Early Expressive and Receptive Language Trajectories in High-Risk Infant Siblings of Children with Autism Spectrum Disorder (ASD)

Background: Prospective studies have examined early expressive and receptive language development of high-risk infant siblings of children with ASD who later received a diagnosis of ASD (“ASD sibs”), relative to high-risk siblings who did not receive an ASD diagnosis (“non-ASD sibs”), and low-risk typically developing controls with no family history of ASD (“controls”). Cross-sectional analyses reveal impaired expressive and receptive language in ASD sibs by 14 months of age (e.g., Landa & Garrett-Mayer, 2006). However, evidence suggests that trajectory analyses may be more informative for risk than cross-sectional comparisons (e.g., Landa et al., 2013). Therefore, the current study sought to extend previous research by examining separate expressive and receptive language trajectories in a combined sample of ASD sibs, non-ASD sibs, and controls.

Objectives: The purpose of the current study was to examine early expressive and receptive language trajectories in high-risk sibs and low-risk controls relative to their 3-year diagnostic outcomes.

Methods: Data were derived from a Canadian multi-site prospective study of high-risk infant siblings of children with ASD. Participants were 523 children (371 high-risk sibs, 56% male; 152 low-risk controls, 52% male) followed from 6 or 12 months of age to 36 months of age. Based on independent, best-estimate clinical diagnoses at 36 months of age, participants were classified as ASD sibs (n = 94; 69% male), non-ASD sibs (n = 277; 52% male), or controls (n = 152; 52% male). Expressive and receptive language trajectories were examined based on corresponding standard scores on the Mullen Scales of Early Learning (MSEL) at 6, 12, 24, and 36 months. In the combined sample of high-risk and low-risk infants, semi-parametric group-based modeling was used to identify distinct trajectories that provided optimal fit to variation in MSEL standard scores over time. 

Results: A 3-group solution provided optimal fit to the variation in both expressive and receptive language. The three trajectories within each language domain were characterized by the following patterns of scores: (1) inclining from average to above average, (2) stable-average, and (3) declining from average to below average. Trajectory membership was examined relative to 3-year diagnostic outcomes using Chi-square analyses (p’s < .001). For expressive language, ASD sibs were most likely to be members of trajectory group 2 (56.4%) or 3 (33.0%), with the remainder (10.6%) in group 1; non-ASD sibs were most likely to be in group 2 (53.8%) or 1 (39.0%), and controls were most likely to be in group 1 (69.1%) or 2 (28.3%). Similarly, for receptive language, ASD sibs were mostly members of trajectory group 2 (45.7%) or 3 (43.6%); non-ASD sibs were most likely in group 2 (53.4%) or 1 (40.4%), and controls were most likely in group 1 (68.4%) or 2 (45.5%).

Conclusions: Membership in the inclining, stable-average, or declining trajectories in both expressive and receptive language was related to 3-year diagnostic outcomes. Although ASD sibs, non-ASD sibs, and controls were in each trajectory group, membership in a declining trajectory (either expressive or receptive) was associated with a diagnosis of ASD.