I have produced below the abstract for an article titled Timing of Increased Autistic Disorder Cumulative Incidence published online at Environmental Science and Technology. I added the bold emphasis to the statement that both genetic and environmental factors are implicated in its etiology. It is long past time that environmental autism, and autistic disorder, research received more funding priority from public authorities which have favored genetic based autism research almost exclusively for decades with few significant results. Authors of the study are Michael E. McDonald and John F. Paul of the National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, MD-B343-06, Research Triangle Park, North Carolina 2771.
It is interesting to note that cumulative increase was observed worldwide beginning in 1988 several years prior to the publication of the DSM-IV in 1994 AND that the data relates to Autistic Disorder not the broader "autism spectrum" of disorders.
Environ. Sci. Technol., 2010, 44 (6), pp 2112–2118, DOI: 10.1021/es902057k, Publication Date (Web): February 16, 2010,Copyright © 2010 American Chemical Society
Autistic disorder (AD) is a severe neurodevelopmental disorder typically identified in early childhood. Both genetic and environmental factors are implicated in its etiology. The number of individuals identified as having autism has increased dramatically in recent years, but whether some proportion of this increase is real is unknown. If real, susceptible populations may have exposure to controllable exogenous stressors. Using literature AD data from long-term (10-year) studies, we determined cumulative incidence of AD for each cohort within each study. These data for each study were examined for a changepoint year in which the AD cumulative incidence first increased. We used data sets from Denmark, California, Japan, and a worldwide composite of studies. In the Danish, California, and worldwide data sets, we found that an increase in AD cumulative incidence began about 1988−1989. The Japanese study (1988−1996) had AD cumulative incidence increasing continuously, and no changepoint year could be calculated. Although the debate about the nature of increasing autism continues, the potential for this increase to be real and involve exogenous environmental stressors exists. The timing of an increase in autism incidence may help in screening for potential candidate environmental stressors.