(RxWiki News) Many different genes have been linked to autism spectrum disorders (ASD). With the idea that no single gene is to blame, researchers looked for how different genes worked together.
A recent study looked at the genes of children with ASD and their families. They found that each gene linked to ASD, by itself, did not do much to create risk for ASD.
But, all these small changes added together to create higher risk.
"Ask a doctor about your child’s risk of autism."
Researchers at multiple locations around the U.S., led by Bernie Devlin, PhD, at the University of Pittsburgh School of Medicine, put together genetic data from two large projects.
They looked at the gene information from the Simons Simplex Collection and the Autism Genome Project.
They compared the genes of families that had multiple children with ASD and families that had only one child with ASD.
They looked to see what genes were related to ASD. They also looked to see which genes were passed from parents to children with ASD and their unaffected siblings.
Genes can take many forms. The different versions of each gene allow for all the differences that we see in people. These versions are called gene variants.
They found that there were many gene variants that were linked to ASD, but no one of them was a major contributor for ASD.
Instead, they concluded that the pattern of genes linked to ASD in these families suggests that a many minor gene variants add together to raise the risk of ASD.
Specifically, they found that, in families with more than one child with ASD, 60 percent of the risk for ASD could be explained by this adding up of risky genes.
In families with only one child with ASD, 40 percent of the risk was explained by the adding together of risky genes.
So, parents can pass along small changes to genes that may add risk. One or two minor changes may not result in ASD.
If many different risky gene variants are passed along, then they can add together to raise the risk of ASD.
Families with more than one child affected are likely passing along more small changes in genes that add together to increase risk of ASD.
In families with only one affected child, the parents are passing along less risk genes. The additive effect is lower risk, so the odds of having more than one affected child are lower.
This research shows that genetic risk is additive. Many different genes come together to influence risk of ASD. This explains the wide variety of symptoms and severity seen in children with ASD.
Testing for genes that confer risk of ASD is not currently available. Researchers are still trying to understand how genes and environment work together to increase risk of ASD.
This study was published October 15 in Molecular Autism. The study was funded by the Simons Foundation. The authors declare no competing interests.