Empirically Established Typologies of Co-Morbid Disorders in Adolescents with ASD

Background: There is growing recognition that emotional and behavioral problems are common among youth with ASD.  Indeed, some have argued that co-morbidity in this population may be the rule rather than the exception (Gillberg & Billstedt, 2000).  Our knowledge about co- morbidity is hampered, however, by several factors.  First, many studies utilize only one diagnostic instrument to determine co-morbidity; there is variability in findings from different instruments.  Second, many studies do not control for concomitant ID in populations with ASD, thus confounding the actual risks.  Third, many studies do not include a comparison group with neither ID nor ASD. Thus, we need further controlled research examining the clinical presentation and consequences of dual diagnosis among youth with ASD.

Objectives: We will present two related papers. This first will report findings about behavior problems and mental disorders in adolescents with ASD, and compare these to rates from adolescents with typical development or ID.  The second will examine the collateral effects of comorbid mental health disorders on domains of family functioning.

Methods: This research is drawn from the Collaborative Family Study, a three-university longitudinal study of mental disorders in children with or without ID.  We report findings from age 13 assessments, when we added a sample of youth with ASD. The current sample,  N=195, contains youth with typical development (IQ >84) and no ASD (n=100), High Functioning Autism (IQ>85; n=29), and ID with (n=27) or without (n=39) comorbid ASD. The primary measures of behavior problems/mental disorders were the Child Behavior Checklist (questionnaire) and the Diagnostic Interview Schedule for Children (interview).

Results: A consistent find is that for youth without ASD, IQ correlates significantly with every measure of behavior/mental disorders; the lower the IQ, the greater incidence of disorder.  Conversely, for youth with ASD, the IQ level does not correlate significantly with any measure of behavior/mental disorders.  Youth with ASD tend to be higher in the incidence of co-morbid disorders, regardless of intellectual functioning.  We found similar heightened problems for youth with ASD (vs. no ASD) on CBCL externalizing and internalizing scales, and clinical scales assessing ADHD, ODD, Affective disorders, and Anxiety disorders. Again we found similar findings on the DISC domains of ADHD (inattentive and hyperactive types) and ODD.  In most cases, there was also a significant effect of intellectual disability (vs. no ID) and in some cases an interaction. 

Conclusions: It appears that, in terms of percentages reaching a diagnostic cut-off, youth with ASD and/or ID are about three times as likely to meet criteria for a disruptive behavior disorder as youth without either diagnosis.  We have considered elsewhere whether a disorder (e.g. ADHD) in youth with ID is simply a reflection of ID characteristics, or represents a separate disorder (similar to ADHD in typically developing youth) that is over and above the ID (Baker et al., 2010; Neece et al., 2012).  We will address this same diagnostic question in reference to disorders in youth with ASD.