Antonio Oliva

Loss-of-Function Mutations in the Cardiac Calcium Channel Underlie a New Clinical Entity Characterized by ST-Segment Elevation, Short QT Intervals, and Sudden Cardiac Death

Background— Cardiac ion channelopathies are responsible for an ever-increasing number and diversity of familial cardiac arrhythmia syndromes. We describe a new clinical entity that consists of an ST-segment elevation in the right precordial ECG leads, a shorter-than-normal QT interval, and a history of sudden cardiac death. Methods and Results— Eighty-two consecutive probands with Brugada syndrome were screened for ion channel gene mutations with direct sequencing. Site-directed mutagenesis was performed, and CHO-K1 cells were cotransfected with cDNAs encoding wild-type or mutant CACNB2b (Cav&bgr;2b), CACNA2D1 (Cav&agr;2&dgr;1), and CACNA1C tagged with enhanced yellow fluorescent protein (Cav1.2). Whole-cell patch-clamp studies were performed after 48 to 72 hours. Three probands displaying ST-segment elevation and corrected QT intervals ≤360 ms had mutations in genes encoding the cardiac L-type calcium channel. Corrected QT ranged from 330 to 370 ms among probands and clinically affected family members. Rate adaptation of QT interval was reduced. Quinidine normalized the QT interval and prevented stimulation-induced ventricular tachycardia. Genetic and heterologous expression studies revealed loss-of-function missense mutations in CACNA1C (A39V and G490R) and CACNB2 (S481L) encoding the &agr;1- and &bgr;2b-subunits of the L-type calcium channel. Confocal microscopy revealed a defect in trafficking of A39V Cav1.2 channels but normal trafficking of channels containing G490R Cav1.2 or S481L Cav&bgr;2b-subunits. Conclusions— This is the first report of loss-of-function mutations in genes encoding the cardiac L-type calcium channel to be associated with a familial sudden cardiac death syndrome in which a Brugada syndrome phenotype is combined with shorter-than-normal QT intervals.

Value of electrocardiographic parameters and ajmaline test in the diagnosis of Brugada syndrome caused by SCN5A mutations.

Background—The Brugada syndrome is an arrhythmogenic disease caused in part by mutations in the cardiac sodium channel gene, SCN5A. The electrocardiographic pattern characteristic of the syndrome is dynamic and is often absent in affected individuals. Sodium channel blockers are effective in unmasking carriers of the disease. However, the value of the test remains controversial. Methods and Results—We studied 147 individuals representing 4 large families with SCN5A mutations. Of these, 104 were determined to be at possible risk for Brugada syndrome and underwent both electrocardiographic and genetic evaluation. Twenty-four individuals displayed an ECG diagnostic of Brugada syndrome at baseline. Of the remaining, 71 received intravenous ajmaline. Of the 35 genetic carriers who received ajmaline, 28 had a positive test and 7 a negative ajmaline test. The sensitivity, specificity, and positive and negative predictive values of the drug challenge were 80% (28:35), 94.4% (34:36), 93.3% (28:30), and 82.9% (34:41), respectively. Penetrance of the disease phenotype increased from 32.7% to 78.6% with the use of sodium channel blockers. In the absence of ST-segment elevation under baseline conditions, a prolonged P-R interval, but not incomplete right bundle-branch block or early repolarization patterns, indicates a high probability of an SCN5A mutation carrier. Conclusions—In families with Brugada syndrome, the data suggest that ajmaline testing is valuable in the diagnosis of SCN5A carriers. In the absence of ST-segment elevation at baseline, family members with first-degree atrioventricular block should be suspected of carrying the mutation. An ajmaline test is often the key to making the proper diagnosis in these patients.

Amplification of spatial dispersion of repolarization underlies sudden cardiac death associated with catecholaminergic polymorphic VT, long QT, short QT and Brugada syndromes.

This review examines the hypothesis that amplification of spatial dispersion of repolarization in the form of transmural dispersion of repolarization (TDR) underlies the development of life‐threatening ventricular arrhythmias associated with inherited ion channelopathies including the long QT, short QT and Brugada syndromes as well as catecholaminergic polymorphic ventricular tachycardia. In the long QT syndrome, amplification of TDR is often secondary to preferential prolongation of the action potential duration (APD) of M cells, whereas in the Brugada syndrome, it is thought to be because of selective abbreviation of the APD of right ventricular epicardium. Preferential abbreviation of APD of either endocardium or epicardium appears to be responsible for amplification of TDR in the short QT syndrome. In catecholaminergic polymorphic VT, the reversal of the direction of activation of the ventricular wall is responsible for the increase in TDR. In conclusion, the long QT, short QT, Brugada and catecholaminergic VT syndromes are pathologies with very different phenotypes and aetiologies, but which share a common final pathway in causing sudden death.

State of the art in forensic investigation of sudden cardiac death.

The sudden death of a young person is a devastating event for both the family and community. Over the last decade, significant advances have been made in understanding both the clinical and genetic basis of sudden cardiac death. Many of the causes of sudden death are due to genetic heart disorders, which can lead to both structural (eg, hypertrophic cardiomyopathy) and arrhythmogenic abnormalities (eg, familial long QT syndrome, Brugada syndrome). Most commonly, sudden cardiac death can be the first presentation of an underlying heart problem, leaving the family at a loss as to why an otherwise healthy young person has died. Not only is this a tragic event for those involved, but it also presents a great challenge to the forensic pathologist involved in the management of the surviving family members. Evaluation of families requires a multidisciplinary approach, which should include cardiologists, a clinical geneticist, a genetic counselor, and the forensic pathologist directly involved in the sudden death case. This multifaceted cardiac genetic service is crucial in the evaluation and management of the clinical, genetic, psychological, and social complexities observed in families in which there has been a young sudden cardiac death. The present study will address the spectrum of structural substrates of cardiac sudden death with particular emphasis given to the possible role of forensic molecular biology techniques in identifying subtle or even merely functional disorders accounting for electrical instability.

Coexistence of epilepsy and Brugada syndrome in a family with SCN5A mutation

Cardiac arrhythmias are associated with abnormal channel function due to mutations in ion channel genes. Epilepsy is a disorder of neuronal function also involving abnormal channel function. It is increasingly demonstrated that the etiologies of long QT syndrome and epilepsy may partly overlap. However, only a few genetic studies have addressed a possible link between cardiac and neural channelopathies. We describe a family showing the association between Brugada syndrome and epilepsy in which a known mutation in the SCN5A gene (p.W1095X, c.3284G>A) was identified. We suggest that this mutation can be responsible for cardiac and brain involvement, probably at different developmental age in the same individual. This observation confirms the possibility that SCN5A mutations may confer susceptibility for recurrent seizure activity, supporting the emerging concept of a genetically determined cardiocerebral channelopathy.

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.

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.

Molecular pathology in forensic medicine —Introduction

Techniques of molecular biology have improved diagnostic sensitivity, accuracy and validity in forensic medicine very much, especially in the field of identification (paternity testing, stain analysis). Since more than 10 years these techniques - meanwhile well established in clinical disciplines - are used also for other applications in forensic medicine: determination of cause and manner of death, tissue identification by mRNA and microRNA, examination of gene expression levels (survival time, time since death, cause of death), toxicogenetics.

Torsades de pointes following acute myocardial infarction: evidence for a deadly link with a common genetic variant

BACKGROUND Although QT prolongation following myocardial infarction (MI) is generally moderate, cases with marked QT prolongation leading to life-threatening torsades de pointes (TdP) have been described. OBJECTIVE To investigate the genetic substrate of this phenomenon. METHODS We studied 13 patients who developed TdP in the subacute phase of MI (2-11 days) and a group of 133 ethnically matched controls with uncomplicated MI. Long QT syndrome genes and the KCNH2-K897T polymorphism were screened by using denaturing high-performance liquid chromatography plus direct sequencing and a specific TaqMan assay, respectively. RESULTS Two of the 13 patients (15%) who presented with QT prolongation and TdP were found to carry long QT syndrome mutations (KCNH2-R744X and SCN5A-E446K). Nine of the remaining 11 patients (82%) carried the KCNH2-K897T polymorphism, which was present in 35% of the controls (P = .0035). Thus, patients with an acute MI carrying the KCNH2-K897T polymorphism had an 8-fold greater risk of experiencing TdP compared with controls (95% confidence interval = 2-40). CONCLUSIONS Our data suggest that the common K897T polymorphism is associated with an increased risk of TdP developing in the subacute phase of MI. Our findings support the concept that the electrical remodeling associated with this healing phase of MI may unmask a genetic substrate predisposing to a time-limited development of life-threatening arrhythmias. They also provide the first line of evidence in support of the hypothesis that a common polymorphism, previously described as a modifier of the severity of LQTS, may increase the risk of life-threatening arrhythmias in a much more prevalent cardiac disease such as myocardial infarction.

Analysis of mRNA from human heart tissue and putative applications in forensic molecular pathology

The usefulness of post-mortem mRNA analysis and its potential applications in forensic casework is currently of interest, especially because of several factors affecting the quality of RNA samples that are not practically predictable. In fact, post-mortem RNA degradation is a complex process that has not been studied systematically. The purpose of this work is to establish whether RNA analysis from post-mortem heart tissue could be used as a forensic tool to investigate the cause of death, with special regard to those cases where a cardiac disease is suspected as the manner of death. We analysed heart tissue from 16 individuals with normal cardiac function, 9 with long post-mortem intervals (L-PMI) and 7 from organ donors with very short PMIs (S-PMIs). Right ventricle tissue was homogenised, and the RNA was isolated and reverse transcribed. The resulting cDNA was used in real-time PCR reactions to quantify the gene expression of beta-glucuronidase (GUSB), Nitric Oxide Synthase 3 (NOS3), Collagen 1 (COL1A1) and Collagen 3 (COL3A1). The percentage of samples with high-quality RNA was higher in samples with S-PMI (7 out of 7) than in samples with L-PMI (4 out of 9, p<0.05). No differences in PMI time or cause of exitus were found between samples with degraded or non-degraded RNA in the L-PMI group. When comparing mRNA levels in samples with non-degraded RNA, we found similar values between the L-PMI and S-PMI groups for GUSB, COL1A1 and COL3A1. The NOS3 gene expression in the L-PMI subgroup was less than half that in the S-PMI. These results suggest that high-quality mRNA can be extracted from post-mortem human hearts only in some cases. Moreover, our data show that mRNA levels are independent from the PMI, even though there are mRNAs in which the expression levels are very susceptible to ischemia times. Clear knowledge about the relationship between mRNA integrity and expression and PMI could allow the use of several mRNAs as forensic tools to contribute to the determination of the cause of death with special regard to cardiovascular diseases.