A study of the pathogenicity of variants in familial heart disease. The value of cosegregation.

With the development of deep sequencing, a significant proportion of mutations already listed in studies have inconclusive pathogenicity. We aim to establish the proportion of cases in which familial studies are possible and cosegregation analysis is informative. We also compare cosegregation analysis with in silico software and a proposed pathogenicity score. 204 consecutive positive tests were reviewed. 4 different in silico software programs were used. Spaendonck-Zwarts' pathogenicity score was also calculated. A total of 73 of the missense variants could be classified by the score as being likely or definitively pathogenic. A high percentage of nonsense variants were found in desmosomal genes and missense variants in sarcomeric genes. 36.3% of the missense variants in our cohort classified as very likely or definitively pathogenic were novel. Cosegregation analysis was positive in 19.5% and could be discarded in 15.6%. There was a significant discrepancy between the in silico tools used in the setting of inherited heart disease. Multiparametric scoring systems which include cosegregation and functional studies seem to perform better than individual prediction software.

Value of the "Standing Test" in the Diagnosis and Evaluation of Beta-blocker Therapy Response in Long QT Syndrome.

INTRODUCTION AND OBJECTIVES: Patients with congenital long QT syndrome (LQTS) have an abnormal QT adaptation to sudden changes in heart rate provoked by standing. The present study sought to evaluate the standing test in a cohort of LQTS patients and to assess if this QT maladaptation phenomenon is ameliorated by beta-blocker therapy. METHODS: Electrographic assessments were performed at baseline and immediately after standing in 36 LQTS patients (6 LQT1 [17%], 20 LQT2 [56%], 3 LQT7 [8%], 7 unidentified-genotype patients [19%]) and 41 controls. The corrected QT interval (QTc) was measured at baseline (QTcsupine) and immediately after standing (QTcstanding); the QTc change from baseline (ΔQTc) was calculated as QTcstanding - QTcsupine. The test was repeated in 26 patients receiving beta-blocker therapy. RESULTS: Both QTcstanding and ΔQTc were significantly higher in the LQTS group than in controls (QTcstanding, 528 ± 46ms vs 420 ± 15ms, P < .0001; ΔQTc, 78 ± 40ms vs 8 ± 13ms, P < .0001). No significant differences were noted between LQT1 and LQT2 patients. Typical ST-T wave patterns appeared after standing in LQTS patients. Receiver operating characteristic curves of QTcstanding and ΔQTc showed a significant increase in diagnostic value compared with the QTcsupine (area under the curve for both, 0.99 vs 0.85; P < .001). Beta-blockers attenuated the response to standing in LQTS patients (QTcstanding, 440 ± 32ms, P < .0001; ΔQTc, 14 ± 16ms, P < .0001). CONCLUSIONS: Evaluation of the QTc after the simple maneuver of standing shows a high diagnostic performance and could be important for monitoring the effects of beta-blocker therapy in LQTS patients.

An R1632C variant in the SCN5A gene causing Brugada syndrome.

Brugada syndrome (BS) is an electrical disease, inherited in an autosomal dominant manner. BS is caused by mutations in up to 13 different genes. SCN5A is the gene most frequently mutated in BS, although this presents an incomplete penetrance. The present case study investigated the SCN5A gene in a family exhibiting BS. Direct sequencing of the SCN5A gene was performed to identify mutations and a familial investigation was performed. A novel variant was identified in the voltage­sensing domain of the SCN5A protein. This familial investigation revealed one novel asymptomatic carrier in the family. Genetic investigations are useful to classify individuals who require more frequent clinical monitoring and to stratify the risk of developing the disease.

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.

Ablation of Premature Ventricular Complexes Triggering Ventricular Fibrillation in a Patient with Long QT Syndrome.

We describe the case of a patient with long QT syndrome and recurrent ventricular fibrillation, triggered by premature ventricular complexes (PVCs) with a left bundle branch block pattern and inferior axis of the QRS. Activation mapping demonstrated the origin of the PVCs to be in the right ventricular outflow tract. Ventricular fibrillation (VF) was successfully treated by catheter ablation of the triggering PVCs and there has been no recurrence of VF during a follow-up period of 14 months.

Insights into genotype-phenotype correlation in hypertrophic cardiomyopathy. Findings from 18 Spanish families with a single mutation in MYBPC3.

BACKGROUND: Mutations in the cardiac myosin-binding protein C (MYBPC3) gene are frequently found as a cause of hypertrophic cardiomyopathy (HCM). However, only a few studies have analysed genotype-phenotype correlations in small series of patients. The present study sought to determine the clinical characteristics, penetrance and prognosis of HCM with an identical mutation in MYBPC3. METHODS: 154 non-related patients with HCM (aged 55±16 years, 100 (64.9%) males) were studied. 18 (11.7%) were found to have an identical mutation in the MYBPC3 gene (IVS23+1G→A). Pedigree analysis, including both clinical evaluation and genotyping, was performed. RESULTS: 152 individuals (mean age 37±18 years, 53.3% males) from 18 families were evaluated. 65 carriers of the IVS23+1G→A mutation were identified, 61.5% of whom met HCM diagnostic criteria. Penetrance of the disease increased with age, with 50% affected at 46 years of age. Males tended to develop the disease earlier than females. 7 (15.6%) had systolic dysfunction. Compared with the rest of the HCM cohort, probands with the mutation had more hypertrophy and were younger at diagnosis. There was a trend towards a reduced survival free from sudden death (SD) (HR 1.71; 95% CI 0.98 to 2.98, p=0.059). There were 17 SD cases in 12 families with the mutation. CONCLUSIONS: The MYBPC3 IVS23+1G→A mutation is associated with middle-age onset disease and poor outcome, with a significant proportion of patients developing systolic impairment and a high SD risk profile.

Penetrance and risk profile in inherited cardiac diseases studied in a dedicated screening clinic.

Genetically transmitted cardiomyopathies can affect several members in a family. Identification of high-risk patients could lead to a preventive treatment. We report the results of a 5-year experience of a dedicated clinic. Family screening was offered to 493 consecutive unrelated patients; 2,328 subjects (40 +/- 19 years old, 52% men) were evaluated (mean 4.4 relatives/family). Electrocardiography and echocardiography were performed in all cases; additional tests were indicated depending on the disease. Familial study was recommended because of a proband with hypertrophic cardiomyopathy (HC) in 57%, idiopathic dilated cardiomyopathy (IDC) in 14%, arrhythmogenic right ventricular cardiomyopathy (ARVC) in 2%, left ventricular noncompaction in 2%, Brugada syndrome (BS) in 15%, long QT syndrome (LQTS) in 3%, and other conditions in 6%. Familial disease was confirmed in 164 (39%); 43% with HC, 47% with IDC, 25% with ARVC, 33% with left ventricular noncompaction, 28% with BS, and 30% with LQTS. Two hundred twenty-two (44 +/- 20 years old, 60% men) affected relatives were identified (129 of whom were newly diagnosed). Sixty-four patients were newly diagnosed with HC, 40 with IDC, 2 with ARVC, 5 with left ventricular noncompaction, 14 with BS, and 2 with LQTS, in whom appropriate risk stratification and medication, if needed, were initiated (specific medication in 40, 31.0%). Cardioverter-defibrillator implantation was indicated in 4 relatives for primary prevention. Ninety-two (18.7%) had a family history of sudden death (FHSCD). Consanguinity was rare but significantly associated to a higher percentage of family disease (75.0% vs 38.3%, p = 0.003) and family history of sudden death (42.1% vs 17.8, p <0.001). In conclusion, the prevalence of familial disease in inherited cardiac conditions is high. Systematic familial study identified many asymptomatic affected patients who could benefit from early treatment to prevent complications. Dedicated clinics and multidisciplinary teams are needed for proper screening programs.

Heat stroke, an unusual trigger of Brugada electrocardiogram.

A young male individual with diagnosis of heat stroke was admitted unconscious to hospital. Electrocardiogram (ECG) at admission demonstrated typical right bundle branch block and ST-segment elevation in V1 and V2 (coved morphology) diagnostic of Brugada syndrome. Maximal creatine kinase was 10,131 (IU/L); creatine kinase-MB, 15 (IU/L); troponin T, 0.039 ng/mL; and creatinine 1.6, mg/dL. Patient recovered from coma on day 6. Electrocardiogram normalized within the first 24 hours; no arrhythmias were documented. Echocardiogram before discharge was normal. Brugada ECG pattern can express intermittently, and challenge tests with a sodium channel blocker are often required for diagnosis. Ventricular arrhythmias and sudden death occur typically at night or during enhanced vagal activity. Fever has been related to polymorphic ventricular tachycardia particularly in children; nevertheless, prevalence is higher within males in their fourth to fifth decade. Mutations in SCN5A gene encoding a sodium channel can be found in up to 30% of cases. This sodium channel is sensitive to temperature changes. Sequencing of the gene failed to find any abnormality in our patient. A possible role of heat shock proteins in ion channels trafficking to cell membrane has been recently described. Despite diffuse ST-T deviations having been described in patients with heat stroke, localized right precordial leads ST elevation consistent with Brugada syndrome have not been reported. Recognition of typical ECG pattern is of importance because this syndrome is associated to an increased risk of sudden cardiac death.