Variable clinical expression of a novel FLNC truncating variant in a large family

BACKGROUND

Variants in Filamin-C (FLNC) have been associated with various hereditary cardiomyopathies. Recent literature reports a prevalence of sudden cardiac death (SCD) of 13-25% among carriers of truncating-variants, with mean age of 42±15 years for first SCD event. This study reports two familial cases of SCD and the results of cascade screening of their large family.

METHODS

Molecular-autopsy of the SCD victims revealed a novel truncating-variant in the FLNC gene (chr 7:128496880 [hg19]; NM_001458.5; c.7467_7474del; p.(Ser2490fs)). We screened thirty-two family members following genetic counseling, and variant carriers underwent a comprehensive workup followed by consultation with a cardiologist with expertise in the genetics of cardiac diseases.

RESULTS

Seventeen variant carriers were identified: ages between 9 and 85 (mean 47±26). Fifteen underwent clinical evaluation. To date, none of the identified carriers has had major adverse events. In evaluated patients, ECG showed right-axis deviation in 60% (n = 9). Holter recorded frequent premature ventricular contractions (PVCs) (991±2030 per 24 h) in 33% (n = 5) with 4 patients having polymorphic PVC morphology. Three carriers had echocardiographic evidence of mild left-ventricular (LV) systolic dysfunction and another with mild LV dilatation. Cardiac magnetic-resonance (CMR) exhibited late‑gadolinium-enhancement in 10 out of 11 exams, mainly in the mid-myocardium and sub-epicardium, frequently involving the septum and the inferior-lateral wall.

CONCLUSION

This large FLNC truncating variant carrier family exhibits high cardiomyopathy penetrance, best diagnosed by CMR, with variable clinical expressions. These findings present a challenge in SCD prevention management and underscoring the imperative for better risk stratification measures.

A case series of patients with filamin-C truncating variants attending a specialized cardiac genetic clinic

Background

FLNC encodes for filamin-C, a protein expressed in Z-discs of cardiac and skeletal muscle, involved in intracellular signalling and mechanical stabilization. Variants can cause diverse phenotypes with skeletal (myofibrillar or distal myopathy) and/or cardiac (hypertrophic, restrictive, and arrhythmogenic cardiomyopathies) manifestations. Truncating variants have recently been implicated in arrhythmogenic cardiomyopathy (ACM) without skeletal disease.

Case summary

Retrospective review of medical records, including cardiac investigations, was performed for families attending a specialized clinic with a FLNC truncating variant (FLNCtv). Variants were classified according to accepted variant interpretation criteria. Of seven families identified, six had primary cardiac phenotypes with one nonsense and five frameshift variants (nonsense-mediated decay competent) identified. One family had no cardiac phenotype, with a pathogenic variant (p.Arg2467Alafs*62) identified as secondary genetic finding. Of the six with cardiac phenotypes, proband age at diagnosis ranged 27-35 years (four females). Five families experienced sudden cardiac death (SCD) of a young relative (age range: 30-43 years), and one patient listed for cardiac transplant. Left ventricular (LV) ejection fraction ranged from 13 to 46%, with LV fibrosis (late gadolinium enhancement) on cardiac imaging or on postmortem histology seen in three families. Two families had one genotype-positive/phenotype-negative relative.

Discussion

The FLNCtv causes a left-sided ACM phenotype with a high risk of severe cardiac outcomes including end-stage heart failure and SCD. Incomplete penetrance is observed with implications for reporting secondary genetic findings.

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.

Genetic Background and Clinical Features in Arrhythmogenic Left Ventricular Cardiomyopathy: A Systematic Review

In recent years a phenotypic variant of Arrhythmogenic cardiomyopathy has been described, characterized by predominant left ventricular (LV) involvement with no or minor right ventricular abnormalities, referred to as Arrhythmogenic left ventricular cardiomyopathy (ALVC). Different disease-genes have been identified in this form, such as Desmoplakin (DSP), Filamin C (FLNC), Phospholamban (PLN) and Desmin (DES). The main purpose of this critical systematic review was to assess the level of knowledge on genetic background and clinical features of ALVC. A search (updated to April 2022) was run in the PubMed, Scopus, and Web of Science electronic databases. The search terms used were “arrhythmogenic left ventricular cardiomyopathy” OR “arrhythmogenic cardiomyopathy” and “gene” OR “arrhythmogenic dysplasia” and “gene”. The most represented disease-gene turned out to be DSP, accounting for half of published cases, followed by FLNC. Overall, ECG abnormalities were reported in 58% of patients. Major ventricular arrhythmias were recorded in 26% of cases; an ICD was implanted in 29% of patients. A total of 6% of patients showed heart failure symptoms, and 15% had myocarditis-like episodes. DSP is confirmed to be the most represented disease-gene in ALVC patients. An analysis of reported clinical features of ALVC patients show an important degree of electrical instability, which frequently required an ICD implant. Moreover, myocarditis-like episodes are common.

Filamin-C variant-associated cardiomyopathy: A pooled analysis of individual patient data to evaluate the clinical profile and risk of sudden cardiac death

BACKGROUND

Mutations in filamin-C (FLNC) are involved in the pathogenesis of arrhythmogenic cardiomyopathy (ACM) and dilated cardiomyopathy (DCM), and have been associated with a left ventricular (LV) phenotype, characterized by nonischemic LV fibrosis, ventricular arrhythmias, and sudden cardiac death (SCD).

OBJECTIVE

The purpose of this study was to investigate the prevalence of FLNC variants in a gene-negative ACM population and to evaluate the clinical phenotype and SCD risk factors in FLNC-associated cardiomyopathies.

METHODS

ACM probands who tested negative for mutations in ACM-related genes underwent FLNC genetic screening. Clinical and genetic data were collected and pooled together with those of previously published FLNC-ACM and FLNC-DCM patients.

RESULTS

In a cohort of 270 gene-elusive ACM probands, 12 (4.4%) had FLNC variants, and 13 additional family members carried the same mutation. Eighteen FLNC variant carriers (72%) had a diagnosis of ACM (72% male; mean age 45 years). On pooled analysis, 145 patients with FLNC-associated cardiomyopathies were included. Electrocardiographic (ECG) low QRS voltages were detected in 37%, and T-wave inversion (TWI) in inferolateral/lateral leads in 24%. Among 67 patients who had cardiac magnetic resonance (CMR), LV nonischemic late gadolinium enhancement (LGE) was found in 75%. SCD occurred in 28 patients (19%), 15 of whom showed LV nonischemic LGE/fibrosis. Compared with patients with no SCD, those who experienced SCD more frequently had inferolateral/lateral TWI (P = .013) and LV LGE/fibrosis (P = .033).

CONCLUSION

Clinical phenotype of FLNC cardiomyopathies is characterized by late-onset presentation and typical ECG and CMR features. SCD is associated with the presence of LV LGE/fibrosis but not with severe LV systolic dysfunction.

Widening the spectrum of filamin-C myopathy: Predominantly proximal myopathy due to the p.A193T mutation in the actin-binding domain of FLNC

We report three patients with a predominantly proximal myopathy due to p.A193T mutation in the actin-binding domain of FLNC, which has so far only been associated with a distal myopathy. They presented with a late onset myopathy characterized by predominant limb-girdle and proximal weakness. We describe the clinical, electrophysiological, pathological, muscle imaging and genetic features. One of our patients did not have typical histological features for a myofibrillar myopathy in muscle biopsy. This observation is important for the recognition of the full clinical spectrum of filamin-C-related myopathies. Muscle imaging has an important role in distinguishing the different filamin-C myopathy types.