During the past several years carbohydrate digestion and absorption has been extensively investigated.1 An important contribution was the conclusive demonstration that disaccharides are absorbed intact and further digested within or on the surface of the intestinal epithelial cell. Hydrolysis to their component monosaccharides is catalyzed by enzymes, the disaccharidases, located in the brush border of the epithelial cells. Under normal circumstances only the monosaccharides enter the blood stream. The disaccharidases that have been defined and characterized and their substrates are shown in Table 1.
Deficiency of all the disaccharidases has been described and implicated in the production of diarrhea and malabsorption states.2 Although understanding of disaccharidase deficiencies is not yet completely clear a tentative classification is proposed in Table 2. Deficiency of all the disaccharidases occurs only in association with widespread mucosal abnormality such as sprue, and, occasionally, regional enteritis. Isolated deficiency of lactase occurs occasionally in infants,