SNCA and Parkinson disease: Taking together this body of evidence and the known inherited forms of PD, one can construct a basic PD model: α-synuclein begins to aggregate, through some innate mechanism, or induced by other factors; the cell recognizes the buildup of cytosolic α-synuclein levels and attempts to degrade the proteins by ubiquitination, and subsequent shuttling to a proteasome for degradation.