Corrigendum: Case Report: Four cases of cardiac sarcoidosis in patients with inherited cardiomyopathy-a phenotypic overlap, co-existence of two rare cardiomyopathies or a second-hit disease

[This corrects the article DOI: 10.3389/fcvm.2023.1328802.].

Case Report: Four cases of cardiac sarcoidosis in patients with inherited cardiomyopathy-a phenotypic overlap, co-existence of two rare cardiomyopathies or a second-hit disease

Cardiac sarcoidosis (CS), a rare condition characterized by non-caseating granulomas, can manifest with symptoms such as atrioventricular block and ventricular tachycardia (VT), as well as mimic inherited cardiomyopathies. A 48-year-old male presented with recurrent VT. The initial 18F-fluorodeoxyglucose positron emission tomography (18FDG-PET) scan showed uptake of the mediastinal lymph node. Cardiovascular magnetic resonance (CMR) demonstrated intramyocardial fibrosis. The follow-up 18FDG-PET scan revealed the presence of tracer uptake in the left ventricular (LV) septum, suggesting the likelihood of CS. Genetic testing identified a pathogenic LMNA variant. A 47-year-old female presented with complaints of palpitations and syncope. An Ajmaline provocation test confirmed Brugada syndrome (BrS). CMR revealed signs of cardiac inflammation. An endomyocardial biopsy (EMB) confirmed the diagnosis of cardiac sarcoidosis. Polymorphic VT was induced during an electrophysiological study, and an implantable cardioverter-defibrillator (ICD) was implanted. A 58-year-old woman presented with sustained VT with a prior diagnosis of hypertrophic cardiomyopathy (HCM). A genetic work-up identified the presence of a heterozygous MYBC3 variant of unknown significance (VUS). CMR revealed late gadolinium enhancement (LGE), while the 18FDG-PET scan demonstrated LV tracer uptake. The immunosuppressive therapy was adjusted, and no further VTs were observed. A 28-year-old male athlete with right ventricular dilatation and syncope experienced a cardiac arrest during training. Genetic testing identified a pathogenic mutation in PKP2. The autopsy has confirmed the presence of ACM and a distinctive extracardiac sarcoidosis. Cardiac sarcoidosis and inherited cardiomyopathies may interact in several different ways, altering the clinical presentation. Overlapping pathologies are frequently overlooked. Delayed or incomplete diagnosis risks inadequate treatment. Thus, genetic testing and endomyocardial biopsies should be recommended to obtain a clear diagnosis.

Pathophysiological Gaps, Diagnostic Challenges, and Uncertainties in Cardiac Sarcoidosis

Cardiac sarcoidosis can mimic any cardiomyopathy in different stages. Noncaseating granulomatous inflammation can be missed, because of the nonhomogeneous distribution in the heart. The current diagnostic criteria show discrepancies and are partly nonspecific and insensitive. Besides the diagnostic pitfalls, there are controversies in the understanding of the causes, genetic and environmental background, and the natural evolution of the disease. Here, we review the current pathophysiological aspects and gaps that are relevant for future cardiac sarcoidosis diagnostics and research.

Effects of positive endomyocardial biopsy on the survival and the outcomes of catheter ablation of ventricular tachycardia in patients with cardiac sarcoidosis

Funding Acknowledgements

Type of funding sources: Private hospital(s). Main funding source(s): Heart center of Leipzig

Background

Cardiac sarcoidosis (CS) is frequently unrecognized cause of non-ischemic cardiomyopathy associated ventricular tachycardia (VT), who eventually require VT ablations because of refractory VTs; however, the reported long-term outcomes after VT ablation are conflicting. Because of the low diagnostic yield of the endomyocardial biopsy (EMB), diagnosis of CS is often based on clinical and imaging criteria, which can lead to misdiagnosing.

Purpose and objectives

The purpose of this study was to identity whether patients with histologically-proven CS (EMB+) have different patient, procedural characteristics and outcomes after VT ablation as compared to those in whom the diagnosis was based on clinical criteria only (EMB-).

Methods

Between 2015-2021, 153 patients with suspected CS were evaluated according to a specified protocol including CMR, 18FDG-PET, EMB, bronchoscopy and EBUS biopsy, and serum markers. Those who fulfilled the latest criteria for CS of the Japanese Circulation Society (JCS) were divided into 2 groups: EMB (+) CS proven by myocardial biopsy, and EMB (-) CS fulfilling the clinical criteria for CS. The following endpoints were defined: 1) VT recurrence after ablation; and 2) the composite endpoint of death, heart transplantation or LVAD implantation.

Results

We identified 76 patients fulfilling the JCS criteria for CS (mean age 50 ± 10.6 years, 38% female, EMB (+) 35.5%). The leading symptoms were as follows: sustained VT in 23 (30%), high-grade AV block in 23 (30%), heart failure in 18 (24%), and other in 12 pts (16%). EMB (+) and the EMB (-) patients had similar clinical characteristics except for the imaging findings. EMB (+) patients exhibit LGE in CMR in 96% vs. 73% in EMB (-); P=0.024, whereas 18FDG-PET showed abnormal myocardial activity in 91% in the EMB (+) vs. 65% in the EMB (-); P=0.028. The primary composite endpoint was reached in 7.4% in EMB (+) group and in 12.2 % in EMB (-) group; P = 0.7. VT ablation was performed in 15 cases: 9 ablations (33%) in EMB (+) vs. 6 ablations (12%) in EMB (-); P=0.037. At the end of the procedure, all inducible VTs were successfully ablated in 100% of the EMB (-) patients vs. 56% in EMB (+) patients; P=0.1. VT recurrence was 78% in EMB (+) group vs. 67% in EMB (-); P = 0.6. The only procedural difference between the groups was the presence of vast RV low-voltage areas in 67% of the EMB (+) vs. 0% in EMB (-); P = 0.028.

Conclusions

Patients with CS and positive EMB exhibit more often LGE in CMR, abnormal 18FDG-PET activity and required more frequently VT ablation. The procedural characteristics between both groups were similar, except for the frequently observed RV low-voltage areas in most EMB (+) patients, whereas the RV was not affected in any of the EMB (-) patients. In spite of these differences, the VT recurrence rates and the survival seemed not to be affected by the histological evidence of CS in EMB.

Cardiomyopathy-associated mutations in the RS domain affect nuclear localization of RBM20

Mutations in RBM20 encoding the RNA-binding motif protein 20 (RBM20) are associated with an early onset and clinically severe forms of cardiomyopathies. Transcriptome analyses revealed RBM20 as an important regulator of cardiac alternative splicing. RBM20 mutations are especially localized in exons 9 and 11 including the highly conserved arginine and serine-rich domain (RS domain). Here, we investigated in several cardiomyopathy patients, the previously described RBM20-mutation p.Pro638Leu localized within the RS domain. In addition, we identified in a patient the novel mutation p.Val914Ala localized in the (glutamate-rich) Glu-rich domain of RBM20 encoded by exon 11. Its impact on the disease was investigated with a novel TTN- and RYR2-splicing assay based on the patients' cardiac messenger RNA. Furthermore, we showed in cell culture and in human cardiac tissue that mutant RBM20-p.Pro638Leu is not localized in the nuclei but causes an abnormal cytoplasmic localization of the protein. In contrast the splicing deficient RBM20-p.Val914Ala has no influence on the intracellular localization. These results indicate that disease-associated variants in RBM20 lead to aberrant splicing through different pathomechanisms dependent on the localization of the mutation. This might have an impact on the future development of therapeutic strategies for the treatment of RBM20-induced cardiomyopathies.

A homozygous DSC2 deletion associated with arrhythmogenic cardiomyopathy is caused by uniparental isodisomy

AIMS

We aimed to unravel the genetic, molecular and cellular pathomechanisms of DSC2 truncation variants leading to arrhythmogenic cardiomyopathy (ACM).

METHODS AND RESULTS

We report a homozygous 4-bp DSC2 deletion variant c.1913_1916delAGAA, p.Q638LfsX647^hom causing a frameshift carried by an ACM patient. Whole exome sequencing and comparative genomic hybridization analysis support a loss of heterozygosity in a large segment of chromosome 18 indicating segmental interstitial uniparental isodisomy (UPD). Ultrastructural analysis of the explanted myocardium from a mutation carrier using transmission electron microscopy revealed a partially widening of the intercalated disc. Using qRT-PCR we demonstrated that DSC2 mRNA expression was substantially decreased in the explanted myocardial tissue of the homozygous carrier compared to controls. Western blot analysis revealed absence of both full-length desmocollin-2 isoforms. Only a weak expression of the truncated form of desmocollin-2 was detectable. Immunohistochemistry showed that the truncated form of desmocollin-2 did not localize at the intercalated discs. In vitro, transfection experiments using induced pluripotent stem cell derived cardiomyocytes and HT-1080 cells demonstrated an obvious absence of the mutant truncated desmocollin-2 at the plasma membrane. Immunoprecipitation in combination with fluorescence measurements and Western blot analyses revealed an abnormal secretion of the truncated desmocollin-2.

CONCLUSION

In summary, we unraveled segmental UPD as the likely genetic reason for a small homozygous DSC2 deletion. We conclude that a combination of nonsense mediated mRNA decay and extracellular secretion is involved in DSC2 related ACM.

Human Induced Pluripotent Stem-Cell-Derived Cardiomyocytes as Models for Genetic Cardiomyopathies

In the last few decades, many pathogenic or likely pathogenic genetic mutations in over hundred different genes have been described for non-ischemic, genetic cardiomyopathies. However, the functional knowledge about most of these mutations is still limited because the generation of adequate animal models is time-consuming and challenging. Therefore, human induced pluripotent stem cells (iPSCs) carrying specific cardiomyopathy-associated mutations are a promising alternative. Since the original discovery that pluripotency can be artificially induced by the expression of different transcription factors, various patient-specific-induced pluripotent stem cell lines have been generated to model non-ischemic, genetic cardiomyopathies in vitro. In this review, we describe the genetic landscape of non-ischemic, genetic cardiomyopathies and give an overview about different human iPSC lines, which have been developed for the disease modeling of inherited cardiomyopathies. We summarize different methods and protocols for the general differentiation of human iPSCs into cardiomyocytes. In addition, we describe methods and technologies to investigate functionally human iPSC-derived cardiomyocytes. Furthermore, we summarize novel genome editing approaches for the genetic manipulation of human iPSCs. This review provides an overview about the genetic landscape of inherited cardiomyopathies with a focus on iPSC technology, which might be of interest for clinicians and basic scientists interested in genetic cardiomyopathies.