It’s a familiar cry, “vaccines do not cause autism”. But what is the assertion based on, and what does the scientific evidence have to say? Below is a collection of study excerpts that show vaccines are indeed implicated in autism. The mechanisms involve:
- An abnormal immune response to the vaccine-derived measles virus
- Aluminium sourced from vaccines
- Acetaminophen (paracetamol) subsequent to MMR vaccine
- Mercury sourced from vaccines
- Conjugated vaccines
- The 1994-1999 US vaccine schedule is shown to induce brain changes identical to those of autism

This post is lengthy, but if you're interested in the causes behind autism, you'll find it fascinating. To make this scientific literature easier to understand I've included additional text in italics.

An abnormal immune response to the vaccine-derived measles virus is implicated in autism
“This report on children with both autistic encephalopathy (brain injury) and intestinal pathology (disease) associated with measles virus persistence describes the detection of measles virus in the cerebrospinal fluid of such children. None of the cases (autistic children studied) or controls (non-autistic children studied) had a history of measles exposure other than MMR vaccination. Serum (blood samples) and cerebrospinal fluid samples were also evaluated for antibodies to myelin basic protein (myelin basic protein is a substance essential for proper functioning of the nervous system, autoantibodies to myelin basic protein mean that body attacks the myelin basic protein, creating inflammation, damage, and cell death). Serum anti-myelin basic protein autoantibodies were detected in all children with autistic encephalopathy (brain injury). Findings are consistent with both a measles virus etiology (cause) for the autistic encephalopathy (brain injury) and active viral replication in these children. They further indicate the possibility of a virally driven cerebral (brain) immunopathology (immune system disease) in some cases of regressive autism. The data support the growing perception that a subset of children with autistic encephalopathy (brain injury) exhibits a complex systemic pathology (disease) consistent with an etiological (causative) role for measles virus (found in the MMR vaccine).” [1]

“Analysis revealed the presence of an unusual MMR antibody in 60% of autistic sera (blood samples) but not in control sera (non-autistic blood samples). The MMR antibody in autistic sera (blood samples) detected measles hemagglutinin protein (a substance found in the measles virus as part of the MMR vaccine that causes the clumping together of red blood cells), which is unique to the measles vaccine. Furthermore, over 90% of MMR antibody-positive autistic sera (blood samples) were also positive for myelin basic protein autoantibodies (myelin basic protein is a substance essential for proper functioning of nervous system, autoantibodies to myelin basic protein mean that body attacks the myelin basic protein, creating inflammation, damage, and cell death), suggesting a strong association between MMR and central nervous system autoimmunity in autism (autoantibodies to myelin basic protein is found in other autoimmune diseases such as multiple sclerosis and traverse myelitis). Stemming from this evidence, we suggest that an inappropriate antibody response to MMR, specifically the measles component thereof, might be related to pathogenesis (cause) of autism.” [2]

“Virus-induced autoimmunity may play a causal role in autism. To examine the etiologic (causative) link of viruses in this brain disorder, we conducted a serologic (blood sample analysis) study of measles virus, mumps virus, and rubella virus. The level of measles antibody, but not mumps or rubella antibodies, was significantly higher in autistic children as compared with normal children or siblings of autistic children. Autistic children have a hyperimmune response to measles virus, which in the absence of a wild type of measles infection might be a sign of an abnormal immune reaction to the vaccine strain or virus reactivation.” [3]

“Autoimmune markers were analyzed in the sera (blood samples) of autistic and normal children, but the cerebrospinal fluid of some autistic children was also analyzed. Autoimmunity was demonstrated by the presence of brain autoantibodies, abnormal viral serology (blood tests), brain and viral antibodies in cerebrospinal fluid, a positive correlation between brain autoantibodies and viral serology (blood tests), elevated levels of proinflammatory cytokines and acute-phase reactants (substances involved in widespread inflammation), and a positive response to immunotherapy (medical treatment of the immune system). Many autistic children harbored brain myelin basic protein autoantibodies and elevated levels of antibodies to measles virus and measles-mumps-rubella (MMR) vaccine. Measles might be etiologically linked to autism because measles and MMR antibodies (a viral marker) correlated positively to brain autoantibodies (an autoimmune marker)--salient features that characterize autoimmune pathology (disease) in autism. Autistic children also showed elevated levels of acute-phase reactants--a marker of systemic inflammation. The scientific evidence is quite credible for our autoimmune hypothesis, leading to the identification of autoimmune autistic disorder (AAD) as a major subset of autism. Autoimmune autistic disorder can be identified by immune tests to determine immune problems before administering immunotherapy. The author has advanced a speculative neuroautoimmune (NAI) model for autism, in which virus-induced autoimmunity is a key player.” [4]

“A new syndrome has been reported in children with autism who exhibited developmental regression and gastrointestinal symptoms (autistic enterocolitis), in some cases soon after MMR vaccine. In order to characterize the strains that may be present, we have carried out the detection of measles RNA in peripheral mononuclear cells. The sequences (samples) obtained from the patients with ulcerative colitis (gastrointestinal dysfunction) and children with autism were consistent with being vaccine (MMR) strains. In this study, the persistence of measles virus in peripheral blood was confirmed in some patients with chronic intestinal inflammation. It was confirmed that both vaccine and sporadic virus could be persistent.” [5]

“MMR vaccination may increase risk for autism via an autoimmune mechanism in autism. MMR antibodies are significantly higher in autistic children as compared to normal children, supporting a role of MMR in autism. Autoantibodies to myelin basic protein, neuron-axon filament protein and glial fibrillary acidic protein are significantly increased in autistic patients (myelin basic protein, neuron-axon filament protein, and glial fibrillary acidic protein are crucial to proper nervous system function, if the body creates autoantibodies to these substances it means the body attacks them, creating inflammation, damage, and cell death). Increase in Th2 may explain the increased autoimmunity (overactivation of Th2 is associated with autoimmune diseases). The possibility of its involvement in autism cannot be ruled out.” [12]

Aluminium sourced from vaccines is implicated in autism
“Dysfunctional immunity and impaired brain function are core deficits in autism spectrum disorders. Aluminium, the most commonly used vaccine adjuvant, is a demonstrated neurotoxin (damages or kills nerve cells) and a strong immune stimulator. Hence, adjuvant aluminium has the potential to induce neuroimmune disorders. When assessing adjuvant toxicity in children, two key points ought to be considered:
(i) children should not be viewed as “small adults” as their unique physiology makes them much more vulnerable to toxic insults; and
(ii) if exposure to aluminium from only few vaccines can lead to cognitive impairment and autoimmunity in adults, is it unreasonable to question whether the current pediatric schedules, often containing 18 aluminium adjuvanted vaccines, are safe for children?
By applying Hill's criteria for establishing causality between exposure and outcome we investigated whether exposure to aluminium from vaccines could be contributing to the rise in autism spectrum disorders prevalence in the Western world. Our results show that:
(i) children from countries with the highest autism spectrum disorders prevalence appear to have the highest exposure to aluminium from vaccines;
(ii) the increase in exposure to aluminium adjuvants significantly correlates with the increase in autism spectrum disorders prevalence in the United States observed over the last two decades and
(iii) a significant correlation exists between the amounts of aluminium administered to preschool children and the current prevalence of autism spectrum disorders in seven Western countries, particularly at 3–4 months of age.
The application of the Hill's criteria to these data indicates that the correlation between aluminium in vaccines and autism spectrum disorders may be causal. Because children represent a fraction of the population most at risk for complications following exposure to aluminium, a more rigorous evaluation of aluminium adjuvant safety seems warranted.” [6]

“Our previous studies of autism spectrum disorder has demonstrated a correlation between increasing autism spectrum disorder rates and aluminium adjuvants in common use in paediatric vaccines in several Western countries. We have now sought to provide an animal model to explore potential behavioural phenotypes (characteristics) and central nervous system alterations using subcutaneous injections of aluminium hydroxide in early postnatal mice. Injections of a "high" and "low" aluminium adjuvant levels were designed to correlate to either the U.S. or Scandinavian paediatric vaccine schedules vs. control saline-injected mice. Male mice in the "high aluminium" group showed significant changes in light-dark box tests (increased anxiety and reduction in exploratory behaviour) and in various measures of behaviour in an open field (shorter distances moved, slower movement, less time in overall movement, and decreased rearing frequency). These current data implicate aluminium injected in early postnatal life in some central nervous system alterations that may be relevant for a better understanding of the aetiology (cause) of autism spectrum disorder.” [7]

“We have examined the neurotoxicity (ability to damage or kill nerve cells) of aluminum in humans and animals under various conditions, following different routes of administration. The literature demonstrates clearly negative impacts of aluminum on the nervous system across the age span. In adults, aluminum exposure can lead to apparently age-related neurological deficits resembling Alzheimer's and has been linked to this disease and to the Guamanian variant, amyotrophic lateral sclerosis/Parkinsonism-dementia complex. Similar outcomes have been found in animal models. In addition, injection of aluminum adjuvants in an attempt to model Gulf War syndrome and associated neurological deficits leads to an amyotrophic lateral sclerosis phenotype in young male mice. In young children, a highly significant correlation exists between the number of pediatric aluminum-adjuvanted vaccines administered and the rate of autism spectrum disorders. Many of the features of aluminum-induced neurotoxicity may arise, in part, from autoimmune reactions, as part of the autoimmune / inflammatory syndrome induced by adjuvants (ASIA) syndrome. [8]

“Autism is a condition characterized by impaired cognitive and social skills, associated with compromised immune function. The incidence is alarmingly on the rise, and environmental factors are increasingly suspected to play a role. This paper investigates word frequency patterns in the U.S. CDC Vaccine Adverse Events Reporting System (VAERS) database. Our results provide strong evidence supporting a link between autism and the aluminum in vaccines. A literature review showing toxicity of aluminum in human physiology offers further support. Mentions of autism in VAERS increased steadily at the end of the last century, during a period when mercury was being phased out, while aluminum adjuvant burden was being increased. Using standard log-likelihood ratio techniques, we identify several signs and symptoms that are significantly more prevalent in vaccine reports after 2000, including cellulitis, seizure, depression, fatigue, pain and death, which are also significantly associated with aluminum-containing vaccines. We propose that children with the autism diagnosis are especially vulnerable to toxic metals such as aluminum and mercury due to insufficient serum sulfate and glutathione. A strong correlation between autism and the MMR (Measles, Mumps, Rubella) vaccine is also observed.” [9]

“It is known that with priming (stimulation) of brain microglia (specific immune cells within the brain and spinal column), repeated episodes of systemic immune activation can trigger a chronic, exaggerated brain immune response. It has now been shown that chronic microglial activation (activation of specific immune cells in the brain and spinal column) is present in autistic brains from age 5 years to age 44 years.  It may be that mercury and aluminium from vaccines as well as other sources, by accumulating in the brain, are acting as the innate (immune) trigger. It has been shown that both of these metals can trigger microglial activation and neurodegenerative (damage and death of nerve cells) effects. By accumulating in the brain, they may act as chronic immune stimulants. The competency of the central nervous systems protective mechanisms, especially the antioxidant systems, DNA repair enzymes, and other cellular mechanisms of protection, determines, to a large extent, the final outcome. The competency of the immune system is also a major determinative factor.” [14]

Vaccination with subsequent acetaminophen (paracetamol) administration is implicated in autism
“A study of the ability of children with the autism diagnosis to dispose of paracetamol found that the ratio of paracetamol-sulfate to paracetamol-glucuronide in the urine of children with severe autism following acetaminophen administration was significantly lower than that measured for normal controls (non-autistic children). This result strongly suggests an impaired ability to metabolize toxic substances via a sulfation pathway. If the MMR vaccine is administered simultaneously with DTaP, an aluminum-containing vaccine (as is often the case), then the acetaminophen would likely interfere with the child’s ability to dispose of the aluminum (a potent neurotoxin).” [9]

“This paper investigates word frequency patterns in the U.S. CDC Vaccine Adverse Events Reporting System (VAERS) database. There were a total of 1840 adverse reactions mentioning fever in the MMR set. This suggests to us that the acetaminophen connection may be correct―that the fever associated with MMR exposure is treated with acetaminophen, which then becomes toxic to the brain of the child predisposed toward autism, because of their inability to dispose of it. Acetaminophen would also deplete sulfate needed to detoxify aluminum in any concurrent aluminum-containing vaccine such as DTaP.” [9]

“The present study was performed to determine whether acetaminophen (paracetamol) use after the measles-mumps-rubella vaccination could be associated with autistic disorder. Acetaminophen (paracetamol) use after measles-mumps-rubella vaccination was significantly associated with autistic disorder when considering children 5 years of age or less (autistic children were over 6 fold more likely to have received acetaminophen after MMR vaccination). After limiting cases to children with regression in development (the likelihood was 4 fold), and when considering only children who had post-vaccination sequelae (damage due to vaccination)(the likelihood was 8.2 fold). This preliminary study found that acetaminophen (paracetamol) use after measles-mumps-rubella vaccination was associated with autistic disorder.” [10]

Mercury sourced from vaccines is implicated in autism
“Exposure to mercury can cause immune, sensory, neurological, motor, and behavioural dysfunctions similar to traits defining or associated with autism, and the similarities extend to neuroanatomy, neurotransmitters, and biochemistry. Thimerosal, a preservative added to many vaccines, has become a major source of mercury in children who, within their first two years, may have received a quantity of mercury that exceeds safety guidelines. A review of medical literature and US government data suggests that:
(i) many cases of idiopathic autism are induced by early mercury exposure from thimerosal;
(ii) this type of autism represents an unrecognized mercurial syndrome; and
(iii) genetic and non-genetic factors establish a predisposition whereby thimerosal’s adverse effects occur only in some children.” [11]

“It is clear that while genetic factors are important to the pathogenesis (cause) of Autism Spectrum Disorders, mercury exposure can induce immune, sensory, neurological, motor, and behavioral dysfunctions similar to traits defining or associated with Autism Spectrum Disorders. A case series of nine patients who presented to the Genetic Centers of America for a genetic/developmental evaluation are discussed. Eight of nine patients (one patient was found to have an Autism Spectrum Disorder due to Rett's syndrome)…
(a) had regressive Autism Spectrum Disorders;
(b) had elevated levels of androgens;
(c) excreted significant amounts of mercury post chelation challenge;
(d) had biochemical evidence of decreased function in their glutathione pathways;
(e) had no known significant mercury exposure except from Thimerosal-containing vaccines/Rho(D)-immune globulin preparations; and
(f) had alternate causes for their regressive Autism Spectrum Disorders ruled out.
There was a significant dose-response relationship between the severity of the regressive Autism Spectrum Disorders observed and the total mercury dose children received from Thimerosal-containing vaccines/Rho (D)-immune globulin preparations. Eight of nine patients examined were exposed to significant mercury from Thimerosal-containing biologic/vaccine preparations during their fetal/infant developmental periods, and subsequently, between 12 and 24 mo of age, these previously normally developing children suffered mercury toxic encephalopathies (brain injury) that manifested with clinical symptoms consistent with regressive Autism Spectrum Disorders. Evidence for mercury intoxication should be considered in the differential diagnosis as contributing to some regressive Autism Spectrum Disorders.” [12]

“Emerging evidence supports the theory that some autism spectrum disorders may result from a combination of genetic/biochemical susceptibility, specifically a reduced ability to excrete mercury, and exposure to mercury at critical developmental periods. Elemental/inorganic mercury is released into the air/water where it becomes methylated and accumulates in animal tissues. The US population is primarily exposed to methyl-mercury by fish consumption. Many pharmaceuticals have been, and some continue to be, a ubiquitous (abundant) source of danger because they contain mercurials. Mercurials may be found in drugs for the eye, ear, nose, throat, and skin; in bleaching creams; as preservatives in cosmetics, tooth pastes, lens solutions, vaccines, allergy test and immunotherapy solutions; in antiseptics, disinfectants, and contraceptives; in fungicides and herbicides; in dental fillings and thermometers; and many other products. mercury has been found to cause immune, sensory, neurological, motor, and behavioural dysfunctions similar to traits defining/associated with autism spectrum disorders, and that these similarities extend to neuroanatomy, neurotransmitters, and biochemistry. Furthermore, a review of molecular mechanisms indicates that mercury exposure can induce death, disorganization and/or damage to selected neurons in the brain similar to that seen in recent autism spectrum disorder brain pathology studies, and this alteration may likely produce the symptoms by which autism spectrum disorders are diagnosed. Finally, a review of treatments suggests that autism spectrum disorder patients who undergo protocols to reduce mercury and/or its effects show significant clinical improvements in some cases. In conclusion, the overwhelming preponderance of the evidence favours acceptance that mercury exposure is capable of causing some autism spectrum disorders.” [13]

“A careful review of autism spectrum disorder cases discloses a number of events that adhere to an immuno-excitotoxic mechanism (by which cells are over stimulated to the point of cell damage or death). This mechanism explains the link between excessive vaccination, use of aluminum and ethylmercury in vaccines, food allergies, gut dysbiosis (bacterial imbalance of the gut), and abnormal formation of the developing brain. It has now been shown that chronic microglial activation (activation of specific immune cells in the brain and spinal column) is present in autistic brains from age 5 years to age 44 years. Any insult to the brain (such as infection, aluminium, or mercury exposure due to vaccination) can trigger rapid activation of microglia. A considerable amount of evidence, both experimental and clinical, indicates that repeated microglial activation can initiate an exaggerated microglial response that can be prolonged. It is also known that one form of microglia activation can result in an outpouring of neurotoxic (nerve damaging) levels of the excitotoxins (substances that can overstimulate, damage and kill cells) glutamate and quinolinic acid. Studies have shown that careful control of brain glutamate levels is essential to brain pathway development and that excesses can result in arrest of neural migration, as well as dendritic and synaptic loss (dendritic cells act as immune system messengers and synapses are the junctions across which nerve impulses pass). It has also been shown that certain cytokines interact with glutamate receptors to enhance the neurotoxic (nerve damaging) reaction. To describe this interaction I have coined the term immunoexcitotoxicity.” [14]

“In this section, I explore the effects of mercury and inflammation on trans-sulfuration reactions, which can lead to elevations in androgens (male hormones), and how this might relate to the male preponderance of autism spectrum disorders. It is known that mercury interferes with these biochemical reactions (trans-sulfuration) and that chronically elevated androgen (male hormone) levels also enhance the neurodevelopmental effects of excitotoxins (substances that over stimulate cells to the point of cell damage or death). Both androgens and glutamate alter neuronal and glial calcium oscillations, which are known to regulate cell migration, maturation, and final brain cytoarchitectural (cell) structure. Studies have also shown high levels of DHEA and low levels of DHEA-S in autism spectrum disorders, which can result from both mercury toxicity and chronic inflammation. Chronic microglial (specific immune cells in the brain and spinal cord) activation appears to be a hallmark of autism spectrum disorders. Peripheral immune stimulation, mercury, and elevated levels of androgens can all stimulate microglial activation. Linked to both trans-sulfuration problems and chronic mercury toxicity are elevations in homocysteine levels in autism spectrum disorders patients. Homocysteine and especially its metabolic products are powerful excitotoxins. Intimately linked to elevations in DHEA, excitotoxicity and mercury toxicity are abnormalities in mitochondrial function. A number of studies have shown that reduced energy production by mitochondria greatly enhances excitotoxicity.” [14]

“There are reports suggesting that some autistic children are unable to mount an adequate response following exposure to environmental toxins. This potential deficit, coupled with the similarity in clinical presentations of autism and some heavy metal toxicities, has led to the suggestion that heavy metal poisoning might play a role in the etiology (cause) of autism in uniquely susceptible individuals. Thimerosal, an anti-microbial preservative previously added routinely to childhood multi-dose vaccines, is composed of 49.6% ethyl mercury (thimerosal is still an ingredient in the Fluzone multidose, Fluvirin multidose, and Afluria multidose pediatric vaccines currently in use). Based on the levels of this toxin that children receive through routine immunization schedules in the first years of life, it has been postulated that thimerosal may be a potential triggering mechanism contributing to autism in susceptible individuals. One potential risk factor in these individuals may be an inability to adequately up-regulate metallothionein (a protein that binds heavy metals and helps protect the body from toxin damage) biosynthesis in response to presentation of a heavy metal challenge (exposure). To investigate this hypothesis, cultured lymphocytes from autistic children and non-autistic siblings were challenged with either 10 microM ethyl mercury, 150 microM zinc, or fresh media (control). Cells challenged (treated) with thimerosal responded by up-regulating numerous heat shock protein transcripts (proteins that are expressed when the body is under stress), but not metallothionein transcripts (proteins that bind heavy metals and help protect the body from toxin damage). The differences in expression profiles between those cells treated with zinc versus thimerosal were dramatic.” [15]

“Emerging epidemiologic evidence and biologic plausibility suggest an association between autistic spectrum disorders and mercury exposure. This study compares mercury excretion after a three-day treatment with an oral chelating agent in children with autistic spectrum disorders and a matched control (non-autistic) population. Overall, urinary mercury concentrations were significantly (3 fold) higher in children with autistic spectrum disorders than in normal (non-autistic) controls. Additionally, vaccinated cases showed a significantly (6 fold) higher urinary mercury concentration than did vaccinated controls. The observed urinary concentrations of mercury could plausibly have resulted from thimerosal in childhood vaccines, although other environmental sources and thimerosal in Rh (D) immune globulin administered to mothers may be contributory.” [16]

Conjugate vaccines are implicated in autism
“The first conjugate vaccine was approved for use in the US in 1988 to protect infants and young children against the capsular bacteria Haemophilus influenzae type b (Hib). Since its introduction in the US, this vaccine has been approved in most developed countries, including Denmark and Israel where the vaccine was added to their national vaccine programs in 1993 and 1994, respectively. There have been marked increases in the reported prevalence of autism spectrum disorders among children in the US beginning with birth cohorts in the late 1980s and in Denmark and Israel starting approximately 4-5 years later. Although these increases may partly reflect ascertainment biases, an exogenous trigger could explain a significant portion of the reported increases in autism spectrum disorders. It is hypothesized here that the introduction of the Hib conjugate vaccine in the US in 1988 and its subsequent introduction in Denmark and Israel could explain a substantial portion of the initial increases in autism spectrum disorders in those countries. The continuation of the trend toward increased rates of autism spectrum disorders could be further explained by increased usage of the vaccine, a change in 1990 in the recommended age of vaccination in the US from 15 to 2 months, increased immunogenicity of the vaccine through changes in its carrier protein, and the subsequent introduction of the conjugate vaccine for Streptococcus pneumoniae. The potential effects of conjugate vaccines on neural development merit close examination. Conjugate vaccines fundamentally change the manner in which the immune systems of infants and young children function by deviating their immune responses to the targeted carbohydrate antigens from a state of hypo(lowered)-responsiveness to a robust B2 cell mediated response (which promotes the production of antibodies; carbohydrate antigens are bacterial-based polysaccharides and glycocojugates that evoke antibodies, many are found in vaccines such the Neisseria meningitidis, Streptococcus pneumoniae, Haemophilus influenzae type b, and Salmonella typhi vaccines). This (biologically normal) period of hypo(lowered)-responsiveness to carbohydrate antigens coincides with the intense myelination process in infants and young children (myelination is a crucial process in the nervous system; problems with myelination are involved in autoimmune diseases), and conjugate vaccines may have disrupted evolutionary forces that (would have normally) favored early brain development over the need to protect infants and young children from capsular (polysaccharide) bacteria.” [17]

The entire 1994-1999 US vaccine schedule is implicated in autism
"In this pilot study, infant macaques receiving the recommended pediatric vaccine regimen from the 1990’s displayed a different pattern of maturational changes in amygdala volume and differences in amygdala-binding of opioid antagonist diprenorphine following the MMR/DTaP/Hib vaccinations between T1 (4 months) and T2 (6 months) compared with non-exposed animals (the amygdala is a part of the brain that plays a primary role in the processing of memory, decision-making, and emotional reactions).... Volumetric analyses identified significantly greater  total brain volume in exposed compared with unexposed animals at both measured time points. These results raise the possibility that multiple vaccine exposures during the previous 3-4 months may have had a significant impact on brain growth and development... Interestingly, a rapid increase in total brain volume between 6 and 14 months is generally considered to be a consistent finding for many children with an Autism Spectrum Disorder (ASD) ( Piven et al. 1995, Courchesne et al. 2001, Sparks et al. 2002)... An enlarged brain volume may be due to a failure in programmed cell death or ‘neuronal pruning’, a process which rids the brain of abnormally functioning neural connections and optimizes coordinated neural functioning (Huttenlocher and Dabholkar 1997). When pruning fails to function, as may be the case in ASD, brain size will increase and neural connectivity will be decreased (Hill and Frith 2003).
In the present study, amygdala volumes were significantly increased in the vaccine exposed animals relative to the unexposed animals at T2 (6 month time point)... Neuropathological and neuroimaging studies of individuals with an ASD, a condition in which social functioning is often severely impaired (Schultz 2005), have provided growing evidence of a central role for the amygdala (Amaral et al. 2008, Kleinhans et al. 2009). Cross-sectional studies that have stratified individuals with ASD by age and behavioral phenotype have shown that the amygdala is enlarged in younger children compared with neurotypical controls, rapidly achieves adult size in childhood, and therefore does not undergo the growth pattern observed during normal male adolescence (Schumann et al. 2004). Several studies have also demonstrated an increase in amygdala volume in young children, with the amygdala typically enlarged by approximately 15% relative to age-matched control subjects (Sparks et al. 2002, Schumann et al. 2004, Mosconi et al. 2009, Schumann et al. 2009).
The data suggest that vaccine exposure may be associated with significant disturbances in central opioidergic pathways in this model. An important role for opioid ligand–receptor interactions in neuro-ontogeny and behavior is recognized during pre- and post-natal development (Zagon and McLaughlin 1985). It has been proposed that the presence of endorphines and exorphines - the latter of dietary origin - may contribute to some behavioral symptoms reported in ASD (Reichelt et al. 1981, Gillberg 1995). Neonatal assessments of this same cohort of primates previously identified significant delays in the acquisition of neonatal reflexes (Hewitson et al. 2010a) and behavioral deficits in tests of cognitive function between 5-8 months of age (Hewitson et al. 2010b) in exposed animals when compared with controls." [18]
Numerous studies that claim to disprove a link between vaccines and autism are highly flawed
Safe Minds has published a 92 page document detailing serious methodological limitations, design flaws, conflicts of interest or other problems related to 16 studies commonly used to justify the safety of vaccines. Fourteen Studies also does a great job of critiquing the autism/vaccine studies often used to promote vaccine safety:
http://www.fourteenstudies.org/studies_thimerosal.html
http://www.fourteenstudies.org/studies_mmr.html

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