Longitudinal Age-Related Impairments in Processing Speed, Anxiety, and Adaptive Functioning from Childhood to Adulthood in Individuals with Autism

Background: Despite special education services and other standard interventions (e.g., speech, language, and social skills therapy) received during childhood, the majority of indivdiuals with autism remain significantly impaired in everyday functioning into adulthood.

Objectives: To compare the trajectories of longitudinal age-related changes from childhood to adulthood in severity of core features of autism, IQ, processing speed, expressive and receptive language, anxiety, and adaptive functioning in individuals with autism compared to typically developing individuals.

Methods: Data were collected from 98 males with autism (age range 4-36 years at first assessment, nonverbal IQ ≥ 70) and 61 typically developing males (age range 4-39 years at assessment). Each participant was assessed 1-3 times, on average every 2.5 years (total of 350 datasets per instrument). At each point, IQ and processing speed (Wechsler Scales), language (EVT, PPVT, CELF-3, CTOPP Non-Word Repetition), quantitative composite of core features of autism (Social Responsiveness Scale), anxiety (SCARED), and everday adaptive functioning (Vineland Adaptive Behavior Scales) were assessed. Mixed effects models were used to describe longitudinal trajectories in the autism group in comparison to the typically developing control group (TDC).

Results: The autism group demonstrated age-related improvements in verbal and performance IQ, as well as expressive and receptive language. Autistic symptoms improved during childhood and adolescence; yet, began to worsen again in the early 20's. In contrast to these longitudinal trajectories showing improvement during childhood and adolescence, adaptive functioning was significantly impaired in the autism group and the degree of impairment remained fixed across development relative to that of the TDC group (age x group interaction, ns). Similarly, processing speed was lower and level of anxiety was higher in the autism group and the degree of severity, relative to the TDC group, remained fixed across development.

Conclusions: The results of this study provide insight as to why everyday functioning remains significantly impaired in the majority of indivdiuals with autism despite overall improvements in autistic symptoms, cognitive functioning, and language. Specifically, findings suggest that both processing speed and anxiety, which are not usually targeted directly by standard interventions in childhood, may contribute to sustained impairment in adaptive functioning from childhood into adulthood in autism. Future study will test these relationships longitudinally at the level of affected individuals.