Co-Occurring Psychopathology in Children with Autism Spectrum Disorder of Normal-Range Intelligence

Background: Increasing evidence indicates that children with Autism Spectrum Disorder (ASD) experience high rates of co-occurring psychopathology, particularly Attention-Deficit-Hyperactivity-Disorder (ADHD), Anxiety and Depression (Salazar et al., 2015; Simonoff et al., 2008). Affected children with co-occurring psychopathology have poorer outcomes, including an increased risk of hospitalisation. In some respects, the reported characteristics of ASD comorbidity resemble equivalent conditions when those are found in typically developing children. For instance, there is a greater prevalence of internalising psychopathology in females and externalising psychopathology in males. Former studies of comorbidity that have evaluated risk for psychopathology have focused largely on children with intellectual disability, but >85% of ASD is nowadays diagnosed in those with normal-range IQ.

Objectives: This study aimed to identify patterns of psychiatric comorbidity among newly diagnosed ASD children with normal or high IQ, by means of a standardized parental interview, the Development and Wellbeing Assessment (DAWBA) (Goodman et al., 2011). Psychiatric disorders included Panic Disorder, Agoraphobia, PTSD, Eating Disorder, OCD, Depression, Tic Disorder, Separation Anxiety, Social Phobia, GAD, Specific Phobia and ADHD. Previous methodological limitations have been minimised by using standardized assessment tools that identified indices of severity, in terms of both ASD and comorbid conditions. Because UK national psychiatric comorbidity data have also been collected by the DAWBA (2016-7), comparisons with general population prevalence and patterns of comorbidity in a non-ASD sample were also possible.

Methods: 78 consecutive referrals (N=78; 44 males, 34 females, 5-17 years, Mage=10.45 years, SD=3.5) were recruited from a specialist ASD assessment service. All had normal-high range intelligence (MFSIQ=92, SD=17) and a clinical diagnosis of ASD (DSM-5 criteria) made based on structured parental interview (3di) and Autism Diagnostic Observation Schedule (ADOS) scores. Parent DAWBA data were available in all cases, plus school reports.

Results: Sixty-five percent met criteria for at least one comorbid disorder, including ADHD (39%) and Specific Phobias (22%). Logistic regression revealed ADHD traits were more common in ASD males than females (OR 3.554 [95% CI 1.245-10.143]). There was no gender difference in the prevalence of comorbid Anxiety or Depression (p>0.05). Depressive traits were more prevalent in older children (OR 1.378 [95% CI 1.046-1.815]). Social Phobia was associated with ASD severity (OR 1.471 [95% CI 1.013-1.983]).

Conclusions: Comorbid psychiatric traits are much more common among children with high-functioning ASD than in typically developing populations. Unless structured screening for comorbidity is undertaken as a routine clinical procedure when assessing children with suspected ASD of normal range intelligence, concurrent disorders may be overlooked, and hence untreated.