Aims: To compare siblings of children with autism (SIBS-A) and siblings of children with typical development (SIBS-TD) at 4 and 14 months of age.
Methods: At 4 months, mother–infant interactional synchrony during free play, infant gaze and affect during the still-face paradigm, and infant responsiveness to a name-calling paradigm were examined (n = 21 in each group). At 14 months, verbal and nonverbal communication skills were examined as well as cognition (30 SIBS-A and 31 SIBS-TD).
Results: Most SIBS-A were functioning as well as the SIBS-TD at 4 and 14 months of age. However, some differences in early social engagement and later communicative and cognitive skills emerged. Synchrony was weaker in the SIBS-A dyads, but only for infant-led interactions. Infant SIBS-A revealed more neutral affect during the still-face procedure and were less upset by it than was true for the SIBS-TD. A surprising result was that significantly more SIBS-A responded to their name being called by their mothers compared to SIBS-TD. At 14 months, SIBS-A made fewer nonverbal requesting gestures and achieved lower language scores on the Bayley Scale. Six SIBS-A revealed a language delay of 5 months and were responsible for some of the significant differences between SIBS-A and SIBS-TD. Furthermore, infant SIBS-A who showed more neutral affect to the still face and were less able to respond to their name being called by their mothers initiated fewer nonverbal joint attention and requesting behaviors at 14 months, respectively.
Discussion: Focused on the genetic liability for the broad phenotype of autism as well as the possible influence of having a sibling with autism.