Heart conditions known as cardiomyopathies include two main subtypes, namely the hypertrophic and dilated cardiomyopathies, in which some portions of the cardiac muscle become stiff or dilated, respectively. Drugs such as the calcium channel blocker verapamil are used to treat the former, while the Na?-K? ATPase inhibitor digoxin (which elevates intracellular calcium concentration in cardiac muscle cells) is sometimes used for the latter. Mutations in the subunits of the troponin complex are among the genetic causes of these diseases, and can be grouped into mutations that result in either decreased (D) or increased (I) calcium-ion sensitivity of actin-myosin contraction. Which of these mutations would you expect to be associated with hypertrophic cardiomyopathy? Write down D or I as your answer.