What can I do if my son has attention deficit hyperactivity disorder (adhd) and I have always wondered why?

Generally inherited. Children have either inherited the traits of adhd or have acquired them from an infection or trauma to the brain. Often a parent , or extended family members have similar features. 75% of affected children are inattentive, not hyperactive. Psychological/neuropsychological testing can check for learning disabilities that may be evident or will develop in the future.