A new study that has found siblings of autistic children are more likely to have the condition suggests genetics may play a larger role in the disorder’s development than lifestyle or environmental factors.
The new study, by researchers at the Washington University School of Medicine in St. Louis, also found half siblings of children with autism – who share about 25 percent of their genes – are more likely to develop the condition.
The study, published online in the journal Molecular Psychiatry, adds to the growing evidence that females – as well as males – can inherit and pass along genetic risks for autism, said lead researcher Dr. John N. Constantino.
"We found that autism risk for half siblings is about half of what it is for full siblings," he said. "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 study’s findings indicate autism is associated with many genes — not just one — with each contributing a small proportion of risk.
For the study, researchers studied more than 5,000 families in which there was a child with autism and at least one additional sibling. The families were enrolled in a national Internet-based family registry for autism, the Interactive Autism Network.
The researchers found that 10 percent to 11 percent of full siblings had been diagnosed with autism, compared to 5 percent to 7 percent of half siblings.
About one in 110 children has an autism spectrum disorder, according to the U.S. Centers for Disease Control and Prevention. Constantino’s study suggests more than 60 percent of those cases of autism are likely to be inherited on the basis of genetic variations inherited from unaffected mothers and fathers.
The study was funded, in part, by the Eunice Kennedy Shriver National Institute of Child Health and Human Development and the National Institute of Mental Health of the National Institutes of Health.