Symptoms of Psychiatric Comorbidity in Children and Adolescents with Autism Spectrum Disorders: An Examination of the Child Behavior Checklist from the Simons Simplex Collection Database

Background:   Children and adolescents with autism spectrum disorder (ASD) frequently exhibit comorbid psychiatric symptoms, and according to a recent population-derived study of 112 children with ASD, 70% meet diagnostic criteria for at least one comorbid disorder, and 41% meet criteria for two or more disorders, such as social anxiety disorder, ADHD, and oppositional defiant disorder (Simonoff et al., 2008).  The individual factors which may be associated with an increased risk of comorbid disorders in ASD have not yet been identified. 

Objectives:   In this study, we will characterize the psychiatric and behavioral profiles of a large sample of children with ASD who participated in the Simons Simplex Collection (SSC), a North American multiple-site, university-based research study that includes 420 families with only one child with an ASD.  We will also examine how age, verbal ability, and autism severity are related to severity of comorbid symptoms, as evaluated by the Child Behavior Checklist (CBCL), a parent report measure.    

Methods:   We will examine data from approximately 420 SSC probands who meet criteria for a research diagnosis of an ASD (Risi et al., 2006), based on the Autism Diagnostic Interview-Revised (ADI-R), the Autism Diagnostic Observation Schedule (ADOS), and clinical consensus.  We will identify the percentage of probands who exhibit elevated internalizing and externalizing symptom scores and elevated DSM-IV-related symptom scores, and will examine how individual factors (e.g., age, verbal ability, and autism severity) are associated with the level of comorbid symptom presentation.  Verbal mental age obtained from the Mullen Scales of Early Learning or the Differential Ability Scales (DAS-II), an ADOS-derived autism severity index (Gotham et al., in press), and the ADI-R domain scores will be used in the analyses.    

Results: Preliminary data analysis of 85 probands (Mean Age = 118.86 months, SD = 34.51) indicates that 30.6% and 20.0% of the probands have elevated CBCL Internalizing and Externalizing behavior scores.  The CBCL-DSM-IV-related subscales are also elevated in a subset of probands: Affective problems, 28.2%; Anxiety problems, 35.3; Somatic problems, 8.2%; ADHD problems, 26.2%; Oppositional Defiant problems, 27.1%; and Conduct problems, 15.3%.  Correlation analysis shows that higher verbal mental age is associated with higher Internalizing and Externalizing problems (r = .48, p < .001, and r = .32, p <.05, respectively) and with higher DSM-IV-related subscale scores (except for the ADHD problems score).  Correlation analysis also reveals that chronological age and autism severity is generally not associated with comorbid symptom scores.

Conclusions: In this study, up to 30% of children and adolescents with ASD exhibit clinically significant comorbid psychiatric symptoms, as evaluated by the CBCL.  An examination of individual factors shows that increased severity of comorbid symptoms is associated with higher levels of verbal ability, but that severity of comorbid symptoms is not associated with age and autism severity.  Our results provide some evidence that comorbid symptoms may reflect the presence of distinct psychiatric disorders, unrelated to the presence of an ASD; however, future studies are needed to examine the onset and the developmental trajectory of comorbid symptom presentation in children with ASD.