Moreover, aberrant aggregation of a-Synuclein has prion-like properties to trigger the intercellular transmission a-Syn fibrils (PFFs); it is time-dependent and changeable, implying that the propagation of a-Syn may be the key contributor to onset and progression of PD (Willis, 2008; Willis and Freelance, 2017; Figure 3). The gene discussed is SNCA; the disease is Parkinson disease.