2010-09-30 07:50:39
By MARIA CHENG, AP Medical Writer Maria Cheng, Ap Medical Writer 1 hr 25 mins
ago
LONDON 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 chromosomal abnormalities.
"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 study's authors.
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 ethnicities.
The condition is estimated to affect millions of children around the world, and
scientists have long thought the disorder has a genetic component.
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 research.
"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 ADHD.
"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 problems.
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."