SMPD1 and Niemann-Pick disease type C: Niemann-Pick disease is an autosomal recessive lysosomal storage disorder, in which two types can be distinguished: 1) acid sphingomyelinase-deficient Niemann-Pick disease with mutation in the SMPD1 gene (types A and B and intermediate forms) and 2) Niemann-Pick disease type C, also with type D, caused by mutations in either the NPC1 or NPC2 gene [81].