Fructosuria: Description, Causes and Risk Factors: FructosuriaFructosuria 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 affects about 1 out of every 130,000 persons in the United States. It affects males and females in equal numbers. Fructosuria is a rare hereditary disorder transmitted as an autosomal-recessive trait. The defective gene has been mapped to the Gene map locus 2p23.2-p23.3. 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. Symptoms: Newborns are asymptomatic as long as they are on breast milk or formulas lacking sucrose. Acute symptoms develop as soon as formulas or solid food containing fructose or sucrose are introduced. Acute symptoms include nausea, vomiting, and refusal to eat. Hypoglycemic episodes results in sweating, trembling, convulsions, lethargy, and coma. Diagnosis: Diagnosis of fructosuria is made by testing the urine for the presence of fructose. Histologically, liver tissue shows fatty infiltration of hepatic cells, scattered necrosis or hepatocytes, biliary duct proliferation, and periportal, as well as intralobular fibrosis. Tests: Phenylhydrazine test.
  • Fructose tolerance test.
  • Seliwanoff test.
Traditionally, definitive diagnosis requires an enzyme assay in liver or intestinal biopsy specimens as this enzyme is not normally found in circulation. A liver biopsy is preferred as this allows assessment of liver tissue damage. Currently, more than 95% of HFI (hereditary fructose intolerance) cases can be diagnosed through amplification of DNA with a limited number of allele-specific oligonucleotide probe circumventing the need for a tissue biopsy. Treatment: No treatment is indicated for essential fructosuria, while the degree of fructosuria depends on the dietary fructose intake, it does not have any clinical manifestations. The amount of fructose routinely lost in urine is quite small. Fructose and sucrose must be restricted in the diet. Long-term management includes complete avoidance of fructose, sucrose, and sorbitol, avoidance of fasting, and following a diet which is low in fat, high in carbohydrate, and moderate in protein. NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.  


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