<prompt> Which of the following conditions is associated with darkening of urine on standing?AlkaptonuriaCystinuriaFabrys diseaseTyrosinemia  <response>: Characteristic sign of alkaptonuria is darkening of urine on standing, especially if the urine is alkaline. Ref: Harrisons 16th Edition, Page 2334; Essential Pediatrics, OP Ghai - 6th Edition, Page 610; Nelsons Paediatrics 17th Edition, Page 403; Lippincotts 3rd Edition, Page 272. 