Identification of Early Temperament Profiles in Infants at Elevated Likelihood for Autism and Attention-Deficit/Hyperactivity Disorder.

Autism and attention-deficit/hyperactivity disorder (ADHD) likely share some common developmental pathways, suggesting the potential for overlapping early risk factors, including aspects of temperament. We employed a transdiagnostic, data-driven approach to identifying temperament-based subgroups at 12 and 18 months across infants at elevated and low genetic likelihood for autism and ADHD. Results revealed general continuity in early temperament, with many infants remaining in well-regulated/socially engaged subgroup (73%), while some (27%) showed shifts over time toward heightened negative reactivity, greater inhibition, and/or reduced social engagement during the toddler period. Importantly, not all infants/toddlers who later met criteria for autism or showed preschool concerns for ADHD demonstrated negative-reactive/inhibitory temperament traits during early development. However, certain temperament profiles were associated with autism and ADHD traits regardless of clinical outcome. Findings contribute to a better understanding of early transdiagnostic markers, and the nuanced developmental pathways related to autism and ADHD.