Disaccharidase deficiency in man.

IT IS STILL commonly taught in physiological textbooks that carbohydrates are completely digested in the lumen of the bowel by the action of pancreatic juices and the succus entericus. This is untrue and in fact the enzymes of the succus entericus probably represent desquamated intestinal cells and are not present in sufficient quantitity to be of physiological significance, while the final stage of digestion takes place on or in the intestinal mucosa; this was realized at the turn of the century by Weymouth Reid. A scheme of sugar digestion and absorption is shown in Fig. 1. Starch comprises straight chains of repeating units of glucose (1-4 linkageamylose) or branched chains (1-4 1-6 linkageamylopectin). Under the action of pancreatic amylase maltose, maltotriose (1-4 glucoseglucoside with 3 glucose units) and isomaltose (1-6 glucose-glucoside) are formed. The other main dietary disaccharides are lactose (galactose plus glucose) and sucrose (fructose plus glucose). There are four main groups of enzymes in the brush-border of the mucosal cell which split the dietary disaccharides; once split, the constituent monosaccharides are pumped across the mucosal cell by a specialized mechanism. It is a good rule in clinical medicine that if an enzyme is present and it is not necessary for life, then some members of the population will be deficient and on occasions this may give rise to symptoms and so it was realized that a group of children who fail to thrive, have acid, fermentative stools with diarrhoea and are cured by withdrawal of the offending disaccharide from the diet are suffering from such a deficiency. This was first well documented by Weijers et al. (1961) who described a child who was unable to tolerate sucrose or starch but could tolerate lactose. This child, in fact, was suffering from the condition of sucrase-isomaltase deficiency and it would seem from this and other studies (Burgess et al., 1964; Auricchio et al., 1965a) that a defic-