A 50-year-old man comes to the clinic for evaluation of chronic back pain. He works as a librarian and notes that the pain is localized to his lower back and worsens after a long day of standing. The pain has not improved despite treatment with ibuprofen. Past medical history is significant for osteoarthritis of his right hip, for which he underwent a total hip replacement 2 years ago. Family history is noncontributory. Temperature is 37.0°C (98.6°F), pulse is 86/min, respirations are 16/min, and blood pressure is 125/85 mmHg. Ophthalmic examination reveals a bluish pigment deposition in the sclera. Dermatological examination reveals hyperpigmentation in the axillary and inguinal regions. Range of motion at the spine is limited. An x-ray of the erect spine is shown below: Osmosis High-Yield Notes Laboratory evaluation reveals elevated levels of homogentisic acid. The production of which of the following end products is likely to be inhibited, considering the most likely diagnosis?

Alkaptonuria is a rare inherited disorder in which a deficiency of an enzyme called homogentisate 1,2 dioxygenase - HGD, results in the accumulation of homogentisic acid in connective tissues. This build-up causes arthritis, increased risk for the formation of renal and gallbladder stones, and the risk of tendon and ligament ruptures. People with alkaptonuria can also present with vision and hearing problems, and have dark urine.

Alkaptonuria

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