CLINICAL HISTORY AND BACKGROUND
A 2-year-old male was referred to the metabolism service after his mother noticed dark-colored staining on his crib sheets on several occasions. She also noted that the child's urine was normal when he urinated but turned a dark color over a short period of time (Fig. 1A). His past medical history, development and physical exam were unremarkable. The family history however was notable for several maternal relatives with dark-colored urine. His parents were nonconsanguineous. A urine specimen was collected for organic acids analysis by GC-MS. The results are shown in Fig. 1B.
DIAGNOSIS AND SUMMARY
This patient has alkaptonuria, a rare disorder (approximately 1 in 250 000) caused by a deficiency of the enzyme homogentisate 1,2-dioxygenase (HGD3; EC.220.127.116.11). Under normal conditions, …