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Oxford Textbook of Medicine (5 ed.)

Edited by David A. Warrell, Timothy M. Cox, John D. Firth

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Latest update

The November 2012 update sees updates to over 70 chapters, focusing on Neurology and Gastroenterology. This update also incorporates a selection of 29 Case Histories taken from related titles in the Oxford Case Histories series, linked to from related chapters. Each case includes several questions followed by detailed answers and discussion to enhance diagnostic and clinical understanding.

Neurology updates include substantial updates to key chapters and new material on a wide range of topics including spinal cord injury, autonomic nervous system disorders, and inherited neurodegenerative diseases. 

Gastroenterology updates include extensive revisions of key chapters on liver failure and acute pancreatitis and new material on a wide range of matters, ranging from the common to the rare: including surgical treatments for colonic diverticular disease, antibody tests for immune disorders, and a revised treatment algorithm for small bowel bacterial overgrowth.

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Publisher:
Oxford University Press
Print Publication Date:
May 2010
Print ISBN-13:
9780199204854
Published to Oxford Medicine:
May 2012
DOI:
10.1093/med/9780199204854.001.1

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Disclaimer

Oxford University Press makes no representation, express or implied, that the drug dosages in this book are correct. Readers must therefore always check the product information and clinical procedures with the most up to date published product information and data sheets provided by the manufacturers and the most recent codes of conduct and safety regulations. The authors and the publishers do not accept responsibility or legal liability for any errors in the text or for the misuse or misapplication of material in this work. Except where otherwise stated, drug dosages and recommendations are for the non-pregnant adult who is not breastfeeding.

Contents

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 November 2012. The previous version of this content can be found here.

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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