This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: FMGE 2018, Subject name: Pediatrics
[{'content': 'Marble bone disease is? \nSelect and explain. \nA. Osteopetrosis, B. Osteomalacia, C. Osteosclerosis, D. Histiocytosis X', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Osteopetrosis/ marble bone disease: * Bone within bone appearance on xray (increased bone density) * Due to mutation in CLCN7 gene. * Leads to defective bone resorption * C/F: Neurological problems present, Deafness, Macrocephaly , hepatosplenomegaly, Pancytopenia * Investigation: Low phosphorus and calcium levels with normal Vit D levels and elevated PTH.', 'role': 'assistant'}]