Urine turns dark on standing in: (Repeat)

Ans: A (Alkaptonuria) Ref: Harrison's Principles of Internal Medicine 18th edition & Harper's illustrated Biochemistry, 28th edition. Chapter 29, pp 254)Explanation:AlkaptonuriaDue to deficiency in homagentisic acid oxidaseResults in the accumulation of homogentisic acidThe illness has three characteristic symptoms;Homogentisicaciduria (the patient's urine contains elevated levels of homogentisic acid, which is oxidized to a dark pigment on standing,Large joint arthritisBlack ochronotic pigmentation of cartilage and collagenous tissue tOochronsis)Diets low in protein--especially in phenylalanine and tyrosine--help reduce the levels of homogentisic acid, and decrease the amount of pigment deposited in body tissues.Although alkaptonuria is not life-threatening, the associated arthritis may be severely crippling.