SMPD1 and Niemann-Pick disease: A SM-cleaving hydrolase, the SM phosphodiesterase also called acid sphingomyelinase (ASM, E.C. 3.1.4.12) was discovered by Shimon Gatt in 1966 [8] and its deficiency identified by R. O. Brady as the cause of the progressive SM accumulation in Niemann-Pick disease [9].