Genetic testing for long QT syndrome and the category of cardiac ion channelopathies

Clinical Heterogeneity in Patients with Long QT Syndrome and Segregation of Single Nucleotide Variants and Clinical Symptoms in 17 Affected Families

Introduction

Long QT syndrome (LQTS) is a disorder of ventricular myocardial repolarization characterized by a prolonged QT interval on the electrocardiogram. It increases the risk of ventricular arrhythmias, which can cause syncope or sudden cardiac death. In this study, we study the genotype-phenotype relationships of patients referred to us with suspected arrhythmia syndrome.

Methods

Seventeen cases and their twenty relatives were evaluated. Next-generation sequencing analysis was performed for 17 LQTS-related genes.

Results

We detected seventeen single nucleotide variants (SNVs) with potential pathogenic significance in 26 of the 36 subjects analyzed. KCNH2 c.172G>A, KCNQ1 c.1768G>A, ANK2 c.4666A>T, c.1484_1485delCT, KCNH2 c.1888G>A were reported as pathogenic or likely pathogenic in HGMD variant classification database.

Conclusion

Current study pointed out that early diagnosis can be life-saving for patients and their families by taking family history and detailed examination. Also, we highlight the clinical heterogeneity of arrhythmia syndrome through a patient with a dual phenotype.

[Congenital long QT syndrome]

Congenital long QT syndrome (LQTS) represents a group of heart diseases of genetic origin characterized by prolongation of the QT interval and an abnormal T wave on the electrocardiogram (ECG). They can have a dominant or recessive expression, the latter associated with sensorineural deafness. In both cases, its clinical presentation is associated with recurrent syncope and sudden death as a consequence of ventricular tachycardia, specifically Torsades de Pointes. Currently they are classified according to the specific genetic defect, being able to compromise around 16 genes and almost 2000 mutations. It should be suspected in individuals with related symptoms, electrocardiographic findings, and family history. Management is based on the reduction or elimination of symptoms, and concomitantly the prevention of sudden death (SD), in those children with congenital deafness, the management requires the application of the otolaryngologist specialist's own measures. The cardiovascular management implies the modification of lifestyles, mainly the prohibition of competitive sports, including swimming, avoiding exposure to loud sounds or triggers. The medications used include beta-blockers, and more rarely flecainide, ranozaline, and verapamil; invasive management consists of the implantation of a cardioverter defibrillator or even left sympathetic denervation, each with its own risks and benefits. In any of the cases, we must avoid the circumstances that increase the QT interval, as well as carry out the appropriate analysis of the benefits and risks of each possible invasive measure.

Treadmill exercise testing improves diagnostic accuracy in children with concealed congenital long QT syndrome

BACKGROUND

Resting electrocardiogram (ECG) identification of long QT syndrome (LQTS) has limitations. Uncertainty exists on how to classify patients with borderline prolonged QT intervals. We tested if exercise testing could help serve to guide which children with borderline prolonged QT intervals may be gene positive for LQTS.

METHODS

Pediatric patients (n = 139) were divided into three groups: Controls (n = 76), gene positive LQTS with borderline QTc (n = 21), and gene negative patients with borderline QTc (n = 42). Borderline QTc was defined between 440-470 (male) and 440-480 (female) ms. ECGs were recorded supine, sitting, and standing. Patients then underwent treadmill stress testing with Bruce protocol followed by a 9-minute recovery phase.

RESULTS

Supine resting QTc, age, and Schwartz score for the three groups were: (a) gene positive: 446 ± 23 ms, 12.4 ± 3.4 years old, 3.2 ± 1.8; (b) gene negative: 445 ± 20 ms, 12.1 ± 2 years old, 2.0 ± 1.2; and (c) control: 400 ± 24 ms, 15.0 ± 3 years old. The three groups could be differentiated by their QTc response at two time points: standing and recovery phase at 6 minutes. Standing QTc ≥460 ms differentiated borderline prolonged QTc patients (gene positive and gene negative) from controls. Late recovery QTc ≥480 ms distinguished gene positive from gene negative patients.

CONCLUSION

Exercise stress testing can be useful to identify children who are gene positive borderline LQTS from a normal population and gene negative borderline QTc children, allowing for selective gene testing in a higher risk group of patients with borderline QTc intervals and intermediate Schwartz scores.

The Multifaced Perspectives of Genetic Testing in Pediatric Cardiomyopathies and Channelopathies

Pediatric inherited cardiomyopathies (CMPs) and channelopathies (CNPs) remain important causes of death in this population, therefore, there is a need for prompt diagnosis and tailored treatment. Conventional evaluation fails to establish the diagnosis of pediatric CMPs and CNPs in a significant proportion, prompting further, more complex testing to make a diagnosis that could influence the implementation of lifesaving strategies. Genetic testing in CMPs and CNPs may help unveil the underlying cause, but needs to be carried out with caution given the lack of uniform recommendations in guidelines about the precise time to start the genetic evaluation or the type of targeted testing or whole-genome sequencing. A very diverse etiology and the scarce number of randomized studies of pediatric CMPs and CNPs make genetic testing of these maladies far more particular than their adult counterpart. The genetic diagnosis is even more puzzling if the psychological impact point of view is taken into account. This review aims to put together different perspectives, state-of-the art recommendations-synthetizing the major indications from European and American guidelines-and psychosocial outlooks to construct a comprehensive genetic assessment of pediatric CMPs and CNPs.

Molecular and tissue mechanisms of catecholaminergic polymorphic ventricular tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a stress-induced cardiac channelopathy that has a high mortality in untreated patients. Our understanding has grown tremendously since CPVT was first described as a clinical syndrome in 1995. It is now established that the deadly arrhythmias are caused by unregulated 'pathological' calcium release from the sarcoplasmic reticulum (SR), the major calcium storage organelle in striated muscle. Important questions remain regarding the molecular mechanisms that are responsible for the pathological calcium release, regarding the tissue origin of the arrhythmic beats that initiate ventricular tachycardia, and regarding optimal therapeutic approaches. At present, mutations in six genes involved in SR calcium release have been identified as the genetic cause of CPVT: RYR2 (encoding ryanodine receptor calcium release channel), CASQ2 (encoding cardiac calsequestrin), TRDN (encoding triadin), CALM1, CALM2 and CALM3 (encoding identical calmodulin protein). Here, we review each CPVT subtype and how CPVT mutations alter protein function, RyR2 calcium release channel regulation, and cellular calcium handling. We then discuss research and hypotheses surrounding the tissue mechanisms underlying CPVT, such as the pathophysiological role of sinus node dysfunction in CPVT, and whether the arrhythmogenic beats originate from the conduction system or the ventricular working myocardium. Finally, we review the treatments that are available for patients with CPVT, their efficacy, and how therapy could be improved in the future.

Fetal arrhythmias: Surveillance and management

Fetal arrhythmias warrant sophisticated surveillance and management, especially for the high-risk pregnancies. Clinically, fetal arrhythmias can be categorized into 3 types: premature contractions, tachyarrhythmias, and bradyarrhythmias. Fetal arrhythmias include electrocardiography, cardiotocography, echocardiography and magnetocardiography. Oxygen saturation monitoring can be an effective way of fetal surveillance for congenital complete AV block or SVT during labor. Genetic surveillance of fetal arrhythmias may facilitate the understanding of the mechanisms of the arrhythmias and provide theoretical basis for diagnosis and treatment. For fetal benign arrhythmias, usually no treatment but a close follow-up is need, while persistant fetal arrhythmias with congestive heart dysfunction or hydrops fetalis, intrauterine or postnatal treatments are required. The prognoses of fetal arrhythmias depend on the type and severity of fetal arrhythmias and the associated fetal conditions. Responses of fetal arrhythmias to individual treatments and clinical schemes are heterogeneous, and the prognoses are poor particularly under such circumstances.

A Systematic Review on the Cost-Effectiveness of Genetic and Electrocardiogram Testing for Long QT Syndrome in Infants and Young Adults

BACKGROUND

Recent improvements in the identification of the genetic basis of long QT syndrome (LQTS) have led to significant changes in the diagnosis and management of this life-threatening condition. Genetic and electrocardiogram (ECG) tests are the most relevant examples among testing strategies for LQTS, yet their cost-effectiveness remains controversial.

OBJECTIVE

The aim of this work was to review the available evidence on the cost-effectiveness of genetic and ECG testing strategies for the diagnosis of LQTS.

METHODS

We performed a systematic review of the literature on the cost-effectiveness of genetic and ECG screening strategies for the early detection of LQTS using MEDLINE, EMBASE, and CRD databases between 2000 and 2013. A weighted version of Drummond checklist was instrumental in further assessing the quality of the included studies.

RESULTS

We identified four eligible articles. Among them, genetic testing in the early detection of LQTS was cost-effective compared with no testing in symptomatic cases and not cost-effective when compared with watchful waiting in asymptomatic first-degree relatives of patients with established LQTS although it reached cost-effectiveness in higher risk subgroups, whereas ECG testing in neonates was highly cost-effective when compared with any screening strategy.

CONCLUSIONS

LQTS profiling and patients' stratification have the potential to improve the disease management. Because of the limited current knowledge in this field, the present review recommends to perform further cost-effectiveness evaluations of the genetic and ECG screening alternatives, especially within European health care systems, which are still not available in the literature on genetic testing.

Provision of cardiovascular genetic counseling services: current practice and future directions

Cardiovascular genetic counseling has emerged as a specialty critical to the care of patients with heritable cardiovascular disease. Current strategies to meet the growing demand are not clear. We sought to characterize practice patterns of cardiac genetic counseling by developing a novel survey distributed to the National Society of Genetic Counselors (NSGC) Listserv to assess clinical practice, cardiovascular training, and education. Descriptive statistics were used to summarize clinical practice; Fisher's exact test and the Cochran-Armitage trend test were used to compare the practice of cardiovascular genetic counselors (CVGCs) to those who did not identify cardiology as a specialty (non-CVGCs). A total of 153 individuals completed the survey. Of the 105 participants who reported seeing a cardiac genetics patient, 42 (40%) identified themselves as a CVGC. The most common conditions for which genetic counseling was provided were hypertrophic cardiomyopathy (HCM) (71% of participants), dilated cardiomyopathy (DCM) (61%), long QT syndrome (LQTS) (56%), and genetic syndromes with cardiovascular disease (55%). CVGCs were significantly more confident than non-CVGCs in providing genetic counseling for seven cardiovascular diseases (2.3 × 10(-6) ≤ p ≤ 0.021). Eighty-six percent of genetic counselors sought additional education related to cardiovascular genetics and listed online courses as the most desirable method of learning. These data suggest a growing interest in cardiovascular genetic counseling and need for additional training resources among the NSGC membership.