Aggregation prone proteins that cause neurodegenerative diseases including pathogenic polyQ proteins, as well as α-synuclein which causes Parkinson’s disease, and tau which causes the tauopathies have recently been suggested to be transmitted between cells, and this may be the mechanism leading to the progressive spread of neuropathology in these diseases [8]–[11]. The gene discussed is MAPT; the disease is Parkinson disease.