Sphingomyelin phosphodiesterase (SMPD1), also called acid sphingomyelinase (ASM), is a lysosomal phosphodiesterase that hydrolyses sphingomyelin to ceramide and phosphocholine (Schuchman et al. 1991, Schuchman et al. 1992). Defects in SMPD1 are the cause of two types of Niemann-Pick disease. Type A (NPDA, Niemann-Pick disease classical infantile form) (MIM:257200) (Ferlinz et al. 1991) and type B (NPDB, Niemann-Pick disease visceral form) (MIM:607616) (Rodriguez-Pascau et al. 2009).