QPCT and Alzheimer disease: In AD pathogenesis, Aβ peptides undergo N-terminal modification of its Glu residue to form an N-terminal PGlu species of Aβ (AβpE3-42) peptides catalyzed by glutaminyl cyclase (QC) activity enriched in the temporal (hypothalamus and nucleus basalis) and frontal lobe structures of AD brains [39,40,41].