Clinical and genetic characterization of families with arrhythmogenic right ventricular dysplasia/cardiomyopathy provides novel insights into patterns of disease expression

Left ventricular noncompaction and cardiomyopathy: cause, contributor, or epiphenomenon?

PURPOSE OF REVIEW

To discuss unresolved issues pertaining to aetiology and diagnosis of isolated left ventricular noncompaction.

RECENT FINDINGS

Left ventricular noncompaction may be sporadic or familial and is linked to mutations in mitochondrial, cytoskeletal, Z-line, and sarcomeric proteins. Severe childhood manifestations include fetal hydrops or sudden infant death syndrome. Adults with severe phenotypes have a similarly guarded prognosis due to heart failure, arrhythmia and thromboembolism. Conversely, healthy individuals may fulfil current imaging criteria for diagnosis. Left ventricular noncompaction is also observed in families with hypertrophic or dilated cardiomyopathy, casting doubt on its acceptance as a distinct disease entity.

SUMMARY

The extent of myocardial compaction may be a continuous trait within the population. Sensitive imaging techniques may detect subtle variations in morphology that fall within the normal range, underscoring the need for more restrictive diagnostic criteria, as in mitral valve prolapse. Conversely, rather than being a root cause of myocardial dysfunction, left ventricular noncompaction may represent a secondary consequence of a genetic alteration, well-tolerated when the heart is otherwise normal. In the presence of a pathogenic mutation, disruption to myocyte function at a molecular level may be the primary disease determinant, with noncompaction arising as a maladaptive remodelling response that compounds the disease process through subendocardial ischaemia and fibrosis.

The challenge of diagnosing arrhythmogenic right ventricular cardiomyopathy in the young

We report two cases of arrhythmogenic right ventricular cardiomyopathy (ARVC) in the pediatric age group. In both cases, the diagnosis was considered and pursued but would not be made utilizing Task Force Criteria. The diagnosis was made based on the morphology of a single beat during exercise testing. We illustrate the difficulty of diagnosing ARVC in the young even with a heightened index of suspicion.

Role of cardiovascular magnetic resonance imaging in arrhythmogenic right ventricular dysplasia

Arrhythmogenic right ventricular dysplasia (ARVD) is a genetic cardiomyopathy characterized clinically by ventricular arrhythmias and progressive right ventricular (RV) dysfunction. The histopathologic hallmark is fibro-fatty replacement of RV myocardium. It is inherited in an autosomal pattern with variable penetrance. ARVD is unique in that it most commonly presents in young, otherwise healthy and highly athletic individuals. The cause of ARVD is not well-known but recent evidence suggests strongly that it is a disease of desmosomal dysfunction. The disease involvement is not limited only to the RV as left ventricle (LV) has also been reportedly affected. Diagnosis of ARVD is challenging and is currently based upon a multi-disciplinary work-up of the patient as defined by the Task Force. Currently, implanted cardioverter defibrillators (ICD) are routinely used to prevent sudden death in patients with ARVD. Cardiovascular MR is an important non-invasive diagnostic modality that allows both qualitative and quantitative evaluation of RV. This article reviews the genetics of ARVD, current status and role of CMR in the diagnosis of ARVD and LV involvement in ARVD.

Genetic evaluation of familial cardiomyopathy

Hereditary forms of hypertrophic, dilated, restrictive, and right ventricular cardiomyopathies are frequently seen. Patterns of inheritance include autosomal dominant, autosomal recessive, X-linked, and matrilinear. Recognition of the mode of inheritance facilitates proper clinical screening of family members in subsequent generations. Report of successful sequence analysis of the human genome 7 years ago has resulted in widespread translation of genomic information into clinical applications. As technologic advances in high throughput sequence determination continue to evolve, an era of personalized medicine based on genomic data is highly anticipated. Today, clinical genetic testing is available for most monogenic forms of cardiomyopathy and the demand among patients and families is increasing. However, physicians and patients should consider the benefits and limitations of such testing. This review will focus on inherited forms of cardiomyopathy, detailing the currently available genetic tests, as well as benefits, limitations, and possible outcomes of such testing.

The utility of magnetic resonance imaging in the evaluation of arrhythmogenic right ventricular cardiomyopathy

PURPOSE OF REVIEW

Perceptions of the utility of cardiovascular magnetic resonance in the evaluation of arrhythmogenic right ventricular cardiomyopathy have changed considerably in the past decade. This review offers an up-to-date perspective on the diagnostic role of cardiovascular magnetic resonance in the genetics era.

RECENT FINDINGS

Originally hailed as a putative gold standard in arrhythmogenic cardiomyopathy, cardiovascular magnetic resonance has received a more guarded reception lately owing to interobserver variability and lack of standardized protocols. Recent studies have nonetheless affirmed its value as an integral component of the diagnostic work-up. Quantitative volume analysis is relatively robust, but visualization of myocardial fat by spin-echo imaging is less reliable. Interpretation of wall motion abnormalities appears reproducible among expert readers. Emerging data suggest a key role for late gadolinium enhancement in detection of left ventricular involvement.

SUMMARY

Cardiovascular magnetic resonance in arrhythmogenic cardiomyopathy is facilitated by appropriate patient selection and preparation, experienced readers and operators, and a dedicated, comprehensive protocol. Indications for magnetic resonance assessment include proven arrhythmogenic cardiomyopathy in the family, unexplained ventricular arrhythmia, inverted T-waves in the right precordial or lateral leads, and/or family history of sudden cardiac death. Arrhythmia suppression is essential for optimal electrocardiographic triggering and image acquisition.

Mechanisms of disease: molecular genetics of arrhythmogenic right ventricular dysplasia/cardiomyopathy

Arrhythmogenic right ventricular dysplasia/cardiomyopathy is an inherited cardiomyopathy estimated to affect approximately 1 in 5,000 individuals. Cardinal manifestations include right ventricular enlargement and dysfunction, fibrofatty replacement of myocytes in the right ventricle, characteristic electrocardiographic abnormalities, and ventricular arrhythmia most commonly arising from the right ventricle. The disease is frequently familial and typically involves autosomal dominant transmission with low penetrance and variable expressivity. Approximately 50% of symptomatic individuals harbor a mutation in one of the five major components of the cardiac desmosome. Nevertheless, other genetic modifiers and environmental factors complicate the clinical management of mutation carriers as well as counseling of their relatives. This Review summarizes the known genetic mutations associated with arrhythmogenic right ventricular dysplasia/cardiomyopathy, describes possible origins of recurrent mutations, presents theories on the pathogenesis of disease following a mutation, and discusses the current issues surrounding clinical use of genetic analysis in the assessment of individuals with this condition.

Arrhythmogenic right ventricular cardiomyopathy type 5 is a fully penetrant, lethal arrhythmic disorder caused by a missense mutation in the TMEM43 gene

Autosomal-dominant arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) causes sudden cardiac death and is characterized by clinical and genetic heterogeneity. Fifteen unrelated ARVC families with a disease-associated haplotype on chromosome 3p (ARVD5) were ascertained from a genetically isolated population. Identification of key recombination events reduced the disease region to a 2.36 Mb interval containing 20 annotated genes. Bidirectional resequencing showed one rare variant in transmembrane protein 43 (TMEM43 1073C-->T, S358L), was carried on all recombinant ARVD5 ancestral haplotypes from affected subjects and not found in population controls. The mutation occurs in a highly conserved transmembrane domain of TMEM43 and is predicted to be deleterious. Clinical outcomes in 257 affected and 151 unaffected subjects were compared, and penetrance was determined. We concluded that ARVC at locus ARVD5 is a lethal, fully penetrant, sex-influenced morbid disorder. Median life expectancy was 41 years in affected males compared to 71 years in affected females (relative risk 6.8, 95% CI 1.3-10.9). Heart failure was a late manifestation in survivors. Although little is known about the function of the TMEM43 gene, it contains a response element for PPAR gamma (an adipogenic transcription factor), which may explain the fibrofatty replacement of the myocardium, a characteristic pathological finding in ARVC.

A genetic framework for improving arrhythmia therapy

Abnormalities in heart rhythm continue to cause high rates of illness and death. Better treatment could be provided by solving two main challenges: the early identification of patients who are at risk, and the characterization of molecular pathways that culminate in arrhythmias. By analysing mechanisms that increase susceptibility to arrhythmia in individuals with genetic syndromes, it might be possible to improve current therapies and to develop new ways to treat and prevent common arrhythmias.

The area composita of adhering junctions connecting heart muscle cells of vertebrates. V. The importance of plakophilin-2 demonstrated by small interference RNA-mediated knockdown in cultured rat cardiomyocytes

In the adult mammalian heart, the cardiomyocytes are connected by large polar arrays of closely spaced or even fused composite, plaque-bearing adhering junctions (areae compositae, ACs), in a region usually termed "intercalated disk" (ID). We have recently reported that during late embryogenesis and postnatally these polar assemblies of AC-junction structures are gradually formed as replacements of distinct embryonal junctions representing desmosomes and fasciae adhaerentes which then may amalgamate to the fused AC structures, in some regions occupying more than 90% of the total ID area. Previous gene knockout results as well as mutation analyses of specific human cardiomyopathies have suggested that among the various AC constituents, the desmosomal plaque protein, plakophilin-2, plays a particularly important role in the formation, architectural organization and stability of these junctions interconnecting mature cardiomyocytes. To examine this hypothesis, we have decided to study losses of--or molecular alterations in--such AC proteins with respect to their effects on myocardiac organization and functions. Here we report that plakophilin-2 is indeed of obvious importance for myocardial architecture and cell-cell coupling of rat cardiomyocytes growing in culture. We show that siRNA-mediated reduction of the cardiomyocyte content of plakophilin-2 but not of some other major plaque components such as desmoplakin results in progressive disintegration--and losses--of AC junction structures and that numerous variously sized vesicles appear, which are plaque protein-associated as demonstrable by immunofluorescence and immunoelectron microscopy. The importance of plakophilin-2 as a kind of "organizer" protein in the formation, stabilization and functions of the AC structure and the ID architecture is discussed in relation to other junction proteins and to causes of certain cardiomyopathies.

Arrhythmogenic right ventricular cardiomyopathy/dysplasia

Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is a heart muscle disease clinically characterized by life-threatening ventricular arrhythmias. Its prevalence has been estimated to vary from 1:2,500 to 1:5,000. ARVC/D is a major cause of sudden death in the young and athletes. The pathology consists of a genetically determined dystrophy of the right ventricular myocardium with fibro-fatty replacement to such an extent that it leads to right ventricular aneurysms. The clinical picture may include: a subclinical phase without symptoms and with ventricular fibrillation being the first presentation; an electrical disorder with palpitations and syncope, due to tachyarrhythmias of right ventricular origin; right ventricular or biventricular pump failure, so severe as to require transplantation. The causative genes encode proteins of mechanical cell junctions (plakoglobin, plakophilin, desmoglein, desmocollin, desmoplakin) and account for intercalated disk remodeling. Familiar occurrence with an autosomal dominant pattern of inheritance and variable penetrance has been proven. Recessive variants associated with palmoplantar keratoderma and woolly hair have been also reported. Clinical diagnosis may be achieved by demonstrating functional and structural alterations of the right ventricle, depolarization and repolarization abnormalities, arrhythmias with the left bundle branch block morphology and fibro-fatty replacement through endomyocardial biopsy. Two dimensional echo, angiography and magnetic resonance are the imaging tools for visualizing structural-functional abnormalities. Electroanatomic mapping is able to detect areas of low voltage corresponding to myocardial atrophy with fibro-fatty replacement. The main differential diagnoses are idiopathic right ventricular outflow tract tachycardia, myocarditis, dialted cardiomyopathy and sarcoidosis. Only palliative therapy is available and consists of antiarrhythmic drugs, catheter ablation and implantable cardioverter defibrillator. Young age, family history of juvenile sudden death, QRS dispersion ≥ 40 ms, T-wave inversion, left ventricular involvement, ventricular tachycardia, syncope and previous cardiac arrest are the major risk factors for adverse prognosis. Preparticipation screening for sport eligibility has been proven to be effective in detecting asymptomatic patients and sport disqualification has been life-saving, substantially declining sudden death in young athletes.

Cardiomyopathy: appearances on ECG-gated 64-detector row computed tomography

Multi-detector row cardiac computed tomography (MDCT) with its high spatial and temporal resolution now has an established clinical role in cardiac imaging. The present review illustrates the MDCT appearances of cardiomyopathy, with reference to the normal myocardium, using multi-planar, near-isotropic imaging, three-dimensional volume rendering, and ECG-gated multi-phasic functional imaging software capabilities of 64-MDCT. MRI and echocardiographic correlations are also provided where appropriate.

Role of genetic analysis in the management of patients with arrhythmogenic right ventricular dysplasia/cardiomyopathy

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a recognized cause of sudden cardiac death, which may be prevented by timely detection and intervention. Clinical diagnosis of ARVC is fraught with difficulties in both index cases and relatives owing to the nonspecific nature of associated features, diverse phenotypic manifestations, and a lack of conspicuous abnormalities in the early, "concealed" phase. During the past 7 years, researchers have isolated causative mutations in several components of the desmosome, shedding light on the molecular mechanisms underlying the disease and offering the promise of genetic testing as a diagnostic tool. Sequence analysis is likely to be the mainstay of genotyping in ARVC because of marked allelic heterogeneity, frequent "private" mutations, and digenicity in a minority, highlighting the importance of comprehensive genetic screening. The main technical obstacle to implementation of genotyping in clinical practice will be the prohibitive costs of performing sequence analysis of a genomic region exceeding 40 kb. Nevertheless, the success rate of genotyping in ARVC is of the order of 40%, and key clinical applications include confirmatory testing of index cases to facilitate interpretation of borderline investigations and cascade screening of families. The latter is particularly attractive in ARVC, because age-related penetrance otherwise demands lifelong clinical reassessment of extended families. A role for genetic analysis in prognostication is more tenuous at present, but increasing identification of individuals with early and familial disease underscores the need for a definitive risk stratification algorithm in this population.

Quantitative assessment of angiographic right ventricular wall motion in arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C)

INTRODUCTION

Angiography of the right ventricle (RV) is a standard, reference technique to diagnose wall motion abnormalities in arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C). RV wall motion is usually assessed by qualitative, visual impression, and has lacked a quantitative basis for defining abnormalities. Since the normal RV has a markedly asymmetric movement, angiographic interpretation can differ, even among experienced clinicians. The purpose of this study was to quantify RV wall motion based on contrast ventriculography in patients with ARVD/C and to specify the severity and location of wall motion abnormalities, as compared with normal subjects.

METHODS AND RESULTS

We analyzed the angiographic contours of the RV in three views from 19 normal subjects and 23 subjects with ARVD/C. Contour area movement during contraction was calculated circumferentially and further analyzed in nine zones. RV ejection fraction was also computed. Wall motion in ARVD/C was depressed by more than 30% at the tricuspid valve and inferior wall regions (P < 0.001) and significantly reduced at the apex (P = 0.003). However, the RVOT and anterior wall motion were not significantly reduced. RV ejection fraction was depressed from 60 +/- 11% in normal subjects to 41 +/- 12% in ARVD/C patients (P < 0.001).

CONCLUSION

Wall motion abnormalities in ARVD/C can be quantified and compared with normal controls, showing primarily reduced movement in the tricuspid and inferior wall regions. This study delineates objective measurements that can be used to aid in the diagnosis of ARVD/C. In addition, they may be incorporated in future refinements of criteria to diagnose ARVD/C.

Long-range silencing and position effects at telomeres and centromeres: parallels and differences

Most of the human genome is compacted into heterochromatin, a form that encompasses multiple forms of inactive chromatin structure. Transcriptional silencing mechanisms in budding and fission yeasts have provided genetically tractable models for understanding heritably repressed chromatin. These silent domains are typically found in regions of repetitive DNA, that is, either adjacent to centromeres or telomeres or within the tandemly repeated ribosomal DNA array. Here we address the mechanisms of centromeric, telomeric and locus-specific gene silencing, comparing simple and complex animals with yeast. Some aspects are universally shared, such as histone-tail modifications, while others are unique to either centromeres or telomeres. These may reflect roles for heterochromatin in other chromosomal functions, like kinetochore attachment and DNA ends protection.