Hereditary Fructose Intolerance
What else is it called?
- ALDOB deficiency
- aldolase B deficiency
- fructose-1-phosphate aldolase deficiency
- fructose-1,6-biphosphate aldolase deficiency
- fructose aldolase B deficiency
- fructose intolerance
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What causes it?
Hereditary fructose intolerance is caused by mutations (changes) in the ALDOB gene. This gene is responsible for making an enzyme called aldolase B. This enzyme is mainly found in the liver and breaks down fructose into energy. Mutations in the ALDOB gene decrease the function of the enzyme, damaging its ability to metabolize (breakdown/absorb) fructose. This leads to a toxic build up of fructose-1-phosphate in the liver cells which over time will result in the death of liver cells.
How common is it?
Hereditary fructose intolerance is estimated to affect 1 in 20,000 to 30,000 individuals each year worldwide.
What are the signs and symptoms?
Symptoms are usually first seen after a baby starts eating food or formula. Early symptoms are similar to the symptoms of galactosemia (inability to use the sugar galactose) whereas later symptoms are more like liver disease.
Symptoms of HFI include:
- Excessive sleepiness
- Yellow tinge to the skin or whites of the eyes (jaundice)
- Poor feeding and growth as a baby, failure to thrive
- Problems after eating fruits and other foods that contain fructose or sucrose
- Convulsions (spasms/shakings)
- Abdominal pain
- Reduced aldolase levels
How is it diagnosed?
Early diagnosis is very important as patients can live without symptoms when removing fructose from their diet.
Physical examinations by a doctor may show an enlarged liver, enlarged spleen and jaundice (yellowish tinge to the skin and the whites of the eye).
When clinical symptoms, nutritional and family history are suggestive towards HFI, a diagnosis of hereditary fructose intolerance can be confirmed through specialised DNA testing. In rare cases, when no mutation is found, a liver biopsy can be used to determine aldolase activity. A fructose tolerance test may also be used to confirm diagnosis.
Can it be treated?
Hereditary fructose intolerance is treated through a restricted diet by cutting out fructose from the diet. All foods containing fructose, sucrose, and sorbitol should be avoided. Any dietary changes require specialist dietitian’s advice and monitoring. The clinical benefits of removing fructose from the diet are usually seen within a few days. You may also be prescribed with supplements, especially vitamin C and folates to replace the vitamins that may be lacking in the body.
Do my family need to be tested?
Hereditary fructose intolerance is an inherited condition. Humans have chromosomes made up of DNA. Genes are pieces of DNA that carry the genetic information. Each chromosome may have several thousand genes. We inherit chromosomes from the egg of the mother and sperm of the father. The genes on those chromosomes carry the instructions that determine a person’s characteristics, which are a combination of the parents.
The pattern of inheritance of hereditary fructose intolerance is autosomal recessive. This means that carriers of the condition do not have the disorder because the other gene of this pair is working normally. Parents of children with hereditary fructose intolerance are carriers.
When both parents are carriers, the risk to the baby in each pregnancy is:
- 25% chance (1 in 4) of developing the condition
- 50% chance (1 in 2) for the baby to be a carrier of the condition
- 25% chance (1 in 4) for the baby to have two working genes and neither have the condition nor be a carrier
Genetic counselling can be requested to get a full explanation.