PSEN1 and Alzheimer disease: Early-onset AD (EOAD, also known as familial AD or FAD), accounts for ∼2% of AD cases, arises at ages <65, and results from a single inherited mutation, typically in the amyloid precursor protein (APP), Presenilin 1 (PSEN1), or Presenilin 2 (PSEN2) genes (Dai et al., 2018).