AD can be classified into two major endotypes based on both symptoms and pathogenesis: the more common “extrinsic” (high serum IgE levels, eosinophilia, atopic background, greater filaggrin (FLG) mutation rate) and the rarer “intrinsic” (normal serum IgE level, delayed onset, female predominance, more preserved barrier function, increased prevalence of metal contact hypersensitivity, lack of other atopic background) types. Here, IGHE is linked to Alzheimer disease.