Humans ; Mutation, Missense ; KCNQ1 Potassium Channel/genetics* ; Long QT Syndrome/genetics* ; Phenotype ; Mutation ; Pedigree

Humans ; Diagnosis, Differential ; Long QT Syndrome/genetics* ; Syncope/diagnosis* ; Epilepsy/diagnosis* ; Electrocardiography

Humans ; Mutation, Missense ; KCNQ1 Potassium Channel/genetics* ; Long QT Syndrome/genetics* ; Phenotype ; Mutation ; Pedigree

The human ether-a-go-go related gene (HERG) encodes the α -subunit of the rapid component of the delayed rectifier K(+) channel, which is essential for the third repolarization of the action potential of human myocardial cells. Mutations of the HERG gene can cause type II hereditary long QT syndrome (LQT2), characterized by prolongation of the QT interval, abnormal T wave, torsade de pointes, syncope and sudden cardiac death. So far more than 300 HERG mutations have been identified, the majority of which can cause LQT2 due to HERG protein trafficking defect. It has been reported that certain drugs can induce acquired long QT syndrome through directly blocking the pore and/or affecting the HERG trafficking. The trafficking defects and K(+) currents can be restored with low temperature and certain drugs. However, the mechanisms underlying defective trafficking caused by HERG mutations and the inhibition/restoration of HERG trafficking by drugs are still unknown. This review summarizes the current understanding of the molecular mechanisms including HERG trafficking under physiological and pathological conditions, and the effects of drugs on the HERG trafficking, in order to provide theoretical evidence for the diagnosis and treatment of long QT syndrome.
Animals ; ERG1 Potassium Channel ; Ether-A-Go-Go Potassium Channels ; genetics ; metabolism ; Humans ; Long QT Syndrome ; genetics ; metabolism ; physiopathology ; Protein Transport

Channelopathies are a heterogeneous group of disorders resulting from the dysfunction of ion channels located in the membranes of all cells and many cellular organelles. These include diseases of the nervous system (e.g., generalized epilepsy with febrile seizures plus, familial hemiplegic migraine, episodic ataxia, and hyperkalemic and hypokalemic periodic paralysis), the cardiovascular system (e.g., long QT syndrome, short QT syndrome, Brugada syndrome, and catecholaminergic polymorphic ventricular tachycardia), the respiratory system (e.g., cystic fibrosis), the endocrine system (e.g., neonatal diabetes mellitus, familial hyperinsulinemic hypoglycemia, thyrotoxic hypokalemic periodic paralysis, and familial hyperaldosteronism), the urinary system (e.g., Bartter syndrome, nephrogenic diabetes insipidus, autosomal-dominant polycystic kidney disease, and hypomagnesemia with secondary hypocalcemia), and the immune system (e.g., myasthenia gravis, neuromyelitis optica, Isaac syndrome, and anti-NMDA [N-methyl-D-aspartate] receptor encephalitis). The field of channelopathies is expanding rapidly, as is the utility of molecular-genetic and electrophysiological studies. This review provides a brief overview and update of channelopathies, with a focus on recent advances in the pathophysiological mechanisms that may help clinicians better understand, diagnose, and develop treatments for these diseases.
Ataxia ; Bartter Syndrome ; Brugada Syndrome ; Cardiovascular System ; Channelopathies* ; Diabetes Insipidus, Nephrogenic ; Diabetes Mellitus ; Endocrine System ; Epilepsy, Generalized ; Genetics ; Hypoglycemia ; Hypokalemic Periodic Paralysis ; Immune System ; Ion Channels ; Isaacs Syndrome ; Long QT Syndrome ; Membranes ; Migraine with Aura ; Myasthenia Gravis ; Nervous System ; Neuromyelitis Optica ; Organelles ; Polycystic Kidney Diseases ; Respiratory System ; Seizures, Febrile

BACKGROUNDCongenital long QT syndrome (LQTS) is an ion channelopathy associated with genetic mutations. It is well known that most LQTS patients (91%) have a single mutation. The purpose of this study was to investigate the clinical characteristics of congenital LQTS patients with bigenic mutations in Taiwan, China.

METHODSCongenital LQTS patients were recruited consecutively at Taiwan University Hospital in Taiwan from 2003 to 2009. The diagnosis of LQTS was defined by an LQTS Schwartz score greater than 4. Mutation screening in KCNQ1, KCNH2, KCNE1, and SCN5A was performed using direct sequencing.

RESULTSThree of 16 LQTS patients (18.7%) were identified with bigenic mutations. One patient had missense mutations in KCNQ1 and KCNH2, the second in KCNQ1 and KCNE1, and the third in KCNH2 and SCN5A. The mean age at onset of LQTS for patients with bigenic mutations was (17 ± 3) years, and all of these patients were female. Two of them experienced seizure and one presented with syncope, although one of them had a family history of syncope. The mean QTc interval was (515 ± 17) ms, similar to those with single mutation or SNPs ((536 ± 74) ms, P = 0.63). Compared to those LQTS patients with single mutation or SNPs, a significantly higher percentage of LQTS patients with bigenic mutations presented with seizure and were younger at onset of the first index event (P = 0.03 and 0.001, respectively), but lower percentage of them presented with sudden cardiac death (P = 0.03).

CONCLUSIONSAlthough the percentage of bigenic mutations in LQTS is less than 10% in Caucasian populations, we identified 3 of 16 LQTS patients (18.7%, 95% confidence interval: 0.04-0.46) with bigenic mutations in Taiwan. However, the severity of their clinical presentations was not higher than those patients with single mutation or SNPs.

Adolescent ; Adult ; Aged ; ERG1 Potassium Channel ; Ether-A-Go-Go Potassium Channels ; genetics ; Female ; Genotype ; Humans ; KCNQ1 Potassium Channel ; genetics ; Long QT Syndrome ; genetics ; pathology ; Male ; Middle Aged ; Mutation ; NAV1.5 Voltage-Gated Sodium Channel ; genetics ; Polymorphism, Single Nucleotide ; genetics ; Potassium Channels, Voltage-Gated ; genetics ; Young Adult

Timothy syndrome, long QT syndrome type 8, is highly malignant with ventricular tachyarrhythmia. A 30-month-old boy had sudden cardiac arrest during anesthesia induction before plastic surgery for bilateral cutaneous syndactyly. After successful resuscitation, prolonged QT interval (QTc, 0.58-0.60 sec) and T-wave alternans were found in his electrocardiogram. Starting beta-blocker to prevent further tachycardia and collapse event, then there were no more arrhythmic events. The genes KCNQ1, KCNH2, KCNE1 and 2, and SCN5A were negative for long QT syndrome. The mutation p.Gly406Arg was confirmed in CACNA1C, which maintains L-type calcium channel depolarization in the heart and other systems.
Anesthesia/*adverse effects ; Calcium Channels, L-Type/*genetics ; Death, Sudden, Cardiac/*etiology ; Electroencephalography ; Humans ; Infant ; Long QT Syndrome/*genetics ; Magnetic Resonance Imaging ; Male ; Methyl Ethers/adverse effects ; Nitric Oxide/adverse effects ; Polymorphism, Single Nucleotide ; Sequence Analysis, DNA ; Surgery, Plastic ; Syndactyly/diagnosis/*genetics/surgery

Arrhythmias, Cardiac ; diagnosis ; genetics ; pathology ; Brugada Syndrome ; diagnosis ; genetics ; pathology ; Channelopathies ; diagnosis ; genetics ; pathology ; DNA Mutational Analysis ; Electrocardiography ; Genetic Testing ; Heart Conduction System ; physiopathology ; Humans ; Infant ; Long QT Syndrome ; diagnosis ; genetics ; pathology ; Muscle Proteins ; genetics ; Mutation ; NAV1.5 Voltage-Gated Sodium Channel ; genetics ; Sodium Channels ; genetics ; Sudden Infant Death ; etiology

Patients with long QT syndrome can sometimes present with a ventricular fibrillation (VF) storm. Catheter ablation of culprit premature ventricular complexes responsible for the triggering of the VF episodes may be required in rare cases of electrical storm that do not respond to conventional measures, and this can be life-saving. We describe a case of emergency catheter ablation in a young woman with a normal corrected QT interval, who presented with malignant VF storm for the first time. We also discuss the diagnostic and management challenges involved, as well as the value of genetic testing in refining the diagnosis.
Cardiology ; Catheter Ablation ; methods ; Electrocardiography ; methods ; Female ; Heart Arrest ; genetics ; therapy ; Heterozygote ; Humans ; Long QT Syndrome ; genetics ; Tachycardia, Ventricular ; therapy ; Treatment Outcome ; Ventricular Fibrillation ; therapy ; Ventricular Premature Complexes ; genetics ; therapy ; Young Adult

Long QT syndrome (LQTs) is an uncommon genetic disease causing sudden cardiac death with Torsade de Pointes (TdP). The first line drug treatment has been known to be beta-blocker. We encountered a 15-year-old female student with LQTs who had prolonged QTc and multiple episodes of syncope or agonal respiration during sleep. Although her T wave morphology in surface electrocardiography resembled LQTs type 1, her clinical presentation was unusual. During the epinephrine test, TdP was aggravated during beta-blocker medication, but alleviated by sodium channel blocker (mexiletine). Therefore, she underwent implantable cardioverter defibrillator implantation.
Adolescent ; Adrenergic beta-Antagonists/*adverse effects/therapeutic use ; Defibrillators, Implantable ; Diagnosis, Differential ; Diagnostic Techniques, Cardiovascular ; Epinephrine/*diagnostic use ; Female ; Humans ; Long QT Syndrome/classification/*diagnosis/genetics/therapy ; Mexiletine/*therapeutic use ; Pedigree ; *Syncope