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Aims Arrhythmogenic cardiomyopathy (ACM) is characterized by progressive loss of cardiomyocytes, and fibrofatty tissue replacement. Extracellular vesicles (EVs) secreted by cardiosphere-derived cells, immortalized, and engineered to express high levels of β-catenin, exert anti-inflammatory, and anti-fibrotic effects. The aim of the current study was to assess efficacy of EVs in an ACM murine model. Methods and results Four-week-old homozygous knock-in mutant desmoglein-2 (Dsg2mt/mt) were randomized to receive weekly EVs or vehicle for 4 weeks. After 4 weeks, DSG2mt/mt mice receiving EVs showed improved biventricular function (left, P < 0.0001; right, P = 0.0037) and less left ventricular dilation (P < 0.0179). Electrocardiography revealed abbreviated QRS duration (P = 0.0003) and QTc interval (P = 0.0006) in EV-treated DSG2mt/mt mice. Further electrophysiology testing in the EV group showed decreased burden (P = 0.0042) and inducibility of ventricular arrhythmias (P = 0.0037). Optical mapping demonstrated accelerated repolarization (P = 0.0290) and faster conduction (P = 0.0274) in Dsg2mt/mt mice receiving EVs. DSG2mt/mt hearts exhibited reduced fibrosis, less cell death, and preserved connexin 43 expression after EV treatment. Hearts of Dsg2mt/mt mice expressed markedly increased levels of inflammatory cytokines that were, in part, attenuated by EV therapy. The pan-inflammatory transcription factor nuclear factor-κB (NF-κB), the inflammasome sensor NLRP3, and the macrophage marker CD68 were all reduced in EV-treated animals. Blocking EV hsa-miR-4488 in vitro and in vivo reactivates NF-κB and blunts the beneficial effects of EVs. Conclusions Extracellular vesicle treatment improved cardiac function, reduced cardiac inflammation, and suppressed arrhythmogenesis in ACM. Further studies are needed prior to translating the present findings to human forms of this heterogenous disease.

Multiple myeloma (MM) is the second most common haematological malignancy and is an incurable disease of neoplastic plasma cells (PC). Newly diagnosed MM patients currently undergo lengthy genetic testing to match chromosomal mutations with the most potent drug/s to decelerate disease progression. With only 17% of MM patients surviving 10-years postdiagnosis, faster detection and earlier intervention would unequivocally improve outcomes. Here, we show that the cell surface protein desmoglein-2 (DSG2) is overexpressed in ˜ 20% of bone marrow biopsies from newly diagnosed MM patients. Importantly, DSG2 expression was strongly predictive of poor clinical outcome, with patients expressing DSG2 above the 70th percentile exhibiting an almost 3-fold increased risk of death. As a prognostic factor, DSG2 is independent of genetic subtype as well as the routinely measured biomarkers of MM activity (e.g. paraprotein). Functional studies revealed a nonredundant role for DSG2 in adhesion of MM PC to endothelial cells. Together, our studies suggest DSG2 to be a potential cell surface biomarker that can be readily detected by flow cytometry to rapidly predict disease trajectory at the time of diagnosis. Refereed/Peer-reviewed

The study of a desmoglein 2 murine model of arrhythmogenic cardiomyopathy revealed cardiac inflammation as a key early event leading to fibrosis. Arrhythmogenic cardiomyopathy (AC) is an inherited heart muscle disorder leading to ventricular arrhythmias and heart failure due to abnormalities in the cardiac desmosome. We examined how loss of desmoglein 2 (Dsg2) in the young murine heart leads to development of AC. Apoptosis was an early cellular phenotype, and RNA sequencing analysis revealed early activation of inflammatory-associated pathways in Dsg2-null (Dsg2−/−) hearts at postnatal day 14 (2 weeks) that were absent in the fibrotic heart of adult mice (10 weeks). This included upregulation of iRhom2/ADAM17 and its associated pro-inflammatory cytokines and receptors such as TNFα, IL6R and IL-6. Furthermore, genes linked to specific macrophage populations were also upregulated. This suggests cardiomyocyte stress triggers an early immune response to clear apoptotic cells allowing tissue remodelling later on in the fibrotic heart. Our analysis at the early disease stage suggests cardiac inflammation is an important response and may be one of the mechanisms responsible for AC disease progression.

We have read the article by Cai et al. and find there is a discrepancy between their data and conclusion. Their statement, "Specifically, DSG2 expression was associated with tumor size", is not supported by their own clinicopathological data and analysis. After reviewing some similar articles, we also found no available evidence showed a statistically significant association between them. Therefore, we would like to suggest Cai et al. to rectify the results they published.

Left ventricular non-compaction cardiomyopathy (LVNC) is a rare heart disease, with or without left ventricular dysfunction, which is characterized by a two-layer structure of the myocardium and an increased number of trabeculae. The study of familial forms of LVNC is helpful for risk prediction and genetic counseling of relatives. Here, we present a family consisting of three members with LVNC. Using a next-generation sequencing approach a combination of two (likely) pathogenic nonsense mutations DSG2-p.S363X and TBX20-p.D278X was identified in all three patients. TBX20 encodes the cardiac T-box transcription factor 20. DSG2 encodes desmoglein–2, which is part of the cardiac desmosomes and belongs to the cadherin family. Since the identified nonsense variant (DSG2-p.S363X) is localized in the extracellular domain of DSG2, we performed in vitro cell transfection experiments. These experiments revealed the absence of truncated DSG2 at the plasma membrane, supporting the pathogenic relevance of DSG2-p.S363X. In conclusion, we suggest that in the future, these findings might be helpful for genetic screening and counseling of patients with LVNC.

BackgroundDesmosomes are specialized intercellular adhesive junctions of cardiac and epithelial cells that provide intercellular mechanical coupling through glycoproteins, one of which is desmoglein (DSG). DSG-2 mutations are frequently associated with biventricular arrhythmogenic cardiomyopathy (ACM). We report a case of left-dominant ACM in a patient who initially was misclassified as dilated cardiomyopathy (DCM).Case summaryA 28-year-old-woman was found to have a moderately reduced left ventricular (LV) systolic function and frequent premature ventricular contractions (PVCs). Targeted genetic testing revealed a heterozygous likely pathogenic variant associated with ACM in exon 15 of the DSG-2 gene (c.3059_3062del; p.Glu1020Alafs*18). Subsequent cardiac magnetic resonance (CMR) imaging showed epicardial and mid-myocardial fatty infiltration involving multiple LV wall segments, multiple areas of mid-myocardial fibrosis/scar, regional dyskinesis involving both ventricles, and an overall reduced left ventricular ejection fraction. The patient’s right ventricular (RV) cavity size and overall RV systolic function were normal. Based on the patient’s frequent PVCs, family history, fibrofatty myocardial replacement in multiple LV segments, and dyskinetic motion of multiple ventricular wall segments (predominantly affecting the LV), the patient was diagnosed with left-dominant ACM.DiscussionIdentifying a likely pathogenic mutation associated with ACM in a patient with ventricular arrhythmias and a family history of sudden cardiac death increased the possibility of ACM. Subsequent CMR imaging confirmed the diagnosis of left-dominant ACM by demonstrating regional biventricular dyskinesia and a characteristic pattern of fibrofatty myocardial replacement. Our case highlights the importance of targeted genetic testing and advanced cardiac imaging in distinguishing left-dominant ACM from DCM.

Background Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited condition, with approximately 60% of patients carrying a possibly disease-causing genetic variant. Known desmosomal genes account for about 50% of those variants. We herein report a family with ARVC in which a pathogenic desmosomal variant was missed because of the initial genetic testing method. Case summary A 54-year-old man diagnosed with ARVC underwent genetic cascade screening for a heterozygous titin variant (TTN: c.26542C>T), detected in his phenotypically affected sister. He did not harbour this TTN variant. Moreover, reclassification of this variant based on the American College of Medical Genetics (ACMG) 2015 criteria showed it to be likely benign. Upon genetic re-screening with a dedicated cardiomyopathy panel a heterozygous missense variant in desmoglein-2 (DSG2: c.152G>C) was found. His sister’s DNA was re-analysed and the same DSG2 variant was detected, and classified as LP (likely pathogenic) by current literature. Discussion The initial genetic screening tool used in the patient’s sister (whole-exome sequencing, WES) failed to detect the likely causative desmosomal variant in our family. While WES represents a good tool in searching for novel genes in Trio Analysis, it has a low DNA coverage in important regions (mean 10×) of known ARVC-associated genes. We therefore propose using smaller panels with better coverage in the clinical setting, such as Trusight-cardio (mean DNA coverage 100–300×) as an initial genetic screening method.

Funding Acknowledgements Type of funding sources: None. Background Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited disease that inevitably leads to terminal heart failure and sudden cardiac death due to ventricular arrhythmias. Excessive exercise accelerates the progress of the disease. At present, there is no curative therapy for ARVC. The disease is mostly caused by mutations in genes encoding desmosomal proteins, and Japanese ARVC patients commonly possess missense mutations in DSG2. Although there are animal models with Dsg2-related cardiomyopathy, they do not reflect the precise human disease caused by missense mutations in DSG2. Purpose We aimed to generate knock-in mouse models of ARVC carrying Dsg2 mutations equivalent to those found in ARVC patients. Methods We introduced Dsg2 mutations (R297C, D499A), which were equivalent to most common mutations in Japanese ARVC patients, to mice by CRSPR/Cas9 genome editing system. Echocardiography and treadmill training were performed to evaluate the cardiac phenotype of the mouse models. Results There is phenotype inequality between the two lines of Dsg2 knock-in mice. In R297C mice, all the homozygotes died suddenly until the age of 20 weeks, and half of the heterozygotes until the age of 25 weeks. Heart examination of the deceased homozygous mice demonstrated enlarged cavities, predominantly in the right ventricles, and scattered pale patches suggesting fibrotic replacement of the myocardium. Echocardiography of four 9-week-old homozygous mice shows acoustically dense zones (white arrows in the left figure) and left ventricular dysfunction (ejection fraction (EF) < 35%). Exploration of the hearts of sacrificed mice confirmed echocardiographical findings (red arrow in the right figure) demonstrating scattered pale regions similar to those in suddenly died mice. In contrast, homozygous and heterozygous D499A mice survived without sudden death. Both mutant mice develop heart failure after the age of 30 weeks. To mimic the effect of exercise, we performed treadmill training for two months started from 11 weeks old in both types of D499A and heterozygous R297C mice. The training significantly accelerated cardiac dysfunction: all D499A mice (homo and hetero) and half of heterozygous R297C developed biventricular dysfunction at the age of 19 weeks though no change in WT. EF for R297C heterozygous mice, D499A heterozygous and D499A homozygous mice decreased from 64.4 ± 4.3%, 71.9 ± 1.7% and 73.9 ± 1.1 to 31.2 ± 5.7%, 16.6 ± 2.1% and 12.4%±1.9, respectively. Treadmill training did not alter significantly EF in WT mice: 71.8 ± 2.3% before and 67.5 ± 1.4 at the end of physical challenge. Conclusion We generated mouse model of ARVC mutations that mimic the exact gene defect found in the humans. Our experimental work confirms significant overlap to the human phenotype. Further investigation will clarify the underlying cellular mechanisms. Abstract Figure. A heart from homozygous R297C mouse

The study of a desmoglein 2 murine model of arrhythmogenic cardiomyopathy revealed cardiac inflammation as a key early event leading to fibrosis. Arrhythmogenic Cardiomyopathy (AC) is an inherited heart muscle disorder leading to ventricular arrhythmias and heart failure due to abnormalities in the cardiac desmosome. We examined how loss of desmoglein 2 (Dsg2) in the young murine heart leads to development of AC. Cardiomyocyte apoptosis was an early cellular phenotype and RNA-Seq analysis revealed early activation of inflammatory-associated pathways in Dsg2 null (Dsg2−/−) hearts at postnatal day 14 (Two weeks) that were absent in the fibrotic heart of adult mice (Ten weeks). This included upregulation of iRhom2/ADAM17 and its associated pro-inflammatory cytokines and receptors such as TNFα, IL6R and IL-6. Furthermore, genes linked to specific macrophage populations were upregulated. This suggests cardiomyocyte stress triggers an early immune response to clear apoptotic cells allowing tissue remodelling later on in the fibrotic heart. Our analysis at different disease stages implicate inflammation related to loss of desmoglein 2 as a major mechanism for disease progression.

Background Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a rare cardiac disease predominantly caused by variants in desmosome genes. Variants in human Desmoglein-2 (DSG2) gene can cause ARVC with incomplete penetrance. However, it remains unknown whether ARVC would penetrate by distal myopathy. Methods We performed targeted next-generation sequencing using a cardiomyopathy/ion channelopathy panel in a Chinese ARVC pedigree. Plasmids of DSG2 were constructed, and pathogenicity of the DSG2 variant was investigated by real-time PCR, western blots, Immunofluorescence, and electron microscope. Results We identified a novel nonsense variant in DSG2 (c.710T > A, p.Leu237Ter) and a reported pathogenic missense variant of distal myopathy in MYH7 (c. 1322C > T, p.Thr441Met) in the proband of an ARVC pedigree. The functional analyses suggested that the nonsense variant could affect the expression and cell location of DSG2, and the number and shape of desmosomes were affected as well, indicating that the variant was implicated in the pathogenesis of ARVC. We found only patients carrying the distal myopathy pathogenic variant would manifested early-onset severe ARVC phenotype, which suggested that MYH7-p.Thr441Met variant could induced the onset of ARVC in the DSG2-p.Leu237Ter variant carriers. Conclusions Our study identified a novel null variant in DSG2 gene (c.710T > A, p.Leu237Ter) in an ARVC pedigree with incomplete penetrance. Only patients who carried a distal myopathy associated variant in MYH7 (c. 1322C > T, p.Thr441Met) would induce the onset of ARVC with early-onset and severe symptoms.

Physiological stressors, such as exercise, can precipitate sudden cardiac death or heart failure progression in patients with arrhythmogenic cardiomyopathy (ACM). Yet, whether and to what extent a highly prevalent and more elusive environmental factor, such as psychosocial stress (PSS), can also increase ACM disease progression is unexplored. Here, we first quantified perceived stress levels in patients with ACM and found these levels correlated with the extent of arrhythmias and cardiac dysfunction. To determine whether the observed correlation is due to causation, we inflicted PSS-via the resident-intruder (RI) paradigm&mdash, upon Desmoglein-2 mutant mice, a vigorously used mammalian model of ACM. We found that ACM mice succumbed to abnormally high in-trial, PSS mortality. Conversely, no sudden deaths occurred in wildtype (WT) counterparts. Desmoglein-2 mice that survived RI challenge manifested markedly worse cardiac dysfunction and remodeling, namely apoptosis and fibrosis. Furthermore, WT and ACM mice displayed similar behavior at baseline, but Desmoglein-2 mice exhibited heightened anxiety following RI-induced PSS. This outcome correlated with the worsening of cardiac phenotypes. Our mouse model demonstrates that in ACM-like subjects, PSS is incisive enough to deteriorate cardiac structure and function per se, i.e., in the absence of any pre-existing anxious behavior. Hence, PSS may represent a previously underappreciated risk factor in ACM disease penetrance.

A 59-year-old Chinese woman presenting with shortness of breath after exertion, pitting oedema of the lower extremities and Raynaud’s phenomenon was evaluated. Strongly positive ANA and ant...

Background Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is an inherited cardiomyopathy mainly caused by desmosomal gene mutation. More than half of Caucasian probands have desmosomal mutations, which lead to earlier onset of ventricular arrhythmias. Among non‐Caucasians, the genetic background of ARVD/C probands and its prognostic impact remain unclear. Methods and Results We genotyped 99 unrelated Japanese ARVD/C probands for plakophilin 2 (PKP2), desmoglein 2 (DSG2), desmoplakin (DSP), and desmocollin 2 (DSC2) between 2005 and 2014. Seventy‐five probands who fulfilled “definite” category according to the 2010 Task Force Criteria (TFC) were enrolled and followed up for 6.4 years. Sixty‐four percent of probands had desmosomal mutations; DSG2 was predominant (48% of mutations) followed by PKP2 (38%). DSG2 mutations were almost missense, whereas over 90% of PKP2 mutations were truncating mutations. Lethal ventricular arrhythmias (VAs, sustained ventricular tachycardia/fibrillation) occurred in 57% of probands as the first manifestation and 71% at the end of follow‐up. Five died during follow‐up. Truncating mutation carriers exhibited earlier lethal VAs onset compared to missense mutation carriers or mutation negatives (age at onset 35 ± 12, 49 ± 16, and 50 ± 19 years, respectively, P

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a rare heart disorder characterized by myocyte loss and fibro-fatty tissue replacement. With the progress of ARVC, patient can present serious ventricular arrhythmias, heart failure, and even sudden cardiac death. Previous studies have revealed that the generation and development of ARVC are related to structural changes of desmosomes. To date, at least 5 genes associated with desmosomes have been identified in patients with ARVC, including Desmoplakin , Plakophilin 2 , Desmoglein 2 , Desmocollin 2 , and Junction plakoglobin . In this study, we applied whole-exome sequencing to explore the potential causative gene in a Chinese family with suspicious ARVC. A novel missense mutation (c.1090 G > A/p.V364 M) of DSC2 was identified and co-segregated with the affected family members. This mutation leads to a substitution of valine by methionine and is predicted to be damaging by bioinformatics tools. In conclusion, our study not only expands the spectrum of DSC2 mutations and contributes to genetic counseling of families with ARVC but also improves the awareness of pathogenesis in Chinese patients with ARVC.

Densely granulated and sparsely granulated (SG) growth hormone (GH) pituitary adenomas differ in biological behavior, which may be correlated with their known differences in cytoplasmic keratin distribution and E-cadherin expression. We wanted to explore candidate genes that might further explain this behavior. Exon expression microarray was performed on 21 GH tumors (10 SG and 11 densely granulated) and 20 normal control pituitaries from autopsy. Bioinformatic analyses confirmed a differential molecular signature between normal pituitary and GH tumors as well as between the GH tumor subtypes. There was a consistent downregulation of transcripts involved in the structure and function of the desmosome, including desmoplakin (eightfold), desmoglein 2 (sixfold), plakophilin 2 (sevenfold), and p53 apoptosis effector related to PMP-22 (PERP; sixfold) in SG tumors compared with normal pituitary. PERP is lost in more aggressive SG human GH pituitary tumors. PERP re-expression in GH3 rat GH tumor cells resulted in decreased colony formation compared with vector transfectants, confirming the role of PERP as a tumor suppressor with no effects on proliferation. Increased PERP expression was associated with loss of a survival advantage in a hypoxic environment, as assessed by terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling (P < 0.05) and cleaved caspase-3 (P < 0.05). Downregulation of desmosomal formation transcripts including PERP may contribute to the aggressive phenotype seen in SG GH pituitary tumors and their behavior in response to surgery and medical therapy.

Arrhythmogenic right ventricular cardiomyopathy is a rare inherited heart-muscle disease that is a cause of sudden death in young people and athletes. Causative mutations in genes encoding desmosomal proteins have been identifi ed and the disease is nowadays regarded as a genetically determined myocardial dystrophy. The left ventricle is so frequently involved as to support the adoption of the broad term arrhythmogenic cardiomyopathy. Clinical diagnosis can be achieved by demonstrating function and structure changes of the right ventricle, electrocardiogram depolarisation and repolarisation abnormalities, ventricular arrhythmias, and fi brofatty replacement through endomyocardial biopsy. Although specifi c, the standardised diagnostic criteria lack sensitivity for early disease and their primary application remains in establishing the diagnosis in probands. However, the main clinical targets are early detection of concealed forms and risk stratifi cation for preventive strategies, which include physical exercise restriction, antiarrhythmic drugs, and implantable cardioverter-defi brillator therapy. Cascade genetic screening of family members of gene-positive probands allows the identifi cation of asymptomatic carriers who would require lifelong follow-up due to the age-related penetrance.

Aims Several data suggest that acute myocarditis could be related to genetic variants involved in familial cardiomyopathies, particularly arrhythmogenic cardiomyopathy, but the management of patients with acute myocarditis and their families regarding their risk for having an associated inherited cardiomyopathy is unclear. Methods and results Families with at least one individual with a documented episode of acute myocarditis and at least one individual with a cardiomyopathy or a history of sudden death were included in the study. Comprehensive pedigree, including genetic testing, and history of these families were analysed. Six families were included. Genetic analysis revealed a variant in desmosomal proteins genes in all the probands [five in desmoplakin (DSP) gene and one in desmoglein 2 gene]. In the five families identified with a DSP variant, genetic testing was triggered by the association of an acute myocarditis with a single case of apparently isolated dilated cardiomyopathy or sudden death. Familial screening identified 28 DSP variant carriers; 39% had an arrhythmogenic left ventricular (LV) cardiomyopathy phenotype. Familial histories of sudden death were frequent, and a remarkable phenotype of isolated LV late gadolinium enhancement on contrast‐enhanced cardiac magnetic resonance without any other structural abnormality was found in 38% of asymptomatic mutation carriers. None of the DSP variant carriers had imaging characteristics of right ventricle involvement meeting current Task Force criteria for arrhythmogenic right ventricular cardiomyopathy. Conclusions Comprehensive familial screening including genetic testing in case of acute myocarditis associated with a family history of cardiomyopathy or sudden death revealed unknown or misdiagnosed arrhythmogenic variant carriers with left‐dominant phenotypes that frequently evade arrhythmogenic right ventricular cardiomyopathy Task Force criteria. In view of our results, acute myocarditis should be considered as an additional criterion for arrhythmogenic cardiomyopathy, and genetic testing should be advised in patients who experience acute myocarditis and have a family history of cardiomyopathy or sudden death.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a rare and potentially life-threatening disorder of the heart. The clinical spectrum of ARVC includes myocyte loss and fibro-fatty tissue replacement. With the progress of ARVC, the patient can present serious ventricular arrhythmias, heart failure, and even sudden cardiac death. Previous studies have demonstrated that desmosomes and intermediate junctions play a crucial role in the generation and development of ARVC. In this study, we enrolled a Chinese patient with suspicious ARVC. The patient suffered from right ventricular enlargement and less thickening of right ventricular wall. ECG record showed an epsilon wave. However, there was no obvious symptom in his parents. After whole-exome sequencing and data filtering, we identified a de novo mutation (c.1729C>T/p.R577C) of junction plakoglobin (JUP) in this patient. Bioinformatics programs predicted that this mutation was deleterious. Western blot revealed that, compared to cells transfected with WT plasmids, the expressions of desmoglein 2 (DSG2) and Connexin 43 were decreased overtly in cells transfected with the mutant plasmid. Previous studies have proven that the reduction of DSG2 and Connexin 43 may disturb the stability of desmosomes. In this research, we reported a novel de novo mutation (c.1729C>T/p.R577C) of JUP in a Chinese patient with suspicious ARVC. Functional research further confirmed the pathogenicity of this novel mutation. Our study expanded the spectrum of JUP mutations and may contribute to the genetic diagnosis and counseling of patients with ARVC.

Background Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a rare cardiac disease predominantly caused by variants in desmosome genes. Variants in human Desmoglein-2 (DSG2) gene can cause ARVC with incomplete penetrance. However, it remains unknown whether ARVC would penetrate by distal myopathy. Methods We performed targeted next-generation sequencing using a cardiomyopathy/ionchannelopathy panel in a Chinese ARVC pedigree. Plasmids of DSG2 were constructed, and pathogenicity of the DSG2 variant was investigated by real-time PCR, western blots, Immunofluorescence, and electron microscope. Results We identified a novel nonsense variant in DSG2 (c.710T > A, p.Leu237Ter) and a reported pathogenic missense variant of distal myopathy in MYH7 (c. 1322C > T, p.Thr441Met) in the proband of an ARVC pedigree. The functional analyses suggested that the nonsense variant could affect the expression and cell location of DSG2, and the number and shape of desmosomes were affected as well, indicating that the variant was implicated in the pathogenesis of ARVC. We found only patients carrying the distal myopathy pathogenic variant would manifested early-onset severe ARVC phenotype, which suggested that MYH7-p.Thr441Met variant could induced the onset of ARVC in the DSG2-p.Leu237Ter variant carriers. Conclusions Our study identified a novel null variant in DSG2 gene (c.710T > A, p.Leu237Ter) in an ARVC pedigree with incomplete penetrance. Only patients who carried a distal myopathy associated variant in MYH7 (c. 1322C > T, p.Thr441Met) would induce the onset of ARVC with early-onset and severe symptoms.

The large number of diseases occurring when desmosome constituents are impaired provides striking evidence for the key role of desmosomes in maintaining tissue integrity. A detailed understanding of the molecular alterations causing desmosomal dysfunction has, in turn, underpinned the development of novel diagnostic tools. This has salient clinical implications for dentists and oral medicine practitioners because the majority of desmosomal diseases affect the oral cavity. In the present article, we review the autoimmune, infectious, genetic, and neoplastic diseases that target the desmosome, with particular emphasis on clinical manifestations, diagnostic pathways, and relevant laboratory investigations.

A case of a 51-year-old female with history of hypertension and a significant family history of premature coronary artery disease presented to the hospital after cardiac arrest. She successfully completed a targeted temperature management therapy with full neurologic recovery. Her hospital course was complicated by several bouts of ventricular fibrillation (VF) arrest which was rescued by timely defibrillation, high quality cardiorespiratory resuscitation, and administration of antiarrhythmic medications and inotropic agents. An automatic implantable cardioverter defibrillator (AICD) was inserted for secondary prevention of sudden cardiac death (SCD). A targeted genetic testing for idiopathic ventricular fibrillation revealed a mutation in the desmoglein-2 (DSG2) gene involved in arrhythmogenic right ventricular cardiomyopathy (ARVC). Eventually, a ventricular fibrillation radiofrequency ablation prevented recurrence of fatal arrhythmia and its associated symptoms.

Aims Arrhythmogenic right ventricular cardiomyopathy (ARVC) is characterized by right ventricular myocardial replacement and life-threatening ventricular arrhythmias. Desmosomal gene mutations are sometimes identified, but clinical and genetic diagnosis remains challenging. Desmosomal skin disorders can be caused by desmosomal gene mutations or autoantibodies. We sought to determine if anti-desmosome antibodies are present in subjects with ARVC. Methods and results We evaluated ARVC subjects and controls for antibodies to cardiac desmosomal cadherin proteins. Desmoglein-2 (DSG2), desmocollin-2, and N-cadherin proteins on western blots were exposed to sera, in primary and validation cohorts of subjects and controls, as well as the naturally occurring Boxer dog model of ARVC. We identified anti-DSG2 antibodies in 12/12 and 25/25 definite ARVC cohorts and 7/8 borderline subjects. Antibody was absent in 11/12, faint in 1/12, and absent in 20/20 of two control cohorts. Anti-DSG2 antibodies were present in 10/10 Boxer dogs with ARVC, and absent in 18/18 without. In humans, the level of anti-DSG2 antibodies correlated with the burden of premature ventricular contractions (r = 0.70), and antibodies caused gap junction dysfunction, a common feature of ARVC, in vitro. Anti-DSG2 antibodies were present in ARVC subjects regardless of whether an underlying mutation was identified, or which mutation was present. A disease-specific DSG2 epitope was identified. Conclusion Anti-DSG2 antibodies are a sensitive and specific biomarker for ARVC. The development of autoimmunity as a result of target-related mutations is unique. Anti-DSG2 antibodies likely explain the cardiac inflammation that is frequently identified in ARVC and may represent a new therapeutic target.

International audience; 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.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) results in an increased risk of sudden death. We sought mutations of desmoglein-2 (DSG2), desmoplakin (DSP), and plakophilin-2 (PKP2) in 15 cases of sudden death whose causes of death could not be determined at autopsy. In three victims, mutations were identified in DSP. Two of these mutations were novel; one had previously been reported in a patient with ARVC that had been diagnosed clinically. Histological findings were not typical of ARVC; however, it was notable that these mutations were present in three of 15 cases, a relatively high proportion. The causal relationship between the mutations and ARVC is unclear, but the mutations might have been associated with faulty desmosomal proteins resulting in fatal arrhythmia. Combining information gathered by the traditional means of gross and histological examination with postmortem genetic analysis of young victims would assist in identifying their cause of death.

Arrhythmogenic right ventricular cardiomyopathy is an inherited cardiac entity characterized by right ventricular, or biventricular, fibrofatty replacement of myocardium. Structural alterations may lead to sudden cardiac death, mainly in young males during exercise. Autosomal dominant pattern of inheritance is reported in most parts of pathogenic genetic variations identified. Currently, 13 genes have been associated with the disease but nearly 40 % of clinically diagnosed cases remain without a genetic diagnosis. New genetic technologies allow further genetic analysis, generating a significant amount of genetic data in novel genes, which is often classified as of ambiguous significance. We focus on genetic advances of arrhythmogenic right ventricular cardiomyopathy, helping clinicians to interpret and translate genetic data into clinical practice.

Dilated cardiomyopathy (DCM) leads to disturbed contraction and force transduction, and is associated with substantial mortality in all age groups. Involvement of a disrupted composition of the intercalated disc (ID) has been reported. However, in children, little is established about such subcellular changes during disease, because of the pathological mix-up with the ongoing cardiac maturation. This leaves maladaptive remodeling often undetected. We aimed at illustrating subcellular alterations in children diagnosed with DCM compared to age-matched controls, focusing on ID proteins known to be crucially stable under healthy conditions and destabilized during cardiac injury in adults. Left ventricular or septal pediatric specimens were collected from 7 individuals diagnosed with DCM (age: 23 weeks in utero to 8 weeks postnatal) and age-matched controls that died of non-cardiovascular cause. We determined the amount of fibrosis and localization of ID proteins by immunohistochemistry. In pediatric DCM, most ID proteins follow similar spatiotemporal changes in localization as in controls. However, although no mutations were found, the signal of the desmosomal protein Desmoglein-2 was reduced in all pediatric DCM specimens, but not in controls or adult DCM patients. Endocardial and transmural fibrosis was increased in all pediatric DCM patients compared to age-matched controls. Composition of the ID in pediatric DCM patients is similar to controls, except for the localization of Desmoglein-2 and presence of severe fibrosis. This suggests that the architecture of desmosomes is already disturbed in the early stages of DCM. These findings contribute to the understanding of pediatric DCM.

We report the case of a 37-year-old male patient admitted to the cardiac intensive care unit for acute pulmonary edema. He had a history of excessive alcoholic consumption and had had a viral syndrome in the preceding 10 days. A transthoracic echocardiogram revealed severe biventricular dysfunction, mild dilatation of the left heart chambers, and severe dilatation of the right chambers. Nonsustained ventricular tachycardia with a left bundle branch block morphology was detected during electrocardiographic monitoring. In the follow-up, he underwent a contrast-enhanced transthoracic echocardiogram and a cardiac resonance which were compatible with the diagnosis of arrhythmogenic right ventricular cardiomyopathy with biventricular involvement. Molecular analysis detected the mutation c.1423+2T>G (IVS10 ds +2T>G) in intron 10 of the gene DSG2 (desmoglein-2) in heterozygosity. To our knowledge, this mutation has not been previously described in arrhythmogenic right ventricular cardiomyopathy.

Background Arrhythmogenic cardiomyopathy (AC) is considered a predominantly right ventricular (RV) desmosomal disease. However, left-dominant forms due to desmosomal gene mutations, including PKP2 variant c.419C>T, have been described. Recently, a nondesmosomal phospholamban ( PLN ) mutation (c.40_42delAGA) has been identified, causing dilated cardiomyopathy and arrhythmias. Objective To gain more insight into pathogenicity of the PKP2 variant c.419C>T by cosegregation analysis of the PKP2 variant c.419C>T vs the PLN mutation c.40_42delAGA. Methods A Dutch family (13 family members, median age 49 years, range 34–71 years) with ventricular tachycardia underwent (1) meticulous phenotypic characterization and (2) screening of 5 desmosomal genes ( PKP2 , DSC2 , DSG2 , DSP , JUP ) and PLN . Results Six family members fulfilled 2010 AC Task Force Criteria. Seven had signs of left ventricular (LV) involvement (inverted T waves in leads V 4 –V 6 , LV wall motion abnormalities and late enhancement, and reduced LV ejection fraction), including 6 family members with proven AC. The PKP2 variant c.419C>T was found as a single variant in 3 family members, combined with the PLN mutation c.40_42delAGA in 3 others. PLN mutation was found in 9 family members, including the 6 with AC and all 7 with LV involvement. The PLN mutation c.40_42delAGA was found as a single mutation in 6, combined with the PKP2 variant c.419C>T in 3 others. A low-voltage electrocardiogram was seen in 4 of 9 PLN mutation-positive subjects. None of the family members with the single PKP2 variant showed any sign of RV or LV involvement. Conclusions The PLN mutation c.40_42delAGA cosegregates with AC and with electrocardiographic and structural LV abnormalities. In this family, there was no evidence of disease-causing contribution of the PKP2 variant c.419C>T.

Rationale: The sympathetic nervous system is a major mediator of heart function. Intercalated discs composed of desmosomes, adherens junctions, and gap junctions provide the structural backbone for coordinated contraction of cardiac myocytes. Objective: Gap junctions dynamically remodel to adapt to sympathetic signaling. However, it is unknown whether such rapid adaption also occurs for the adhesive function provided by desmosomes and adherens junctions. Methods and Results: Atomic force microscopy revealed that β-adrenergic signaling enhances both the number of desmoglein 2-specific interactions along cell junctions and the mean desmoglein 2-mediated binding forces, whereas N-cadherin-mediated interactions were not affected. This was accompanied by increased cell cohesion in cardiac myocyte cultures and murine heart slices. Enhanced desmoglein 2-positive contacts and increased junction length as revealed by immunofluorescence and electron microscopy reflected cAMP-induced reorganization of intercellular contacts. The mechanism underlying cAMP-mediated strengthening of desmoglein 2 binding was dependent on expression of the intercalated disc plaque protein plakoglobin (Pg) and direct phosphorylation at S665 by protein kinase A: Pg deficiency as well as overexpression of the phospho-deficient Pg-mutant S665A abrogated both cAMP-mediated junctional remodeling and increase of cohesion. Moreover, Pg knockout hearts failed to functionally adapt to adrenergic stimulation. Conclusions: Taken together, we provide first evidence for positive adhesiotropy as a new cardiac function of sympathetic signaling. Positive adhesiotropy is dependent on Pg phosphorylation at S665 by protein kinase A. This mechanism may be of high medical relevance because loss of junctional Pg is a hallmark of arrhythmogenic cardiomyopathy.

Friedreich ataxia (FRDA) is an autosomal recessive disorder with a complex clinical and neuropathological phenotype, but the most frequent cause of death is cardiomyopathy. The principal autopsy findings in FRDA hearts are concentric hypertrophy, enlargement of cardiomyocytes, myofiber necrosis, inflammatory infiltration, scarring, and random accumulation of iron. In addition, the myocardium shows generalized disorganization of intercalated discs (ICD), the Velcro-like end-to-end connections of heart fibers that provide mechanical cohesion and ionic coupling. The principal components of ICD are fascia adherens junctions (FAJ), desmosomes, and gap junctions. Frataxin deficiency in FRDA may cause improper assembly of ICD early in life, making hearts vulnerable to mechanical stress in childhood and adolescence. We studied the ICD in the myocardium of left ventricular wall (LVW), right ventricular wall, and ventricular septum in 18 genetically confirmed FRDA patients (age of death, 10 to 87years) and 12 normal controls (age of death, 13 to 69years). In cases with juvenile onset, electron microscopy and immunohistochemistry of N-cadherin and vinculin, two abundant FAJ proteins, showed enlargement of ICD, discontinuity, and hyperconvolution. Reaction product of the desmosomal protein desmoglein 2 was similar. The distribution of the gap junction protein connexin 43 at ICD was also irregular and displayed abnormal lateralization to the plasma membranes of cardiomyocytes. Confocal immunofluorescence microscopy of α-actinin, affinity fluorescence microscopy of actin with rhodamine-labeled phalloidin, and electron microscopy, revealed the principal integrity of sarcomeres of the myocardium in FRDA. In two late-onset long-surviving FRDA patients (ages 79 and 87), clinical cardiomyopathy was absent, and ICD were normal. The described observations in patients with a broad range of disease onset and duration allow us to conclude that faulty assembly of ICD interferes with proper end-to-end adhesion of cardiomyocytes of the growing heart and contributes to the pathogenesis of FRDA cardiomyopathy.

Background— Analysis of myocardium has revealed mechanistic insights into arrhythmogenic cardiomyopathy but cardiac samples are difficult to obtain from probands and especially from family members. To identify a potential surrogate tissue, we characterized buccal mucosa cells. Methods and Results— Buccal cells from patients, mutation carriers, and controls were immunostained and analyzed in a blinded fashion. In additional studies, buccal cells were grown in vitro and incubated with SB216763. Immunoreactive signals for the desmosomal protein plakoglobin and the major cardiac gap junction protein Cx43 were markedly diminished in buccal mucosa cells from arrhythmogenic cardiomyopathy patients with known desmosomal mutations when compared with controls. Plakoglobin and Cx43 signals were also reduced in most family members who carried disease alleles but showed no evidence of heart disease. Signal for the desmosomal protein plakophilin-1 was reduced in buccal mucosa cells in patients with PKP2 mutations but not in those with mutations in other desmosomal genes. Signal for the desmosomal protein desmoplakin was reduced in buccal mucosa cells from patients with mutations in DSP , DSG2 , or DSC2 but not in PKP2 or JUP . Abnormal protein distributions were reversed in cultured cells incubated with SB216763, a small molecule that rescues the disease phenotype in cardiac myocytes. Conclusions— Buccal mucosa cells from arrhythmogenic cardiomyopathy patients exhibit changes in the distribution of cell junction proteins similar to those seen in the heart. These cells may prove useful in future studies of disease mechanisms and drug screens for effective therapies in arrhythmogenic cardiomyopathy.

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.

Mice carrying a deletion of the adhesive extracellular domain of the desmosomal cadherin desmoglein 2 develop an arrhythmogenic right ventricular cardiomyopathylike phenotype with ventricular dilation, fibrosis and arrhythmia. To unravel the sequence of myocardial alterations and to identify potential pathomechanisms, histological analyses were performed on mutant hearts from the juvenile to the adult state, i.e., between 2 and 13 weeks. At an age of 2 weeks 30% of mutants presented lesions,which were visible as white plaques on the heart surface or in the septum. From 4 weeks onwards, all mutants displayed a cardiac phenotype. Dying cardiomyocytes with calcification were found in lesions of all ages. But lesions of young mutant animals contained high amounts of CD45+ immune cells and little collagen fibers, whereas lesions of the older animals were collagen-rich and harbored only a small but still significantly increased number of CD45+ cells. Electron microscopy further showed that distinct desmosomes cannot be distinguished in intercalated discs of mutant hearts. Widening of the intercellular cleft and even complete dissociation of intercalated discs were often observed close to lesions. Disturbed sarcomer structure, altered Z-discs, multiple autophagic vacuoles and swollen mitochondria were other prominent pathological features. Taken together, the following scenario is suggested: mutant desmoglein 2 cannot fully support the increased mechanical requirements placed on intercalated disc adhesion during postnatal heart development, resulting in compromised adhesion and cell stress. This induces cardiomyocyte death, aseptic inflammation and fibrotic replacement. The acute stage of scar formation is followed by permanent impairment of the cardiac function.

Objectives: Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is characterized by fibrofatty replacement of cardiomyocytes. In around 50% of index patients, a genetic predisposition is demonstrated. The purpose of this study was to examine a plakophilin-2 (PKP2) splice site mutation, c.2489+4A>C, identified in 4 separately ascertained Dutch ARVD/C families. Methods: Genealogical studies and comprehensive screening of 5 desmosomal genes were undertaken. Reverse transcriptase PCR (RT-PCR) and subsequent sequencing was performed. Results: An A-to-C change (c.2489+4A>C) near the splice donor site of intervening sequence 12 of PKP2 was found in all 4 families. Based on pedigree data and haplotype sharing, a common ancestor should be situated more than 7 generations ago. RT-PCR demonstrated the presence of aberrant messenger RNA. Clinical manifestations ranged from severe disease to nonpenetrance in elderly mutation carriers. Conclusions: This founder mutation in PKP2 is predicted to lead to the presence of a dysfunctional PKP2 protein, whereas most truncating mutations are expected to lead to loss of protein. Mutation carriers displayed a wide range of disease severity, suggesting that PKP2 mutations alone are not sufficient to cause disease, which results in the variable expression and incomplete penetrance characteristic of ARVD/C mutations.

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. Electronic supplementary material The online version of this article (doi:10.1007/s00395-011-0175-y) contains supplementary material, which is available to authorized users.

Background The diagnosis of arrhythmogenic right ventricular cardiomyopathy can be challenging. Disease-causing mutations in desmosomal genes have been identified. A novel diagnostic feature, loss of immunoreactivity for plakoglobin from the intercalated disks, recently was proposed. Objective The purpose of this study was to identify two novel mutations in the intracellular cadherin segment of desmoglein-2 (G812S and C813R in exon 15). Co-segregation of the G812S mutation with disease expression was established in a large Caucasian family. Endomyocardial biopsies of two individuals showed reduced plakoglobin signal at the intercalated disk. Methods To understand the pathologic changes occurring in the diseased myocardium, functional studies on three mutations in exon 15 of desmoglein-2 (G812C, G812S, C813R) were performed. Results Localization studies failed to detect any differences in targeting or stability of the mutant proteins, suggesting that they act via a dominant negative mechanism. Binding assays were performed to probe for altered binding affinities toward other desmosomal proteins, such as plakoglobin and plakophilin-2. Although no differences were observed for the mutated proteins in comparison to wild-type desmoglein-2, binding to plakophilin-2 depended on the expression system (i.e., bacterial vs mammalian protein expression). In addition, abnormal migration of the C813R mutant protein was observed in gel electrophoresis. Conclusion Loss of plakoglobin immunoreactivity from the intercalated disks appears to be the endpoint of complex pathologic changes, and our functional data suggest that yet unknown posttranslational modifications of desmoglein-2 might be involved.

Arrhythmogenic right ventricular cardiomyopathy is a rare inherited heart-muscle disease that is a cause of sudden death in young people and athletes. Causative mutations in genes encoding desmosomal proteins have been identified and the disease is nowadays regarded as a genetically determined myocardial dystrophy. The left ventricle is so frequently involved as to support the adoption of the broad term arrhythmogenic cardiomyopathy. Clinical diagnosis can be achieved by demonstrating function and structure changes of the right ventricle, electrocardiogram depolarisation and repolarisation abnormalities, ventricular arrhythmias, and fibrofatty replacement through endomyocardial biopsy. Although specific, the standardised diagnostic criteria lack sensitivity for early disease and their primary application remains in establishing the diagnosis in probands. However, the main clinical targets are early detection of concealed forms and risk stratification for preventive strategies, which include physical exercise restriction, antiarrhythmic drugs, and implantable cardioverter-defibrillator therapy. Cascade genetic screening of family members of gene-positive probands allows the identification of asymptomatic carriers who would require lifelong follow-up due to the age-related penetrance.

Mutations in the cardiac desmosomal protein desmoglein-2 (DSG2) are associated with arrhythmogenic right ventricular cardiomyopathy (ARVC). We studied the explanted heart of a proband carrying the DSG2-N266S mutation as well as transgenic mice (Tg-NS) with cardiac overexpression of the mouse equivalent of this mutation, N271S-dsg2, with the aim of investigating the pathophysiological mechanisms involved. Transgenic mice recapitulated the clinical features of ARVC, including sudden death at young age, spontaneous ventricular arrhythmias, cardiac dysfunction, and biventricular dilatation and aneurysms. Investigation of transgenic lines with different levels of transgene expression attested to a dose-dependent dominant-negative effect of the mutation. We demonstrate for the first time that myocyte necrosis is the key initiator of myocardial injury, triggering progressive myocardial damage, including an inflammatory response and massive calcification within the myocardium, followed by injury repair with fibrous tissue replacement, and myocardial atrophy. These observations were supported by findings in the explanted heart from the patient. Insight into mechanisms initiating myocardial damage in ARVC is a prerequisite to the future development of new therapies aimed at delaying onset or progression of the disease.

Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is an inherited myocardial disorder associated with arrhythmias, heart failure, and sudden death. To date, mutations in four genes encoding major desmosomal proteins (plakoglobin, desmoplakin, plakophilin-2, and desmoglein-2) have been implicated in the pathogenesis of ARVD/C. We screened 77 probands with ARVD/C for mutations in desmocollin-2 (DSC2), a gene coding for a desmosomal cadherin. Two heterozygous mutations--a deletion and an insertion--were identified in four probands. Both mutations result in frameshifts and premature truncation of the desmocollin-2 protein. For the first time, we have identified mutations in desmocollin-2 in patients with ARVD/C, a finding that is consistent with the hypothesis that ARVD/C is a disease of the desmosome.

Aims The ultrastructural features of the myocardium in arrhythmogenic right ventricular cardiomyopathy (ARVC) have not been systematically investigated so far. The recent discovery of gene mutations encoding intercalated disc proteins prompted us to perform a transmission electron microscopy study on endomyocardial biopsies. Methods and results Twenty-one ARVC probands who fulfilled the international Task Force diagnostic criteria underwent right ventricular endomyocardial biopsy and screening of desmosome (D) protein encoding genes. Myocyte intercalated discs were analysed by transmission electron microscope and the data were compared with those of 10 controls and 10 patients with idiopathic dilated cardiomyopathy. Extensive fibro-fatty replacement with a residual myocardium of 59+ 23% was found in ARVC biopsy samples. Pathogenic D gene mutations were identified in 10 (48%): desmoglein-2 in four, desmoplakin in three and plakophilin-2 in three. Mean D length and D percent length of intercalated disc were significantly higher, D number was significantly lower and D gap was widened in ARVC. Moreover, abnormally located D in 75%, abnormal small junctions in 52%, and pale internal plaques in 32% of ARVC patients were found in the presence of a normal intercalated disc convolution index. Conclusion The ultrastructural evidence of intercalated discs remodelling in ARVC, together with the positive screening of D protein encoding genes in half of probands, are in keeping with an intercellular junction cardiomyopathy.

Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is a disorder characterized by fibrofatty replacement of cardiac myocytes that typically manifests in the right ventricle. It is inherited as an autosomal dominant disease with reduced penetrance, although autosomal recessive forms of the disease also occur. We identified four probands with ARVD/C caused by mutations in DSG2, which encodes desmoglein-2, a component of the cardiac desmosome. No association between mutations in this gene and human disease has been reported elsewhere. One of these probands has compound-heterozygous mutations in DSG2, and the remaining three have isolated heterozygous missense mutations, each disrupting known functional components of desmoglein-2. We report that mutations in DSG2 contribute to the development of ARVD/C.

Background— Mutations in the plakophilin-2 gene ( PKP2 ) have been found in patients with arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVC). Hence, genetic screening can potentially be a valuable tool in the diagnostic workup of patients with ARVC. Methods and Results— To establish the prevalence and character of PKP2 mutations and to study potential differences in the associated phenotype, we evaluated 96 index patients, including 56 who fulfilled the published task force criteria. In addition, 114 family members from 34 of these 56 ARVC index patients were phenotyped. In 24 of these 56 ARVC patients (43%), 14 different (11 novel) PKP2 mutations were identified. Four different mutations were found more than once; haplotype analyses revealed identical haplotypes in the different mutation carriers, suggesting founder mutations. No specific genotype-phenotype correlations could be identified, except that negative T waves in V 2 and V 3 occurred more often in PKP2 mutation carriers ( P PKP2 mutations were identified in 16 of these 23 ARVC index patients (70%) with familial ARVC. On the other hand, no PKP2 mutations at all were found in 11 probands without additional affected family members ( P Conclusions— PKP2 mutations can be identified in nearly half of the Dutch patients fulfilling the ARVC criteria. In familial ARVC, even the vast majority (70%) is caused by PKP2 mutations. However, nonfamilial ARVC is not related to PKP2 . The high yield of mutational analysis in familial ARVC is unique in inherited cardiomyopathies.

Desmoglein-2 (DSG2), a member of the desmosomal cadherin superfamily, has been linked to arrhythmogenic right ventricular cardiomyopathy (ARVC)which may cause life-threatening ventricular arrhythmias and sudden death. Fatal arrhythmias resulting in sudden death also occur in the absence of morphologic cardiac abnormalities at autopsy. We sequenced all 15 exons of DSG2 in DNA extracted from post-mortem heart tissues of 25 patients dying with ARVC and 25 from sudden unexplained death (SUD). The primers were designed using the Primer Express 3.0 software. Direct sequencing for both sense and antisense strands was performed with a BigDye Terminator DNA sequencing kit on a 3130 xl Genetic Analyzer. Mutation damage prediction was made using Mutation Taster, Polyphen and SIFT software. 2 DSG2 mutations (p. S1026Q fsX12, p. G678R)in two ARVC samples and 2 DSG2 mutations(p. E 896K, p. A858 V) in two SUD samples were identified, all the mutations were novel. We concluded that DSG2 mutations may not specific for ARVC and may be related to the fatal arrhythmic events even in patients with a morphological normal heart.

AIMS: We determined the contribution of the desmosomal cadherin desmoglein-2 to cell-cell cohesion in cardiomyocytes. In the intercalated disc, providing mechanical strength and electrical communication between adjacent cardiomyocytes, desmoglein-2 is closely associated with N-cadherin and gap junctions. METHODS AND RESULTS: We studied intercalated discs of HL-1 cardiomyocytes by immunostaining of desmoglein-2 and N-cadherin. Cohesion was measured using a liberase-based dissociation-assay and compared with cell-free single-molecule atomic force microscopy measurements. L-tryptophan caused irregular desmoglein-2 condensation, weakened cell-cell cohesion and impaired both homophilic desmoglein-2 and N-cadherin trans-interaction, whereas l-phenylalanine had no effect. L-tryptophan did not affect N-cadherin localization and its inhibitory effect on cell-cohesion and desmoglein-2 binding, but not on N-cadherin interaction, was blocked by a desmoglein-specific tandem peptide. Moreover, Ca(2+)-depletion, desmoglein-2 knockdown, a desmoglein-specific single peptide and certain desmoglein-2 mutations associated with arrhythmogenic cardiomyopathy reduced cell-cell cohesion, whereas cell adhesion was strengthened by desmoglein-2 overexpression. Since single peptide did not interfere with N-cadherin trans-interaction, these data indicate that (i) desmoglein-2 binding is crucial for cardiomyocyte cohesion and (ii) L-tryptophan reduced both desmoglein-2 and N-cadherin binding, whereas single and tandem peptide can be used to specifically target desmoglein-2-mediated adhesion. L-tryptophan and single peptide also induced ultrastructural alterations of areae compositae. Functional analyses at the organ level revealed reduced cardiomyocyte function and inefficient response to adrenergic stimulation in both L-tryptophan- and single peptide-challenged murine Langendorff hearts paralleled by redistribution of connexin 43 in L-tryptophan-treated heart slices. CONCLUSION: Our data demonstrate that desmoglein-2 plays a critical role in cardiomyocyte cohesion and function.

Objectives We tested the hypothesis that defective interactions between adhesion junctions and the cytoskeleton caused by the plakoglobin mutation in Naxos disease lead to remodeling of gap junctions and altered expression of the major gap junction protein, connexin43. Background Naxos disease, a recessive form of arrhythmogenic right ventricular cardiomyopathy, is associated with a high incidence of arrhythmias and sudden cardiac death. Naxos disease is caused by a mutation in plakoglobin, a protein that links cell-cell adhesion molecules to the cytoskeleton. Methods Myocardial expression of connexin43 and other intercellular junction proteins was characterized in 4 patients with Naxos disease. Immunohistochemistry was performed in all 4 patients, and immunoblotting and electron microscopy were performed in 1 patient who died in childhood before overt arrhythmogenic right ventricular cardiomyopathy had developed. Results Connexin43 expression at intercellular junctions was reduced significantly in both right and left ventricles in all patients with Naxos disease. Electron microscopy revealed smaller and fewer gap junctions interconnecting ventricular myocytes. Mutant plakoglobin was expressed but failed to localize normally at intercellular junctions. Localization of N-cadherin, α- and β-catenins, plakophilin-2, desmoplakin-1, and desmocollin-2 at intercalated disks appeared normal. Conclusions Remodeling of gap junctions occurs early in Naxos disease, presumably because of abnormal linkage between mechanical junctions and the cytoskeleton. Gap junction remodeling may produce a coupling defect which, combined with the subsequent development of pathologic changes in myocardium, could contribute to a highly arrhythmogenic substrate and enhance the risk of sudden death in Naxos disease.