Alkaptonuria: Symptoms & Signs

Medically Reviewed on 9/13/2021

Alkaptonuria is an inherited condition that is caused by a deficiency of the enzyme homogentisic acid (HGA) dioxygenase.

The three main features of alkaptonuria include

  • ochronosis (bluish-black pigmentation in connective tissue),
  • urine that turns black when exposed to air, and
  • arthritis.

The discoloration of connective tissue usually begins after age 30. Other associated signs and symptoms can include

Cause of alkaptonuria

The condition results from an inherited mutation in the homogentisate 1,2-dioxygenase (HGD) gene. This condition is inherited in an autosomal recessive pattern, in which a mutation must be inherited from each parent to cause the condition.

Other alkaptonuria symptoms and signs

  • Arthritis
  • Discoloration of the Earwax
  • Heart Problems
  • Kidney Stones
  • Ochronosis (Bluish-Black Pigmentation in Connective Tissue)
  • Prostate Stones
  • Urine That Turns Black When Exposed to Air

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Jameson, J. Larry, et al. Harrison's Principles of Internal Medicine, 20th Ed. New York: McGraw-Hill Education, 2018.