LAUSR

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.