Alkaptonuria

Infobox_Disease
Name = PAGENAME


Caption = Homogentisic acid
Width = 180
DiseasesDB = 409
ICD10 = ICD10|E|70|2|e|70
ICD9 = ICD9|270.2
ICDO =
OMIM = 203500
MedlinePlus =
eMedicineSubj = ped
eMedicineTopic = 64
MeshID = D000474

Alkaptonuria (black urine disease or alcaptonuria) is a rare inherited genetic disorder of tyrosine metabolism. This is an autosomal recessive condition that is due to a defect in the enzyme homogentisate 1,2-dioxygenase (EC number|1.13.11.5), which participates in the degradation of tyrosine. As a result, a toxic tyrosine byproduct called homogentisic acid (or alkapton) accumulates in the blood, and is excreted in urine in large amounts(hence "-uria"). Excessive homogentisic acid causes damage to cartilage (ochronosis, leading to osteoarthritis) and heart valves as well as precipitating as kidney stones. Treatment with nitisinone, which suppresses homogentisic acid production, is being studied.cite journal |author=Phornphutkul C, Introne WJ, Perry MB, "et al" |title=Natural history of alkaptonuria |journal=New England Journal Medicine |volume=347 |issue=26 |pages=2111–21 |year=2002 |pmid=12501223 |doi=10.1056/NEJMoa021736| url=http://content.nejm.org/cgi/content/full/347/26/2111] Alkaptonuria is more common in Slovakia and the Dominican Republic than in other countries.cite journal |author=Zatková A, de Bernabé DB, Poláková H, "et al" |title=High frequency of alkaptonuria in Slovakia: evidence for the appearance of multiple mutations in HGO involving different mutational hot spots |journal=American Journal of Human Genetics |volume=67 |issue=5 |pages=1333–9 |year=2000 |pmid=11017803 |doi=] cite journal |author=Milch RA |title=Studies of Alcaptonuria: Inheritance of 47 Cases in Eight Highly Inter-related Dominican Kindreds |journal=Am. J. Hum. Genet. |volume=12 |issue=1 |pages=76–85 |year=1960 |pmid=17948450 PMC|1932065]

igns and symptoms

Alkaptonuria itself is asymptomatic, but the sclera of the eyes may be pigmented (often only at a later age) and the skin is darkened in sun-exposed areas as well as around sweat glands; sweat may be coloured brown. Urine may turn brown on standing, especially when left for a period of time (which may alert parents of children using diapers).Fact|date=December 2007 Kidney stones and stone formation in the prostate (in men) are common, and may occur in more than a quarter of cases.

The main symptoms of alkaptonuria are due to the accumulation of homogentisic acid in tissues. In the joints this leads to cartilage damage, specifically in the spine and leading to low back pain at a young age in most cases, but also of the hip and shoulder. Joint replacement surgery (hip and shoulder) is often necessary at a relatively young age.

Valvular heart disease, mainly calcification and regurgitation of the aortic and mitral valves, may occur, and in severe and progressive cases valve replacement may be necessary. Coronary artery disease may be accelerated in alkaptonuria.

A distinctive characteristic of alkaptonuria is that ear wax exposed to air turns red or black (depending on diet) after several hours because of the accumulation of homogentisic acid.cite journal |author=Srsen S |title=Dark pigmentation of ear cerumen in alkaptonuria |journal=Lancet |volume=2 |issue=8089 |pages=577 |year=1978 |pmid=79943 |doi=10.1016/S0140-6736(78)92912-4]

Diagnosis

The diagnosis of alkaptonuria needs to be suspected before diagnostic testing can be performed, using paper chromatography and thin layer chromatography. Both blood plasma and urine can be used for diagnosis. In healthy subjects, homogentisic acid is absent in both blood and plasma. In alkaptonuria, plasma levels are 6.6 micrograms/ml on average, and urine levels are on average 3.12 mmol/mmol of creatinine.

Pathophysiology

Homogentisic acid is a natural intermediary of the metabolism of tyrosine, an amino acid. Hepatic homogentisate 1,2-dioxygenase (coded by the "HGD" gene) metabolises homogentisic acid into 4-maleylacetoacetate. Alkaptonuria arises in people who have inherited two abnormal "HGD" genes: one from each parent. Numerous different "HGD" mutations have been identified.

In a patient who underwent a liver transplant for an unrelated problem, alkaptonuria resolved and joint disease stabilised after the transplant, confirming that the liver is the main site of homogentisic acid production in alkaptonuria. [cite journal |author=Kobak AC, Oder G, Kobak S, Argin M, Inal V |title=Ochronotic arthropathy: disappearance of alkaptonuria after liver transplantation for hepatitis B-related cirrhosis |journal=Journal of Clinical Rheumatology |volume=11 |issue=6 |pages=323–5 |year=2005 |pmid=16371803 |doi=]

Treatment

No treatment modality has been unequivocally demonstrated to reduce the complications of alkaptonuria. Commonly recommended treatments include dietary restriction of phenylalanine and tyrosine and large doses of ascorbic acid (vitamin C). Dietary restriction may be effective in children, but benefits in adults have not been demonstrated. [cite journal |author=de Haas V, Carbasius Weber EC, de Klerk JB, "et al" |title=The success of dietary protein restriction in alkaptonuria patients is age-dependent |journal=Journal of Inherited Metabolic Disease |volume=21 |issue=8 |pages=791–8 |year=1998 |pmid=9870204 |doi=]

The insecticide nitisinone inhibits 4-hydroxyphenylpyruvate dioxygenase, the enzyme that generates homogentisic acid from 4-hydroxyphenylpyruvic acid. This reduces homogentisic acid. The main side-effect is irritation of the cornea, and there is a concern that it will cause the symptoms of hereditary tyrosinaemia type III because of the possible accumulation of tyrosine or other intermediaries. [cite journal |author=Suwannarat P, O'Brien K, Perry MB, "et al" |title=Use of nitisinone in patients with alkaptonuria |journal=Metabolism: Clinical and Experimental |volume=54 |issue=6 |pages=719–28 |year=2005 |pmid=15931605 |doi=10.1016/j.metabol.2004.12.017] Further studies are being conducted. [ClinicalTrials|NCT00107783]

Epidemiology

In Slovakia the disease occurs in 1:19,000 people. In other ethnic groups, the normal prevalence is between 1:100,000 and 1:250,000. It is reported frequently in the Dominican Republic, but exact prevalence there is not known.

History

Alkaptonuria was one of the four diseases described by Sir Archibald Edward Garrod, as being the result of the accumulation of intermediates due to metabolic deficiencies. He linked ochronosis with the accumulation of alkaptans in 1902, [cite journal|author=Garrod AE|year=1902|title=The incidence of alkaptonuria: a study in clinical individuality|journal=Lancet|volume=2|pages=1616−1620|doi=10.1016/S0140-6736(01)41972-6 Reproduced in cite journal | author=Garrod AE| title=The incidence of alkaptonuria: a study in clinical individuality|journal=Yale Journal of Biology and Medicine | volume=75 | pages=221–31 |year=2002| pmid=12784973] and his views on the subject, including its mode of heritance, were summarised in a 1908 Croonian lecture at the Royal College of Physicians. [cite journal|author=Garrod AE|year=1908|title=The Croonian lectures on inborn errors of metabolism: lecture II: alkaptonuria|journal=Lancet|volume=2|pages=73–79] The defect was narrowed down to homogentisic acid oxidase deficiency in a study published in 1958. [cite journal |author=La Du BN, Zannoni VG, Laster L, Seegmiller JE |title=The nature of the defect in tyrosine metabolism in alcaptonuria |journal= Journal of Biological Chemistry |volume=230 |issue=1 |pages=251–60 |year=1958 |pmid=13502394 |url=http://www.jbc.org/cgi/reprint/230/1/251|format=PDF] The genetic basis was elucidated in 1996, when HGO mutations were demonstrated. [cite journal |author=Fernández-Cañón JM, Granadino B, Beltrán-Valero de Bernabé D, "et al" |title=The molecular basis of alkaptonuria |journal=Nature Genetics |volume=14 |issue=1 |pages=19–24 |year=1996 |pmid=8782815 |doi=10.1038/ng0996-19]

A 1977 study showed that an ochronotic Egyptian mummy had probably suffered from alkaptonuria. [cite journal |author=Stenn FF, Milgram JW, Lee SL, Weigand RJ, Veis A |title=Biochemical identification of homogentisic acid pigment in an ochronotic egyptian mummy |journal=Science |volume=197 |issue=4303 |pages=566–8 |year=1977 |pmid=327549 |doi= 10.1126/science.327549]

ee also

* Ochronosis
* Tyrosinemia

References

External links

* [http://www.alkaptonuria.info/ Alkaptonuria Society (UK)]