TTN and familial dilated cardiomyopathy: DCM is highly genetically heterogeneous, with up to ~60 implicated genes.20,25,26 In the clinical cohorts, truncating variants in TTN were most common (14.6%), in accordance with our findings in large research cohorts.27,28 The prevalence of rare variants in other well-characterized DCM genes was modest (MYH7, 5.3%; LMNA, 4.4%; TNNT2, 2.9%; and TPM1, 1.9%) but significantly enriched compared with ExAC (Figure 1 and Table 1 and Supplementary Table S5b online).