LONDON (AP) - Children with attention deficit hyperactivity
disorder are twice as likely to have missing or extra chromosomes
than other children - the first evidence that the disorder is
genetic, a new study says.
British researchers compared the genomes of 366 white British
children from 5 to 17 years old with attention deficit
hyperactivity, or ADHD, to those of more than 1,000 similar
children without the disorder. The scientists focused on a sequence
of genes linked to brain development that has previously been
connected to conditions like autism and schizophrenia.
In children without ADHD, about 7 percent of them had deleted or
doubled chromosomes in the analyzed gene sequence. But among
children with the disorder, researchers discovered about 14 percent
had such genetic alterations. Scientists also found that 36 percent
of children with learning disabilities in the study had the
"This is the first time we've found that children with ADHD
have chunks of DNA that are either duplicated or missing," said
Anita Thapar, a professor at the MRC Centre in Neuropsychiatric
Genetics and Genomics at Cardiff University who was one of the
She said the findings are too early to affect diagnosis or
treatment and are only applicable to people of European Caucasian
descent because studies have not been done yet on other
The condition is estimated to affect millions of children around
the world, and scientists have long thought the disorder has a
U.S. experts estimate that ADHD affects from three to five
percent of school-age children in the United States. There are no
figures for developing nations.
The study was paid for by Action Research, Baily Thomas
Charitable Trust, the Wellcome Trust, Britain's Medical Research
Council and the European Union. It was published online Wednesday
in the medical journal Lancet.
Peter Burbach, a professor of molecular neuroscience at
University Medical Center Utrecht in the Netherlands, was surprised
some of the genetic defects found for ADHD were identical to ones
for autism and schizophrenia. He was not connected to the Lancet
"There's a great chance the environment is modifying these
genes," Burbach said, adding the genes could lead to several brain
disorders, depending on things like the child's upbringing and
other genetic factors.
He also thought scientists might eventually be able to reverse
"This is not a structural abnormality in the brain, it's just
the last phase of development that's gone wrong," he said. "It
could be the brain just needs to be fine-tuned."
Philip Asherson, a professor of molecular psychiatry at the
Institute of Psychiatry at King's College London, said the study
only dealt with a subset of people with ADHD and said the
environment should still be considered a cause. In the case of some
Romanian orphans, Asherson said there was proof that severe
deprivation at an early age can lead to ADHD or other neurological
Asherson said the medical world was still years away from being
able to correct ADHD.
"The study doesn't tell us a lot about what's going on in the
brains of people with ADHD," he said. "If we can find out more
about these genes and how they affect brain development, that may
give us inroads, but it's hard to say when that will be."
(Copyright 2010 by The Associated Press. All Rights Reserved.)