One in five children with autistic older sibling will have disorder, study shows

NEARLY one in five children with an autistic older sibling will also develop the disorder — a much higher incidence than previously thought, a study has found.

Researchers followed 664 babies who had at least one older brother or sister with autism. Overall, 132 infants, or about 19%, were diagnosed with an autism by their third birthdays. Previous smaller or less diverse studies reported a prevalence of between 3% and 14%.

“We were all a bit surprised and taken aback about how high it is,” said lead author Sally Ozonoff, a psychiatry and behavioural sciences professor with the Mind Institute at University of California at Davis.