Early Gesture and Vocabulary Development in Infant Siblings of Children with Autism Spectrum Disorder.

This study examined longitudinal growth in gestures and words in infants at heightened (HR) versus low risk (LR) for ASD. The MacArthur-Bates Communicative Development Inventory was administered monthly from 8 to 14 months and at 18 and 24 months to caregivers of 14 HR infants diagnosed with ASD (HR-ASD), 27 HR infants with language delay (HR-LD), 51 HR infants with no diagnosis (HR-ND), and 28 LR infants. Few differences were obtained between LR and HR-ND infants, but HR-LD and HR-ASD groups differed in initial skill levels and growth patterns. While HR-LD infants grew at rates comparable to LR and HR-ND infants, growth was attenuated in the HR-ASD group, with trajectories progressively diverging from all other groups.