Patients with extrinsic disease have high levels of serum IgE, and often also a personal or family history of atopy and specific IgEs to food or aeroallergens [62], while intrinsic AD patients have normal total IgEs, absence of other atopic diseases, negative allergen-specific IgEs, and lower rates of filaggrin mutations [56,61]. This evidence concerns the gene FLG and Alzheimer disease.