Jan. 26, 2015 -- Scientists searching for the genetic roots of autism have found something surprising: In families where two children have been diagnosed with the disorder, siblings don’t often share the same gene changes.
The new study fits into a larger body of research suggesting the genetics of autism are still poorly understood. It also raises the possibility that the disorder isn’t usually inherited, even when it runs in families.
Instead, it could be that some other factor, like a shared environment or common conditions during pregnancy, might explain why children with an older brother or sister with autism have a 7 times' higher risk of getting the condition themselves, compared to kids in the general population.
Exactly what the shared risk might be is anyone’s guess.
“This is still the million dollar question,” says Stephen Scherer, PhD. He’s the director of the Centre for Applied Genomics at the Hospital for Sick Children and the senior author of the study, which is published in the journal Nature Medicine.
Study Details
The researchers also found some intriguing new clues about biological causes of the disorder, which affects 1 in 68 children and appears to be on the rise in the U.S.
For the study, they sequenced all the genes of parents and children in 85 families where two children had been diagnosed with autism.
They found gene changes known to be linked to autism in 36 -- or slightly less than half -- of the affected families.
Of the 36 families where the cause of autism could be tied to specific gene changes, only 11 sets of siblings shared the same changes, and only 10 sets -- or less than a third -- got those changes from their parents.
In two-thirds of those families, there's at least one different gene change between siblings. “So they have their own form of autism,” Scherer says.
And siblings who didn’t share the same "risk genes" tended to have autism that looked very different, with different problems and challenges. One brother or sister might not be able to speak or communicate, for example, while the other might have close-to-normal language development.
source : Genes May Not Explain Autism That Runs in Families
