Abstract
BackgroundAutism spectrum disorder (ASD) is defined by standardized criteria of qualitative impairments in social interaction, qualitative impairments in communication, and restricted and stereotyped patterns of behavior, interests, and activities. A significant number of children diagnosed with ASD suffer a loss of previously-acquired skills, which is suggestive of neurodegeneration or a type of progressive encephalopathy with an etiological pathogenic basis occurring after birth. To date, the etiology of ASD remains under debate, however, many studies suggest toxicity, especially from mercury (Hg), in individuals diagnosed with an ASD. The present study evaluated concerns about the toxic effects of organic-Hg exposure from Thimerosal (49.55% Hg by weight) in childhood vaccines by conducting a two-phased (hypothesis generating/hypothesis testing) study with documented exposure to varying levels of Thimerosal from vaccinations.MethodsA hypothesis generating cohort study was undertaken to evaluate the relationship between exposure to organic-Hg from a Thimerosal-containing Diphtheria-Tetanus-acellular-Pertussis (DTaP) vaccine in comparison to a Thimerosal-free DTaP vaccine administered, from 1998 through 2000, for the risk of ASD as reported in the Vaccine Adverse Event Reporting System (VAERS) database (phase I). A hypothesis testing case–control study was undertaken to evaluate the relationship between organic-Hg exposure from Thimerosal-containing hepatitis B vaccines administered at specific intervals in the first six months of life among cases diagnosed with an ASD and controls born between 1991 through 1999 in the Vaccine Safety Datalink (VSD) database (phase II).ResultsIn phase I, it was observed that there was a significantly increased risk ratio for the incidence of ASD reported following the Thimerosal-containing DTaP vaccine in comparison to the Thimerosal-free DTaP vaccine. In phase II, it was observed that cases diagnosed with an ASD were significantly more likely than controls to receive increased organic-Hg from Thimerosal-containing hepatitis B vaccine administered within the first, second, and sixth month of life.ConclusionsRoutine childhood vaccination is an important public health tool to reduce the morbidity and mortality associated with infectious diseases, but the present study provides new epidemiological evidence supporting an association between increasing organic-Hg exposure from Thimerosal-containing childhood vaccines and the subsequent risk of an ASD diagnosis.
Highlights
Autism spectrum disorder (ASD) is defined by standardized criteria of qualitative impairments in social interaction, qualitative impairments in communication, and restricted and stereotyped patterns of behavior, interests, and activities
Over the past two decades, the prevalence of individuals diagnosed with autism spectrum disorder (ASD) has risen dramatically [1], and currently at least 1 in 88 children are diagnosed with ASD in the US [2]
The importance of postnatal loss of neurological function in those diagnosed with an ASD between 6 and 18 months of age, as observed in affected children who have regressed, is this phenomena is suggestive of neurodegeneration or a type of progressive encephalopathy with an etiological pathogenic basis occurring after birth [5]
Summary
Autism spectrum disorder (ASD) is defined by standardized criteria of qualitative impairments in social interaction, qualitative impairments in communication, and restricted and stereotyped patterns of behavior, interests, and activities. A significant number of children diagnosed with ASD suffer a loss of previously-acquired skills, which is suggestive of neurodegeneration or a type of progressive encephalopathy with an etiological pathogenic basis occurring after birth. The etiology of ASD remains under debate, many studies suggest toxicity, especially from mercury (Hg), in individuals diagnosed with an ASD. The importance of postnatal loss of neurological function in those diagnosed with an ASD between 6 and 18 months of age, as observed in affected children who have regressed, is this phenomena is suggestive of neurodegeneration or a type of progressive encephalopathy with an etiological pathogenic basis occurring after birth [5]. Recent evidence suggests that mercury (Hg) may be either a causal factor in or contributory to the brain pathology in ASD, possibly working synergistically with other toxic compounds or pathogens to produce the abnormal brain pathology observed in those diagnosed with an ASD [7]
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