By Maggie Fox, Health and Science Correspondent
WASHINGTON (Reuters) – Using a new method that separates
patients by their symptoms, U.S. researchers said on Friday
they found a new genetic link to autism and suggested the
approach might be used to pinpoint the genetic causes of
other diseases as well.
The research also suggests that several different causes may
be behind autism, a disturbing and increasingly common
behavioral disorder that baffles parents and doctors alike.
The new study, published in the American Journal of Human
Genetics, links certain types of autism to a place on
chromosome 15 linked with several other disorders.
It had been suspected in autism for some time, but
researchers had been unable to show that people with certain
versions of genes on chromosome 15 were more likely to have
autism. The team at Duke University Medical Center in North
Carolina and at the University of South Carolina decided to
separate out autistic children by their actual behaviors.
Autism, which affects one in 1,000 children in the United
States, is defined by a wide range of symptoms, many of
which are just an exaggeration of normal childhood behavior.
“All kids with autism by definition have some form of
repetitive behavior,” Duke child psychologist Michael
Cuccaro, who helped lead the study, said in a telephone
interview. “One kind of a classical autism feature … may
be a child doing something with his hands and arms. He might
be flapping them, might be waving them in front of the
eyes.” Cuccaro’s team focused on children with other, more
prominent symptoms. “These are kids who if you changed the
furniture in the room, they become extremely upset and have
difficulty with that. If they normally went to bed at 7:30
and before they did that they took a bath and put pajamas
on, if you changed that they would have great difficulty
with that.”
SIMILAR MUTATIONS
When those particular children and teen-agers were separated
out, the researchers were able to find a series of mutations
on chromosome 15 that seemed to be similar, said Dr.
Margaret Pericak-Vance, a Duke geneticist who led the study.
They used a statistical trick, but they double-checked and
the association was clear, Pericak-Vance said. Both she and
Cuccaro say that supports what many researchers have said —
that autism is a complex disease and may not be caused by
the same thing in every patient. “It’s like any complex
disease — there are a number of underlying causes for it
and they manifest similarly,” she said. “The next thing is
to look at possible interactions between the genes in this
region. This region seems to be involved in a lot of
different disorders.”
Pericak-Vance said her team was already trying the new
approach to separate out different kinds of Alzheimer’s
disease (news – web sites). Alzheimer’s has different forms
— some are seen earlier in life than others, and
Pericak-Vance hopes the method might find a genetic
difference among them.
The gene on chromosome 15 that seems to be affected in the
autism patients controls a neurotransmitter called GABA.
That message-carrying chemical acts to turn off brain cells.
As the behavior seen in these children seems to be an
extreme version of what every child does at one time or
another, it could be that these particular symptoms are
caused by the brain’s failure to turn off a signal. In other
words, it does not know when to stop — thus the obsessive
behavior.
The research did little to answer questions about whether
environmental causes may be behind autism, Cuccaro said. One
group of parents believes childhood vaccines may be a cause,
although several studies aimed at finding out if that is
true have shown no link. “What we are coming to find about
vaccines now is that there is not a lot of support for a
link between the vaccine and autism,” said Cuccaro.
The study may help scientists find a way to treat autism,
which is now incurable. If a precise genetic cause of one
behavior is found, it might be possible to design a drug
that will correct it.
That would not be a cure — autism is too complex for that
— but it may be possible to moderate some of the symptoms,
Cuccaro said.