PSMC4 and Parkinson disease: Intriguingly, prior inquiries into the expression of genes associated with these degradation machineries in blood and brain tissues of individuals afflicted by PD, including PSMC4 (an integral component of the 19S proteasomal particle), SKP1 (an essential constituent of the SCF complex endowed with E3 ubiquitin ligase activity), UBE2K (an ubiquitin-conjugating enzyme E2K), and HSPA8 (a 70kDa heat shock protein exerting chaperone functions), have yielded divergent results (Grunblatt et al., 2004; Mandel et al., 2005, 2012b; Molochnikov et al., 2012; Su et al., 2018).