Severity of Symptoms Varies in Identical Twins.

Identical twins with autism spectrum disorder (ASD) often experience large differences in symptom severity even though they share the same DNA, according to an analysis by John Constantino, professor of psychiatry and pediatrics at Washington University, St. Louis, Mo. The findings, published in Behavior Genetics, suggest that identifying the causes of this variability may inform the treatment of ASD-related symptoms.

ASD is a developmental disorder that affects how a person behaves, interacts with others, and learns. Previous studies have found that when one identical twin has ASD, chances are extremely likely that the other twin has it, too.

The authors analyzed data from three previous studies comprising a total of 366 identical twin pairs with and without ASD. The severity of autism traits and symptoms in the twins was measured by a clinician's assessment or by parents' ratings on a standardized questionnaire. Some cases...