Siblings with autism do not share the same contributory genetic factor in almost 70 percent of cases, a study has revealed.
The findings, published in Nature Medicine, overturn a prevailing theory that genetic factors for autism run in families.
'We believe every child with autism is like a snowflake – unique from the other', said lead author Dr Stephen Scherer in a press statement.
It has always been clear that autism is a complex disorder and the study confirms its large genetic and behavioural diversity, even in closely related people. The researchers sequenced 340 whole genomes from 85 families in which two siblings were affected by autism. They found that 69.4 percent of siblings with autism carried different gene mutations known to contribute to the condition.
The team also noted that siblings who shared risk alleles tended to display similar clinical features while those with different alleles were more likely to have distinct autism symptoms. This means that most siblings with autism will display different behaviour patterns, a finding supported by many parental anecdotes.
There are known to be over 100 contributory risk genes for autism. Having a sibling with autism will increase an individual's risk of autism by 2-18 percent, and this rises to 36-96 percent for an identical sibling, according to the US Centers for Disease Control and Prevention. This had led researchers to hypothesise that siblings with autism inherit the same genetic variant from their parents. The findings from the 85 families involved in the present study were therefore unexpected.
Not only was this the largest ever autism genome study but, alongside it, 1,000 autism genomes were simultaneously uploaded to the Google Cloud to aid further research.
'By using the cloud to make data like this openly accessible to researchers around the world we're breaking down barriers in a way never done before', said Dr Robert Ring, co-author of the paper and chief science officer of Autism Speaks, which funded the study. The group hope to upload 10,000 autism genomes as part of the project, in partnership with Google.
'This is an example for a future where open access genomics will lead to personalised treatments for many developmental and medical disorders', said Dr Scherer, adding, 'This is a historic day'.