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': 'The commonest cause of congenital hypothyroidism: September 2012 \nSelect and explain. \nA. Thyroid dysgenesis, B. Pendred syndrome, C. Defective iodine release, D. Deficiency of de-iodinase', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. A i.e. Thyroid dysgenesis Congenital hypothyroidism Large & open posterior fontanelle, Absent social smile & eyebrows, Growth retardation, Delayed pubey, Cold extremities, Large tongue, Prolongation of physiological jaundice & Epiphyseal dysgenesis', 'role': 'assistant'}]