KCNH2 variants in a family with epilepsy and long QT syndrome: A case report and literature review

OBJECTIVE

Genes associated with Long QT syndromes (LQTS), such as KCNQ1, KCNH2, and SCN5A, are common causes of epilepsy. The Arg 744* variant of KCNH2 has been previously reported in people with epilepsy or LQTS, but none of these patients were reported to simultaneously suffer from epilepsy and LQTS. Herein, we report the case of a family with epilepsy and cardiac disorders.

METHOD

The proband, a 25-year-old woman, with a family history of epilepsy and LQTS was followed at West China Hospital. The proband experienced her first seizure at the age of seven. Video electroencephalograms (vEEGs) showed epileptic discharges. Her 24-h dynamic electrocardiograms 2 (ECGs) showed QTc prolongation. The proband's mother, who is 50 years old, had her first generalized tonic-clonic seizure (GTCS) at the age of 18 years old. After she gave birth at the age of 25, the frequency of seizures increased, so antiepileptic therapy was initiated. When she was 28 years old, she complained of palpitations and syncope for the first time, and QTc prolongation was detected on her 24-h dynamic ECGs. The proband's grandmother also had complaints of palpitations and syncope at the age of 73. Her 24-h dynamic ECGs indicated supraventricular arrhythmia, with the lowest heart rate being 41 bpm, so she agreed to a pacemaker. Considering the young patient's family history, blood samples of the patient and her parents were collected for genetic analysis.

RESULTS

A heterozygous variant of KCNH2 [c.2230 (exon9) C>T, p. Arg744Ter, 416, NM_000238, rs189014161] was found in the proband and her mother. According to the guidelines of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology, we classified the KCNH2 variant as pathogenic.

SIGNIFICANCE

This study expands the clinical phenotype of the Arg 744* KCNH2 pathogenic variant. In the context of channelopathies, because of the genetic susceptibility of the brain and the heart, the risk of comorbidity should be considered. This also indicates the importance of precise antiepileptic drug (AED) management and regular ECG monitoring for patients with channelopathies.

Identification of a novel pathogenic variant in KCNH2 in an Iranian family with long QT syndrome 2 by whole-exome sequencing

Background

Long QT syndrome (LQTS) is a lethal cardiac condition. However, the clinical implementation of genetic testing has now made LQTS eminently treatable. Next-generation sequencing has remarkable potential for both clinical diagnostics and research of LQTS. Here, we investigated the genetic etiology in an LQTS-suspected Iranian pedigree by whole-exome sequencing and collected all KCNH2 variants with consensus based on publications.

Methods

WES was performed on the proband of this pedigree to reveal the underlying cause of sudden cardiac death (SCD). The variant found was validated and segregated by polymerase chain reaction and Sanger sequencing. Based on the literature review, KCNH2 variants were retrospectively analyzed to identify pathogenic variants, likely pathogenic variants, and variants of uncertain significance by using different prediction tools.

Results

WES identified an autosomal dominant nonsense variant, c.1425C>A: p.Tyr475Ter, in the KCNH2 gene, which appeared to be the most likely cause of LQTS in this pedigree. Moreover, our comprehensive literature review yielded 511 KCNH2 variants in association with the LQTS phenotype, with c.3002G>A (CADD Phred=49) being the most pathogenic variant.

Conclusions

Variants in the KCNH2 gene are considered a major cause of LQTS worldwide. The detected c.1425C>A is a novel variant to be reported from Iran for the first time. This result indicates the importance of KCNH2 screening in a pedigree with SCD cases.

A need for exhaustive and standardized characterization of ion channels activity. The case of KV11.1

hERG, the pore-forming subunit of the rapid component of the delayed rectifier K⁺ current, plays a key role in ventricular repolarization. Mutations in the KCNH2 gene encoding hERG are associated with several cardiac rhythmic disorders, mainly the Long QT syndrome (LQTS) characterized by prolonged ventricular repolarization, leading to ventricular tachyarrhythmias, sometimes progressing to ventricular fibrillation and sudden death. Over the past few years, the emergence of next-generation sequencing has revealed an increasing number of genetic variants including KCNH2 variants. However, the potential pathogenicity of the majority of the variants remains unknown, thus classifying them as variants of uncertain significance or VUS. With diseases such as LQTS being associated with sudden death, identifying patients at risk by determining the variant pathogenicity, is crucial. The purpose of this review is to describe, on the basis of an exhaustive examination of the 1322 missense variants, the nature of the functional assays undertaken so far and their limitations. A detailed analysis of 38 hERG missense variants identified in Long QT French patients and studied in electrophysiology also underlies the incomplete characterization of the biophysical properties for each variant. These analyses lead to two conclusions: first, the function of many hERG variants has never been looked at and, second, the functional studies done so far are excessively heterogeneous regarding the stimulation protocols, cellular models, experimental temperatures, homozygous and/or the heterozygous condition under study, a context that may lead to conflicting conclusions. The state of the literature emphasizes how necessary and important it is to perform an exhaustive functional characterization of hERG variants and to standardize this effort for meaningful comparison among variants. The review ends with suggestions to create a unique homogeneous protocol that could be shared and adopted among scientists and that would facilitate cardiologists and geneticists in patient counseling and management.

New insights of the role of the KCNH2 gene in schizophrenia: An fMRI case-control study

The KCNH2 gene, encoding for a subunit of a voltage-gated potassium channel, has been identified as a key element of neuronal excitability and a promising novel therapeutic target for schizophrenia (SZ). Nonetheless, evidence highlighting the role of KCNH2 on cognitive and brain activity phenotypes comes mainly from studies based on healthy controls (HC). Therefore, we aimed to study the role of KCNH2 on the brain functional differences between patients with SZ and HC. The fMRI sample comprised 78 HC and 79 patients with SZ (matched for age, sex and premorbid IQ). We studied the effect of the polymorphism KCNH2-rs3800779 on attention and working memory-related brain activity, evaluated through the N-back task, in regions with detected diagnostic differences (regression model, controlled for age, sex and premorbid IQ, FEAT-FSL). We report a significant diagnosis x KCNH2 interaction on brain activity (1-back vs baseline contrast) at the medial superior prefrontal cortex (Zmax=3.55, p = 0.00861). In this region, patients with SZ carrying the risk genotype (AA) show a deactivation failure, while HC depict the opposite pattern towards deactivation. The brain region with significant diagnosis x KCNH2 interaction has been previously associated with SZ. The results of this study, in which the role of KCNH2 on fMRI response is analysed for the first time in patients, suggest that KCNH2 variability contributes to inefficient brain activity modulation during the N-back task in affected subjects. These data may pave the way to further understand how KCNH2 genetic variability is related to the pathophysiological mechanisms underlying schizophrenia.

Anesthetic Care of a Child Harboring the KCNH2 Gene

Epilepsy is a heterogeneous group of disorders characterized by recurrent and generally unprovoked seizures. Genetic mutations may play an important role in the etiology of epilepsy. Over the past few years, genetic mutations in various genes have been identified in patients with epilepsy. One of the more common mutations responsible for seizures involves the KCNH2 gene. The KCNH2 gene encodes the Kv11.1 protein, which involves the pore-forming subunit of a rapidly activating-delayed rectifier potassium channel. This channel plays an essential role in phases 2 and 3 of the cardiac action potential involving cardiac repolarization as well as being expressed in various parts of the central nervous system where it regulates neuronal function. As such, patients presenting with this gene mutation may be at risk not only for seizures, but also abnormalities in cardiac repolarization leading to lethal arrhythmias. We present an 11-year-old girl who required general anesthesia for magnetic resonance imaging as part of her evaluation for non-convulsive status epilepticus. An epilepsy gene panel evaluated revealed a KCNH2 gene mutation. End-organ involvement of KCNH2 gene mutations is presented, previous reports of anesthetic care for these patients are reviewed, and options for anesthetic care are discussed.

A Novel Mutation in the KCNH2 Gene Associatedwith Long QT Syndrome: A Case Report

OBJECTIVE

Long QT syndrome is a cardiovascular disease with a prolonged QT interval.

CASE REPORT

We report a 22-year-old woman presenting with frequent syncopal episodes two months after childbirth. Electrocardiography showed a sinus rhythm, QT interval prolongation, and Torsade de Pointes. Her mother had experienced an episode of syncope, but her father had not. Genetic analyses revealed that a new mutation in the KCNH2 gene, the c.2108dupA mutation (p.H703Qfs*20, exon8, M_000238), was found in the patient and in her mother and sister.

CONCLUSION

The c.2108dupA mutation (p.H703Qfs*20, exon8, M_000238) is the first reported case of a KCNH2 mutation at this site.

Heterogeneous Phenotype of Long QT Syndrome Caused by the KCNH2-H562R Mutation: Importance of Familial Genetic Testing

INTRODUCTION AND OBJECTIVES

Long QT syndrome is an inherited ion channelopathy that leads to syncope and sudden death. Because of the heterogeneous phenotype of this disease, genetic testing is fundamental to detect individuals with concealed long QT syndrome. In this study, we determined the features of a family with 13 carriers of the KCNH2-H562R missense mutation, which affects the pore region of the HERG channel.

METHODS

We identified the KCNH2-H562R mutation in a 65-year-old man with a prolonged QTc interval who had experienced an episode of torsade de pointes. Subsequently, a total of 13 mutation carriers were identified in the family. Carriers (age 48 [26] years; 46% males) underwent clinical evaluation, electrocardiography and echocardiography.

RESULTS

The mean (standard deviation) QTc in carriers was 493 (42) ms (3 [23%] showed normal QTc); 6 (46%) had symptoms (4, syncope; 1, sudden death; 1, aborted sudden death [proband]). While under treatment with beta-blockers, 11 of 12 carriers (92%) remained asymptomatic at 5 years of follow-up (1 patient required left cardiac sympathectomy). The QTc shortening with beta-blockers was 50 (37) ms. There was 1 sudden death in a patient who refused treatment.

CONCLUSIONS

Family study is essential in the interpretation of a genetic testing result. This article describes the heterogeneous and variable phenotype of a large family with the KCNH2-H562R mutation and highlights the role of genetic study for the appropriate identification of at-risk individuals who would benefit from treatment.