Alkaptonuria is a disorder, which is rare and is inherited by generations. It happens when your body can not produce homogentisate dioxygenase (HGD) enzyme enough for the body to breakdown the homogentisic acid, which is toxic to the body.

Homogentisic acid is produced more when your body cannot provide the homogentisic dioxygenase enzyme. This build-up causes bones and cartilages to be brittle and somehow discolored, which leads to osteoarthritis, especially in the spine and large joints. Alkaptonuria patients have urine that turns dark when exposed to air.


What causes Alkaptonuria?

Alkaptonuria is caused by the changes in genes or mutations, especially on the homogentisate 1,2- dioxygenase gene. This is acquired when both of your parents have these genes and are passed into the child.

Alkaptonuria, known to be rare, has an unknown number of cases. But it is estimated to be acquired by people in only one out of every 250,000 to 1 million people. There are places where Alkaptonuria is more commonly found; these places are in some regions of Slovakia, Germany, and the Dominican Republic.


The earliest signs of having Alkaptonuria occur in childhood. Children may have dark stains on their diapers. But symptoms are easily spotted as you age, like in the urine. People with Alkaptonuria have urine that turns dark when exposed to air. People aged 20 to 20 years old may notice symptoms of early osteoarthritis like chronic stiffness or having pain in the lower back portion of the large joints.

Other symptoms include;

  • Dark spots in the white of your eyes
  • Thickened and darkened ear cartilage
  • Blue speckled discoloration of the skin, especially in the sweat glands
  • Sweat and sweat stainsthat are dark-colored
  • Earwax is black
  • Having kidney stones or prostate stones

Alkaptonuria may also lead to heart problems because the heart valves are hardened due to the build-up of homogentisic acid. It keeps the valves closed, causing aortic and mitral valve disorders.


Diagnosing alkaptonuria is often successful, especially with the help of family history. However, people do not realize that they are carrying the gene until they have symptoms.

The first thing that your doctor might notice if you have alkaptonuria is your urine when it turns brown or dark when exposed to air. Your doctor might also test you if you have developed the condition of early-onset osteoarthritis.

Your doctor can use DNA testing for checking if there are mutated genes in your blood. They also use a test to look for traces of homogentisic acid in your urine called gas chromatography.



If you are having alkaptonuria, your doctor may ask you to start a low-protein diet and may recommend large doses of ascorbic acid or vitamin C to slow down homogentisic acid build up in your cartilage. But long term use of Vitamin C has been proven ineffective for treating alkaptonuria, according to NORD.

If you’re given treatments for alkaptonuria, it may not be for the condition itself because there no cure for alkaptonuria as of the moment. Still, it is used to prevent and relieve complications such as arthritis, heart disease, and kidney stones.

Researchers are currently studying nitisinone as a possible treatment for alkaptonuria, but it may need time for it to get approved.

Related Articles


Overview and FactsTypes and SymptomsDiagnosis & MedicationsOverview and Facts Referred pain is a phenomenon where pain is perceived at a [...]


Overview and FactsTypes and SymptomsDiagnosis & MedicationsOverview and Facts Quinoline yellow is a synthetic food colorant commonly used in the [...]


Overview and FactsTypes and SymptomsDiagnosis & MedicationsOverview and Facts Pneumothorax is a condition characterized by the presence of air in [...]