Autism and attention deficit hyperactivity disorder often coincide, but the search for common biological roots has turned up conflicting evidence...Until about five years ago, the American Psychiatric Association’s diagnostic bible held the two conditions to be mutually exclusive: Only in 2013, with the debut of the current “Diagnostic and Statistical Manual of Mental Disorders” (DSM-5), did a dual diagnosis become permissible. But in fact, autism and ADHD often coincide.