Q. A 21-year-old man comes to the college clinic before joining the baseball team. He currently has no symptoms. His past medical history is not significant for any medical or psychiatric condition. The patient's family history is positive for sudden cardiac death in the patient's brother at age 35. The patient's vital signs are normal. ECG shows no abnormality apart from poor R wave progression. The college physician asks for an echocardiography which shows focal septal hypertrophy and mitral regurgitation. Which of the following is the most common mutated gene in the above patient?