Null mutations in the FLG gene result in reduced levels of UCA and PCA, which may contribute to increased skin pH in a proportion of patients with AD.26,34In vitro studies have shown the TH2 cytokines IL-4 and IL-13 act synergistically in reducing FLG expression so that these breakdown products may be reduced in active AD lesions even in individuals wild-type for FLG. 38. Here, FLG is linked to Alzheimer disease.