Thimerosal: Autism’s Scapegoat

March 5, 2004

Scientific Method: Debunking PseudoscienceMalia Bender

Thimerosal, a mercury-based preservative, has been

keeping vaccine vials bacteria and fungus free since 1930. The need

for thimerosal became apparent when people started experiencing

bacterial infections after receiving vaccinations, due to the fact that

the vaccines were kept in bottles that would have multiple doses

drawn from them over the course of their short shelf lives. By adding

thimerosal to the stock bottles, the vaccines would be kept clean of

harmful microbes and preserved for a longer period of time. In recent

years, a controversy has been raised concerning the true nature of

thimerosal and its potentially harmful side effects. This paper will

explore the misconception, primarily found among organizations

comprised of parents with autistic children and Christian Scientists,

that thimerosal causes autism.1

According to the Stanford University Medical Center’s website,

autism is classified as a pervasive developmental disorder (PDD) which

is a complex neurodevelopmental disorder that typically appears

during the first three years of life.2 One known cause of autism is drug

use, e.g. thalidomide, during pregnancy. Other causes of autism are

genetic, resulting from a mutation or nondisjunction during meiosis.3

1 It is understandable that Christian Scientists would be a large proponent in the cause to eliminate vaccinations, as they do not believe in modern medicine, like immunizations, and doctors. They believe that illness is a “false-reality” that can be removed through prayer and positive thought with the help of “Christian Science Practicioners.”2 Lucile Packard Children’s Hospital. “Autism and Pervasive Developmental Disorders.” http://www.lpch.org/clinicalSpecialtiesServices/COE/BrainBehavior/Psychiatry/autismPervasiveDevelopmentalPsych.html3 Laumonnier Frederic, Bonnet-Brilhault Frederique, et al. “X-Linked Mental Retardation and Autism are Associated with a Mutation in the NLGN4 Gene, a Member of the Neuroligin Family.” American Journal of Human Genetics. Mar 2004, Vol. 74 Issue 3, p552.

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When nondisjunction occurs, a copy of a chromosome fails to separate

during cell division and upon fertilization the zygote carries 47

chromosomes instead of the normal 46. Usually this process results in

a nonviable fertilized cell that is unable to continue cell division and

aborts itself. However, when this occurs at the 21st chromosome, the

zygote is able to continue dividing and a fetus develops with Trisomy

21, more commonly known as Down’s Syndrome, which will result in

an autistic child. Children with autism are characterized by

“abnormal or impaired development in social interaction and communication, and limited repertoires of activities or interests. . . Typically, they present with communication delays, both verbal and nonverbal, and some never develop language at all. Cognitive skills are also impaired; 75% to 80% of individuals with autism also meet the criteria for mental retardation.”4

Children diagnosed with autism suffer from the disorder

throughout their entire lifetimes and treatment is limited.

A reasonable starting point in the quest for the truth about

thimerosal and its harmful, or benign, side effects is to look at why

people insist that the two are related. The first obvious reason is the

coincidence of timing. Babies receive vaccinations in a series of

rounds within the first 15 months after birth. This is a reasonable time

to administer vaccinations since the developing baby has not yet

encountered many pathogens, and thus has a weak immune system.

Due to the baby’s inadequate immune system, vaccinations allow 4 Goin Robin P, Myers Barbara J. “Infantile Autism: Moving Toward Earlier Detection.” Focus on Autism & Other Developmental Disabilities. Spring 2004, Vol. 19 Issue 1. P 5.

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exposure to the antigens in a controlled environment that will allow the

baby to build resistance to the specific antigen. Since early signs of

autism usually present themselves within the first three years of life,

right around the time when the vaccinations are given, people might

think that there is a correlation between the two.

Though it may seem reasonable for parents to recognize this

overlapping of time as a link between autism and thimerosal, it is not a

scientifically supported inference. This is because not all disorders or

diseases manifest themselves immediately after contact. For instance,

a person may contract the herpes simplex virus type two and not

experience signs such as an outbreak for days, weeks, or even years.

The virus has the ability to remain dormant until the host’s body

presents a favorable environment for the virus to propagate itself.

Genetic disorders can work in much the same way, therefore the fact

that autism is usually first diagnosed at around the same time that the

thimerosal-containing vaccinations are given is not evidence for a

causal relationship.

Another reason why people might be inclined to assume that

thimerosal causes autism is the view that the characteristics of

children with autism are remarkably similar to those of children with

mercury poisoning. The study by Bernard et al. is the benchmark

study for thimerosal critics. It is commonly referred to on websites by

organizations of parents with autistic children as a source of scientific

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evidence that supports their claim that thimerosal caused their child’s

autism.5 First, a note about the credibility of the one “scientific”

journal that published the Bernard et al. study: Medical Hypotheses.6

Since this is not a widely referenced journal, a brief look at the

journal’s website helps elucidate the quality of the journal as well as its

intentions. For those unfamiliar with the journal, the “aims and scope”

as listed on the publisher website is, “Medical Hypotheses takes a

deliberately different approach to peer review. Most contemporary

practice tends to discriminate against radical ideas that conflict with

current theory and practice. Medical Hypotheses will publish radical

ideas, so long as they are coherent and clearly expressed.”7 With this

being said and keeping in mind that the practice of scientific method

and presentation of accurate data are not criteria for the journal to

publish its submitted articles, a look at thimerosal protestors’

“scientific” support is in order.

The study claims to examine the signs and symptoms of autism

and mercury poisoning and then states, “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

5 Bernard S, Enayati A, Binstock T, Roger H, Redwood L, McGinnis W. “Autism: A Unique Type of Mercury Poisoning.” April 3, 2000. Rev. April 21, 2000. Article can be accessed from the following website: http://www.jorsm.com/~binstock/thimerosal.htm6 Bernard S, Enayati A, Binstock T, Roger H, Redwood L, McGinnis W. “Autism: A Novel Form of Mercury Poisoning.” Medical Hypotheses. April 2001. Vol. 56. Issue 4. P 462-471.7 Taken from the Medical Hypotheses publisher website http://www.harcourt-international.com/journals/mehy/

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poisoning.” 8 A chart is presented in order to outline more clearly the

“parallels” and demonstrate how the shear volume of seemingly equal

characteristics can be overwhelming and therefore convincing that the

data is true. The chart is displayed as appendix 1.9 The table lists

about 95 experimental findings that are almost identical in mercury

poisoning and autism. Bernard et al. use exact wording between the

two columns to stress that the signs and symptoms of both conditions

are exactly the same. With such a seemingly comprehensive list of

findings, one can only wonder why they neglected to include that

mercury poisoning affects periphery nerves which would cause

neuropathy in other organs and areas in addition to the brain, whereas

only the brain is subject to impairment with autism.

Contrary to Bernard et al.’s findings, Drs. Karin B. Nelson and

Margaret L. Bauman published a commentary in the scientific journal,

Pediatrics, which points out that the table from the Bernard et al. study

“does not distinguish typical and characteristic manifestations of either

disorder from the rare, unusual, and highly atypical.”10 The table from

Bernard et al. lumps every single possible sign of each disorder

together in an attempt to show striking parallels between the two,

however, a characteristic that is common for one may present itself

8 Bernard S, Enayati A, Binstock T, Roger H, Redwood L, McGinnis W. “Autism: A Unique Type of Mercury Poisoning.” April 3, 2000. Rev. April 21, 2000. P 5-7. Article can be accessed from the following website: http://www.jorsm.com/~binstock/thimerosal.htm9 Ibid. P 5-7. 10 Nelson, Karin B. Bauman, Margaret L. “Thimerosal and Autism?” Pediatrics. March 2003. Vol. III. Issue 3. p.674.

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only in extremely rare cases for the other. The article goes on to point

out that mercury poisoning and autism do not share many of the

characteristics outlined in the table. They included a table with

complete documentation of experimentation and their findings. Their

table is displayed in appendix 2.11 It seems that there is quite a

discrepancy between the two tables, however, Drs. Nelson and

Bauman clearly address each finding in the article with a scientific

experiment to support their conclusions.12 No such scientific

documentation is found in the Bernard et al. article, therefore it does

not hold as scientific proof that autism and mercury poisoning produce

the same results.

According to the commentary by Drs. Nelson and Bauman,

“Bernard et al. state that ‘elevated mercury has been detected in

biological samples of autistic patients,’ but unfortunately do not

provide references. [Peers] found no paper published in the peer-

reviewed literature that reported an abnormal body burden of mercury,

or an excess of mercury in hair, urine, or blood.”13 Bernard et al. do

not offer any data in support of their claim that autistic patients’

biological samples contain high levels of mercury. In fact they admit

otherwise when they state, “In each case we have tried to identify

potential sources of exposure, although we have not been able to

11 Ibid. p.675.12 Ibid. P.674-676.13 Nelson, Karin B. Bauman, Margaret L. “Thimerosal and Autism?” Pediatrics. March 2003. Vol. III. Issue 3. p.675

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identify the exact amounts in some cases due to inadequate

documentation.”14 Without adequate documentation, their claim that

the mercury from thimerosal remains in the body has not been proven.

In spite of the lack of evidence that thimerosal is responsible for

autism, one might be convinced that the sheer amount of mercury

injected into a baby is enough to cause harm. This, however, is not the

case. There are two different compounds of mercury that need to be

considered in the case for or against the danger of thimerosal: methyl

mercury and ethyl mercury. Methyl mercury is the mercury that is

studied in mercury poisoning research, not ethyl mercury. Sources of

methyl mercury include contamination of fish due to waste from power

plants seeping into water supplies and the major component of older

tooth fillings. The only difference between the two compounds is just

the absence of one carbon and two hydrogens, but it is significant.

Similarly, thalidomide, a drug used widely in Europe to alleviate the

nausea that comes with pregnancy, comes in two forms. The only

difference between the two is the spatial placement of one hydrogen

atom, either slightly above or slightly below the plane of the molecule.

However, one form effectively ameliorates morning sickness and the

other causes severe birth defects.15 Such a slight difference can have

incredibly drastic effects in the body because enzymes and transport 14 Bernard S, Enayati A, Binstock T, Roger H, Redwood L, McGinnis W. “Autism: A Unique Type of Mercury Poisoning.” April 3, 2000. Rev. April 21, 2000. P 52. Article can be accessed from the following website: http://www.jorsm.com/~binstock/thimerosal.htm15 Voet Donald, Voet Judith G, Pratt Charlotte W. Fundamentals of Biochemistry. Upgrade edition. John Wiley & Sons, Inc. P. 88.

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proteins in the body are extremely stereospecific. The wrong form of a

chemical can throw a wrench in the body’s system and cause

significant harm to the individual.

The fact that thimerosal is composed of ethyl mercury is

important to note because the mechanism of uptake once in the body

and elimination is quite different from that of methyl mercury in that

“the passage of methyl mercury across the blood-brain barrier is

facilitated by an active transport mechanism, whereas the passage of

ethyl mercury into the brain does not have such a transport system

and is further hindered by its larger molecular size and faster

decomposition.”16 Methyl mercury is much more toxic to humans than

ethyl mercury because the body does have a way to transport methyl

mercury into the brain. People speaking out against thimerosal make

it a point to stress that the amount of “mercury” given to babies in

vaccines is above the Environmental Protection Agency’s (EPA)

guideline for safe amounts of “mercury” uptake without stressing the

fact that they are comparing two different compounds of mercury.

The mercury used in the formulation of safe dosage guidelines in place

by the EPA, Food and Drug Administration, and World Health

Organization is methyl mercury, the more toxic form. This means, “At

between 12.5 and 25 mg mercury per vaccine dose, the infants may

be receiving over 100 mg [of] ethyl mercury in the first 6 months of

16 Nelson, Karin B. Bauman, Margaret L. “Thimerosal and Autism?” Pediatrics. March 2003. Vol. III. Issue 3. p.676

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life.” 17 Even though the EPA recommends that the safe level of methyl

mercury intake is 0.1 µg/kg body weight/day, the use of thimerosal is

completely acceptable because it is shown that “the [ethyl mercury]

levels in blood are much lower than the prescribed limits and that

much of the ethyl mercury appears to be eliminated rapidly in feces.

This study gives comforting reassurance about the safety of ethyl

mercury as a preservative in childhood vaccines.”18 When obtaining

information about thimerosal and its link to autism it is important to

note if the source makes the distinction between ethyl and methyl

mercury. Most websites bashing thimerosal and vaccines in general

only refer to “mercury” levels which are usually referring to methyl

mercury, the compound of mercury that is more harmful compared to

ethyl form.

Another misguided attempt to cast doubt on the safety of

thimerosal is to inquire about the continual rise in the number of cases

of autism through the past couple of decades. Many people attribute

the increase to the use of thimerosal and the increase in the number of

vaccines that are currently required. Scientific data collected in

various medical journals centered around children or autism, as well as

from Denmark, does confirm that the number of cases of autism is

increasing exponentially.19 The connection between thimerosal and 17 Henderson, D C. “Heavy Metal.” Lancet. November 30, 2002. Vol 360, Issue 9347. P. 1712.18 Madsen Kreesten M, Lauritsne Marlene B, et al. “Thimerosal and the Occurrence of Autism: Negative Ecological Evidence from Danish Population-Based Data.” Pediatrics. September 2003. Vol 112. P 604.19 Henderson, D C. “Heavy Metal.” Lancet. November 30, 2002. Vol 360, Issue 9347. P. 1712.

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autism cannot be drawn from the fact that cases of autism are still

increasing in number. If thimerosal were a cause of autism, then it

would be reasonable to conclude that the number of cases of autism

would also decrease after thimerosal was completely removed from all

vaccinations administered to children. This is actually a testable

hypothesis that was tested in 1992 when thimerosal was removed

from the vaccinations given to children, but the graph of autism rates

in Denmark from appendix 3 clearly shows that the number of cases of

autism continues to increase significantly from 1992 to 1995 and then

again to 2000.20 The increase in frequency of autism can be seen all

over the world, including in the United States. This increase could

possibly be due to the fact that doctors have devised more accurate

methods of detecting autism. Autistic children that may have gone

undiagnosed in the past are now being tested earlier and more

thoroughly. Another possibility for the increase is that the criteria for

diagnosis have evolved over the years and are now including a wider

range of conditions under the umbrella of autism.

Conclusive evidence that thimerosal does not cause autism can

be found in the Denmark study. The purpose of the study was to

determine whether or not there was a correlation between the people

who received thimerosal-containing vaccinations with autism. The

study was designed so that the researchers would look at the Danish

Psychiatric Central Research Register that records all psychiatric 20 Madsen Kreesten M, Lauritsen Marlen B, et al. Pediatrics. September 2003. Vol III. Issue 3. p 605.

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admissions since 1971, and all outpatient contacts in psychiatric

departments in Denmark since 1995.21 Since everyone in Denmark has

a personal identification number, much like the social security number

in the United States, the researchers would be able to keep track of

people diagnosed with autism. They were able to keep track of how

many cases of autism were reported every year from 1971 to 2000 and

watch for a change subsequent to the removal of thimerosal from their

vaccines. An increase in the incidence of autism was observed

throughout the entire study, which would point to the conclusion that

there is no causal relationship between thimerosal and autism.

The Bernard et al. study is an important source for anti-

thimerosal advocates. As always, even scientific data should be

closely examined for under-the-table funding from certain groups, e.g.

a law firm wanting to take vaccine manufacturers to court. At the end

of the article published by Bernard et al., Ayda Halker is listed as a

person that they would like to thank for her “important

contributions.”22 She is also the founder and president of

AutismOnline.org as well as a parent of a child with autism and sister

to a young man who has autism.23 This could be seen as a conflict of

interest since she is heavily influenced by autism and its effects, yet an

avid supporter of Bernard. Scientific research should be an objective 21 Ibid. p 604.22 Bernard S, Enayati A, Binstock T, Roger H, Redwood L, McGinnis W. “Autism: A Unique Type of Mercury Poisoning.” April 3, 2000. Revision April 21, 2000. P 62. Article can be accessed from http://www.jorsm.com/~binstock/thimerosal.htm23 Information obtained from http://www.icdri.org/ASH.htm

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process with sheer motivation of uncovering the truth, not necessarily

to reach conclusions that were previously expected. The Bernard

study does not invoke a feeling of confidence in its findings when the

research supporters are revealed because of the obvious intention to

“prove” that thimerosal causes autism.

The published Denmark study also includes a section for

acknowledgments at the end of the article. The authors state that

their research was funded by a grant from the Danish National

Research Foundation and supported by the Stanley Medical Research

Institute. They also include that no funding sources were involved in

the study design.24 Since the funding came from an unbiased source,

as opposed to an individual who has already established a firm opinion

on what the outcome should be, the data presented by this study can

be accepted with less suspicion.

In 1997, The Food and Drug Administration (FDA) Modernization

Act of 1997 called for the FDA to review and assess the risk of all

mercury containing food and drugs. As part of this effort, the FDA

conducted a review of mercury content in vaccines.25 As the vaccines

began to be reviewed, Christian Scientists and others against

immunizations saw their chance to become even more vocal in the

protest. Pressure from these groups helped push the American

Academy of Pediatrics (AAP) and the United States Public Health 24 Madsen Kreesten M, Lauritsen Marlen B, et al. Pediatrics. September 2003. Vol III. Issue 3. p 605.25 Taken from the Center for Disease Control and Prevention website http://www.cdc.gov/nip/vacsafe/concerns/thimerosal/faqs-thimerosal.htm

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Service (PHS) toward issuing a recommendation to remove thimerosal

from vaccines as a precaution. Since it is cheaper to manufacture

single use vials now and there are more non-mercury-based

preservatives available, the need for thimerosal is virtually eliminated.

The decision to remove thimerosal from vaccines given to infants has

inevitably caused parents to consider that it was harmful in the first

place.

When glancing at the just the raw numbers of amounts of ethyl

mercury in thimerosal and guidelines for methyl mercury set by

government agencies, it is understandable to question the safety of

the vaccines. The Center for Disease Control and Prevention website

states that “A review conducted by the Food and Drug Administration

(FDA) concluded that the use of thimerosal as a preservative in

vaccines might result in the intake of mercury during the first 6 months

of life that exceeds the Environmental Protection Agency (EPA), but not

the FDA, the Agency for Toxic Substances and Disease Registry

(ATSDR), or the World Health Organization (WHO) guidelines for methyl

mercury intake.”26 It is important to keep in mind that the ethyl

mercury in vaccines cannot be compared with the methyl mercury

limits set by the above organizations because they differ in degree of

toxicity: with methyl mercury being more toxic than ethyl mercury.

26 Taken from the Center for Disease Control and Prevention website http://www.cdc.gov/nip/vacsafe/concerns/thimerosal/faqs-thimerosal.htm

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Also, it is worth noting the purpose for these federal guidelines

as well as the means by which they are determined. The guidelines

are in place in order to recommend a safe mercury exposure level for a

woman who is pregnant in order to prevent harm to a fetus’s

developing brain. A developing fetus in utero is more susceptible to

mercury poisoning than a fully developed infant because it’s central

nervous system has not yet completed development. Also, it’s liver

and kidneys are not functioning to their fullest capacity and break

down the mercury less efficiently. The key point here is that these

limits are in place for a developing fetus in the womb, not a fully

developed infant. Another point to keep in mind is what exactly the

“recommended allowable daily exposure” means. This is a value for

the estimated maximum amount of daily oral intakes of methyl

mercury during pregnancy that “were not associated with measurable

adverse outcomes in their children.”27 These values only reflect the

estimated amount of methyl mercury that could elicit detectable

change in the fetus, not measurable harm to the fetus. Even if the

ethyl mercury was as toxic as the methyl mercury used to set these

guidelines, the dosage in the vaccines is still less than the FDA’s

recommendation and the FDA is the agency responsible for setting the

limit in vaccines, not the EPA who has a much more conservative limit

than any of the other organizations.27 Taken from the American Academy of Pediatrics: Thimerosal in Vaccines – an Interim Report to Clinicians on the Indiana State Department of Health website http://www.state.in.us/isdh/programs/immunization/thimerosal.htm

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With the understanding that there is no evidence supporting a

link between thimerosal and the incidence of autism, the new question

is “Why do so many people continue to insist that thimerosal causes

autism?” The question can easily be answered by examining why

some people willingly spend thousands of dollars for a one-hour

session of twenty questions with a “psychic.” People need closure and

hope after dealing with a traumatic experience. Having a child with

autism is no doubt a profound and constant emotional and financial

burden. Though autistic children can be as loving and rewarding as

any other child, they do demand a copious amount of attention and

care. Parents of autistic children are searching for answers as to why

their child happened to have the disorder. It is appealing to blame the

vaccine manufacturers who are large nameless entities that can accept

the blame for their child’s abnormality. Their large bank accounts

sweeten the pot and lead to the next logical step in justice for their

child: lawsuits. This is not to say that parents are only after the

manufactures for money, although the increase in volume of

thimerosal cases may point to otherwise. On most anti-thimerosal

websites is a link to a law firm, specializing in thimerosal cases. In a

world where every person believes he is entitled to zero-risk

healthcare, thimerosal is perfect to blame. Now that vaccines come in

single-use vials, eliminating the need for thimerosal, what will be the

next scapegoat?

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Appendix 1: Summary Comparison of Characteristics of Autism

& Mercury Poisoning28

Mercury Poisoning AutismPsychiatric Social deficits, shyness, social

withdrawalSocial deficits, social withdrawal, shyness

Disturbances Depression, mood swings; mask face

Depressive traits, mood swings; flat affect

Anxiety AnxietySchizoid tendencies, OCD traits Schizophrenic & OCD traits;

repetitivenessLacks eye contact, hesitant to engage others

Lack of eye contact, avoids conversation

Irrational fears Irrational fearsIrritability, aggression, temper tantrums

Irritability, aggression, temper tantrums

Impaired face recognition Impaired face recognition

Speech, Loss of speech, failure to develop speech

Delayed language, failure to develop speech

Language & Dysarthria; articulation problems Dysarthria; articulation problems Hearing Speech comprehension deficits Speech comprehension deficitsDeficits Verbalizing & word retrieval

problemsEcholalia; word use & pragmatic errors

Sound sensitivity Sound sensitivityHearing loss; deafness in very high doses

Mild to profound hearing loss

Poor performance on language IQ tests

Poor performance on verbal IQ tests

Sensory Abnormal sensation in mouth & extremities

Abnormal sensation in mouth & extremities

Abnormalities Sound sensitivity Sound sensitivityAbnormal 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

28 Bernard S, Enayati A, Binstock T, Roger H, Redwood L, McGinnis W. “Autism: A Unique Type of Mercury Poisoning.” April 3, 2000. Revision April 21, 2000. P 62. Article can be accessed from http://www.jorsm.com/~binstock/thimerosal.htm

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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 difficultiesDeficits in understanding abstract ideas & symbolism; degeneration of higher mental powers

Deficits in abstract thinking & symbolism, understanding other’s mental states, sequencing, planning & organizing

Unusual Stereotyped sniffing (rats) Stereotyped, repetitive behaviorsBehaviors ADHD traits ADHD traits

Agitation, unprovoked crying, grimacing, staring spells

Agitation, unprovoked crying, grimacing, staring spells

Sleep difficulties Sleep difficultiesEating disorders, feeding problems

Eating disorders, feeding problems

Self injurious behavior, e.g. head banging

Self injurious behavior, e.g. head banging

Visual Poor eye contact, impaired visual fixation

Poor eye contact, problems in joint attention

Impairments “Visual impairments,” blindness, near-sightedness, decreased visual acuity

“Visual impairments”; inaccurate/slow saccades; decreased rod functioning

Light sensitivity, photophobia Over-sensitivity to lightBlurred or hazy vision Blurred visionConstricted visual fields Not described

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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

Gastroenteritis, diarrhea; abdominal pain, constipation, “colitis”

Diarrhea, constipation, gaseousness, abdominal discomfort, colitis

Disturbances 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 presentCauses 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 Selectively targets brain areas Specific areas of brain pathology;

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Pathology unable to detoxify or reduce Hg-induced oxidative stress

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 aspartateLeads 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 Causes abnormal EEGs, epileptiform activity

Abnormal EEGs, epileptiform activity

Abnormalities/ Causes seizures, convulsions Seizures; epilepsyEpilepsy Causes subtle, low amplitude

seizure activitySubtle, low amplitude seizure activities

Population Effects more males than females Male:female ratio estimated at 4:1Charact-eristics

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

Symptoms emerge from 4 months to 2 years old; symptoms emerge gradually, starting with movement & sensation

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movement & sensation

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Appendix 2 Characteristic Findings in Autism and in Mercury Poisoning29

Autism Mercurism

Motor Stereotypies Ataxia, dysarthriaVision No abnormality Constricted visual fieldsSpeech Delay, echolalia DysarthriaSensory Hyper-responsiveness Peripheral neuropathyPsychiatric Socially aloof,

insistence on samenessToxic psychosis; in mild cases, nonspecific depression, anxiety

Head size Large Small

Appendix 3: Autism Rates in Denmark30

29 Nelson, Karin B. Bauman, Margaret L. “Thimerosal and Autism?” Pediatrics. March 2003. Vol. III. Issue 3. p.674.

30 Madsen Kreesten M, Lauritsen Marlen B, et al. Pediatrics. September 2003. Vol III. Issue 3. p 605.

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Autism rates began to climb in 1991, but continued to rise through 2000, even after thimerosal use was discontinued in 1992.