Clues to the Genetic Roots of ADHD

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Too much soda, candy and bad parenting have been cleared of full blame for children’s hyperactivity and uncontrollable behavior — at least according to a new study that has identified certain genetic abnormalities associated with ADHD.

It is the first study to link such a large genetic effect with attention deficit hyperactivity disorder, a condition that is known to run in families.

Experts at Cardiff University analyzed stretches of DNA from 366 children who had been diagnosed with the disorder. The scientists then compared the genetic samples from the ADHD children with DNA from 1,047 children without the condition. (More on ADHD: A Global Epidemic or Just a Bunch of Fidgety Kids?)

Compared with the control group, more children with ADHD had rare but large portions of DNA that were either missing or duplicated. These abnormal areas are called copy-number variants (CNV). Other studies have suggested that such copy-number variants may be associated with schizophrenia, autism, epilepsy and other neurodevelopmental disorders.

According to, which has a good explanation of the new findings:

Most strikingly, the rate of CNVs was six times as high as normal in ADHD children who had IQs lower than 70 and so had a more severe form of the disorder — there were 50 such children. “That’s huge,” says [Philip] Asherson, [who studies the genetics of ADHD at the Institute of Psychiatry in London].

Also, the ADHD children had CNVs in sites on chromosome 16 that overlapped with CNVs previously found in children with schizophrenia. The implication, says Asherson, is that these regions may be crucial to development of the brain in the womb or in infancy, and that disruption in this region may play a role in many psychiatric conditions.

Although the current study, published in The Lancet, didn’t find a specific gene associated with the disorder, scientists are hopeful that the preliminary results will help researchers better understand and breakdown the biological basis of ADHD.

—By Claire Mc Cormack

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