Ages of Language Milestones As Predictors of Developmental Trajectories in Young Children with ASD

Background:  Recognizing early risk-markers and prognostic indicators in young children with autism spectrum disorder (ASD) is critical for timely diagnosis and intervention (Luyster, Seery, Talbott, & Tager-Flusberg, 2011).  Recent studies have identified language milestones, most notably age of first words (Mayo, Chlebowski, Fein, & Eigsti, 2013) and age of first phrases (Kenworthy et al., 2012), to be good predictors of later developmental outcomes.  However, previous research has been limited by examination of only a single language milestone, exclusion of children considered to be low functioning or those with a history of regression, and risk of telescoping in parent report for older children (Hus, Taylor, & Lord, 2011).     

Objectives:  The purpose of the current study was to extend previous findings to a longitudinal design, in which ages of language milestones could serve as predictors of developmental trajectories in a heterogeneous sample of young children with ASD.  We hypothesized that age of first word production and, for children for whom these milestones were applicable, age of first phrases and age of regaining babbling after loss would predict level and rate of change for language, nonverbal cognition, and adaptive skills. 

Methods:  Participants (N=98; age in months at first assessment: M=31.63, SD=4.51) were drawn from a larger longitudinal study on early development in ASD with up to four annual assessments.  Age of language milestones was determined by parent report at the initial assessment using the Toddler Research Autism Diagnostic Interview-Revised (LeCouteur, Rutter, Lord, & DiLavore, 2006).  Hierarchical linear models were estimated separately for each of four outcome variables, indexing receptive language, expressive language, nonverbal cognition, and adaptive behavior: auditory comprehension and expressive communication standard scores on the Preschool Language Scales-4, Visual Reception T-scores on the Mullen Scales of Early Learning, and adaptive behavior composite standard scores on the Vineland Adaptive Behavior Scales-II. 

Results:  Age of first words positively predicted rate of change for adaptive behavior, t(96)=2.04, p=.045.  For the 30 participants with phrases, age of first words negatively predicted level of expressive language, controlling for age of first phrases, t(27)=-2.19, p=.037.  Age of first phrases was not a significant predictor for any outcome.  For the 26 participants who had lost and regained babbling, age of regaining babbling negatively predicted level of receptive language, t(23)=-2.42, p=.024, expressive language, t(23)=-2.93, p=.008, and nonverbal cognition, t(21)=-2.10, p=.048, controlling for age of first words.  Age of first words was not a significant predictor for any outcome for this subgroup, controlling for age of regaining babbling. 

Conclusions:  Age of first words predicted trajectories of expressive language and adaptive skills, but not receptive language or nonverbal cognition.  Young children with earlier first words had higher levels of expressive language; those with later first words made faster gains in adaptive skills.  Prognostic indicators other than first words, such as age of regaining babbling, may be important for children who have experienced babbling regression.  Ages of some language milestones relate to developmental trajectories and may help define when immediate intervention is justified, with implications for service delivery (Paul & Ellis Weismer, 2013).