SMPD1 and acid sphingomyelinase deficiency: Niemann-Pick disease type A/B (NPD A/B), also known as acid sphingomyelinase deficiency (ASMD; OMIM #257200, #607616), is a rare inborn error of metabolism and lysosomal storage disorder characterized by deficient activity of the acid sphingomyelinase (ASM) enzyme, resulting in the accumulation of sphingomyelin and other lipids in various tissues [1].