SMPD1 and Niemann-Pick disease type A: In humans, loss-of-function mutations in the ASM gene (also called SMPD1) cause the familial Niemann–Pick disease, type A, with severe neurological deterioration and lysosomal accumulation of excessive sphingomyelins in brain, liver, spleen and lung cells, leading to the death of affected individuals at 1 or 2 years of age (Schuchman, 2007).