Developmental origins of ADHD: sex-specific influences of early life unpredictability on symptom profiles.

Exposure to early life adversity (ELA) increases risk of poor mental health outcomes, including attention deficit/hyperactivity disorder (ADHD). In fact, ELA, especially in the form of "household ACEs" (e.g., socioeconomic disadvantage, incarceration of a caregiver), is among the most robust environmental predictors of a later ADHD diagnosis. Exposure to unpredictability is an understudied form of ELA that captures instability or inconsistency in routines, household experiences, and family relationships. The purpose of this study was to examine associations between unpredictability and ADHD symptoms in children and adolescents. Participants were drawn from two independent cohorts (Cohort 1: N = 99, Mage = 7.31 years [SD = 0.31]; Cohort 2: N = 217, Mage = 14.39 years [SD = 1.32]) participating in ongoing longitudinal studies of exposure to ELA. Unpredictability was measured by the Questionnaire of Unpredictability in Childhood, and ADHD symptoms were measured by the Child Behavior Checklist Attention Deficit/Hyperactivity Problems subscale, the Behavior Rating Inventory of Executive Function, and the Kiddie Schedules for Affective Disorders and Schizophrenia ADHD Screener. Childhood experiences of unpredictability were associated with ADHD symptoms in both cohorts and during childhood and adolescence. Further, associations were stronger in females than males. These findings show that unpredictability is a risk factor for ADHD which suggests that it should be explored as an early target for intervention to reduce the development of ADHD symptoms.