Gesture Development and Autism Severity in High-Risk Infants

Background:  Children with autism often demonstrate deficits in gesture use. Studying populations at increased risk for developing autism may illuminate shared or distinct pathways leading to deficits in gestures later in development. Two populations at high risk for autism are infants with fragile X syndrome (FXS; Kover & Abbeduto, 2010) and infants with an older sibling with autism (ASIB; Ozonoff et al, 2011). Given the importance of gesture use on language development, characterizing the emergence of gesture delays contrasted across high-risk populations can have important implications on earlier and more targeted intervention strategies.

Objectives:  Identify the effect of autism severity on developmental trajectories of gesture use in infants with FXS and ASIBs, controlling for nonverbal abilities.

Methods: Sample included 35 males (15 FXS, 20 ASIB) recruited through an ongoing longitudinal study conducted at the University of South Carolina. We measured gesture use using the Early Gesture score on the MacArthur-Bates Communicative Development Inventories (CDI), nonverbal ability using a composite of the Visual Reception and Fine Motor domains of the Mullen Scales of Early Learning (MSEL), and autism severity using the ADOS-2 CSS. The MSEL and the CDI were collected at 9, 12 and 24 months, and the ADOS-2 was administered at 24 months.

Results: All models were time-centered at 24 months. The first growth model determined whether number and rate of gestures used differed in FXS and ASIBs. At 24 months, infants with FXS had developed about 4 less gestures than ASIBs (β=4.20, p<0.001), while the rate of gesture development did not differ between groups (β=0.05, p=0.56). When nonverbal abilities were added as a predictor in this model, results were non-significant, suggesting group differences in gesture use at 24 months may be driven by developmental delay in FXS. Next, two growth models were run to determine the relationship of autism severity on gesture use, controlling for nonverbal abilities for each group. In FXS, higher autism severity at outcome was associated with reduced gesture use at 24 months with a trend statistically (β=-0.61, SE=0.31, p=.06), but not the rate of gesture development (β=-0.02, SE=0.02, p=.34). For ASIBs, higher autism severity at outcome was associated with reduced gesture use at 24 months (β=-0.54, SE=0.23, p=.03), but not the rate of gesture development (β=-0.03, SE=0.02, p=.21).

Conclusions: Results indicated that after accounting for nonverbal abilities in FXS, ASIBs and FXS demonstrated profiles of gesture use that were similarly affected by autism severity, where autism severity was related to reduced gesture use at 24 months, but did not affect the rate at which these groups acquire gestures. These results provide evidence that early gesture use may be a shared behavioral profile across these two etiologically distinct populations, such that reduced number of gestures at 24 months in may be a similar marker for autism symptoms as it is in ASIBs. These similar patterns in gesture profiles, and the impact of autism severity on those profiles, also suggest that similar treatments may be effective in both groups.