Exon 3 deletion of RYR2 encoding cardiac ryanodine receptor is associated with left ventricular non-compaction

Genophenotypic correlates and long-term outcome prognosticators of left ventricular non-compaction in children

BACKGROUND

To investigate the outcomes, clinical prognosticators, and genetic profiles of pediatric left ventricular non-compaction (LVNC).

METHODS

All subjects were <18 years old, diagnosed with LVNC between January 2008 and December 2020. Whole-exome sequencing was undertaken. The primary endpoint was composite outcome, including death, heart transplant, and left ventricular assist device implantation.

RESULTS

Thirty-three patients were enrolled, males predominating (57.6%). Median age at diagnosis was 0.33 (0.1-7.2) years. Family history was documented in four (12.1%). Five (15.2%) had sustained arrhythmias. Mean follow-up period was 9.5 years, and 5- and 10-year event-free survival were 84.8% and 66.9%, respectively. Seven died of heart failure, four received heart transplants, and one required left ventricular assist device placement. Log of baseline NT-proBNP (adjusted odds ratio [aOR] = 4.4, p = 0.012) and lack of improvement in NT-proBNP (aOR = 41.2, p = 0.033) impacted the primary outcome most significantly. Eighteen out of 25 genetic testing (72%) revealed chromosomal anomalies, or pathogenic or likely pathogenic variants. Three genetic variants (PLEKHM2 p.G419R, RYR2 p.V2571A, and SCN5A p.M1676I) were significantly associated with the primary outcome (p = 1.52 × 10-6).

CONCLUSIONS

Pediatric LVNC is a rare disorder with variable genetic underpinnings. Baseline NT-proBNP values and lack of improvement in NT-proBNP levels were important predictors of poor long-term outcomes. Pathogenic genetic variants or chromosomal anomalies are not unusual.

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.

Left Ventricular Non-Compaction in Children: Aetiology and Diagnostic Criteria

Left ventricular non-compaction (LVNC) is a heterogeneous myocardial disorder characterized by prominent trabeculae protruding into the left ventricular lumen and deep intertrabecular recesses. LVNC can manifest in isolation or alongside other heart muscle diseases. Its occurrence among children is rising due to advancements in imaging techniques. The origins of LVNC are diverse, involving both genetic and acquired forms. The clinical manifestation varies greatly, with some cases presenting no symptoms, while others typically manifesting with heart failure, systemic embolism, and arrhythmias. Diagnosis mainly relies on assessing heart structure using imaging tools like echocardiography and cardiac magnetic resonance. However, the absence of a universally agreed-upon standard and limitations in diagnostic criteria have led to ongoing debates in the scientific community regarding the most reliable methods. Further research is crucial to enhance the diagnosis of LVNC, particularly in early life stages.

Human Genetics of Cardiac Arrhythmias

Inherited forms of cardiac arrhythmias mostly are rare diseases (prevalence <1:2000) and considered to be either "primary electrical heart disorders" due to the absence of structural heart abnormalities or "cardiac ion channel disorders" due to the myocellular structures involved. Precise knowledge of the electrocardiographic features of these diseases and their genetic classification will enable early disease recognition and prevention of cardiac events including sudden cardiac death.The genetic background of these diseases is complex and heterogeneous. In addition to the predominant "private character" of a mutation in each family, locus heterogeneity involving many ion channel genes for the same familial arrhythmia syndrome is typical. Founder pathogenic variants or mutational hot spots are uncommon. Moreover, phenotypes may vary and overlap even within the same family and mutation carriers. For the majority of arrhythmias, the clinical phenotype of an ion channel mutation is restricted to cardiac tissue, and therefore, the disease is nonsyndromic.Recent and innovative methods of parallel DNA analysis (so-called next-generation sequencing, NGS) will enhance further mutation and other variant detection as well as arrhythmia gene identification.

Flecainide Is Associated With a Lower Incidence of Arrhythmic Events in a Large Cohort of Patients With Catecholaminergic Polymorphic Ventricular Tachycardia

BACKGROUND

In severely affected patients with catecholaminergic polymorphic ventricular tachycardia, beta-blockers are often insufficiently protective. The purpose of this study was to evaluate whether flecainide is associated with a lower incidence of arrhythmic events (AEs) when added to beta-blockers in a large cohort of patients with catecholaminergic polymorphic ventricular tachycardia.

METHODS

From 2 international registries, this multicenter case cross-over study included patients with a clinical or genetic diagnosis of catecholaminergic polymorphic ventricular tachycardia in whom flecainide was added to beta-blocker therapy. The study period was defined as the period in which background therapy (ie, beta-blocker type [beta1-selective or nonselective]), left cardiac sympathetic denervation, and implantable cardioverter defibrillator treatment status, remained unchanged within individual patients and was divided into pre-flecainide and on-flecainide periods. The primary end point was AEs, defined as sudden cardiac death, sudden cardiac arrest, appropriate implantable cardioverter defibrillator shock, and arrhythmic syncope. The association of flecainide with AE rates was assessed using a generalized linear mixed model assuming negative binomial distribution and random effects for patients.

RESULTS

A total of 247 patients (123 [50%] females; median age at start of flecainide, 18 years [interquartile range, 14-29]; median flecainide dose, 2.2 mg/kg per day [interquartile range, 1.7-3.1]) were included. At baseline, all patients used a beta-blocker, 70 (28%) had an implantable cardioverter defibrillator, and 21 (9%) had a left cardiac sympathetic denervation. During a median pre-flecainide follow-up of 2.1 years (interquartile range, 0.4-7.2), 41 patients (17%) experienced 58 AEs (annual event rate, 5.6%). During a median on-flecainide follow-up of 2.9 years (interquartile range, 1.0-6.0), 23 patients (9%) experienced 38 AEs (annual event rate, 4.0%). There were significantly fewer AEs after initiation of flecainide (incidence rate ratio, 0.55 [95% CI, 0.38-0.83]; P=0.007). Among patients who were symptomatic before diagnosis or during the pre-flecainide period (n=167), flecainide was associated with significantly fewer AEs (incidence rate ratio, 0.49 [95% CI, 0.31-0.77]; P=0.002). Among patients with ≥1 AE on beta-blocker therapy (n=41), adding flecainide was also associated with significantly fewer AEs (incidence rate ratio, 0.25 [95% CI, 0.14-0.45]; P<0.001).

CONCLUSIONS

For patients with catecholaminergic polymorphic ventricular tachycardia, adding flecainide to beta-blocker therapy was associated with a lower incidence of AEs in the overall cohort, in symptomatic patients, and particularly in patients with breakthrough AEs while on beta-blocker therapy.

The Trouble with Trabeculation: How Genetics Can Help to Unravel a Complex and Controversial Phenotype

Excessive trabeculation of the cardiac left ventricular wall is a complex phenotypic substrate associated with various physiological and pathological processes. There has been considerable conjecture as to whether hypertrabeculation contributes to disease and whether left ventricular non-compaction (LVNC) cardiomyopathy is a distinct pathology. Building on recent insights into the genetic basis of LVNC cardiomyopathy, in particular three meta-analysis studies exploring genotype-phenotype associations using different methodologies, this review examines how genetic research can advance our understanding of trabeculation. Three groups of genes implicated in LVNC are described-those associated with other cardiomyopathies, other cardiac/syndromic conditions and putatively with isolated LVNC cardiomyopathy-demonstrating how these findings can inform the underlying pathologies in LVNC patients and aid differential diagnosis and management in clinical practice despite the limited utility suggested for LVNC genetic testing in recent guidelines. The outstanding questions and future research priorities for exploring the genetics of hypertrabeculation are discussed.

Assessment of Sudden Cardiac Death Risk in Pediatric Primary Electrical Disorders: A Comprehensive Overview

Sudden cardiac death (SCD) in children is a devastating event, often linked to primary electrical diseases (PED) of the heart. PEDs, often referred to as channelopathies, are a group of genetic disorders that disrupt the normal ion channel function in cardiac cells, leading to arrhythmias and sudden cardiac death. This paper investigates the unique challenges of risk assessment and stratification for channelopathy-related SCD in pediatric patients-Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, idiopathic ventricular fibrillation, long QT syndrome, Anderson-Tawil syndrome, short QT syndrome, and early repolarization syndrome. We explore the intricate interplay of genetic, clinical, and electrophysiological factors that contribute to the complex nature of these conditions. Recognizing the significance of early identification and tailored management, this paper underscores the need for a comprehensive risk stratification approach specifically designed for pediatric populations. By integrating genetic testing, family history, and advanced electrophysiological evaluation, clinicians can enhance their ability to identify children at the highest risk for SCD, ultimately paving the way for more effective preventive strategies and improved outcomes in this vulnerable patient group.

RyR2 C-terminal truncating variants identified in patients with arrhythmic phenotypes exert a dominant negative effect through formation of wildtype-truncation heteromers

Gain-of-function missense variants in the cardiac ryanodine receptor (RyR2) are linked to catecholaminergic polymorphic ventricular tachycardia (CPVT), whereas RyR2 loss-of-function missense variants cause Ca2+ release deficiency syndrome (CRDS). Recently, truncating variants in RyR2 have also been associated with ventricular arrhythmias (VAs) and sudden cardiac death. However, there are limited insights into the potential clinical relevance and in vitro functional impact of RyR2 truncating variants. We performed genetic screening of patients presenting with syncope, VAs, or unexplained sudden death and in vitro characterization of the expression and function of RyR2 truncating variants in HEK293 cells. We identified two previously unknown RyR2 truncating variants (Y4591Ter and R4663Ter) and one splice site variant predicted to result in a frameshift and premature termination (N4717 + 15Ter). These 3 new RyR2 truncating variants and a recently reported RyR2 truncating variant, R4790Ter, were generated and functionally characterized in vitro. Immunoprecipitation and immunoblotting analyses showed that all 4 RyR2 truncating variants formed heteromers with the RyR2-wildtype (WT) protein. Each of these C-terminal RyR2 truncations was non-functional and suppressed [3H]ryanodine binding to RyR2-WT and RyR2-WT mediated store overload induced spontaneous Ca2+ release activity in HEK293 cells. The expression of these RyR2 truncating variants in HEK293 cells was markedly reduced compared with that of the full-length RyR2 WT protein. Our data indicate that C-terminal RyR2 truncating variants are non-functional and can exert a dominant negative impact on the function of the RyR2 WT protein through formation of heteromeric WT/truncation complex.

Increased Ca2+ Transient Underlies RyR2-Related Left Ventricular Noncompaction

BACKGROUND

A loss-of-function cardiac ryanodine receptor (RyR2) mutation, I4855M+/-, has recently been linked to a new cardiac disorder termed RyR2 Ca2+ release deficiency syndrome (CRDS) as well as left ventricular noncompaction (LVNC). The mechanism by which RyR2 loss-of-function causes CRDS has been extensively studied, but the mechanism underlying RyR2 loss-of-function-associated LVNC is unknown. Here, we determined the impact of a CRDS-LVNC-associated RyR2-I4855M+/- loss-of-function mutation on cardiac structure and function.

METHODS

We generated a mouse model expressing the CRDS-LVNC-associated RyR2-I4855M+/- mutation. Histological analysis, echocardiography, ECG recording, and intact heart Ca2+ imaging were performed to characterize the structural and functional consequences of the RyR2-I4855M+/- mutation.

RESULTS

As in humans, RyR2-I4855M+/- mice displayed LVNC characterized by cardiac hypertrabeculation and noncompaction. RyR2-I4855M+/- mice were highly susceptible to electrical stimulation-induced ventricular arrhythmias but protected from stress-induced ventricular arrhythmias. Unexpectedly, the RyR2-I4855M+/- mutation increased the peak Ca2+ transient but did not alter the L-type Ca2+ current, suggesting an increase in Ca2+-induced Ca2+ release gain. The RyR2-I4855M+/- mutation abolished sarcoplasmic reticulum store overload-induced Ca2+ release or Ca2+ leak, elevated sarcoplasmic reticulum Ca2+ load, prolonged Ca2+ transient decay, and elevated end-diastolic Ca2+ level upon rapid pacing. Immunoblotting revealed increased level of phosphorylated CaMKII (Ca2+-calmodulin dependent protein kinases II) but unchanged levels of CaMKII, calcineurin, and other Ca2+ handling proteins in the RyR2-I4855M+/- mutant compared with wild type.

CONCLUSIONS

The RyR2-I4855M+/- mutant mice represent the first RyR2-associated LVNC animal model that recapitulates the CRDS-LVNC overlapping phenotype in humans. The RyR2-I4855M+/- mutation increases the peak Ca2+ transient by increasing the Ca2+-induced Ca2+ release gain and the end-diastolic Ca2+ level by prolonging Ca2+ transient decay. Our data suggest that the increased peak-systolic and end-diastolic Ca2+ levels may underlie RyR2-associated LVNC.

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.

RYR2-ryanodinopathies: from calcium overload to calcium deficiency

The sarcoplasmatic reticulum (SR) cardiac ryanodine receptor/calcium release channel RyR2 is an essential regulator of cardiac excitation-contraction coupling and intracellular calcium homeostasis. Mutations of the RYR2 are the cause of rare, potentially lethal inherited arrhythmia disorders. Catecholaminergic polymorphic ventricular tachycardia (CPVT) was first described more than 20 years ago and is the most common and most extensively studied cardiac ryanodinopathy. Over time, other distinct inherited arrhythmia syndromes have been related to abnormal RyR2 function. In addition to CPVT, there are at least two other distinct RYR2-ryanodinopathies that differ mechanistically and phenotypically from CPVT: RYR2 exon-3 deletion syndrome and the recently identified calcium release deficiency syndrome (CRDS). The pathophysiology of the different cardiac ryanodinopathies is characterized by complex mechanisms resulting in excessive spontaneous SR calcium release or SR calcium release deficiency. While the vast majority of CPVT cases are related to gain-of-function variants of the RyR2 protein, the recently identified CRDS is linked to RyR2 loss-of-function variants. The increasing number of these cardiac 'ryanodinopathies' reflects the complexity of RYR2-related cardiogenetic disorders and represents an ongoing challenge for clinicians. This state-of-the-art review summarizes our contemporary understanding of RYR2-related inherited arrhythmia disorders and provides a systematic and comprehensive description of the distinct cardiac ryanodinopathies discussing clinical aspects and molecular insights. Accurate identification of the underlying type of cardiac ryanodinopathy is essential for the clinical management of affected patients and their families.

CPVT and Complete Atrio-Ventricular Block: The Flipside of the Same Coin

Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT) is a rare electrical genetic disease characterized by ventricular polymorphic tachycardia and/or bidirectional ventricular tachycardia induced by the release of catecholamines caused by intense physical or emotional stress in structurally normal hearts. Mostly, it is caused by mutations in genes that are involved in calcium homeostasis, in particular in the gene encoding for cardiac ryanodine receptor (RyR2). Our observation is the first description of familial CPVT caused by mutation of the RyR2 gene, linked to the complete AV block.

The Electrocardiogram in the Diagnosis and Management of Patients With Left Ventricular Non-Compaction

PURPOSE OF THE REVIEW

Left ventricular non-compaction (LVNC) is characterised by prominent left ventricular trabeculae and deep inter-trabecular recesses. Although considered a distinct cardiomyopathy, prominent trabeculations may also be found in other cardiomyopathies, in athletes or during pregnancy. Clinical presentation includes heart failure symptoms, systemic embolic events, arrhythmias and sudden cardiac death. Currently, LVNC diagnosis relies on imaging criteria, and clinicians face several challenges in the assessment of patients with prominent trabeculations. In this review, we summarise the available information on the role of the ECG in the diagnosis and management of LVNC.

RECENT FINDINGS

ECG abnormalities have been reported in 75-94% of adults and children with LVNC. The lack of specificity of these ECG abnormalities does not allow (in isolation) to diagnose the condition. However, when considered in a set of diagnostic criteria including family history, clinical information, and imaging features, the ECG may differentiate between physiological and pathological findings or may provide clues raising the possibility of specific underlying conditions. Finally, some ECG features in LVNC constitute ominous signs that require a stricter patient surveillance or specific therapeutic measures. The ECG remains a cornerstone in the diagnosis and management of patients with cardiomyopathies, including LVNC.

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.

Provocation Testing and Therapeutic Response in a Newly Described Channelopathy: RyR2 Calcium Release Deficiency Syndrome

BACKGROUND

A novel familial arrhythmia syndrome, cardiac ryanodine receptor (RyR2) calcium release deficiency syndrome (CRDS), has recently been described. We evaluated a large and well characterized family to assess provocation testing, risk factor stratification and response to therapy in CRDS.

METHODS

We present a family with multiple unheralded sudden cardiac deaths and aborted cardiac arrests, primarily in children and young adults, with no clear phenotype on standard clinical testing.

RESULTS

Genetic analysis, including whole genome sequencing, firmly established that a missense mutation in RYR2, Ala4142Thr, was the underlying cause of disease in the family. Functional study of the variant in a cell model showed RyR2 loss-of-function, indicating that the family was affected by CRDS. EPS (Electrophysiological Study) was undertaken in 9 subjects known to carry the mutation, including a survivor of aborted sudden cardiac death, and the effects of flecainide alone and in combination with metoprolol were tested. There was a clear gradation in inducibility of nonsustained and sustained ventricular arrhythmia between subjects at EPS, with the survivor of aborted sudden cardiac death being the most inducible subject. Administration of flecainide substantially reduced arrhythmia inducibility in this subject and abolished arrhythmia in all others. Finally, the effects of additional metoprolol were tested; it increased inducibility in 4/9 subjects.

CONCLUSIONS

The Ala4142Thr mutation of RYR2 causes the novel heritable arrhythmia syndrome CRDS, which is characterized by familial sudden death in the absence of prior symptoms or a recognizable phenotype on ambulatory monitoring or exercise stress testing. We increase the experience of a specific EPS protocol in human subjects and show that it is helpful in establishing the clinical status of gene carriers, with potential utility for risk stratification. Our data provide evidence that flecainide is protective in human subjects with CRDS, consistent with the effect previously shown in a mouse model.

An International Multi-Center Cohort Study on β-blockers for the Treatment of Symptomatic Children with Catecholaminergic Polymorphic Ventricular Tachycardia

Background: Symptomatic children with catecholaminergic polymorphic ventricular tachycardia (CPVT) are at risk for recurrent arrhythmic events. Beta-blockers (BBs) decrease this risk, but studies comparing individual BBs in sizeable cohorts are lacking. We aimed to assess the association between risk for arrhythmic events and type of BB in a large cohort of symptomatic children with CPVT. Methods: From two international registries of patients with CPVT, RYR2 variant-carrying symptomatic children (defined as syncope or sudden cardiac arrest prior to BB initiation and age at start of BB therapy <18 years), treated with a BB were included. Cox-regression analyses with time-dependent covariates for BB and potential confounders were used to assess the hazard ratio (HR). The primary outcome was the first occurrence of sudden cardiac death, sudden cardiac arrest, appropriate implantable cardioverter-defibrillator shock, or syncope. The secondary outcome was the first occurrence of any of the primary outcomes except syncope. Results: We included 329 patients (median age at diagnosis 12 [interquartile range, 7-15] years, 35% females). Ninety-nine (30.1%) patients experienced the primary and 74 (22.5%) experienced the secondary outcome during a median follow-up of 6.7 [interquartile range, 2.8-12.5] years. Two-hundred sixteen patients (66.0%) used a non-selective BB (predominantly nadolol [n=140] or propranolol [n=70]) and 111 (33.7%) used a β1-selective BB (predominantly atenolol [n=51], metoprolol [n=33], or bisoprolol [n=19]) as initial BB. Baseline characteristics did not differ. The HR for both the primary and secondary outcomes were higher for β1-selective compared with non-selective BBs (HR, 2.04 95% CI, 1.31-3.17; and HR, 1.99; 95% CI, 1.20-3.30, respectively). When assessed separately, the HR for the primary outcome was higher for atenolol (HR, 2.68; 95% CI, 1.44-4.99), bisoprolol (HR, 3.24; 95% CI, 1.47-7.18), and metoprolol (HR, 2.18; 95% CI, 1.08-4.40) compared with nadolol, but did not differ from propranolol. The HR of the secondary outcome was only higher in atenolol compared with nadolol (HR, 2.68; 95% CI, 1.30-5.55). Conclusions: B1-selective BBs were associated with a significantly higher risk for arrhythmic events in symptomatic children with CPVT compared with non-selective BBs, specifically nadolol. Nadolol, or propranolol if nadolol is unavailable, should be the preferred BB for treating symptomatic children with CPVT.

Overlap phenotypes of the left ventricular noncompaction and hypertrophic cardiomyopathy with complex arrhythmias and heart failure induced by the novel truncated DSC2 mutation

Background

The left ventricular noncompaction cardiomyopathy (LVNC) is a rare subtype of cardiomyopathy associated with a high risk of heart failure (HF), thromboembolism, arrhythmia, and sudden cardiac death.

Methods

The proband with overlap phenotypes of LVNC and hypertrophic cardiomyopathy (HCM) complicates atrial fibrillation (AF), ventricular tachycardia (VT), and HF due to the diffuse myocardial lesion, which were diagnosed by electrocardiogram, echocardiogram and cardiac magnetic resonance imaging. Peripheral blood was collected from the proband and his relatives. DNA was extracted from the peripheral blood of proband for high-throughput target capture sequencing. The Sanger sequence verified the variants. The protein was extracted from the skin of the proband and healthy volunteer. The expression difference of desmocollin2 was detected by Western blot.

Results

The novel heterozygous truncated mutation (p.K47Rfs*2) of the DSC2 gene encoding an important component of desmosomes was detected by targeted capture sequencing. The western blots showed that the expressing level of functional desmocollin2 protein (~ 94kd) was lower in the proband than that in the healthy volunteer, indicating that DSC2 p.K47Rfs*2 obviously reduced the functional desmocollin2 protein expression in the proband.

Conclusion

The heterozygous DSC2 p.K47Rfs*2 remarkably and abnormally reduced the functional desmocollin2 expression, which may potentially induce the overlap phenotypes of LVNC and HCM, complicating AF, VT, and HF.

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.

Phenotype/Genotype Relationship in Left Ventricular Noncompaction: Ion Channel Gene Mutations Are Associated With Preserved Left Ventricular Systolic Function and Biventricular Noncompaction: Phenotype/Genotype of Noncompaction

BACKGROUND

Few data exist concerning genotype-phenotype relationships in left ventricular noncompaction (LVNC).

METHODS AND RESULTS

From a multicenter French Registry, we report the genetic and clinical spectrum of 95 patients with LVNC, and their genotype-phenotype relationship. Among the 95 LVNC, 45 had at least 1 mutation, including 14 cases of mutation in ion channel genes. In a complementary analysis including 16 additional patients with ion channel gene mutations, for a total of 30 patients with ion channel gene mutation, we found that those patients had higher median LV ejection fraction (60% vs 40%; P < .001) and more biventricular noncompaction (53.1% vs 18.5%; P < .001) than the 81 other patients with LVNC. Among them, both the 19 patients with an HCN4 mutation and the 11 patients with an RYR2 mutation presented with a higher LV ejection fraction and more frequent biventricular noncompaction than the 81 patients with LVNC but with no mutation in the ion channel gene, but only patients with HCN4 mutation presented with a lower heart rate.

CONCLUSIONS

Ion channel gene mutations should be searched systematically in patients with LVNC associated with either bradycardia or biventricular noncompaction, particularly when LV systolic function is preserved. Identifying causative mutations is of utmost importance for genetic counselling of at-risk relatives of patients affected by LVNC.

RyR2 disease mutations at the C-terminal domain intersubunit interface alter closed-state stability and channel activation

Ryanodine receptors (RyRs) are ion channels that mediate the release of Ca²⁺ from the sarcoplasmic reticulum/endoplasmic reticulum, mutations of which are implicated in a number of human diseases. The adjacent C-terminal domains (CTDs) of cardiac RyR (RyR2) interact with each other to form a ring-like tetrameric structure with the intersubunit interface undergoing dynamic changes during channel gating. This mobile CTD intersubunit interface harbors many disease-associated mutations. However, the mechanisms of action of these mutations and the role of CTD in channel function are not well understood. Here, we assessed the impact of CTD disease-associated mutations P4902S, P4902L, E4950K, and G4955E on Ca²⁺− and caffeine-mediated activation of RyR2. The G4955E mutation dramatically increased both the Ca²⁺-independent basal activity and Ca²⁺-dependent activation of [³H]ryanodine binding to RyR2. The P4902S and E4950K mutations also increased Ca²⁺ activation but had no effect on the basal activity of RyR2. All four disease mutations increased caffeine-mediated activation of RyR2 and reduced the threshold for activation and termination of spontaneous Ca²⁺ release. G4955D dramatically increased the basal activity of RyR2, whereas G4955K mutation markedly suppressed channel activity. Similarly, substitution of P4902 with a negatively charged residue (P4902D), but not a positively charged residue (P4902K), also dramatically increased the basal activity of RyR2. These data suggest that electrostatic interactions are involved in stabilizing the CTD intersubunit interface and that the G4955E disease mutation disrupts this interface, and thus the stability of the closed state. Our studies shed new insights into the mechanisms of action of RyR2 CTD disease mutations.

Early Lethal Noncompaction Cardiomyopathy in Siblings With Compound Heterozygous RYR2 Variant

Two siblings presented with early lethal noncompaction cardiomyopathy (NCCM). Both carry compound heterozygous variants in the ryanodine receptor gene (RYR2). Evolving animal and human data have begun to implicate a role for RYR2 dysfunction in the development of NCCM. The identified RYR2 variants are therefore likely causative for this early lethal NCCM phenotype. Further research is needed to understand the role of RYR2 in the heart compaction process.

The genetics of left ventricular noncompaction

PURPOSE OF REVIEW

This article summarises current understanding of the genetic architecture underpinning left ventricular noncompaction (LVNC) and highlights the difficulty in differentiating LVNC from hypertrabeculation seen in normal, healthy individuals, that caused by physiological adaptation or that seen in association with cardiomyopathy phenotypes.

RECENT FINDINGS

Progress has been made in better defining the LVNC phenotype and those patients who may benefit from genetic testing. Yield of diagnostic genetic testing may be low in the absence of syndromic features, systolic dysfunction and a family history of cardiomyopathy. Sarcomeric gene variants are most commonly identified but a wide-range of genes are implicated, emphasising the high degree of heterogeneity of studied cohorts.

SUMMARY

More accurate phenotyping and genotype-phenotype correlation are required to better characterise the genetic architecture of LVNC.

Identification of loss-of-function RyR2 mutations associated with idiopathic ventricular fibrillation and sudden death

Mutations in cardiac ryanodine receptor (RyR2) are linked to catecholaminergic polymorphic ventricular tachycardia (CPVT). Most CPVT RyR2 mutations characterized are gain-of-function (GOF), indicating enhanced RyR2 function as a major cause of CPVT. Loss-of-function (LOF) RyR2 mutations have also been identified and are linked to a distinct entity of cardiac arrhythmia termed RyR2 Ca²⁺ release deficiency syndrome (CRDS). Exercise stress testing (EST) is routinely used to diagnose CPVT, but it is ineffective for CRDS. There is currently no effective diagnostic tool for CRDS in humans. An alternative strategy to assess the risk for CRDS is to directly determine the functional impact of the associated RyR2 mutations. To this end, we have functionally screened 18 RyR2 mutations that are associated with idiopathic ventricular fibrillation (IVF) or sudden death. We found two additional RyR2 LOF mutations E4146K and G4935R. The E4146K mutation markedly suppressed caffeine activation of RyR2 and abolished store overload induced Ca²⁺ release (SOICR) in human embryonic kidney 293 (HEK293) cells. E4146K also severely reduced cytosolic Ca²⁺ activation and abolished luminal Ca²⁺ activation of single RyR2 channels. The G4935R mutation completely abolished caffeine activation of and [³H]ryanodine binding to RyR2. Co-expression studies showed that the G4935R mutation exerted dominant negative impact on the RyR2 wildtype (WT) channel. Interestingly, the RyR2-G4935R mutant carrier had a negative EST, and the E4146K carrier had a family history of sudden death during sleep, which are different from phenotypes of typical CPVT. Thus, our data further support the link between RyR2 LOF and a new entity of cardiac arrhythmias distinct from CPVT.

Identification of a Novel Homozygous Multi-Exon Duplication in RYR2 Among Children With Exertion-Related Unexplained Sudden Deaths in the Amish Community

Importance

The exome molecular autopsy may elucidate a pathogenic substrate for sudden unexplained death.

Objective

To investigate the underlying cause of multiple sudden deaths in young individuals and sudden cardiac arrests that occurred in 2 large Amish families.

Design, Setting, and Participants

Two large extended Amish families with multiple sudden deaths in young individuals and sudden cardiac arrests were included in the study. A recessive inheritance pattern was suggested based on an extended family history of sudden deaths in young individuals and sudden cardiac arrests, despite unaffected parents. A family with exercise-associated sudden deaths in young individuals occurring in 4 siblings was referred for postmortem genetic testing using an exome molecular autopsy. Copy number variant (CNV) analysis was performed on exome data using PatternCNV. Chromosomal microarray validated the CNV identified. The nucleotide break points of the CNV were determined by mate-pair sequencing. Samples were collected for this study between November 2004 and June 2019.

Main Outcomes and Measures

The identification of an underlying genetic cause for sudden deaths in young individuals and sudden cardiac arrests consistent with the recessive inheritance pattern observed in the families.

Results

A homozygous duplication, involving approximately 26 000 base pairs of intergenic sequence, RYR2's 5'UTR/promoter region, and exons 1 through 4 of RYR2, was identified in all 4 siblings of a family. Multiple distantly related relatives experiencing exertion-related sudden cardiac arrest also had the identical RYR2 homozygous duplication. A second, unrelated family with multiple exertion-related sudden deaths and sudden cardiac arrests in young individuals, with the same homozygous duplication, was identified. Several living, homozygous duplication-positive symptomatic patients from both families had nondiagnostic cardiologic testing, with only occasional ventricular ectopy occurring during exercise stress tests.

Conclusions and Relevance

In this analysis, we identified a novel, highly penetrant, homozygous multiexon duplication in RYR2 among Amish youths with exertion-related sudden death and sudden cardiac arrest but without an overt phenotype that is distinct from RYR2-mediated catecholaminergic polymorphic ventricular tachycardia. Considering that no cardiac tests reliably identify at-risk individuals and given the high rate of consanguinity in Amish families, identification of unaffected heterozygous carriers may provide potentially lifesaving premarital counseling and reproductive planning.

Genetic Association Between Hypoplastic Left Heart Syndrome and Cardiomyopathies

BACKGROUND

Hypoplastic left heart syndrome (HLHS) with risk of poor outcome has been linked to MYH6 variants, implicating overlap in genetic etiologies of structural and myopathic heart disease.

METHODS

Whole genome sequencing was performed in 197 probands with HLHS, 43 family members, and 813 controls. Data were filtered for rare, segregating variants in 3 index families comprised of an HLHS proband and relative(s) with cardiomyopathy. Whole genome sequencing data from cases and controls were compared for rare variant burden across 56 cardiomyopathy genes utilizing a weighted burden test approach, accounting for multiple testing using a Bonferroni correction.

RESULTS

A pathogenic MYBPC3 nonsense variant was identified in the first proband who underwent cardiac transplantation for diastolic heart failure, her father with left ventricular noncompaction, and 2 fourth-degree relatives with hypertrophic cardiomyopathy. A likely pathogenic RYR2 missense variant was identified in the second proband, a second-degree relative with aortic dilation, and a fourth-degree relative with dilated cardiomyopathy. A pathogenic RYR2 exon 3 in-frame deletion was identified in the third proband diagnosed with catecholaminergic polymorphic ventricular tachycardia and his father with left ventricular noncompaction and catecholaminergic polymorphic ventricular tachycardia. To further investigate HLHS-cardiomyopathy gene associations in cases versus controls, rare variant burden testing of 56 genes revealed enrichment in MYH6 (P=0.000068). Rare, predicted-damaging MYH6 variants were identified in 10% of probands in our cohort-4 with familial congenital heart disease, 4 with compound heterozygosity (3 with systolic ventricular dysfunction), and 4 with MYH6-FLNC synergistic heterozygosity.

CONCLUSIONS

Whole genome sequencing in multiplex families, proband-parent trios, and case-control cohorts revealed defects in cardiomyopathy-associated genes in patients with HLHS, which may portend impaired functional reserve of the single-ventricle circulation.

Copy number alterations involving 59 ACMG-recommended secondary findings genes

In clinical exome/genome sequencing, the American College of Medical Genetics and Genomics (ACMG) recommends reporting of secondary findings unrelated to a patient's phenotype when pathogenic single-nucleotide variants (SNVs) are observed in one of 59 genes associated with a life-threatening, medically actionable condition. Little is known about the incidence and sensitivity of chromosomal microarray analysis (CMA) for detection of pathogenic copy number variants (CNVs) comprising medically-actionable genes. Clinical CMA has been performed on 8865 individuals referred for molecular cytogenetic testing. We retrospectively reviewed the CMA results to identify patients with CNVs comprising genes included in the 59-ACMG list of secondary findings. We evaluated the clinical significance of these CNVs in respect to pathogenicity, phenotypic manifestations, and heritability. We identified 23 patients (0.26%) with relevant CNV either deletions comprising the entire gene or intragenic alterations involving one or more secondary findings genes. A number of patients and/or their family members with pathogenic CNVs manifest or expected to develop an anticipated clinical phenotype and would benefit from preventive management similar to the patients with pathogenic SNVs. To improve patients' care standardization should apply to reporting of both sequencing and CNVs obtained via clinical genome-wide analysis, including chromosomal microarray and exome/genome sequencing.

A rare HCN4 variant with combined sinus bradycardia, left atrial dilatation, and hypertrabeculation/left ventricular noncompaction phenotype

INTRODUCTION AND OBJECTIVES

HCN4 variants have been reported to cause combined sick sinus syndrome (SSS) and left ventricular noncompaction (LVNC) cardiomyopathy. This relationship has been proven in few cases and no previous patients have associated left atrial dilatation (LAD). Our objective was to study a familial disorder characterized by SSS, LAD, and hypertrabeculation/LVNC and to identify the underlying genetic and electrophysiological characteristics.

METHODS

A family with SSS and LVNC underwent a clinical, genetic, and electrophysiological assessment. They were studied via electrocardiography, Holter recording, echocardiography, and exercise stress tests; cardiac magnetic resonance imaging was additionally performed in affected individuals. Genetic testing was undertaken with targeted next-generation sequencing, as well as a functional study of the candidate variant in Chinese hamster ovary cells.

RESULTS

Twelve members of the family had sinus bradycardia, associated with complete criteria of LVNC in 4 members and hypertrabeculation in 6 others, as well as LAD in 9 members. A HCN4 c.1123C>T;(p.R375C) variant was present in heterozygosis in all affected patients and absent in unaffected individuals. Electrophysiological analyses showed that the amplitude and densities of the HCN4 currents (I_HCN4) generated by mutant p.R375C HCN4 channels were significantly lower than those generated by wild-type channels.

CONCLUSIONS

The combined phenotype of SSS, LAD, and LVNC is associated with the heritable HCN4 c.1123C>T;(p.R375C) variant. HCN4 variants should be included in the genetic diagnosis of LVNC cardiomyopathy and of patients with familial forms of SSS, as well as of individuals with sinus bradycardia and LAD.

Structure and Function of the Human Ryanodine Receptors and Their Association with Myopathies-Present State, Challenges, and Perspectives

Cardiac arrhythmias are serious, life-threatening diseases associated with the dysregulation of Ca2+ influx into the cytoplasm of cardiomyocytes. This dysregulation often arises from dysfunction of ryanodine receptor 2 (RyR2), the principal Ca2+ release channel. Dysfunction of RyR1, the skeletal muscle isoform, also results in less severe, but also potentially life-threatening syndromes. The RYR2 and RYR1 genes have been found to harbor three main mutation “hot spots”, where mutations change the channel structure, its interdomain interface properties, its interactions with its binding partners, or its dynamics. In all cases, the result is a defective release of Ca2+ ions from the sarcoplasmic reticulum into the myocyte cytoplasm. Here, we provide an overview of the most frequent diseases resulting from mutations to RyR1 and RyR2, briefly review some of the recent experimental structural work on these two molecules, detail some of the computational work describing their dynamics, and summarize the known changes to the structure and function of these receptors with particular emphasis on their N-terminal, central, and channel domains.

Molecular characterization of the calcium release channel deficiency syndrome

We identified a potentially novel homozygous duplication involving the promoter region and exons 1–4 of the gene encoding type 2 cardiac ryanodine receptor (RYR2) that is responsible for highly penetrant, exertion-related sudden deaths/cardiac arrests in the Amish community without an overt phenotype to suggest RYR2-mediated catecholaminergic polymorphic ventricular tachycardia (CPVT). Homozygous RYR2 duplication (RYR2-DUP) induced pluripotent stem cell cardiomyocytes (iPSC-CMs) were generated from 2 unrelated patients. There was no difference in baseline Ca²⁺ handling measurements between WT-iPSC-CM and RYR2-DUP-iPSC-CM lines. However, compared with WT-iPSC-CMs, both patient lines demonstrated a dramatic reduction in caffeine-stimulated and isoproterenol-stimulated (ISO-stimulated) Ca²⁺ transient amplitude, suggesting RyR2 loss of function. There was a greater than 50% reduction in RYR2 transcript/RyR2 protein expression in both patient iPSC-CMs compared with WT. Delayed afterdepolarization was observed in the RYR2-DUP-iPSC-CMs but not in the WT-iPSC-CMs. Compared with WT-iPSC-CMs, there was significantly elevated arrhythmic activity in the RYR2-DUP-iPSC-CMs in response to ISO. Nadolol, propranolol, and flecainide reduced erratic activity by 8.5-fold, 6.8-fold, and 2.4-fold, respectively, from ISO challenge. Unlike the gain-of-function mechanism observed in RYR2-mediated CPVT, the homozygous multiexon duplication precipitated a dramatic reduction in RYR2 transcription and RyR2 protein translation, a loss of function in calcium handling, and a calcium-induced calcium release apparatus that is insensitive to catecholamines and caffeine.

Molecular and functional characterization of the calcium release channel deficiency syndrome in patient-specific induced pluripotent stem cell-cardiomyocytes.

[RyR2 mutation-linked arrhythmogenic diseases and its therapeutic strategies]

The type 2 ryanodine receptor (RyR2) is a sarcoplasmic reticulum Ca²⁺ release channel that plays a central role in cardiac excitation-contraction coupling. Abnormal activity of the RyR2 is linked to abnormal Ca²⁺ signaling in cardiac cells, which often results in cardiac arrhythmias. For example, amino acid mutations in RyR2 have been reported to cause various types of arrhythmias, including catecholaminergic polymorphic ventricular tachycardia (CPVT), idiopathic ventricular fibrillation, and left ventricular non-compaction. At present, the total number of disease-associated RyR2 mutations exceeds 300. In addition, in chronic heart failure, modification of RyR2 by phosphorylation, oxidation or S-nitrosylation may cause abnormal channel activity. Arrhythmogenic mechanisms of these various disorders are not yet fully understood. We have recently established a method to quantitatively evaluate the effects of various arrhythmogenic mutations and modifications on RyR2 channels by using HEK293 expression system. We found that arrhythmogenic mutations in RyR2 are classified into two groups: gain-of-function and loss-of-function of the channel. Since they are indistinguishable in clinical diagnosis, our analysis is very useful for diagnosis and choice of treatment strategies for RyR2-linked arrhythmogenic diseases. This review describes the current advances and issues of research on RyR2 mutation-related arrhythmogenic disorders.

Sudden Cardiac Death and Copy Number Variants: What Do We Know after 10 Years of Genetic Analysis?

Over the last ten years, analysis of copy number variants has increasingly been applied to the study of arrhythmogenic pathologies associated with sudden death, mainly due to significant advances in the field of massive genetic sequencing. Nevertheless, few published reports have focused on the prevalence of copy number variants associated with sudden cardiac death. As a result, the frequency of these genetic alterations in arrhythmogenic diseases as well as their genetic interpretation and clinical translation has not been established. This review summarizes the current available data concerning copy number variants in sudden cardiac death-related diseases.

Classification and correlation of RYR2 missense variants in individuals with catecholaminergic polymorphic ventricular tachycardia reveals phenotypic relationships

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is predominantly caused by heterozygous missense variants in the cardiac ryanodine receptor, RYR2. However, many RYR2 missense variants are classified as variants of uncertain significance (VUS). We systematically re-evaluated all RYR2 variants in healthy individuals and those with CPVT or arrhythmia using the 2015 American College of Medical Genomics guidelines. RYR2 variants were identified by the NW Genomic Laboratory Hub, from the published literature and databases of sequence variants. Each variant was assessed based on minor allele frequencies, in silico prediction tools and appraisal of functional studies and classified according to the ACMG-AMP guidelines. Phenotype data was collated where available. Of the 326 identified RYR2 missense variants, 55 (16.9%), previously disease-associated variants were reclassified as benign. Application of the gnomAD database of >140,000 controls allowed reclassification of 11 variants more than the ExAC database. CPVT-associated RYR2 variants clustered predominantly between amino acid positions 3949-4332 and 4867-4967 as well as the RyR and IP3R homology-associated and ion transport domains (p < 0.005). CPVT-associated RYR2 variants occurred at more conserved amino acid positions compared with controls, and variants associated with sudden death had higher conservation scores (p < 0.005). There were five potentially pathogenic RYR2 variants associated with sudden death during sleep which were located almost exclusively in the C-terminus of the protein. In conclusion, control sequence databases facilitate reclassification of RYR2 variants but the majority remain as VUS. Notably, pathogenic variants in RYR2 are associated with death in sleep.

Co-Phenotype of Left Ventricular Non-Compaction Cardiomyopathy and Atypical Catecholaminergic Polymorphic Ventricular Tachycardia in Association With R169Q, a Ryanodine Receptor Type 2 Missense Mutation

BACKGROUND

Left ventricular non-compaction (LVNC) is a cardiomyopathy characterized by prominent trabeculae and intertrabecular recesses. We present the cases of 3 girls with the sameryanodine receptor type 2(RYR2) mutation who had phenotypes of both catecholaminergic polymorphic ventricular tachycardia (CPVT) and LVNC.

METHODS AND RESULTS

Clinical characteristics and genetic background of the 3 patients were analyzed retrospectively. Age at onset was 5, 6, and 7 years, respectively. Clinical presentation included syncope during exercise in all 3 patients and cardiac arrest in 2 patients. LVNC diagnosis was confirmed on echocardiography according to previously defined criteria. Exercise stress testing provoked ventricular arrhythmia in two of the patients. Beta-blockers (n=3) and flecainide (n=2) were given, and an implantable cardioverter defibrillator was used in 1 patient. Genotyping identified the sameRYR2-R169Q missense mutation and no other CPVT- or LVNC-related gene mutations. Functional analysis of the mutation using HEK293 cells with single-cell Ca2+imaging and [3H]ryanodine binding analysis, indicated a gain of function: a reduced threshold for overload-induced Ca2+release from the sarcoplasmic reticulum and increased fractional Ca2+release.

CONCLUSIONS

The rare association of LVNC and CPVT phenotypes withRYR2mutations is less likely to be coincidental. Screening for life-threatening arrhythmias using exercise or pharmacologic stress tests is recommended in LVNC patients to prevent sudden cardiac death in those with preserved LV function.

[Left ventricular non - compaction: contemporary view of genetic background, clinical course, diagnostic and treatment]

This review highlights and discusses recent advances in understanding left ventricular non - compaction (LVNC). Clinical profile, prognosis and even diagnosis are still a great challenge faced by the world. The population prevalence of left ventricular non - compaction remains unknown. High variability of clinical manifestations, genetic heterogenity with overlap of different phenotypes, variability of hereditary patterns suggests that LVNC seems to be rather an isolated trait or a part of phenotypic expression of different cardiac diseases or complex genetic syndromes.

Epidemiology of inherited arrhythmias

The primary electrical disorders are a group of inherited cardiac ventricular arrhythmias that are a major cause of sudden cardiac death in young individuals. Inherited ventricular arrhythmias result from mutations in genes encoding cardiac ion channels or their modulatory subunits. Advances in genetic screening in the past three decades have led to the assembly of large patient cohorts with these disorders. Studies in these patients, as well as in the general population, have striven to define the prevalence of these inherited arrhythmias and the characteristics of patients with different genetic subtypes of the disease. In this Review, we provide a comprehensive update on the epidemiology of inherited ventricular arrhythmias, focusing on natural history, prevalence and patient demographics. In addition, we summarize the various founder populations (groups of individuals with a disease that is caused by a genetic defect inherited from a common ancestor) that have been identified for some of these disorders and which lead to increased prevalence in some geographical regions. To date, although numerous studies have markedly increased our understanding of the epidemiology of these disorders, demographic data, especially from non-Western countries, remain scarce. Furthermore, defining the true prevalence of these disorders remains challenging. International collaboration will undoubtedly accelerate the collection of demographic information and improve the accuracy of prevalence data.

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.

Identification of a novel exon3 deletion of RYR2 in a family with catecholaminergic polymorphic ventricular tachycardia

BACKGROUND

RYR2, encoding cardiac ryanodine receptor, is the major responsible gene for catecholaminergic polymorphic ventricular tachycardia (CPVT). Meanwhile, KCNJ2, encoding inward-rectifier potassium channel (I_K1 ), can be the responsible gene for atypical CPVT. We recently encountered a family with CPVT and sought to identify a responsible gene variant.

METHODS

A targeted panel sequencing (TPS) was employed in the proband. Copy number variation (CNV) in RYR2 was identified by focusing on read numbers in the TPS and long-range PCR. Cascade screening was conducted by a Sanger method and long-range PCR. KCNJ2 wild-type (WT) or an identified variant was expressed in COS-1 cells, and whole-cell currents (I_K1 ) were recorded using patch-clamp techniques.

RESULTS

A 40-year-old female experienced cardiopulmonary arrest while cycling. Her ECG showed sinus bradycardia with prominent U-waves (≥0.2 mV). She had left ventricular hypertrabeculation at apex. Exercise induced frequent polymorphic ventricular arrhythmias. Her sister died suddenly at age 35 while bouldering. Her father and paternal aunt, with prominent U-waves, received permanent pacemaker due to sinus node dysfunction. The initial TPS and cascade screening identified a KCNJ2 E118D variant in all three symptomatic patients. However, after focusing on read numbers, we identified a novel exon3 deletion of RYR2 (RYR2-exon3 deletion) in all of them. Functional analysis revealed that KCNJ2 E118D generated I_K1 indistinguishable from KCNJ2 WT, even in the presence of catecholaminergic stimulation.

CONCLUSIONS

Focusing on the read numbers in the TPS enabled us to identify a novel CNV, RYR2-exon3 deletion, which was associated with phenotypic features of this family.

Practical Aspects in Genetic Testing for Cardiomyopathies and Channelopathies

Genetic testing has an increasingly important role in the diagnosis and management of cardiac disorders, where it confirms the diagnosis, aids prognostication and risk stratification and guides treatment. A genetic diagnosis in the proband also enables clarification of the risk for family members by cascade testing. Genetics in cardiac disorders is complex where epigenetic and environmental factors might come into interplay. Incomplete penetrance and variable expressivity is also common. Genetic results in cardiac conditions are mostly probabilistic and should be interpreted with all available clinical information. With this complexity in cardiac genetics, testing is only indicated in patients with a strong suspicion of an inheritable cardiac disorder after a full clinical evaluation. In this review we discuss the genetics underlying the major cardiomyopathies and channelopathies, and the practical aspects of diagnosing these conditions in the laboratory.

Targeted panel sequencing in adult patients with left ventricular non-compaction reveals a large genetic heterogeneity

Left ventricular non-compaction (LVNC) is a cardiomyopathy that may be of genetic origin; however, few data are available about the yield of mutation, the spectrum of genes and allelic variations. The aim of this study was to better characterize the genetic spectrum of isolated LVNC in a prospective cohort of 95 unrelated adult patients through the molecular investigation of 107 genes involved in cardiomyopathies and arrhythmias. Fifty-two pathogenic or probably pathogenic variants were identified in 40 patients (42%) including 31 patients (32.5%) with single variant and 9 patients with complex genotypes (9.5%). Mutated patients tended to have younger age at diagnosis than patients with no identified mutation. The most prevalent genes were TTN, then HCN4, MYH7, and RYR2. The distribution includes 13 genes previously reported in LVNC and 10 additional candidate genes. Our results show that LVNC is basically a genetic disease and support genetic counseling and cardiac screening in relatives. There is a large genetic heterogeneity, with predominant TTN null mutations and frequent complex genotypes. The gene spectrum is close to the one observed in dilated cardiomyopathy but with specific genes such as HCN4. We also identified new candidate genes that could be involved in this sub-phenotype of cardiomyopathy.

Contemporary genetic testing in inherited cardiac disease: tools, ethical issues, and clinical applications

Inherited cardiac diseases comprise a wide and heterogeneous spectrum of diseases of the heart, including the cardiomyopathies and the arrhythmic diseases in structurally normal hearts, that is, channelopathies. With a combined estimated prevalence of 3% in the general population, these conditions represent a relevant epidemiological entity worldwide, and are a major cause of cardiac morbidity and mortality in the young. The extraordinary progress achieved in molecular genetics over the last three decades has unveiled the complex molecular basis of many familial cardiac conditions, paving the way for routine use of gene testing in clinical practice. In current practice, genetic testing can be used in a clinically affected patient to confirm diagnosis, or to formulate a differential diagnosis among overlapping phenotypes or between hereditary and acquired (nongenetic) forms of disease. Although genotype–phenotype correlations are generally unpredictable, a precise molecular diagnosis can help predict prognosis in specific patient subsets and may guide management. In clinically unaffected relatives, genetic cascade testing is recommended, after the initial identification of a pathogenic variation, with the aim of identifying asymptomatic relatives who might be at risk of disease-related complications, including unexpected sudden cardiac death. Future implications include the identification of novel therapeutic targets and development of tailored treatments including gene therapy. This document reflects the multidisciplinary, ‘real-world’ experience required when implementing genetic testing in cardiomyopathies and arrhythmic syndromes, along the recommendations of various guidelines.

Deletion of Nkx2-5 in trabecular myocardium reveals the developmental origins of pathological heterogeneity associated with ventricular non-compaction cardiomyopathy

Left ventricular non-compaction (LVNC) is a rare cardiomyopathy associated with a hypertrabeculated phenotype and a large spectrum of symptoms. It is still unclear whether LVNC results from a defect of ventricular trabeculae development and the mechanistic basis that underlies the varying severity of this pathology is unknown. To investigate these issues, we inactivated the cardiac transcription factor Nkx2-5 in trabecular myocardium at different stages of trabecular morphogenesis using an inducible Cx40-creERT2 allele. Conditional deletion of Nkx2-5 at embryonic stages, during trabecular formation, provokes a severe hypertrabeculated phenotype associated with subendocardial fibrosis and Purkinje fiber hypoplasia. A milder phenotype was observed after Nkx2-5 deletion at fetal stages, during trabecular compaction. A longitudinal study of cardiac function in adult Nkx2-5 conditional mutant mice demonstrates that excessive trabeculation is associated with complex ventricular conduction defects, progressively leading to strain defects, and, in 50% of mutant mice, to heart failure. Progressive impaired cardiac function correlates with conduction and strain defects independently of the degree of hypertrabeculation. Transcriptomic analysis of molecular pathways reflects myocardial remodeling with a larger number of differentially expressed genes in the severe versus mild phenotype and identifies Six1 as being upregulated in hypertrabeculated hearts. Our results provide insights into the etiology of LVNC and link its pathogenicity with compromised trabecular development including compaction defects and ventricular conduction system hypoplasia.

During fetal heart morphogenesis, formation of the mature ventricular wall requires coordinated compaction of the inner trabecular layer and growth of the outer layer of myocardium. Arrested trabecular development has been implicated in the pathogenesis of hypertrabeculation associated with ventricular non-compaction cardiomyopathy. However much uncertainty still exists among clinicians concerning the physiopathology of ventricular non-compaction cardiomyopathy, including its clinical characteristics, prognosis, classification and even the definition of hypertrabeculation. In particular, distinguishing between pathological and non-pathological subtypes of non-compaction is currently a major issue. Here we show that deletion of the gene encoding the transcription factor Nkx2-5 at critical steps during trabecular development recapitulates pathological features of hypertrabeculation, providing the first model of ventricular non-compaction cardiomyopathy in adult mice. We demonstrate that excessive trabeculation due to failure of trabecular compaction during fetal development is associated with Purkinje fiber hypoplasia and subendocardial fibrosis. Longitudinal functional studies reveal that these mice present all the clinical signs of symptomatic left ventricular non-compaction cardiomyopathy, including conduction defects, strain defects and progressive heart failure. Our results, including transcriptomic analysis, suggest that pathological features of non-compaction are primarily developmental defects. This study clarifies the origin of the pathological outcomes associated with LVNC and may provide helpful information for clinicians concerning the etiology of this rare cardiomyopathy.

Copy number variations of SCN5A in Brugada syndrome

BACKGROUND

Loss-of-function mutations in SCN5A are associated in ∼20% of Brugada syndrome (BrS) patients. Copy number variations (CNVs) have been shown to be associated with several inherited arrhythmia syndromes.

OBJECTIVE

The purpose of this study was to investigate SCN5A CNVs among BrS probands.

METHODS

The study cohort consisted of 151 BrS probands who were symptomatic or had a family history of BrS, sudden death, syncope, or arrhythmic diseases. We performed sequence analysis of SCN5A by the Sanger method. For detecting CNVs in SCN5A, we performed multiplex ligation-dependent probe amplification analysis of the 151 BrS probands.

RESULTS

We identified pathogenic SCN5A mutations in 20 probands by the Sanger method. In 140 probands in whom multiplex ligation-dependent probe amplification was successfully performed, 4 probands were found to present different CNVs (deletion in 3 and duplication in 1). Three of them had fatal arrhythmia events; the remaining 1 was asymptomatic but had a family history. Mean age at diagnosis was 23 ± 14 years. All of the baseline 12-lead electrocardiograms showed PQ-interval prolongation. The characteristics of these 4 probands with CNVs were similar to those of the probands with mutations leading to premature truncation of the protein or missense mutations causing peak I_Na reduction >90%.

CONCLUSION

We identified SCN5A CNVs in 2.9% of BrS probands who were symptomatic or had a family history.

Reduced expression of cardiac ryanodine receptor protects against stress-induced ventricular tachyarrhythmia, but increases the susceptibility to cardiac alternans

Reduced protein expression of the cardiac ryanodine receptor type 2 (RyR2) is thought to affect the susceptibility to stress-induced ventricular tachyarrhythmia (VT) and cardiac alternans, but direct evidence for the role of RyR2 protein expression in VT and cardiac alternans is lacking. Here, we used a mouse model (crr^m1) that expresses a reduced level of the RyR2 protein to determine the impact of reduced RyR2 protein expression on the susceptibility to VT, cardiac alternans, cardiac hypertrophy, and sudden death. Electrocardiographic analysis revealed that after the injection of relatively high doses of caffeine and epinephrine (agents commonly used for stress test), wild-type (WT) mice displayed long-lasting VTs, whereas the crr^m1 mutant mice exhibited no VTs at all, indicating that the crr^m1 mutant mice are resistant to stress-induced VTs. Intact heart Ca²⁺ imaging and action potential (AP) recordings showed that the crr^m1 mutant mice are more susceptible to fast-pacing induced Ca²⁺ alternans and AP duration alternans compared with WT mice. The crr^m1 mutant mice also showed an increased heart-to-body-weight ratio and incidence of sudden death at young ages. Furthermore, the crr^m1 mutant hearts displayed altered Ca²⁺ transients with increased time-to-peak and decay time (T₅₀), increased ventricular wall thickness and ventricular cell area compared with WT hearts. These results indicate that reduced RyR2 protein expression suppresses stress-induced VTs, but enhances the susceptibility to cardiac alternans, hypertrophy, and sudden death.

Catecholaminergic polymorphic ventricular tachycardia, an update

Catecholaminergic polymorphic ventricular tachycardia is a rare devastating lethal inherited disorder or sporadic cardiac ion channelopathy characterized by unexplained syncopal episodes, and/or sudden cardiac death (SCD), aborted SCD (ASCD), or sudden cardiac arrest (SCA) observed in children, adolescents, and young adults without structural heart disease, consequence of adrenergically mediated arrhythmias: exercise-induced, by acute emotional stress, atrial pacing, or β-stimulant infusion, even when the electrocardiogram is normal. The entity is difficult to diagnose in the emergency department, given the range of presentations; thus, a familiarity with and high index of suspicion for this pathology are crucial. Furthermore, recognition of the characteristic findings and knowledge of the management of symptomatic patients are necessary, given the risk of arrhythmia recurrence and SCA. In this review, we will discuss the concept, epidemiology, genetic background, genetic subtypes, clinical presentation, electrocardiographic features, diagnosis criteria, differential diagnosis, and management.

Repeat genetic testing with targeted capture sequencing in primary arrhythmia syndrome and cardiomyopathy

In inherited primary arrhythmia syndromes (PAS) and cardiomyopathies (CMP), the yield of genetic testing varies between 20 and 75% in different diseases according to studies performed in the pre next-generation sequencing (NGS) era. It is unknown whether retesting historical negative samples with NGS techniques is worthwhile. Therefore, we assessed the value of NGS-based panel testing in previously genotype negative-phenotype positive probands. We selected 107 patients (47 PAS and 60 CMP) with a clear phenotype who remained genotype negative after genetic analysis of the main genes implicated in their specific phenotype. Targeted sequencing of the coding regions of 71 PAS- and CMP-related genes was performed. Variant interpretation and classification was done according to a cardiology-specific scoring algorithm ('Amsterdam criteria') and the ACMG-AMP criteria. Co-segregation analysis was performed when DNA and clinical data of family members were available. Finally, a genetic diagnosis could be established in 21 patients (20%), 5 PAS (11%) and 16 CMP (27%) patients, respectively. The increased detection rate was due to sequencing of novel genes in 52% of the cases and due to technical failures with the historical analysis in 48%. A total of 118 individuals were informed about their carrier state and either reassured or scheduled for proper follow-up. To conclude, genetic retesting in clinically overt PAS and CMP cases, who were genotype negative with older techniques, resulted in an additional genetic diagnosis in up to 20% of the cases. This clearly supports a policy for genetic retesting with NGS-based panels.