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Hereditary Fructose Intolerance


Matt Demczko

, MD, Mitochondrial Medicine, Children's Hospital of Philadelphia

Reviewed/Revised Dec 2021 | Modified Sep 2022
  • Fructose intolerance is caused by the lack of an enzyme needed to break down fructose.

  • Typical symptoms include low blood sugar, sweating, confusion, and kidney damage.

  • The diagnosis is made by analyzing a sample of liver tissue.

  • Treatment includes avoiding fructose in the diet and, when needed, taking glucose tablets.

Fructose is a sugar present in table sugar (sucrose), honey, and many fruits. Fructose is also present in sorbitol (a sugar substitute).

Children who have one of these disorders are missing one of the enzymes needed to break down (metabolize) fructose. As a result, a by-product of fructose accumulates in the body, blocking the formation of glycogen and its conversion to glucose for use as energy.

Symptoms of Hereditary Fructose Intolerance

Ingesting more than tiny amounts of fructose or sucrose causes low blood sugar levels (hypoglycemia Hypoglycemia Hypoglycemia is abnormally low levels of sugar (glucose) in the blood. Hypoglycemia is most often caused by medications taken to control diabetes. Much less common causes of hypoglycemia include... read more ), with sweating, confusion, and sometimes seizures and coma. Affected children who continue to eat foods containing fructose develop kidney and liver damage, resulting in jaundice (yellow skin and eyes—see Jaundice in the Newborn Jaundice in the Newborn Jaundice is a yellow color to the skin and/or eyes caused by an increase in bilirubin in the bloodstream. Bilirubin is a yellow substance formed when hemoglobin (the part of red blood cells... read more Jaundice in the Newborn ), vomiting, mental deterioration, seizures, and death.

Chronic symptoms include poor eating, failure to thrive, digestive symptoms, liver failure, and kidney damage. For most types of this disorder, early diagnosis and dietary restrictions started early in infancy can help prevent these more serious problems.

Fructokinase deficiency, which is a type of hereditary fructose intolerance, does not cause any symptoms.

Diagnosis of Hereditary Fructose Intolerance

  • Analysis of liver sample

Doctors base the diagnosis of hereditary fructose intolerance on the person's symptoms after consuming fructose and on a chemical analysis of a sample of liver tissue. The analysis helps doctors determine that the enzyme is missing.

People who may carry the gene that causes this disorder can undergo blood tests to determine whether they are carriers. Carriers Genetic Carrier Screening Genetic disorders are caused by abnormalities in one or more genes or chromosomes. Some genetic disorders are hereditary and others are spontaneous. Hereditary genetic disorders are passed down... read more are people who have an abnormal gene for a disorder but who do not have symptoms or visible evidence of the disorder.

Treatment of Hereditary Fructose Intolerance

  • Eliminating fructose, sucrose, and sorbitol from the diet

  • For hypoglycemia, glucose

Treatment of hereditary fructose intolerance involves excluding fructose (generally present in sweet fruits), sucrose, and sorbitol from the diet.

Severe attacks of hypoglycemia are relieved by glucose given by vein. Milder attacks are treated with glucose tablets, which should be carried by anyone who has hereditary fructose intolerance.

More Information

The following are some English-language resources that may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

Drugs Mentioned In This Article

Generic Name Select Brand Names
Numoisyn, Saliva Substitute
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