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: Medicine
[{'content': 'Newborn 7 days old with vomiting and dehydration clinical examination was normal except for hyperpigmentation of nipple. Electrolytes Na: 120 meq. K: 9 meq. most likely diagnosis - \nSelect and explain. \nA. Cong, adrenal hyperplasia, B. Primary hypothyroidism, C. Panhypopituitarism, D. Pyloric stenosis', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Congenital adrenal hyperplasia due to a defect in CYP21A2 is suggested by episodes of acute adrenal insufficiency with hyponatremia, hyperkalemia, dehydration & vomiting', 'role': 'assistant'}]