ADHD is a neurological disorder and research indicates that it may be due to alterations in the brain and the way it functions. The causes of these differences are not entirely known, but family and twin studies reveal ADHD is genetic. Between 10 percent and 35 percent of children with ADHD have a close relative with ADHD, and nearly half of parents who had ADHD as a child also have a child with the disorder. Studies in families of children with ADHD show that relatives are at high risk for ADHD, other psychiatric disorders and learning disabilities.