<prompt> Which protein is defective most commonly in dilated cardiomyopathy?DystrophinTropomyosinTitinTroponin  <response>: In dilated cardiomyopathy, mutations in TTN, a gene that encodes titin so-called because it is the largest protein expressed in humans, may account for approximately 20 of all cases of DCM. Additionally, mutations affecting the membrane-associated dystrophin protein that couples cytoskeleton to the extracellular matrix are also repoed. 