Purpose: A recent approach to identifying early markers of risk for autism spectrum disorder (ASD) has been to study infants who have an older sibling with ASD. These infants are at heightened risk (HR) for ASD and for other developmental difficulties, and even those who do not receive an eventual ASD diagnosis manifest a high degree of…

In this study we examined early motor, vocal, and communicative development in a group of younger siblings of children diagnosed with autism (Infant Siblings). Infant Siblings and no-risk comparison later-born infants were videotaped at home with a primary caregiver each month from 5 to 14 months, with follow-up at 18 months. As a group, Infant…