Patients with coronary heart disease, dilated cardiomyopathy and idiopathic ventricular tachycardia share overlapping patterns of pathogenic variation in cardiac risk genes

Functional profiling of KCNE1 variants informs population carrier frequency of Jervell and Lange-Nielsen syndrome type 2

Congenital long-QT syndrome (LQTS) is most often associated with pathogenic variants in KCNQ1 encoding the pore-forming voltage-gated potassium channel subunit of the slow delayed rectifier current ( I Ks ). Generation of I Ks requires assembly of KCNQ1 with an auxiliary subunit encoded by KCNE1 , which is also associated with LQTS but causality of autosomal dominant disease is disputed. By contrast, KCNE1 is an accepted cause of recessive type 2 Jervell and Lange-Nielson syndrome (JLN2). The functional consequences of most KCNE1 variants have not been determined and the population prevalence of JLN2 is unknown. Methods : We determined the functional properties of 95 KCNE1 variants co-expressed with KCNQ1 in heterologous cells using high-throughput voltage-clamp recording. Experiments were conducted with each KCNE1 variant expressed in the homozygous state and then a subset was studied in the heterozygous state. The carrier frequency of JLN2 was estimated by considering the population prevalence of dysfunctional variants. Results : There is substantial overlap between disease-associated and population KCNE1 variants. When examined in the homozygous state, 68 KCNE1 variants exhibited significant differences in at least one functional property compared to WT KCNE1, whereas 27 variants did not significantly affect function. Most dysfunctional variants exhibited loss-of-function properties. We observed no evidence of dominant-negative effects. Most variants were scored as variants of uncertain significance (VUS) and inclusion of functional data resulted in revised classifications for only 14 variants. The population carrier frequency of JLN2 was calculated as 1 in 1034. Peak current density and activation voltage-dependence but no other biophysical properties were correlated with findings from a mutational scan of KCNE1. Conclusions : Among 95 disease-associated or population KCNE1 variants, many exhibit abnormal functional properties but there was no evidence of dominant-negative behaviors. Using functional data, we inferred a population carrier frequency for recessive JLN2. This work helps clarify the pathogenicity of KCNE1 variants.

Structural and functional consequences of non-synonymous SNPs within the LAMA2 protein: a molecular dynamics perspective

Clinical phenotypic presentations associated with LAMA2 deficiency have shown a variety of manifestations. LAMA2 mutations are mainly linked to congenital muscular dystrophy, but there is also mounting evidence suggesting their presence in inflammatory breast cancer, laryngopharyngeal squamous cell carcinoma, and ventricular tachycardia related to coronary artery disease and cardiomyopathy. This study examined the structural and functional impacts of 144 non-synonymous single nucleotide polymorphisms (nsSNPs) within the LAMA2 gene. Through multi-tiered sequence and structure-based methods, 11 deleterious and destabilizing mutations were identified (A1362T, E1308Q, E1360G, I1276S, L1195P, M1359T, P1232H, P1238A, P1272L, Y1234H, Y1338C). Further, four mutations (L1195P, Y1234H, P1238A, A1362T), which aligned with conserved positions, were subjected to 500 ns molecular dynamics (MD) simulations. RMSD calculated from MD trajectories highlighted structural disparities between wild-type and mutant forms, with the latter showing greater flexibility. Radius of gyration analysis indicated reduced compactness, solvent accessibility changes suggested unfolding, and hydrogen bond (HB) analysis demonstrated disrupted integrity. The HB analysis revealed disruptions in structural integrity due to diminished hydrogen bonds in mutants. Secondary structure analysis revealed significant alterations in secondary structural content. Principal Component Analysis unveiled increased dynamic behavior in mutants. Gibbs free energy landscape analysis reflected distinct energy minima regions in mutants, indicating structural destabilization. Overall, this study revealed the functional and structural ramifications of nsSNPs in the LAMA2 gene, providing valuable insights into potential disease-causing mutations and warranting future research on understanding LAMA2 associated diseases and disorders.

Diverse Concepts in Definitions of Dilated Cardiomyopathy: Theory and Practice

Our understanding of dilated cardiomyopathy (DCM) is evolving as new insights into the underlying pathophysiology become available. Professional organizations and clinical experts are improving definitions of DCM, allowing for more accurate treatment recommendations. This review summarized key published literature describing definitions and/or diagnostic criteria for DCM. Embase was searched from database inception to September 19, 2022 for 1) publications reporting definitions of DCM by major professional organizations and related opinion papers, and 2) clinical studies in DCM and heart failure with reduced ejection fraction. Sixty-eight records were included in this review. Definitions of DCM provided by two major professional organizations (American Heart Association (AHA) and European Society of Cardiology (ESC)) agreed on the clinical presentation of DCM; however, they differed in the classification of DCM within the larger context of cardiomyopathy taxonomies. Both organizations agreed that DCM could be clinically defined by the presence of left ventricular dilation and contractile dysfunction in the absence of abnormal loading conditions and severe coronary artery disease. AHA guidelines divided cardiomyopathies into two major groups (primary and secondary) based on predominant organ involvement. DCM was classified as primary cardiomyopathy with mixed (genetic and/or acquired) etiology. Conversely, ESC published a clinically oriented taxonomy in which cardiomyopathies were grouped into specific morphological and functional phenotypes; each was subclassified into familial or non-familial forms. Opinion papers further elaborated on the complex interplay between genetics and environment in the etiology of DCM. Several articles summarized the importance of the new and updated diagnostic tools, such as cardiac magnetic resonance imaging, electrocardiogram, and other biomarkers, in correctly identifying the etiology of DCM. Within clinical studies, most inclusion criteria used standard definitions proposed by leading professional associations (AHA and ESC). Clinical study investigators sometimes used a narrower definition of DCM using additional criteria for the left ventricular ejection fraction threshold value and left ventricular dilatation. Current efforts in cardiology research are focused on a more granular understanding of DCM etiology and the natural history of the disease. Definitions of DCM found in clinical studies mainly rely on published guidelines, with some studies adding idiosyncratic inclusion criteria refining the broad definitions of DCM.

Sudden Cardiac Arrest in the Postpartum Period Due to Long QT Syndrome and Dilated Cardiomyopathy

We describe the case of a previously healthy patient presenting with sudden cardiac arrest in the postpartum period as a result of concomitant congenital type 1 long QT syndrome and BAG3 dilated cardiomyopathy. This case highlights the increased rate of cardiac events for patients with long QT syndrome in the postpartum period. (Level of Difficulty: Advanced.).

Significance of α-Myosin Heavy Chain (MYH6) Variants in Hypoplastic Left Heart Syndrome and Related Cardiovascular Diseases

Hypoplastic left heart syndrome (HLHS) is a severe congenital heart disease (CHD) with complex genetic inheritance. HLHS segregates with other left ventricular outflow tract (LVOT) malformations in families, and can present as either an isolated phenotype or as a feature of a larger genetic disorder. The multifactorial etiology of HLHS makes it difficult to interpret the clinical significance of genetic variants. Specific genes have been implicated in HLHS, including rare, predicted damaging MYH6 variants that are present in >10% of HLHS patients, and which have been shown to be associated with decreased transplant-free survival in our previous studies. MYH6 (α-myosin heavy chain, α-MHC) variants have been reported in HLHS and numerous other CHDs, including LVOT malformations, and may provide a genetic link to these disorders. In this paper, we outline the MYH6 variants that have been identified, discuss how bioinformatic and functional studies can inform clinical decision making, and highlight the importance of genetic testing in HLHS.