Essential fructosuria
{{Infobox medical condition (new)
| name = Essential fructosuria
| image = Fructose.svg
| caption = Fructose
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| field = Medical genetics
| synonyms = Ketohexokinase deficiency{{Cite web |title=Essential fructosuria |url=https://www.orpha.net/consor/cgi-bin/OC_Exp.php?lng=EN&Expert=2056 |access-date=11 April 2019 |website=Orphanet}}
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Essential fructosuria, caused by a deficiency of the enzyme hepatic fructokinase, is a clinically benign condition characterized by the incomplete metabolism of fructose in the liver, leading to its excretion in urine.{{Cite book |last=Steinmann |first=Beat |title=Inborn Metabolic Diseases: Diagnosis and Treatment |last2=Santer |first2=Rene |publisher=Springer |year=2012 |isbn=978-3-642-15719-6 |editor-last=Saudubray |editor-first=Jean-Marie |edition=5th |location=New York |pages=157–165 |chapter=Disorders of Fructose Metabolism |editor-last2=van den Berghe |editor-first2=Georges |editor-last3=Walter |editor-first3=John H. |name-list-style=vanc}} Fructokinase (sometimes called ketohexokinase) is the first enzyme involved in the degradation of fructose to fructose-1-phosphate in the liver.{{OMIM|229800}}
This defective degradation does not cause any clinical symptoms, fructose is either excreted unchanged in the urine or metabolized to fructose-6-phosphate by alternate pathways in the body, most commonly by hexokinase in adipose tissue and muscle.
Signs and symptoms
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Cause
Essential fructosuria is a genetic condition that is inherited in an autosomal recessive manner. Mutations in the KHK gene, located on chromosome 2p23.3-23.2 are responsible. The incidence of essential fructosuria has been estimated at 1:130,000.{{Cite book |last=Steinmann |first=Beat |title=Inborn Metabolic Diseases. Diagnosis and Treatment. |last2=Santer |first2=René |last3=van den Berghe |first3=Georges |date=2006 |publisher=Springer |isbn=978-3-540-28783-4 |editor-last=Berghe |editor-first=Georges |edition=fourth |page=137 |chapter=9.1 Essential Fructosuria] |editor-last2=Fernandes |editor-first2=John |editor-last3=Saudubray |editor-first3=Jean-Marie |editor-last4=Walter |editor-first4=John H |chapter-url=http://eknygos.lsmuni.lt/springer/223/II%20Part/135-142.pdf |name-list-style=vanc}} The actual incidence is likely higher, because those affected are asymptomatic.{{cn|date=September 2021}}
Diagnosis
A diagnosis of essential fructosuria is typically made after a positive routine test for reducing sugars in the urine. An additional test with glucose oxidase must also be carried out (with a negative result indicating essential fructosuria) as a positive test for reducing sugars is most often a result of glucosuria secondary to diabetes mellitus. The excretion of fructose in the urine is not constant, it depends largely on dietary intake.{{Cite journal |vauthors=Tran C |date=April 2017 |title=Inborn Errors of Fructose Metabolism. What Can We Learn from Them? |journal=Nutrients |volume=9 |issue=4 |page=356 |doi=10.3390/nu9040356 |pmc=5409695 |pmid=28368361 |doi-access=free}}
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.{{Cite book |last=Katz |first=Jordan |title=Anesthesia and Uncommon Diseases |last2=Benumof |first2=Jonathan |last3=Kadis |first3=Leslie B |date=1990 |publisher=Saunders |isbn=978-0-7216-2367-2 |edition=third |location=Philadelphia |name-list-style=vanc}} Other errors in fructose metabolism have greater clinical significance. Hereditary fructose intolerance, or the presence of fructose in the blood (fructosemia), is caused by a deficiency of aldolase B, the second enzyme involved in the metabolism of fructose. {{cn|date=September 2021}}
This enzyme deficiency results in an accumulation of fructose-1-phosphate, which inhibits the production of glucose and results in diminished regeneration of adenosine triphosphate. Clinically, patients with hereditary fructose intolerance are much more severely affected than those with essential fructosuria, with elevated uric acid, growth abnormalities and can result in coma if untreated.
References
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External links
{{Medical resources
|DiseasesDB = 5001
|ICD10 = {{ICD10|E|74|1|e|70}}
|ICD9 = {{ICD9|271.2}}
|ICDO = |
|OMIM = 229800
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{{Carbohydrate metabolic pathology}}