In addition to its role in cell activation, differentiation, and apoptosis, ASM has great importance for sphingolipid homeostasis as reflected by the development of severe, often fatal sphingolipidoses upon genetic ASM deficiency in mice and humans, where it is called Niemann–Pick disease (Horinouchi et al., 1995; Smith and Schuchman, 2008; Schuchman and Desnick, 2017). The gene discussed is SMPD1; the disease is Niemann-Pick disease.