Genetic testing in the management of inherited cardiac disorders: two cases of Filamin-C arrhythmogenic left ventricular cardiomyopathy

Background

Arrhythmogenic left ventricular cardiomyopathy (ALVC) is a left ventricle-dominant arrhythmogenic cardiomyopathy (ACM) subtype often associated with malignant ventricular arrhythmias, left ventricular (LV) scar and sudden cardiac death. Awareness about LV involvement is now on the rise. The diagnosis relies on structural abnormalities on cardiac magnetic resonance (CMR) imaging and known ACM-causing genetic mutations.

Case summary

A 28-year-old lady (Case 1) was referred for cardiac screening after her father passed away suddenly. Her paternal uncle (Case 2) had been diagnosed with supposed dilated cardiomyopathy prior to referral. Both cases were worked up extensively with an electrocardiogram (ECG), 24-h ambulatory ECG monitor, exercise testing, and CMR imaging. Investigations of Case 1 showed T-wave inversion in the infero-lateral leads and a ventricular ectopic burden of 3% on ambulatory monitoring. Cardiac magnetic resonance imaging revealed moderately reduced LV systolic function (ejection fraction of 40%) with circumferential macroscopic fibrosis. Her uncle (Case 2) also had an impaired and dilated ventricle with extensive scar on CMR. Following the recent introduction of a cardiogenetic service in our unit, both were heterozygous for a pathogenic Filamin-C variant (c.7384+1G>A). Based on CMR findings and genetic results, the diagnosis of both patients was deemed to be ALVC. After years of surveillance, Patient 1 now has an implantable cardioverter defibrillator (ICD) indication.

Discussion

The importance of diagnosing patients with ACM lies in the predisposition to sudden cardiac death. Gene-specific treatment algorithms in ACM may alter management strategies, including ICD implantation as primary prevention. An in-depth multidisciplinary discussion and respecting patient autonomy are key factors in any decision pertaining to ICD implantation.

Cardiomyopathies in children: An overview

Paediatric cardiomyopathies form a heterogeneous group of disorders characterized by structural and electrical abnormalities of the heart muscle, commonly due to a gene variant of the myocardial cell structure. Mostly inherited as a dominant or occasionally recessive trait, they might be part of a syndromic disorder of underlying metabolic or neuromuscular defects or combine early developing extracardiac abnormalities (i.e., Naxos disease). The annual incidence of 1 per 100,000 children appears higher during the first two years of life. Dilated and hypertrophic cardiomyopathy phenotypes share an incidence of 60% and 25%, respectively. Arrhythmogenic right ventricular cardiomyopathy (ARVC), restrictive cardiomyopathy, and left ventricular noncompaction are less commonly diagnosed. Adverse events such as severe heart failure, heart transplantation, or death usually appear early after the initial presentation. In ARVC patients, high-intensity aerobic exercise has been associated with worse clinical outcomes and increased penetrance in at-risk genotype-positive relatives. Acute myocarditis in children has an incidence of 1.4-2.1 cases/per 100,000 children per year, with a 6-14% mortality rate during the acute phase. A genetic defect is considered responsible for the progression to dilated cardiomyopathy phenotype. Similarly, a dilated or arrhythmogenic cardiomyopathy phenotype might emerge with an episode of acute myocarditis in childhood or adolescence. This review provides an overview of childhood cardiomyopathies focusing on clinical presentation, outcome, and pathology.

Familial risk of dilated and hypertrophic cardiomyopathy: a national family study in Sweden

AIMS

This study aims to determine the familial incidence of dilated (DCM) and hypertrophic cardiomyopathy (HCM) in first-degree, second-degree, and third-degree relatives of affected individuals.

METHODS AND RESULTS

In this population-based multigenerational cohort study, full-siblings, half-siblings, and cousin pairs born to Swedish parents between 1932 and 2015 were included, and register-based DCM and HCM diagnoses among relatives were ascertained. Adjusted odds ratios (ORs) for DCM and HCM were calculated for relatives of individuals with DCM and HCM compared with relatives of individuals without DCM and HCM for reference. Total study population included 6 334 979 subjects and consisted of 5 577 449 full-siblings, 1 321 414 half-siblings, and 3 952 137 cousins. Overall, 10 272 (0.16%) unique individuals were diagnosed with DCM and 3769 (0.06%) with HCM. Of these, 7716 (75.12%) and 2375 (63.01%) were males, respectively. Familial risk ORs for DCM were 5.35 [95% confidence intervals (CI): 4.85-5.90] for full-siblings, 2.68 (95% CI:1.86-3.87) for half-siblings, and 1.72 (95% CI:1.12-2.64) for cousins of affected individuals. The ORs for HCM were 42.44 (95% CI:37.66-47.82) for full-siblings, 32.70 (95% CI:21.32-50.15) for half-siblings, and 36.96 (95% CI:29.50-46.31) for cousins of affected individuals. In sex-stratified analysis, relatives of affected females were found more likely to be affected than were relatives of affected males, with stronger aggregation observed for HCM.

CONCLUSIONS

Familial risk of HCM and DCM is high and associated with genetic resemblance, with strongest aggregations observed in relatives of affected females with HCM, whereas this association was distinctly attenuated for DCM. The finding of a Carter effect, more pronounced in HCM, suggests a multifactorial threshold model of inheritance.

Cardiac arrest as first presentation of arrhythmogenic left ventricular cardiomyopathy due to Filamin C mutation: a case report

Background

Arrhythmogenic left ventricular cardiomyopathy (ALVC) is a rare form of arrhythmogenic cardiomyopathy characterized by fibrofatty replacement of left ventricular myocardium, malignant arrhythmia, and sudden cardiac death. The definition incorporates several genetic causes, including pathogenic variation in the Filamin C gene (FLNC). Although awareness of ALVC has improved, identification remains challenging and diagnostic criteria continue to evolve.

Case summary

A 50-year-old athletic male was admitted following an out-of-hospital cardiac arrest due to ventricular tachycardia (VT) whilst playing football. Coronary angiography revealed unobstructed epicardial vessels and the diagnosis of ALVC was suggested by cardiovascular magnetic resonance imaging, which demonstrated a mildly dilated and moderately impaired left ventricle with epicardial late gadolinium enhancement in the basal to mid-lateral walls and subendocardial septum. Initial testing with a cardiomyopathy and arrhythmia gene panel was negative but extended testing uncovered a likely pathogenic variant in FLNC. Subsequently, the patient experienced a recurrence of sustained VT necessitating implantable cardioverter-defibrillator (ICD) therapies, ultimately undergoing a combined epicardial and endocardial VT ablation 4 years after presentation. Six months post-ablation, he was asymptomatic and his arrhythmia rendered quiescent.

Discussion

Arrhythmogenic cardiomyopathy should be considered in the evaluation of an initially unexplained cardiac arrest. This case characterizes the clinical features of a patient with FLNC cardiomyopathy and emphasizes the utility of genetic testing using modern gene panels in patients with comparable phenotypes. We also demonstrate that optimal medical therapy with antiarrhythmic drugs, exercise restriction, ICD insertion, and catheter ablation can be useful in the management of ALVC with positive outcomes

When genetic burden reaches threshold

Rare cardiac genetic diseases have generally been considered to be broadly Mendelian in nature, with clinical genetic testing for these conditions predicated on the detection of a primary causative rare pathogenic variant that will enable cascade genetic screening in families. However, substantial variability in penetrance and disease severity among carriers of pathogenic variants, as well as the inability to detect rare Mendelian variants in considerable proportions of patients, indicates that more complex aetiologies are likely to underlie these diseases. Recent findings have suggested genetic variants across a range of population frequencies and effect sizes may combine, along with non-genetic factors, to determine whether the threshold for expression of disease is reached and the severity of the phenotype. The availability of increasingly large genetically characterized cohorts of patients with rare cardiac diseases is enabling the discovery of common genetic variation that may underlie both variable penetrance in Mendelian diseases and the genetic aetiology of apparently non-Mendelian rare cardiac conditions. It is likely that the genetic architecture of rare cardiac diseases will vary considerably between different conditions as well as between patients with similar phenotypes, ranging from near-Mendelian disease to models more akin to common, complex disease. Uncovering the broad range of genetic factors that predispose patients to rare cardiac diseases offers the promise of improved risk prediction and more focused clinical management in patients and their families.

An unusual case of severe myocarditis in a genetic cardiomyopathy: a case report

Background

Myocarditis is an inflammatory disease of the myocardium caused by infectious pathogens, immune-mediated conditions, or toxic agents. This report explores a rare case of severe myocarditis occurring in an inherited cardiomyopathy.

Case summary

A 24-year-old female patient presented with progressing dyspnoea and chest discomfort. Echocardiography and cardiac magnetic resonance imaging revealed dilated cardiomyopathy (DCM) with severe biventricular dysfunction [left ventricle ejection fraction (LV-EF) 10%]. Myocardial inflammation was suspected due to extensive subendocardial to transmural late gadolinium enhancement. Endomyocardial biopsy (EMB) showed severe chronic lymphocytic myocarditis. As inflammatory DCM was assumed, immunosuppressive therapy with prednisolone was initiated in addition to standard heart failure therapy. Endomyocardial biopsy after 3 months showed resolving inflammation. However, a marked architectural disarray observed in all biopsies raised the suspicion of an inherited cardiomyopathy. Genetic testing revealed a de novo mutation with effect on splicing of lysosome-associated membrane protein 2, as found in Danon disease. Periodic acid–Schiff (PAS) staining confirmed a glycogen storage disorder. Immunosuppressive therapy was intensified due to reactivation of myocardial inflammation and led to improvement of LV-EF and to significant symptom relief over a 16-month follow-up period.

Discussion

This is the first report of Danon disease initially presenting as a severe myocarditis. It illustrates the clinical value of EMB for diagnosis and immunosuppressive therapy monitoring in chronic myocarditis. Increasing evidence suggests that myocardial inflammation may modify disease progression and prognosis in inherited cardiomyopathies. The causal role of cardiac protein mutations in the pathophysiology of myocarditis remains to be determined.

Family Communication About Genetic Risk of Hereditary Cardiomyopathies and Arrhythmias: an Integrative Review

Screening for hereditary cardiomyopathies and arrhythmias (HCA) may enable early detection, treatment, targeted surveillance, and result in effective prevention of debilitating complications and sudden cardiac death. Screening at-risk family members for HCA is conducted through cascade screening. Only half of at-risk family members are screened for HCA. To participate in screening, at-risk family members must be aware of their risk. This often relies on communication from diagnosed individuals to their relatives. However, family communication is not well understood and is ripe for developing interventions to improve screening rates. Until very recently, family communication of genetic risk has been mostly studied in non-cardiac disease. Using this non-cardiac literature, we developed the family communication of genetic risk (FCGR) conceptual framework. The FCGR has four main elements of the communication process: influential factors, communication strategies, communication occurrence, and reaction to communication. Using the FCGR, we conducted an integrated review of the available literature on genetic risk communication in HCA families. Descriptive analysis of 12 articles resulted in the development of categories describing details of the FCGR elements in the context of HCA. This review synthesizes what is known about influential factors, communication strategies, communication occurrence, and outcomes of communication in the context of HCA.