SMPD1 and Parkinson disease: Several genetic risk loci in PD affect ceramide metabolism and cellular sphingolipid content (Ferrazza et al., 2016, Gan-Or et al., 2013, Henry et al., 2015, Lin et al., 2019, Plotegher et al., 2019), including mutations in ASM-3/SMPD1 (Foo et al., 2013, Gan-Or et al., 2015, Gan-Or et al., 2013, Ylönen et al., 2017) and GBA (the lysosomal glucocerebrosidase).