Social Impairments Emerge in Infancy and Persist into Childhood in Fragile X Syndrome

Background: Fragile X syndrome (FXS) is the leading genetic cause of autism spectrum disorder (ASD) symptoms, with approximately 60% of individuals with FXS meeting diagnostic criteria for ASD (Lee, Martin, Berry-Kravis, & Losh, 2016). Social-communicative impairments in FXS are characterized in part by reduced and/or atypical social approach behaviors when interacting with unfamiliar adults. However, no studies to date have examined social approach behaviors longitudinally in young children with FXS, so the emergence and trajectories of atypical social approach in FXS are unknown.

Objectives: This study aimed to characterize the trajectory of social approach behaviors across infancy and early childhood in FXS and typical development (TD).

Methods:

The Social Approach Scale (SAS; Roberts et al., 2007) was used to longitudinally measure approach behaviors in children ranging from 4 to 72 months of age (FXS n = 66; TD n = 59). In total, 290 observations were included (FXS n = 153; TD n = 137). Physical Movement, Facial Expression, and Eye Contact were rated in the first minute (Rating 1 = R1) and last hour (Rating 2 = R2) of social interaction during a research assessment. Hierarchical generalized linear models (HGLMs) were employed to examine R1 and R2 scores on all three scales, with chronological age nested within participants. To assess whether children with FXS were more likely to “warm up” to examiners over the course of an assessment, the proportion of participants in each group that was rated better at R2 than R1 was compared using Chi-square analyses.

Results:

For Physical Movement, Facial Expression, and Eye Contact, the FXS group was less likely to exhibit normal approach behaviors at both R1 and R2 (bs > ± 1.49, ps < .05) with both the FXS and TD groups demonstrating reduced social approach with age at R1 (bs > ± .02, ps < .05) but not R2 (bs < ± .01, ps > .10) (Figure 1). Age by group interactions were non-significant (bs < ± .02, ps > .25). Similar proportions of participants in both groups exhibited improved Physical Movement (Χ²(1) = 0.17, p = .68) over the course of the assessment, but that the FXS group had a larger proportion of participants exhibit a “warm-up” effect on Facial Expression (Χ²(1) = 5.22, p < .05), and Eye Contact (Χ²(1) = 14.47, p < .001).

Conclusions: As young children with FXS and TD children age, they are less likely to exhibit normal approach behaviors upon initial introduction to a stranger, with atypical approach behaviors more likely in the FXS group. Interestingly, age did not impact ratings at the end of the assessment, suggesting that approach behaviors once the child is familiar with an adult do not change with age. The lack of an age by group interaction suggests that atypical social approach is evident at infancy and persists across early childhood in those with FXS. Children with FXS were more likely to exhibit a “warm-up” effect for Facial Expression and Eye Contact over the course of the assessment.