Psychiatrists and psychologists have traditionally classified ADHD as belonging to one of three types: inattention or distractibility, hyperactivity and impulsivity, and a third form involving problems in both areas. But the children in this study provided the researchers with good evidence for only two of those subtypes.
"We found an inattentive subtype characterized by the inability to concentrate, and another subtype combining both inattention and hyperactivity," Neuman says. "It may be that what we once thought of as the strictly hyperactive and impulsive group is very rare or is really the combined type, and treatment for ADHD would improve both problems. But we found good evidence for only two subtypes."
By including twins in the study, the investigators were able to determine that genes play a role in the risk for ADHD. Identical twins suffered from the same class of symptoms 80 percent of the time. Non-identical, or fraternal twins, only matched up about half of the time.
"It's clear that ADHD runs in families," Todd explains. "That has important treatment implications because other children in a family are at higher risk, and the risk for parents to have similar problems is high. Obviously, if a parent is having a problem with attention, it is more difficult to successfully treat a child."
Todd says the finding that genetic factors influence risk may make it possible to create better treatments in the future. "On the basis of these twin studies, we believe ADHD has a genetic component, and if we could identify genes that predispose kids to ADHD, we might be able to develop better, more specific treatments."
Treatment for ADHD has been controversial. Child psychiatrists and pediatricians
prescribe methylphenidate (Ritalin) and other stimulants. Todd agrees with
critics that
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Contact: Jim Dryden
dryden@medicine.wustl.edu
314-286-0110
Washington University in St. Louis
8-Apr-1999