Circulating miR-185-5p as a Potential Biomarker for Arrhythmogenic Right Ventricular Cardiomyopathy.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a genetic cardiac disease characterized by progressive myocardial fibro-fatty replacement, arrhythmias and risk of sudden death. Its diagnosis is challenging and often it is achieved after disease onset or postmortem. In this study, we sought to identify circulating microRNAs (miRNAs) differentially expressed in ARVC patients compared to healthy controls. In the pilot study, we screened the expression of 754 miRNAs from 21 ARVC patients and 20 healthy controls. After filtering the miRNAs considering a log fold-change cut-off of ±1, p-value < 0.05, we selected five candidate miRNAs for a subsequent validation study in which we used TaqMan-based real-time PCR to analyse samples from 37 ARVC patients and 30 healthy controls. We found miR-185-5p significantly upregulated in ARVC patients. Receiver operating characteristic analysis indicated an area under the curve of 0.854, corroborating the link of this miRNA and ARVC pathophysiology.

A targeted next-generation gene panel reveals a novel heterozygous nonsense variant in the TP63 gene in patients with arrhythmogenic cardiomyopathy.

BACKGROUND: Arrhythmogenic cardiomyopathy (ACM) is associated with arrhythmias and risk of sudden death. Mutations in genes encoding proteins of cardiac intercalated discs account for ∼60% of ACM cases, but the remaining 40% is still genetically elusive. OBJECTIVE: The purpose of this study was to identify the underlying genetic cause in probands with ACM. METHODS: DNA samples from 40 probands with ACM, negative for mutations in the 3 major ACM genes-DSP, PKP2, and DSG2, were screened by using a targeted gene panel consisting of 15 known ACM genes and 53 candidate genes. RESULTS: About half of patients were found to carry rare variant(s) predicted to be damaging; specifically, 9 (22.5%) showed ≥1 variants in genes associated with ACM and/or with other inherited heart diseases and 10 (25%) showed variants in candidate genes. Among the latter, we focused on 2 novel variants in TP63 and PPP1R13L candidate genes (c.796C>T, p.(R266*) and c.1858G>C, p.(A620P), respectively). The encoded proteins p63 and inhibitor of apoptosis stimulating p53 protein are known to be interacting partners. Inhibitor of apoptosis stimulating p53 protein is a shuttling multifunctional protein: in the nucleus it is critical for inhibiting p63 function, whereas in the cytoplasm it regulates desmosome integrity. According to the American College of Medical Genetics and Genomics guidelines, the variant in TP63 has been scored as likely pathogenic and the variant in PPP1R13L as a variant of uncertain significance. Importantly, the mutant TP63 allele leads to nonsense-mediated messenger RNA decay, causing haploinsufficiency. CONCLUSION: Our findings identify TP63 as a putative novel disease gene for ACM, while the possible involvement of PPP1R13L remains to be determined.

A novel murine model for arrhythmogenic cardiomyopathy points to a pathogenic role of Wnt signalling and miRNA dysregulation.

AIMS: Arrhythmogenic cardiomyopathy (AC) is one of the most common inherited cardiomyopathies, characterized by progressive fibro-fatty replacement in the myocardium. Clinically, AC manifests itself with ventricular arrhythmias, syncope, and sudden death and shows wide inter- and intra-familial variability. Among the causative genes identified so far, those encoding for the desmosomal proteins plakophilin-2 (PKP2), desmoplakin (DSP), and desmoglein-2 (DSG2) are the most commonly mutated. So far, little is known about the molecular mechanism(s) behind such a varied spectrum of phenotypes, although it has been shown that the causative mutations not only lead to structural abnormalities but also affect the miRNA profiling of cardiac tissue. Here, we aimed at studying the pathogenic effects of a nonsense mutation of the desmoglein-2 gene, both at the structural level and in terms of miRNA expression pattern. METHODS AND RESULTS: We generated transgenic mice with cardiomyocyte-specific overexpression of a FLAG-tagged human desmoglein-2 harbouring the Q558* nonsense mutation found in an AC patient. The hearts of these mice showed signs of fibrosis, decrease in desmosomal size and number, and reduction of the Wnt/ß-catenin signalling. Genome-wide RNA-Seq performed in Tg-hQ hearts and non-transgenic hearts revealed that 24 miRNAs were dysregulated in transgenic animals. Further bioinformatic analyses for selected miRNAs suggested that miR-217-5p, miR-499-5p, and miR-708-5p might be involved in the pathogenesis of the disease. CONCLUSION: Down-regulation of the canonical Wnt/ß-catenin signalling might be considered a common key event in the AC pathogenesis. We identified the miRNA signature in AC hearts, with miR-708-5p and miR-217-5p being the most up-regulated and miR-499-5p the most down-regulated miRNAs. All of them were predicted to be involved in the regulation of the Wnt/ß-catenin pathway and might reveal the potential pathophysiology mechanisms of AC, as well as be useful as therapeutic targets for the disease.

Whole-Exome Sequencing Identifies Pathogenic Variants in TJP1 Gene Associated With Arrhythmogenic Cardiomyopathy.

BACKGROUND: Arrhythmogenic cardiomyopathy (ACM) is an inherited cardiac disease characterized by progressive fibro-fatty myocardial replacement, ventricular arrhythmia, heart failure, and sudden death. Causative mutations can be identified in 60% of patients, and most of them are found in genes encoding mechanical junction proteins of the intercalated disk. METHODS: Whole-exome sequencing was performed on the proband of an ACM family. Sanger sequencing was used to screen for mutations the tight junction protein 1 ( TJP1) gene in unrelated patients. Predictions of local structure content and molecular dynamics simulations were performed to investigate the structural impact of the variants. RESULTS: A novel c.2006A>G p.(Y669C) variant in TJP1 gene was identified by whole-exome sequencing in a patient with ACM. TJP1 encodes zonula occludens 1, an intercalated disk protein interacting with proteins of gap junctions and area composita. Additional rare TJP1 variants have been identified in 1 of 40 Italian probands (c.793C>T p.(R265W)) with arrhythmogenic right ventricular cardiomyopathy and in 2 of 43 Dutch/German patients (c. 986C>T, p.(S329L) and c.1079A>T, p.(D360V)) with dilated cardiomyopathy and recurrent ventricular tachycardia. The p.(D360V) variant was identified in a proband also carrying the p.(I156N) pathogenic variant in DSP. All 4 TJP1 variants are predicted to be deleterious and affect highly conserved amino acids, either at the GUK (guanylate kinase)-like domain (p.(Y669C)) or at the disordered region of the protein between the PDZ2 and PDZ3 domains (p.(R265W), p.(S329L), and p.(D360V)). The local unfolding induced by the former promotes structural rearrangements of the GUK domain, whereas the others are predicted to impair the function of the disordered region. Furthermore, rare variants in TJP1 are statistically enriched in patients with ACM relative to controls. CONCLUSIONS: We provide here the first evidence linking likely pathogenic TJP1 variants to ACM. Prevalence and pathogenic mechanism of TJP1-mediated ACM remain to be determined.

Large Genomic Rearrangements of Desmosomal Genes in Italian Arrhythmogenic Cardiomyopathy Patients.

BACKGROUND: Arrhythmogenic cardiomyopathy (AC) is an inherited heart muscle disease associated with point mutations in genes encoding for cardiac desmosome proteins. Conventional mutation screening is positive in ≈50% of probands. Copy number variations (CNVs) have recently been linked to AC pointing to the need to determine the prevalence of CNVs in desmosomal genes and to evaluate disease penetrance by cosegregation analysis in family members. METHODS AND RESULTS: A total of 160 AC genotype-negative probands for 5 AC desmosomal genes by conventional mutation screening underwent multiplex ligation-dependent probe amplification. Nine heterozygous CNVs were identified in 11 (6.9%) of the 160 probands. Five carried a deletion of the entire plakophilin-2 (PKP2) gene, 2 a deletion of only PKP2 exon 4, 1 a deletion of the PKP2 exons 6 to 11, 1 a PKP2 duplication of 5' untranslated region till exon 1, 1 the desmocollin-2 (DSC2) duplication of exons 7 to 9, and 1 a large deletion of chromosome 18 comprising both DSC2 and desmoglein-2 genes. All probands were affected by moderate-severe forms of the disease, whereas 10 (32%) of the 31 family members carrying one of these deletions fulfilled the diagnostic criteria. CONCLUSIONS: Genomic rearrangements were detected in ≈7% of AC probands negative for pathogenic point mutations in desmosomal genes, highlighting the potential of CNVs analysis to substantially increase the diagnostic yield of genetic testing. Genotype-phenotype correlation demonstrated the presence of the disease in about one third of family members carrying the CNV, underlying the role of other factors in the development and progression of the disease.

Wnt/ß-catenin pathway in arrhythmogenic cardiomyopathy.

Wnt/ß-catenin signaling pathway plays essential roles in heart development as well as cardiac tissue homoeostasis in adults. Abnormal regulation of this signaling pathway is linked to a variety of cardiac disease conditions, including hypertrophy, fibrosis, arrhythmias, and infarction. Recent studies on genetically modified cellular and animal models document a crucial role of Wnt/ß-catenin signaling in the molecular pathogenesis of arrhythmogenic cardiomyopathy (AC), an inherited disease of intercalated discs, typically characterized by ventricular arrhythmias and progressive substitution of the myocardium with fibrofatty tissue. In this review, we summarize the conflicting published data regarding the Wnt/ß-catenin signaling contribution to AC pathogenesis and we report the identification of a new potential therapeutic molecule that prevents myocyte injury and cardiac dysfunction due to desmosome mutations in vitro and in vivo by interfering in this signaling pathway. Finally, we underline the potential function of microRNAs, epigenetic regulatory RNA factors reported to participate in several pathological responses in heart tissue and in the Wnt signaling network, as important modulators of Wnt/ß-catenin signaling transduction in AC. Elucidation of the precise regulatory mechanism of Wnt/ß-catenin signaling in AC molecular pathogenesis could provide fundamental insights for new mechanism-based therapeutic strategy to delay the onset or progression of this cardiac disease.

Co-inheritance of mutations associated with arrhythmogenic cardiomyopathy and hypertrophic cardiomyopathy.

Arrhythmogenic cardiomyopathy (ACM) and hypertrophic cardiomyopathy (HCM) are genetically and phenotypically distinct disorders of the myocardium. Here we describe for the first time co-inheritance of mutations in genes associated with ACM or HCM in two families with recurrence of both cardiomyopathies. Among the double heterozygotes for mutations in desmoplakin (DSP) and myosin binding protein C (MYBPC3) genes identified in Family A, two were diagnosed with ACM and two with HCM. In Family B, one patient was identified to carry mutations in α-T-catenin (CTTNA3) and ß-myosin (MYH7) genes, but he does not fulfill the current diagnostic criteria neither for ACM nor for HCM. Interestingly, the double heterozygotes showed a variable clinical expression of both cardiomyopathies and they do not exhibit a more severe phenotype than family members carrying only one of the two mutations.

Arrhythmogenic right-ventricular cardiomyopathy: molecular genetics into clinical practice in the era of next generation sequencing.

Sudden death, ventricular arrhythmia and heart failure are common features in arrhythmogenic right-ventricular cardiomyopathy (ARVC), an inheritable heart muscle disease, characterized by clinical and genetic heterogeneity. So far, 13 disease genes have been identified, responsible for around 60% of all ARVC cases. In this review, we summarize the main clinical and pathological aspects of ARVC, focusing on the importance of the genetic testing and the application of the new sequencing techniques referred to next generation sequencing technology.

Homozygous Desmocollin-2 Mutations and Arrhythmogenic Cardiomyopathy.

Dominant mutations in desmocollin-2 (DSC2) gene cause arrhythmogenic cardiomyopathy (ACM), a progressive heart muscle disease characterized by ventricular tachyarrhythmias, heart failure, and risk of juvenile sudden death. Recessive mutations are rare and are associated with a cardiac or cardiocutaneous phenotype. Here, we evaluated the impact of a homozygous founder DSC2 mutation on clinical expression of ACM. An exon-by-exon analysis of the DSC2 coding region was performed in 94 ACM index patients. The c.536A>G (p.D179G) mutation was identified in 5 patients (5.3%), 4 of which resulted to be homozygous carriers. The 5 subjects shared a conserved haplotype, strongly indicating a common founder. Genetic and clinical investigation of probands' families revealed that p.D179G homozygous carriers displayed severe forms of biventricular cardiomyopathy without hair or skin abnormalities. The only heterozygous proband, who carried an additional variant of unknown significance in αT-catenin gene, showed a mild form of ACM without left ventricular involvement. All heterozygous family members were clinically asymptomatic. In conclusion, this is the first homozygous founder mutation in DSC2 gene identified among Italian ACM probands. Our findings provide further evidence of the occurrence of recessive DSC2 mutations in patients with ACM predominantly presenting with biventricular forms of the disease.

A founder MYBPC3 mutation results in HCM with a high risk of sudden death after the fourth decade of life.

BACKGROUND: Mutations in the cardiac myosin binding protein C (MYBPC3) gene account for a significant proportion of patients affected with hypertrophic cardiomyopathy (HCM). The aim of this study was to evaluate the penetrance and the impact of a frequent founder MYBPC3 mutation on HCM clinical expression and prognosis. METHODS AND RESULTS: Mutation screening of MYBPC3 gene was performed in 97 HCM probands. Nineteen (19.5%) resulted to be carriers of the founder p.F305Pfs*27 mutation and other 45 mutation carriers were identified during the evaluation of 14 families. Eleven (38%) mutation carriers were diagnosed between ages 30 years and 40 years. Disease penetrance was incomplete (64.4%), age-related and was greater in men than women (85% vs 48%, p=0.009). Probands carrying the founder mutation exhibited highest prevalence of non-sustained ventricular tachycardia (63% vs 22%, p=0.003; 63% vs 23%, p=0.01) and implantable cardioverter-defibrillator (58% vs 17%, p=0.001; 58% vs 18%, p=0.005) when compared with probands without MYBPC3 mutations or carrying other MYBPC3 mutations. Reduced survival due to sudden cardiac death (SCD) or aborted SCD occurred more frequently after the fourth decade of life in probands carrying p.F305Pfs*27 mutation than those without MYBPC3 mutations (32% vs 15%, p=0.01). CONCLUSIONS: p.F305Pfs*27 mutation carriers have a high probability to develop the disease between ages 30 years and 40 years with a significant major risk if they are men. This founder mutation is associated with an increase of SCD/aborted SCD events after the fourth decade of life.These findings are of relevant importance for management and clinical decision-making in patients with HCM.

Arrhythmogenic cardiomyopathy: a disease of intercalated discs.

Arrhythmogenic cardiomyopathy (ACM) is an acquired progressive disease having an age-related penetrance and showing clinical manifestations usually during adolescence and young adulthood. It is characterized clinically by a high incidence of severe ventricular tachyarrhythmias and sudden cardiac death and pathologically by degeneration of ventricular cardiomyocytes with replacement by fibro-fatty tissue. Whereas, in the past, the disease was considered to involve only the right ventricle, more recent clinical studies have established that the left ventricle is frequently involved. ACM is an inherited disease in up to 50% of cases, with predominantly an autosomal dominant pattern of transmission, although recessive inheritance has also been described. Since most of the pathogenic mutations have been identified in genes encoding desmosomal proteins, ACM is currently defined as a disease of desmosomes. However, on the basis of the most recent description of the intercalated disc organization and of the identification of a novel ACM gene encoding for an area composita protein, ACM can be considered as a disease of the intercalated disc, rather than only as a desmosomal disease. Despite increasing knowledge of the genetic basis of ACM, we are just beginning to understand early molecular events leading to cardiomyocyte degeneration, fibrosis and fibro-fatty substitution. This review summarizes recent advances in our comprehension of the link between the molecular genetics and pathogenesis of ACM and of the novel role of cardiac intercalated discs.

Compound and digenic heterozygosity predicts lifetime arrhythmic outcome and sudden cardiac death in desmosomal gene-related arrhythmogenic right ventricular cardiomyopathy.

BACKGROUND: Mutations in genes encoding for desmosomal proteins are the most common cause of arrhythmogenic right ventricular cardiomyopathy (ARVC). We assessed the value of genotype for prediction of lifetime major arrhythmic events and sudden cardiac death (SCD) in desmosomal gene-related ARVC. METHODS AND RESULTS: The overall study population included 134 desmosomal gene mutation carriers (68 men; median age 36 years [22-52]) from 44 consecutive ARVC families undergoing comprehensive genetic screening. The probability of experiencing a first major arrhythmic event or SCD during a lifetime was determined by using date of birth as start point for the time-to-event analysis, and was stratified by sex, desmosomal genes, mutation types, and genotype complexity (single versus multiple mutations). One hundred thirteen patients (84%) carried a single desmosomal gene mutation in desmoplakin (n=44; 39%), plakophilin-2 (n=38; 34%), desmoglein-2 (n=30; 26%), and desmocollin-2 (n=1; 1%), whereas 21 patients (16%) had a complex genotype with compound heterozygosity in 7 and digenic heterozygosity in 14. Over a median observation period of 39 (22-52) years, 22 patients (16%) from 20 different families had arrhythmic events, such as SCD (n=1), aborted SCD because of ventricular fibrillation (n=6), sustained ventricular tachycardia (n=14), and appropriate defibrillator intervention (n=1). Multiple desmosomal gene mutations and male sex were independent predictors of lifetime arrhythmic events with a hazard ratio of 3.71 (95% confidence interval, 1.54-8.92; P=0.003) and 2.76 (95% confidence interval, 1.19-6.41; P=0.02), respectively. CONCLUSIONS: Compound/digenic heterozygosity was identified in 16% of ARVC-causing desmosomal gene mutation carriers and was a powerful risk factor for lifetime major arrhythmic events and SCD. These results support the use of comprehensive genetic screening of desmosomal genes for arrhythmic risk stratification in ARVC.

Identification of a PKP2 gene deletion in a family with arrhythmogenic right ventricular cardiomyopathy.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a primary heart muscle disease characterized by progressive myocardial loss, with fibro-fatty replacement, and high frequency of ventricular arrhythmias that can lead to sudden cardiac death. ARVC is a genetically determined disorder, usually caused by point mutations in components of the cardiac desmosome. Conventional mutation screening of ARVC genes fails to detect causative mutations in about 50% of index cases, suggesting a further genetic heterogeneity. We performed a genome-wide linkage study and a copy number variations (CNVs) analysis, using high-density SNP arrays, in an ARVC family showing no mutations in any of the desmosomal genes. The CNVs analysis identified a heterozygous deletion of about 122 kb on chromosome 12p11.21, including the entire plakophilin-2 gene and shared by all affected family members. It was not listed on any of available public CNVs databases and was confirmed by quantitative real-time PCR. This is the first SNP array-based genome-wide study leading to the identification of a CNV segregating with the disease phenotype in an ARVC family. This result underscores the importance of performing additional analysis for possible genomic deletions/duplications in ARVC patients without point mutations in known disease genes.

R25C mutation in the NKX2.5 gene in Italian patients affected with non-syndromic and syndromic congenital heart disease.

AIMS: Heterozygous mutations in the transcription factor Nkx2.5 indicate a genetic cause for congenital heart diseases (CHDs) in human beings. The present study aimed to assess the prevalence of NKX2.5 mutations in Italian patients with sporadic non-syndromic and syndromic CHD, as well as to appraise any genotype-phenotype correlations. METHODS: One hundred Italian patients affected with CHD (90 had sporadic non-syndromic CHD and 10 had syndromic CHD) were screened for NKX2.5 mutations. The coding region and flanking regions involved in gene splicing of the CSX/NKX2.5 gene were amplified from genomic DNA by PCR, and mutational analysis was performed using denaturing high performance liquid chromatography and DNA sequencing. RESULTS: One previously reported NKX2.5 mutation (c.73C>T, p.R25C) was identified in two of the 100 CHD patients (2%). We have detected the p.R25C alteration in a woman showing aneurysm of the membranous septum, aortic coarctation and bicuspid aortic valve, that was a different phenotype from those previously reported, and for the first time in a patient with syndromic CHD with Down's syndrome (posterior ventricular septal defect, atrial septal defect, left superior cava vein ' sinus, and patent ductus arteriosus). CONCLUSION: Our results confirm that NKX2.5 mutations are not a common cause of CHD; furthermore, the p.R25C variation may increase susceptibility to development of CHD in patients with and without chromosomal abnormalities.

Mutations in the area composita protein αT-catenin are associated with arrhythmogenic right ventricular cardiomyopathy.

AIMS: Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a major cause of juvenile sudden death and is characterized by fibro-fatty replacement of the right ventricle. Mutations in several genes encoding desmosomal proteins have been identified in ARVC. We speculated that αT-catenin, encoded by CTNNA3, might also carry mutations in ARVC patients. Alpha-T-catenin binds plakophilins and this binding contributes to the formation of the area composita, which strengthens cell-cell adhesion in contractile cardiomyocytes. METHODS AND RESULTS: We used denaturing high-performance liquid chromatography and direct sequencing to screen CTNNA3 in 76 ARVC patients who did not carry any mutations in the desmosomal genes commonly mutated in ARVC. Mutations c.281T > A (p.V94D) and c.2293_2295delTTG (p.del765L) were identified in two probands. They are located in important domains of αT-catenin. Yeast two-hybrid and cell transfection studies showed that the interaction between the p.V94D mutant protein and ß-catenin was affected, whereas the p.del765L mutant protein showed a much stronger dimerization potential and formed aggresomes in HEK293T cells. CONCLUSION: These findings might point to a causal relationship between CTNNA3 mutations and ARVC. This first report on the involvement of an area composita gene in ARVC shows that the pathogenesis of this disease extends beyond desmosomes. Since the frequency of CTNNA3 mutations in ARVC patients is not rare, systematic screening for this gene should be considered to improve the clinical management of ARVC families.

Desmin mutations and arrhythmogenic right ventricular cardiomyopathy.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited heart muscle disease characterized by fibrofatty replacement of the myocardium and ventricular arrhythmias, associated with mutations in the desmosomal genes. Only a missense mutation in the DES gene coding for desmin, the intermediate filament protein expressed by cardiac and skeletal muscle cells, has been recently associated with ARVC. We screened 91 ARVC index cases (53 negative for mutations in desmosomal genes and an additional 38 carrying desmosomal gene mutations) for DES mutations. Two rare missense variants were identified. The heterozygous p.K241E substitution was detected in 1 patient affected with a severe form of ARVC who also carried the p.T816RfsX10 mutation in plakophilin-2 gene. This DES substitution, showing an allele frequency of <0.01 in the control population, is predicted to cause an intolerant amino acid change in a highly conserved protein domain. Thus, it can be considered a rare variant with a possible modifier effect on the phenotypic expression of the concomitant mutation. The previously known p.A213V substitution was identified in 1 patient with ARVC who was negative for mutations in the desmosomal genes. Because a greater prevalence of p.A213V has been reported in patients with heart dilation than in control subjects, the hypothesis that this rare variant could have an unfavorable effect on cardiac remodeling cannot be ruled out. In conclusion, our data help to establish that, in the absence of skeletal muscle involvement suggestive of a desminopathy, the probability of DES mutations in ARVC is very low. These findings have important implications in the mutation screening strategy for patients with ARVC.

Clinical phenotype and diagnosis of arrhythmogenic right ventricular cardiomyopathy in pediatric patients carrying desmosomal gene mutations.

BACKGROUND: Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited heart muscle disease carrying a risk of sudden death. Information about the clinical features during childhood and the age at disease onset is scanty. OBJECTIVE: The aim of the study was to describe the ARVC phenotype as its initial clinical manifestation in a pediatric population (<18 years) with desmosomal gene mutations. METHODS: Fifty-three ARVC desmosomal gene mutation carriers (mean age 12.3 ± 3.9 years) were investigated by electrocardiogram (ECG), signal-averaged ECG, 24-hour Holter, echocardiogram, and contrast-enhanced cardiac magnetic resonance (CMR). RESULTS: None of the children ≤10 years old fulfilled the 1994 criteria, as opposed to six (33%) aged 11-14 years and eight aged >14 years (42%). At the end of follow-up (9 ± 7 years), 21 (40%) fulfilled the 1994 diagnostic criteria (mean age 16 ± 4 years). By using the 2010 criteria in subjects aged ≤18 years, 53% were unaffected, versus 62% by using the traditional criteria. More than two-thirds of affected subjects had moderate-severe forms of the disease. Contrast-enhanced CMR was performed in 21 (40%); of 13 unaffected gene mutation carriers, six showed ARVC morphological and/or tissue abnormalities. CONCLUSION: In pediatric ARVC mutation carriers, a diagnosis was achieved in 40% of cases, confirming that the disease usually develops during adolescence and young adulthood. The 2010 modified criteria seem to be more sensitive than the 1994 ones in identifying familial pediatric cases. Contrast-enhanced CMR can provide diagnostic information on gene mutation carriers not fulfilling either traditional or modified criteria. Management of asymptomatic gene mutation carriers remains the main clinical challenge.

The p.A897KfsX4 frameshift variation in desmocollin-2 is not a causative mutation in arrhythmogenic right ventricular cardiomyopathy.

Mutations in genes encoding desmosomal proteins have been reported to cause arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D), an autosomal-dominant disease characterised by progressive myocardial atrophy with fibro-fatty replacement. We screened 112 ARVC/D probands for mutations in desmocollin-2 (DSC2) gene and detected two different amino-acid substitutions (p.E102K, p.I345T) and a frameshift variation (p.A897KfsX4) in 7 (6.2%) patients. DSC2a variant p.A897KfsX4, previously reported as a p.E896fsX900 mutation, was identified in five unrelated probands. Four of them were found to carry one or two mutations in different ARVC/D genes. Unexpectedly, p.A897KfsX4 variation was also found in 6 (1.5%) out of 400 control chromosomes. In vitro functional studies showed that, unlike wild-type DSC2a, this C-terminal mutated protein was localised in the cytoplasm. p.A897KfsX4 variation affects the last five amino acids of the DSC2a isoform but not of DSC2b. In contrast with what we found in other human tissues, in the heart DSC2b is more expressed than DSC2a, suggesting that relative deficiency of DSC2a might be compensated by isoform b. In conclusion, DSC2 gene mutations are not frequently involved in ARVC/D. The p.A897KfsX4 variation, identified in several Italian healthy control subjects, which affects only one of the two DSC2 isoforms, may be considered a rare variant, though possibly affecting phenotypic expression of concomitant ARVC/D mutations.

Multiple mutations in desmosomal proteins encoding genes in arrhythmogenic right ventricular cardiomyopathy/dysplasia.

BACKGROUND: Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is a progressive cardiomyopathy showing a wide clinical spectrum in terms of clinical expressions and prognoses. OBJECTIVE: This study sought to estimate the occurrence of compound and double heterozygotes for mutations in desmosomal proteins encoding genes in a cohort of ARVC/D Italian index cases, and to assess the clinical phenotype of mutations carriers. METHODS: Fourty-two consecutive ARVC/D index cases who fulfilled the International Task Force diagnostic criteria were screened for mutations in PKP2, DSP, DSG2, DSC2, and JUP genes by denaturing high-performance liquid chromatography (DHPLC) and direct sequencing. RESULTS: Three probands (7.1%) showing a family history of sudden death carried multiple mutations. Family screening identified an additional 7 multiple-mutation carriers. Among the 7 double heterozygotes for mutations in different genes, 2 were clinically unaffected, 2 were affected, and 3 showed some clinical signs of ARVC/D even if they did not fulfill the diagnostic criteria. Two compound heterozygotes for mutations in the same gene and 1 subject carrying 3 different mutations showed a severe form of the disease with heart failure onset at a young age. Moreover, multiple-mutation carriers showed a higher prevalence of left ventricular involvement (P = .025) than single-mutation carriers. CONCLUSION: Occurrence of compound and double heterozygotes in ARVC/D index cases is particularly relevant to mutation screening strategy and to genetic counseling. Even if multiple-mutation carriers show a wide variability in clinical expression, the extent of the disease is higher compared to that in single-mutation carriers.

Compound and digenic heterozygosity contributes to arrhythmogenic right ventricular cardiomyopathy.

OBJECTIVES: The aim of this study was to define the genetic basis of arrhythmogenic right ventricular cardiomyopathy (ARVC). BACKGROUND: Arrhythmogenic right ventricular cardiomyopathy, characterized by right ventricular fibrofatty replacement and arrhythmias, causes sudden death. Autosomal dominant inheritance, reduced penetrance, and 7 desmosome-encoding causative genes are known. The basis of low penetrance is poorly understood. METHODS: Arrhythmogenic right ventricular cardiomyopathy probands and family members were enrolled, blood was obtained, lymphoblastoid cell lines were immortalized, deoxyribonucleic acid was extracted, polymerase chain reaction (PCR) amplification of desmosome-encoding genes was performed, PCR products were sequenced, and diseased tissue samples were studied for intercellular junction protein distribution with confocal immunofluorescence microscopy and antibodies against key proteins. RESULTS: We identified 21 variants in plakophilin-2 (PKP2) in 38 of 198 probands (19%), including missense, nonsense, splice site, and deletion/insertion mutations. Pedigrees showed wide intra-familial variability (severe early-onset disease to asymptomatic individuals). In 9 of 38 probands, PKP2 variants were identified that were encoded in trans (compound heterozygosity). The 38 probands hosting PKP2 variants were screened for other desmosomal genes mutations; second variants (digenic heterozygosity) were identified in 16 of 38 subjects with PKP2 variants (42%), including desmoplakin (DSP) (n = 6), desmoglein-2 (DSG2) (n = 5), plakophilin-4 (PKP4) (n = 1), and desmocollin-2 (DSC2) (n = 1). Heterozygous mutations in non-PKP 2 desmosomal genes occurred in 14 of 198 subjects (7%), including DSP (n = 4), DSG2 (n = 5), DSC2 (n = 3), and junctional plakoglobin (JUP) (n = 2). All variants occurred in conserved regions; none was identified in 700 ethnic-matched control subjects. Immunohistochemical analysis demonstrated abnormalities of protein architecture. CONCLUSIONS: These data suggest that the genetic basis of ARVC includes reduced penetrance with compound and digenic heterozygosity. Disturbed junctional cytoarchitecture in subjects with desmosomal mutations confirms that ARVC is a disease of the desmosome and cell junction.