CTSD and multiple system atrophy: Additionally, the finding of increased expression of the three proteases kallikrein-6 (KLK6), calpain-1 (CAPN1), and cathepsin-D (CTSD) in various brain regions of MSA patients, such as the putamen, pontine base, and cerebellar white matter, has been proposed to be a compensatory response to the presence of increased αSyn load [46]; however, the levels of other proteases (i.e., matrix metalloproteinase-3, MMP-3, and endothelin-converting enzyme, ECE) remain to be investigated in the context of MSA [47,48].