-- Robert Preidt
FRIDAY, April 20 (HealthDay News) -- Half-siblings of children
with autism are at increased risk for the disorder, according to a
recent study that provides new genetic clues about autism.
Previous research has shown that full siblings of children with
autism are also at higher risk for the developmental disability.
The new finding may not be surprising -- given that half-siblings
share about 25 percent of their genes -- but provides new clues to
how autism is inherited.
The study included more than 5,000 U.S. families enrolled in a
nationwide autism registry in which there was a child with autism
and at least one other sibling. Included were 619 families with at
least one maternal half-sibling, meaning the children shared the
same mother but not the same father. The researchers compared
autism recurrence among the half-siblings to the rate among the
The researchers also looked at half-siblings in a group of St.
Louis families to try to replicate the findings from the larger
Overall, they found autism had been diagnosed in 10 percent to
11 percent of full siblings and 5 percent to 7 percent of
"We found that autism risk for half-siblings is about half of what it is for full siblings," principal investigator Dr. John Constantino, director of child and adolescent psychiatry at the Washington University School of Medicine in St. Louis and psychiatrist-in-chief at St. Louis Children's Hospital, said in a university news release.
"Most of the half-siblings we studied had the same mothers. Given that half of the risk of transmission was lost and half was preserved among those maternal half-siblings, mothers and fathers appear to be transmitting risk equally in families in which autism recurs," Constantino said.
The findings also suggest that in many families, the
transmission of autism from parents to children is the result of
the effects of many genes, with each contributing a small
proportion of the risk, he said.
The study was published online April 16 in the journal
The U.S. National Institute of Neurological Disorders and Stroke
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