Siblings born with autism spectrum disorder (ASD) share more of their father's genome and not their mother's, as thought previously, according to a study.

Autism spectrum disorders cover a range of neurological and developmental conditions. They can affect how a person communicates, socialises, learns, and behaves. ASD may also manifest as repetitive behaviours or restricted interests.

"There are children diagnosed with autism who are high functioning," said Ivan Iossifov, Associate Professor at Cold Spring Harbor Laboratory, a US-based non-profit.

"They have a completely productive life, although they have some minor troubles in social interactions, as most of us do. But also, there are children diagnosed with autism who never learn to speak, and they definitely have a difficult life," Iossifov added.

Over the last two decades, scientists have led a multimillion-dollar effort to uncover the genetic origins of autism. They discovered thousands of genes that, when damaged, may cause a child to be born with ASD. But their work was not able to account for all cases of ASD.

The team analysed the genomes of over 6,000 volunteer families. They found that in families that have two or more children with ASD, the siblings shared more of their father's genome.

Meanwhile, in families where only one sibling had ASD, the children shared less of their father's genome. While the discovery reveals a new potential source of ASD, it also poses a provocative question. Could other disorders play by the same genetic rules?

No one is sure how the father's genome makes its mark on children with ASD. But Iossifov thinks some fathers may carry protective mutations that fail to get passed on. Or fathers may pass down mutations that trigger the mother's immune system to attack the developing embryo.

Both theories offer hope for parents of children with ASD and other neurological disorders like schizophrenia. "Our future research is exciting," Iossifov said. "If one of those theories or two of them prove to be true, then it opens different treatment strategies, which can, in the future, affect quite a lot of families."