Two sisters reading a bookWhen infants have an older sibling diagnosed with an autism spectrum disorder (ASD), they are more likely to exhibit atypical development or have autism themselves, according to research from the University of California, Davis MIND Institute and the University of California, Los Angeles. The research indicates that parents of children with autism should pay special attention to their younger children to identify early signs of developmental abnormalities. Early detection means that the children can promptly take part in effective interventions.

The research team evaluated 294 infant siblings of children with autism and 116 infant siblings of children without autism. All of the infants were enrolled in the study before 18 months of age. The researchers collected developmental data when the children were 6, 12, 18, 24, and 36 months old using standard developmental tests for ASD symptoms.

They found that almost half of younger siblings of children with autism have some form of atypical development—17% develop an autism spectrum disorder. Another 28% of the younger siblings have other developmental or behavioral delays, primarily in social, communication, cognitive, or motor development—extreme shyness, less-than-typical levels of eye contact, or delayed pointing were among the most commonly observed. The delays were apparent by the time the infants reached 12 months.

Parents who already have one child with ASD must be extra attentive to their younger children. Clinicians and parents need to cooperate to ensure that younger children are regularly screened for developmental and behavioral issues so that they can receive interventions as soon as delays are identified.

“This research should give parents and clinicians hope that clinical symptoms of atypical development can be picked up earlier, so we can, perhaps, reduce some of the difficulties that these families often face by intervening earlier,” said Sally Ozonoff, lead study author and professor of psychiatry and behavioral sciences at the UC Davis MIND Institute.

This research is published in the Journal of the American Academy of child and Adolescent Psychiatry.

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