SMPD1 and Niemann-Pick disease type A: Acid sphingomyelinase deficiency (ASMD), also known as Niemann Pick disease type A and type B, is a rare lysosomal storage disorder resulting from deficiency of the lysosomal enzyme acid sphingomyelinase (ASM) due to bi-allelic mutations in the sphingomyelin phosphodiesterase 1 gene, SMPD1 [1,2].