black urine

A 2yearold boy was born at term of healthy, nonconsanguineous iranian parents. his mother attended in the clinic with the history of sometimes discoloration of diapers after passing urine. she noticed that first at the age of one month with intensified in recent months. his physical examination and growth parameters were normal. his mother denied taking any medication (sorbitol, nitrofurantoin, metronidazole, methocarbamol, sena and methyldopa (5)). qualitative urine examination showed dark black discoloration. by this history, alkaptonuria was the most clinical suspicious. a 24hoururine sle was collected and sent for quantitative measurements. the urine sle was highly positive for homogentisic acid and negative for porphyrin metabolites.