Expression of filaggrin gene is down-regulated in AD skin by Th2 cytokines (IL-4 and IL-13) [105] and normal human keratinocytes by sphingosylphosphorylcholine, which is proinflammatory and proprurigenic in AD [106,107], suggesting that filaggrin defects can develop as an acquired and/or genetic defect. This evidence concerns the gene FLG and Alzheimer disease.