Researchers from America, Canada and Israel tested 664 children from families with at least one child with autism at 36 months old, using the Autism Diagnostic Observation Schedule and the Mullen Scales of Early Leaning, which measure non-verbal cognitive, language and motor skills.
The overall risk for children with siblings with autism developing the disorder was nearly 19 per cent. However, this increased to over 26 per cent for boys. And for children with more than one sibling with autism the risk of them developing the disorder was 32 per cent.
Previous studies have estimated between 3 and 10 per cent of children with older siblings with autism developing the condition. The researchers said that their study was the largest prospective investigation of autism spectrum disorder and sibling recurrence to date.
It is more common for boys to be affected with autism than girls, with, on average, 80 per cent of all children that are diagnosed with the disorder being boys. The US Centers for Disease Control and Prevention places the current incidence of autism at 1 in 110 children.
The authors say that the study highlights the importance of routine surveillance and rapid referral for the treatment of infant siblings of children with autism. They suggest that primary care professionals monitor the development of these children closely and refer them for early intervention when concerns arise.
Sally Ozonoff, professor of psychiatry and behavioural sciences at the MIND Institute at the University of California-Davis in America, who led the study, said, ‘This research shows that the younger siblings of children with autism spectrum disorders need to be tracked very carefully, and this may require more than the normal surveillance that a paediatrician might typically do. This should include very explicitly and regularly checking in with parents on whether developmental milestones are being reached.’
The study, Recurrence Risk for Autism Spectrum Disorders: A Baby Siblings Research Consortium Study, is published online in the journal Paediatrics.