Background: Increasing evidence suggests a positive association between attention-deficit hyperactivity disorder (ADHD) and atopic diseases. However, the risk of atopic diseases in unaffected siblings of patients with ADHD has not been investigated. Objective: To investigate the risk of developing atopic diseases among unaffected siblings of ADHD probands. Methods: Using data from the Taiwan National Health Insurance Research Database, 20,170 unaffected siblings of patients with ADHD born between 1980 and 2000 and 80,680 age-, birth time-, and residence-matchedcontrols were included in this study. Diagnoses of atopic diseases, including asthma, atopic dermatitis, allergic rhinitis, and allergic conjunctivitis, were ascertained from 1996 or the birth time until the end of 2011. Results: Breslow-Cox proportional hazard regression analyses with adjustment for demographic data showed that compared with the controls, unaffected siblings of patients with ADHD had a higher risk of developing asthma (relative risk [RR], 1.19; 95% confidence interval [CI], 1.15-1.24), atopic dermatitis (RR, 1.10; 95% CI, 1.04-1.16), allergic rhinitis (RR, 1.17; 95% CI, 1.14-1.21), allergic conjunctivitis (RR, 1.13; 95% CI, 1.09-1.17), and any of these atopic diseases (RR, 1.13; 95% CI, 1.10-1.15). Conclusion: The unaffected siblings of ADHD probands were more likely to develop atopic diseases compared with the controls, suggesting shared risk factors for both diseases.
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