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al·cap·ton·u·ri·a, alkaptonuria (al-kap-ton-yū'rē-ă), [MIM*203500]
Excretion of homogentisic acid (alkapton) in the urine resulting from congenital lack of the enzyme homogentisate 1,2-dioxygenase, which mediates an essential step in the catabolism of phenylalanine and tyrosine; urine turns dark if it is allowed to stand or is alkalinized (a result of formation of polymerization products of homogentisic acid); frequently occurs throughout relatively long periods or may appear at irregular intervals; arthritis and ochronosis are late complications; autosomal recessive inheritance; caused by mutation in the homogentisate 1,2-dioxygenase gene (HGD) on chromosome 3q.
[alkapton + G. ouron, urine]
An inherited disorder that affects phenylalanine and tyrosine metabolism and leads to the excretion of homogentisic acid in the urine.
alkaptonuriaBlack pain disease, black urine disease, alcaptonuria, alcaptonuric ochronosis An AR defect in tyrosine and phenylalanine metabolism, more common in ♂, due to homogentisic acid oxidase–HAO deficiency; metabolic pathway of phenylalanine and tyrosine → ring opening of homogentisic acid → malylacetoacetic acid; alkaptonuria is first recognized by the mother who cannot clean the children's diaper as the urine oxidizes to a pitch black color upon exposure to air Clinical Arthritis due to homogentisic acid deposition in cartilage, tendons, as well as in the sclera, viscera, skin; when severe, pigment deposition can compromise cardiac, renal, or pulmonary function, and spill into the urine as a melanin-like substance. Cf Blue diaper syndrome.
al·cap·to·nu·ri·a, alkaptonuria (al-kap'tŏ-nyūr'ē-ă)
Excretion of homogentisic acid (alkapton) in the urine due to congenital lack of the enzyme homogentisate 1,2-dioxygenase; urine turns dark if allowed to stand; may recur and subside at irregular intervals; arthritis and ochronosis are late complications.
[alkapton + G. ouron, urine]
alkaptonuriaA genetic disease in which a gene mutation on chromosome 3 results in a defective enzyme that leads to the accumulation of a coloured polymer molecule homogentisic acid. This binds to the COLLAGEN of cartilage, making it brittle and easily worn away. The result is a form of OSTEOARTHRITIS. In alkaptonuria, the urine turns black on exposure to light or alkali.
A rare, hereditary, metabolic disorder characterized by dark urine. It is caused by mutation in the homogentisate 1, 2-dioxygenase gene (HGD), which produces an error in the metabolism of the amino acids tyrosine and phenylalanine, which normally break down by oxidation to homogentisic acid. However, in this condition homogentisic acid is not broken down but stored in tissues, especially cartilage, which it turns bluish-black, and excreted in the urine. Ocular signs are pigmentation of the sclera, most markedly near the insertions of the recti muscles, and of the cornea and conjunctiva.