Dilated cardiomyopathy (DCM) is a myocardial disease characterized by left ventricular (LV) dilatation and systolic dysfunction.1 In a subgroup of DCM patients, the disease progresses to a terminal stage, requiring heart transplantation (HT), despite current pharmacological and device therapies. This unfavorable progression may be due to various factors, such as an aggressive initial toxic insult, initiation of therapy late in the course of the disease, or, especially, the presence of an adverse genetic background or of harmful genetic interactions with environmental factors. Based on family screening studies, the percentage of inheritable disease (causality attributed to genetic factors) is estimated to be over 30-50% in so-called idiopathic cases.2 Examples of deleterious variants associated with sudden cardiac death or evolution to terminal DCM have been particularly reported in the LMNA gene.3 Bearing these issues in mind, it is important to explore the molecular mechanisms involved in failure to respond to therapy, knowledge of which is necessary to develop further alternative therapeutic strategies in heart failure syndromes. Until now, assessment of DCM genetics has been hampered by genetic heterogeneity between families, with more than 50 different genes associated with DCM4 and with most of the known genes, except titin, accounting for fewer than 10% of cases.5 The recent development of next-generation sequencing (NGS) techniques has enabled identification of a large and growing number of genetic variants in DCM patients,6 but the major challenge with this technology is the establishment of causal relationships between identified genetic variants and cardiomyopathy phenotypes.7 Recently, the European Society of Cardiology's working group on myocardial and pericardial diseases recommended the use of NGS with very large panels of genes only when the family structure permits segregation analysis.1

Few studies to date have specifically assessed the genetic background of cohorts of HT recipients due to DCM,3,8,9 and even fewer have used NGS approaches.10 Such studies are essential to provide data on the clinical utility of genetic tests in non-responsive DCM patients.

In this work we aim to contribute to knowledge of genetic variants in adult patients undergoing HT due to end-stage DCM, reporting the results obtained in our single-center tertiary hospital series and using target NGS.

DCM is a major indication for HT, and a lower LVEF indicates a higher risk for this therapeutic option.14 However, HT is not necessarily a definitive treatment, due to complications arising from graft failure and chronic immunosuppression. The median life expectancy of transplant patients is still around 15 years.15 At the same time, insufficient donor hearts are available for all candidates and many patients die while on the waiting list. Given this situation, it is essential to further explore the mechanisms behind failure to respond to heart failure therapies in patients who progress to end-stage disease.

Genetics appears to explain a significant proportion of DCM cases. However, in most HT recipients, due to the scarcity of specific etiologic markers and the fact that genetic alterations are not systematically analyzed in these patients, DCM is frequently categorized as idiopathic. Systemic manifestations can occasionally alert the clinician to the possibility of a genetic disease, such as the presence of skeletal myopathy or atrioventricular block in carriers of LMNA variants.

The recently developed NGS technologies are more effective in detecting genetic variants in HT candidates, but the most efficient way to use NGS in clinical practice remains to be established, in particular how to select the panel of genes to be included in a target gene approach.

The few reports of genetic yields obtained specifically in HT cohorts of DCM patients use different approaches. Initial studies with Sanger DNA sequencing revealed a relatively high frequency of LMNA variants,3 while more recently, Cuenca et al., after screening a significant number of genes by NGS, reported pathogenic variants in 40% of patients, the most frequent in emerin and titin genes.10

In our study, genetic variants were a common finding (46%), but only one variant was categorized as likely pathogenic, due to the small and non-informative families. We also found a high percentage of LMNA variants (23%), followed by variants in LBD3 and TNNT2. The patient with the pathogenic LMNA variant presented elevated serum creatine kinase, but this observation was only detected once, and has not been associated with overt clinical myopathy. This missense variant, located in the coil 2 domain of the lamin A protein, has also been reported in another DCM patient with no evidence of muscular dystrophy, who required an ICD due to ventricular tachycardia and underwent HT at the age of 39.13

Two other patients presented stable rigid spine syndrome and limb-girdle myopathy, respectively, but in neither case did skeletal involvement limit HT. These cases highlight the well-known importance of neuromuscular assessment in DCM patients.16

Concerning the presence of two or more genetic variants in the same individual, it is not known if or how this may modify the phenotype. Double heterozygosity for LMNA and titin variants has been shown to be associated with a more severe clinical course, in terms of age of terminal heart failure and HT in a DCM family.17 Compound and digenic heterozygosity also appear to be common among hypertrophic cardiomyopathy (HCM) patients who develop end-stage heart failure.18 Of note, it is possible that end-stage DCM may represent end-stage HCM, but this is less likely in our patients, given the follow-up before HT, and since histopathology of the explanted hearts did not reveal myofibril disarray in any of the cases. On the other hand, the lack of segregation of genetic variants does not mean they have no biological effects, particularly when detected in family members with more severe phenotypes.

Major limitations of our study are the small number of patients and the limited number of studied genes, especially the fact that we did not include titin, in which genetic variants appear to have an important role in the pathogenesis of DCM.19

The application of NGS may help to expand our knowledge of the genetic mechanisms of cardiomyopathies that do not respond to medical therapy, including in DCM patients undergoing HT. It is important to clarify the pathogenicity of identified variants, and until more data are available, most variants will be classified as of uncertain significance, as in our patients. The impact of compound or digenic heterozygosity should also be investigated, in view of the growing number of clinical and genetic reports of patients with such mutations.

LMNA is one of the most frequently mutated genes in HT patients and should be included in all target gene assessments of end-stage DCM patients.

The authors have no conflicts of interest to declare.