As the number of children diagnosed with Autism Spectrum Disorder (ASD) rises, there will be an increasingly large adult population. Although families often ask about long-term outcome, few studies have followed individuals diagnosed in childhood into adulthood. Previous studies have used a cross sectional approach or only followed individuals into early adulthood. For example, using a cross sectional design, Mayes and Calhoun (2003) found that IQ increased until around 8 years and then plateaued. Using a longitudinal design, Smith et al (2012) found that adaptive behavior improved during adolescence but then plateaued in early adulthood. More longitudinal research is needed to examine whether these skills truly plateau during development.
The database for the TEACCH Autism Program was created in 1965 and includes a large sample (N=400) of individuals with ASD who were evaluated multiple times across development. The purpose of this study is to examine the longitudinal course of adaptive behavior and IQ for individuals diagnosed with ASD between 1965 and 2000.
Participants were assessed longitudinally at 3 or more times throughout childhood extending into adulthood (assessments conducted on individuals ranging in age from 1 – 36 years). All participants had scores from the Children Autism Rating Scale (CARS), age appropriate IQ, and Vineland Adaptive Behavior Scales. IQ scores averaged 56.31 (range 20-122). Hierarchical linear mixed model analyses were conducted on mental ages derived from IQ (n=156) and adaptive behavior (n=168) measures. Data entry is ongoing with additional participants.
Hierarchical linear mixed model analyses used chronological age to predict mental age derived from IQ and adaptive behavior measures. Both the linear and quadratic components of age were examined. For intellectual mental age, the linear component of chronological age significantly predicted mental age. The slope of the chronological age effect was approximately .40 (p<.001) indicating that for every year of chronological age, participants increased approximately 5 months in mental age. For adaptive behavior age equivalent, both the linear and quadratic effects of chronological age were significant (p<.001). Across young ages (2 to 9 years), adaptive behavior age increased at a similar rate to intellectual mental age (approximately 5 months improvement for every year of chronological age). From age 9 to 18 years the slope becomes shallow with approximately 3 months gain in adaptive functioning for every year of age. After age 18 years the slope becomes flat (no gain in functioning with age) to a slightly negative slope that may indicate a loss in adaptive functioning age.
Findings suggest that both intellectual ability and adaptive behavior increased during early childhood commensurate with predictions based on IQ. However, during adolescence adaptive behavior appears to slow and then plateaus or declines at entry into adulthood. These results have important implications for long-term outcome (employment and independent living skills) that rely on adaptive behavior skills.
See more of: Clinical Phenotype
See more of: Symptoms, Diagnosis & Phenotype