The impact of attention deficit/hyperactivity disorder on adaptive functioning in children diagnosed late with autism spectrum disorder—A comparative analysis

• We investigated the relationship between ASD, ADHD, and adaptive behavior in a population-based sample of children aged 7–17 years at their first ASD diagnosis.
• In this relatively high functioning group of children, ADHD symptoms were common as 68.1% had the clinical diagnosis of ADHD in addition to ASD.
• When comparing the ASD-only and ASD + ADHD groups while controlling for age, gender, IQ, and autistic symptoms, the only adaptive behavior domain that remained significant was communication. However, this finding was limited to high functioning boys.

This study investigated the relationship between ASD, ADHD and adaptive behavior in children aged 7–17 years at the time of their first ASD diagnosis. Results showed that 68.1% of the participants had a clinical diagnosis of ADHD in addition to ASD. A hypothesis of an additive negative effect of ADHD on adaptive behavior of children with ASD was partly supported. When controlling for age, gender, IQ, and autistic symptoms, communication was the only adaptive behavior domain that remained significant. Further analyses of the data showed that this effect was limited to high functioning boys (IQ ≥ 80). The reasons why ADHD did not impinge on the adaptive behavior of low functioning boys and low and high functioning girls are discussed.