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Fructosuria is a rare but benign inherited metabolic disorder. It is characterized by the excretion of fruit sugar (fructose) in the urine. Normally, no fructose is excreted in the urine. This condition is caused by a deficiency of the enzyme fructokinase in the liver. This enzyme is needed for the synthesis of glycogen (the body's form of stored energy) from fructose. The presence of fructose in the blood and urine may lead to an incorrect diagnosis of diabetes mellitus.
Fructosuria is characterized by the presence of fructose in the urine. There are no other symptoms. However, the fructose may be mistaken for glucose (blood sugar) leading to an incorrect diagnosis of Diabetes Mellitus.
Fructosuria is a rare hereditary disorder transmitted as an autosomal recessive trait. The defective gene has been mapped to the Gene Map Locus 2p23.3-p23.2. Chromosomes, which are present in the nucleus of human cells, carry the genetic characteristics of each individual. Pairs of human chromosomes are numbered from 1 through 22, with an unequal 23rd pair of X and Y chromosomes for males, and two X chromosomes for females. Each chromosome has a short arm designated as "p" and a long arm identified by the letter "q". Chromosomes are further subdivided into many bands that are numbered. For example, chromosome 2p23.3 refers to band 23 on the short arm of chromosome 2.
Recessive genetic disorders occur when an individual inherits the same abnormal gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the defective gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents and be genetically normal for that particular trait is 25%. The risk is the same for males and females.
All individuals carry 4-5 abnormal genes. Parents who are close relatives (consanguineous) have a higher chance than unrelated parents to both carry the same abnormal gene, which increases the risk to have children with a recessive genetic disorder.
Fructosuria affects about 1 out of every 130,000 persons in the United States. It affects males and females in equal numbers.
Comparison of the following disorder with Fructosuria may be useful for a differential diagnosis:
Diabetes Mellitus is a common disorder in which the body does not produce enough insulin and is, therefore, unable to convert nutrients into the energy necessary for daily activity. The disorder affects females and males approximately equally. Although the causes of Insulin-Dependent Diabetes are not known, genetic factors seem to play a role. Symptoms of Diabetes Mellitus can be very debilitating if left untreated, whereas Fructosuria does not cause excessive thirst, weight loss or fatigue. (For more information, choose "Diabetes" as your search term in the Rare Disease Database.)
Diagnosis of Fructosuria is made by testing the urine for the presence of fructose. Fructosuria does not require treatment as the symptoms are harmless.
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NORD Guide to Rare Disorders. Lippincott Williams & Wilkins. Philadelphia, PA. 2003:444-45.
Gitzelmann R, Steinmann B, Van den Berghe G. In: Scriver CR, Beaudet AL, Sly WS, et al. Eds. The Metabolic Molecular Basis of Inherited Disease. 7th ed. McGraw-Hill Companies. New York, NY; 1995:905-34.
Kozak M, Hayward B, Borek D, et al. Expression, purification and preliminary crystallographic studies of human ketohexokinase. Acta Crystallogr D Biol Crystallogr. 2001;57:586-88.
Boesiger P, Buchli R, Meier D, et al. Changes in liver metabolite concentrations in adults with disorders of fructose metabolism after intravenous fructose by 31P magnetic resonance spectroscopy. Pediatr Res. 1994;36:436-40.
Bonthron DT, Brady N, Donaldson IA, et al. Molecular basis of essential fructosuria: molecular cloning and mutational analysis of human ketohexokinase (fructokinase). Hum Mol Genet. 1994;3:1627-31.
Froesch ER. Disorders of fructose metabolism. 1976;5:599-611.
FROM THE INTERNET
McKusick VA, Ed. Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Entry Number; 229800: Last Edit Date; 11/1/1996.
Fructose Metabolism. nd. 4pp.
Monosaccharides and interconversion of sugars. Lecture 21. Dated: September 23, 2002:7pp.
Benign Fructosuria. PEDBASE. Last Updated: 8/01/1994:2pp.
Report last updated: 2007/09/17 00:00:00 GMT+0