Hereditary fructose intolerance is a carbohydrate metabolism disorder that is caused by a lack of the enzyme needed to metabolize fructose. Very small amounts of fructose cause low blood sugar levels and can lead to kidney and liver damage. Fructose intolerance disorders occur when parents pass on to their children the defective genes that cause these disorders.
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.
There are different types of inherited disorders. In hereditary fructose intolerance, both parents of the affected child carry 1 copy of the abnormal gene. Because usually 2 copies of the abnormal (recessive) gene are necessary for the disorder to occur, usually neither parent has the disorder. (See also Overview of Hereditary Metabolic Disorders.)
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), 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), 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
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 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.
National Organization for Rare Disorders (NORD): This resource provides information to parents and families about rare diseases, including a list of rare diseases, support groups, and clinical trial resources.
Genetic and Rare Diseases Information Center (GARD): This resource provides and easy to understand information about rare or genetic diseases.
