Attainment of the Sit Milestone Is Related to Trajectories of Social Communication in Children with Autism Spectrum Disorder
Objectives: (1) Model longitudinal growth in social communication for children with ASD and TD age-matched peers. (2) Assess the extent to which attainment of the sit milestone impacts within-group trajectories of social communication. (3) Assess the extent to which attainment of the sit milestone relates to future social communication scores.
Methods: 81 age-matched infants (38 ASD; 43 TD) were administered the Communication and Symbolic Behavior Scales (CSBS) at 9 and 12 months of age. A parent caregiver questionnaire (PCQ) was completed by a primary caregiver, and the age at which each infant first sat without support was collected. Trajectories were modeled for social communication scores on the CSBS across the two time points using (a) chronological age and (b) an adjusted age based on age at attainment of sitting (Figure 1). "Early" and "late" sitters were identified relative to group median sit-onset age, and scores were plotted and compared for each group. Within-group analyses were run to test for correlations between sit onset and social communication scores at 9 and 12 months.
Results: Trajectories of CSBS scores adjusted for age-of-sitting show improved goodness-of-fit statistics (r-square, SSE, RMSE, adjusted r-square) compared to unadjusted, chronological-age trajectories (Figure 1). Early sitters exhibit higher CSBS scores at 9 months than late sitters: sit onset is significantly correlated with CSBS total scores and with Symbolic and Speech composites (p’s<.05), and approaches significance for Social composite scores (p=.0503)(Figure 2).
Conclusions: This study reveals a relationship between the attainment of the sit milestone and trajectories of social communication in children with ASD, such that adjusted age based on sit onset better models growth in social communication than chronological age alone. In addition, infants who sit earlier exhibit stronger social communication at 9 months, suggesting that sitting affords these infants experiences that may have positive cascading effects on communication development. These findings highlight the dynamic nature of co-occurring and interrelated domains of development in the first year of life. Knowledge of how early motor milestones relate to emerging communication skills in children with ASD can provide insight into mechanisms that impact the unfolding of the social-developmental disorders, and in turn may aid development of timely and effective interventions to support communicative growth in this vulnerable population.