Enzyme deficiencies

Carbohydrates are hydrolyzed in the intestinal lumen by specific enzymes to monosaccharides before transport across the brush border membrane of epithelial cells into the cell interior. The enzymes implicated in the digestion of carbohydrates in the intestinal lumen are membrane-bound glycoproteins that are expressed at the apical domain of the enterocytes.

Absent or reduced activity of one of these enzymes is the cause of disaccharide intolerance and malabsorption, the symptoms of which are abdominal pain, cramps or distention, flatulence, nausea and osmotic diarrhea.

In case of congenital sucrase-isomaltase deficiency and hypolactasia, the corresponding enzymes - sucrase-isomaltase and lactase-phlorizin hydrolase, respectively - are missing, missorted or not functional. Thus consuming sucrose or lactose is resulting in excess gas production and diarrhea.