SNCA and Parkinson disease: In relation to PD, one study has shown that the extracellular secretion of α-synuclein is mediated by exophagy, a mode of secretion from an autophagy intermediate produced by impaired autophagosome-lysosome fusion, similar to secretory autophagy, and that this secretion is enhanced by overexpression of the tubulin polymerization-promoting protein (TPPP/p25α) (Ejlerskov et al., 2013).