Youth with ADHD, autism or comorbid ADHD and autism in Iceland: Comparisons of attentional and cognitive profiles and the effects of anxiety on cognitive performance.

Attentional and cognitive profiles of youth diagnosed with attention-deficit/hyperactivity disorder (ADHD), autism spectrum disorder (ASD), or co-occurring ADHD and ASD were examined in a large, nationwide clinical sample in Iceland. The impact of anxiety disorders on cognitive performance in this neurodiverse sample was also examined. Clinical medical records at a government-run assessment center serving youth from all of Iceland comprised the study sample of 872 youth aged 7-18 years. All participants had been diagnosed with ADHD, ASD, or ADHD+ASD without intellectual impairment; of these, 239 youth were also diagnosed with co-occurring anxiety. All participants completed the Wechsler´s Intelligence Scale for Children-Fourth Edition (WISC-IV) and the Conners Continuous Performance Test 3rd Edition (CPT-3) as part of their diagnostic process. Results indicated that children with ADHD+ASD performed better on the Perceptual Reasoning Index (PRI) on the WISC-IV compared with children with ADHD but showed no difference compared to the ASD only group. On the CPT, differences emerged for children with ADHD, who showed more variability in their performance compared with children with ASD or ADHD+ASD. Children with neurodevelopmental disorders (ADHD and/or ASD) and a co-occurring anxiety disorder performed worse on the Verbal Comprehension Index (VCI) on the WISC-IV. Still, they performed better on the CPT compared with children with neurodevelopmental disorders without anxiety. The findings reveal patterns of cognitive performance for children with ASD and/or ADHD with co-occurring anxiety disorders that need to be considered for appropriate accommodation in clinical, teaching and testing approaches for neurodiverse children.