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Alkaptonuria is an inherited condition that causes urine to turn black when exposed to air. Ochronosis, a buildup of dark pigment in connective tissues such as cartilage and skin, is also characteristic of the disorder. This blue-black pigmentation usually appears after age 30. People with alkaptonuria typically develop arthritis, particularly in the spine and large joints, beginning in early adulthood. Other features of this condition can include heart problems, kidney stones, and prostate stones.
This condition is rare, affecting 1 in 250,000 to 1 million people worldwide. Alkaptonuria is more common in certain areas of Slovakia (where it has an incidence of about 1 in 19,000 people) and in the Dominican Republic.
Mutations in the HGD gene cause alkaptonuria.
The HGD gene provides instructions for making an enzyme called homogentisate oxidase. This enzyme helps break down the amino acids phenylalanine and tyrosine, which are important building blocks of proteins. Mutations in the HGD gene impair the enzyme's role in this process. As a result, a substance called homogentisic acid, which is produced as phenylalanine and tyrosine are broken down, accumulates in the body. Excess homogentisic acid and related compounds are deposited in connective tissues, which causes cartilage and skin to darken. Over time, a buildup of this substance in the joints leads to arthritis. Homogentisic acid is also excreted in urine, making the urine turn dark when exposed to air.
This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. Most often, the parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but do not show signs and symptoms of the condition.
'''Alkaptonuria''' also known as '''alcaptonuria''' or '''ochronosis''' is a rare inherited genetic disorder of tyrosine metabolism. This is an autosomal recessive gene that is caused by a defect in the enzyme homogentisic acid oxidase. The enzyme normally breaks down a toxic tyrosine byproduct, homogentisic acid (also called alkapton), which is harmful to bones and cartilage and is excreted in urine. A distinctive characteristic of alkaptonuria is that urine exposed to air turns dark (or black) after several hours because of the homogentisic acid. In adulthood, persons suffering from alkaptonuria develop progressive arthritis (especially of the spine), due to its degenerative effects on bones and cartilage. Prevention is not possible and the treatment is aimed at ameliorating symptoms. [ Read More ]
Alkaptonuria and Ochronosis - A detailed look at these disorders, how it affects the many body parts, diagnosis, diet and treatment are discussed.
Alkaptonuria - A brief discussion about this disease and its statistics world wide. Followed by a case study of a 4 year old boy, whose parents noted the darkening of the urine to an almost black color when it was left standing.
MedicineNet.com : Alkaptonuria - An article about this disease beginning with an explanation as to what it is, followed by how it is inherited, how it affects the joints, symptoms, diagnosis and treatment.
eMedicine Online Text: Alkaptonuria - An in depth look at this disorder written by Karl S Roth, MD. From a description to treatment all aspects of this disease are discussed.
The Alkaptonuria Society - An information and support network for those people diagnosed with Alkaptonuria. Includes discussions, articles and related resources.
The Alkaptonuria Society - Information about this genetic metabolic disorder for patients and professionals. Includes an FAQ, and a registration page for sufferers.