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A 40-year-old presents with premature arthritis of the spine and large joints. His urine turns dark when left standing. On exam, his ear cartilage appears bluish-black (ochronosis).
AR; HGD (homogentisate 1,2-dioxygenase)
- Dark urine (homogentisic acid oxidizes)
- Ochronosis (bluish-black pigmentation of cartilage, sclera)
- Premature degenerative arthritis (spine, large joints)
- Cardiac valve disease
- Kidney stones
- Urine homogentisic acid elevated; dark urine on standing
- Nitisinone (reduces homogentisic acid); symptomatic management
"Ow, my Knee Kap hurts a ton": "Ow-Kap-ton-uria" recalls the early-onset osteoarthritis from homogentisic acid toxicity to cartilage.
AKU = Arthritis, Kardiac Kalcification (aortic/mitral valve), Kidney stones, dArK Urine and Cartilage damage.
"Kartilage in alKaptonuria": homogentisic acid accumulates in cartilage. "Blkaptonuria": affected tissues (nose, ears, sclera, joints) are dark (ochronosis).