ADHD a complex neuropsychiatric disorder
affects around 7 percent of school-age children and around the same percentage of adults.
Its causes are unknown, but it usually runs in families; drug treatment can be affective but not always in extreme cases.
The research subjects were 1,000 children with ADHD and over 4,000 without the disorder. The team from The Children's Hospital of Philadelphia
, did whole-genome analyses of both groups searching for copy number variations (CNVs), which are deletions or duplications of DNA sequences.
After evaluating their initial findings further using multiple independent cohorts that included nearly 2,500 cases with ADHD and 9,200 control subjects, the research team identified four genes with a significantly higher number of CNVs in children with ADHD.
In the press release
, and report
also published in December 2011, in Nature Genetics, study leader Hakon Hakonarson, M.D., Ph.D.
, director of the Center for Applied Genomics at The Children's Hospital of Philadelphia says:
At least 10 percent of the ADHD patients in our sample have these particular genetic variants. 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.
All the genes identified were members of the glutamate receptor gene family. Glutamate is a neurotransmitter, a protein that transmits signals between neurons in the brain.
Hakonarson also explains that:
Members of the GMR gene family, along with genes they interact with, affect nerve transmission, the formation of neurons, and interconnections in the brain, so the fact that children with ADHD are more likely to have alterations in these genes reinforces previous evidence that the GRM pathway is important in ADHD. Our findings get to the cause of the ADHD symptoms in a subset of children with the disease.
In the U.S. alone this could be close to half a million children.
Co-first author Josephine Elia, M.D., a child psychiatrist at Children's Hospital and an ADHD expert says that the research will help the development of new therapies that can be aimed at treating underlying causes of ADHD. Thus "individualizing treatment to a child’s genetic profile."