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

BACKGROUND: 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. METHODS: 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. RESULTS: 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). CONCLUSION: Heterozygous carriers of JLNS variants have a lower risk of cardiac arrhythmic events than other type 1 LQTS patients.

Molecular genetic screening after non-ischaemic sudden cardiac arrest and no overt cardiomyopathy in real life: A major tool for the aetiological diagnostic work-up.

BACKGROUND: With the development of advanced sequencing techniques, genetic testing has emerged as a valuable tool for the work-up of non-ischaemic sudden cardiac arrest (SCA). AIMS: To evaluate the effectiveness of genetic testing in patients with unexplained SCA, according to clinical phenotype. METHODS: All patients who underwent molecular genetic testing for non-ischaemic SCA with no left ventricular cardiomyopathy between 2012 and 2021 in two French university hospitals were included. RESULTS: Of 66 patients (mean age 36.7±11.9years, 54.5% men), 21 (31.8%; 95% confidence interval 22.4-45.3%) carried a genetic variant: eight (12.1%) had a pathogenic or likely pathogenic (P/LP) variant and 13 (19.7%) had a variant of uncertain significance (VUS). Among 37 patients (56.1%) with no phenotypic clues, genetic testing identified a P/LP variant in five (13.5%), mainly in RYR2 (n=3) and SCN5A (n=2), and a VUS in nine (24.3%). None of the nine patients with phenotypic evidence of channelopathies had P/LP variants, but two had VUS in RYR2 and NKX2.5. Among the 20 patients with suspected arrhythmogenic cardiomyopathy, three P/LP variants (15.0%) and two VUS (10.0%) were found in DSC2, PKP2, SCN5A and DSG2, TRPM4, respectively. Genetic testing was performed sooner after cardiac arrest (P<0.001) and results were obtained more rapidly (P=0.02) after versus before 2016. CONCLUSION: This study highlights the utility of molecular genetic testing with a genetic variant of interest identified in one-third of patients with unexplained SCA. Genetic testing was beneficial even in patients without phenotypic clues, with one-fourth of patients carrying a P/LP variant that could have direct implications.

Type 3 long QT syndrome: Is the effectiveness of treatment with beta-blockers population-specific?

BACKGROUND: The efficacy of beta-blocker treatment in type 3 long QT syndrome (LQT3) remains debated. OBJECTIVES: The purpose of this study was to test the hypothesis that beta-blocker use is associated with cardiac events (CEs) in a French cohort of LQT3 patients. METHODS: All patients with a likely pathogenic/pathogenic variant in the SCN5A gene (linked to LQT3) were included and followed-up. Documented ventricular tachycardia/ventricular fibrillation, torsades de pointes, aborted cardiac arrest, sudden death, and appropriate shocks were considered as severe cardiac events (SCEs). CEs also included syncope. RESULTS: We included 147 patients from 54 families carrying 23 variants. Six of the patients developed symptoms before the age of 1 year and were analyzed separately. The 141 remaining patients (52.5% male; median age at diagnosis 24.0 years) were followed-up for a median of 11 years. The probabilities of a CE and an SCE from birth to the age of 40 were 20.5% and 9.9%, respectively. QTc prolongation (hazard ratio [HR] 1.12 [1.0-1.2]; P = .005]) and proband status (HR 4.07 [1.9-8.9]; P <.001) were independently associated with the occurrence of CEs. Proband status (HR 8.13 [1.7-38.8]; P = .009) was found to be independently associated with SCEs, whereas QTc prolongation (HR 1.11 [1.0-1.3]; P = .108) did not reach statistical significance. The cumulative probability of the age at first CE/SCE was not lower in patients treated with a beta-blocker. CONCLUSION: In agreement with the literature, proband status and lengthened QTc were associated with a higher risk of CEs. Our data do not show a protective effect of beta-blocker treatment.

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. Graphical Abstract.

Correlations Between Endocardial Voltage Mapping, Diagnosis, and Genetics in Patients With Arrhythmogenic Right Ventricular Cardiomyopathy.

The relations between endocardial voltage mapping and the genetic background of patients with arrhythmogenic right ventricular cardiomyopathy (ARVC) have not been investigated so far. A total of 97 patients with proved or suspected ARVC who underwent 3-dimensional endocardial mapping and genetic testing have been retrospectively included. Presence, localization, and size of scar areas were correlated to ARVC diagnosis and the presence of a pathogenic variant. A total of 78 patients (80%) presented with some bipolar or unipolar scar on endocardial voltage mapping, whereas 43 carried pathogenic variants (44%). Significant associations were observed between presence of endocardial scars on voltage mapping and previous or inducible ventricular tachycardia, right ventricular function and dimensions, or electrocardiogram features of ARVC. A total of 60 of the 78 patients (77%) with an endocardial scar fulfilled the criteria for a definitive arrhythmogenic right ventricular dysplasia diagnosis versus 8 of 19 patients (42%) without scar (p = 0.003). Patients with a definitive diagnosis of ARVC had more scars from any location and the scars were larger in patients with ARVC. In the 68 patients with a definitive diagnosis of ARVC, the presence of any endocardial scar was similar whether an ARVC-causal mutation was present or not. Only scar extent was significantly greater in patients with pathogenic variants. There was no difference in the presence and characteristics of scars in PKP2 mutated versus other mutated patients. The 3-dimensional endocardial mapping could have an important role for refining ARVC diagnosis and may be able to detect minor forms with otherwise insufficient criteria for diagnosis. The trend for larger scar extent were observed in mutated patients, without any difference according to the mutated genes.

Clinical course of arrhythmogenic right ventricular cardiomyopathy with end-stage heart failure and outcome after heart transplantation.

BACKGROUND: Few data exist on the characteristics and outcomes of patients with arrhythmogenic right ventricular cardiomyopathy and advanced heart failure who undergo heart transplantation. AIM: To explore the pretransplant course and outcomes of patients with arrhythmogenic right ventricular cardiomyopathy after heart transplantation. METHODS: This observational retrospective monocentric study included all consecutive patients with arrhythmogenic right ventricular cardiomyopathy who underwent heart transplantation during a 13-year period (2006-2019) at Pitié-Salpêtrière University Hospital (Paris). RESULTS: A total of 23 patients with arrhythmogenic right ventricular cardiomyopathy underwent heart transplantation between 2006 and 2019. The median time from diagnosis to heart transplantation was 9 years, and the median age at transplantation was 50 years. At diagnosis, half of the patients had left ventricular dysfunction, 59% had extensive T-wave inversion and 43% had a history of sustained ventricular tachycardia. Only five patients were involved in intensive sport activity. Indications for heart transplantation were end-stage biventricular dysfunction in 13 patients, end-stage right ventricular heart failure in seven and electrical storm in three. Only three patients had pulmonary hypertension, and half of the patients had atrial arrhythmias. The survival rate 1 year after heart transplantation was 74% (95% confidence interval 53-88%). Eight patients experienced primary graft dysfunction needing extracorporeal membrane oxygenation. CONCLUSIONS: Patients with arrhythmogenic right ventricular cardiomyopathy who eventually needed heart transplantation mostly exhibited extended disease with biventricular dysfunction at diagnosis. Intensive sport activity did not seem to be a major determinant. Advanced heart failure usually occurred late in the course of the disease. Primary graft dysfunction after heart transplantation was frequent, and should be anticipated. Additional data are needed to identify the optimal timing for heart transplantation and predictors of end-stage heart failure in patients with arrhythmogenic right ventricular cardiomyopathy.

Novel CALM3 Variant Causing Calmodulinopathy With Variable Expressivity in a 4-Generation Family.

BACKGROUND: CaM (calmodulin), encoded by 3 separate genes (CALM1, CALM2, and CALM3), is a multifunctional Ca2+-binding protein involved in many signal transduction events including ion channel regulation. CaM variants may present with early-onset long QT syndrome (LQTS), catecholaminergic polymorphic ventricular tachycardia, or sudden cardiac death. Most reported variants occurred de novo. We identified a novel CALM3 variant, p.Asn138Lys (N138K), in a 4-generation family segregating with LQTS. The aim of this study was to elucidate its pathogenicity and to compare it with that of p.D130G-CaM-a variant associated with a severe LQTS phenotype. METHODS: We performed whole exome sequencing for a large, 4-generation family affected by LQTS. To assess the effect of the detected CALM3 variant, the intrinsic Ca2+-binding affinity was measured by stoichiometric Ca2+ titrations and equilibrium titrations. L-type Ca2+ and slow delayed rectifier potassium currents (ICaL and IKs) were recorded by whole-cell patch-clamp. Cav1.2 and Kv7.1 membrane expression were determined by optical fluorescence assays. RESULTS: We identified 14 p.N138K-CaM carriers in a family where 2 sudden deaths occurred in children. Several members were only mildly affected compared with CaM-LQTS patients to date described in literature. The intrinsic Ca2+-binding affinity of the CaM C-terminal domain was 10-fold lower for p.N138K-CaM compared with wild-type-CaM. ICaL inactivation was slowed in cells expressing p.N138K-CaM but less than in p.D130G-CaM cells. Unexpectedly, a larger IKs current density was observed in cells expressing p.N138K-CaM, but not for p.D130G-CaM, compared with wild-type-CaM. CONCLUSIONS: The p.N138K CALM3 variant impairs Ca2+-binding affinity of CaM and ICaL inactivation but potentiates IKs. The variably expressed phenotype of this variant compared with previously published de novo LQTS-CaM variants is likely explained by a milder impairment of ICaL inactivation combined with IKs augmentation.

Challenging indication of cardioverter defibrillator implantation after sudden cardiac arrest in the very young: a case series of catecholaminergic polymorphic ventricular tachycardia secondary to de novo calmodulin p.Asn98Ser.

BACKGROUND: Calmodulinopathy is an emerging group of primary electrical disease with various, severe, and early onset phenotype. Sudden cardiac arrest (SCA)/death can be the first symptom and current medical management seems insufficient to prevent recurrences. Implantable cardioverter-defibrillator (ICD) in the young is challenging and can be harmful. CASE SUMMARY: We report the management of two very young boys (aged 3.5 and 5.5 years old) who survived an SCA due to calmodulin mutation responsible of a catecholaminergic polymorphic ventricular tachycardia phenotype. In both case, SCA had an adrenergic trigger. Despite SCA, ICD implantation was denied by the parents. After thorough discussion with the family, the patients were managed with solely betablocker treatment and loop recorder implantation. At last follow-up of 30 and 23 months, respectively, there were no recurrence of any cardiac event. DISCUSSION: The benefits of ICD implantation at a very young age must be weighed against the risk complication. In the youngest, whom recreative activities are under constant supervision, the decision, jointly made with the parents, could be to postpone ICD.

A Type 2 Ryanodine Receptor Variant in the Helical Domain 2 Associated with an Impairment of the Adrenergic Response.

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is triggered by exercise or acute emotion in patients with normal resting electrocardiogram. The major disease-causing gene is RYR2, encoding the cardiac ryanodine receptor (RyR2). We report a novel RYR2 variant, p.Asp3291Val, outside the four CPVT mutation hotspots, in three CPVT families with numerous sudden deaths. This missense variant was first identified in a four-generation family, where eight sudden cardiac deaths occurred before the age of 30 in the context of adrenergic stress. All affected subjects harbored at least one copy of the RYR2 variant. Three affected sisters were homozygous for the variant. The same variant was found in two additional CPVT families. It is located in the helical domain 2 and changes a negatively charged amino acid widely conserved through evolution. Functional analysis of D3291V channels revealed a normal response to cytosolic Ca2+, a markedly reduced luminal Ca2+ sensitivity and, more importantly, an absence of normal response to 8-bromo-cAMP and forskolin stimulation in both transfected HEK293 and HL-1 cells. Our data support that the D3291V-RyR2 is a loss-of-function RyR2 variant responsible for an atypical form of CPVT inducing a mild dysfunction in basal conditions but leading potentially to fatal events through its unresponsiveness to adrenergic stimulation.

Novel G1481V and Q1491H SCN5A Mutations Linked to Long QT Syndrome Destabilize the Nav1.5 Inactivation State.

BACKGROUND: Nav1.5, which is encoded by the SCN5A gene, is the predominant voltage-gated Na+ channel in the heart. Several mutations of this gene have been identified and reported to be involved in several cardiac rhythm disorders, including type 3 long QT interval syndrome, that can cause sudden cardiac death. We analyzed the biophysical properties of 2 novel variants of the Nav1.5 channel (Q1491H and G1481V) detected in 5- and 12-week-old infants diagnosed with a prolonged QT interval. METHODS: The Nav1.5 wild-type and the Q1491H and G1481V mutant channels were reproduced in vi tr o. Wild-type or mutant channels were cotransfected in human embryonic kidney (HEK) 293 cells with the beta 1 regulatory subunit. Na+ currents were recorded using the whole-cell configuration of the patch-clamp technique. RESULTS: The Q1491H mutant channel exhibited a lower current density, a persistent Na+ current, an enhanced window current due to a +20-mV shift of steady-state inactivation, a +10-mV shift of steady-state activation, a faster onset of slow inactivation, and a recovery from fast inactivation with fast and slow time constants of recovery. The G1481V mutant channel exhibited an increase in current density and a +7-mV shift of steady-state inactivation. The observed defects are characteristic of gain-of-function mutations typical of type 3 long QT interval syndrome. CONCLUSIONS: The 5- and 12-week-old infants displayed prolonged QT intervals. Our analyses of the Q1491H and G1481V mutations correlated with the clinical diagnosis. The observed biophysical dysfunctions associated with both mutations were most likely responsible for the sudden deaths of the 2 infants.

INTRODUCTION: Le canal Nav1.5, codé par le gène SCN5A, est le canal Na+ dépendant du voltage prédominant dans le cœur. Plusieurs mutations de ce gène sont impliquées dans plusieurs anomalies du rythme cardiaque, dont le syndrome du QT long de type 3, qui peut provoquer la mort subite d'origine cardiaque. Nous avons analysé les propriétés biophysiques de deux nouveaux variants du canal Nav1.5 (Q1491H et G1481V) détectés chez deux bébés âgés respectivement de 5 et 12 semaines qui avaient une prolongation de l'intervalle QT. MÉTHODES: Le canal Nav1.5 de type sauvage et les canaux mutants Q1491H et G1481V ont été reproduits in vi tr o. Les canaux de type sauvage ou mutants ont été co-transfectés dans les cellules des reins embryonnaires humains (REH) 293 avec la sous-unité régulatrice bêta 1. Les courants Na+ ont été enregistrés à partir de la configuration en cellule entière via la technique de patch-clamp. RÉSULTATS: Le canal mutant Q1491H montre une densité de courant plus faible, un courant Na+ persistant, un courant fenêtre augmenté en raison d'un changement dép de +20 mV de l'inactivation à l'état stable, un changement de +10 mV de l'activation à l'état stable, une entrée plus rapide de l'inactivation lente et une récupération de l'inactivation rapide avec des constantes de temps rapides et lentes. Le canal mutant G1481V montre une augmentation de la densité de courant et un changement de +7 mV de l'inactivation à l'état stable. Les anomalies observées sont caractéristiques des mutations avec gain de fonction typiques du syndrome du QT long de type 3. CONCLUSIONS: Les deux bébés âgés respectivement de cinq 5 et 12 semaines montraient une prolongation des intervalles QT. Nos analyses des mutations Q1491H et G1481V montrent une corrélation avec le diagnostic clinique. Les dysfonctions biophysiques observées qui sont associées aux deux mutations étaient fort probablement responsables des morts subites des deux bébés.

[Usefulness of combined sequencing of the mitochondrial genome and a targeted panel of nuclear genes involved in mitochondrial diseases]. / Intérêt du séquençage combiné du génome mitochondrial et d'un panel ciblé de gènes nucléaires impliqués dans les maladies mitochondriales.

The molecular study of mitochondrial diseases, essential for diagnosis, is special due to the dual genetic origin of these pathologies: mitochondrial DNA and nuclear DNA. Complete mtDNA sequencing still remains the first line diagnostic test followed if negative, by resequencing panels of several hundred mitochondrially-encoded nuclear genes. This strategy, with an initial entire mtDNA sequencing, is currently justified by the presence of nuclear mitochondrial DNA sequences (NUMTs) in the nuclear genome. We designed a resequencing panel combining the mtDNA and 135 nuclear genes which was evaluated compared to the performances of the standard mtDNA sequencing. Method validation was performed on the reading depth and reproducibility of the results. Thirty patients were analyzed by both methods. We were able to demonstrate that NUMTs did not impact the mtDNA sequencing quality, as the identified variants and mutant loads were identical with the reference mtDNA sequencing method. Reading depths were higher than the recommendations of the MitoDiag French diagnostic network, for the entire mtDNA for muscle and for 70% of the mtDNA for blood. These results highlight the usefulness of combining both mtDNA and mitochondrially nuclear-encoded genes and thus obtain more complete results and faster turnaround time for mitochondrial disease patients.

Clinical impact of post-mortem genetic testing in cardiac death and cardiomyopathy.

Post-mortem genetic analyses may help to elucidate the cause of cardiac death. The added value is however unclear when a cardiac disease is already suspected or affirmed. Our aim was to study the feasibility and medical impact of post-mortem genetic analyses in suspected cardiomyopathy. We studied 35 patients with cardiac death and suspected cardiomyopathy based on autopsy or clinical data. After targeted sequencing, we identified 15 causal variants in 15 patients (yield 43%) in sarcomeric (n = 8), desmosomal (n = 3), lamin A/C (n = 3) and transthyretin (n = 1) genes. The results had various impacts on families, i.e. allowed predictive genetic testing in relatives (15 families), planned early therapeutics based on the specific underlying gene (5 families), rectified the suspected cardiomyopathy subtype (2 families), assessed the genetic origin of cardiomyopathy that usually has an acquired cause (1 family), assessed the diagnosis in a patient with uncertain borderline cardiomyopathy (1 family), reassured the siblings because of a de novo mutation (2 families) and allowed prenatal testing (1 family). Our findings suggest that post-mortem molecular testing should be included in the strategy of family care after cardiac death and suspected cardiomyopathy, since genetic findings provide additional information useful for relatives, which are beyond conventional autopsy.

Psychosocial Impact of Predictive Genetic Testing in Hereditary Heart Diseases: The PREDICT Study.

Predictive genetic testing (PGT) is offered to asymptomatic relatives at risk of hereditary heart disease, but the impact of result disclosure has been little studied. We evaluated the psychosocial impacts of PGT in hereditary heart disease, using self-report questionnaires (including the State-Trait Anxiety Inventory) in 517 adults, administered three times to the prospective cohort (PCo: n = 264) and once to the retrospective cohort (RCo: n = 253). The main motivations for undergoing PGT were "to remove doubt" and "for their children". The level of anxiety increased between pre-test and result appointments (p <0.0001), returned to baseline after the result (PCo), and was moderately elevated at 4.4 years (RCo). Subjects with a history of depression or with high baseline anxiety were more likely to develop anxiety after PGT result (p = 0.004 and p <0.0001, respectively), whatever it was. Unfavourable changes in professional and/or family life were observed in 12.4% (PCo) and 18.7% (RCo) of subjects. Few regrets about PGT were expressed (0.8% RCo, 2.3% PCo). Medical benefit was not the main motivation, which emphasises the role of pre/post-test counselling. When PGT was performed by expert teams, the negative impact was modest, but careful management is required in specific categories of subjects, whatever the genetic test result.

A novel gain-of-function mutation in SCN5A responsible for multifocal ectopic Purkinje-related premature contractions.

Recently, four SCN5A mutations have been associated with Multifocal Ectopic Purkinje-related Premature Contractions (MEPPC), a rare cardiac syndrome combining polymorphic ventricular arrhythmia with dilated cardiomyopathy (DCM). Here, we identified a novel heterozygous mutation in SCN5A (c.611C>A, pAla204Glu) in a young woman presenting with polymorphic premature ventricular contractions (PVCs) and DCM. After failure of antiarrhythmic drugs and an attempt of radiofrequency catheter ablation showing three exit-sites of PVCs, all with presystolic Purkinje potentials, a treatment by hydroquinidine was tried, leading to an immediate and spectacular disappearance of all PVCs and normalization of cardiac function. Electrophysiological studies showed that Nav 1.5-A204E mutant channels exhibited a significant leftward shift of 8 mV of the activation curve, leading to a larger hyperpolarized window current when compared to wild-type. Action potential modeling using Purkinje fiber and ventricular cell models predicted an arrhythmogenic effect predominant in Purkinje fibers for the A204E mutation. Comparison with other MEPPC-associated Nav 1.5 mutations revealed a common electrophysiological pattern of abnormal voltage-dependence of activation leading to a larger hyperpolarized window current as a shared biophysical mechanism of this syndrome. These features of the mutant sodium channels are likely to be responsible for the hyperexcitability of the fascicular-Purkinje system observed in patients with MEPPC.

Desmoglein-2 mutations in propeptide cleavage-site causes arrhythmogenic right ventricular cardiomyopathy/dysplasia by impairing extracellular 1-dependent desmosomal interactions upon cellular stress.

AIMS: Desmoglein-2 (DSG2) mutations, which encode a heart-specific cadherin crucial for desmosomal adhesion, are frequent in arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D). DSG2 mutations have been associated with higher risk of biventricular involvement. Among DSG2 mutations, mutations of the inhibitory propeptide consensus cleavage-site (Arg-X-Arg/Lys-Arg), are particularly frequent. In the present work, we explored the functional consequences of DSG2 propeptide cleavage site mutations p.Arg49His, p.Arg46Trp, and p.Arg46Gln on localization, adhesive properties, and desmosome incorporation of DSG2. METHODS AND RESULTS: We studied the expression of mutant-DSG2 in human heart and in epithelial and cardiac cellular models expressing wild-type or mutant (p.Arg49His, p.Arg46Trp, and p.Arg46Gln) proDSG2-GFP fusion proteins. The consequences of the p.Arg46Trp mutation on DSG2 adhesiveness were studied by surface plasmon resonance. Incorporation of mutant p.Arg46Trp DSG2 into desmosomes was studied under low-calcium culture conditions and cyclic mechanical stress. We demonstrated in human heart and cellular models that all three mutations prevented N-terminal propeptide cleavage, but did not modify intercellular junction targeting. Surface plasmon resonance experiments showed a propeptide-dependent loss of interaction between the cadherin N-terminal extracellular 1 (EC1) domains. Additionally, proDSG2 mutant proteins were abnormally incorporated into desmosomes under low-calcium culture conditions or following mechanical stress. This was accompanied by an epidermal growth factor receptor-dependent internalization of proDSG2, suggesting increased turnover of unprocessed proDSG2. CONCLUSION: Our results strongly suggest weakened desmosomal adhesiveness due to abnormal incorporation of uncleaved mutant proDSG2 in cellular stress conditions. These results provide new insights into desmosomal cadherin regulation and ARVC/D pathophysiology, in particular, the potential role of mechanical stress on desmosomal dysfunction.

High risk of heart failure associated with desmoglein-2 mutations compared to plakophilin-2 mutations in arrhythmogenic right ventricular cardiomyopathy/dysplasia.

BACKGROUND: Previous studies suggested that genetic status affects the clinical course of arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) patients. The aim of this study was to compare the outcome of desmoglein-2 (DSG2) mutation carriers to those who carry the plakophilin-2 (PKP2) mutation, the most common ARVC/D-associated gene. METHODS AND RESULTS: Consecutive ARVC/D patients carrying a pathogenic mutation in PKP2 or DSG2 were selected from a national ARVC/D registry. The cumulative freedom from sustained ventricular arrhythmia and cardiac transplantation/death from heart failure (HF) during follow-up was assessed, compared between PKP2 and DSG2, and predictors for ventricular arrhythmia and HF events determined. Overall, 118 patients from 78 families were included: 27 (23%) carried a DSG2 mutation and 91 (77%) a PKP2 mutation. There were no significant differences between DSG2 and PKP2 mutation carriers concerning gender, proband status, age at diagnosis, T-wave inversion, or right ventricular dysfunction at baseline. DSG2 patients displayed more frequent epsilon wave (37% vs. 17%, P = 0.048) and left ventricular dysfunction at diagnosis (54% vs. 10%, P < 0.001). During a median follow-up of 5.6 years (2.5-16), DSG2 and PKP2 mutation carriers displayed a similar risk of sustained ventricular arrhythmia (log-rank P = 0.20), but DSG2 mutation carriers were at higher risk of transplantation/HF-related death (log-rank P < 0.001). The presence of a DSG2 mutation vs. PKP2 mutation was a predictor of transplantation/HF-related death in univariate Cox analysis (P = 0.0005). CONCLUSIONS: In this multicentre cohort, DSG2 mutation carriers were found to be at high risk of end-stage HF compared to PKP2 mutation carriers, supporting careful haemodynamic monitoring of these patients. The benefit of early HF treatment needs to be assessed in DSG2 carriers.

SCN5A mutations in 442 neonates and children: genotype-phenotype correlation and identification of higher-risk subgroups.

Aims: To clarify the clinical characteristics and outcomes of children with SCN5A-mediated disease and to improve their risk stratification. Methods and results: A multicentre, international, retrospective cohort study was conducted in 25 tertiary hospitals in 13 countries between 1990 and 2015. All patients ≤16 years of age diagnosed with a genetically confirmed SCN5A mutation were included in the analysis. There was no restriction made based on their clinical diagnosis. A total of 442 children {55.7% boys, 40.3% probands, median age: 8.0 [interquartile range (IQR) 9.5] years} from 350 families were included; 67.9% were asymptomatic at diagnosis. Four main phenotypes were identified: isolated progressive cardiac conduction disorders (25.6%), overlap phenotype (15.6%), isolated long QT syndrome type 3 (10.6%), and isolated Brugada syndrome type 1 (1.8%); 44.3% had a negative electrocardiogram phenotype. During a median follow-up of 5.9 (IQR 5.9) years, 272 cardiac events (CEs) occurred in 139 (31.5%) patients. Patients whose mutation localized in the C-terminus had a lower risk. Compound genotype, both gain- and loss-of-function SCN5A mutation, age ≤1 year at diagnosis in probands and age ≤1 year at diagnosis in non-probands were independent predictors of CE. Conclusion: In this large paediatric cohort of SCN5A mutation-positive subjects, cardiac conduction disorders were the most prevalent phenotype; CEs occurred in about one-third of genotype-positive children, and several independent risk factors were identified, including age ≤1 year at diagnosis, compound mutation, and mutation with both gain- and loss-of-function.