Familial hypertrophic cardiomyopathy is most likely to be secondary to a mutation in:
a) Myosin regulatory proteins
b) Myosin binding protein-C
c) Myosin light chains
d) Troponin I
e) Troponin T
The correct answer is B
Molecular genetic research has demonstrated that familial hypertrophic cardiomyopathy is caused by a mutation in one of nine genes that encode sarcomere proteins. Sarcomeres are the contractile units within the cardiac cells; these are composed of many proteins that are organized into thin and thick filaments. These filaments slide with respect to each other during cardiac contraction.
Mutations in thick filament proteins called cardiac B myosin heavy chain or cardiac myosin binding protein-C appear to account for approximately 82% of hypertrophic cardiomyopathy. Mutations in thin filament proteins cardiac troponin T and a tropomyosin account for about 13% of hypertrophic cardiomyopathy. Mutations in two other sarcomere proteins, the myosin regulatory and essential light chains are quite rare and contribute less than 5% to hypertrophic cardiomyopathy. Although these percentages are only estimates, they indicate that more disease-causing genes will be identified.
A tenth gene has been identified that is a non-sarcomere protein (a subunit of protein kinase A) is associated with individuals who have both hypertrophic cardiomyopathy and Wolf-Parkinson-White syndrome.