This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Musculoskeletal  disorders, Subject name: Pediatrics
[{'content': 'An infant present with hypotonia and hyporeflexia with significant prenatal history of polyhydraminos and decreased fetal movements. What do you suspect? \nSelect and explain. \nA. Spinal muscular atrophy, B. Classical myotonic dystrophy, C. Duchenne muscular dystrophy, D. Emery-Dreifuss syndrome', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Among the given options, only spinal muscular atrophy presents in infancy and the rest in late childhood. Spinal Muscular atrophy (SMA) It is a degenerative disease of motor neurons, caused by the mutation of SMN gene with autosomal-recessive inheritance. Clinical features: Usually stas in infancy with hypotonia, hyporeflexia, and thin muscle mass Diagnosis: Genetic testing for SMN gene mutation. Muscle biopsy for cases of negative genetic testing. Treatment: Symptomatic and suppoive Ref: nelson textbook of pediatrics 21st edition Pgno: 3246', 'role': 'assistant'}]