NGF and early-onset autosomal dominant Alzheimer disease: IgM seropositivity is indicative of viral reactivation which again can be induced by several of the risk factors relevant to Alzheimer's disease and its underlying genetic pathways (e.g., NGF deprivation, 17-beta oestradiol, hypoxia, or fever and interleukin 6 activation, with the latter being common and general consequences of infection [1]).