Background: Dilated cardiomyopathy (DCM), which is characterized by left ventricular enlargement and systolic dysfunction, is divided into cases with a clear predisposing condition (eg, hypothyroidism, chemotherapeutic agents, alcoholism, ischemia) and those of unknown cause (idiopathic DCM). Many cases (20%-35%) of DCM are familial, implicating a genetic contribution to the etiology. More than 30 genes have been identified, many involving ''private'' mutations not shared among families. Evidence suggests that nonfamilial cases also have a genetic predisposition, again involving many genes. The goal of this study was to identify mutations in genes associated with DCM in a Québec study sample including familial and nonfamilial DCM cases. Hypothesis: A prioritized gene study conducted within a framework for the classification of identified genetic variants could yield etiological information even in the absence of family data. Methods: We sequenced 4 previously identified genes: lamin A/C (LMNA), cardiac troponin T type 2 (TNNT2), titin-cap (TCAP), and phospholamban (PLN). Results: We discovered a nonsense mutation in the LMNA gene and a frameshift mutation in the TNNT2 gene, as well as other clinically significant variants that were not observed in publicly available databases or in Québec-based controls. PLN was sequenced to investigate a previously published promoter variant. However, our data confirm that this variant does not have a causal role in DCM. Conclusions: Despite high locus and allele heterogeneity, we demonstrate that a prioritized gene study, combined with next-generation exome-sequencing data, can be fruitful for the identification of DCM mutations. IntroductionDilated cardiomyopathy (DCM) affects 1 in 2500 individuals. 1 It is characterized by left ventricular (LV) enlargement and systolic dysfunction, resulting in impaired heart function that causes significant mortality and morbidity, including heart failure (HF). 2 -4 Idiopathic DCM (IDC) is diagnosed when detectable causes of DCM (eg, hypothyroidism, chemotherapeutic agents, alcoholism, ischemia) are excluded. Clinical screening of first-degree relatives reveals that 20% to 35% of idiopathic cases are familial