The risk of younger siblings developing an autism spectrum disorder is 14 times higher if an older sibling has the disorder, says a study.
Autism is a neurodevelopmental disorder defined by impairments in social interaction and communication, as well as restricted and repetitive patterns of behaviour.
The findings showed that children with older siblings who had autism had the disease rate of 11.3 per cent compared to 0.92 per cent for those with unaffected older siblings.
The risk level was found consistent across gestational age at birth.
Younger siblings who were born at preterm (28-36 gestational weeks) and had an older sibling diagnosed with autism were at 10 times increased risk for developing the developmental disorder.
“Our study provides additional insights into how autism affects siblings,” said Darios Getahun, Scientist at Kaiser Permanente – a US-based health care company.
Further, younger boys with Autism who had older brothers were much more likely to be affected by the disorder than younger girls with older sisters (15 per cent vs. 7 per cent, respectively.)
“The study also contributes to a better understanding of the influence of factors such as gender on autism risk,” Getahun added.
Previous studies have found that second-born children who are conceived sooner than two years or later than six years after the arrival of their older sibling have a significantly increased risk of autism.
In addition, children born at term (37-42 gestational weeks) who had an older sibling diagnosed with autism had more than 15 times the increased risk for autism diagnosis.