SMPD1 and synucleinopathy: Other genes involved in sphingolipid metabolism that have been linked to the pathogenesis of synucleinopathies include SMPD1 (acid sphingomyelinase, i.e., the enzyme converting sphingomyelins into ceramide), and PSAP, which encodes the precursor of the saposin protein that acts as an activator of ceramidases that control the metabolism of complex sphingolipids [124,125].