This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pediatrics
[{'content': "Darkening of urine on standing is associated with – \nSelect and explain. \nA. Alkaptonuria, B. Cystinuria, C. Fabry's disease, D. Tyrosinemia", 'role': 'user'}, {'content': 'Answer: A \nExplanation: Alkaptonuria\n\nIt is an autosomal recessive disorder.\nIt is due to deficiency of enzyme homogentisic oxidase.\nA large amount of homogentisic acid is accumulated in the body and excreted in urine.\n\nClinical manifestations\n\nClinical features consist of -\n\n\nOchronosis → Dark spot on the sclera or ear cartilage.\nArthritis → Spine, hip, knee.\n\n\nBut both these occur in adulthood.\nThe only sign of disease in children is a blackening of urine on standing. This is caused by oxidation and polymerization of homogentisic acid.\nHigh incidences of heart disease (mitral and aortic valvulitis, calcification of heart valves, MI) have been noted.', 'role': 'assistant'}]