Introduction

Alkaptonuria, or 'black urine disease', is a very rare inherited disorder that prevents the body fully breaking down two protein building blocks (amino acids) called tyrosine and phenylalanine.

It results in a build-up of a chemical called homogentisic acid in the body.

Thiscan turn urine and parts of the body a dark colour andlead to a range of problems over time.

Normally, amino acids are broken down in a series of chemical reactions. But in alkaptonuria, a substance produced along the way homogentisic acid cannot be broken down any further.

This is becausethe enzyme that normally breaks it down doesn't work properly (enzymes are proteins thatmake chemical reactions happen).

One of the earliest signs of the condition is dark-stained nappies, as homogentisic acid causes urine to turn black when exposed to air for a few hours.

If this sign is missed or overlooked, the disorder may go unnoticed until adulthood, as there are usually no other noticeable symptoms until the person reaches their late 20s to early 30s.

Content supplied by the NHS Website

Medically Reviewed by a doctor on 30 Nov 2016