<prompt> Darkening of urine on standing is associated with:AlkaptonuriaCystinuriaFabrys diseaseTyrosinemia  <response>: a. AlkaptonuriaRef: Nelsons 20e p 636-642, Ghai 8e p 653-655Darkening of urine on standing is associated with Alkaptonuria, due to Homogentisic acid oxidase deficiency. 