TTN and familial dilated cardiomyopathy: For four of these loci, the top gene according to OPEN had been shown to be mutated in DCM (PLN, ACTN2, TNNT2, TTN) [39], while for two others, the top gene was known to be mutated in HCM (MYL2) or an arrhythmogenic form of cardiac disease (CASQ2) [40].