There is no doubt that an environmental factor has contributed to the dramatic increase in the incidence of autism over the past 15 years. Genetic factors are a component in the condition—concurrent rates of autism in identical twins approach 90 percent— but rates of inherited genetic diseases do not change abruptly in one generation, whereas autism rates skyrocketed during the 1990s. Rates of autism in the United States increased from fewer than 6 cases per 10,000 children in the 1980s to more than 60 per 10,000 children today (Blaxill 2004a). The American Academy of Pediatrics and the Centers for Disease Control (CDC) currently estimate that autism affects one in every 166 children (AAP 2004). Improved diagnosis does not adequately account for this increase (Blaxill 2004a, Croen 2003).
There has been little progress in identifying pre- and post-natal environmental exposures that might trigger the severe impacts to brain development, intestinal and immune dysregulation that characterize autism disorders (London 2000). Hundreds of studies have explored the genetic roots of the autism epidemic, but none has uncovered a single gene or vulnerability to account for more than a fraction of cases.
Children's exposure to mercury in immunizations has been a long-standing concern of autism advocates.
A Recent study shows that children with regressive autism have consistently elevated levels of oxidative stress as compared to normal healthy children. Individuals with reduced glutathione antioxidant capacity will be under chronic oxidative stress and will be more vulnerable to toxic compounds that act primarily through oxidative damage, including mercury (Dr. Jill James of the University of Arkansas School of Medicine) These findings shift the focus of research from single genes to a broader metabolic disorder shared by the vast majority of autistic children. They also indicate a mechanism by which autistic children would be more sensitive to chemicals that cause oxidative stress and damage their developing brain and nervous system