No one’s exactly sure what causes ADHD, whether in adult or children, but scientists believe it could be in imbalance in neurotransmitters, the chemicals that regulate how the brain processes and regulates responses to stimuli. Genetics may also play a role. Like many mental conditions, along with other traits ranging from diabetes to alcoholism to red hair, ADHD seems to run in families. However, since the disorder (called minimal brain dysfunction or hyperactivity in previous decades) may have gone undiagnosed, parents will have to look for clues on their family tree. School failures, delinquency, multiple divorces, employment problems and addictions can all be signs that family members may have had undiagnosed and untreated ADHD.