This subgroup includes the following three closely related glycosyl hydrolase family 31 (GH31) enzymes: maltase-glucoamylase (MGAM), sucrase-isomaltase (SI), and lysosomal acid alpha-glucosidase (GAA), also known as acid-maltase. MGAM is one of the two enzymes responsible for catalyzing the last glucose-releasing step in starch digestion. SI is implicated in the digestion of dietary starch and major disaccharides such as sucrose and isomaltose, while GAA degrades glycogen in the lysosome, cleaving both alpha-1,4 and alpha-1,6 glucosidic linkages. MGAM and SI are anchored to small-intestinal brush-border epithelial cells. The absence of SI from the brush border membrane or its malfunction is associated with malabsorption disorders such as congenital sucrase-isomaltase deficiency (CSID). The domain architectures of MGAM and SI include two tandem GH31 catalytic domains, an N-terminal domain found near the membrane-bound end, and a C-terminal luminal domain. Both of the tandem GH31 domains of MGAM and SI are included in this family. The domain architecture of GAA includes an N-terminal TFF (trefoil factor family) domain in addition to the GH31 catalytic domain. Deficient GAA expression causes Pompe disease, an autosomal recessive genetic disorder also known as glycogen storage disease type II (GSDII).