Which of the following conditions is associated with darkening of urine on standing?
Alkaptonuria
Cystinuria
Fabry's disease
Tyrosinemia
Characteristic sign of alkaptonuria is darkening of urine on standing, especially if the urine is alkaline. Ref: Harrison's 16th Edition, Page 2334; Essential Pediatrics, OP Ghai - 6th Edition, Page 610; Nelson's Paediatrics 17th Edition, Page 403; Lippincotts 3rd Edition, Page 272.