They also stressed that further studies replicating the results, "preferably in larger samples, will be required to corroborate this relationship."
Dr. Stephan Zuchner, an associate professor and director of the Center for Human Molecular Genomics at the University of Miami Miller School of Medicine, said there is considerable debate of how much of ADHD is genetically based.
"There is an extreme spectrum, from people who think it's not so much to people who think it's a lot," he said. "I think it's certainly significant -- the genetic contribution. There is little doubt that ADHD has a genetic component."
However, Zuchner thinks that developing ADHD is a result of both genetics and environment. "It is rare to see that genetics alone can cause ADHD," he said.
Zuchner also noted this is a small study, so it is premature to try to identify the risk of developing ADHD based on these genetic mutations. "I would be careful from this small study not to draw any larger conclusions," he said.
At least one other study has found some evidence of a genetic basis for ADHD.
A report in the Sept. 30 online edition of The Lancet found that many who suffer from ADHD appear to have a genetic abnormality that may predispose them to the condition, British researchers report.
The U.K. team analyzed the genetic information of 366 children with ADHD, comparing it to more than 1,000 unrelated but ethnically matched individuals in a control group. Children with ADHD were significantly more likely to have missing or duplicated segments of DNA -- called copy number variations (CNVs) -- than were children without ADHD, the researchers found. This type of genetic variation is more common in those with brain disorders, they noted.
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