SMPD1 and Niemann-Pick disease type C: A recent peer review [8] divides this condition into two entities: i) acid sphingomyelinase-deficient disease resulting from mutations in the SMPD1 gene (encompassing type A, B and intermediate forms), and ii) Niemann-Pick disease type C (including also type D), resulting from mutations in either the NPC1 or the NPC2 gene.