Non-ASD outcomes at 36 months in siblings at familial risk for autism spectrum disorder (ASD): A baby siblings research consortium (BSRC) study

Lay Abstract: This study characterized developmental outcomes of a large sample of siblings at familial high-risk of autism spectrum disorder (ASD), who themselves did not have ASD (n=859), and low-risk controls with no family history of ASD (n=473). We characterized outcomes at age 3 years using a developmental assessment of language and learning and an observational measure of ASD symptoms and, where available, parent interviews about ASD behaviors and adaptive functioning. Around one-in-ten high-risk siblings had mild-to-moderate levels of developmental delay, a rate significantly higher than the low-risk controls. The groups did not differ in the proportion of toddlers with mild-to-moderate language delay. High-risk siblings were also more likely to have higher levels of observer-rated and parent-reported levels of ASD symptoms and lower adaptive functioning. Males were more likely to show higher levels of ASD symptoms and lower levels of developmental ability and adaptive behavior than females across most measures. Lower maternal education was associated with lower developmental and adaptive behavior outcomes. We discuss these findings as evidence for early emerging characteristics related to the "broader autism phenotype" previously described in older family members of individuals with ASD. There is a need for ongoing clinical monitoring of high-risk siblings who do not show clear signs of ASD by age 3 years, as well as continued follow-up into school age to determine their developmental and behavioral outcomes.