QPCT and Alzheimer disease: Pyroglutamylation of truncated Aβ species carrying a glutamate residue at position 3 or 11 (including Aβ3-40, Aβ11-40, Aβ3-42 and Aβ11-42) is catalysed by enzyme glutaminyl cyclase (QC) [15–17], whose expression is increased in temporal and enthorinal cortices of AD patients and correlates with insoluble pE-Aβ aggregates [18].