Hereditary fructose intolerance

Other Names: Fructose-1-phosphate aldolase deficiency; ALDOB deficiency; Aldolase B deficiency; Fructose-1,6-bisphosphate aldolase B deficiency; Fructose intolerance, hereditary

Hereditary fructose intolerance (HFI) is a metabolic disease caused by the absence of an enzyme called aldolase B. In people with HFI, ingestion of fructose (fruit sugar) and sucrose (cane or beet sugar, table sugar) causes severe hypoglycemia (low blood sugar) and the build up of dangerous substances in the liver. HFI may be relatively mild or a very severe disease. Fructose is a simple sugar found primarily in fruits. Affected individuals develop signs and symptoms of the disorder in infancy when fruits, juices, or other foods containing fructose are introduced into the diet.

Epidemiology

The incidence of hereditary fructose intolerance is estimated to be 1 in 20,000 to 30,000 individuals each year worldwide.

Cause

Mutations in the ALDOB gene cause hereditary fructose intolerance. The ALDOB gene provides instructions for making the aldolase B enzyme. This enzyme is found primarily in the liver and is involved in the breakdown (metabolism) of fructose so this sugar can be used as energy. Aldolase B is responsible for the second step in the metabolism of fructose, which breaks down the molecule fructose-1-phosphate into other molecules called glyceraldehyde and dihydroxyacetone phosphate.

ALDOB gene mutations reduce the function of the enzyme, impairing its ability to metabolize fructose. A lack of functional aldolase B results in an accumulation of fructose-1-phosphate in liver cells. This buildup is toxic, resulting in the death of liver cells over time. Additionally, the breakdown products of fructose-1-phosphase are needed in the body to produce energy and to maintain blood sugar levels. The combination of decreased cellular energy, low blood sugar, and liver cell death leads to the features of hereditary fructose intolerance.

Inheritance

Autosomal recessive inheritance, a 25% chance

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

Signs and symptoms

The symptoms of HFI include:

• Poor feeding as a baby
• Irritability
• Increased or prolonged neonatal jaundice
• Vomiting
• Convulsions
• Excessive sleepiness
• Intolerance for fruits
• Avoidance of fruits and fructose/sucrose-containing foods
• Doing well after eating foods without fructose/sucrose

The early symptoms of fructose intolerance may resemble those of galactosemia: irritability, jaundice, vomiting, convulsions and an enlarged liver and spleen. Later problems relate more to liver disease.

For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. 80%-99% of people have these symptoms

• Abdominal pain(Pain in stomach)
• Reduced aldolase level

30%-79% of people have these symptoms

• Diarrhea(Watery stool)
• Growth delay(Delayed growth)
• Nausea

5%-29% of people have these symptoms

• Abdominal distention(Abdominal bloating)
• Abnormality of the coagulation cascade
• Chronic hepatic failure(Chronic liver failure)
• Chronic kidney disease
• Constipation
• Episodic hyperhidrosis(Sporadic excessive sweating)
• Hepatomegaly(Enlarged liver)
• Hypermagnesemia(High blood magnesium levels)
• Hyperuricemia(High blood uric acid level)
• Hypophosphatemia(Low blood phosphate level)
• Jaundice(Yellow skin)
• Metabolic acidosis
• Reactive hypoglycemia(Low blood sugar after a meal)
• Vomiting(Throwing up)

1%-4% of people have these symptoms

• Cataract(Clouding of the lens of the eye)
• Coma
• Lethargy
• Seizure

Diagnosis

Physical examination may show:

• Enlarged liver and spleen
• Jaundice

Tests that confirm the diagnosis include:

• Blood clotting tests
• Blood sugar test
• Enzyme studies
• Genetic testing
• Kidney function tests
• Liver function tests
• Liver biopsy
• Uric acid blood test
• Urinalysis
• Blood sugar will be low, especially after receiving fructose or sucrose. Uric acid levels will be high.

Treatment

Removing fructose and sucrose from the diet is an effective treatment for most people. Complications may be treated. For example, some people can take a medicine to lower the level of uric acid in their blood and decrease their risk for gout.

Prognosis

Hereditary fructose intolerance may be mild or severe. Avoiding fructose and sucrose helps most children with this condition. The prognosis is good in most cases. A few children with a severe form of the disease will develop severe liver disease. Even removing fructose and sucrose from the diet may not prevent severe liver disease in these children.

How well a person does depends on:

• How soon the diagnosis is made
• How soon fructose and sucrose can be removed from the diet
• How well the enzyme works in the body

Possible Complications These complications may occur:

• Avoidance of fructose-containing foods due to their effects
• Bleeding
• Gout
• Illness from eating foods containing fructose or sucrose
• Liver failure
• Low blood sugar (hypoglycemia)
• Seizures
• Death

NIH genetic and rare disease info

• NIH info on Hereditary fructose intolerance

Hereditary fructose intolerance is a rare disease.

Hereditary fructose intolerance Resources
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Hereditary fructose intolerance Resources
Latest articles Most recent articles Ongoing trials	Wikipedia