U.S. researchers analyzed genetic influences on attention-deficit/hyperactivity disorder and found changes in some genes affected brain signaling pathways.Study leader Dr. Hakon Hakonarson, director of the Center for Applied Genomics at The Children\'s Hospital of Philadelphia, said the discovery raises the possibility that drugs acting on those pathways might offer a new treatment option for patients with ADHD who have those gene variants.\"At least 10 percent of the ADHD patients in our sample have these particular genetic variants,\" Hakonarson said in a statement.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, which are deletions or duplications of DNA sequences, and evaluated the initial findings in multiple independent cohorts that included nearly 2,500 cases with ADHD and 9,200 control subjects.Co-first author Dr. Josephine Elia, a child psychiatrist at Children\'s Hospital, said thousands of genes may contribute to the risk of ADHD, but identifying a gene family responsible for 10 percent of cases is a robust finding in a common neuropsychiatric disorder such as ADHD.The study appears online in Nature Genetics.