FLG and Alzheimer disease: Filaggrin deficiency is associated with impaired barrier function and the development of AD.11 Filaggrin deficiency in children seems to define a specific endotype of AD, characterized by a predilection to exposed areas of the body, in particular the cheeks and hands.12 Profilaggrin, the phosphorylated precursor to filaggrin, is expressed in the upper stratum granulosum, where processing is initiated.