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: Pathology
[{'content': 'True about Fragile X syndrome: \nSelect and explain. \nA. Chromosomal breaking, B. Mitochondrial mutation, C. Triplet nucleotide repeat sequence, D. Centrochrome absent', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Fragile X syndrome is the prototype of the disease in which the mutation is characterized by a long repeating sequences of three nucleotides -\n"Fragile sites are a region of the chromosome that show a tendency for separation, breakage or attenuation under particular growth conditions. One fragile site (of a total of 120 in the human genome) that has clinical significance is that on the distal long arm of chromosome Xql 7.3 associated with fragile syndrome"-\nNelson 18th/515\nFragile X Syndrome - Second most common genetic causes of mental retardation, after Down syndrome\nThe only distinctive feature that can be detected in at least 90% of postpubertal males with fragile -X Syndrome is macroorchidism\n\xa0Long face with a large mandible & large everted ears\n\xa0Hyperextensible joints, a high arched palate & mitral valve prolapsed is noted in some patients\xa0As with all X-linked disease fragile X syndrome affects males', 'role': 'assistant'}]