The NEW YORK TIMES published the report of the "California Autism Twins Study" on July 8, 2011. This study was headed by Dr. Joachim Hallmayer, an associate professor of psychiatry and behavioral science at Stanford University. The study involved 192 pairs of mono-zygotic and dizyotic twins. One twin in each pair had the classic form of autism (withdrawal, communication problems and repetitive behaviors.) In many cases, the other twin also had classic autism or a milder"autism spectrum" disorder like Asperger's syndrome. Because identical twins share 100% of their genes and fraternal twins share 50% of their genes, the researchers were able to measure the importance of genes versus shared environment. The study by Dr, Joachim Hallmayer found that autism or autism spectrum disorders occurred in both children: 77% of the male identical twins and 50% in the female identical twins. These figures were expected as that is the general rate of occurrence. However, the rates among the fraternal twins were lower: 31% of males and 36% of females.

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The surprise factor: shared environmental factors appeared to be at work in 58% of the cases! This suggests that environmental factors, such as the environment of the womb, may be at least as important as genes in causing autism! "We, like everyone else, were very surprised because we didn't expect it to be that high," said a senior author of the study, Neil Risch, a geneticist and epidemiologist at the University of California in San Francisco. The rate of autism that occurs in two siblings who are not twins is much lower giving thought to the idea that the conditions the twins shared in the womb, rather than what they were exposed to after birth, contributed to the development of autism. This release has led to a marked and important shift in thinking about the causes of autism. The researchers have not said which environmental influences might be at work, but the study does suggest that environmental factors, including conditions in the womb, may be at least as important as genes in causing autism. Dr. Hallmayer sums the study by saying: "I think we now understand that both genetic and environment factors have to be taken seriously." Dr. Hallmayer's colleague, Dr. Peter Szatmari, a leading autism researcher who heads child psychiatry and behavioral neuroscience at McMaster University in Ontario, added: "This is a very significant study because it confirms that genetic factors are involved in the cause of the disorder. But, it shifts the focus to the possibility that environmental factors could also be really important." The full report of the California Autism Twins Study will be released in the November issue of Archives of General Psychiatry. If you would like to read more about this subject, go to www.archivesofgeneralpsychiatry.com. Be sure to not miss the findings that are released in November, 2011.