisoning, just like acrodynia, Minamata disease, and Mad Hatter's disease represent distinct yet closely related presentations of mercurialism. A unique expression would be expected in cases of autism, given that the effects of repeated vaccinal administration of ethylmercury to infants and toddlers have never been described before in mercury-related literature. We maintain that the diverse phenotype that is autism matches the diverse phenotype that is mercurialism to a far greater degree that could reasonably be expected to occur by chance. Given the known exposure to mercury via vaccination of autistic children and the presence of mercury found in biologic samples from a number of autistic subjects, also described here, we are confident that our claim is substantiated. Our paper discusses some important medical and societal ramifications of this conclusion.

I. Symptom Comparison

The overt symptoms of ASD and mercury poisoning, described in the literature and presented here, are strikingly similar. Summary tables have been provided after each section to aid in symptom comparisons.

a. Affect/Psychological Presentation

Since its initial description in 1943 by Leo Kanner, a psychiatrist, autism has been defined primarily as a psychiatric condition. One of the three requirements for diagnosis is a severe deficit in social interactions (APA, 1994). Self and parental reports describe children and adults who prefer to be alone and who will withdraw to their rooms if given the chance (MAAP, 1996-1999). Even high functioning autistics tend to be aloof, have poor social skills, are unable to make friends, and find conversation difficult (Tonge et al, 1999; Capps et al, 1998). Face recognition and what psychologists call "theory of mind" are impaired (Klin et al, 1999, Baron-Cohen et al, 1993). Poor eye contact or gaze avoidance is present in most cases, especially in infancy and childhood (Bernabei et al, 1998).

The second psychobehavioral diagnostic characteristic of autism is the presence of repetitive, stereotyped activities and the need for sameness (APA, 1994). Traits in this domain strongly resemble obsessive-compulsive tendencies in both thought and behavior (Lewis, 1996; Gillberg & Coleman, 1992, p.27), especially as the individual becomes more high functioning (Roux et al, 1998): "it [is] very difficult.to distinguish between obsessive ideation and the bizarre preoccupations so commonly seen in autistic individuals" (Howlin, 2000). Serotonin uptake inhibitors known to be effective for OCD also reduce repetitive behaviors in some autistic patients (Lewis, 1996). Most autistic subjects - 84% in one study - show high levels of anxiety and meet diagnostic criteria for anxiety disorder (Muris et al, 1998).

ASD has been linked to depression, based on symptoms, familial history of depression and the positive response to SSRIs among many autistics (Clarke et al, 1999; DeLong, 1999; Piven and Palmer, 1999). One subset of autistics has been described as "passive", with flat affect, "absence of facial expression," lack of initiative, and diminished outward emotional reactions. Some autistics have a strong family history of manic depression and mood swings, and, among those who are verbal, psychotic talk is frequently observed (Plioplys, 1989). Autism is also said to strongly resemble childhood schizophrenia. In the past it was often misdiagnosed as such (Gillberg & Coleman, 1992, p.100), and there are a number of instances of dual ASD-schizophrenia diagnoses in the literature (Clarke et al, 1999). Furthermore, irrational fears, aggressive behaviors, and severe temper tantrums are common (Muris et al, 1998; McDougle et al, 1994), as are chronic hyperarousal and irritability (Jaselskis et al, 1992). "Inexplicable changes of mood can occur, with giggling and laughing or crying for no apparent reason" (Wing & Attwood, 1987).

Mercury poisoning, when undetected, is often initially diagnosed as a psychiatric disorder in both children and adults (Fagala and Wigg, 1992). Common psychiatric symptoms are (a) depression, including "lack of interest" and "mental confusion;" (b) "extreme shyness," indifference to others, active avoidance of others or "a desire to be alone"; (c) irritability in adults and tantrums in children; and (d) anxiety and fearfulness. Neurosis, including schizoid and obsessive-compulsive traits, has been reported in a number of cases (Fagala and Wigg, 1992; Kark et al, 1971; O'Carroll et al, 1995; Florentine and Sanfilippo, 1991; Amin-Zaki, 1974 and 1979; Matheson et al, 1980; Joselow et al, 1972; Smith, 1972; Lowell, 1996; Tuthill, 1899; Clarkson, 1997; Camerino et al, 1981; Grandjean et al, 1997; Piikivi et al, 1984; Rice, 1996; Vroom & Greer, 1972; Adams et al, 1973; Hua et al, 1996).

Juvenile monkeys prenatally exposed to mercury exhibit decreased social play and increased passive behavior (Gunderson et al, 1986, 1988), as well as impaired face recognition (Rice, 1996). Humans exposed to mercury vapor also perform poorly on face recognition tests and may present with a "mask face" (Vroom & Greer, 1972); emotional instability can occur in children and adults exposed to Hg. For instance, Iraqi children poisoned by methylmercury had a tendency "to cry, laugh, or smile without obvious provocation" (Amin-Zaki et al, 1974 & 1979), like the autistic group described by Wing and Attwood (1987).

Table II: Summary of Psychiatric Disturbances
Found in Autism & Mercury Poisoning

Mercury Poisoning	Autism
Extreme shyness, social withdrawal, feeling overly sensitive, introversion	Social deficits, social withdrawal, self reports of extreme shyness, aloofness
Mood swings; flat affect; mask face; laughing or crying without provocation; episodes of hysteria	Mood swings; flat affect in some; no facial expression; laughing or crying without reason
Anxiety; nervousness; tremulousness; somatization of anxious feelings	Anxiety, nervousness; anxiety disorder
Schizoid tendencies, neurosis, obsessive-compulsive traits, repetitive dreams	Schizophrenic traits; OCD traits; repetitive behaviors and thoughts
Lack of eye contact; being less talkative; hesitancy to engage others	Lack of eye contact, gaze avoidance; avoids conversation
Depression, lack of interest in life, lassitude, fatigue, apathy; feelings of hopelessness; melancholy	Association with depression; lack of initiative, diminished outward emotions
On the one hand, less overtly active, unwilling to go outside or be with others; on the other hand, increased restlessness	Tendency to withdraw, especially to own rooms, prefer to be alone; hyperactivity
Irrational fears	Irrational fears
Irritability, anger, and aggression; in children this may manifest as frequent and severe temper tantrums	Irritability and aggression; severe temper tantrums in children
Psychotic episodes; hallucinations, hearing voices; paranoid thoughts	Psychotic talk, paranoid thoughts
Impaired face recognition	Impaired face recognition

Since traditionally autism has been characterized and studied by researchers primarily in psychiatric terms, providing case studies illustrating the psychiatric aspects of ASD and of mercurialism are necessary in establishing the similarities of the two disorders on this critical domain. Also included is a comparison of "Lenny," an autistic adult described by Rhea Paul (1987), and the Mad Hatter from Alice in Wonderland, considered to be an accurate portrayal of victims of the disease. Of particular relevance in all these cases are social withdrawal and deficits in social communication, traits (i) always prominent in autism and (ii) clearly associated with mercurialism.

Case Studies: Autism
"I am 18 years old. My parents found out I was autistic when I was 18 months old. My parents said I banged my head a lot when I got frustrated when I was young. Head banging motions help me deal with nervousness. I also take 2 medications to help me cope with stress. I have very few friends. It is also somewhat painful for me to look people in the eye. This sometimes makes people think I am not paying attention" (The MAAP, Vol. II, 1997).

"I have a high-functioning autistic eight-year-old boy. My mistake was putting him in the second grade with a teacher who was determined to 'socialize' him. After three months, the anxiety proved to be too great for him. He spent a lot of time crying, withdrawing to his room, becoming compulsive and belligerent. In another era, he would have been seen as having a 'nervous breakdown'" (The MAAP, Vol. II, 1997).

"I am writing regarding our 25 year old son who was diagnosed only a few months ago as having Asperger's Syndrome. All his life he displayed the 'classic' symptoms of Asperger's (lack of social skills, disorganization, anxiety, etc.). A few months ago, he became clinically depressed, phobic about being around people for fear of more rejection or being laughed at. He now has obsessive thoughts that our home is electronically 'bugged' and all his actions are being observed and belittled" (The MAAP, Vol. II, 1997).

"Several people have asked me what it's like to have Asperger's Syndrome. Today, I still prefer to work on my computer or with electronics rather than socialize. I've never been able to tolerate any kind of physical contact or intimacy. I like wrestling and rough-housing, but I hate being caressed or held." (The MAAP, Vol. II, 1997).

"My son Brian is a 6-year-old with high functioning autism. Our main problem now is his rigidity and obsessive/compulsive behaviors. He gets extremely upset when activities don't go as he thinks they should. He first gets mad, screaming and yelling, then begins to obsessively talk about how he can remedy the situation, then often begins to cry uncontrollably. These tantrums can go on for hours" (The MAAP, Vol. IV, 1996).

"[I'm] age 12r. I have Autism/PDD. I don't really know any real social skills, though my brother Isaiah says I am a social outcast. I do have trouble making new friends because I get real shy and nervous" (The MAAP, Vol. IV, 1997).

"I am the mother of three autistic boys. Nate was considered very shy. Poor eye contact but very smart and doing well in school. Nate was also diagnosed with Hypotonia of the face (which answered all the mumbling he did wasn't just shyness) and extremities" (The MAAP, Vol. III, 1999)

"I spent many hours sitting in the trees or under the bed or in a dark closet. I had a loud flat voice. Socialization has always been beyond me" (The MAAP, Vol. II, 1998).

"I sit in my room a prisoner to my autism. Mom and sis doing their loving best to get me out. I wanted to get out - really get out. I wanted to love, to feel, to connect. But, I couldn't. I was stuck. I was slowly dying. There were days I truly wanted to end it all. If any days were good, I didn't deserve it. I shouldn't be happy. Autism teaches you that - because it's a life sentence" (The MAAP, Vol. VI, 1996).

Case Studies: Mercury Poisoning
A 12 year old girl with recent mercury vapor poisoning was initially diagnosed as having a psychiatric disturbance. Her behavior was more normal when she was unaware of being watched. She became upset when people were around, was reluctant to speak when others were present, spoke in a soft, mumbling voice, lacked eye contact, had a flat affect, was sometimes tearful, experienced auditory hallucinations of voices laughing at her, wished to stay alone in her room with the lights off and her head covered, and had frequent temper tantrums (Fagala and Wigg, 1992).

Sufferers of Mad Hatter's disease, arising from prolonged mercury vapor exposure, were known to suffer from depression, lassitude, acute anxiety, and irrational fears. They also became nervous, timid, and shy. They blushed readily, were embarrassed in social situations, objected to being watched, and sought to avoid people. They felt a constant impulse to return home. They were easily upset, and were prone to agitation, irritability, anger, and aggressive behavior (O'Carroll et al, 1995).

A survey on an Internet site of adult acrodynia victims, which compared the symptoms of adults who suffered from acrodynia as children with controls, reported the following symptoms as seen to a greater degree in acrodynia sufferers than in controls: dislikes being touched or hugged, is a loner, lacks self confidence, feels nervousness and has a racing heart, has depression and suicidal feelings (Farnesworth, 1997). One acrodynia victim described his own situation: "not having learnt normal social skills I spent a lot of my time alone.Gradually by age 11 or so, I was becoming 'normal'.But, I have never overcome the headache problem, irritability, shyness with real people, not wanting to be touched, depression, fear of doctors, great anxiety." (Neville's Recollection, Pink Disease site)

A doctor from the 19th century described several cases of mercury poisoning from dental amalgams: "There is mental excitability as well as mental depression; perplexing events cause the highest degree of excitement, ordinary conversation sometimes causes complete confusion, headache, palpitation, intense solicitude, and anxiety, without reason for it. Such are some of the symptoms attending these cases." As an example he cites the case of a young woman who "had come to be melancholic and to withdraw herself from her family and friends, seeking the seclusion of her room -- refusing to go out or to associate with others, or even with the members of her own household." (Tuthill, 1899)

Nearly a century later, initial questioning of a 28 year old woman, subsequently found to have mercury vapor poisoning, "elicited the fact that she had become increasingly withdrawn from social activities and had felt most uncomfortable when with strangers. She also felt that her friends had turned against her. She had a repetitive disturbing dream of electric fire around the frames of the windows in her bedroom." (Ross et al, 1977)

Lenny and The Mad Hatter
(a) Rigid literal interpretation of word meaning; word meaning and pragmatic errors which interfere with social communication

Lenny - "He was very literal minded, and words spoken to him became matters of immutable fact. For example, he was trying on new shoes. His mother asked him if they slipped up and down. He said they didn't, and when asked again if he were sure, he replied, 'No, they don't slip up and down; they slip down and then they slip up.' "

The Mad Hatter - "Take some more tea," the March Hare said to Alice, very earnestly.
"I've had nothing yet," Alice replied in an offended tone: "so I ca'n't take more."
"You mean you ca'n't take less," said the Hatter: "It's very easy to take more than nothing."

(b) Social deficits, inability to interpret social rules, leading to perceived rude behavior

Lenny - "Although he tried working in his father's business for a time, his immaturity, self-centered behavior, and lack of social judgment required his return to a sheltered setting."

The Mad Hatter - "Your hair wants cutting," said the Hatter. He had been looking at Alice for some time with great curiosity, and this was his first speech.
"You should learn not to make personal remarks," Alice said with some severity: "it's very rude."
The Hatter opened his eyes wide upon hearing this; but all he said was "Why is a raven like a writing desk?"

(c) Inability to engage in meaningful social conversation; poor conversational interpretation skills; perseverative thoughts

Lenny - "During one interview he engaged in a 20 minute monologue about a broken washing mashine. The interviewer momentarily dozed off. Upon rousing, the interviewer exclaimed, 'Oh, Lenny, I'm sorry!' 'It's all right,' Lenny replied calmly, 'the washing machine got fixed."

The Mad Hatter (who talks obsessively/perseveratively about Time for a good portion of the chapter) - "What a funny watch!" she remarked. "It tells the day of the month, and doesn't tell what o'clock it is!"
"Why should it?" muttered the Hatter. "Does your watch tell you what year it is?"
"Of course not, " Alice replied very readily: "but that's because it stays the same year for such a long time altogether."
"Which is just the case with mine," said the Hatter.
Alice felt dreadfully puzzled. The Hatter's remark seemed to her to have no sort of meaning in it, and yet it was certainly plain English.

b. Language and Hearing

The third diagnostic criterion for autism is a qualitative impairment in communication (APA, 1994), and such impairment is a primary feature of mercury poisoning.

Delayed language onset is often among the first overt signs of ASD (Eisenmajer et al, 1998). Historically, half of those with classic autism failed to develop meaningful speech (Gillberg & Coleman, 1992; Prizant, 1996); and oral-motor deficits (e.g. chewing, swallowing) are often present (Filipek et al, 1999). When speech develops, there may be "specific neuromotor speech disorders," including verbal dyspraxia, a dysfunction in the ability to plan the coordinated movements to produce intelligible sequences of speech sounds, or dysarthria, a weakness or lack of control of the oral musculature" leading to articulation problems (Filipek et al, 1999). Echolalic speech and pronoun reversals are typically found in younger children. Many ASD subjects show poorer performance on tests of verbal IQ relative to performance IQ (Dawson, 1996; Filipek at al, 1999). Higher functioning individuals, such as those with Asperger's Syndrome, may have language fluency but still exhibit semantic (word meaning) and pragmatic (use of language to communicate) errors (Filipek et al, 1999).

Auditory impairment is also common. Two separate studies, for example, both found that 24% of autistic subjects have a hearing deficit (Gillberg & Coleman, 1992). More recently Rosenhall et al (1999) have diagnosed hearing loss ranging from mild to profound, as well as hyperacusis, otitis media, and conductive hearing loss, in a minority of ASD subjects, and these traits were independent of IQ status. Among the earliest signs of autism noted by mothers were strange reactions to sound and abnormal babble (Gillberg & Coleman, 1992), and many ASD children are tested for deafness before receiving a formal autism diagnosis (Vostanis et al, 1998). "Delayed or prompted response to name" differentiates 9-12 months old toddlers, later diagnosed with autism, from mentally retarded and typical controls (Baranek, 1999). In fact, "bizarre responses" to auditory stimuli are nearly universal in autism and may present as "either a lack of responsiveness or an exaggerated reaction to auditory stimuli" (Roux et al, 1998), possibly due to sound sensitivity (Grandin, 1996). Kanner noted an aversion to certain types of sounds, such as vacuum cleaners (Kanner, 1943). Severe deficits in language comprehension are often present (Filipek et al, 1999). Difficulties in picking out conversational speech from background noise are commonly reported by high functioning ASD individuals (Grandin, 1995; MAAP, 1997-1998).

In regard to language and auditory phenomena, autism's parallels to mercurialism are striking. Emerging signs of mercury poisoning are dysarthria (defective articulation in speech due to CNS dysfunction) and then auditory disturbance, leading to deafness in very high doses (Clarkson, 1992). In some cases, hearing impairment manifests as an inability to comprehend speech rather than an inability to hear sound (Dales, 1972). Hg poisoning can also result in aphasia, the inability to understand and/or physically express words (Kark et al, 1971). Speech difficulties may arise from "intention tremor, which can be noticeable about the mouth, tongue, face, and head, as well as in the extremities" (Adams et al, 1983).

Mercury-exposed children especially show a marked difficulty with speech (Pierce et al, 1972; Snyder, 1972; Kark et al, 1971). Even children exposed prenatally to "safe" levels of methylmercury performed less well on standardized language tests than did unexposed controls (Grandjean et al, 1998). Iraqi babies exposed prenatally either failed to develop language or presented with severe language deficits in childhood. They exhibited "exaggerated reaction" to sudden noise and some had reduced hearing (Amin-Zaki, 1974 and 1979). Iraqi children who were postnatally poisoned from bread containing either methyl or ethylmercury developed articulation problems, from slow, slurred word production to the inability to generate meaningful speech. Most had impaired hearing and a few became deaf (Amin-Zaki, 1978). In acrodynia, symptoms of sufferers (vs. controls) include noise sensitivity and hearing problems (Farnesworth, 1997).

Adults also exhibit these same Hg-induced impairments. There is slurred or explosive speech (Dales, 1972), as well as difficulty in picking out one voice from a group (Joselow et al, 1972). Poisoned Iraqi adults developed articulation problems (Amin-Zaki, 1974). A 25 year old man with elemental mercury poisoning had reduced hearing at all frequencies (Kark et al, 1971). Thimerosal injected into a 44 year old man initially led to difficulty verbalizing, even though his abilities in written expression were uncompromised; he then progressed to slow and slurred speech, although he could still comprehend verbal language; and he finally lost speech altogether (Lowell et al, 1996). In Mad Hatter's disease, there were word retrieval and articulation difficulties (O'Carroll et al, 1995). A scientist who recently died from dimethylmercury poisoning demonstrated an inability to understand speech despite having good hearing sensitivity for pure tones (Musiek and Hanlon, 1999). Workers exposed to mercury vapor showed decreased verbal intelligence relative to performance IQ (Piikivi et al, 1984; Vroom and Greer, 1972).

Table III: Summary of Speech, Language
& Hearing Deficits in Autism & Mercury Poisoning

Mercury Poisoning	Autism
Complete loss of speech in adults or children; failure to develop speech in infants	Delayed language onset; failure to develop speech
Dysarthria; speech difficulties from intention tremor; slow and slurred speech	Dysarthria; dyspraxia and oral-motor planning difficulties; unintelligible speech
Aphasia, the inability to use or understand words, inability to comprehend speech although ability to hear sound is intact	Speech comprehension deficits, although ability to hear sound is intact
Difficulties verbalizing; word retrieval problems	Echolalia; pronoun reversals, word meaning and pragmatic errors; limited speech production
Auditory disturbance; difficulties differentiating voices in a crowd	Difficulties following conversational speech with background noise
Sound sensitivity	Sound sensitivity
Hearing loss; deafness in very high doses	Mild to profound hearing loss
Poor performance on standardized language tests	Poor performance on verbal IQ tests

c. Sensory Perception

Sensory impairment is considered by many researchers to be a defining characteristic of autism (Gillberg and Coleman, 1992; Williams, 1996). Baranek (1999) detected sensory-motor problems - touch aversion, poor non-social visual attention, excessive mouthing of objects, and delayed response to name - in 9-12 month old infants later diagnosed with autism, and suggests that these impairments both underlie later social deficits and serve to differentiate ASD from mental retardation and typical controls. Besides sensitivity to sound, as previously noted, ASD often involves insensitivity to pain, even to a burning stove (Gillberg & Coleman, 1992), while on the other hand there may be an overreaction to stimuli, so that even light to moderate touches are painful. Pinprick tests are usually normal. Children with autism have been described as "stiff to hold," and one of the earliest signs reported by mothers is an aversion to being touched (Gillberg & Coleman, 1992). Abnormal sensation in the extremities and mouth are common. Toe-walking is frequently seen. Oral sensitivity often results in feeding difficulties (Gillberg & Coleman, 1992, p.31). Autistic children frequently have vestibular impairments and difficulty orienting themselves in space (Grandin, 1996; Ornitz, 1987).

As in ASD, sensory issues are reported in nearly all cases of mercury toxicity, and serve to demonstrate the similarities between the two conditions. Paresthesia, or abnormal sensation, tingling, and numbness around the mouth and in the extremities, is the most common sensory disturbance in Hg poisoning, and is usually the first sign of toxicity (Fagala and Wigg, 1992; Joselow et al, 1972; Matheson et al, 1980; Amin-Zaki, 1979). In Japanese who ate contaminated fish, there was numbness in the extremities, face and tongue (Snyder, 1972; Tokuomi et al, 1982). Iraqi children who ate bread experienced sensory changes including numbness in the mouth, hands and feet, and a feeling that there were "ants crawling under the skin." These children could still feel a pinprick (Amin-Zaki, 1978). Loss of position in space has also been noted (Dales, 1972). Acrodynia sufferers describe excessive pain when bumping limbs, numbness, and poor circulation (Farnesworth, 1997). One adult acrodynia victim described himself as a boy as "shying away from people wanting to touch me" due to extreme touch sensitivity (Neville Recollection, Pink Disease Support Group). Iraqi babies exposed to mercury prenatally showed excessive crying, irritability, and exaggerated reaction to stimulation such as sudden noise or when touched (Amin-Zaki et al, 1974 and 1979).

Table IV: Summary of Sensory Abnormalities
in Mercury Poisoning & Autism

Mercury Poisoning	Autism
Abnormal sensation or numbness around mouth and extremities (paresthesia); burning feet	Abnormal sensation in mouth and extremities; excessive mouthing of objects (infants); toe walking; difficulty grasping objects
Sound sensitivity	Sound sensitivity
Excessive pain when bumping; abnormal touch sensations; touch aversion	Insensitivity or overreaction to pain and touch; touch aversion; stiff to hold
Loss of position in space	Vestibular system abnormalities; difficulty orienting self in space
Normal pinprick tests	Normal pinprick tests

d. Movement/Motor Function

Nearly all cases of autism include disorders of physical movement. Movement disturbances have been detected in infants as young as four to six months old who were later diagnosed as autistic: Teitelbaum et al (1998) have observed that these children do not lie, roll over, sit up or crawl like normal infants; impairment in motor control sometimes caused these babies to fall over while sitting, consistently to avoid using one of their arms, or to rest on their elbows for stability while crawling. Later, when trying to walk their gait was abnormal, and some degree of asymmetry, mostly right-sided, was present in all cases studied. Kanner noted in several of his subjects the absence of crawling and a failure to assume an anticipatory posture preparatory to being picked up in infancy (Kanner, 1943). Arm flapping, abnormal posture, jumping, and hand-finger mannerisms (choreiform movements) are common (Tsai, 1996). Many individuals with Asperger's syndrome are typically characterized as uncoordinated or clumsy (Kugler, 1998). Other autism movement disorders include praxis (problems with intentional movement), stereotypies, circling or spinning, rocking, toe walking, myoclonal jerks, difficulty swallowing and chewing, difficulty writing with or even holding a pen, limb apraxia, and poor eye-hand coordination (Caesaroni and Garber, 1991; Gillberg and Coleman, 1992; Filipek et al, 1999).

Like ASD, movement disorders have been a feature of virtually all descriptions of mercury poisoning in humans (Snyder, 1972). Even children prenatally exposed to "safe" levels of methylmercury had deficits in motor function (Grandjean et al, 1998). The movement-related behaviors are extremely diverse: Iraqi infants and children exposed postnatally, for example, developed ataxia that ranged from clumsiness and gait disturbances to an "inability to stand or even sit" (Amin-Zaki et al, 1978). The various movement behaviors are listed more fully in Table V (Adams et al, 1983; Kark et al, 1971; Pierce et al, 1972; Snyder, 1972; O'Carroll et al, 1995; Tokuomi et al, 1982; Amin-Zaki, 1979; Florentine and Sanfilippo, 1991; Rohyans et al, 1984; Fagala and Wigg, 1992; Smith, 1977; Grandjean et al, 1998; Farnesworth, 1997; Dales, 1972; Matheson et al, 1980; Lowell et al, 1996; O'Kusky et al, 1988; Vroom and Greer, 1972; Warkany and Hubbard, 1953).

Noteworthy because of similarities to movement disorders in autism are reports in the Hg literature of (a) an infant with "peculiar tremulous movements of the extremities which were principally proximal and can best be described as flapping in nature" (Pierce et al, 1972; Snyder, 1972); (b) "jerking movements of the upper extremities" in a man injected with thimerosal (Lowell et al, 1996); (c) "constant choreiform movements affecting the fingers and face" in mercury vapor intoxication (Kark et al, 1971); (d) myoclonal jerks, associated with epilepsy among Iraqi subjects (Amin-Zaki et al, 1978); (e) poor coordination and clumsiness among victims of acrodynia (Farnesworth, 1997); (f) rocking among infants with acrodynia (Warkany and Hubbard, 1953); (g) "unusual postures" observed in both acrodynia and mercury vapor poisoning (Vroom and Greer, 1972; Warkany and Hubbard, 1953); and (h) toe walking among less severely poisoned children in the Minamata epidemic (Minamata Disease, 1973). In animal studies, cats exposed to mercury by eating fish developed "circling movements" (Snyder, 1972), and subcutaneous administration of methylmercury to rats during postnatal development has resulted in postural disorders (O'Kusky et al, 1988).

As summarized in Table V, movement similarities in autism and Hg poisoning are clear.

Table V: Summary of Motor Disorder Behaviors
in Mercury Poisoning & Autism

Mercury Poisoning	Autism
Involuntary jerking movements, e.g., arm flapping, ankle jerks, myoclonal jerks; choreiform movements; circling (cats); rocking; purposeless movement of extremities; twitching, shaking; muscular spasticity	Stereotyped movements such as arm flapping, jumping, circling, spinning, rocking; myoclonal jerks; choreiform movements
Unsteadiness in handwriting or an inability to hold a pen; deficits in eye-hand coordination; limb apraxia; intention tremors; loss of fine motor skills	Difficulty in writing with or holding a pen; poor eye-hand coordination; limb apraxia; problems carrying out intentional movements (praxia)
Ataxia: gait impairment; severity ranging from mild incoordination, clumsiness to complete inability to walk, stand, or sit; staggering, stumbling; loss of motor control	Abnormal gait and posture, clumsiness and incoordination; difficulties sitting, lying, crawling, and walking in infants and toddlers
Toe walking	Toe walking
Difficulty in chewing or swallowing	Difficulty chewing or swallowing
Unusual postures	Unusual postures
Areflexia	None described
Tremors in general, tremors of the face and tongue, hand tremors	None described

e. Cognition/Mental Function

Nearly all autistic individuals show impairment in some aspects of mental function, even as other cognitive abilities remain intact. Most individuals may test in the retarded range, while others have normal to above average IQs. These characteristics are true in mercurialism. Moreover, the specific areas of impairment are similar in the two disorders.

The impaired areas in autism are generally in (a) short term or working memory and auditory and verbal memory; (b) concentration and attention, particularly attention shifting; (c) visual motor and perceptual motor skills, including eye-hand coordination; (d) language/verbal expression and comprehension; and (e) using visually presented information when constraints are placed on processing time. Relatively unimpaired areas include rote memory skills, pattern recognition, matching, perceptual organization, and stimuli discrimination. Higher level mental skills requiring complex processing are typically deficient; these include (a) processing and filtering of multiple stimuli; (b) following multiple step commands; (c) sequencing, planning and organizing; and (d) abstract/conceptual thinking and symbolic understanding (Rumsey & Hamburger, 1988; Plioplys, 1989; Bailey et al, 1996; Filipek et al, 1999; Rumsey, 1985; Dawson, 1996; Schuler, 1995; Grandin, 1995; Sigman et al, 1987). Younger or more mentally impaired children may have difficulties with symbolic play and understanding object permanence or the mental state of others (Bailey et al, 1996). Some autistic children are hyperlexic, showing superior decoding skills while lacking comprehension of the words being read (Prizant, 1996). As mentioned before, for most autistic individuals verbal IQ is lower than performance IQ.

As in autism, Hg exposure causes some level of impairment primarily in (a) short term memory and auditory and verbal memory; (b) concentration and attention, including response inhibition; (c) visual motor and perceptual motor skills, including eye-hand coordination; (d) language/verbal expression and comprehension; and (e) simple reaction time. Hg-affected individuals may present as "forgetful" or "confused." Performance IQ may be higher than verbal IQ. "Degeneration of higher mental powers" has resulted in (a) difficulty carrying out complex commands; (b) impairment in abstract and symbolic thinking; and (c) deficits in constructional skills and conceptual abstraction. One study mentions alexia, the inability to comprehend the meaning of words, although reading of the words is intact (Yeates & Mortensen, 1994; O'Carroll et al, 1995; Pierce et al, 1972; Snyder, 1972; Adams et al, 1983; Kark et al, 1971; Amin-Zaki, 1974 and 1979; Davis et al, 1994; Grandjean et al, 1997 & 1998; Myers & Davidson, 1998; Gilbert & Grant-Webster 1995; Dales, 1972; Fagala and Wigg, 1992; Farnesworth, 1997; Tuthill, 1899; Joselow et al, 1972; Rice, 1997; Piikivi et al, 1984; Vroom and Greer, 1972). Even children exposed prenatally to "safe" levels of methylmercury show lower scores on selective subtests of cognition, especially in the domains of memory and attention, relative to unexposed controls (Grandjean et al, 1998). In exposed juvenile monkeys, tests have revealed delays in the development of object permanence, or the ability to conceptualize the existence of a hidden object (Rice, 1996).

Research on mental retardation in autism is contradictory (Schuler, 1995). The finding that "mental retardation or borderline intelligence often co-exists with autism" (Filipek et al, 1999) is based on using standard measures of intelligence (Gillberg & Coleman, 1992, p.32; Bryson, 1996); other intelligence tests, designed to circumvent the language and attentional deficits of autistic children, show significantly higher intelligence test scores (Koegel et al, 1997; Russell et al, 1999). One study using such a modified rating instrument has found 20% of autistic children to be mentally retarded (Edelson et al, 1998), rather than the 70%-80% so scored on standard tests. ASD individuals also show "strikingly uneven scores" on IQ subtests, "unlike other disorders involving mental retardation, in which subtest scores seem to be more or less even" (Bailey et al, 1996). Also unlike typical cases of mental retardation, which is nearly always noted in the peri- or neonatal periods, most parents of ASD children report infants of seemingly normal appearance and development who were later characterized as mentally retarded on tests. For example, one study compared early developmental aberrations in mentally retarded children with and without autism. Findings indicated that, whereas nearly all parents of the non-autistic mentally retarded study group were aware of their child's impairment by age 3 months, nearly all parents of the autistic children failed to notice any developmental delays or issues until after 12 months of age (Baranek, 1999). Finally, there are several case reports of autistic adults who were labeled mentally retarded as children based on tests, who later "emerged" from their autism and had normal IQs (ARI Newsletter, 1993, review).

As in autism, symptomatic mercury-poisoned victims can present with normal IQs, borderline intelligence, or mental retardation; some may be so impaired as to be untestable (Vroom and Greer, 1972; Davis et al, 1994). When lowered intelligence is found, it is always reported as an obvious deterioration among previously normally functioning people; this includes children exposed as infants or toddlers (Dale, 1972; Vroom and Greer, 1972; Amin-Zaki, 1978). Once the Hg-exposure source is removed, many (although not all) of these patients "recover" their normal IQ, suggesting that "real" IQ was not affected (Vroom and Greer, 1972; Davis et al, 1994). Infant monkeys given low doses of Hg, while clearly impaired in visual, auditory, and sensory functions, had intact central processing speed, which has been shown to correlate with IQ in humans (Rice, 1997).

Table VI: Summary of Areas of Mental Impairment
in Mercury Poisoning & Autism

Mercury Poisoning	Autism
Some aspect of mental impairment in all symptomatic cases	Some aspect of mental impairment in all cases
Borderline intelligence on testing among previously normal individuals; mental retardation occurring in severe cases of pre-/postnatal exposure; some cases of MR reversible; primate studies indicate core intelligence spared with low exposures	Borderline intelligence or mental retardation on standard tests among previously normally appearing infants; some cases of MR "reversible"; indications that normal IQ might be present in MR-labeled individuals
Uneven performance on subtests of intelligence	Uneven performance on subtests of intelligence
Verbal IQ higher than performance IQ; compromised language/verbal expression and comprehension	Verbal IQ higher than performance IQ; compromised language/verbal expression and comprehension
Poor concentration, shortened attention span, general lack of attention; poor response inhibition	Lack of concentration, short attention span, lack of attention, difficulty shifting attention
Forgetfulness, loss of memory, particularly short term, verbal and auditory memory; mental confusion	Poor short term/working memory; poor auditory and verbal memory; lower verbal encoding abilities
Poor visual and perceptual motor skills, poor eye-hand coordination; impairment in simple reaction time	Poor visual and perceptual motor skills, poor eye-hand coordination; lowered performance on timed tests
Not reported as being tested	Difficulty processing multiple stimuli
Difficulty carrying out complex commands	Difficulty carrying out multiple commands
Alexia (inability to comprehend the meaning of written words)	Hyperlexia (ability to decode words while lacking word comprehension)
Deficits in constructional skills, conceptual abstraction, understanding abstract ideas and symbolism; degeneration of higher mental powers	Deficits in abstract/conceptual thinking, symbolism, understanding other's mental states; impairment in sequencing, planning, organizing
Lack of understanding of object permanence (primates)	Deficient understanding of object permanence (children)

f. Behaviors

Autism is associated with difficulties initiating and/or maintaining sleep; hyperactivity and other ADHD traits; and self injurious behavior such as head banging, even in the absence of mental retardation. Agitation, screaming, crying, staring spells, stereotypical behaviors, and grimacing are common (Gaedye, 1992; Gillberg and Coleman, 1992; Plioplys, 1989; Kanner, 1943; Richdale, 1999; Stores & Wiggs, 1998). Kanner (1943) made a point of noting excessive and open masturbation in two of the eleven young children comprising his initial cases. Feeding and suckling problems are typical (Wing, 1980), and restricted diets and narrow food preferences "are the rule rather than the exception" (Gillberg and Coleman, 1992; Clark et al, 1993); some autistics show a preference for salty foods (Shattock, 1997). Kanner, in his 1943 article, noted feeding problems from infancy, including vomiting and a refusal to eat, in six of the eleven autistic children he described. There are case studies of anorexia nervosa occurring in ASD patients, as well as an increased likelihood of this eating disorder in families with ASD (Gillberg & Coleman, 1992, p.99).

Humans and animals exposed to mercury develop unusual, abnormal, and "inappropriate" behaviors (Florentine and Sanfilippo, 1991). Rats exposed to mercury during gestation have exhibited stereotyped sniffing (Cuomo et al, 1984) and hyperactivity (Fredriksson et al, 1996). "Restlessness" has already been noted, and Davis et al (1994) found poor response inhibition in their human subjects; both of these behaviors are closely associated with ADHD in children. Babies and children with Hg poisoning exhibit agitation, crying for no observable reason, grimacing, and insomnia (Pierce et al, 1972; Snyder, 1972; Kark et al, 1971; Amin-Zaki, 1979; Florentine and Sanfilippo, 1991; Aronow and Fleischmann, 1976). An 18 month old toddler with otitis media, exposed to thimerosal in ear drops, had staring spells and unprovoked screaming episodes (Rohyans et al, 1984). Symptoms of acrodynia in babies and toddlers include continuous crying, anorexia and insomnia (Matheson et al, 1980; Aronow and Fleischmann, 1976). These children were said to bang their heads, have difficulty falling asleep, be irritable, and either refuse to eat or only eat a few foods (Neville Recollection, Pink Disease Support Group Site; Farnesworth, 1997). The frequent temper tantrums of a previously normal 12 year old, poisoned by mercury vapor, included hitting herself on the head and screaming; furthermore, she had extreme genital burning and was observed to masturbate even in front of others (Fagala and Wigg, 1992). Similarly, priapism, persistent erection of the penis due to a pathologic condition resulting in pain and tenderness, has been noted in boys with mercury poisoning (Amin-Zaki et al, 1978).

Adults with mercury poisoning present with insomnia, agitation, and poor appetite (Tuthill, 1899; Adams et al, 1983; Fagala and Wigg, 1992). Relative to controls, more adults who had acrodynia in childhood have eating idiosyncrasies, particularly a preference for salty foods to sweet ones (Farnesworth, 1997), possibly because mercury causes excessive sodium excretion, as shown in studies of dental amalgam placed in monkeys and sheep (Lorscheider et al, 1995).

Table VII: Summary of Unusual Behaviors
in Mercury-Poisoned Animals and Humans & in Autism

Mercury Poisoning	Autism
Stereotyped sniffing (rats)	Stereotyped, repetitive behaviors
Hyperactivity (rats); poor response inhibition (humans), restlessness	Hyperactivity; ADHD-traits
Agitation (humans)	Agitation
Insomnia; difficulty falling asleep (humans)	Insomnia; difficulty falling or staying asleep
Eating disorders: anorexia, poor appetite, food aversion, narrow food preferences, decided food preferences (salty food) (humans)	Eating disorders: anorexia; restricted diet/narrow food preferences; feeding and suckling problems
Masturbation, priapism (children)	Masturbatory tendencies
Unintelligible cries; continuous crying; unprovoked crying (infants and children)	Unprovoked crying
Self injurious behavior, including head banging and hitting the head (toddlers and children)	Self injurious behavior, including head banging and hitting the head
Grimacing (children)	Grimacing
Staring spells (infants and children)	Staring spells

g. Vision

In autism, one of the earliest signs detected by mothers is a lack of eye contact (Gillberg & Coleman, 1992), and an early diagnostic behavior is failure to engage in joint attention based on the ability to "look where you are pointing" (CHAT, Baron-Cohen et al, 1992). Of 11 autistic children studied, ten had inaccurate or slow visual saccades (Rosenhall et al, 1988). Although some adults with ASD report exceptional visual acuity, visual problems are common, with two separate studies reporting 50% of ASD subjects having some type of unusual visual impairment (Steffenburg, in Gillberg & Coleman, 1992). Ritvo et al (1986) and Creel et al (1989) found decreased function of the rods in a study of autistic people, including a retinal sheen, and noted that many such individuals tend to use peripheral vision because of this. A number of case reports describe over-sensitivity to light and blurred vision (Sperry, 1998; Gillberg & Coleman, 1992, p.29; O'Neill & Jones, 1997).

Mercury can lead to a variety of vision problems, especially in children (Pierce et al, 1972; Snyder, 1972). Children who ate high doses of mercury from contaminated pork developed blindness (Snyder, 1972). In Iraqi babies exposed prenatally there was blindness or impaired vision (Amin-Zaki, 1974 and 1979). Iraqi children exposed postnatally developed visual disturbances, which ranged from blurred or hazy vision to constriction of the visual fields to complete blindness (Amin-Zaki et al, 1978). Two girls with mercury vapor poisoning were found to have visual field defects (Snyder, 1972), and, as previously noted, one child with Hg poisoning developed gaze avoidance (Fagala & Wigg, 1992). Acrodynia sufferers report vision problems, including near-sightedness and light sensitivity or photophobia (Diner and Brenner, 1998; Neville Recollection, Pink Disease site; Farnesworth, 1997; Matheson et al, 1980; Aronow and Fleischmann, 1976). A 25 year old man with elemental mercury poisoning exhibited decreased visual acuity, difficulty with visual fixation, and constricted visual fields (Kark et al, 1971). In Japanese victims, there was blurred vision as well as constriction of visual fields (Snyder, 1972; Tokuomi et al, 1982). Iraqi mothers exposed to Hg had visual disturbance (Amin-Zaki, 1979).

In dogs exposed to daily doses of methylmercury, distortion of the visual evoked response from the visual cortex was the first sign. Damage occurred in the preclinical silent stage, demonstrating that CNS damage is occurring before overt symptoms appear (Mattsson et al, 1981). Monkeys treated at birth with low level methylmercury exhibited impaired spatial vision and visual acuity at age 3 and 4 years (Rice and Gilbert, 1982). Disturbances caused by methylmercury in rat optic nerves were observed (Kinoshita et al, 1999).

Table VIII: Summary of Visual Impairments
Seen in Mercury Poisoning & Autism

Mercury Poisoning	Autism
Lack of eye contact; difficulties with visual fixation	Lack of eye contact; gaze abnormalities; problems in joint attention
"Visual impairments," blindness, near-sightedness, decreased visual acuity	"Visual impairments"; inaccurate or slow saccades; decreased functioning of the rods; retinal sheen
Light sensitivity, photophobia	Over-sensitivity to light
Blurred or hazy vision	Blurred vision
Constricted visual fields	Not described

h. Physical Presentations

There is a much higher rate of autism among children with cerebral palsy than would be expected by chance (Nordin and Gillberg, 1996). Many autistic children have abnormal muscle tone including hyper- and hypotonia, and many are incontinent or have difficulty being toilet trained (Filipek et al, 1999; Church and Coplan, 1995). Several of the infants which Teitelbaum and colleagues (1998) observed showed decreased arm strength, and Schuler (1995) describes greater muscle weakness in the upper than the lower body. Impairments in oral-motor function, including problems chewing and swallowing, are common, as noted previously.

These impairments are seen in mercurialism as well. In the Iraqi and Japanese epidemics, many children developed clinical cerebral palsy (Amin-Zaki, 1979; Myers & Davidson, 1998; Gilbert & Grant-Webster 1995; Dale, 1972). Amin-Zaki et al (1978) reported muscle wasting and lack of motor power and control in most cases, complete paralysis in several cases, and athetotic movements in 2 cases, of postnatally exposed children. In the Iraqi babies and children, some had increased muscle tone, while others had decreased muscle tone. Abnormal reflexes, spasticity, and weakness were common. One child said "my hands are weak and do not obey me" (Amin-Zaki et al, 1974 and 1978). The 12 year old who inhaled mercury vapor exhibited weakness and decreased muscle strength (Fagala and Wigg, 1992). As in autism, muscle weakness from mercury poisoning is most prominent in the upper body (Adams et al, 1983). Acrodynia, for example, is marked by poor muscle tone in general and loss of arm strength in particular (Farnesworth, 1997). Finally, difficulty in chewing and swallowing, salivation, and drooling are common in children as well as adults; incontinence was observed in children in the Iraqi Hg-crisis (Amin-Zaki, 1974 and 1978; Pierce et al, 1972; Snyder, 1972; Joselow et al, 1972; Smith, 1977).

The presence of rashes and dermatitis is sometimes reported in descriptions of ASD subjects. Whiteley et al (1998) found that 63% of the ASD children had a history of eczema or other skin complaints. "Some children with autism are frequent scratchers. Gentle rubbing and scratching can become a calming self-stimulation; but when it becomes clawing, and there are rashes and open scrapes on the skin, a tactile intolerance can be responsible" (O'Neill, 1999).

Rashes and itching are common disturbances in mercury toxicity as well (Kark et al, 1971). A 4 year old with Hg poisoning developed an itchy, peeling rash on the extremities (Florentine and Sanfilippo, 1991). Mercury vapor inhalation caused a rash and peeling on the palms and soles of a pre-adolescent (Fagala and Wigg, 1992). An acrodynia victim described himself as a child as having severe itching and a constant burning sensation at the extremities, resulting in him rubbing his hands and feet raw (Neville Recollection, Pink Disease Support Group). Acrodynia symptoms in an adult poisoned by ethylmercury injection included pink scaling palms and soles, flushed cheeks, and itching (Matheson et al, 1980). In acrodynia the skin may be rough and dry, and the soles and palms are usually but not necessarily red (Aronow and Fleischmann, 1976). Thimerosal ingested by 44 year old man led to dermatitis (Pfab et al, 1996).

In autism, "signs of autonomic disturbance may be noticed at times, including sweating, irregular breathing, and rapid pulse" (Wing and Attwood, 1987). There may be elevated blood flow and heart rate (Ornitz, 1987). An increased incidence of acrocyanosis has been observed in Asperger's syndrome. Acrocyanosis is an uncommon disorder of poor circulation in which skin on the hands and feet turn red and blue; there is profuse sweating; and the fingers and toes are persistently cold (Carpenter and Morris, 1991).

Sweating and circulatory abnormalities are also common in some forms of mercury poisoning. Acrodynia in adults and children results in excessive sweating, poor circulation, and rapid heart rate (Farnesworth, 1997; Matheson et al, 1980; Cloarec et al, 1995; Warkany and Hubbard, 1953). The 12 year old with mercury vapor poisoning sweated profusely, especially at night (Fagala and Wigg, 1992), and elevated blood pressure has been reported in exposed workers (Vroom and Greer, 1972). Autonomic system abnormalities can be caused by disturbances in acetylcholine levels, known to be deficient in both autism and Hg poisoning (see neurotransmitter section below).

Table IX: Physical Disturbances
in Mercury Poisoning & Autism

Mercury Poisoning	Autism
Increase in cerebral palsy; hyper- or hypotonia; paralysis, abnormal reflexes; spasticity; decreased muscle strength and motor power, especially in the upper body; incontinence; problems chewing, swallowing, and salivating	Increase in cerebral palsy; hyper- or hypotonia; decreased muscle strength, especially in the upper body; incontinence/toilet training difficulties; problems chewing and swallowing
Rashes, dermatitis, dry skin, itching; burning sensation	Rashes, dermatitis, eczema; itching
Autonomic disturbances: excessive sweating; poor circulation; elevated heart rate	Autonomic disturbances: sweating abnormalities; poor circulation; elevated heart rate

j. Gastrointestinal Function

Many if not most autistic individuals have gastrointestinal problems, the most common complaints being chronic diarrhea, constipation, gaseousness, and abdominal discomfort and distention (D'Eufemia et al, 1996; Horvath et al, 1999; Whitely et al, 1998). Colitis is not uncommon (Wakefield et al, 1998). As noted previously, anorexia is sometimes associated with ASD (Gillberg & Coleman, 1992). Kanner noted that over half his initial cases had feeding difficulties and excessive vomiting as infants (1943). O'Reilly and Waring (1993) have described sulfur deficiencies in autism, an effect of which can be clumping of proteins on the gut wall, which is lined with sulfated proteins. The clumping can lead to increased intestinal permeability, or leaky gut syndrome (Shattock, 1997), found in many autistic individuals (D'Eufemia, 1996). Some ASD individuals have unusual opioid peptide fragments in urine; these peptides are believed to enter the bloodstream due to a leaky gut and to result from an incomplete breakdown of gluten and casein in the diet possibly arising from "inadequacy of the [endopeptidase] enzyme systems which are responsible for their breakdown" (Shattock, 1997).

Mercury, which binds to sulfur groups (Clarkson, 1992), is known to cause gastroenteritis (Kark et al, 1971). For example, a four year old with diarrhea was initially diagnosed with gastroenteritis (Florentine and Sanfilippo, 1991). A pre-adolescent with mercury vapor poisoning developed nausea, abdominal pain, poor appetite, rectal itching, and diarrhea; she frequently strained to have a bowel movement, and was at one point diagnosed with colitis (Fagala and Wigg, 1992). Acrodynia is marked by both constipation and diarrhea (Diner and Brenner, 1998). Incontinence of urine and stool are observed in infants and children exposed pre- and postnatally in Iraq (Amin-Zaki, 1974 and 1978). In another case, a 28 year old woman with occupational exposure to mercury vapor developed watery stools (Ross et al, 1977). Diarrhea and digestive disturbance were seen in a dentist with measurable mercury levels; there was obesity in another dentist (Smith, 1977). A 44 year old man poisoned with thimerosal given intramuscularly developed gastrointestinal bleeding, which looked like hemorrhaging colitis (Lowell et al, 1996). Intense exposure to mercury vapor can cause abdominal pain, nausea, and vomiting (Feldman, 1982). Severe constipation, anorexia, weight loss, and other "disturbances of gastrointestinal function" have been noted in other cases (Adams et al, 1983; Joselow et al, 1972). Rats tested with mercuric chloride were observed with "lesions of the ileum and colon with abnormal deposits of IgA in the basement membranes of the intestinal glands and of IgG in the basement membranes of the lamina propria" (Andres, 1984, reviewed in EPA, 1997, p.3-36). In another rat experiment, Hg was found to increase the permeability of intestinal epithelial tissues (Watzl et al, 1999). Mercury also inhibits the peptidase - dipeptidyl peptidase IV - which cleaves, among other substances, casomorphin during the digestive process (Puschel et al, 1982).

There is no reported increase in incidence in kidney problems in autism. Although renal function is commonly impaired from Hg exposure, such impairment would not be expected if the mercury exposure occurred from thimerosal injections, since kidney function may be unaffected when mercury is injected or inhaled (Davis et al, 1994; Fagala and Wigg, 1992). For example, although thimerosal ingested orally by a 44 year old man resulted in renal tubular failure and gingivitis (Pfab et al, 1996), renal function was normal in another 44 year old man injected intramuscularly with thimerosal (Lowell et al, 1996).

Table X: Summary of Gastrointestinal Problems
in Mercury Poisoning & Autism

Mercury Poisoning	Autism
Gastroenteritis, diarrhea; abdominal pain, rectal itching, constipation, "colitis"	Diarrhea, constipation, gaseousness, abdominal discomfort, colitis
Anorexia, weight loss, nausea, poor appetite	Anorexia; feeding difficulties, vomiting as infants
Lesions of the ileum and colon; increased intestinal permeability	Leaky gut syndrome from sulfur deficiency
Inhibits dipeptidyl peptidase IV, which cleaves casomorphin	Inadequate endopeptidase enzymes responsible for breakdown of casein and gluten

II. Comparison of Biological Abnormalities

Like the similarities seen in observable symptoms, parallels between autism and mercury poisoning clearly exist even at cellular and subcellular levels. These similarities are summarized in tables after each individual section.

a. Biochemistry

Sulfur: Studies of autistic children with known chemical or food intolerances show a low capacity to oxidize sulfur compounds and low levels of sulfate (O'Reilly & Waring, 1993; Alberti et al, 1999). These findings were interpreted as suggesting that "there may be a fault either in the manufacture of sulfate or that sulfate is being used up dramatically on an unknown toxic substance these children may be producing" (O'Reilly and Waring, 1993). Alternatively, these observations may be linked to mercury, since mercury preferentially forms compounds with molecules rich in sulfhydryl groups (--SH), such as cysteine and glutathione, making them unavailable for normal cellular and enzymatic functions (Clarkson, 1992). Relatedly, mercury may cause low sulfate by its ability to irreversibly inhibit the sulfate transporter Na-Si cotransporter NaSi-1 present in kidneys and intestines, thus preventing sulfate absorption (Markovitch and Knight, 1998).

Among the sulfhydryl groups, or thiols, mercury has special affinity for purines and pyrimidines, as well as other subcellular substances (Clarkson, 1992; Koos and Longo, 1976). Errors in purine or pyrimidine metabolism are known to result in classical autism or autistic features in some cases (Gillberg and Coleman, 1992, p.209; Page et al, 1997; Page & Coleman, 2000; The Purine Research Society), thereby suggesting that mercury's disruption of this pathway might also lead to autistic traits.

Likewise, yeast strains sensitive to Hg are those which have innately low levels of tyrosine synthesis. Mercury can deplete cellular tyrosine by binding to the SH-groups of the tyrosine uptake system, preventing colony growth (Ono et al, 1987), and Hg-depleted tyrosine would be particularly significant in cells known to accumulate mercury (e.g., neurons of the CNS, see below). Similarly, disruptions in tyrosine production in hepatic cells, arising from a genetic condition called Phenylketonuria (PKU), also results in autism (Gillberg & Coleman, 1992, p.203).

Glutathione: Glutathione is one of the primary means through which the cells detoxify heavy metals (Fuchs et al, 1997), and glutathione in the liver is a primary substrate by which body clearance of organic mercury takes place (Clarkson, 1992). Mercury, by preferentially binding with glutathione and/or preventing absorption of sulfate, reduces glutathione bioavailability. Many autistic subjects have low levels of glutathione. O'Reilly and Waring (1993) suggest this is due to an "exotoxin" binding glutathione so it is unavailable for normal biological processes. Edelson and Cantor (1998) have found a decreased ability of the liver in autistic subjects to detoxify heavy metals. Alternatively, low glutathione can be a manifestation of chronic infection (Aukrust et al, 1996, 1995; Jaffe et al, 1993), and infection-induced glutathione deficiency would be more likely in the presence of immune impairments derived from mercury (Shenkar et al, 1998).

Glutathione peroxidase activities were reported to be abnormal in the erythrocytes of autistic children (Golse et al, 1978). Mercury generates reactive oxygen species (ROS) levels in cells, which increases ROS scavenger enzyme content and thus glutathione, to relieve oxidative stress (Hussain et al, 1999). At high enough levels, mercury depletes rat hepatocytes of glutathione (GSH) and causes significant reduction in glutathione peroxidase and glutathione reductase (Ashour et al, 1993).

Mitochondria: Disturbances of brain energy metabolism have prompted autism to be hypothesized as a mitochondrial disorder (Lombard, 1998). There is a frequent association of lactic acidosis and carnitine deficiency in autistic patients, which suggests excessive nitric oxide production in mitochondria (Lombard, 1998; Chugani et al, 1999), and again, mercury may be a participant. Methylmercury accumulates in mitochondria, where it inhibits several mitochondrial enzymes, reduces ATP production and Ca2+ buffering capacity, and disrupts mitochondrial respiration and oxidative phosphorylation (Atchison & Hare, 1994; Rajanna and Hobson, 1985; Faro et al, 1998). Neurons have increased numbers of mitochondria (Fuchs et al, 1997), and since Hg accumulates in neurons of the CNS, an Hg effect upon neuronal mitochondria function seems likely - especially in children having substandard mercury detoxification.

Table XI: Abnormalities in Biochemistry
Arising from Hg Exposure & Present in Autism

Mercury Poisoning	Autism
Ties up sulfur groups; prevents sulfate absorption	Low sulfate levels
Has special affinity for purines and pyrimidines	Errors in purine and pyrimidine metabolism can lead to autistic features
Depletes cellular tyrosine in yeast	PKU, arising from disruption in tyrosine production, results in autism
Reduces bioavailability of glutathione, necessary in cells and liver for heavy metal detoxification	Low levels of glutathione; decreased ability of liver to detoxify heavy metals
Can cause significant reduction in glutathione peroxidase and glutathione reductase	Abnormal glutathione peroxidase activities in erythrocytes
Disrupts mitochondrial activities, especially in brain	Mitochondrial dysfunction, especially in brain

b. Immune System

A variety of immune alterations are found in autism-spectrum children (Singh et al, 1993; Gupta et al, 1996; Warren et al, 1986 & 1996; Plioplys et al, 1994), and these appear to be etiologically significant in a variety of ways, ranging from autoimmunity to infections and vaccination responses (e.g., Fudenberg, 1996; Stubbs, 1976). Mercury's effects upon immune cell function are well documented and may be due in part to the ability of Hg to reduce the bioavailability of sulfur compounds:

"It has been known for a long time that thiols are required for optimal primary in vitro antibody response, cytotoxicity, and proliferative response to T-cell mitogens of murine lymphoid cell cultures. Glutathione and cysteine are essential components of lymphocyte activation, and their depletion may result in lymphocyte dysfunction. Decreasing glutathione levels profoundly affects early signal transduction events in human T-cells" (Fuchs & Sch"fer, 1997).

Allergy, asthma, and arthritis: Individuals with autism are more likely to have allergies and asthma, and autism occurs at a higher than expected rate in families with a history of autoimmune diseases such as rheumatoid arthritis and hypothyroidism (Comi and Zimmerman, 1999; Whitely et al, 1998). Relative to the general population, prevalence of selective IgA deficiency has been found in autism (Warren et al); individuals with selective IgA deficiency are more prone to allergies and autoimmunity (Gupta et al, 1996). Furthermore, lymphocyte subsets of autistic subjects show enhanced expression of HLA-DR antigens and an absence of interleuken-2 receptors, and these findings are associated with autoimmune diseases like rheumatoid arthritis (Warren et al). These observations suggest autoimmune processes are present in ASD (Plioplys, 1989; Warren et al); and this possibility is reinforced by Singh's findings of elevated antibodies against myelin-basic protein (Singh et al, 1993).

Atypical responses to mercury have been ascribed to allergic or autoimmune reactions (Gosselin et al, 1984; Fournier et al, 1988), and a genetic predisposition for Hg reaction may explain why sensitivity to this metal varies so widely by individual (Rohyans et al, 1984; Nielsen & Hultman, 1999). Acrodynia can present as a hypersensitivity reaction (Pfab et al, 1996), or it may arise from immune over-reactivity, and "children who incline to allergic reactions have an increased tendency to develop acrodynia" (Warkany & Hubbard, 1953). Those with acrodynia are also more likely to suffer from asthma, to have poor immune system function (Farnesworth, 1997), and to experience intense joint pains suggestive of rheumatism (Clarkson, 1997). Methylmercury has altered thyroid function in rats (Kabuto, 1991).

Rheumatoid arthritis with joint pain has been observed as a familial trait in autism (Zimmerman et al, 1993). A subset of autistic subjects had a higher rate of strep throat and elevated levels of B lymphocyte antigen D8/17, which has expanded expression in rheumatic fever and may be implicated in obsessive-compulsive behaviors (DelGiudice-Asch & Hollander, 1997).

Mercury exposure frequently results in rheumatoid-like symptoms. Iraqi mothers and children developed muscle and joint pain (Amin-Zaki, 1979), and acrodynia is marked by joint pain (Farnesworth, 1997). Sore throat is occasionally a presenting sign in mercury poisoning (Vroom and Greer, 1972). A 12 year old with mercury vapor poisoning, for example, had joint pains as well as a sore throat; she was positive on a streptozyme test, and a diagnosis of rheumatic fever was made; she improved on penicillin (Fagala and Wigg, 1992). Acrodynia, which is almost never seen in adults, was also observed in a 20 year old male with a history of sensitivity reactions and rheumatoid-like arthritis, who received ethylmercury via injection in gammaglobulin (Matheson et al, 1980). One effective chelating agent, penicillamine, is also effective for rheumatoid arthritis (Florentine and Sanfilippo, 1991).

Mercury can induce an autoimmune response in mice and rats, and the response is both dose-dependent and genetically determined. Mice "genetically prone to develop spontaneous autoimmune diseases [are] highly susceptible to mercury-induced immunopathological alterations" (al-Balaghi, 1996). The autoimmune response depends on the H-2 haplotype: if the strain of mice does not have the susceptibility haplotype, there is no autoimmune response; the most sensitive strains show elevated antibody titres at the lowest dose; and the less susceptible strain responds only at a medium dose (Nielsen & Hultman, 1999). Interestingly, Hu et al (1997) were able to induce a high proliferative response in lymphocytes from even low responder mouse strains by washing away excess mercury after pre-treatment, while chronic exposure to mercury induced a response only in high-responder strains.

Autoimmunity and neuronal proteins: Based upon research and clinical findings, Singh has been suggesting for some time an autoimmune component in autism (Singh, Fudenberg et al, 1988). The presence of elevated serum IgG "may suggest the presence of persistent antigenic stimulation" (Gupta et al, 1996). Connolly and colleagues (1999) report higher rates in autistic vs. control groups of elevated antinuclear antibody (ANA) titers, as well as presence of IgG and IgM antibodies to brain endothelial cells. On the one hand, since mercury remains in the brain for years after exposure, autism's persistent symptoms may be due to an on-going autoimmune response to mercury remaining in the brain; on the other hand, activation and continuation of an autoimmune response does not require the continuous presence of mercury ions: in fact, once induced, autoimmune processes in the CNS might remain exacerbated because removal of mercury after an initial exposure can induce a greater proliferative response in lymphocytes than can persistent Hg exposure (Hu et al, 1997).

In sera of male workers exposed to mercury, autoantibodies (primarily IgG) to neuronal cytoskeletal proteins, neurofilaments (NFs), and myelin basic protein (MBP) were prevalent. These findings were confirmed in rats and mice, and there were significant correlations between IgG titers and subclinical deficits in sensorimotor function. These findings suggest that peripheral autoantibodies to neuronal proteins are predictive of neurotoxicity, since histopathological findings were associated with CNS and PNS damage. There was also evidence of astrogliosis (indicative of neuronal CNS damage) and the presence of IgG concentrated along the bbb (El-Fawal et al, 1999). Autoimmune response to mercury has also been shown by the transient presence of antinuclear antibodies (ANA) and antinucleolar antibodies (ANolA) (Nielsen & Hultman, 1999; Hu et al, 1997; Fagala and Wigg, 1992).

A high incidence of anti-cerebellar immunoreactivity which was both IgG and IgM in nature has been found in autism, and there is a higher frequency of circulating antibodies directed against neuronal antigens in autism as compared to controls (Plioplys, 1989; Connolly et al, 1999). Furthermore, Singh and colleagues have found that 50% to 60% of autistic subjects tested positive for the myelin basic protein antibodies (1993) and have hypothesized that autoimmune responses are related to an increase in select cytokines and to elevated serotonin levels in the blood (Singh, 1996; Singh, 1997). Weitzman et al (1982) have also found evidence of reactivity to MBP in autistic subjects but none in controls.

Since anti-cerebellar antibodies have been detected in autistic blood samples, ongoing damage may arise as these antibodies find and react with neural antigens, thus creating autoimmune processes possibly producing symptoms such as ataxia and tremor. Relatedly, the cellular damage to Purkinje and granule cells noted in autism (see below) may be mediated or exacerbated by antibodies formed in response to neuronal injury (Zimmerman et al, 1993).

T-cells, monocytes, and natural killer cells: Many autistics have skewed immune-cell subsets and abnormal T-cell function, including decreased responses to T-cell mitogins (Warren et al, 1986; Gupta et al, 1996). One recent study reported increased neopterin levels in urine of autistic children, indicating activation of the cellular immune system (Messahel et al, 1998).

Workers exposed to Hgo exhibit diminished capacity to produce the cytokines TNF (alpha) and IL-1 released by monocytes and macrophages (Shenkar et al, 1998). Both high dose and chronic low-level mercury exposure kills lymphocytes, T-cells, and monocytes in humans. This occurs by apoptosis due to perturbation of mitochondrial dysfunction. At low, chronic doses, the depressed immune function may appear asymptomatic, without overt signs of immunotoxicity. Methylmercury exposure would be especially harmful in individuals with already suppressed immune systems (Shenker et al, 1998). Mercury increases cytosolic free calcium levels [Ca2+]i in T lymphocytes, and can cause membrane damage at longer incubation times (Tan et al, 1993). Hg has also been found to cause chromosomal aberrations in human lymphocytes, even at concentrations below those causing overt poisoning (Shenkar et al, 1998; Joselow et al, 1972), and to inhibit rodent lymphocyte proliferation and function in vitro.

Depending on genetic predisposition, mercury causes activation of the immune system, especially Th2 subsets, in susceptible mouse strains (Johansson et al, 1998; Bagenstose et al, 1999; Hu et al, 1999). Many autistic children have an immune portrait shifted in the Th2 direction and have abnormal CD4/CD8 ratios (Gupta et al, 1998; Plioplys, 1989). This may contribute to the fact that many ASD children have persistent or recurrent fungal infections (Romani, 1999).

Many autistic children have reduced natural killer cell function (Warren et al, 1987; Gupta et al, 1996), and many have a sulfation deficiency (Alberti, 1999). Mercury reduces --SH group/sulfate availability, and this has immunological ramifications. As noted previously, decreased levels of glutathione, observed in autistic and mercury poisoned populations, are associated with impaired immunity (Aukrust et al, 1995 and 1996; Fuchs and Sch"fer, 1997). Decreases in NK T-cell activity have in fact been detected in animals after methylmercury exposure (Ilback, 1991).

Singh detected elevated IL-12 and IFNg in the plasma of autistic subjects (1996). Chronic mercury exposure induces IFNg and IL-2 production in mice, while intermittent presence of mercury suppresses IFNg and enhances IL-4 production (Hu et al, 1997). Interferon gamma (IFNg) is crucial to many immune processes and is released by T lymphocytes and NK cells, for example, in response to chemical mitogens and infection; sulfate participates in IFNg release, and "the effector phase of cytotoxic T-cell response and IL-2-dependent functions is inhibited by even a partial depletion of the intracellular glutathione pool" (Fuchs & Sch"fer, 1997). A mercury-induced sulfation problem might, therefore, impair responses to viral (and other) infections - via disrupting cell-mediated immunity as well as by impairing NK function (Benito et al, 1998). In animals, Hg exposure has led to decreases in production of antibody-producing cells and in antibody titres in response to inoculation with immune-stimulating agents (EPA, 1997, review, p.3-84).

Table XII: Summary of Immune System Abnormalities
in Mercury Exposure & Autism

Mercury Poisoning	Autism
Individual sensitivity due to allergic or autoimmune reactions; sensitive individuals more likely to have allergies and asthma, autoimmune-like symptoms, especially rheumatoid-like ones	More likely to have allergies and asthma; familial presence of autoimmune diseases, especially rheumatoid arthritis; IgA deficiencies
Can produce an immune response, even at low levels; can remain in CNS for years	Indications of on-going immune response in CNS
Presence of autoantibodies (IgG) to neuronal cytoskeletal proteins, neurofilaments, and myelin basic protein; astrogliosis; transient ANA and AnolA	Presence of autoantibodies (IgG and IgM) to cerebellar cells, myelin basis protein
Causes overproduction of Th2 subset; diminishes capacity to produce TNF(alpha) and IL-1; kills lymphocytes, T-cells, and monocytes; inhibits lymphocyte production; decreases NK T-cell activity; may induce or suppress IFN(gamma) and IL-2 production	Skewed immune-cell subset in the Th2 direction and abnormal CD4/CD8 ratios; decreased responses to T-cell mitogens; increased neopterin; reduced NK T-cell function; increased IFN(gamma) and IL-12

c. CNS Structure

Autism is primarily a neurological disorder (Minshew, 1996), and mercury preferentially targets nerve cells and nerve fibers (Koos and Longo, 1976). Experimentally, primates have the highest levels in the brain relative to other organs (Clarkson, 1992). Methylmercury easily crosses the blood-brain barrier by binding with cysteine to form a molecule that is nearly identical to methionine. This molecule - methylmercury cysteine - is transported on the Large Neutral Amino Acid across the bbb (Clarkson, 1992).

Once in the CNS, organic mercury is converted to the inorganic form (Vahter et al, 1994). Inorganic mercury is unable to cross back out of the bbb (Pedersen et al, 1999) and is more likely than the organic form to induce an autoimmune response (Hultman and Hansson-Georgiadis, 1999). Furthermore, although most cells respond to mercurial injury by modulating levels of glutathione, metallothionein, hemoxygenase, and other stress proteins, "with few exceptions, neurons appear to be markedly deficient in these responses" and thus more prone to injury and less able to remove the metal (Sarafian et al, 1996).

While damage has been observed in a number of brain areas in autism, many functions are spared (Dawson, 1996). In mercury exposure, damage is also selective (Ikeda et al, 1999; Clarkson, 1992), and the list of Hg-affected areas is remarkably similar to the neuroanatomy of autism.

Cerebellum, Cerebral Cortex, & Brainstem: Autopsy studies of carefully selected autistic individuals revealed cellular changes in cerebellar Purkinje and granule cells (Bauman and Kemper, 1988; Ritvo et al, 1986). MRI studies by Courchesne and colleagues (1988; reviewed in ARI Newslett, 1994) described cerebellar defects in autistic subjects, including smaller vermal lobules VI and VII and volume loss in the parietal lobes. The defects were present independently of IQ. "No other part of the nervous system has been shown to be so consistently abnormal in autism." Courchesne (1989) notes that the only neurobiological abnormality known to precede the onset of autistic symptomatology is Purkinje neuron loss in the cerebellum. Piven found abnormalities in the cerebral cortex in seven of 13 high-functioning autistic adults using MRI (1990). Although more recent studies have called attention to amygdaloid and temporal lobe irregularities in autism (see below), and cerebellar defects have not been found in all ASD subjects studied (Bailey et al, 1996), the fact remains that many and perhaps most autistic children have structural irregularities within the cerebellum.

Mercury can induce cellular degeneration within the cerebral cortex and leads to similar processes within granule and Purkinje cells of the cerebellum (Koos and Longo, 1976; Faro et al, 1998; Clarkson, 1992; see also Anuradha, 1998; Magos et al, 1985). Furthermore, cerebellar damage is implicated in alterations of coordination, balance, tremors, and sensations (Davis et al, 1994; Tokuomi et al, 1982), and these findings are consistent with Hg-induced disruption in cerebellar synaptic transmission between parallel fibers or climbing fibers and Purkinje cells (Yuan & Atchison, 1999).

MRI studies have documented Hg-effects within visual and sensory cortices, and these findings too are consistent with the observed sensory impairments in victims of mercury poisoning (Clarkson, 1992; Tokuomi et al, 1982). Acrodynia, a syndrome with symptoms similar to autistic traits, is considered a pathology mainly of the CNS arising from degeneration of the cerebral and cerebellar cortex (Matheson et al, 1980). In monkeys, mercury preferentially accumulated in the deepest pyramidal cells and fiber systems.

Mercury causes oxidative stress in neurons. The CNS cells primarily affected are those which are unable to produce high levels of protective metallothionein and glutathione. These substances tend to inhibit lipid peroxidation and thereby suppress mercury toxicity (Fukino et al, 1984). Importantly, granule and Purkinje cells have increased risk for mercury toxicity because they produce low levels of these protective substances (Ikeda et al, 1999; Li et al, 1996). Naturally low production of glutathione, when combined with mercury's ability to deplete usable glutathione reserves, provides a mechanism whereby mercury is difficult to clear from the cerebellum -- and this is all the more significant because glutathione is a primary detoxicant in brain (Fuchs et al, 1997).

Mercury's induction of cerebellar deterioration is not restricted to high-doses. Micromolar doses of methylmercury cause apoptosis of developing cerebellar granule cells by antagonizing insulin-like growth factor (IGF-I) and increasing expression of the transcription factor c-Jun (Bulleit and Cui, 1998).

Several researchers have found evidence of a brainstem defect in a subset of autistic subjects (Hashimoto et al, 1992 and 1995; McClelland et al, 1985); and MRI studies have revealed brainstem damage in a few cases of mercury poisoning (Davis et al, 1994). The peripheral polyneuropathy examined in Iraqi victims was believed to have resulted from brain stem damage (Von Burg and Rustam, 1974).

Amygdala & Hippocampus: Atypicalities in other brain areas are remarkably similar in ASD and mercury poisoning. Pathology affecting the temporal lobe, particularly the amygdala, hippocampus, and connected areas, is seen in autistic patients and is characterized by increased cell density and reduced neuronal size (Abell et al, 1999; Hoon and Riess, 1992; Otsuka, 1999; Kates et al, 1998; Bauman and Kemper, 1985). The basal ganglia also show lesions in some cases (Sears, 1999), including decreased blood flow (Ryu et al, 1999).

Mercury can accumulate in the hippocampus and amygdala, as well as the striatum and spinal chord (Faro et al, 1998; Lorscheider et al, 1995; Larkfors et al, 1991). One study has shown that areas of hippocampal damage from Hg were those which were unable to synthesize glutathione (Li et al, 1996). A 1994 study in primates found that mercury accumulates in the hippocampus and amygdala, particularly the pyramidal cells, of adults and offspring exposed prenatally (Warfvinge et al, 1994).

The documenting of temporal lobe mercury provides a direct link between autism and mercury because, as cited previously, (i) mercury alters neuronal function, and (ii) the temporal lobe, and the amygdala in particular, are strongly implicated in autism (e.g., Aylward et al, 1999; Bachevalier, 1994; Baron-Cohen, 1999; Bauman & Kemper, 1985; Kates et al, 1998; Nowell et al, 1990; Warfvinge et al, 1994). Bachevalier (1996) has shown that infant monkeys with early damage to the amygdaloid complex exhibit many autistic behaviors, including social avoidance, blank expression, lack of eye contact and play posturing, and motor stereotypies. Hippocampal lesions, when combined with amygdaloid damage, increases the severity of symptoms.

Also noteworthy is the fact that amygdala findings in autism and mercury literatures are paralleled in fragile X syndrome, a genetic disorder wherein many affected individuals have traits worthy of an autism diagnosis. These traits include sensory alterations, emotional lability, appetite dysregulation, social deficits, and eye-contact aversion (Hagerman). Not only are fraX-related proteins (FRM1, FMR2) implicated in amygdaloid function (Binstock, 1995; Yamagata, 1999), but neurons involved in gaze- and eye-contact-aversion have been identified within the primate temporal lobe and amygdaloid subareas (Rolls 1992, reviewed in Binstock 1995). These various findings in ASD, mercury poisoning, and fragile X suggest that amygdaloid mercury is a mechanism for inducing traits central to or associated with autism and the autism-spectrum of disorders.

Neuronal Organization & Head Circumference: Several autism brain studies have found evidence of increased neuronal cell replication, a lowered ratio of glia to neurons, and an increased number of glial cells (Bailey et al, 1996). Based on these and other neuropathological findings, autism can be characterized as "a disorder of neuronal organization, that is, the development of the dendritic tree, synaptogenesis, and the development of the complex connectivity within and between brain regions" (Minshew, 1996).

Mercury can interfere with neuronal migration and depress cell division in the developing brain. Post-mortem brain tissue studies of exposed Japanese and Iraqi infants revealed "abnormal neuronal cytoarchitecture characterized by ectopic cells and disorganization of cellular layers" (EPA, 1997, p.3-86; Clarkson, 1997). Developmental neurtoxicity of Hg may also be due to binding of mercury to sulfhydryl-rich tubulin, a component of microtubules (Pendergrass et al, 1997). Intact microtubules are necessary for proper cell migration and cell division (EPA, review, 1997, p.32-88).

Rat pups dosed postnatally with methylmercury had significant reductions in neural cell adhesion molecules (NCAMs), which are critical during neurodevelopment for proper synaptic structuring. Sensitivity of NCAMs to methylmercury decreased as the developmental age of the rats increased. "Toxic perturbation of the developmentally-regulated expression of NCAMs during brain formation may disturb the stereotypic formation of neuronal contacts and could contribute to the behavioral and morphological disturbances observed following methylmercury poisoning" (Deyab et al, 1999). Plioplys et al (1990) have found depressed expression of NCAM serum fragments in autism.

Abnormalities in neuronal growth during development are implicated in head size differences found in both autism and mercury poisoning. In autism, Fombonne and colleagues (1999) have found a subset of subjects with macrocephaly and a subset with microcephaly. The circumference abnormalities were progressive, so that, while micro- and macrocephaly were present in 6% and 9% respectively of children under 5 years, among those age 10-16 years, the rates had increased to 39% and 24% respectively. Another study, by Stevenson et al (1997), had found just one subject out of 18 with macrocephaly who had this abnormality present at birth. The macrocephaly in autism is generally believed to result from "increased neuronal growth or decreased neuronal pruning." The cause of microcephaly has not been investigated.

The most detailed study of head size in mercury poisoning, by Amin-Zaki et al (1979), involved 32 Iraqi children exposed prenatally and followed up to age 5 years. Eight (25%) had progressive microcephaly, i.e., the condition was not present at birth. None had developed macrocephaly, at least at the time of the study. The microcephaly has been ascribed to neuronal death or apoptosis from Hg intoxication.

Table XIII: CNS Lesions
in Mercury Poisoning & Autism

Mercury Poisoning	Autism
Primarily impacts CNS	Neurological impairments primary
Selectively targets brain areas - those unable to detoxify heavy metals or reduce Hg-induced oxidative stress	Specific areas of brain pathology; many functions spared
Damage to Purkinje and granular cells	Damage to Purkinje and granular cells
Accummulates in amygdala and hippocampus	Pathology in amygdala and hippocampus
Causes abnormal neuronal cytoarchitecture; interferes with neuronal migration and depresses cell division in developing brains; reduces NCAMs	Neuronal disorganization; increased neuronal cell replication, small glia to neuron ration, increased glial cells; depressed expression of NCAMs
Head size differences: progressive microcephaly	Head size differences: progressive microcephaly and macrocephaly
Brain stem defects in some cases	Brain stem defects in some cases

d. Neurons & Neurochemicals

The brains of autistic subjects show disturbances in many neurotransmitters, primarily serotonin, catecholamines, the amino acid neurotransmitters, and acetylcholine. Mercury poisoning causes disturbances in these same neurotransmitters: primarily serotonin, the catecholamines, glutamate, and acetlycholine.

Serotonin: Serotonin synthesis is decreased in the brains of autistic children and increased in autistic adults, relative to age-matched controls (Chugani et al, 1999), while whole blood serotonin in platelets is elevated regardless of age (Leboyer; Cook, 1990). Autistic patients frequently respond well to SSRIs as well as Risperidone (McDougal; 1997; Zimmerman et al, 1996). Likewise, a number of animal studies have found serotonin abnormalities from mercury exposure. For example, subcutaneous administration of methylmercury to rats during postnatal development increases tissue concentration of 5-HT and HIAA in cerebral cortex (O'Kusky