The debate about what causes autism continues, with two new studies suggesting there might be more of an environmental component at play than previously thought.
The first, published online Monday in the Archives of General Psychiatry, suggests that at least half of what the authors call "liability to autism" might be explained by environmental factors.
Researchers considered more than 50 sets of identical twins and 130 sets of fraternal twins, in which at least one child had a diagnosis of strict autism or Autism Spectrum Disorder (ASD). Relying on both parental reports and direct observation, they then used existing twin models, which rely on the degrees of shared genetics among fraternal and identical twins to determine how much certain factors are associated with autism risk. They found that only 40 percent of the risk of autism development was owed to genetic heritability, while 55 percent was linked to environmental factors.
"The take home message is that we really have to take more seriously the environmental factors, and how these come together with the genetic factors to play a role in the etiology of autism," said Dr. Joachim Hallmayer, an associate professor of psychiatry and behavioral science at the Stanford School of Medicine. Environmental factors, he explained, could include anything from a virus to drugs taken during pregnancy.
Medication during pregnancy was the subject of a second study published in the same journal, which suggests that prenatal exposure to certain antidepressants may "modestly" increase the risk of ASD development.