PHILADELPHIA, Dec. 4, 2011 /PRNewswire-USNewswire/ -- Pediatric researchers analyzing genetic influences in attention-deficit/hyperactivity disorder (ADHD) have found alterations in specific genes involved in important brain signaling pathways. The study raises the possibility that drugs acting on those pathways might offer a new treatment option for patients with ADHD who have those gene variants—potentially, half a million U.S. children.

"At least 10 percent of the ADHD patients in our sample have these particular genetic variants," said study leader Hakon Hakonarson, M.D., Ph.D., director of the Center for Applied Genomics at The Children's Hospital of Philadelphia. "The genes involved affect neurotransmitter systems in the brain that have been implicated in ADHD, and we now have a genetic explanation for this link that applies to a subset of children with the disorder."

The study appears online today in Nature Genetics.

ADHD is a common but complex neuropsychiatric disorder, estimated to occur in as many as 7 percent of school-age children and in a smaller percentage of adults. There are different subtypes of ADHD, with symptoms such as short attention span, impulsive behavior and excessive activity. Its causes are unknown, but it tends to run in families and is thought to be influenced by many interacting genes. Drug treatment is not always effective, particularly in severe cases.

The study team did whole-genome analyses of 1,000 children with ADHD recruited at The Children's Hospital of Philadelphia, compared to 4,100 children without ADHD. The researchers searched for copy number variations (CNVs), which are deletions or duplications of DNA sequences. They then evaluated these initial findings in multiple independent cohorts that included nearly 2,500 cases with ADHD and 9,200 control subjects. All the study subjects were children of European ancestry.

Among those cohorts, the research team identified fo