Novel Association of a De Novo CALM2 Mutation With Long QT Syndrome and Hypertrophic Cardiomyopathy

Calmodulin mutation in long QT syndrome 15 associated with congenital heart defects further complicated by a functional 2:1 atrioventricular block: Management from foetal life to postpartum

We report a long QT syndrome 15 whose diagnosis was suspected during foetal life and confirmed at birth and was associated with congenital heart disease. Genetic testing revealed a rare mutation associated with the CALM2 gene. At 23 weeks of gestation, severe foetal sinus bradycardia (∼100 bpm) was detected. In the third trimester, the foetus developed severe right ventricular hypertrophy. At birth, the electrocardiogram showed a long QT interval of 640 ms, and after 1 hour, the newborn showed functional 2:1 atrioventricular block at ventricular rate of 50 bpm. After further pharmacological therapies, epicardial wires were surgically implanted for transient pacing in VVI mode at 90 bpm. Echocardiogram showed aneurysmatic left atrial appendage, dilated right segments, hypertrophied right ventricle, ostium secundum type atrial septal defect, and muscular ventricular septal defect. At two weeks of postpartum, a permanent dual-chamber pacemaker was implanted in the DDD mode and the patient was discharged with a prescription of beta-blockers and calcium therapy.

Calmodulin Mutations in Human Disease

Calcium ions (Ca²⁺) are the basis of a unique and potent array of cellular responses. Calmodulin (CaM) is a small but vital protein that is able to rapidly transmit information about changes in Ca²⁺ concentrations to its regulatory targets. CaM plays a critical role in cellular Ca²⁺ signaling, and interacts with a myriad of target proteins. Ca²⁺-dependent modulation by CaM is a major component of a diverse array of processes, ranging from gene expression in neurons to the shaping of the cardiac action potential in heart cells. Furthermore, the protein sequence of CaM is highly evolutionarily conserved, and identical CaM proteins are encoded by three independent genes (CALM1-3) in humans. Mutations within any of these three genes may lead to severe cardiac deficits including severe long QT syndrome (LQTS) and/or catecholaminergic polymorphic ventricular tachycardia (CPVT). Research into disease-associated CaM variants has identified several proteins modulated by CaM that are likely to underlie the pathogenesis of these calmodulinopathies, including the cardiac L-type Ca²⁺ channel (LTCC) Ca_V1.2, and the sarcoplasmic reticulum Ca²⁺ release channel, ryanodine receptor 2 (RyR2). Here, we review the research that has been done to identify calmodulinopathic CaM mutations and evaluate the mechanisms underlying their role in disease.

Long QTc in hypertrophic cardiomyopathy: A consequence of structural myocardial damage or a distinct genetic disease?

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant disease, characterized by the presence of unexplained left ventricular hypertrophy. This condition is often associated with electrocardiographic abnormalities including QTc prolongation occurring in 13% of patients. The main explanation for prolonged QTc in HCM is myocardial hypertrophy and the related structural damage. However, other mechanisms, including long QT syndrome (LQTS) genes mutations, may be involved. In the present study we explored the hypothesis of a distinct genetic basis underlying QTc prolongation in HCM by investigating the potential co-inheritance of pathogenic gene variants associated with LQTS and HCM. For this purpose, starting from a cohort of 150 HCM patients carrying pathogenic variants in sarcomere genes, we selected 25 patients carrying a QTc prolongation unexplained by any other cause. The QTc was considered prolonged if greater than 450 ms in males and greater than 470 ms in females. The NGS analysis was performed with Illumina TrueSight Cardio panel genes on Illumina MiniSeq platform. We identified pathogenic/likely pathogenic variants in the KCNQ1 in two patients (c.1781G > A, p. Arg594Gln; c.532G > A, p. Ala178Thr) (8%). Variants of uncertain significance were identified in SCN5A, KCNJ5, AKAP9 and ANK2 in four patients (16%). Although the results are limited by the small number of patients included in the study, they highlight a minor contribution of LQTS genes for QTc prolongation in HCM patients. The screening for ion channel genes mutations may be considered in HCM patients with prolonged QTc unexplained by any other cause. This in-depth molecular diagnosis may contribute to improve risk stratification and treatment planning.

Drug-Targeted Genomes: Mutability of Ion Channels and GPCRs

Mutations of ion channels and G-protein-coupled receptors (GPCRs) are not uncommon and can lead to cardiovascular diseases. Given previously reported multiple factors associated with high mutation rates, we sorted the relative mutability of multiple human genes by (i) proximity to telomeres and/or (ii) high adenine and thymine (A+T) content. We extracted genomic information using the genome data viewer and examined the mutability of 118 ion channel and 143 GPCR genes based on their association with factors (i) and (ii). We then assessed these two factors with 31 genes encoding ion channels or GPCRs that are targeted by the United States Food and Drug Administration (FDA)-approved drugs. Out of the 118 ion channel genes studied, 80 met either factor (i) or (ii), resulting in a 68% match. In contrast, a 78% match was found for the 143 GPCR genes. We also found that the GPCR genes (n = 20) targeted by FDA-approved drugs have a relatively lower mutability than those genes encoding ion channels (n = 11), where targeted genes encoding GPCRs were shorter in length. The result of this study suggests that the use of matching rate analysis on factor-druggable genome is feasible to systematically compare the relative mutability of GPCRs and ion channels. The analysis on chromosomes by two factors identified a unique characteristic of GPCRs, which have a significant relationship between their nucleotide sizes and proximity to telomeres, unlike most genetic loci susceptible to human diseases.

Case report: Prenatal diagnosis of fetal non-compaction cardiomyopathy with bradycardia accompanied by de novo CALM2 mutation

We herein report what appears to be the first case of fetal non-compaction cardiomyopathy in both ventricles accompanied by a mutation in the calmodulin gene (CALM2). A 25-year-old woman was referred to our hospital at 25⁺¹ weeks of gestation for evaluation of fetal defects. Prenatal echocardiography showed biventricular non-compaction cardiomyopathy with sinus bradycardia. After termination of the pregnancy, fetal biventricular non-compaction cardiomyopathy was confirmed by autopsy and histopathologic examination. Additionally, whole-exome sequencing of genomic DNA demonstrated a de novo heterozygous mutation (c.389A > G; p.D130G) in CALM2, whereas the parents were normal. In this case report, we highlight the importance of prenatal ultrasound and genetic testing in fetal non-compaction cardiomyopathy with arrhythmia.

Genetic basis and molecular biology of cardiac arrhythmias in cardiomyopathies

Cardiac arrhythmias are common, often the first, and sometimes the life-threatening manifestations of hereditary cardiomyopathies. Pathogenic variants in several genes known to cause hereditary cardiac arrhythmias have also been identified in the sporadic cases and small families with cardiomyopathies. These findings suggest a shared genetic aetiology of a subset of hereditary cardiomyopathies and cardiac arrhythmias. The concept of a shared genetic aetiology is in accord with the complex and exquisite interplays that exist between the ion currents and cardiac mechanical function. However, neither the causal role of cardiac arrhythmias genes in cardiomyopathies is well established nor the causal role of cardiomyopathy genes in arrhythmias. On the contrary, secondary changes in ion currents, such as post-translational modifications, are common and contributors to the pathogenesis of arrhythmias in cardiomyopathies through altering biophysical and functional properties of the ion channels. Moreover, structural changes, such as cardiac hypertrophy, dilatation, and fibrosis provide a pro-arrhythmic substrate in hereditary cardiomyopathies. Genetic basis and molecular biology of cardiac arrhythmias in hereditary cardiomyopathies are discussed.

Could Sodium/Glucose Co-Transporter-2 Inhibitors Have Antiarrhythmic Potential in Atrial Fibrillation? Literature Review and Future Considerations

The global burden of atrial fibrillation (AF) is constantly increasing, necessitating novel and effective therapeutic options. Sodium glucose co-transporter 2 (SGLT2) inhibitors have been introduced in clinical practice as glucose-lowering medications. However, they have recently gained prominence for their potential to exert substantial cardiorenal protection and are being evaluated in large clinical trials including patients with type 2 diabetes and normoglycemic adults. In this review we present up-to-date available evidence in a pathophysiology-directed manner from cell to bedside. Preclinical and clinical data regarding a conceivable antiarrhythmic effect of SGLT2 inhibitors are beginning to accumulate. Herein we comprehensively present data that explore the potential pathophysiological link between SGLT2 inhibitors and AF. With regard to clinical data, no randomized controlled trials evaluating SGLT2 inhibitors effects on AF as a pre-specified endpoint are available. However, data from randomized controlled trial post-hoc analysis as well as observational studies point to a possible beneficial effect of SGLT2 inhibitors on AF. Meta-analyses addressing this question report inconsistent results and the real magnitude of AF prevention by SGLT2 inhibition remains unclear. Still, while (i) pathophysiologic mechanisms involved in AF might be favorably affected by SGLT2 inhibitors and (ii) emerging, yet inconsistent, clinical data imply that SGLT2 inhibitor-mediated cardiorenal protection could also exert antiarrhythmic effects, the argument of whether these novel drugs will reduce AF burden is unsettled and mandates appropriately designed and adequately sized randomized controlled studies.

Genetic Mosaicism in Calmodulinopathy

BACKGROUND

CaM (calmodulin) mutations are associated with congenital arrhythmia susceptibility (calmodulinopathy) and are most often de novo. In this report, we sought to broaden the genotype-phenotype spectrum of calmodulinopathies with 2 novel calmodulin mutations and to investigate mosaicism in 2 affected families.

METHODS

CaM mutations were identified in 4 independent cases by DNA sequencing. Biochemical and electrophysiological studies were performed to determine functional consequences of each mutation.

RESULTS

Genetic studies identified 2 novel CaM variants (CALM3-E141K in 2 cases; CALM1-E141V) and one previously reported CaM pathogenic variant (CALM3-D130G) among 4 probands with shared clinical features of prolonged QTc interval (range 505-725 ms) and documented ventricular arrhythmia. A fatal outcome occurred for 2 of the cases. The parents of all probands were asymptomatic with normal QTc duration. However, 2 of the families had multiple affected offspring or multiple occurrences of intrauterine fetal demise. The mother from the family with recurrent intrauterine fetal demise exhibited the CALM3-E141K mutant allele in 25% of next-generation sequencing reads indicating somatic mosaicism, whereas CALM3-D130G was present in 6% of captured molecules of the paternal DNA sample, also indicating mosaicism. Two novel mutations (E141K and E141V) impaired Ca²⁺ binding affinity to the C-domain of CaM. Human-induced pluripotent stem cell-derived cardiomyocytes overexpressing mutant or wild-type CaM showed that both mutants impaired Ca²⁺-dependent inactivation of L-type Ca²⁺ channels and prolonged action potential duration.

CONCLUSIONS

We report 2 families with somatic mosaicism associated with arrhythmogenic calmodulinopathy, and demonstrate dysregulation of L-type Ca²⁺ channels by 2 novel CaM mutations affecting the same residue. Parental mosaicism should be suspected in families with unexplained fetal arrhythmia or fetal demise combined with a documented CaM mutation.