Cognitive Ability Is Associated with Different Outcome Trajectories in Autism Spectrum Disorders

Background:

Children with autism spectrum disorder (ASD) comprise a highly heterogeneous group with great variability in clinical expressions and in intervention outcome.  Some achieve marked progress in development, while others achieve only modest or no significant gains. One of the most reported predictors of outcome in ASD that can explain this variability in outcome is the baseline cognitive ability. Most of the follow-up studies in ASD looked at outcome at a single time point after 1-2 years of intervention and only a few compared developmental gains after the first versus the second year of treatment.

Objectives:  

1. To compared outcomes in autism symptoms severity and adaptive skills after the first versus the second year of early intensive behavioral intervention (EIBI). 2. To further look at the impact of the cognitive ability at baseline on outcome trajectories in these domains in these two time periods.

Methods:  

The study included 46 participants, 39 boys and 7 girls, (mean age=25.5m, SD=3.95, age range 17 to 33 months) diagnosed with ASD. All participants completed three assessments, at diagnosis (T1), after one year (T2) and two years (T3) of center-based EIBI. The entire group was divided according to the median of the DQ composite scores (70 points) into a higher cognitive (HC≥70) group and a lower cognitive (LC<70) group. Outcome was assessed in autism symptoms severity using the Autism Diagnostic Observation Scales (ADOS) severity scales and in adaptive skills using the Vineland Adaptive Behavior Scales (VABS).  

Results:

The entire group showed a significant decrease in autism severity scale scores from T1 to T3.  Significant improvement in the social-affect domain was noted during the first intervention year, whereas the restricted repetitive behaviors severity scores declined gradually during the entire period. No significant Time X Group interaction was found, meaning that the two cognitive groups did not significantly differ in their intervention outcome trajectories in those measures.  Regarding adaptive skills, a different trajectory for the two cognitive groups was noted (Time X Group interaction, p <.05). Only the HC group showed significant increase in the communication (p<.001), but only in the first year (p<.01)], in daily living skills (p=.003), and in socialization (p=.002) but only in the second year. A decline in motor skills domain was significant for both groups in the first year (p<.001).  The LC group maintained but did not increase their adaptive skills standard scores level over time. 

Conclusions:

The two cognitive groups acquired more typical social-communication skills and showed decrease in the stereotypic behaviors.  However, having a higher baseline cognitive level seemed to enable the incorporation of the new acquired socio-communication skills better in daily life. Having lower cognitive ability at baseline was still associated with acquisition of new adaptive skills with time, but prevented the marked progress seen in children with higher cognition. As some of the examined skills were improved only after the second year of intervention, it may accentuate the importance of continuing intensive intervention in ASD. Future long-term studies should highlight other potential moderators of outcomes.