Congenital or hereditary fructose intolerance is a genetic condition in which the body is unable to break down the sugar fructose. Fructose is a fruit sugar found in nearly every fruit and vegetable as well as certain processed foods and medications. Fructose intolerance is a rare disease occurring in approximately one in every 22,000 births, according to the HFI Laboratory at Boston University. Although there is no cure, avoiding fructose in the diet can prevent complications from arising.
Definition
In individuals diagnosed with fructose intolerance, the liver enzyme aldolase B is not produced by the body due to a mutation in a specific gene. Aldolase B is responsible for breaking down fructose to be used as energy by the body. The inability to properly break down fructose results in the production of toxic substances that can harm the body, according to MedlinePlus.
Symptoms
Symptoms are generally apparent soon after an infant starts eating food or formula and may include abdominal pain, vomiting, undereating and slow weight gain, neonatal jaundice (yellowing of the skin) and lethargy. More severe symptoms include convulsions and a progression toward liver or kidney disease. Prolonged ingestion of fructose-containing foods can even lead to death, according to Boston University.
Diagnosis
Congenital fructose intolerance is generally first identified by a description of symptoms and is then diagnosed using one of two methods. The first involves a liver biopsy in which a piece of liver tissue is surgically extracted and analyzed for aldolase enzyme activity. The second method is a fructose intolerance test in which fructose is injected into the body and the levels of glucose, fructose and phosphate are measured under controlled conditions, according to Boston University. Both methods may not be ideal for newborn infants, and a presumptive diagnosis may be made through symptom identification and a DNA test.
Treatment
Because no cure exists for congenital fructose intolerance, those with it must follow a strict fructose- and sucrose-free diet to avoid unwanted side effects and complications for the rest of their lives. Sorbitol is converted into fructose in the body and should also be avoided, according to the Mayo Clinic. It is important to check the ingredients label of foods before consumption to identify the presence of these sugars. Common foods such as sports drinks, honey, fruit and fruit juices, certain vegetables and certain medications all may contain fructose.
Fructose Malabsorption
Fructose intolerance must not be confused with another condition called fructose malabsorption, or the inability to absorb fructose in the small intestines, resulting in an accumulation of fructose in the colon. Bacteria in the colon break this fructose down into several gases, leading to gastrointestinal disturbances such as bloating, flatulence, diarrhea and abdominal pain. Individuals may be able to tolerate small amounts of fructose depending on the severity of the disease, and often a low-fructose diet is the recommended treatment. Fructose malabsorption is a less-serious disorder compared with fructose intolerance because it does not cause liver or kidney damage, according to the Mayo Clinic.
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