To investigate this question, we first used neuropathological information from 7,259 postmortem samples of European ancestry available through the Religious Orders Study and Memory and Aging Project (29) and the National Institute on Aging–AD Center cohorts 1 to 7 (30), looking at the effect of HLA-DRB1 on tau Braak staging and neuritic plaque density in pathological samples. Here, HLA-DRB1 is linked to Alzheimer disease.