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In Autism, it Depends on Which Parent Passes on the Genetic Abnormality

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Duke Health News 919-660-1306

Hold for release: 8 a.m. EDT , Friday, Oct. 6, 2000

PHILADELPHIA -- While it has been known that genetic
abnormalities are implicated in susceptibility to autism, new
research by Duke University Medical Center researchers has
added another variable - the particular parent who contributes
the defective gene can determine whether or not the child
acquires autism.

The researchers point out that autism is an extremely
complex disease with a wide spectrum of behavioral
manifestations and it is likely that other genes or
environmental factors are involved. However, their
sophisticated genetic analysis has for the first time suggested
that a phenomenon known as genetic imprinting is at work in
autism and that it appears to be an important factor in the
disorder.

Genetic imprinting is a process by which a gene's expression
is governed solely by which parent donates the gene copy,
rather than by the classic laws of Mendelian genetics, in which
genes are either dominant or recessive. Imprinted genes
typically become inactivated, or turned off, during the
development of egg or sperm cells, or shortly after
fertilization.

"Autism is not a simple genetic disease, caused by the
presence or absence of a single gene," said Allison
Ashley-Koch, a post-doctoral fellow at Duke's Center for Human
Genetics. "We're finding that it is much more complex."

Ashley-Koch prepared the results of the Duke study for
presentation Friday at the annual scientific sessions of the
American Society for Human Genetics. The autism research is
sponsored by numerous grants from the National Institutes of
Health.

"We've always known that imprinting exists - there are
examples in less complicated organisms," said Margaret
Pericak-Vance, director of Duke's Center for Human Genetics
(CHG) and senior autism researcher. "Now, with the new
technologies in genomics, we can look at more complex
inheritance patterns in human disorders. These findings suggest
a possible mechanism behind the underlying genetic cause of
autism."

The researchers examined 82 families who had at least two
family members afflicted with some form of autism. By applying
the latest genetic sleuthing techniques, the researchers were
able to demonstrate that imprinted genes may be at work.
Specifically, they found preliminary data suggesting a paternal
effect on chromosome 7 and a maternal effect on chromosome
15.

Genetic imprinting has recently been shown to be involved in
several rare human disorders, including Prader-Willi Syndrome
and Angelman syndrome, which both can produce autism-like
symptoms. All are considered neurodevelopmental disorders.

"Many children with these syndromes have altered genes in
the same region of chromosome 15 that we are looking at in
autism," Pericak-Vance noted. "This area of chromosome 15 is
highly unstable and prone to genetic rearrangement."

Autism is a complex disease that affects two to 10 per
10,000 people, making it the third most common developmental
disability - almost as common as Down syndrome. But because of
the broad differences in severity of the disease, doctors have
difficulty diagnosing it with certainty. Some children simply
talk later than normal, while others have severe withdrawal and
self-destructive patterns of repetitive head banging and
difficulty sleeping or other manifestations.

Doctors believe that the disorder begins during development
of the brain, possibly even before birth, and that the change
prevents affected people from properly processing sensory
information from their environment.

"Once we better understand the genetic factors involved in
autism, genetic testing can theoretically be offered to
families at risk," Ashley-Koch said. "In addition,
identification of such genes will pave the way for development
of therapies to improve the quality of life for these
children."

The team included the following investigators, from Duke:
Marisa Menold, Kimberly Joyner, Shonda Mason, Christie Poole,
Shannon Donnelly, Chantelle Wolpert, Dr. Robert DeLong, Dr.
Jeffery Vance and Dr. John Gilbert. Other collaborators
include: Sarah Ravan, Ruth Abramson, Michael Cuccaro and Harry
Wright, all from the University of South Carolina; Lennord von
Wendt from the Helsinki University Central Hospital, Finland;
and Cate McCain from the University of New Mexico.

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