MAPT and Alzheimer disease: However, when evaluating each diagnosis group separately, we observed higher correlations of QC activity with Aβ42 in the control group (r = 0.56) and mild AD group (r = 0.66) and with tau and p-tau for both AD groups (r = up to 0.77 for QC-ptau correlation in moderate AD) (Fig. 3c–e, coloured lines).