Clinical characteristics of children with ASD and comorbid ADHD: Association with social impairment and externalizing and internalizing behaviours

Background: Autism spectrum disorder (ASD) and attention-deficit hyperactivity disorder (ADHD) are frequently occurring conditions that are often associated (ASD + ADHD). However, there are few comparative studies concerning the clinical presentation in patients formally diagnosed with both ASD and ADHD. Here, we aimed to 1) compare social impairment and externalizing/ internalizing behavioural problems across four groups of children: ASD + ADHD, ASD alone, ADHD alone, and typical development and 2) examine their bidirectional relationship with ASD and/or ADHD symptoms. Methods: This study included 186 participants from 6 to 12 years of age: single ASD (n = 98), ASD + ADHD (n = 29), single ADHD (n = 28), and TD (n = 31). Results: The results showed that children in the ASD + ADHD and single ASD groups had a higher level of social impairment than those in the single ADHD group. In addition, children in the single ADHD group presented a greater attention deficit than those in the single ASD group. Externalizing /internalizing behaviours were more frequent in all groups with neuro-developmental disorders than in typical development. In addition, externalizing behavioural problems were related to ADHD severity in the ASD + ADHD and single ADHD groups, whereas internalizing behaviours were related to ASD severity. Conclusions: These findings highlight the specific needs of children who have both ASD and ADHD and underscore the necessity of individualizing their interventions.