Valvulopathies and Genetics: Where are We?

Valvulopathies are among the most common cardiovascular diseases, significantly increasing morbidity and mortality. While many valvular heart diseases are acquired later in life, an important genetic component has been described, particularly in mitral valve prolapse and bicuspid aortic valve. These conditions can arise secondary to genetic syndromes such as Marfan disease (associated with mitral valve prolapse) or Turner syndrome (linked to the bicuspid aortic valve) or may manifest in a non-syndromic form. When cardiac valve disease is the primary cause, it can appear in a familial clustering or sporadically, with a clear genetic component. The identification of new genes, regulatory elements, post-transcriptional modifications, and molecular pathways is crucial to identify at-risk familial carriers and for developing novel therapeutic strategies. In the present review we will discuss the numerous genetic contributors of heart valve diseases.

Investigating cardiac genetic background in sudden infant death syndrome (SIDS).

Sudden infant death syndrome (SIDS) is still the leading cause of death for newborns in developed countries. The pathophysiological mechanisms have not been fully clarified, but in some of SIDS cases variants of genes associated with inherited cardiac conditions are found. In this study, an analysis of SCD-related genes was performed to determine the prevalence of rare pathogenic (P) or likely pathogenic (LP) variants that could provide an unambiguous explanation for the fatal event. A cohort of 76 SIDS cases underwent Next-Generation Sequencing (NGS) analysis with a custom panel of SCD-related genes. Rare variants were classified according to the guidelines provided by the American College of Medical Genetics and Genomics (ACMG) and the specifications of the ClinGen association. Post-mortem genetic testing identified 50 (65.8%) carriers of at least one variant in SCD genes. 104 rare genetic variants were found, 65.4% in genes encoding structural proteins. Only 4 out of 76 cases (5.3%) hosted at least a P or LP variant found in genes with structural or structural/arrhythmogenic functions (SLC22A5, SCN5A, MYL3and TTN). 99 variants were classified as of uncertain significance (VUS). The difference in the distribution of variants between gene groups by function was not statistically significant (chi square, p = 0,219). Despite this, most of the variants concerned structural genes that were supposed to have a close interaction with ion channels, thus providing an explanation for the arrhythmic event. Segregation analysis, reclassification of VUS variants and identification of new associated genes could clarify the implications of the current findings.

Implementing a New Algorithm for Reinterpretation of Ambiguous Variants in Genetic Dilated Cardiomyopathy.

Dilated cardiomyopathy is a heterogeneous entity that leads to heart failure and malignant arrhythmias. Nearly 50% of cases are inherited; therefore, genetic analysis is crucial to unravel the cause and for the early identification of carriers at risk. A large number of variants remain classified as ambiguous, impeding an actionable clinical translation. Our goal was to perform a comprehensive update of variants previously classified with an ambiguous role, applying a new algorithm of already available tools. In a cohort of 65 cases diagnosed with dilated cardiomyopathy, a total of 125 genetic variants were classified as ambiguous. Our reanalysis resulted in the reclassification of 12% of variants from an unknown to likely benign or likely pathogenic role, due to improved population frequencies. For all the remaining ambiguous variants, we used our algorithm; 60.9% showed a potential but not confirmed deleterious role, and 24.5% showed a potential benign role. Periodically updating the population frequencies is a cheap and fast action, making it possible to clarify the role of ambiguous variants. Here, we perform a comprehensive reanalysis to help to clarify the role of most of ambiguous variants. Our specific algorithms facilitate genetic interpretation in dilated cardiomyopathy.

Reevaluation of ambiguous genetic variants in sudden unexplained deaths of a young cohort.

Sudden death cases in the young population remain without a conclusive cause of decease in almost 40% of cases. In these situations, cardiac arrhythmia of genetic origin is suspected as the most plausible cause of death. Molecular autopsy may reveal a genetic defect in up to 20% of families. Most than 80% of rare variants remain classified with an ambiguous role, impeding a useful clinical translation. Our aim was to update rare variants originally classified as of unknown significance to clarify their role. Our cohort included fifty-one post-mortem samples of young cases who died suddenly and without a definite cause of death. Five years ago, molecular autopsy identified at least one rare genetic alteration classified then as ambiguous following the American College of Medical Genetics and Genomics' recommendations. We have reclassified the same rare variants including novel data. About 10% of ambiguous variants change to benign/likely benign mainly because of improved population frequencies. Excluding cases who died before one year of age, almost 21% of rare ambiguous variants change to benign/likely benign. This fact makes it important to discard these rare variants as a cause of sudden unexplained death, avoiding anxiety in relatives' carriers. Twenty-five percent of the remaining variants show a tendency to suspicious deleterious role, highlighting clinical follow-up of carriers. Periodical reclassification of rare variants originally classified as ambiguous is crucial, at least updating frequencies every 5 years. This action aids to increase accuracy to enable and conclude a cause of death as well as translation into the clinic.

Clinical impact of rare variants associated with inherited channelopathies: a 5-year update.

A proper interpretation of the pathogenicity of rare variants is crucial before clinical translation. Ongoing addition of new data may modify previous variant classifications; however, how often a reanalysis is necessary remains undefined. We aimed to extensively reanalyze rare variants associated with inherited channelopathies originally classified 5 years ago and its clinical impact. In 2016, rare variants identified through genetic analysis were classified following the American College of Medical Genetics and Genomics' recommendations. Five years later, we have reclassified the same variants following the same recommendations but including new available data. Potential clinical implications were discussed. Our cohort included 49 cases of inherited channelopathies diagnosed in 2016. Update show that 18.36% of the variants changed classification mainly due to improved global frequency data. Reclassifications mostly occurred in minority genes associated with channelopathies. Similar percentage of variants remain as deleterious nowadays, located in main known genes (SCN5A, KCNH2 and KCNQ1). In 2016, 69.38% of variants were classified as unknown significance, but now, 53.06% of variants are classified as such, remaining the most common group. No management was modified after translation of genetic data into clinics. After 5 years, nearly 20% of rare variants associated with inherited channelopathies were reclassified. This supports performing periodic reanalyses of no more than 5 years since last classification. Use of newly available data is necessary, especially concerning global frequencies and family segregation. Personalized clinical translation of rare variants can be crucial to management if a significant change in classification is identified.

Eosinophilic Infiltration of the Sino-Atrial Node in Sudden Cardiac Death Caused by Long QT Syndrome.

Sudden death is defined as the unexpected death of a healthy person that occurs within the first hour of the onset of symptoms or within 24 h of the victim being last seen alive. In some of these cases, rare deleterious variants of genes associated with inherited cardiac disorders can provide a highly probable explanation for the fatal event. We report the case of a 21-year-old obese woman who lost consciousness suddenly in a public place and was pronounced dead after hospital admission. Clinical autopsy showed an inconclusive gross examination, while in the histopathological analysis an eosinophilic inflammatory focus and interstitial fibrosis in the sino-atrial node were found. Molecular autopsy revealed an intronic variant in the KCNQ1 gene (c.683 + 5G > A), classified as likely pathogenic for long QT syndrome according to the guidelines provided by the American College of Medical Genetics and Genomics. Therefore, there were many anomalies that could have played a role in the causation of the sudden death, such as the extreme obesity, the cardiac anomalies and the KNCQ1 variant. This case depicts the difficult interpretation of rare cardiac structural abnormalities in subjects carrying rare variants responsible for inherited arrhythmic disorders and the challenge for the forensic pathologist to make causal inferences in the determinism of the unexpected decease.

Unpredicted Aberrant Splicing Products Identified in Postmortem Sudden Cardiac Death Samples.

Molecular screening for pathogenic mutations in sudden cardiac death (SCD)-related genes is common practice for SCD cases. However, test results may lead to uncertainty because of the identification of variants of unknown significance (VUS) occurring in up to 70% of total identified variants due to a lack of experimental studies. Genetic variants affecting potential splice site variants are among the most difficult to interpret. The aim of this study was to examine rare intronic variants identified in the exonic flanking sequence to meet two main objectives: first, to validate that canonical intronic variants produce aberrant splicing; second, to determine whether rare intronic variants predicted as VUS may affect the splicing product. To achieve these objectives, 28 heart samples of cases of SCD carrying rare intronic variants were studied. Samples were analyzed using 85 SCD genes in custom panel sequencing. Our results showed that rare intronic variants affecting the most canonical splice sites displayed in 100% of cases that they would affect the splicing product, possibly causing aberrant isoforms. However, 25% of these cases (1/4) showed normal splicing, contradicting the in silico results. On the contrary, in silico results predicted an effect in 0% of cases, and experimental results showed >20% (3/14) unpredicted aberrant splicing. Thus, deep intron variants are likely predicted to not have an effect, which, based on our results, might be an underestimation of their effect and, therefore, of their pathogenicity classification and family members' follow-up.

The role of clinical assessment and electrophysiology study in Brugada syndrome patients with syncope.

BACKGROUND: Cardiogenic syncope in Brugada syndrome (BrS) increases the risk of major events. Nevertheless, clinical differentiation between cardiogenic and vasovagal syncope can be challenging. We characterized the long-term incidence of major events in a large cohort of BrS patients who presented with syncope. METHODS: From a total of 474 patients, syncope was the initial manifestation in 135 (28.5%) individuals (43.9 ±â€¯13.9 years, 71.1% male). The syncope was classified prospectively as cardiogenic, vasovagal, or undefined if unclear characteristics were present. Clinical, electrocardiographic, genetic, and electrophysiologic features were analyzed. Cardiogenic syncope, sustained ventricular arrhythmias, and sudden death were considered major events in follow-up. RESULTS: In 66 patients (48.9%), the syncope was cardiogenic; in 51 (37.8%), vasovagal and in 18 (13.3%); undefined. The electrophysiology study (EPS) inducibility was more frequent in patients with cardiogenic syncope and absent in all patients with undefined syncope (28 [53.8%] vs 5 [12.2%] vs 0 [0%]; P < .01). During follow-up (7.7 ±â€¯5.6 years), only patients with cardiogenic syncope presented major events (16 [11.9%]). Among patients with inducible EPS, 7 (21.2%) presented major events (P = .04). The negative predictive value of the EPS for major events was 92.4%. The incidence rate of major events was 2.6% person-year. Parameters associated with major events included cardiogenic syncope (hazard ratio [HR] 6.3; 95% CI 1.1-10.4; P = .05), spontaneous type 1 electrocardiogram (HR 3.7; 95% CI 1.3-10.5; P = .01), and inducible EPS (HR 2.8; 95% CI 1.1-8.8; P = .05). CONCLUSIONS: An accurate syncope classification is crucial in BrS patients for risk stratification. In patients with syncope of unclear characteristics, the EPS may be helpful to prevent unnecessary implantable cardioverter defibrillators.

Genetic interpretation and clinical translation of minor genes related to Brugada syndrome.

Brugada syndrome (BrS) is an inherited arrhythmogenic disease associated with sudden cardiac death. The main gene is SCN5A. Additional variants in 42 other genes have been reported as deleterious, although these variants have not yet received comprehensive pathogenic analysis. Our aim was to clarify the role of all currently reported variants in minor genes associated with BrS. We performed a comprehensive analysis according to the American College of Medical Genetics and Genomics guidelines of published clinical and basic data on all genes (other than SCN5A) related to BrS. Our results identified 133 rare variants potentially associated with BrS. After applying current recommendations, only six variants (4.51%) show a conclusive pathogenic role. All definitively pathogenic variants were located in four genes encoding sodium channels or related proteins: SLMAP, SEMA3A, SCNN1A, and SCN2B. In total, 33.83% of variants in 19 additional genes were potentially pathogenic. Beyond SCN5A, we conclude definitive pathogenic variants associated with BrS in four minor genes. The current list of genes associated with BrS, therefore, should include SCN5A, SLMAP, SEMA3A, SCNN1A, and SCN2B. Comprehensive genetic interpretation and careful clinical translation should be done for all variants currently classified as potentially deleterious for BrS.

Sudden death due to catecholaminergic polymorphic ventricular tachycardia following negative stress-test outcome: genetics and clinical implications.

This paper discusses the case of a young boy who died suddenly during a football match. The victim's personal and family medical histories were negative for cardiac events. He had undergone a cardiological investigation some months before his death, enabling him to participate in competitive sports. Only post-mortem molecular analysis allowed for a clearer determination of the most plausible cause of death, which was identified as inherited arrhythmogenic heart disease, known as catecholaminergic polymorphic ventricular tachycardia. It was possible to detect a novel, previously undescribed, variant in the RYR2 gene. This case report highlights the importance of a meaningful forensic multidisciplinary investigation in such cases, and also discusses possible medical malpractice claims.

Sudden infant death syndrome caused by cardiac arrhythmias: only a matter of genes encoding ion channels?

Sudden infant death syndrome is the unexpected demise of a child younger than 1 year of age which remains unexplained after a complete autopsy investigation. Usually, it occurs during sleep, in males, and during the first 12 weeks of life. The pathophysiological mechanism underlying the death is unknown, and the lethal episode is considered multifactorial. However, in cases without a conclusive post-mortem diagnosis, suspicious of cardiac arrhythmias may also be considered as a cause of death, especially in families suffering from any cardiac disease associated with sudden cardiac death. Here, we review current understanding of sudden infant death, focusing on genetic causes leading to lethal cardiac arrhythmias, considering both genes encoding ion channels as well as structural proteins due to recent association of channelopathies and desmosomal genes. We support a comprehensive analysis of all genes associated with sudden cardiac death in families suffering of infant death. It allows the identification of the most plausible cause of death but also of family members at risk, providing cardiologists with essential data to adopt therapeutic preventive measures in families affected with this lethal entity.

Genetic investigation of sudden unexpected death in epilepsy cohort by panel target resequencing.

Sudden unexpected death in epilepsy (SUDEP) is defined as the abrupt, no traumatic, witnessed or unwitnessed death, occurring in benign circumstances, in an individual with epilepsy, with or without evidence for a seizure and excluding documented status epilepticus (seizure duration ≥ 30 min or seizures without recovery), and in which postmortem examination does not reveal a cause of death. Although the physiopathological mechanisms that underlie SUDEP remain to be clarified, the genetic background has been described to play a role in this disorder. Pathogenic variants in genes associated with epilepsy and encoding cardiac ion channels could explain the SUDEP phenotype. To test this we use the next-generation sequencing technology to sequence a cohort of SUDEP cases and its translation into clinical and forensic fields. A panel target resequencing was used to study 14 SUDEP cases from both postmortem (2 cases) and from living patients (12 cases). Genes already associated with SUDEP and also candidate genes had been investigated. Overall, 24 rare genetic variants were identified in 13 SUDEP cases. Four cases showed rare variants with complete segregation in the SCN1A, FBN1, HCN1, SCN4A, and EFHC1 genes, and one case with a rare variant in KCNQ1 gene showed incomplete pattern of inheritance. In four cases, rare variants were detected in CACNA1A, SCN11A and SCN10A, and KCNQ1 genes, but familial segregation was not possible due to lack of DNA from relatives. Finally, in the four remaining cases, the rare variants did not segregate in the family. This study confirms the link between epilepsy, sudden death, and cardiac disease. In addition, we identified new potential candidate genes for SUDEP: FBN1, HCN1, SCN4A, EFHC1, CACNA1A, SCN11A, and SCN10A. Further confirmation in larger cohorts will be necessary especially if genetic screening for SUDEP is applied to forensic and clinical medicine. Nevertheless, this study supports the emerging concept of a genetically determined cardiocerebral channelopathy.

A novel mutation in lamin a/c causing familial dilated cardiomyopathy associated with sudden cardiac death.

BACKGROUND: Dilated cardiomyopathy (DCM), a cardiac heterogeneous pathology characterized by left ventricular or biventricular dilatation, is a leading cause of heart failure and heart transplantation. The genetic origin of DCM remains unknown in most cases, but >50 genes have been associated with DCM. We sought to identify the genetic implication and perform a genetic analysis in a Spanish family affected by DCM and sudden cardiac death. METHODS AND RESULTS: Clinical assessment and genetic screening were performed in the index case as well as family members. Of all relatives clinically assessed, nine patients showed clinical symptoms related to the pathology. Genetic screening identified 20 family members who carried a novel mutation in LMNA (c.871 G>A, p.E291K). Family segregation analysis indicated that all clinically affected patients carried this novel mutation. Clinical assessment of genetic carriers showed that electrical dysfunction was present previous to mechanical and structural abnormalities. CONCLUSIONS: Our results report a novel pathogenic mutation associated with DCM, supporting the benefits of comprehensive genetic studies of families affected by this pathology.

Genetics of inherited arrhythmias in pediatrics.

PURPOSE OF REVIEW: Recent international expert consensus statements have updated the clinical and genetic diagnoses of patients suffering from arrhythmogenic diseases. However, a lack of genotype-phenotype correlations has hampered the development of a risk stratification scale for sudden cardiac death. RECENT FINDINGS: The improvement in the field of genetics has prompted the discovery of new genes associated with sudden cardiac death. Sudden cardiac death is a socially devastating event, especially when it occurs in the pediatric population. Physical activity can often trigger the arrhythmia and sudden death may be the first symptom. These inherited cardiac diseases may be difficult to diagnose, leaving family members also at risk. Thanks to the development of new high-throughput technologies, genetics may be used in the diagnosis of these diseases and even cases that remain unexplained after a comprehensive autopsy. Genetic testing cannot only identify the causative genetic variant in the index case, but it enables the detection of relatives at risk of sudden death, despite remaining clinically asymptomatic. SUMMARY: We review the recent advances in the genetics of inherited arrhythmias associated with sudden cardiac death. We focus on the pediatric population, the main group of people suffering from lethal inherited arrhythmias.

Rare Titin (TTN) Variants in Diseases Associated with Sudden Cardiac Death.

A leading cause of death in western countries is sudden cardiac death, and can be associated with genetic disease. Next-generation sequencing has allowed thorough analysis of genes associated with this entity, including, most recently, titin. We aimed to identify potentially pathogenic genetic variants in titin. A total of 1126 samples were analyzed using a custom sequencing panel including major genes related to sudden cardiac death. Our cohort was divided into three groups: 432 cases from patients with cardiomyopathies, 130 cases from patients with channelopathies, and 564 post-mortem samples from individuals showing anatomical healthy hearts and non-conclusive causes of death after comprehensive autopsy. None of the patients included had definite pathogenic variants in the genes analyzed by our custom cardio-panel. Retrospective analysis comparing the in-house database and available public databases also was performed. We identified 554 rare variants in titin, 282 of which were novel. Seven were previously reported as pathogenic. Of these 554 variants, 493 were missense variants, 233 of which were novel. Of all variants identified, 399 were unique and 155 were identified at least twice. No definite pathogenic variants were identified in any of genes analyzed. We identified rare, mostly novel, titin variants that seem to play a potentially pathogenic role in sudden cardiac death. Additional studies should be performed to clarify the role of these variants in sudden cardiac death.

Negative autopsy and sudden cardiac death.

Forensic medicine defines the unexplained sudden death as a death with a non-conclusive diagnosis after autopsy. Molecular diagnosis is being progressively incorporated in forensics, mainly due to improvement in genetics. New genetic technologies may help to identify the genetic cause of death, despite clinical interpretation of genetic data remains the current challenge. The identification of an inheritable defect responsible for arrhythmogenic syndromes could help to adopt preventive measures in family members, many of them asymptomatic but at risk of sudden death. This multidisciplinary translational research requires a specialized team.

Genetics of arrhythmogenic right ventricular cardiomyopathy.

Arrhythmogenic right ventricular cardiomyopathy is a rare clinical entity characterised by fibro-fatty replacement of myocardium, mainly involving right ventricular free wall, leading to malignant electrical instability and sudden cardiac death. The disease is inherited in up to 50% of cases, with incomplete penetrance and variable phenotypic expression. To date, more than 300 pathogenic mutations have been identified in 12 genes, mainly with autosomal dominant inheritance. Here, we focus on recent advances in the genetics of arrhythmogenic right ventricular cardiomyopathy. Despite continuous improvements, current genotype-phenotype studies have not contributed yet to establish a genetic risk stratification of the disease.

The importance of variant reinterpretation in inherited cardiovascular diseases: Establishing the optimal timeframe.

Inherited cardiovascular diseases are rare diseases that are difficult to diagnose by non-expert professionals. Genetic analyses play a key role in the diagnosis of these diseases, in which the identification of a pathogenic genetic variant is often a diagnostic criterion. Therefore, genetic variant classification and routine reinterpretation as data become available represent one of the main challenges associated with genetic analyses. Using the genetic variants identified in an inherited cardiovascular diseases unit during a 10-year period, the objectives of this study were: 1) to evaluate the impact of genetic variant reinterpretation, 2) to compare the reclassification rates between different cohorts of cardiac channelopathies and cardiomyopathies, and 3) to establish the most appropriate periodicity for genetic variant reinterpretation. All the evaluated cohorts (full cohort of inherited cardiovascular diseases, cardiomyopathies, cardiac channelopathies, hypertrophic cardiomyopathy, dilated cardiomyopathy, arrhythmogenic cardiomyopathy, Brugada syndrome, long QT syndrome and catecholaminergic polymorphic ventricular tachycardia) showed reclassification rates above 25%, showing even higher reclassification rates when there is definitive evidence of the association between the gene and the disease in the cardiac channelopathies. Evaluation of genetic variant reclassification rates based on the year of the initial classification showed that the most appropriate frequency for the reinterpretation would be 2 years, with the possibility of a more frequent reinterpretation if deemed convenient. To keep genetic variant classifications up to date, genetic counsellors play a critical role in the reinterpretation process, providing clinical evidence that genetic diagnostic laboratories often do not have at their disposal and communicating changes in classification and the potential implications of these reclassifications to patients and relatives.

A missense mutation in the sodium channel ß2 subunit reveals SCN2B as a new candidate gene for Brugada syndrome.

Brugada Syndrome (BrS) is a familial disease associated with sudden cardiac death. A 20%-25% of BrS patients carry genetic defects that cause loss-of-function of the voltage-gated cardiac sodium channel. Thus, 70%-75% of patients remain without a genetic diagnosis. In this work, we identified a novel missense mutation (p.Asp211Gly) in the sodium ß2 subunit encoded by SCN2B, in a woman diagnosed with BrS. We studied the sodium current (INa ) from cells coexpressing Nav 1.5 and wild-type (ß2WT) or mutant (ß2D211G) ß2 subunits. Our electrophysiological analysis showed a 39.4% reduction in INa density when Nav 1.5 was coexpressed with the ß2D211G. Single channel analysis showed that the mutation did not affect the Nav 1.5 unitary channel conductance. Instead, protein membrane detection experiments suggested that ß2D211G decreases Nav 1.5 cell surface expression. The effect of the mutant ß2 subunit on the INa strongly suggests that SCN2B is a new candidate gene associated with BrS.

Genetics of sudden cardiac death in children and young athletes.

Sudden cardiac death is a rare but socially devastating event. The most common causes of sudden cardiac death are congenital electrical disorders and structural heart diseases. The majority of these diseases have an incomplete penetrance and variable expression; therefore, patients may be unaware of their illness. In several cases, physical activity can be the trigger for sudden cardiac death as first symptom. Our purpose is to review the causes of sudden cardiac death in sportive children and young adults and its genetic background. Symptomatic individuals often receive an implantable cardioverter-defibrillator, the preventive treatment for sudden cardiac death in most of cases due to channelopathies, which can become a challenging option in young and active patients. The identification of one of these diseases in asymptomatic patients has similarly a great impact on their everyday life, especially on their ability to undertake competitive physical activities, and the requirement of prophylactic treatment. We review main causes of sudden cardiac death in relation to its genetics and diagnostic work-up