Importantly, tau protein levels are reduced in FTD (Papegaey et al., 2016), intellectual disability (Mazzon et al., 2018), Parkinson’s disease (PD) (Lei et al., 2012), normal aging (Mukaetova-Ladinska et al., 1996) and AD (Nieto et al., 1989). The gene discussed is MAPT; the disease is Parkinson disease.