Age at Diagnosis and Clinical and Genetic Profiles Among Adults With Attention-Deficit/Hyperactivity Disorder

Importance Adult attention-deficit/hyperactivity disorder (ADHD) diagnoses are rising, yet distinctions between those diagnosed in childhood or adolescence vs adulthood remain underexplored. Objectives To characterize differences in demographic, clinical, and genetic profiles between adults with ADHD diagnosed in childhood or adolescence (youth-diagnosed) vs adulthood (adult-diagnosed), and to compare the profile of each group with that from matched individuals without ADHD. Design, Setting, and Participants This cross-sectional, multicenter study used data collected in the All of Us Research Program, a nationwide US cohort integrating clinical and genetic data, from June 2017 to September 2023. Analyses were performed between July and December 2025. Participants were adults who self-reported an ADHD diagnosis, dichotomized by age at first diagnosis into youth-diagnosed (0-17 years) and adult-diagnosed (≥18 years) ADHD groups. Each ADHD group was independently matched 1:2 via propensity scores to controls without ADHD on age, sex, race and ethnicity, educational attainment, and income. Main Outcomes and Measures The primary outcomes were self-reported psychiatric or somatic co-occurring conditions, measures of functional impairment (general health and daily functioning), and ADHD polygenic risk scores. Results Of 13 527 adults with ADHD, 3853 (28.5%; mean [SD] age, 34.8 [11.5] years; 71.5% female) were youth-diagnosed and 9674 (71.5%; mean [SD] age, 43.8 [14.3] years; 75.3% female) adult-diagnosed. Adult-diagnosed individuals were older and had higher educational attainment (eg, 548 [14.2%] vs 2690 [27.8%] for advanced degree) and annual household income (eg, 364 [9.4%] vs 1407 [14.5%] for $100 001-$150 000). Adjusting for age and sex, adult- versus youth-diagnosed ADHD was associated with lower adjusted probabilities of most psychiatric comorbidities (8 of 9 conditions) with the largest absolute differences for posttraumatic stress disorder (−7.50 [95% CI, −9.25 to −5.88] percentage points [pp]), bipolar disorder (−7.44 [95% CI, −8.99 to −6.00] pp), and personality disorder (−4.78 [95% CI, −5.89 to −3.81] pp). For somatic conditions (6 of 9 categories), the largest absolute differences were for lung conditions (−7.88 [95% CI, −9.73 to −5.79] pp), digestive conditions (−7.27 [95% CI, −9.12 to −5.28] pp), and bone, joint, and muscle conditions (−7.00 [95% CI, −8.78 to −5.20] pp). For impairment in overall health and daily functioning (7 of 9 measures), the largest absolute differences were for physical health (−3.63 [95% CI, −4.83 to −2.44] pp), being bothered by emotional problems in the past 7 days (−2.51 [95% CI, −3.79 to −1.24] pp), and general health (−2.26 [95% CI, −3.40 to −1.18] pp). Compared with their matched controls without ADHD, both ADHD groups showed markedly higher probability differences of comorbid psychiatric (eg, for depression, 39.33 [95% CI, 38.19-40.48] pp for adult-diagnosed ADHD and 36.92 [95% CI, 35.05-38.83] pp for youth-diagnosed ADHD) and somatic (eg, for brain and nervous system conditions, 21.86 [95% CI, 20.64-22.93] pp for adult-diagnosed ADHD and 22.84 [95% CI, 21.05-24.83] pp for youth-diagnosed ADHD) conditions, and functional impairments (eg, for bothered by emotional problems past 7 days, 6.11 [95% CI, 5.45-6.80] pp for adult-diagnosed ADHD and 7.29 [95% CI, 5.99-8.60] pp for youth-diagnosed ADHD). ADHD polygenic risk scores were lower in adult- vs youth-diagnosed groups (Cohen d , −0.17 [95% CI, −0.21 to −0.12]) and higher in youth-diagnosed (Cohen d , 0.21 [95% CI, 0.16-0.26]) and adult-diagnosed (Cohen d , 0.12 [95% CI, 0.09-0.15]) groups compared with controls. Conclusions and Relevance In this cross-sectional study of adults with ADHD, individuals first diagnosed with ADHD in adulthood showed a milder ADHD-like clinical and genetic profile than those diagnosed in childhood or adolescence, which may contribute to later recognition of the disorder. Nonetheless, adults diagnosed either as youths or adults exhibited profiles characteristic of ADHD relative to matched controls without ADHD, including substantial burden, supporting adult-diagnosed ADHD as a clinically important subgroup warranting recognition and management.