Brugada syndrome and fever: genetic and molecular characterization of patients carrying SCN5A mutations.

OBJECTIVE: Brugada syndrome (BrS) is characterized by ventricular tachyarrhythmias leading to sudden cardiac death and is caused, in part, by mutations in the SCN5A gene encoding the sodium channel Na(v)1.5. Fever can trigger or exacerbate the clinical manifestations of BrS. The aim of this work was to characterize the genetic and molecular determinants of fever-dependent BrS. METHODS: Four male patients with typical BrS ST-segment elevation in V1-V3 or ventricular arrhythmias during fever were screened for mutations in the SCN5A gene. Wild-type (WT) and mutant Na(v)1.5 channels were expressed in HEK293 cells. The sodium currents (I(Na)) were analysed using the whole-cell patch clamp technique at various temperatures. Protein expression of WT and mutant channels was studied by Western blot experiments. RESULTS: Two mutations in SCN5A, L325R and R535X, were identified. Expression of the two mutant Na(v)1.5 channels in HEK293 cells revealed in each case a severe loss-of-function. Upon the increase of temperature up to 42 degrees C, we observed a pronounced acceleration of Na(v)1.5 activation and fast inactivation kinetics. Cardiac action potential modelling experiments suggest that in patients with reduced I(Na), fever could prematurely shorten the action potential by virtue of its effect on WT channels. Further experiments revealed that L325R channels are likely misfolded, since their function could be partially rescued by mexiletine or curcumin. In co-expression experiments, L325R channels interfered with the proper function of WT channels, suggesting that a dominant negative phenomenon may underlie BrS triggered by fever. CONCLUSIONS: The genetic background of BrS patients sensitive to fever is heterogeneous. Our experimental data suggest that the clinical manifestations of fever-exacerbated BrS may not be mutation specific

A Systematic Analysis of the Clinical Outcome Associated with Multiple Reclassified Desmosomal Gene Variants in Arrhythmogenic Right Ventricular Cardiomyopathy Patients

The presence of multiple pathogenic variants in desmosomal genes (DSC2, DSG2, DSP, JUP, and PKP2) in patients with arrhythmogenic right ventricular cardiomyopathy (ARVC) has been linked to a severe phenotype. However, the pathogenicity of variants is reclassified frequently, which may result in a changed clinical risk prediction. Here, we present the collection, reclassification, and clinical outcome correlation for the largest series of ARVC patients carrying multiple desmosomal pathogenic variants to date (n = 331). After reclassification, only 29% of patients remained carriers of two (likely) pathogenic variants. They reached the composite endpoint (ventricular arrhythmias, heart failure, and death) significantly earlier than patients with one or no remaining reclassified variant (hazard ratios of 1.9 and 1.8, respectively). Periodic reclassification of variants contributes to more accurate risk stratification and subsequent clinical management strategy. [Figure not available: see fulltext.]

Desmoglein 2 mutant mice develop cardiac fibrosis and dilation

Desmosomes are cell–cell adhesion sites and part of the intercalated discs, which couple adjacent cardiomyocytes. The connection is formed by the extracellular domains of desmosomal cadherins that are also linked to the cytoskeleton on the cytoplasmic side. To examine the contribution of the desmosomal cadherin desmoglein 2 to cardiomyocyte adhesion and cardiac function, mutant mice were prepared lacking a part of the extracellular adhesive domain of desmoglein 2. Most live born mutant mice presented normal overall cardiac morphology at 2 weeks. Some animals, however, displayed extensive fibrotic lesions. Later on, mutants developed ventricular dilation leading to cardiac insufficiency and eventually premature death. Upon histological examination, cardiomyocyte death by calcifying necrosis and replacement by fibrous tissue were observed. Fibrotic lesions were highly proliferative in 2-week-old mutants, whereas the fibrotic lesions of older mutants showed little proliferation indicating the completion of local muscle replacement by scar tissue. Disease progression correlated with increased mRNA expression of c-myc, ANF, BNF, CTGF and GDF15, which are markers for cardiac stress, remodeling and heart failure. Taken together, the desmoglein 2-mutant mice display features of dilative cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy, an inherited human heart disease with pronounced fibrosis and ventricular arrhythmias that has been linked to mutations in desmosomal proteins including desmoglein 2

Plakophilin-2: a cell-cell adhesion plaque molecule of selective and fundamental importance in cardiac functions and tumor cell growth

Within the characteristic ensemble of desmosomal plaque proteins, the armadillo protein plakophilin-2 (Pkp2) is known as a particularly important regulatory component in the cytoplasmic plaques of various other cell–cell junctions, such as the composite junctions (areae compositae) of the myocardiac intercalated disks and in the variously-sized and -shaped complex junctions of permanent cell culture lines derived therefrom. In addition, Pkp2 has been detected in certain protein complexes in the nucleoplasm of diverse kinds of cells. Using a novel set of highly sensitive and specific antibodies, both kinds of Pkp2, the junctional plaque-bound and the nuclear ones, can also be localized to the cytoplasmic plaques of diverse non-desmosomal cell–cell junction structures. These are not only the puncta adhaerentia and the fasciae adhaerentes connecting various types of highly proliferative non-epithelial cells growing in culture but also some very proliferative states of cardiac interstitial cells and cardiac myxomata, including tumors growing in situ as well as fetal stages of heart development and cultures of valvular interstitial cells. Possible functions and assembly mechanisms of such Pkp2-positive cell–cell junctions as well as medical consequences are discussed

Mutations with pathogenic potential in proteins located in or at the composite junctions of the intercalated disk connecting mammalian cardiomyocytes: a reference thesaurus for arrhythmogenic cardiomyopathies and for Naxos and Carvajal diseases

In the past decade, an avalanche of findings and reports has correlated arrhythmogenic ventricular cardiomyopathies (ARVC) and Naxos and Carvajal diseases with certain mutations in protein constituents of the special junctions connecting the polar regions (intercalated disks) of mature mammalian cardiomyocytes. These molecules, apparently together with some specific cytoskeletal proteins, are components of (or interact with) composite junctions. Composite junctions contain the amalgamated fusion products of the molecules that, in other cell types and tissues, occur in distinct separate junctions, i.e. desmosomes and adherens junctions. As the pertinent literature is still in an expanding phase and is obviously becoming important for various groups of researchers in basic cell and molecular biology, developmental biology, histology, physiology, cardiology, pathology and genetics, the relevant references so far recognized have been collected and are presented here in the following order: desmocollin-2 (Dsc2, DSC2), desmoglein-2 (Dsg2, DSG2), desmoplakin (DP, DSP), plakoglobin (PG, JUP), plakophilin-2 (Pkp2, PKP2) and some non-desmosomal proteins such as transmembrane protein 43 (TMEM43), ryanodine receptor 2 (RYR2), desmin, lamins A and C, striatin, titin and transforming growth factor-β3 (TGFβ3), followed by a collection of animal models and of reviews, commentaries, collections and comparative studies

Desmosomal gene analysis in arrhythmogenic right ventricular dysplasia/cardiomyopathy: spectrum of mutations and clinical impact in practice

AIMS: Five desmosomal genes have been recently implicated in arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) but the clinical impact of genetics remains poorly understood. We wanted to address the potential impact of genotyping. METHODS AND RESULTS: Direct sequencing of the five genes (JUP, DSP, PKP2, DSG2, and DSC2) was performed in 135 unrelated patients with ARVD/C. We identified 41 different disease-causing mutations, including 28 novel ones, in 62 patients (46%). In addition, a genetic variant of unknown significance was identified in nine additional patients (7%). Distribution of genes was 31% (PKP2), 10% (DSG2), 4.5% (DSP), 1.5% (DSC2), and 0% (JUP). The presence of desmosomal mutations was not associated with familial context but was associated with young age, symptoms, electrical substrate, and extensive structural damage. When compared with other genes, DSG2 mutations were associated with more frequent left ventricular involvement (P = 0.006). Finally, complex genetic status with multiple mutations was identified in 4% of patients and was associated with more frequent sudden death (P = 0.047). CONCLUSION: This study supports the use of genetic testing as a new diagnostic tool in ARVC/D and also suggests a prognostic impact, as the severity of the disease appears different according to the underlying gene or the presence of multiple mutations

Modifications des lipoprotéines de basse densité (LDL) par radiolyse γ de l'eau : reconnaissance par les récepteurs APO B/E et «scavenger», et cytotoxicité vis-à-vis de fibroblastes humains en culture

Le but de ce travail était d'étudier la reconnaissance par le récepteur B/E de fibroblastes humains et le récepteur "scavenger" de macrophages, de LDL d'origine humaine oxydées par radiolyse γ de l'eau (O2°-/OH°). Leur cytotoxicité vis-à-vis de fibroblastes humains en culture a également été testée. Nous avons montré que les LDL oxydées (doses comprises entre 600 et 1800 Gy) étaient encore partiellement reconnues par le récepteur apo B/E des fibroblastes MRC5. Ces LDL oxydées étaient cytotoxiques vis-à-vis de fibroblastes humains en culture et cet effet était dépendant de la dose d'irradiation. En revanche, la reconnaissance par le récepteur "scavenger" des macrophages ne semblait pas dépendante de la dose d'irradiation, dans nos conditions expérimentales. La peroxydation des LDL par les radicaux générés par radiolyse γ de l'eau semblerait se distinguer de celle induite par le cuivre et pourrait constituer un modèle expérimental intéressant pour l'introduction de lipides peroxydés dans le milieu intracellulaire

Genetic characterization of KCNQ1 variants improves risk stratification in type 1 long QT syndrome patients.

KCNQ1 mutations cause QTc prolongation increasing life-threatening arrhythmias risks. Heterozygous mutations (type-1 LQTS) are common. Homozygous KCNQ1 mutations cause type-1 Jervell and Lange-Nielsen syndrome (JLNS) with deafness and higher sudden cardiac death risk. KCNQ1 variants causing JLNS or type-1 LQTS might have distinct phenotypic expressions in heterozygous patients. The aim of this study is to evaluate QTc duration and incidence of LQTS-related cardiac events according to genetic presentation. We enrolled LQT1 or JLNS patients with class IV/V KCNQ1 variants from our inherited arrhythmia clinic (September 1993 to January 2023). Medical history, ECG, follow-up were collected. Additionally, we conducted a thorough literature review for JLNS variants. Survival curves were compared between groups, and multivariate Cox regression models identified genetic and clinical risk factors. Among 789 KCNQ1 variants carriers, 3 groups were identified; 30 JLNS (JLNS), 161 heterozygous carriers of JLNS variants (HTZ-JLNS), 550 LQT1 heterozygous carriers of non-JLNS variants (HTZ-Non-JLNS).At diagnosis, mean age was, 3.4±4.7 years (JLNS), 26.7±21 years (HTZ-JLNS), and 26±21 years (HTZ-non-JLNS), 55.3% were female, and the mean QTc was 551±54ms (JLNS), 441±32ms (HTZ-JLNS), 467±36ms (HTZ-Non-JLNS).Patients with heterozygous JLNS mutations (HTZ-JLNS) represented 22% of heterozygous KCNQ1 variants carriers and had a lower risk of cardiac events than heterozygous non-JLNS variants carriers (HTZ-Non-JLNS) (HR 0.34 [0.22-0.54]; p<0.01).After multivariate analysis, 4 genetic parameters were independently associated with events: haploinsufficiency (HR=0.60 [0.37-0.97]; p=0.04), pore localization (HR=1.61 [1.14-1.2.26]; p<0.01), C-terminal localization (HR=0.67 [0.46-0.98]; p=0.04), and group (HR=0.43 [0.27-0.69]; p<0.01). Heterozygous carriers of JLNS variants have a lower risk of cardiac arrhythmic events than other type 1 LQTS patients