Alkaptonuria is a very rare genetically determined hereditary disorder of amino acid metabolism. The disease manifests in childhood and its frequency is only 1 child out of 200,000 live births.


A genetic disorder is the cause of alkaptonuria. A child is born ill when he or she gets from one mutated gene from both parents. Parents do not need to express symptoms of the disease; they are just carriers of the mutated gene.

The presence of mutated gene causes disturbance in metabolism of amino acids phenylalanine and tyrosine. These amino acids are decomposed through complex metabolic pathways and one of metabolic products is called homogentisic acid. This substance is in normal conditions further decomposed but genetic mutation damages proper enzyme function and that leads to accumulation of homogentisic acid in connective tissues and acid excretion into urine.


The urine darkens in contact with air due to high concentration of homogentisic acid . In addition homogentisic acid deposits in joints and causes their inflammation - attacks of pain and swollen joints. Joint cartilage may get darker color. In the urinary tract homogentisic crystal may emerge causing formation of urinary stones with all unpleasant consequences. Deposits of homogentisic acid can also cause darkening of pinna and formation of dark spots in the eyes.


It is very suspicious when child’s nappies darken. When it happens special methods exist to determine the presence and concentration of homogentisic acid in urine and blood. Most precise form of examination is genetic testing.


The disease is genetically determined and inherited and therefore no prevention exists.


No effective therapy exists but it is said that vitamin C has some positive effect. Patients are recommended to a special diet with a lower amount of amino acids tyrosine and phenylalanine but it is virtually impossible to completely avoid these substances. Urologists solve problems with urinary stones. Lucky for the patients with alkaptonuria the disease is not fatal and overall prognosis is quite good.

Jiri Stefanek, MD  Author of texts: Jiri Stefanek, MD
 Sources: basic text sources