PPA1 and Alzheimer disease: Moreover, Handa et al68 reported decreased levels of gamma-synuclein (SNCG), prefoldin subunit 2 (PFDN2), and pyridoxal phosphate binding protein (PLPBP), and increased inorganic pyrophosphatase 1 (PPA1) in human cases, the trajectories that were largely shared by the rTg-D HOM rats and TgSD-AD rats.