MAPT and Mental deterioration: Concerning the prediction of cognitive decline in PD, the most consistent role as predictive factor is played by low CSF Aβ42 levels (Parnetti et al., 2008; Alves et al., 2010; Siderowf et al., 2010; Leverenz et al., 2011) although also tau species have been postulated to represent prognostic factors (Zhang et al., 2013).