APP and Alzheimer disease: One study examining APP, PSEN1, PSEN2, and MAPT in entorhinal cortex from 72 SAD and 58 non-AD controls found and validated three possibly damaging low-frequency SNVs: MAPT Q124K at a frequency of 1.1%, PSEN2 S130L at a frequency of 1.6%, and MAPT S735A at a frequency of 0.7% [67].