Another deletion occurred in a gene for a glutamate receptor. Glutamate is a neurotransmitter, a protein that carries signals in the brain. While ADHD medications act on dopamine and serotonin, which are also neurotransmitters, this new finding may suggest an important role for glutamate as well, at least for some ADHD patients.

"As we delve into the genetics of very complex diseases such as ADHD, we find many contributing genes, often differing from one family to another," added White. "Studying the functions of different genes allows us to identify biological pathways that may be involved in this neuropsychiatric disorder."

Some of the biological pathways involved in ADHD may also be common to other neurological conditions, say the researchers. Likewise, there is some overlap among the CNVs found in ADHD that also occur in autism, schizophrenia and other neurological disorders. This overlap was not surprising, said Elia, because ADHD patients frequently also have one of more of these disorders. However, as researchers learn more about specific genes in neurological conditions, the hope is that researchers might in the future personalize treatments to a patient's own genetic profile, to achieve more targeted, specific therapies.

Elia and White stressed that much further work must be done before genetic findings lead to ADHD treatments.

The National Institutes of Health provided grant support for the study, as did the University of Pennsylvania, the Pennsylvania Department of Health, the Cotswold Foundation and the ADHD: Climbing to a Cure Foundation. Elia, White and Hakonarson all are faculty members of the University of Pennsylvania School of Medicine (Penn). Xiaowu Gai, Ph.D., of the Center for Biomedical Informatics at Children's Hospital, was a co-first author with Elia. Other collaborators were from Children's Hospital and Penn.

Elia et al, "Rare Structural Variants Found in Attention-Deficit Hyperactivity Disorder Are Preferentially Associated with Neurodevelopmental Genes," Molecular Psychiatry, published online, June 23, 2009.

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