Genotype-Phenotype correlation in Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)

ABSTRACT 1 Background. With recognition of disease-causing genes in arrhythmogenic right ventricular cardiomyopathy, mutation analysis is being applied. Methods and Results. The role of genotyping in familial assessment for arrhythmogenic right ventricular cardiomyopathy was investigated, including the prevalence of mutations in known causal genes, the penetrance and expressivity in genotyped families, and the utility of the 2010 Task Force criteria in clinical diagnosis. Clinical and molecular genetic evaluation was performed in 210 first-degree and 45 second-degree relatives from 100 families. In 51 families, the proband was deceased. The living probands had a high prevalence of ECG abnormalities (89%) and ventricular arrhythmia (78%) and evidence of more severe disease than relatives. Definite or probable causal mutations were found in 58% of families and 73% of living probands, of whom 28% had an additional desmosomal variant (ie, mutation or polymorphism). Ninety-three relatives had a causal mutation; 33% fulfilled the 2010 criteria, whereas only 19% satisfied the 1994 version (P=0.03). An additional desmosomal gene variant was found in 10% and was associated with a 5-fold increased risk of developing penetrant disease (odds ratio, 4.7; 95% confidence interval, 1.1 to 20.4; P=0.04). Conclusions. Arrhythmogenic right ventricular cardiomyopathy is a genetically complex disease characterized by marked intrafamilial phenotype diversity. Penetrance is definition dependent and is greater with the 2010 criteria compared with the 1994 criteria. Relatives harboring >1 genetic variant had significantly increased risk of developing clinical disease, potentially an important determinant of the phenotypic heterogeneity seen within families with arrhythmogenic right ventricular cardiomyopathy. ABSTRACT 2 Aims. Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited heart muscle disease predominantly caused by mutations in desmosomal protein genes. Lamin A/C gene (LMNA) mutations are associated with dilated cardiomyopathy, conduction abnormalities and high incidence of sudden cardiac death. In this study we screened a large cohort of ARVC patients for LMNA mutations. Methods and Results. One hundred and eight patients from unrelated families with borderline (n= 27) or definite (n= 81) diagnosis of ARVC were genetically tested for five desmosomal genes and LMNA. Sixty-one (56.5 %) were positive for desmosomal gene mutations. Standard polymerase chain reaction (PCR) amplification of the 12 protein-coding LMNA exons was performed and mutational screening performed by direct sequencing. Four patients (4%) without desmosomal gene mutations carried LMNA variants. Three had severe RV involvement, and during follow-up three died (two suddenly and one from congestive heart failure); all three had conduction abnormalities on resting 12 lead ECG. Myocardial tissue from two patients showed myocyte loss and fibro-fatty replacement. In one of these, immunohistochemical staining with antibody to plakoglobin showed reduced/absent staining of the intercalated discs in the myocardium. Conclusion. LMNA mutations can be found in severe forms of ARVC. LMNA should be added to desmosomal genes when genetically testing patients with suspected ARVC, particularly when they also have ECG evidence for conduction disease.Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited heart muscle disease characterised by potentially lethal ventricular arrhythmias of predominantly right ventricular (RV) origin. It is one of the commonest causes of sudden death (SD) in the young. Post mortem typically reveals fibrous and/or fibro-fatty replacement of myocytes in specific areas of the RV. Left ventricular (LV) involvement occurs with disease development and recently forms with predominant LV involvement have been described. ARVC has only been recognised in the last 3 decades and only when it is more obvious clinical and pathological manifestations are present. During the past decade, the genetic basis has begun to be elucidated. Five genes encoding important desmosomal proteins have been identified and shown to cause disease in up to 70% of patients. Recently, non-desmosomal gene mutations have been associated with ARVC: transmembrane protein 43 and desmin. Some authors suggested ryanodine receptor-2 (RYR2) and transforming growth factor-beta3 (TGFβ3) genes to be associated with the condition, but their pathogenicity has been questioned. Identification of disease within families is revealing a wider spectrum of disease than has been previously recognized in probands. The concept that ARVC is typified by individuals with left bundle brunch block ventricular tachycardia (LBBB VT) is incorrect or, at best, limited. In 1994, Task Force criteria for the clinical diagnosis of ARVC were published by the Working Group on Myocardial and Pericardial Diseases of the European Society of Cardiology and the Scientific Council on Cardiomyopathies of the International Society and Federation of Cardiology. The criteria included a score based on right ventricular morphological and functional abnormalities, electrocardiographic (repolarization and depolarization) abnormalities, histopathological abnormalities, ventricular arrhythmias and family history. In 2010, a modification of the Task Force criteria has been proposed, with the recognition of the lack of sensitivity of the 1994 criteria for early and familial disease. Current genotype-phenotype studies suggest that: (1) mutations in desmosomal genes account for disease in 30-60% of cases; (2) compound heterozygotes and homozygotes have severe disease expression; (3) desmoplakin mutations at the C-terminal end (binding to intermediate filaments) are associated with an LV phenotype; (4) mutations in plakophilin-2 are common but, in isolation, many may not be disease causing; (5) mutations in transmembrane protein 43 (TMEM43) gene are of uncertain prevalence but cause a severe form of ARVC. The data on genotype-phenotype, however, have some limitations: 1) They are based on few probands and the data on family members is often not available. 2) Most of the cohorts have selected symptomatic patients with high event rates. 3) Studies based on probands only do not allow co-segregation analysis, which is important to prove that gene mutations are disease causing, especially for missense mutations. 4) No consistent data on the penetrance of the disease are available, due to small numbers. 5) Genotype-phenotype studies are based on single genes and 1994 criteria. The aims of our study were: • To study in a large, genotyped population of probands and relatives the prevalence of mutations in known causal genes, penetrance, disease expression and natural history of the disease. • To evaluate the utility of 2010 diagnostic criteria in familial diagnosis. • To identify new non-desmosomal candidate genes associated with the disease. This study was undertaken in collaboration with the National Referral Center for Diagnosis and Treatment of Inherited Cardiac Diseases at The Heart Hospital, University College of London Hospital, NHS Trust, under the supervision of Professor William J McKenna.PhD Fellowship from the University “La Sapienza” of Rome, European Society of Cardiology Research Fellowship and InGenious Hypercare