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Hereditary Fructose Intolerance


Matt Demczko

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

Reviewed/Revised Mar 2024
  • 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 based on the person's symptoms after consuming fructose.

  • 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

In children who have 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 Failure to Thrive in Children Failure to thrive is a delay in weight gain and physical growth that can lead to delays in development and maturation. Medical disorders and a lack of proper nutrition are causes of failure... read more , 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

  • Symptoms after consuming fructose

Doctors base the diagnosis of hereditary fructose intolerance on the person's symptoms after consuming fructose.

The diagnosis is confirmed by an analysis of the person's DNA.

People who may carry the gene that causes this disorder can undergo blood tests to determine whether they are carriers. Carriers Inheritance of Single-Gene Disorders Genes are segments of deoxyribonucleic acid (DNA) that contain the code for a specific protein that functions in one or more types of cells in the body or code for functional RNA molecules.... 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 English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

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