Hereditary fructose intolerance is a disorder in which a person lacks the protein needed to break down fructose. Fructose is a fruit sugar that naturally occurs in the body. Man-made fructose is used as a sweetener in many foods, including baby food and drinks.

This condition occurs when the body is missing an enzyme called aldolase B. This substance is needed to break down fructose.

If a person without this substance eats fructose and sucrose (cane or beet sugar, table sugar), complicated chemical changes occur in the body. The body cannot change its energy storage material, glycogen, into glucose. As a result, the blood sugar falls and dangerous substances build up in the liver.

Hereditary fructose intolerance is inherited, which means it is passed down through families. If both parents carry an abnormal gene, each of their children has a 25% chance of being affected. The condition may be as common as 1 in 20,000 people in some European countries.

Symptoms can be seen after a baby starts eating food or formula.

The early symptoms of fructose intolerance are similar to those of galactosemia. Later symptoms relate more to liver disease.

Symptoms may include:

• Convulsions
• Excessive sleepiness
• Irritability
• Jaundice
• Poor feeding as a baby
• Problems after eating fruits and fructose/sucrose-containing foods
• Vomiting

Physical examination may show:

• Enlarged liver and spleen (hepatosplenomegaly)
• Yellow skin or eyes

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.

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

Hereditary fructose intolerance may be mild or severe.

Avoiding fructose and sucrose helps most children with this condition.

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

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

Call your health care provider if your child develops symptoms of this condition after feeding starts. If your child has this condition, experts recommend seeing a doctor who specializes in biochemical genetics or metabolism.

Couples with a family history of fructose intolerance who wish to have a baby may consider genetic counseling.

Most of the damaging effects of the disease can be prevented by sticking to a fructose-free diet.

Steinmann B, Santer R, van den Berghe G. Disorders of Fructose Metabolism. In: Fernandes J, Saudubray JM, van den Berghe G, Walter JH, eds. Inborn Metabolic Diseases. 4th ed. New York, NY:Springer;2006:chap 9.