It’s a story we hear regularly: A child is diagnosed with ADHD and one of his parents, recognizing the symptoms, realizes that he (or she) has the disorder, too. It’s often a surprise to the mom or dad, but to clinicians it’s not surprising. “We know ADHD is highly familial,” explains Mark Stein, a clinical psychologist and director of the ADHD and Related Disorders Program (PEARL Clinic) at Seattle Children’s Hospital. “That means 25 percent of the parents of kids we diagnose are going to have it.”