A 15-year-old survived a sudden cardiac death caused by vent…

A 15-year-old survived a sudden cardiac death caused by ventricular arrhythmia during a soccer match. He had an uncle who passed away at a young age due to uncertain etiology. On physical examination, the resident hears a harsh systolic murmur, which increases in intensity during valsalva and standing up. Which of the following is the most likely cause for the patient’s physical findings?