MAPT and Cognitive impairment: It has been demonstrated that PD patients with cognitive impairment and olfactory dysfunction are associated with increased Aβ and tau pathology (Fujishiro et al., 2008; Irwin et al., 2013), and in the RBCs of PD patients, these proteins were found to interact with α-syn to form the α-syn-Aβ or the α-syn-Aβ heterocomplex (Daniele et al., 2018a,b).