Sex and ASD Risk Status Predict Both 3-Year Expressive Language and Expressive Language Growth from 1 to 3 Years in Children at High and Low Risk for ASD

Background: Sex differences have been found in both language development and ASD severity; relative to males, typically developing females show slightly better expressive language from 12-24 months (Eriksson et al., 2012), and females with ASD may show more severe ASD symptoms (Frazier et al., 2014).  The purpose of this study was to examine early expressive language development in males and females at high and low risk for an ASD diagnosis.  The potential importance of this question is twofold: (1) to characterize the developmental trajectories of expressive language of toddlers who have an older sibling with ASD (high-risk, HR-sibs) and toddlers without a sibling with ASD (low-risk, LR-sibs); and (2) to understand the extent to which a child’s sex, in addition to risk status, contributes to language development.  Results may have implications for developmental monitoring as well as understanding genetic underpinnings of ASD.  

Objectives: To examine the effect of sex and risk status for ASD on children’s expressive language (EL) development from 12-36 months and EL outcome at 36 months.

Methods: Expressive language was measured for HR-sibs (n=69; male=36) and LR-sibs (n=42; male=23) at 12, 24, and 36 months as age equivalency scores (in months) using the expressive language (EL) subscale from the Mullen Scales of Early Learning (MSEL; Mullen, 1995). Hierarchical linear modeling was used to examine both growth from 12 to 36 months in EL and 36-month level of EL

Results: The overall trajectory of EL from 12 to 36 months was best characterized by significant positive, linear growth, p<.01. EL at 12 months showed little variability across individuals; therefore, the intercept was set at 36 months. EL growth and 36-month EL level were both modeled as random effects. Sex significantly predicted EL growth and 36-month EL, with males showing decreased growth and lower EL compared to females at 36 months.  Males gained 0.85 years of EL growth for every year that females gained, b=-.15, p=.01, and at 36 months, their EL was almost 4 months lower, b=-3.61, p<.01. Risk status also significantly predicted EL growth and 36-month EL level, with HR-sibs showing decreased growth and lower EL compared to LR-sibs at 36 months. HR-sibs gained 0.85 years of EL growth for every year that LR-sibs gained, b=.15, p=.02, and at 36 months had an age equivalent EL almost 5 months lower than that of LR children, (b=4.75, p<.01). Sex and risk status did not interact to predict growth in language between 12 and 36 months or level of EL at 36 months. 

Conclusions: Although sex and risk status independently affect children’s expressive language, no interaction was found.  Males and HR-sibs each showed slower EL growth and lower EL at 36 months relative to their counterparts. The lack of an interaction suggests that HR-sibs males are not at multiplicative risk for slower language growth and deficits by 3 years.