RBM20-Associated Ventricular Arrhythmias in a Patient with Structurally Normal Heart

Imagenetics for Precision Medicine in Dilated Cardiomyopathy

Dilated cardiomyopathy (DCM) is a common heart muscle disorder of nonischemic etiology associated with heart failure development and the risk of malignant ventricular arrhythmias and sudden cardiac death. A tailored approach to risk stratification and prevention of sudden cardiac death is required in genetic DCM given its variable presentation and phenotypic severity. Currently, advances in cardiogenetics have shed light on disease mechanisms, the complex genetic architecture of DCM, polygenic contributors to disease susceptibility and the role of environmental triggers. Parallel advances in imaging have also enhanced disease recognition and the identification of the wide spectrum of phenotypes falling under the DCM umbrella. Genotype-phenotype associations have been also established for specific subtypes of DCM, such as DSP (desmoplakin) or FLNC (filamin-C) cardiomyopathy but overall, they remain elusive and not readily identifiable. Also, despite the accumulated knowledge on disease mechanisms, certain aspects remain still unclear, such as which patients with DCM are at risk for disease progression or remission after treatment. Imagenetics, that is, the combination of imaging and genetics, is expected to further advance research in the field and contribute to precision medicine in DCM management and treatment. In the present article, we review the existing literature in the field, summarize the established knowledge and emerging data on the value of genetics and imaging in establishing genotype-phenotype associations in DCM and in clinical decision making for DCM patients.

Mechanisms of RBM20 Cardiomyopathy: Insights From Model Systems

RBM20 (RNA-binding motif protein 20) is a vertebrate- and muscle-specific RNA-binding protein that belongs to the serine-arginine-rich family of splicing factors. The RBM20 gene was first identified as a dilated cardiomyopathy-linked gene over a decade ago. Early studies in Rbm20 knockout rodents implicated disrupted splicing of RBM20 target genes as a causative mechanism. Clinical studies show that pathogenic variants in RBM20 are linked to aggressive dilated cardiomyopathy with early onset heart failure and high mortality. Subsequent studies employing pathogenic variant knock-in animal models revealed that variants in a specific portion of the arginine-serine-rich domain in RBM20 not only disrupt splicing but also hinder nucleocytoplasmic transport and lead to the formation of RBM20 biomolecular condensates in the sarcoplasm. Conversely, mice harboring a disease-associated variant in the RRM (RNA recognition motif) do not show evidence of adverse remodeling or exhibit sudden death despite disrupted splicing of RBM20 target genes. Thus, whether disrupted splicing, biomolecular condensates, or both contribute to dilated cardiomyopathy is under debate. Beyond this, additional questions remain, such as whether there is sexual dimorphism in the presentation of RBM20 cardiomyopathy. What are the clinical features of RBM20 cardiomyopathy and why do some individuals develop more severe disease than others? In this review, we summarize the reported observations and discuss potential mechanisms of RBM20 cardiomyopathy derived from studies employing in vivo animal models and in vitro human-induced pluripotent stem cell-derived cardiomyocytes. Potential therapeutic strategies to treat RBM20 cardiomyopathy are also discussed.

Scientific Basics of Personalized Medicine: Realities and Opportunities

Modern trends in the development of health care suggest its focus on the interests of the patient and its holistic nature, as well as deep penetration into all parts of health care information technology. The driving force behind the ongoing changes, of course, are scientific achievements, the importance of which in the development of new medical technologies and the creation of innovative diagnostic devices, as well as medicines, has grown significantly in recent years. These processes provide conditions for the introduction into clinical practice of a new model of medical care-personalized medicine, based on the choice of methods of diagnosis and treatment with account for the individual characteristics of the course of the disease, as well as the patient's lifestyle. Personalized medicine technologies, which involve the creation of an appropriate, often expensive, infrastructure of omics technologies, should ultimately lead to an increase in the efficiency, quality, and, most importantly, safety of medical care. In the Russian Federation, this area is actively developing in four world-class research centers, including the Almazov National Medical Research Center. The current state and prospects of research in the field of personalized medicine are discussed in this article, prepared by the author on the basis of his scientific report at a meeting of the Presidium of the Russian Academy of Sciences.

I536T variant of RBM20 affects splicing of cardiac structural proteins that are causative for developing dilated cardiomyopathy

RBM20 is one of the genes predisposing to dilated cardiomyopathy (DCM). Variants in the RS domain have been reported in many DCM patients, but the pathogenicity of variants within the RNA-recognition motif remains unknown. Two human patients with the I536T-RBM20 variant without an apparent DCM phenotype were identified in sudden death cohorts. A splicing reporter assay was performed, and an I538T knock-in mouse model (Rbm20^I538T) was generated to determine the significance of this variant. The reporter assay demonstrated that the human I536T variant affected the TTN splicing pattern compared to wild-type. In the mouse experiments, Rbm20^I538T mice showed different splicing patterns in Ttn, Ldb3, Camk2d, and Ryr2. The expressions of Casq1, Mybpc2, and Myot were upregulated in Rbm20^I538T mice, but Rbm20^I538T mice showed neither DCM nor cardiac dysfunction on histopathological examination and ultrasound echocardiography. The I536T-RBM20 (I538T-Rbm20) variant changes gene splicing and affects gene expression, but the splicing and expression changes in Ttn and Ca handling genes such as Casq1, Camk2d, and Ryr2 do not cause DCM morphology in the mouse model. KEY MESSAGES: • Two human patients with the I536T-RBM20 variant without a DCM phenotype were identified. • A splicing reporter assay demonstrated that the variant affected the TTN splicing. • Rbm20^I538T mice showed neither DCM nor cardiac dysfunction. • Rbm20^I538T mice showed different splicing patterns and the gene expressions.

RBM20-Related Cardiomyopathy: Current Understanding and Future Options

Splice regulators play an essential role in the transcriptomic diversity of all eukaryotic cell types and organ systems. Recent evidence suggests a contribution of splice-regulatory networks in many diseases, such as cardiomyopathies. Adaptive splice regulators, such as RNA-binding motif protein 20 (RBM20) determine the physiological mRNA landscape formation, and rare variants in the RBM20 gene explain up to 6% of genetic dilated cardiomyopathy (DCM) cases. With ample knowledge from RBM20-deficient mice, rats, swine and induced pluripotent stem cells (iPSCs), the downstream targets and quantitative effects on splicing are now well-defined and the prerequisites for corrective therapeutic approaches are set. This review article highlights some of the recent advances in the field, ranging from aspects of granule formation to 3D genome architectures underlying RBM20-related cardiomyopathy. Promising therapeutic strategies are presented and put into context with the pathophysiological characteristics of RBM20-related diseases.

RBM20 mutation and ventricular arrhythmias in a young patient with dilated cardiomyopathy: a case report

Gene mutations in RBM20 have been identified in a minority of familial and sporadic dilated cardiomyopathy cases. Recent studies of carriers of RBM20 mutations not only highlight the aforementioned association with dilated cardiomyopathy but also indicate a link with increased incidence of ventricular arrhythmias. Herein we describe a case of 17-year-old female patient with dilated cardiomyopathy carrying a p.(Arg634Trp) RBM20 mutation and presenting with frequent premature ventricular contractions and episodes of non-sustained ventricular tachycardia.