Fructose aldolase B-deficiency

Alternative names 
Fructosemia; Fructose intolerance; Hereditary fructose intolerance

Definition
Hereditary fructose intolerance is a metabolic disease caused by the absence of an enzyme, 1-phosphofructaldolase.

Causes, incidence, and risk factors

Fructose is a naturally-occuring fruit sugar. Man-made fructose is used as a sweetener in many foods (including baby food) and drinks. Hereditary fructose intolerance is an autosomal recessive disease. It may be as common as 1 in 20,000 in some European countries.

In fructose-intolerant people, ingestion of fructose (fruit sugar) and sucrose (cane or beet sugar, table sugar) produces complicated chemical changes that cannot be corrected because of the absence of the enzyme 1-phosphofructaldolase. Ingestion of fructose causes profound hypoglycemia (low blood sugar) and progressive liver damage. The body is unable to convert its energy storage material, glycogen, into glucose. Subsequently, the blood sugar falls (hypoglycemia). In addition, blocks in the metabolic pathway of fructose processing cause a build-up of substances that damage the liver.

Hereditary fructose intolerance can be relatively mild or very severe disease. In the severe form, even eliminating fructose and sucrose from the diet may not prevent progressive liver disease.

Symptoms

     
  • Onset of symptoms after starting an infant on food or formula  
  • 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

Note: 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.

Signs and tests
Physical examination may also show:

     
  • Jaundice (yellow skin) or icterus (yellow eyes)  
  • Hepatosplenomegaly (enlarged liver and spleen)

Tests that confirm the diagnosis include:

     
  • Positive urine test for reducing substances  
  • Hypoglycemia (low blood sugar), especially after receiving fructose/sucrose  
  • Excess uric acid in blood (hyperuricemia)  
  • Failure of the kidney to work properly with abnormally high amounts of sugars, amino acids and salts appearing in urine  
  • Liver failure shown with blood test  
  • Bleeding tendency revealed by coagulation tests of blood  
  • Liver biopsy  
  • Enzyme studies

Genetic testing for fructose intolerance may be available

Treatment
Complete elimination of fructose and sucrose from the diet is an effective treatment for most patients. Treatment of individual complications follows mainstream medical guidelines. For example, some patients can take medication to lower the level of uric acid in their blood and thereby decrease their risk for gout.

Expectations (prognosis)
Absolute elimination of fructose and glucose produces good results in most children with fructose intolerance. A few children will go on to develop progressive liver disease. The prognosis depends on how soon the diagnosis is made and how soon fructose and sucrose can be eliminated from the baby’s diet.

Complications

     
  • Hypoglycemia  
  • Illness due to eating fructose- or sucrose-containing foods  
  • Strong avoidance of fructose-containing foods due to noxious effects  
  • Seizures  
  • Bleeding  
  • Gout  
  • Liver failure  
  • Death

Calling your health care provider

Call your health care provider if your child has developed the above symptoms after you began feeding the child formula or solid food. The care of a medical specialist in Biochemical Genetics or Metabolism is strongly recommended if your child has this disorder.

Preliminary evidence suggests that parents of a child with this disorder (as well as other carriers of the mutant gene) may be at increased risk for gout (arthritis caused by excess uric acid in the body and uric acid crystals in the joints). Therefore, it is important to notify your physician if you have a family history of hereditary fructose intolerance.

Prevention
Genetic counseling may be of value to prospective parents with a family history of fructose intolerance. Most of the damaging effects of the disease can be prevented by strict adherence to a fructose-free diet.

Johns Hopkins patient information

Last revised: December 4, 2012
by Amalia K. Gagarina, M.S., R.D.

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