The role of filaggrin (FLG) null alleles and their association with susceptibility to atopic dermatitis (AD) eczema herpeticum (ADEH), AD severity and increased serum IgE levels were investigated. The population studied included 397 European Americans (EAs) - 245 with AD and 81 with ADEH - and 152 normal controls (NCs). A significant association between FLG R501X and risk of AD was found in the EA population (p=0.003). This was strengthened in the ADEH subset (p = 8.55 x 10-8). AD severity was assessed by the Eczema Area and Severity Index (EASI) and increased serum IgE levels were also associated with mutation R501X (p = 0.0001 and 7.81 x 10-5, respectively) ...