IQ, Age, and Internalizing Disorders In Autism Spectrum Disorders

Background: Individuals with autism spectrum disorder (ASD) who possess relative strengths in cognitive and language abilities are at risk for internalizing psychiatric disorders (Ghaziuddin, et al, 2002). Studies also suggest that in ASD, the risk of developing anxiety and depression increases with age (Kim, J. et al, 2000; Ghaziuddin et al., 1998). Increased mental faculties and social insight have been theorized to account for this finding. However existing studies have relied on limited sample sizes and restricted age ranges. Given the wide variability of symptom presentation in ASD, information describing risk factors for the co-morbidity of internalizing disorders obtained from a wide age range and large sample of children with ASD is needed. 

Objectives: The purpose of this study is to examine the relationship between clinically relevant internalizing symptoms, cognitive abilities, and age in a large, well-characterized sample of children with ASD. 

Methods: Participants (N= 1657) included children (ages 4-17:11 years) meeting ADI-R and ADOS cutoff criteria for ASD who are participating in the ongoing Simons Simplex Collection Project (SSC; Distribution 8.2; http:SFARI.org). As a measure of internalizing symptoms, the internalizing subscale of Achenbach’s Child Behavioral Check List (CBCL) was utilized. Participants were divided into 2 groups based on CBLC cut-offs for clinically significant symptom levels (T > 61, clinically significant).  Nonverbal and verbal intelligence quotient estimates (assessed with the DAS-2, WISC, WASI, and Mullen) were used as a measure of cognitive abilities and age at testing was recorded. 

Results: The sample consisted of 1433 males and 224 females (M = 8.9 years). Over 50% of the sample (52.3%) met cutoffs for clinically significant internalizing symptoms. Mean Full Scale IQ was estimated at 83.4.  MANOVA results compared individuals with clinically significant internalizing symptoms to those below the clinically significant threshold on cognitive abilities indicated significant main effects in both the verbal and nonverbal domains. Individuals falling in the clinical range for internalizing disorder symptoms on the CBCL had a significantly higher standardized VIQ scores (F(1, 1656) = 38.18, p < .001) and NVIQ scores (F(1,1656) = 15.41, p < .001). 

Conclusions: Results indicate that individuals with ASD who scored in the clinical range for internalizing disorders on the CBCL had a higher IQ across both the verbal and nonverbal domains and were older than individuals who scored in the normal range.  These findings in a large, well-characterized sample lend support to previous work indicating a relationship between IQ, age, and internalizing disorders in ASD. Better developed cognitive abilities may provide an individual with tools that allow for greater insight to social awareness, interest in relationships, and the understanding of repeated negative social experiences and isolation. Given the potential for elevated risk for co-morbidity of internalizing disorders in individuals with ASD with a higher IQ, consideration of cognitive abilities is necessary for treatment planning.