Filaggrin loss-of-function mutations are not a predisposing factor for atopic dermatitis in an Ishigaki Island under subtropical climate

Background: Filaggrin (FLG) is a major protein component of the stratum corneum (SC) layer, and FLG loss-of-function mutations are a predisposing factor for atopic dermatitis (AD). Previous cohort studies of children from northern and western Europe have reported FLG loss-of-function mutation frequencies of 15.1-20.9% and 5.8-13.0% in AD and non-AD groups, respectively. Objective: To elucidate the association between AD prevalence of FLG loss-of-function mutation carriers and climate conditions, we determined the AD prevalence and FLG loss-of-function mutation frequencies in a cohort of children from Ishigaki Island. Ishigaki Island has a subtropical climate with high humidity (monthly average, 60.8-78.7%) and high temperature (monthly average, 18.5-29.4. °C) throughout the year. Methods: We diagnosed AD prevalence and analyzed eight FLG loss-of-function mutations in the Japanese population against a cohort of 721 children from the Kyushu University Ishigaki Atopic Dermatitis Study (KIDS) cohort. Parents gave consent for the mutation analysis during their medical examinations from 2001 to 2006. Results: Average AD prevalence was 7.3% per year, and a total of 127 children (17.6%) were diagnosed with AD at least once between 2001 and 2006. The average total serum IgE level differed significantly between the AD and non-AD groups (199.0 and 69.0. IU/ml, respectively). Although five kinds of FLG loss-of-function mutations isolated in previous Japanese FLG mutation studies were identified, the FLG loss-of-function mutation frequency in children of the KIDS cohort was not significantly different between the AD and non-AD groups (7.9% and 6.1%, respectively; P=0.174). Conclusion: The FLG loss-of-function mutation frequency was not significantly different between the AD and non-AD groups in a cohort of children from Ishigaki Island, which has a subtropical climate, suggesting that FLG loss-of-function mutations are not always a predisposing factor for AD prevalence.