Paternal intelligence affects school grades in children with and without ADHD - a register-based study.

ADHD profoundly impacts educational attainment, quality of life, and health in young adults. However, certain subgroups of ADHD patients seem to do quite well, potentially due to differences in intelligence and socioeconomic status. Here we used paternal intelligence from the Swedish Defence Conscription and Assessment register, to investigate the role of genetic propensity for intelligence, on school performance in a large cohort of ADHD patients and matched controls. Patients treated for ADHD in Linköping, Sweden between 1995 and 2020 (n = 3262), sex- and age-matched controls (n = 9591) as well as their parents and siblings were identified using regional and national registers. Socioeconomic and demographic data, ADHD diagnosis and treatment and school grades at age 16 for the study population were extracted from Swedish National registers. We explored the associations between paternal intelligence and child school performance using linear mixed models and mediation analyses, taking a wide range of potential covariates into account. Results indicate that paternal intelligence was positively associated with standardized school grades in their offspring (Z_adjusted=0.09, 95%CI 0.07, 0.10). This effect was present in both ADHD patients and controls, but ADHD patients had significantly lower standardized grades (Z_adjusted=-1.03, 95%CI -1.08, -0.98). Child ADHD did not serve as a mediator for how paternal intelligence affected school grades. Our findings indicate that ADHD prevents children from reaching their academic potential at all levels of paternal intelligence. Increased understanding of the contributions of ADHD, intelligence, and SES to functional outcomes can help clinicians to better personalize interventions to the unique preconditions in each patient.