TTN and familial dilated cardiomyopathy: While the interpretation of TTNtv remains difficult due to the high frequency of these variants across normal populations and the lack of penetrance, the situation is far more complex for TTN missense variants, which have been identified in patients affected with different cardiac conditions, such as DCM, HCM, arrhythmogenic cardiomyopathy, restrictive cardiomyopathy and left ventricular non-compaction cardiomyopathy (Arimura et al. 2009; Gerull et al. 2002; Hastings et al. 2016; Itoh-Satoh et al. 2002; Matsumoto et al. 2005; Peled et al. 2014; Satoh et al. 1999; Taylor et al. 2011).