A 3-year-old boy is brought to the office by his parents due to a concern of abnormal urine color. After he urinated in the toilet last night, his parents forgot to flush the toilet and noticed that the boy's urine turned black overnight. The child has no significant past medical history and takes no medications. He has no abnormal growth and developmental milestone. Examination shows a well-nourished child with no swelling or tenderness of any joints. Urinalysis results are as follows: Which of the following conversion pathways is most likely deficient in this patient?

Question

A 3-year-old boy is brought to the office by his parents due to a concern of abnormal urine color.  After he urinated in the toilet last night, his parents forgot to flush the toilet and noticed that the boy's urine turned black overnight.  The child has no significant past medical history and takes no medications. He has no abnormal growth and developmental milestone.  Examination shows a well-nourished child with no swelling or tenderness of any joints.  Urinalysis results are as follows:  Which of the following conversion pathways is most likely deficient in this patient?

Quizplus · Accepted Answer

Eductional Objective: Alkaptonuria is an autosomal recessive disorder in which the lack of homogentisic acid dioxygenase blocks the metabolism of tyrosine, leading to an accumulation of homogentisic acid.  Clinical features include a black urine color when exposed to air, a blue-black pigmentation on the face, and ochronotic arthropathy.

A 3-Year-Old Boy Is Brought to the Office by His