Familial association of attention-deficit hyperactivity disorder with autoimmune diseases in the population of Sweden

Aims In the era of genome-wide association studies, familial risks are used to estimate disease heritability and success in gene identification. We wanted to estimate associations of 42 autoimmune diseases with attention-deficit hyperactivity disorder (ADHD) between individuals and family members. Participants and methods The availability of a Multigeneration Register in Sweden provides reliable access to family data that covers the last century. An open cohort design of the diseases in individual and family members was obtained through linkage to the Hospital Discharge Register. Standardized incidence ratios were calculated as relative risks for ADHD in family members of affected patients compared with those without affected family members. Results Among a total of 86 493 patients, 18 153 had a family history of autoimmune diseases. ADHD was associated with 14 autoimmune diseases in the first-degree relatives, including ankylosing spondylitis (standardized incidence ratio:1.13), celiac disease (1.16), Crohn's disease (1.07), diabetes mellitus type 1 (1.19), discoid lupus erythematosus (1.26), glomerular nephritis chronic (1.13), Hashimoto/hypothyroidism (1.11), lupoid hepatitis (1.44), multiple sclerosis (1.11), psoriasis (1.18), Reiter's disease (1.38), rheumatoid arthritis (1.07), Sjögren's syndrome (1.21), and ulcerative colitis (1.05). Conclusion Familial associations with several autoimmune diseases suggest genetic sharing and challenge to gene identification.