Symptoms:

Urine in an infant's diaper may darken and can turn almost black after several hours. However, many persons with this condition may not know they have it until mid-adulthood, around age 40, when joint and other problems occur.

Symptoms may include:

• Progressive arthritis, especially of the spine
• Darkening of the ear
• Dark spots on the white of the eye (sclera) and cornea

Signs and tests:

A urine test (urinalysis) is done to test for alkaptonuria. If ferric chloride is added to the urine, it will turn the urine a black color in patients with this condition.