MAPT and Parkinson disease: Several meta-analyses have shown that PD patients with cognitive impairment have elevated total Tau (t-Tau) and phosphorylated Tau (p-Tau) and reduced Aβ42 levels compared with those without cognitive impairment (Buongiorno et al. 2011; W. T. Hu et al. 2010; X. Hu et al. 2017).