Five percent of all school-age children in the United States have some form of attention deficit/hyperactivity disorder, or A-D-H-D. A research team at Washington University in St. Louis is studying A-D-H-D to identify the genes that seem to increase the risk of developing the disorder. Washington University child psychiatrist Richard Todd says it is clear that A-D-H-D runs in families. "ADHD has always been shown in twin and family studies to be extremely heritable - on the order of 70-80 percent - just as heritable as height, intelligence and many other behaviors."

Some people with A-D-H-D are hyperactive. Others cannot focus. Still others suffer from both problems. Todd says several genes might be involved and slight differences among them might predispose a person to inattention or hyperactivity. "What probably distinguishes these different syndromes is which parts of the brain are involved," he says and adds, "It may very well be that all forms of ADHD that have prominent problems with inattention involve prefrontal areas of the brain, whereas those forms that also involve hyperactivity or impulsivity may also have abnormalities in other parts of the brain."

Todd says understanding how genetics influence risk may make it possible to develop better and more specific treatment for the disorder. The study appears in the Journal of the American Academy of Child and Adolescent Psychiatry.