Gesture Development from 9 to 24 Months in Infants with Fragile X Syndrome, Infant Siblings of Children with Autism and Typically Developing Infants

Background: Individuals with autism experience deficits in the realm of social communication. One important and early emerging aspect of social communication is gesture use, an area shown to predict important later communication outcomes (Rowe, Özçalışkan, & Goldin-Meadow, 2008). Two populations at risk of developing autism and social communication deficits are individuals with fragile X syndrome (FXS; Kover & Abbeduto, 2010) and children who have an older sibling diagnosed with autism (ASIB; Yirmiya et al., 2006). Characterizing gesture development is an important first step in identifying the best approach to intervention in these populations.

Objectives: Identify developmental trajectories of gesture use in infants with fragile X syndrome and infants with an older sibling with autism contrasted to typically developing infants. 

Methods: The sample includes 80 males recruited through two longitudinal studies conducted at UNC-Chapel Hill and at the University of South Carolina. Participants included 31 infants with FXS, 25 ASIBs and 24 TD infants. The Visual Reception domain of the Mullen Scales of Early Learning (MSEL) was used as a measure of nonverbal ability, and the Early Gesture score on the MacArthur-Bates Communication Development Inventory (CDI) was used as a measure of gesture use. The MSEL and the CDI were collected at 9, 12 and 24 months of age.  

Results: A growth model was run with time centered at 24 months to determine whether rates of gesture development differed between groups, controlling for nonverbal ability. Analyses indicated that at 24 months, infants with FXS have developed, on average, about 4 less gestures than TD infants (β=-4.29, p=0.00), while ASIB infants have developed about 3 less gestures than TD infants (β=-2.94, p=0.01). All three groups increased in the number of gestures used over time (β=0.46, p=0.00).  The rate of increase did not differ between the TD and FXS groups (β=0.15, p=0.07) or between the TD and ASIB groups (β=-0.12, p=0.12).

Conclusions: FXS and ASIB infants both demonstrate fewer gestures used by 24 months than TD infants. The rates of gesture development in these two high-risk groups do not differ from the rate of gesture development in TD infants. Therefore, while FXS and ASIB infants are delayed, they are still gaining gestures at a similar rate as TD infants in their first two years of life. These findings suggest that targeting gesture use before 24 months for these high-risk groups may improve their chances of demonstrating gesture use consistent with typical development at later time points.