Abstract
Attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) are neurodevelopmental disorders with an early onset. Guidelines recommend a careful evaluation of developmental history when assessing the disorders, but it is unclear how children with ADHD and ASD differ from their peers growing up. In this study, physical, family, psychological, social, and educational information were examined in 3623 ethnically diverse children that were prospectively followed from birth to age 15 as part of the Fragile Families and Child Wellbeing Study. Fifteen-thousand variables were screened, and 506 variables included in the final analyses. Accuracy of the most indicative information to predict ADHD and ASD diagnoses in adolescence was evaluated. Adolescents with ADHD (n = 627) and ASD (n = 91) differed from their peers on a plethora of developmental signs, with signs closely related to the core symptoms of the disorders after age 5 being most indicative of the disorders. Predictive models correctly identified 66% of individuals with ADHD and 81% of those with ASD, but 62-88% of identified cases were false positives. The mean proportion of developmental deviations was 18.7% in the ADHD group, 20.0% in the ASD group, and 15.6% in peers; youth with both ADHD and ASD (n = 50) deviated on 21.8% of all developmental signs and had more pronounced deviations than those with ADHD or ASD alone. ADHD and ASD are characterized by broad and non-specific developmental deviations. Developmental information alone cannot be used to accurately predict diagnostic status in adolescence and false positives are likely if the diagnostic process relies heavily on such information. Developmental deviations are part of normal development and common in children without ADHD and ASD. Etiological heterogeneity and considerable temporal fluctuation in the core characteristics of ADHD and ASD may explain the lack of distinct developmental patterns.