Study co-author Clara Lajonchere, vice president of clinical programs for Autism Speaks, says the study used data from the California Autism Twins Study. The study, published online in the Archives of General Psychiatry, suggests both genetic and shared environmental factors significantly increase risk for autism spectrum disorder -- with an estimated 38 percent of risk being associated with genetic heritability and 58 percent with environmental factors that twins share during pregnancy, and perhaps early infancy.
The study involved 192 pairs of twins, both identical and non-identical, in which at least one of the twins in the pair had autism.
Study of identical twins, who share 100 percent of their genes, helps researchers determine the degree to which a disorder is inherited or genetic. Comparison to fraternal twins, who share around 50 percent of their DNA, allows researchers to understand how environmental influences add to the risk of autism spectrum disorder, Lajonchere says.
"It has been well-established that genetic factors contribute to risk for autism," Lajonchere says. "We now have strong evidence that, on top of genetic heritability, a shared prenatal environment may have a greater than previously realized role in the development of autism."