A 40 yr old woman presents with progressive palmoplantar pigmentation. X-ray spine shows calcification of intervertebral discs. Adding Benedict’s reagent to urine, gives greenish brown precipitate and blue-black supernatant fluid. What is the diagnosis?
B. Alkapt onuria
C. Tyrosinemia type-2
D. Argininosuccinic aciduria
Ans.B. Alkaptonuria/Black urine disease
- It is a rare inherited genetic disorder of phenylalanine and tyrosine metabolism.
- This is an autosomal recessive condition that is due to a defect in the enzyme homogentisate 1,2-dioxygenase, which participates in the degradation of tyrosine.
- As a result, homogentisic acid and its oxide, called alkapton, accumulate in the blood and are excreted in the urine in large amounts (hence -uria).
- Excessive homogentisic acid causes damage to the cartilage (ochronosis, leading to osteoarthritis) and heart valves as well as precipitating as kidney stones.