ADHD Gene Discovered

Attention Deficit More Common in Kids with 'Snap-25' Mutation

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Sept. 24, 2002 -- A gene missing in hyperactive mice may explain some human cases of ADHD.

ADHD -- attention deficit/hyperactivity disorder -- runs in families. It's more common in boys than in girls. If one twin has ADHD, the other is very likely to have it, too. These facts make scientists think that the tendency to get ADHD is inherited. So far, the search for an ADHD gene has turned up many clues, but no smoking gun.

One of these clues came in 1996, when researchers found that a strain of hyperactive mice lacked a gene called SNAP-25. When genetic engineers put the gene back into these mice, they weren't hyperactive any more.

Now an Irish research team finds that humans with a certain variation of their SNAP-25 gene are 50% more likely than those without the variation to be hyperactive. The researchers did genetic tests on 93 families in which at least two members had ADHD. Not everyone who had the SNAP-25 variation had ADHD. Not everyone with ADHD had a variation in their SNAP-25 gene. But carrying the variant gene increased the chance of having ADHD, especially when the gene was inherited from the father.

The research team, led by Michael Gill, MD, PhD, of Trinity College, Dublin, concludes that ADHD is the result of many things acting together. They note that because there were relatively few people in their study, the link between SNAP-25 and ADHD must be confirmed in other studies.

The study appears in the September issue of Molecular Psychiatry.

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