Siblings of autistic children 20% more likely to have condition, finds study

New Delhi: Siblings of children with autism are at a 20 per cent higher chance of being diagnosed with the condition, compared to those without the neurodevelopmental disorder, a new research has found.

Other factors such as the sex of the first autistic child and that of the later-born were also found to influence the chances of the disorder recurring within a family.

Autism is marked by repetitive behaviour, along with affected social communication.

"If a family's first autistic child was a girl, they were 50 per cent more likely to have another child with autism than if their first autistic child was a boy," said corresponding author Sally Ozonoff, a professor at the University of California Davis, US.

"This points to genetic differences that increase recurrence likelihood in families who have an autistic daughter," said Ozonoff.

The study, published in the journal Pediatrics, was conducted in 1,600 infants from across the US, Canada, and the UK, all of them having an elder autistic sibling. The infants were evaluated for autism from the age of six months to three years and data was collected from 2010-2019.

"A total of 20.2 per cent of siblings developed autism spectrum disorder, which is not significantly higher than the previously reported rate of 18.7 per cent," the authors wrote, referring to their 2011 study which included 664 children.

Furthermore, the researchers found that if the sibling of an autistic child was a boy, he was nearly twice as likely as a girl to be on the spectrum.

"The familial recurrence rate if the new baby was a boy was 25 per cent, whereas it was 13 per cent if the new baby was a girl," said Ozonoff.

"This is in line with the fact that boys are diagnosed with autism about four times as often as girls in general," the researcher added.

The study also found that a child having multiple autistic siblings is at a higher risk of having the condition (37 per cent), compared to a child having only one autistic sibling (21 per cent).

The findings regarding recurrence of autism in a family should help them plan for and support future children, along with reassuring providers who are counselling and monitoring development, according to Ozonoff.

However, it is critical that the findings be replicated, as that may indicate that there are social factors of health which can lead to higher rates of autism in families, she said.

Therefore, more research is needed, said Ozonoff.