SMPD1 and mucopolysaccharidosis: Thirdly, to increase the number of enzymes, an initial study established an assay for 5-plex LSD enzymes, including α-glucosidase (GAA) for Pompe disease, α-galactosidase A (GLA) for Fabry disease, acid β-glucosidase (ABG) for Gaucher disease, acid sphingomyelinase (ASM) for Niemann-Pick disease type A/B, and galactosylcerebrosidase (GALC) for Krabbe disease [7], followed by the inclusion of α-L-iduronidase (IDUA) for mucopolysaccharidosis (MPS) I in a subsequent study [10].