The Stability of Atypical Developmental Outcomes in Young Children at Risk for Developing ASD

Background:  Prospective studies of infants at risk for developing Autism Spectrum Disorder (HR-sibs) estimate that 18.7% of siblings develop ASD themselves (Ozonoff et al., 2011). Another approximately 19- 28% of siblings evidence other developmental atypicalities (Georgiades et al., 2013; Ozonoff et al., 2014). While the diagnosis of ASD made prior to age 3 is relatively stable in HR-sib cohorts (Ozonoff et al., 2015), the diagnostic stability and clinical presentation of the “atypical” group is less clear. 

Objectives:  To examine the stability of atypical developmental outcomes between 24 and 36 months in a high-risk sample.   

Methods:  Seventy-nine HR-sibs (68.5% males) were comprehensively assessed at the ages of 24 and 36 months utilizing the Mullen Scales of Early Learning, Vineland Adaptive Behavior Scales, and Autism Diagnostic Observation Schedule. For the Mullen and Vineland higher standard score indicates higher functioning, while a higher score on the ADOS indicates poorer functioning. Each participant was assigned a Clinician Best Estimate (CBE) diagnosis at each time point. The following CBEs were utilized: ASD (Autistic Disorder or PDD-NOS), non-TD (Broader Autism Phenotype (BAP): sub-threshold ASD-related symptoms that supersede other developmental delays, and Developmental Delays: language, cognitive, and/or behavioral problems), and TD (no clinical diagnosis or mild symptom presentation that did not warrant a diagnosis). Stability of diagnostic presentation and clinical features were subsequently evaluated in the non-TD group. Pearson correlations were conducted to examine the relationship between developmental skills, adaptive communication and socialization, and autism severity between 24 and 36 months.  

Results: Of the 79 HR-sibs, 27 (34%) were identified as having BAP or other developmental issues (non-TD) at 24 months. At the age of 36 months, 19 (70.4%) maintained a non-TD classification, 5 (18.5%) were considered TD, and 3 (11.1%) met criteria for ASD. Verbal DQ (r(23)=.643, p<.01), Vineland Communication (r(22)=.757, p<.001), and Vineland Socialization (r(22)=.504, p<.05) were significantly correlated between 24 and 36 months, while Nonverbal DQ and ADOS severity were not (ps>.1). 

Conclusions:  Out of the 34% of HR-sibs identified as non-TD at 24 months, the majority (70.4%) continues to demonstrate difficulties consistent with non-TD presentations at 36 months. Approximately 20% of them appear to catch up to their TD peers, but in approximately 10%, symptoms worsen and are consistent with ASD. While verbal abilities and adaptive communication and socialization were significantly correlated across time points for the non-TD group, nonverbal abilities and autism symptom severity were not. Diagnostic stability and clinical presentation can be variable for many HR-sibs, particularly those demonstrating atypical developmental patterns early in life. The results of this study highlight the need for continued monitoring and later follow-up of HR-sibs to confirm later (and potentially more stable) diagnostic outcomes.