<prompt> If urine sample darkens on standing, the most likely condition is :PhenylketonuriaAlkaptonuriaMaple syrup diseaseTyrosinemia  <response>: Alkaptonuria a condition dt defective homogentisate 1, 2- dioxygenase 1t defective tyrosine degradation usually presents after age of 40 with characteristic triad of Homogentisic aciduria which blackendarkens on exposure to air standing and is strongly Benedicts positive, Ochronosis i.e black pigmentation of cailage collagenous connective tissue, and Ahritis of large joints 