Familial aggregation of atopic dermatitis and co-aggregation of allergic diseases in affected families in Taiwan

Background: Atopic dermatitis (AD) is contributed from a result of genetic and environmental interaction. The evidence for familial aggregation in AD has been reported but population-based studies and co-aggregation with other allergic diseases are rarely reported. Objective: This study examined familial aggregation and heritability of atopic dermatitis (AD) and to estimate the relative risks (RRs) of other allergic diseases in individuals with relatives diagnosed with AD. Methods: We used Taiwan National Health Insurance Research Database to identify all registered beneficiaries (n = 26,525,074) in 2015; among them, 1,248,594 individuals had AD. We estimated familial risks of AD and other allergic diseases by using marginal Cox proportional models. Results: Prevalence of AD in individuals with relatives affected with atopic dermatitis was 3.1-fold higher than the general population (12.4 % vs. 4.0 %, respectively). The adjusted relative risks (RR) for individuals with an affected first-degree relative (FDR) was 2.25 (95 % CI, 2.25-2.26). The adjusted RRs for subjects with an affected parent, an affected offspring or an affected sibling was 2.39 (95 % CI, 2.37-2.41), 2.26 (95 % CI, 2.24-2.28) and 2.30 (95 % CI, 2.29-2.31) respectively. The RRs in individuals with an FDR with AD was 1.34 (95 %CI, 1.34 - 1.34) for asthma and 1.23 (95 %CI, 1.23-1.24) for allergic rhinitis. Conclusion: This nationwide study ascertains that a family history of atopic dermatitis is a risk factor for atopic dermatitis. Individuals with relatives affected by atopic dermatitis have slightly higher risks of developing asthma and allergic rhinitis. (C) 2020 Published by Elsevier B.V. on behalf of Japanese Society for Investigative Dermatology.