Hereditary fructose intolerance is a disorder of metabolism 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 a substance 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. It may be as common as 1 in 20,000 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:

• Yellow skin or eyes
• Hepatosplenomegaly (enlarged liver and spleen)

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.

Complete elimination of fructose and sucrose from the diet is an effective treatment for most patients. Individual complications are treated as appropriate. For example, some patients can take medication to lower the level of uric acid in their blood and thereby decrease their risk for gout.

Hereditary fructose intolerance may be relatively mild or a very severe disease.

Complete avoidance of fructose and sucrose produces good results in most children with this condition. A few children will go on to develop severe liver disease.

In the severe form, even eliminating fructose and sucrose from the diet may not prevent severe liver disease.

How well a person does depends on how soon the diagnosis is made and how soon fructose and sucrose can be eliminated from the diet.

• 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

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 strict adherence to a fructose-free diet.