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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®

Glucose-galactose malabsorption

Reviewed July 2007

What is glucose-galactose malabsorption?

Glucose-galactose malabsorption is a condition in which the cells lining the intestine cannot take in the sugars glucose and galactose, which prevents proper digestion of these molecules and larger molecules made from them.

Glucose and galactose are called simple sugars, or monosaccharides. Sucrose (table sugar) and lactose (the sugar found in milk) are called disaccharides because they are made from two simple sugars, and are broken down into these simple sugars during digestion. Sucrose is broken down into glucose and another simple sugar called fructose, and lactose is broken down into glucose and galactose. As a result, lactose, sucrose and other compounds made from sugar molecules (carbohydrates) cannot be digested by individuals with glucose-galactose malabsorption.

Glucose-galactose malabsorption generally becomes apparent in the first few weeks of a baby's life. Affected infants experience severe diarrhea resulting in life-threatening dehydration, increased acidity of the blood and tissues (acidosis), and weight loss when fed breast milk or regular infant formulas. However, they are able to digest fructose-based formulas that do not contain glucose or galactose. Some affected children are better able to tolerate glucose and galactose as they get older.

Small amounts of glucose in the urine (mild glucosuria) may occur intermittently in this disorder. Affected individuals may also develop kidney stones or more widespread deposits of calcium within the kidneys.

How common is glucose-galactose malabsorption?

Glucose-galactose malabsorption is a rare disorder; only a few hundred cases have been identified worldwide. However, as many as 10 percent of the population may have a somewhat reduced capacity for glucose absorption without associated health problems. This condition may be a milder variation of glucose-galactose malabsorption.

What genes are related to glucose-galactose malabsorption?

Mutations in the SLC5A1 gene cause glucose-galactose malabsorption.

The SLC5A1 gene provides instructions for producing a sodium/glucose cotransporter protein called SGLT1. This protein is found mainly in the intestinal tract and, to a lesser extent, in the kidneys, where it is involved in transporting glucose and the structurally similar galactose across cell membranes.

The sodium/glucose cotransporter protein is important in the functioning of intestinal epithelial cells, which are cells that line the walls of the intestine. These cells have fingerlike projections called microvilli that absorb nutrients from food as it passes through the intestine. Based on their appearance, groups of these microvilli are known collectively as the brush border. The sodium/glucose cotransporter protein is involved in the process of using energy to move glucose and galactose across the brush border membrane for absorption, a mechanism called active transport. Sodium and water are transported across the brush border along with the sugars in this process.

Mutations that prevent the sodium/glucose cotransporter protein from performing this function result in a buildup of glucose and galactose in the intestinal tract. This failure of active transport prevents the glucose and galactose from being absorbed and providing nourishment to the body. In addition, the water that normally would have been transported across the brush border with the sugar instead remains in the intestinal tract to be expelled with the stool, resulting in dehydration of the body's tissues and severe diarrhea.

Related Gene(s)

Changes in this gene are associated with glucose-galactose malabsorption.

  • SLC5A1

How do people inherit glucose-galactose malabsorption?

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. Most often, the parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but do not show signs and symptoms of the condition. In some cases, individuals with one altered gene have reduced levels of glucose absorption capacity as measured in laboratory tests, but this has not generally been shown to have significant health effects.

Where can I find information about diagnosis or management of glucose-galactose malabsorption?

These resources address the diagnosis or management of glucose-galactose malabsorption and may include treatment providers.

  • Genetic Testing Registry: Congenital glucose-galactose malabsorption (

You might also find information on the diagnosis or management of glucose-galactose malabsorption in Educational resources and Patient support.

General information about the diagnosis ( and management ( of genetic conditions is available in the Handbook. Read more about genetic testing (, particularly the difference between clinical tests and research tests (

To locate a healthcare provider, see How can I find a genetics professional in my area? ( in the Handbook.

Where can I find additional information about glucose-galactose malabsorption?

You may find the following resources about glucose-galactose malabsorption helpful. These materials are written for the general public.

You may also be interested in these resources, which are designed for healthcare professionals and researchers.

What other names do people use for glucose-galactose malabsorption?

  • carbohydrate intolerance
  • complex carbohydrate intolerance
  • GGM
  • monosaccharide malabsorption

For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines ( and How are genetic conditions and genes named? ( in the Handbook.

What if I still have specific questions about glucose-galactose malabsorption?

Ask the Genetic and Rare Diseases Information Center (

What glossary definitions help with understanding glucose-galactose malabsorption?

acidity ; acidosis ; autosomal ; autosomal recessive ; brush border ; calcium ; carbohydrate ; cell ; dehydration ; digestion ; epithelial ; fructose ; galactose ; gene ; glucose ; inherited ; intestine ; kidney ; kidney stones ; malabsorption ; microvilli ; monosaccharide ; population ; protein ; recessive ; simple sugar ; sodium ; stool

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


  • Brown GK. Glucose transporters: structure, function and consequences of deficiency. J Inherit Metab Dis. 2000 May;23(3):237-46. Review. (
  • El-Naggar W, Balfe JW, Barbar M, Taha D. Nephrocalcinosis in glucose-galactose malabsorption, association with renal tubular acidosis. Pediatr Nephrol. 2005 Sep;20(9):1336-9. Epub 2005 Jul 12. (
  • Lam JT, Martín MG, Turk E, Hirayama BA, Bosshard NU, Steinmann B, Wright EM. Missense mutations in SGLT1 cause glucose-galactose malabsorption by trafficking defects. Biochim Biophys Acta. 1999 Feb 24;1453(2):297-303. (
  • Tasic V, Slaveska N, Blau N, Santer R. Nephrolithiasis in a child with glucose-galactose malabsorption. Pediatr Nephrol. 2004 Feb;19(2):244-6. Epub 2003 Dec 11. (
  • Wright EM, Hirayama BA, Loo DF. Active sugar transport in health and disease. J Intern Med. 2007 Jan;261(1):32-43. Review. (
  • Wright EM, Martín MG, Turk E. Intestinal absorption in health and disease--sugars. Best Pract Res Clin Gastroenterol. 2003 Dec;17(6):943-56. Review. (
  • Wright EM, Turk E, Martin MG. Molecular basis for glucose-galactose malabsorption. Cell Biochem Biophys. 2002;36(2-3):115-21. Review. (
  • Wright EM. I. Glucose galactose malabsorption. Am J Physiol. 1998 Nov;275(5 Pt 1):G879-82. Review. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: July 2007
Published: February 8, 2016