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Causes of Alkaptonuria

Alkaptonuria, a rare genetic disorder, stems from a defect in the HGD gene, causing accumulation of homogentisic acid. This leads to ochronosis and mental health challenges.

  • 12 Mar 2024
  • 2 min read

Alkaptonuria is a health disorder that is very rare and inherited. The condition is also known as black urine disease, whereby a person’s urine turns dark brown or black when exposed to air. The disorder prevents the body from fully breaking down two protein-building amino acids, tyrosine and phenylalanine. The body is unable to produce an enzyme called homogentisic dioxygenase acid (HGD), which discolours the bones and cartilage and makes them brittle. This condition signals the onset of osteoarthritis, especially in the spine and large joint areas. Alkaptonuria is a rare genetic inborn error of protein metabolism. So, what causes alkaptonuria?

What are the Causes of Alkaptonuria?

Alkaptonuria is caused by a defect in the homogentisate 1, 2- dioxygenase (HGD) gene. Studies have found the condition to be autonomously recessive, wherein two inherited copies of the faulty HGD gene (one from each parent) are passed onto the offspring. Generally, the HGD gene provides instructions for making an enzyme called homogentisate oxidase, which is needed to break down homogentisic acid. 

However, in this condition, the body cannot produce enough HGD, resulting in the accumulation of homogentisic acid in the bones and cartilage. This accumulation leads to a condition called ochronosis, which is characterised by a blue-black discolouration of the skin and cartilage. When the homogentisic acid leaves the body through urine, turning the urine brownish-black as it comes in contact with air.

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The causes of alkaptonuria are inherited as it is an autonomous recessive condition arising from

the homogentisate 1, 2- dioxygenase (HGD) gene in the patient. It is a life-long condition that can be overwhelming to the mental health of a patient, triggering anxiousness and depression. Such genetic disorders can be very taxing on the well-being of the patient and their immediate family members, both mentally and financially. Hence, it is always a wise move to seek comprehensive health insurance policy, as doing so will help cover a considerable part of financial expenses.

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