Assessing cognition in autistic youth with and without attention‐deficit/hyperactivity disorder using the NIH Toolbox Cognition Battery: An Environmental influences on Child Health Outcomes‐Wide Cohort Study

Background Prior work has suggested poorer performance on Fluid, but not Crystallized, NIH Toolbox Cognition Battery (NTCB) subtests in autistic youth relative to neurotypical individuals. This study sought to extend previous findings using a larger sample from a nationwide multi‐cohort study and to examine the effect of attention‐deficit/hyperactivity disorder (ADHD) status on cognitive functioning. Methods We used NTCB data from 1035 children ages 12–18 in five cohorts drawn from the Environmental influences on Child Health Outcomes (ECHO) Program. Participants with autism only (AUT; n = 81), ADHD only ( n = 162), co‐occurring autism and ADHD (AUT + ADHD; n = 55), and a comparison group with neither autism nor ADHD (noAUTADHD; n = 737) were included in the analyses. We used a general linear model framework to examine group differences in task performance, and we used latent profile analysis (LPA) to identify subgroups of individuals with similar cognitive profiles. Results The AUT and AUT + ADHD groups had lower NTCB Fluid Cognition Index Scores compared to the noAUTADHD group, whereas no group differences in the Crystallized Cognition Index Score were observed. No significant differences in the NTCB subtest or index scores were found between the AUT and AUT + ADHD groups. Sex‐stratified analyses revealed no sex differences. LPA identified four distinct NTCB groups, with a substantial proportion of the AUT group (19%) assigned to the class with higher Crystallized versus Fluid Cognition Index Scores; however, there was considerable overlap between the diagnostic groups within the LPA classes. Conclusions Autistic individuals experience difficulties with fluid NTCB tasks and those with co‐occurring ADHD do not appear to face greater difficulties than those with autism alone. However, there was a notable proportion of autistic individuals with average or superior cognitive performance, highlighting the importance of strength‐based and transdiagnostic research approaches.