Intraluminal and mucosal starch digestion in congenital deficiency of intestinal sucrase and isomaltase activities

Abstract

Ten patients affected by congenital deficiency of intestinal sucrase and isomaltase activities were studied. The intraluminal α-amylolysis of amylopectin was found to be normal in these patients. It is incomplete during the 1st year of life, both in patients and in controls, as a consequence of the lower α-amylase activity in this age group. Maltotriose was well tolerated in two normal controls ages 32 and 3 months and in one 31-month-old patient: in these subjects an oral tolerance test with the trisaccharide was followed by a rapid increase of blood glucose (46-58 mg/100 ml) and did not cause diarrhea. However, in a 6-month-old patient fermentative diarrhea and low increase of blood glucose (24 mg/100 ml) followed oral load with maltotriose. In all patients, enzyme assays on intestinal biopsy specimens showed that the glucamylase activity of the heat-resistant maltase(s) was normal, while that of the sucrase-isomaltase complex was decreased. These results suggest that starch malabsorption in congenital sucrose and isomaltose intolerance results from deficiency of the enzymatic activities of the sucrase-isomaltase complex involved in starch digestion. Malabsorption of starch can be expected to result from: (1) deficiency of pancreatic amylase; (2) congenital or acquired deficiency of the glucosidase activities of the brush border; (3) glucose malabsorption; (4) higher intestinal flow rate. The results in this study show that one particular form of starch malabsorption is a consequence of congenital deficiency of the activities of the sucrase-isomaltase complex involved in starch digestion. The methods used here should prove to be useful also in the investigation of other forms of starch malabsorption. © 1972 International Pediatric Research Foundation, Inc.