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Disaccharidase deficiency 

Disaccharidase deficiency

Chapter:
Disaccharidase deficiency
Author(s):

T.M. Cox

DOI:
10.1093/med/9780199204854.003.151005_update_001

Update:

New references to the evolutionary significance of genetic variation in human intestinal lactase expression and its biological significance.

More explicit guidance on the management of the carbohydrate intolerance syndrome.

Updated on 28 Nov 2012. The previous version of this content can be found here.
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date: 30 March 2017

Disaccharidases occur in the microvilli of the small intestine and are required for the complete assimilation of nearly all carbohydrate present in food and drinks, apart from free glucose and fructose. The enzymes cleave disaccharides such as sucrose, maltose, and lactose, as well as dextrins derived from starch, into their component monosaccharides, and their activity is reduced in hereditary conditions or in generalized intestinal diseases.

Disaccharidase deficiency causes carbohydrate intolerance induced by bacterial fermentation of undigested sugars which are delivered to the colon. Abdominal symptoms (e.g. nausea, bloating, distension, colicky pain, watery diarrhoea) are usually noticed within an hour of the ingestion of foods containing the offending sugars.

By far the most common cause of disaccharidase deficiency is lactose intolerance. During infancy, when milk is the principal food, lactase activity is high, but in most humans it declines after weaning and remains low (lactase nonpersistence), with such individuals having a low capacity to breakdown lactose. By contrast, in other healthy subjects a mendelian dominant trait maintains high intestinal lactase expression throughout life (lactase persistence); such individuals can tolerate and digest large quantities (loading doses >50 g). The global distribution of lactase activity in adult populations is subject to wide variation: nonpersistence of lactase expression predominates in nearly every population in East Asia, whereas in those of northern and central European origin, and in Afro-Arabian nomads who have developed or maintained pastoralist dairy cultures, lifelong intestinal lactase expression is sustained.

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. Disaccharide intolerance is readily treated by institution of a strict exclusion diet; enzymatic supplementation may benefit patients with severe enzymatic deficiency.

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