This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiomyopathies, Subject name: Medicine
Which of these is not a single gene disorder? 
Select and explain. 
A. Mitral Valve Prolapse, B. Hyperophic Obstructive Cardiomyopathy, C. Dilated Cardiomyopathy, D. Arrhythmogenic Right Ventricular Cardiomyopathy
B: Hyperophic Obstructive Cardiomyopathy
Answer: B: Hyperophic Obstructive Cardiomyopathy 
Explanation: Familial HCM, AD Mendelian inherited disease in approximately 50% of cases. Greater than 100 mutations have been identified in at least 12 sarcomeric genes with b-myosin heavy chain being most frequently affected, followed by myosin-binding protein C and troponin T. These three genes account for 70% to 80% of all cases of HCM. In Arrhythmogenic right ventricular dysplasia the ventricular wall is severely thinned as a result of myocyte replacement by massive fatty infiltration and lesser amounts of fibrosis.