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.