Children with autism spectrum disorder comorbid with attention-deficit/hyperactivity disorder examined by the Wisconsin card sorting test: Analysis by age-related differences.

The DSM-5 confirmed that autism spectrum disorder (ASD) might be comorbid with attention-deficit/hyperactivity disorder (ADHD). This study investigated the executive function of ASD comorbid with ADHD (ASD + ADHD), ASD, and typically developed (TD) children using the Keio version of the modified Wisconsin card sorting test (KWCST). Children with ASD + ADHD (n = 43), ASD (n = 69), and TD (n = 69) were examined in two age groups: 5-9 years and 10-15 years. Both of the younger clinical groups showed significantly unfavorable scores for many indices in the second step compared to the TD group. As for the older groups, the ASD children showed significantly unfavorable scores in total errors in the second step, while the ASD + ADHD children did not show significant differences in either step. However, some index scores of the two older clinical groups were comparable to the older TD group in the second step. For the cognitive differences between clinical groups, the younger ASD + ADHD showed unfavorable scores in numbers of response cards until the first category achieved in the second step, while the older ASD showed unfavorable scores in categories achieved and perseverative errors of Nelson in the first step. For the degree of improvements in the second step, the older groups did not show significant group differences, while the younger ASD group showed significantly fewer improvements compared to the TD group. Based on these results, it is presumed that younger ASD + ADHD individuals are not sufficiently able to sustain attention and/or memory, and that the older ASD patients have difficulty in terms of flexibility.