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Glucose-galactose malabsorption
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Glucose-galactose malabsorption

Glucose-galactose malabsorption is a rare genetic metabolic disorder that prevents the absorption of key simple sugars, causing life-threatening diarrhea and dehydration in infants upon feeding.

Overview

Glucose-galactose malabsorption is a condition in which the body cannot absorb the simple sugars glucose and galactose. The signs and symptoms of the condition appear early in life when affected infants are fed breast milk or regular infant formulas. These foods contain glucose, galactose, and lactose (a sugar that breaks down into glucose and galactose during digestion). When individuals with this disorder ingest these sugars, it leads to severe diarrhea and other health complications. If foods containing glucose, galactose, and lactose are removed from the diet, the diarrhea stops.

Symptoms

The primary symptoms of glucose-galactose malabsorption begin in infancy and include:

  • Severe diarrhea, which leads to weight loss and life-threatening dehydration
  • Small amounts of glucose in the urine (mild glucosuria)
  • Kidney stones due to calcium deposits in the kidneys (nephrocalcinosis), which occurs rarely

Frequency

Glucose-galactose malabsorption is a rare disorder, with only a few hundred cases identified worldwide. However, as much as 10 percent of the general population may have a somewhat reduced capacity for glucose absorption without experiencing associated health problems.

Causes

The condition is caused by mutations in the SLC5A1 gene, which provides instructions for making the sodium/glucose cotransporter protein 1 (SGLT1). This protein is primarily located in the kidneys and the intestinal tract, where it spans cell membranes to transport glucose, galactose, sodium, and water from outside the cell to the inside.

  • In the intestinal tract: The SGLT1 protein helps the body absorb glucose and galactose from food during digestion, moving the sugars into the intestinal epithelial cells lining the intestinal wall.
  • In the kidneys: The SGLT1 protein helps maintain normal blood glucose levels by transporting filtered glucose back into specialized kidney cells so it can return to the bloodstream rather than being excreted in urine.

Mutations in the SLC5A1 gene impair or eliminate the function of the SGLT1 protein. Consequently, glucose and galactose cannot be absorbed and instead accumulate in the intestinal tract. Water that would normally be transported alongside these sugars also remains in the intestines, resulting in severe diarrhea and dehydration. Although the SGLT1 protein in the kidneys is also nonfunctional, other kidney proteins are able to absorb enough glucose back into the bloodstream so that glucosuria remains mild or absent.

Inheritance

This condition is inherited in an autosomal recessive pattern. This means both copies of the gene in each cell must have mutations for the disorder to manifest. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene but typically do not show signs and symptoms of the condition.

Other Names for This Condition

  • Carbohydrate intolerance
  • Complex carbohydrate intolerance
  • Congenital glucose-galactose intolerance
  • Congenital glucose-galactose malabsorption
  • GGM
  • Monosaccharide malabsorption

Frequently Asked Questions

Glucose-galactose malabsorption is an autosomal recessive disorder. This means an individual must inherit two copies of the mutated SLC5A1 gene (one from each parent) to develop the condition. Parents of an affected child are typically carriers, meaning they each have one copy of the mutated gene but do not show symptoms. For each subsequent pregnancy, there is a 25% chance the child will be affected, a 50% chance they will be a carrier, and a 25% chance they will not inherit the mutation at all. Genetic counseling is highly recommended for families.
If an infant exhibits severe diarrhea and signs of dehydration (like lethargy, dry mouth, reduced urination) after feeding, it's a medical emergency. Seek immediate medical attention. Healthcare providers will focus on rehydration, often intravenously, and will need to quickly remove all sources of glucose, galactose, and lactose from the infant's diet. This typically involves switching to a specialized formula free of these sugars.
For infants with glucose-galactose malabsorption, all breast milk and standard infant formulas must be immediately discontinued, as they contain lactose, glucose, or galactose. The essential dietary change is to switch to a specialized formula that uses fructose as its carbohydrate source. These formulas are specifically designed to provide complete nutrition while avoiding the sugars that cannot be absorbed.
Yes, strict dietary management is lifelong. As individuals with glucose-galactose malabsorption grow, they must continue to avoid foods containing glucose, galactose, and lactose. This means carefully reading food labels and avoiding many common foods, including most dairy products, certain fruits, and many processed foods. A registered dietitian specializing in metabolic disorders can provide guidance on maintaining a balanced and safe diet as they age.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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