GPNMB and Parkinson disease: Specifically, GPNMB was proposed as a potential therapeutic target for interrupting the transmission of pathological α-synuclein in PD based on observations that GPNMB concentration in plasma positively correlated with UPDRS score, and knock-down of GPNMB in iPSC-derived neurons reduced α-synuclein pre-formed fibril (PFF) uptake [53].