SMPD1 and acid sphingomyelinase deficiency: Acid sphingomyelinase deficiency (ASMD), historically known as Niemann–Pick disease types A, A/B, and B, is a rare lysosomal storage disease resulting from the deficiency of lysosomal enzyme acid sphingomyelinase (ASM) due to pathogenic variants in the sphingomyelin phosphodiesterase 1 (SMPD1) gene [1, 2].