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Disaccharidase deficiency 

Disaccharidase deficiency
Chapter:
Disaccharidase deficiency
Author(s):

Timothy M. Cox

DOI:
10.1093/med/9780198746690.003.0302
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date: 07 March 2021

Disaccharidases are abundant enzymes expressed on the microvillous membrane of the small intestine: apart from free glucose and fructose, disaccharidases are required for the complete assimilation of nearly all carbohydrate present in food and drinks. The enzymes cleave disaccharides such as sucrose, maltose, and lactose, as well as dextrins derived from starch, into their component monosaccharides. Their activity is reduced in hereditary conditions or in generalized intestinal diseases. Disaccharidase deficiency causes dietary intolerance of carbohydrate induced by the fermentation of undigested sugars in the distal small intestine and colon. Abdominal symptoms are usually noticed within an hour of the ingestion of foods containing the offending sugars. By far the most common symptomatic disaccharidase deficiency is lactose intolerance. Lactase activity is high in healthy infants when milk is the principal food, but in most humans the activity declines after weaning and remains low (lactase nonpersistence), which greatly reduces the capacity to break down lactose. In contrast, those inheriting a Mendelian dominant trait that leads to sustained high intestinal lactase expression throughout life (lactase persistence) digest and tolerate large quantities. The distribution of lactase activity in adult populations is subject to great variation. Intestinal lactase phenotypes can be identified by assay of mucosal biopsy samples or appropriate sugar tolerance tests, as can other (much rarer) genetically determined disaccharidase variants. The most convenient diagnostic screen involves hydrogen breath testing after oral loading. Disaccharide intolerance is readily treated by institution of a strict exclusion diet; oral enzymatic supplementation may benefit patients with severe enzymatic deficiency. Innovative and early phase clinical trials suggest that modulation of the host intestinal microbiome with a pure short-chain galacto-oligosaccharide may be beneficial in symptom control and in favouring the outgrowth of lactose-fermenting flora.

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