Neurodevelopmental variations cascading from age 10 months to 3 years leading to attention‐deficit hyperactivity disorder/autism traits at age 9 in a general population

Abstract Background Neurodevelopmental delay precedes attention‐deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) diagnoses. However, exactly when this emerges in association with these outcomes remains unclear. We investigated (1) the earliest representations of neurodevelopmental variation and (2) what neurodevelopmental variations at an early age (10 months to 3 years) are specifically associated with the emergence of parentally reported behavioral traits of ADHD, ASD, and related disorders at age 9. Methods Children from the Hamamatsu Birth Cohort of Mothers and Children (HBC Study) born between December 2007 and March 2012 were enrolled and followed from birth to age 9. Standardized scores of neurodevelopment across five domains (gross motor, visual reception, fine motor, receptive language, and expressive language) were calculated using the Mullen Scales of Early Learning at ages 10, 14, 18, 24, 32, and 40 months. ADHD and ASD traits were ascertained as Z ‐scores using the ADHD‐Rating Scale and Social Responsiveness Scale‐2 at age 9. To explore the earliest recognition of neurodevelopmental variation with credibility, structural equation modeling (SEM) was used to estimate the total effects of the linear associations between exposures and outcomes. Results 836 children (405 females, 48%) were enrolled in the analysis. The ADHD trait was associated with visual reception score before age 1 and was concurrent with both fine motor and receptive language scores between ages 1–2. The ASD trait was associated with gross motor score before age 1 and expressive language score between ages 1.5 and 3. Conclusion Suboptimal visual‐motor coordination can be a prototype of the ADHD trait, while a cascading pattern of suboptimalities from gross motor to language domains can be a prototype of the ASD trait. The distinct neurodevelopmental variations related to ADHD and ASD traits running in the general population can be found before age 1.