A trio of studies make the strongest case to date that autism and attention deficit hyperactivity disorder (ADHD) share similar genetic causes. The findings could help explain why up to 80 percent of children with autism also meet the criteria for ADHD. Several studies have shown that autism and ADHD co-occur in families, but researchers have yet to identify overlapping genes...One of the new studies explores the genetic basis of autism and ADHD traits in the general population, another examines how autism and ADHD co-occur in families, and the third reveals how features of autism relate to those of ADHD. Together, they show that the two conditions are closely related.