Genes Reveal That Siblings with Autism Don't Share Genetic Risk Factors

The majority of siblings diagnosed with autism spectrum disorder have different genetic risk factors and unique autistic behaviors. These findings, from a study published online in Nature Medicine, may come as a surprise to doctors and families. Because autism often runs in families, researchers long assumed that siblings shared the same risk factors in their genes.

Scientists used whole genome sequencing to analyze the entire genetic material, called the genome, of siblings from 85 families. The technique maps out the entire sequence of a person’s DNA. This includes every change and minor variation. Researchers focused on 100 genetic changes known to be linked to the development of autism. Mutations in these genes showed up in 42 percent of the families who participated in the study.

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Majority of Siblings with Autism Don’t Share Genetic Changes

Less than a third of the sibling pairs shared the same changes in autism-related genes, while 69 percent did not. Siblings with the same genetic mutations also showed similar changes in behaviors commonly affected by autism, compared to those who didn’t have those mutations.


The study findings emphasize the difficulty of diagnosing and treating autism, even in related people. Currently, some hospitals analyze the genetic information of one sibling to predict the risk of another sibling developing autism. For more accurate results, doctors may need to consider each child individually.

Moreover, examining the genes of one child may not offer advance information about the odds of the parents having a second child with autism.

“This means we should not be looking just for suspected autism-risk genes, as is typically done in diagnostic genetic testing,” said lead study author Dr. Stephen Scherer, the director of the Centre for Applied Genomics at Toronto's Hospital for Sick Children and the McLaughlin Centre at the University of Toronto, in a press release. “A full assessment of each individual's genome is needed to determine how to best use knowledge of genetic factors in personalized autism treatment.”

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Researchers Make Genetic Data Available Online

This is the largest genome study of autism to date. In spite of the large amount of data collected, researchers still need to look at the gene sequences of many more affected people. One of the aims of the project, which is funded by the advocacy group Autism Speaks, is to support the collection of this information.

As part of the project, researchers made the genomes of 1,000 people with autism available online through the Google Cloud platform. The data, and tools to help analyze it, are available for free to researchers around the world. The ultimate goal of the project is to upload at least 10,000 genomes from people with autism. Researchers hope that making the genetic information available will speed up the research process. It will hopefully help scientists discover the underlying biological basis of autism.

We believe that each child with autism is like a snowflake — unique from the other.
Dr. Stephen Scherer, Hospital for Sick Children

As researchers analyze the genes of more people affected by autism, they should gain a better understanding of how often siblings share a common genetic basis for the disorder. As gene sequencing becomes more affordable, it makes truly individualized treatments for kids with the disorder possible.

“We knew that there were many differences in autism, but our recent findings firmly nail that down,” said Scherer. “We believe that each child with autism is like a snowflake — unique from the other.”

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