Over a hundred human gene products, including all of the major Alzheimer's disease susceptibility gene products (APOE4, clusterin, complement receptor 1, and PICALM) and most of many other diverse genes that have been implicated in Alzheimer's disease in genetic association studies contain intraprotein sequences that are identical to those within herpes simplex viral proteins. Here, CR1 is linked to early-onset autosomal dominant Alzheimer disease.