Compound heterozygous CASQ2 mutations and long-term course of catecholaminergic polymorphic ventricular tachycardia

Catecholaminergic polymorphic ventricular tachycardia (and seizure) caused by a novel homozygous likely pathogenic variant in CASQ2 gene

BACKGROUND

Although structural heart disease is frequently present among patients who experience sudden cardiac death (SCD), inherited arrhythmia syndromes can also play an important role in the occurrence of SCD. CPVT2, which is the second-most prevalent form of CPVT, arises from an abnormality in the CASQ2 gene.

OBJECTIVE

We represent a novel CASQ2 variant that causes CPVT2 and conduct a comprehensive review on this topic.

METHODS

The proband underwent Whole-exome sequencing (WES) in order to ascertain the etiology of CPVT. Subsequently, the process of segregating the available family members was carried out through the utilization of PCR and Sanger Sequencing. We searched the google scholar and PubMed/Medline for studies reporting CASQ2 variants, published up to May 10,2023. We used the following mesh term "Calsequestrin" and using free-text method with terms including "CASQ2","CASQ2 variants", and "CASQ2 mutation".

RESULTS

The CASQ2 gene was found to contain an autosomal recessive nonsense variant c.268_269insTA:p.Gly90ValfsTer4, which was identified by WES. This variant was determined to be the most probable cause of CPVT in the pedigree under investigation.

CONCLUSION

CASQ2 variants play an important role in pathogenesis of CPVT2. Notabely, based on results of our study and other findings in the literature the variant in this gene may cause an neurological signs in the patients with CPVT2. Further studies are needed for more details about the role of this gene in CPVT evaluation, diagnosis, and gene therapy.

Clinical and genetic characteristics of catecholaminergic polymorphic ventricular tachycardia combined with left ventricular non-compaction

BACKGROUND

Catecholaminergic polymorphic ventricular tachycardia is an ion channelopathy, caused by mutations in genes coding for calcium-handling proteins. It can coexist with left ventricular non-compaction. We aim to investigate the clinical and genetic characteristics of this co-phenotype.

METHODS

Medical records of 24 patients diagnosed with catecholaminergic polymorphic ventricular tachycardia in two Chinese hospitals between September, 2005, and January, 2020, were retrospectively reviewed. We evaluated their clinical and genetic characteristics, including basic demographic data, electrocardiogram parameters, medications and survival during follow-up, and their gene mutations. We did structural analysis for a novel variant ryanodine receptor 2-E4005V.

RESULTS

The patients included 19 with catecholaminergic polymorphic ventricular tachycardia mono-phenotype and 5 catecholaminergic polymorphic ventricular tachycardia-left ventricular non-compaction overlap patients. The median age of onset symptoms was 9.0 (8.0,13.5) years. Most patients (91.7%) had cardiac symptoms, and 50% had a family history of syncope. Overlap patients had lower peak heart rate and threshold heart rate for ventricular tachycardia and ventricular premature beat during the exercise stress test (p < 0.05). Sudden cardiac death risk may be higher in overlap patients during follow-up. Gene sequencing revealed 1 novel ryanodine receptor 2 missense mutation E4005V and 1 mutation previously unreported in catecholaminergic polymorphic ventricular tachycardia, but no left ventricular non-compaction-causing mutations were observed. In-silico analysis showed the novel mutation E4005V broke down the interaction between two charged residues.

CONCLUSIONS

Catecholaminergic polymorphic ventricular tachycardia overlapping with left ventricular non-compaction may lead to ventricular premature beat/ventricular tachycardia during exercise stress test at lower threshold heart rate than catecholaminergic polymorphic ventricular tachycardia alone; it may also indicate a worse prognosis and requires strict follow-up. ryanodine receptor 2 mutations disrupted interactions between residues and may interfere the function of ryanodine receptor 2.

The function and regulation of calsequestrin-2: implications in calcium-mediated arrhythmias

Cardiac arrhythmias are life-threatening events in which the heart develops an irregular rhythm. Mishandling of Ca²⁺ within the myocytes of the heart has been widely demonstrated to be an underlying mechanism of arrhythmogenesis. This includes altered function of the ryanodine receptor (RyR2)-the primary Ca²⁺ release channel located to the sarcoplasmic reticulum (SR). The spontaneous leak of SR Ca²⁺ via RyR2 is a well-established contributor in the development of arrhythmic contractions. This leak is associated with increased channel activity in response to changes in SR Ca²⁺ load. RyR2 activity can be regulated through several avenues, including interactions with numerous accessory proteins. One such protein is calsequestrin-2 (CSQ2), which is the primary Ca²⁺-buffering protein within the SR. The capacity of CSQ2 to buffer Ca²⁺ is tightly associated with the ability of the protein to polymerise in response to changing Ca²⁺ levels. CSQ2 can itself be regulated through phosphorylation and glycosylation modifications, which impact protein polymerisation and trafficking. Changes in CSQ2 modifications are implicated in cardiac pathologies, while mutations in CSQ2 have been identified in arrhythmic patients. Here, we review the role of CSQ2 in arrhythmogenesis including evidence for the indirect and direct regulation of RyR2 by CSQ2, and the consequences of a loss of functional CSQ2 in Ca²⁺ homeostasis and Ca²⁺-mediated arrhythmias.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12551-021-00914-6.

Advances in the Molecular Genetics of Catecholaminergic Polymorphic Ventricular Tachycardia

Catecholaminergic polymorphic ventricular tachycardia is a primary arrhythmogenic syndrome with genetic features most commonly seen in adolescents, with syncope and sudden death following exercise or agitation as the main clinical manifestations. The mechanism of its occurrence is related to the aberrant release of Ca²⁺ from cardiomyocytes caused by abnormal RyR2 channels or CASQ2 proteins under conditions of sympathetic excitation, thus inducing a delayed posterior exertional pole, manifested by sympathetic excitation inducing adrenaline secretion, resulting in bidirectional or polymorphic ventricular tachycardia. The mortality rate of the disease is high, but patients usually do not have organic heart disease, the clinical manifestations may not be obvious, and no significant abnormal changes in the QT interval are often observed on electrocardiography. Therefore, the disease is often easily missed and misdiagnosed. A number of genetic mutations have been linked to the development of this disease, and the mechanisms are different. In this paper, we would like to summarize the possible genes related to catecholaminergic polymorphic ventricular tachycardia in order to review the genetic tests currently performed, and to further promote the development of genetic testing techniques and deepen the research on the molecular level of this disease.

Phylogenetic and biochemical analysis of calsequestrin structure and association of its variants with cardiac disorders

Calsequestrin is among the most abundant proteins in muscle sarcoplasmic reticulum and displays a high capacity but a low affinity for Ca²⁺ binding. In mammals, calsequestrin is encoded by two genes, CASQ1 and CASQ2, which are expressed almost exclusively in skeletal and cardiac muscles, respectively. Phylogenetic analysis indicates that calsequestrin is an ancient gene in metazoans, and that the duplication of the ancestral calsequestrin gene took place after the emergence of the lancelet. CASQ2 gene variants associated with catecholaminergic polymorphic ventricular tachycardia (CPVT) in humans are positively correlated with a high degree of evolutionary conservation across all calsequestrin homologues. The mutations are distributed in diverse locations of the calsequestrin protein and impart functional diversity but remarkably manifest in a similar phenotype in humans.

An International Multicenter Evaluation of Inheritance Patterns, Arrhythmic Risks, and Underlying Mechanisms of CASQ2-Catecholaminergic Polymorphic Ventricular Tachycardia

BACKGROUND

Genetic variants in calsequestrin-2 (CASQ2) cause an autosomal recessive form of catecholaminergic polymorphic ventricular tachycardia (CPVT), although isolated reports have identified arrhythmic phenotypes among heterozygotes. Improved insight into the inheritance patterns, arrhythmic risks, and molecular mechanisms of CASQ2-CPVT was sought through an international multicenter collaboration.

METHODS

Genotype-phenotype segregation in CASQ2-CPVT families was assessed, and the impact of genotype on arrhythmic risk was evaluated using Cox regression models. Putative dominant CASQ2 missense variants and the established recessive CASQ2-p.R33Q variant were evaluated using oligomerization assays and their locations mapped to a recent CASQ2 filament structure.

RESULTS

A total of 112 individuals, including 36 CPVT probands (24 homozygotes/compound heterozygotes and 12 heterozygotes) and 76 family members possessing at least 1 presumed pathogenic CASQ2 variant, were identified. Among CASQ2 homozygotes and compound heterozygotes, clinical penetrance was 97.1% and 26 of 34 (76.5%) individuals had experienced a potentially fatal arrhythmic event with a median age of onset of 7 years (95% CI, 6-11). Fifty-one of 66 CASQ2 heterozygous family members had undergone clinical evaluation, and 17 of 51 (33.3%) met diagnostic criteria for CPVT. Relative to CASQ2 heterozygotes, CASQ2 homozygote/compound heterozygote genotype status in probands was associated with a 3.2-fold (95% CI, 1.3-8.0; P=0.013) increased hazard of a composite of cardiac syncope, aborted cardiac arrest, and sudden cardiac death, but a 38.8-fold (95% CI, 5.6-269.1; P<0.001) increased hazard in genotype-positive family members. In vitro turbidity assays revealed that p.R33Q and all 6 candidate dominant CASQ2 missense variants evaluated exhibited filamentation defects, but only p.R33Q convincingly failed to dimerize. Structural analysis revealed that 3 of these 6 putative dominant negative missense variants localized to an electronegative pocket considered critical for back-to-back binding of dimers.

CONCLUSIONS

This international multicenter study of CASQ2-CPVT redefines its heritability and confirms that pathogenic heterozygous CASQ2 variants may manifest with a CPVT phenotype, indicating a need to clinically screen these individuals. A dominant mode of inheritance appears intrinsic to certain missense variants because of their location and function within the CASQ2 filament structure.

Calsequestrin, a key protein in striated muscle health and disease

Calsequestrin (CASQ) is the most abundant Ca²⁺ binding protein localized in the sarcoplasmic reticulum (SR) of skeletal and cardiac muscle. The genome of vertebrates contains two genes, CASQ1 and CASQ2. CASQ1 and CASQ2 have a high level of homology, but show specific patterns of expression. Fast-twitch skeletal muscle fibers express only CASQ1, both CASQ1 and CASQ2 are present in slow-twitch skeletal muscle fibers, while CASQ2 is the only protein present in cardiomyocytes. Depending on the intraluminal SR Ca²⁺ levels, CASQ monomers assemble to form large polymers, which increase their Ca²⁺ binding ability. CASQ interacts with triadin and junctin, two additional SR proteins which contribute to localize CASQ to the junctional region of the SR (j-SR) and also modulate CASQ ability to polymerize into large macromolecular complexes. In addition to its ability to bind Ca²⁺ in the SR, CASQ appears also to be able to contribute to regulation of Ca²⁺ homeostasis in muscle cells. Both CASQ1 and CASQ2 are able to either activate and inhibit the ryanodine receptors (RyRs) calcium release channels, likely through their interactions with junctin and triadin. Additional evidence indicates that CASQ1 contributes to regulate the mechanism of store operated calcium entry in skeletal muscle via a direct interaction with the Stromal Interaction Molecule 1 (STIM1). Mutations in CASQ2 and CASQ1 have been identified, respectively, in patients with catecholamine-induced polymorphic ventricular tachycardia and in patients with some forms of myopathy. This review will highlight recent developments in understanding CASQ1 and CASQ2 in health and diseases.

CASQ2 variants in Chinese children with catecholaminergic polymorphic ventricular tachycardia

Background

Biallelic variants of the CASQ2 are known to cause the autosomal recessive form of catecholaminergic polymorphic ventricular tachycardia (CPVT), an inherited disease that predisposes young individuals to syncope and sudden cardiac death. To date, only about 24 CASQ2 variants have been reported in association with CPVT pathogenesis; furthermore, studies in Asians, especially in the Chinese population, are relatively rare. The aim of this study was to detect CASQ2 variants in Chinese patients with CPVT.

Methods

We used targeted next‐generation sequencing (NGS) to identify CASQ2 variants in Chinese patients with CPVT. A screening process was performed to prioritize rare variants of potential functional significance. Sanger sequencing was conducted to conform the candidate variants and determine the parental origin.

Results

We identified seven different CASQ2 variants, of which three (c.1074_1075delinsC, c.1175_1178delACAG, and c.838+1G>A) have not been previously reported. The variants exhibited autosomal recessive inheritance, and were detected in four unrelated Chinese families with CPVT. They included a nonsense variant c.97C>T (p.R33*) and a missense variant c.748C>T (p.R250C) in Family 1 with three CPVT patients; two heterozygous frameshift variants, c.1074_1075delinsC (p.G359Afs*12) and c.1175_1178delACAG (p.D392Vfs*84), in Family 2 with one CPVT patient; one pathogenic homozygous variant c.98G>A (p.R33Q) of CASQ2 in the CPVT patient of Family 3; and two heterozygous splicing variants, (c.532+1G>A) and (c.838+1G>A), in Family 4 with one CPVT patient.

Conclusion

To our knowledge, this is the first systematic study of Chinese children with CASQ2 variants. Our work further expands the genetic spectrum of CASQ2‐associated CPVT.

Genetic Variants Associated with FDNY WTC-Related Sarcoidosis

Sarcoidosis is a systemic granulomatous disease of unknown etiology. It may develop in response to an exposure or inflammatory trigger in the background of a genetically primed abnormal immune response. Thus, genetic studies are potentially important to our understanding of the pathogenesis of sarcoidosis. We developed a case-control study which explored the genetic variations between firefighters in the Fire Department of the City of New York (FDNY) with World Trade Center (WTC)-related sarcoidosis and those with WTC exposure, but without sarcoidosis. The loci of fifty-one candidate genes related to granuloma formation, inflammation, immune response, and/or sarcoidosis were sequenced at high density in enhancer/promoter, exonic, and 5’ untranslated regions. Seventeen allele variants of human leukocyte antigen (HLA) and non-HLA genes were found to be associated with sarcoidosis, and all were within chromosomes 1 and 6. Our results also suggest an association between extrathoracic involvement and allele variants of HLA and non-HLA genes found not only on chromosomes 1 and 6, but also on chromosomes 16 and 17. We found similarities between genetic variants with WTC-related sarcoidosis and those reported previously in sporadic sarcoidosis cases within the general population. In addition, we identified several allele variants never previously reported in association with sarcoidosis. If confirmed in larger studies with known environmental exposures, these novel findings may provide insight into the gene-environment interactions key to the development of sarcoidosis.

Compound heterozygous CASQ2 mutations and long-term course of catecholaminergic polymorphic ventricular tachycardia

BACKGROUND

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a potentially lethal inherited cardiac disorder characterized by episodic ventricular tachycardia during adrenergic stimulation. It is associated with significant morbidity and mortality. Knowledge of the underlying genetic cause, pathogenesis, and the natural history of the disease remains incomplete. Approximately 50% of CPVT cases are caused by dominant mutations in the cardiac ryanodine receptor (RYR2) gene, <5% of cases are accounted for by recessive mutations in cardiac calsequestrin (CASQ2) or Triadin (TRDN).

METHODS

We report a family with two CASQ2 gene mutations. A research-based next-generation sequencing (NGS) initiative was used in a patient with a severe CPVT phenotype and her clinically unaffected son. Reverse transcription polymerase chain reaction (RT-PCR) from platelet RNA was used to assess the consequences of predicted splice variants.

RESULTS

NGS revealed that the proband carried a novel c.199C>T (p.Gln67*) mutation and a previously reported splice site mutation c.532+1G>A in CASQ2. Her son is a heterozygous carrier of the c.199C>T (p.Gln67*) mutation alone and the proband was compound heterozygous at CASQ2. RNA analysis demonstrated that the splice site mutation results in the retention of intron 3 with no full-length CASQ2 mRNA.

CONCLUSION

This study describes a novel CPVT genotype and further characterizes the effect of a previously reported CASQ2 splice site mutation. The long-term follow-up of 23 years since first symptom provides additional insight into the natural history of CASQ2-associated CPVT.