SMPD1 and Parkinson disease: Rare mutations in the lysosomal disorder genes GBA (Gaucher disease) and SMPD1 (Niemann-Pick types A and B disease) were shown to represent susceptibility factors for PD [18], [19], and the fundamental involvement of the lysosome in PD pathogenesis is supported by the observation that known PD genes such as SNCA, LRRK2, parkin, PINK1, and ATP13A2 regulate lysosome-dependent pathways or lysosomal activity [20].