Glucose-Galactose Malabsorption

What else is it called?

  • Carbohydrate intolerance  
  • Complex carbohydrate intolerance  
  • GGM 
  • Monosaccharide malabsorption  
  • SGLT1 deficiency 

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What causes it?

This disorder is caused by a mutation (change) in the SLC5A1 gene. This gene provides instructions for a protein called SGLT1. This protein is responsible for transporting glucose and galactose across the cell membranes. The protein is found mainly in intestinal tract and less so in the kidneys.  

The SGLT1 protein is important for the functioning of intestinal epithelial cells (cells that line the walls of the intestine). It is involved in the process of using energy to move glucose and galactose across the cell membrane for absorption. 

Mutation in the SLC5A1 gene, prevents the SGLT1 protein from performing its function which leads to a build up of glucose and galactose in the intestinal tract. This prevents the glucose and galactose from being absorbed to provide the body with nutrition. The water that usually would have been transported across the membrane with the sugars, stay in the intestinal tract instead and are removed through the stool. This leads to dehydration and severe diarrhoea.  

How common is it?

Glucose-galactose malabsorption is a very rare disorder. There have been approximately 200 cases worldwide. Two-thirds of the individuals affected are females.  

However, 10% of the population has been affected with some degree of a reduced capacity for glucose absorption without related health problems. This may be a mild variation of glucose-galactose malabsorption.  

What are the signs and symptoms?

Symptoms may start as early as first day of life or a few days after birth when exposed to lactose from milk. These symptoms include:  

  • Severe chronic (recurring) diarrhoea  
  • Life threatening dehydration  
  • Increased acidity in the blood and tissues (acidosis)  
  • Failure to thrive (failure to grow or gain or maintain weight)  

In infants the diarrhoea may be severe and lead to nutritional wasting (low weight for height) and severe dehydration.  

Throughout childhood, the patient may suffer from chronic but intermittent (occasional) diarrhoea, worsened by sugary meals. Other symptoms in childhood include:  

  • Sugar in the urine (glucosuria)  
  • Development of kidney stones 

Symptoms in adults include:  

  • Bloating  
  • Nausea  
  • Diarrhoea  
  • Abdominal cramps  
  • Rumbling sounds caused by gas in the intestine (borborygmi)  
  • Excessive urination  

Early diagnosis and treatment are important. The disorder may become life-threatening in severe cases.  


How is it diagnosed?

The disorder is usually diagnosed after the individual presenting the signs, especially extreme and ongoing diarrhoea. The diagnosis is confirmed with a simple test known as the “glucose breath hydrogen test”. This test involves blowing into a bag followed by drinking a solution containing different types of sugar and breathing into a bag every 15 to 20 minutes while your body digests the solution.  

Can it be treated?

The disorder is treated with a restricted diet by cutting out all products containing lactose, sucrose and glucose. All milk and milk products need to be avoided as they contain lactose which is broken down to glucose and galactose. Any dietary changes require a specialist dietitian’s advice and monitoring. These sugars can be replaced by fructose-based nutrients as fructose is absorbed differently from glucose and galactose.  

Do my family need to be tested?

Glucose-Galactose malabsorption is an inherited condition. Humans have chromosomes made up of DNA. Genes are pieces of DNA that carry the genetic information. Each chromosome may have several thousand genes. We inherit chromosomes from the egg of the mother and sperm of the father. The genes on those chromosomes carry the instructions that determine a person’s characteristics, which are a combination of the parents. 

The pattern of inheritance of Glucose-Galactose malabsorption is autosomal recessive. This means that carriers of the condition do not have the disorder because the other gene of this pair is working normally. Parents of children with Glucose-Galactose malabsorption are carriers.  

When both parents are carriers, the risk to the baby in each pregnancy is 

  • 25% chance (1 in 4) of developing the condition 
  •  50% chance (1 in 2) for the baby to be a carrier of the condition 
  •  25% chance (1 in 4) for the baby to have two working genes and neither have the condition nor be a carrier 

Genetic counselling can be requested to get a full explanation.  

Diagram showing the autosomal recessive inheritance pattern.

Relevant Organisations

References are available on request. Please contact us by phoning 0845 241 2173 or emailing [Resource Library No: GCM012].


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