Familial dilated cardiomyopathy associated with a novel heterozygous RYR2 early truncating variant

A novel RyR2 mutation associated with co-morbid catecholaminergic polymorphic ventricular tachycardia (CPVT) and benign epilepsy with centrotemporal spikes (BECTS)

In this case report, we describe a 14-year-old patient with a novel RyR2 gene mutation (c.6577G > T/p.Val2193Leu), identified through a comprehensive review of medical history, examination findings, and follow-up data. The pathogenic potential of this mutation, which results in the loss of some interatomic forces and compromises the closure of the RyR2 protein pore leading to calcium leakage, was analyzed using the I-TASSER Suite to predict the structural changes in the protein. This mutation manifested clinically as co-morbid catecholaminergic polymorphic ventricular tachycardia (CPVT) and benign epilepsy with centrotemporal spikes (BECTS), a combination not previously documented in the same patient. While seizures were successfully managed with levetiracetam, the patient's exercise-induced syncope episodes could not be controlled with metoprolol, highlighting the complexity and challenge in managing CPVT associated with this novel RyR2 variation.

Genetic Risk Stratification in Arrhythmogenic Left Ventricular Cardiomyopathy

Arrhythmogenic left ventricular cardiomyopathy is characterized by early malignant ventricular arrhythmia associated with varying degrees and times of onset of left ventricular dysfunction. Variants in numerous genes have been associated with this phenotype. Here, the authors review the literature on recent cohort studies of patients with variants in desmoplakin, lamin A/C, filamin-C, phospholamban, RBM20, TMEM43, and selected channelopathy genes also associated with structural disease. Unlike traditional sudden cardiac death risk assessment in nonischemic cardiomyopathy, left ventricular systolic function is an insensitive predictor of risk in patients with these genetic diagnoses.

Inosine triphosphate pyrophosphatase: A guardian of the cellular nucleotide pool and potential mediator of RNA function

Inosine triphosphate pyrophosphatase (ITPase), encoded by the ITPA gene in humans, is an important enzyme that preserves the integrity of cellular nucleotide pools by hydrolyzing the noncanonical purine nucleotides (deoxy)inosine and (deoxy)xanthosine triphosphate into monophosphates and pyrophosphate. Variants in the ITPA gene can cause partial or complete ITPase deficiency. Partial ITPase deficiency is benign but clinically relevant as it is linked to altered drug responses. Complete ITPase deficiency causes a severe multisystem disorder characterized by seizures and encephalopathy that is frequently associated with fatal infantile dilated cardiomyopathy. In the absence of ITPase activity, its substrate noncanonical nucleotides have the potential to accumulate and become aberrantly incorporated into DNA and RNA. Hence, the pathophysiology of ITPase deficiency could arise from metabolic imbalance, altered DNA or RNA regulation, or from a combination of these factors. Here, we review the known functions of ITPase and highlight recent work aimed at determining the molecular basis for ITPA-associated pathogenesis which provides evidence for RNA dysfunction. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA in Disease and Development > RNA in Development.

Impaired Cardiomyocyte Maturation Leading to DCM: A Case Report and Literature Review

Background: The maturation of cardiomyocytes is a rapidly evolving area of research within the field of cardiovascular medicine. Understanding the molecular mechanisms underlying cardiomyocyte maturation is essential to advancing our knowledge of the underlying causes of cardiovascular disease. Impaired maturation can lead to the development of cardiomyopathy, particularly dilated cardiomyopathy (DCM). Recent studies have confirmed the involvement of the ACTN2 and RYR2 genes in the maturation process, facilitating the functional maturation of the sarcomere and calcium handling. Defective sarcomere and electrophysiological maturation have been linked to severe forms of cardiomyopathy. This report presents a rare case of DCM with myocardial non-compaction, probably resulting from allelic collapse of both the ACTN2 and RYR2 genes. Case Presentation: The proband in this case was a four-year-old male child who presented with a recurrent and aggressive reduction in activity tolerance, decreased ingestion volume, and profuse sweating. Electrocardiography revealed significant ST-T segment depression (II, III, aVF V3-V6 ST segment depression >0.05 mV with inverted T-waves). Echocardiography showed an enlarged left ventricle and marked myocardial non-compaction. Cardiac magnetic resonance imaging revealed increased left ventricular trabeculae, an enlarged left ventricle, and a reduced ejection fraction. Whole exome sequencing revealed a restricted genomic depletion in the 1q43 region (chr1:236,686,454-237,833,988/Hg38), encompassing the coding genes ACTN2, MTR, and RYR2. The identified variant resulted in heterozygous variations in these three genes, with the ACTN2 g.236,686,454-236,764,631_del and RYR2 g.237,402,134-237,833,988_del variants being the dominant contributors to the induction of cardiomyopathy. The patient was finally diagnosed with DCM and left ventricular myocardial non-compaction. Conclusions: This study reports a rare case of DCM with myocardial non-compaction caused by the allelic collapse of the ACTN2 and RYR2 genes. This case provides the first human validation of the critical role of cardiomyocyte maturation in maintaining cardiac function and stability and confirms the key findings of previous experimental research conducted by our group. This report emphasizes the connection between genes involved in regulating the maturation of cardiomyocytes and the development of cardiomyopathy.

Molecular, Subcellular, and Arrhythmogenic Mechanisms in Genetic RyR2 Disease

The ryanodine receptor (RyR2) has a critical role in controlling Ca²⁺ release from the sarcoplasmic reticulum (SR) throughout the cardiac cycle. RyR2 protein has multiple functional domains with specific roles, and four of these RyR2 protomers are required to form the quaternary structure that comprises the functional channel. Numerous mutations in the gene encoding RyR2 protein have been identified and many are linked to a wide spectrum of arrhythmic heart disease. Gain of function mutations (GoF) result in a hyperactive channel that causes excessive spontaneous SR Ca²⁺ release. This is the predominant cause of the inherited syndrome catecholaminergic polymorphic ventricular tachycardia (CPVT). Recently, rare hypoactive loss of function (LoF) mutations have been identified that produce atypical effects on cardiac Ca²⁺ handling that has been termed calcium release deficiency syndrome (CRDS). Aberrant Ca²⁺ release resulting from both GoF and LoF mutations can result in arrhythmias through the Na⁺/Ca²⁺ exchange mechanism. This mini-review discusses recent findings regarding the role of RyR2 domains and endogenous regulators that influence RyR2 gating normally and with GoF/LoF mutations. The arrhythmogenic consequences of GoF/LoF mutations will then be discussed at the macromolecular and cellular level.

Understanding the molecular basis of cardiomyopathy

Inherited cardiomyopathies are a major cause of mortality and morbidity worldwide and can be caused by mutations in a wide range of proteins located in different cellular compartments. The present review is based on Dr. Ju Chen's 2021 Robert M. Berne Distinguished Lectureship of the American Physiological Society Cardiovascular Section, in which he provided an overview of the current knowledge on the cardiomyopathy-associated proteins that have been studied in his laboratory. The review provides a general summary of the proteins in different compartments of cardiomyocytes associated with cardiomyopathies, with specific focus on the proteins that have been studied in Dr. Chen's laboratory.

State of the Art Review on Genetics and Precision Medicine in Arrhythmogenic Cardiomyopathy

Arrhythmogenic cardiomyopathy (ACM) is an inherited cardiomyopathy characterised by ventricular arrhythmia and an increased risk of sudden cardiac death (SCD). Numerous genetic determinants and phenotypic manifestations have been discovered in ACM, posing a significant clinical challenge. Further to this, wider evaluation of family members has revealed incomplete penetrance and variable expressivity in ACM, suggesting a complex genotype-phenotype relationship. This review details the genetic basis of ACM with specific genotype-phenotype associations, providing the reader with a nuanced perspective of this condition; whilst also proposing a future roadmap to delivering precision medicine-based management in ACM.