Predictors of Co-Morbid Psychopathology in High-Functioning Children and Adolescents with Autism Spectrum Disorders

Background: Symptoms of internalizing (e.g., anxiety, and depression) and externalizing (e.g., Oppositional Defiant Disorder [ODD], Conduct Disorder [CD]) disorders are commonly seen in children and adolescents with Autism Spectrum Disorders (ASD) (Gadow et al., 2008; Simonoff et al., 2012; Weisbrot et al., 2005).  However, predictors of these co-occurring conditions have received limited attention.  In the broader literature, high levels of callous-unemotional (C-U) traits are consistently related to conduct problems (Essau et al., 2006).  Moreover, strong associations between ADHD and internalizing and externalizing disorders are also documented (Barkley et al., 1990; Hartung et al., 2002; Pardini & Fite, 2010).  Given these high rates of co-morbidity, identifying unique predictors of common co-occurring psychiatric symptoms in youth with ASD becomes a vital question.    

Objectives: The purpose of the current study is to assess how well ADHD symptomatology and C-U traits concurrently and uniquely predict internalizing and externalizing symptoms within a well-characterized sample of youth with high functioning ASD.  We hypothesize that ADHD symptoms will significantly predict internalizing symptoms (for generalized anxiety disorder [GAD] and dysthymia) and that C-U traits will significantly predict externalizing symptoms (for ODD and CD) in youth with ASD.   

Methods: Ninety-five children, adolescents, and young adults with high functioning ASD (FSIQ: M=109.06, SD=17.77) ages 6-28 years (M=13.36, SD=4.63) participated in the study.  ADHD, internalizing, and externalizing symptomatology were assessed via parent report using the Child and Adolescent Symptom Inventory-4R (CASI) or the Adult Inventory-4 (AI).  C-U trait ratings were also provided by parents using the Inventory of Callous-Unemotional (ICU) traits.  Hierarchical linear regression analyses were run to examine how well age, full-scale IQ, C-U trait ratings, and ADHD ratings sequentially predicted GAD, dysthymia, CD, and ODD symptoms.   

Results:  Regression analyses revealed that ADHD symptoms were a significant predictor of GAD symptoms, explaining 26% of the variance (p<.001).  Age also predicted GAD symptoms, though it explained only 1% of the variance (p<.01).  Age and ADHD significantly predicted dysthymia symptoms; age explained 21% of the variance and ADHD explained an additional 8% of the variance (ps<.001).  As expected, C-U traits significantly and uniquely predicted CD symptoms, explaining 21% of the variance (p<.001).  Both C-U traits and ADHD significantly predicted ODD symptoms; C-U traits explained 15% of the variance, and ADHD explained an additional 11% of the variance (ps<.01).  Full-scale IQ was not a significant predictor of internalizing or externalizing symptoms.

Conclusions: The present study showed that ADHD significantly predicted GAD, dysthymia, and ODD symptoms whereas C-U traits significantly predicted CD and ODD symptoms in youth with ASD.  Age was also a significant positive predictor of primarily dysthymia symptoms.  Collectively, the results indicate that the degree of ADHD symptoms and C-U traits in ASD impacts the severity of internalizing and externalizing symptoms, respectively.  These findings highlight the importance of assessing comorbid psychopathology in children with ASD to identify potential risk factors and to develop more effective treatment plans.