If urine sample darkens on standing, the most likely condition is :: (A) Phenylketonuria, (B) Alkaptonuria, (C) Maple syrup disease, (D) Tyrosinemia
Answer is B. Alkaptonuria a condition d/t defective homogentisate 1, 2- dioxygenase (1/t defective tyrosine degradation) usually presents after age of 40 with characteristic triad of Homogentisic aciduria (which blacken/darkens on exposure to air /standing and is strongly Benedict's positive), Ochronosis (i.e black pigmentation of cailage & collagenous connective tissue), and Ahritis of large joints