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Research shows
genetic mutation is linked
to autism
(March 2008
Issue)
By Catherine Robertson Souter
Researchers at Boston's Autism Consortium recently made a landmark
discovery that takes autism research one step closer to understanding
the disease.
Published in the January 9 online edition of New England Journal
of Medicine, the study reported a connection between a deleted or
duplicated 25-gene segment of Chromosome-16 and the occurrence of
autism.
Looking to uncover any possible chromosomal abnormalities that
might predict the occurrence of inherited autism, the researchers
used a new gene scanning technology to observe genetic variations
in 751 families in the Boston area who have more than one autistic
child. Patterns of deleted or duplicated genes found in that group
were compared to the gene patterns of 512 autistic children at Children's
Hospital Boston and in 299 autistic children from a research project
done by DeCODE Genetics of Iceland. The results were compared to
thousands of controls.
In the study, a total of 13 children were found to have a deleted
segment of the chromosome. Researchers also found 11 children with
an extra copy of this same genetic material (segment 16p11.2).
The researchers concluded that these mutations, found within the
exact same 25-gene segment of the chromosome may account for up
to one percent of autism cases. They did not believe that the abnormalities
could be attributed to heredity but perhaps occurred during conception
or early in fetal development because they were not found in most
of the children's parents.
They also found that both duplication and deletion of the segment
did not necessarily lead to full-blown autism but that missing a
piece of a segment will lead to cognitive problems.
"The deletion of the segment does seem to cause cognitive impairment,"
says David Miller, M.D., Ph.D., division of genetics at Children's
Hospital Boston, a researcher on the study. "But, there were a
few cases where we found the gene duplication in a parent who is
not known to have cognitive impairment. So maybe duplication is
not as detrimental. The missing piece of chromosome appears to cause
more problems than having an extra piece."
For autism researchers, the findings are a major step towards understanding
the disease. While geneticists have long known that genes play a
key role in autism, there had been few genetic mutations linked
specifically to the disease. explains the study's leader, Mark J.
Daly, Ph.D., an assistant genetics professor at Harvard Medical
School and an investigator for the consortium.
"The importance of finding those specific genetic links is they
give us rock solid clues," says Daly. "At a fundamental level, biology
plays an essential role and with this clue, we can generate ideas
for how to therapeutically intervene. This is just one piece of
the puzzle in autism, but it is substantial because it is one of
the first conclusively linked regions of genome to autism."
Geraldine Dawson, Ph.D., chief science officer of Autism Speaks,
an autism advocacy organization, agrees.
"This is a very important study," she says. "If we can isolate
the specific genes in this region of chromosome 16 that are related
to autism, this will be an important step toward understand the
biological basis of the disorder which is necessary for developing
medical treatments."
On the diagnostic side, the discovery could also aid in diagnosis
of the disease and help parents of an autistic child with early
detection in the child's siblings.
"This is such a significant risk factor that diagnostic tests are
being created and used in diagnostic practices to provide information
to clinicians and families," says Daly. "We've had so little evidence
in any psychiatric or developmental disease so it's a start."
With this discovery, future research will most likely focus on
the specific genetic strand, trying to ascertain if other abnormalities
can be found.
"Researchers might look at other people who have autism and use
a different technique to see if there are other changes within that
same segment," says Miller. "We could take a fine tooth comb look
at each of those 25 genes to see if there are other problems. It's
possible if we found another genetic change within that chromosome
16, we might be able to explain other cases."
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