Up to now, genetics were thought to account for 90 percent of a child’s risk for autism, but a new Stanford University School of Medicine study suggests environmental factors could play a much larger role than previously thought.
The largest study of its kind, the research focused on autism in 192 pairs of twins — 54 identical, 138 fraternal. The surprise came when Stanford researchers found a greater number of fraternal twins shared autism than identical twins. Fraternal twins share only half their genes with each other, thus, when both fraternal twins are autistic, it suggests factors other than genetics are at work.
In fact, “About half of what we see is due to environmental factors, and half of what we see is due to genetic factors,” Dr. Joachim Hallmayer tells Guy Raz, host of weekends on All Things Considered. Hallmayer is the lead author of the study.