Clinical phenotypic variability in AD may include time of disease onset (infancy, adolescence, adulthood), likelihood of persistence into adulthood, severity (mild-moderate, severe), co-existence of other allergic disease, co-existence of mendelian disorders associated with AD (e.g., Netherton's syndrome), IgE-mediated food or aeroallergen sensitization, presence of Staphylococcus aureus colonization and presence or absence of viral infections (e.g., eczema herpeticum) (22, 26). This evidence concerns the gene IGHE and Alzheimer disease.