GTR Home > Conditions/Phenotypes > Alkaptonuria

Disease characteristics

Excerpted from the GeneReview: Alkaptonuria
Alkaptonuria is caused by deficiency of homogentisate 1,2-dioxygenase, an enzyme that converts homogentisic acid (HGA) to maleylacetoacetic acid in the tyrosine degradation pathway. The three major features of alkaptonuria are the presence of HGA in the urine, ochronosis (bluish-black pigmentation in connective tissue), and arthritis of the spine and larger joints. Oxidation of the HGA excreted in the urine produces a melanin-like product and causes the urine to turn dark upon standing. Ochronosis occurs only after age 30 years; arthritis often begins in the third decade. Other manifestations include pigment deposition, aortic or mitral valve calcification or regurgitation and occasionally aortic dilatation, renal stones, and prostate stones.

Available tests

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Associated genes

Clinical features

  • Hypertension
  • Kyphosis
  • Blue sclerae
  • Pigmentation of the sclera
  • Irregular hyperpigmentation
  • Arthralgia
  • Back pain
  • Reduced bone mineral density
  • Intervertebral disc degeneration
  • Prostatitis
  • Abnormality of the urinary system
  • Hearing abnormality
  • Abnormality of the nose
  • Abnormality of the ear
  • Nephrolithiasis
  • Chondrocalcinosis
  • Arthritis
  • Limitation of joint mobility
  • Joint swelling
  • Growth abnormality
  • Abnormality of the nail
  • Abnormality of the aortic valve
  • Coronary artery disease
  • Coronary artery calcification
  • Mitral stenosis
  • Aortic dilatation
  • Abnormality of metabolism/homeostasis
  • Osteoarthritis
  • Vertebral fusion
  • Arthropathy
  • Aminoaciduria
  • Aortic valve calcification
  • Mitral valve calcification
  • Thickened Achilles tendon
  • Calcification of the auricular cartilage
  • Intervertebral disk calcification
  • Abnormal tendon morphology
  • Calcification of cartilage
  • Cartilage destruction
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