Jacob Tfelt-Hansen

Common variants at SCN5A-SCN10A and HEY2 are associated with Brugada syndrome, a rare disease with high risk of sudden cardiac death

Brugada syndrome is a rare cardiac arrhythmia disorder, causally related to SCN5A mutations in around 20% of cases. Through a genome-wide association study of 312 individuals with Brugada syndrome and 1,115 controls, we detected 2 significant association signals at the SCN10A locus (rs10428132) and near the HEY2 gene (rs9388451). Independent replication confirmed both signals (meta-analyses: rs10428132, P = 1.0 × 10−68; rs9388451, P = 5.1 × 10−17) and identified one additional signal in SCN5A (at 3p21; rs11708996, P = 1.0 × 10−14). The cumulative effect of the three loci on disease susceptibility was unexpectedly large (Ptrend = 6.1 × 10−81). The association signals at SCN5A-SCN10A demonstrate that genetic polymorphisms modulating cardiac conduction can also influence susceptibility to cardiac arrhythmia. The implication of association with HEY2, supported by new evidence that Hey2 regulates cardiac electrical activity, shows that Brugada syndrome may originate from altered transcriptional programming during cardiac development. Altogether, our findings indicate that common genetic variation can have a strong impact on the predisposition to rare diseases.

THE CALCIUM-SENSING RECEPTOR IN NORMAL PHYSIOLOGY AND PATHOPHYSIOLOGY: A Review

Abstract The discovery of a G protein–coupled, calcium-sensing receptor (CaR) a decade ago and of diseases caused by CaR mutations provided unquestionable evidence of the CaRs critical role in the maintenance of systemic calcium homeostasis. On the cell membrane of the chief cells of the parathyroid glands, the CaR “senses” the extracellular calcium concentration and, subsequently, alters the release of parathyroid hormone (PTH). The CaR is likewise functionally expressed in bone, kidney, and gut—the three major calcium-translocating organs involved in calcium homeostasis. Intracellular signal pathways to which the CaR couples via its associated G proteins include phospholipase C (PLC), protein kinase B (AKT); and mitogen-activated protein kinases (MAPKs). The receptor is widely expressed in various tissues and regulates important cellular functions in addition to its role in maintaining systemic calcium homeostasis, i.e., protection against apoptosis, cellular proliferation, and membrane voltage. Functionally significant mutations in the receptor have been shown to induce diseases of calcium homeostasis owing to changes in the set point for calcium-regulated PTH release as well as alterations in the renal handling of calcium. Gain-of-function mutations cause hypocalcemia, whereas loss-of-function mutations produce hypercalcemia. Recent studies have shown that the latter clinical presentation can also be caused by inactivating autoantibodies directed against the CaR. Newly discovered type II allosteric activators of the CaR have been found to be effective as a medical treatment for renal secondary hyperparathyroidism.

Nationwide study of sudden cardiac death in persons aged 1–35 years

AIMS The aim of this investigation was to study the incidence of sudden cardiac death (SCD) in persons aged 1-35 years in a nationwide setting (5.38 million people) by systematic evaluation of all deaths. METHODS AND RESULTS All deaths in persons aged 1-35 years in Denmark in 2000-06 were included. Death certificates were read independently by two physicians. The National Patient Registry was used to retrieve information on prior medical history. All autopsy reports were read and the cause of death was revised based on autopsy findings. We identified 625 cases of sudden unexpected death (10% of all deaths), of which 156 (25%) were not autopsied. Of the 469 autopsied cases, 314 (67%) were SCD. The most common cardiac cause of death was ischaemic heart disease (13%); 29% of autopsied sudden unexpected death cases were unexplained. In 45% of SCD cases, the death was witnessed; 34% died during sleep; 89% were out-of-hospital deaths. Highest possible incidence rate of SCD in the young was 2.8 per 100 000 person-years including non-autopsied cases of sudden unexpected death. Excluding those, the incidence rate declined to 1.9 per 100 000 person-years. CONCLUSIONS A total of 7% of all deaths in the young can be attributed to SCD, when including non-autopsied cases (autopsy ratio 75%). The incidence rate of SCD in the young of 2.8 per 100 000 person-years is higher than previously reported.

Incidence and etiology of sports-related sudden cardiac death in Denmark—Implications for preparticipation screening

BACKGROUND Studies on incidences of sports-related sudden cardiac death (SrSCD) are few and data are needed for the discussion of preparticipation screening for cardiac disease. OBJECTIVE We sought to chart the incidence and etiology of SrSCD in the young in Denmark (population 5.4 million) and to compare this to the incidence of sudden cardiac death (SCD) in the background population. METHODS All 5,662 death certificates for decedents in the period 2000 to 2006 in the age group 12 to 35 years in Denmark were read independently by 2 physicians to identify cases of SCD. Information from autopsy reports, selected hospital records, and multiple registries was used to identify cases of SCD and SrSCD. SrSCD was defined as SCD occurring during or within 1 hour after exercise in a competitive athlete. The size of the athlete population was estimated from national survey data. RESULTS Fifteen (range 0 to 5 per year) cases of SrSCD were found, 8 of which had antecedent symptoms. The incidence rate was 1.21 (95% confidence interval [CI]: 0.68 to 2.00) per 100,000 athlete person-years. The most common autopsy findings were arrhythmogenic right ventricular cardiomyopathy (n = 4), sudden unexplained death (n = 4), and coronary artery disease (n = 2). The incidence of SCD in the general population age 12 to 35 was 3.76 (95% CI: 3.42 to 4.14) per 100,000 person-years. CONCLUSION In Denmark, SrSCD is a rare occurrence and the incidence rate is lower than that of SCD in the general population. This may imply a low value of preparticipation screening of athletes in Denmark.

High prevalence of genetic variants previously associated with Brugada syndrome in new exome data

More than 300 variants in 12 genes have been associated with Brugada syndrome (BrS) which has a prevalence ranging between 1:2000 and 1:100,000. Until recently, there has been little knowledge regarding the distribution of genetic variations in the general population. This problem was partly solved, when exome data from the NHLI GO Exome Sequencing Project (ESP) was published. In this study, we aimed to report the prevalence of previously BrS‐associated variants in the ESP population. We performed a search in ESP for variants previously associated with BrS. In addition, four variants in ESP were genotyped in a second Danish control population (n = 536) with available electrocardiograms. In ESP, we identified 38 of 355 (10%) variants, distributed on 272 heterozygote carriers and two homozygote carriers. The genes investigated were on average screened in 6258 individuals. This corresponds to a surprisingly high genotype prevalence of 1:23 (274:6258). Genotyping the four common ESP‐derived variants CACNA2D1 S709N, SCN5A F2004L, CACNB2 S143F, and CACNB2 T450I in the Danish controls, we found a genotype prevalence comparable with that found in ESP. We suggest that exome data are used in research, as an additive tool to predict the pathogenicity of variants in patients suspected for BrS.

Sudden cardiac death in children (1–18 years): symptoms and causes of death in a nationwide setting

AIMS Hitherto, sudden cardiac death in children (SCDc)-defined as sudden cardiac death (SCD) in the 1-18 years old-has been incompletely described in the general population. Knowledge on incidence rates, causes of death and symptoms prior to death is sparse and has been affected by reporting and referral bias. METHODS AND RESULTS In a nationwide setting all deaths in children aged 1-18 years in Denmark in 2000-06 were included. To chart causes of death and incidence rates, death certificates and autopsy reports were collected and read. By additional use of the extensive healthcare registries in Denmark, we were also able to investigate prior disease and symptoms. During the 7-year study period there was an average of 1.11 million persons aged 1-18 years. There were a total of 1504 deaths (214 deaths per year) from 7.78 million person-years. A total of 114 (7.5%) were sudden and unexpected. A cardiac disease was known prior to death in 18% of all sudden unexpected death cases. In two-thirds of all sudden unexpected death cases no previous medical history was registered. Causes of death in autopsied cases were cardiac or unknown in 70%. Unexplained deaths, presumed to be a primary cardiac arrhythmia, accounted for 28% of autopsied sudden unexpected death cases. Autopsy rate was 77%. There were a total of 87 cases of SCDc (5.8% of all deaths). Prodromal symptoms were noted in 26% and antecedent symptoms in 45% of SCDc cases. The most frequent antecedent symptoms were seizures, dyspnoea, and syncope. In total, 61% of SCDc were not known with any prior disease; 23% were known with congenital or other heart disease prior to death. In total, 43 (49%) of all sudden unexpected deaths died of a potential inherited cardiac disease. The incidence rate of sudden unexpected death was 1.5 per 100 000 person-years. The highest possible incidence rate of SCDc was 1.1 per 100 000 person-years. CONCLUSION From a nationwide study of all deaths in a 7-year period more than half of all victims of SCDc experienced antecedent and/or prodromal symptoms prior to death. The incidence rate of sudden death and SCDc was 1.5 and 1.1 per 100 000 person-years, respectively. Cardiac symptoms in young persons should warrant clinical work-up and an autopsy should be performed in all cases of sudden unexpected death in which the deceased was not known with congenital heart disease prior to death. This is pivotal, in the subsequent familial cascade screening, to diagnose and treat potential inherited cardiac diseases in family members.

Inherited Cardiac Diseases Caused by Mutations in the Nav1.5 Sodium Channel

Cardiac Diseases Caused by SCN5A Mutations.  A prerequisite for a normal cardiac function is a proper generation and propagation of electrical impulses. Contraction of the heart is obtained through a delicate matched transmission of the electrical impulses. A pivotal element of the impulse propagation is the depolarizing sodium current, responsible for the initial depolarization of the cardiomyocytes. Recent research has shown that mutations in the SCN5A gene, encoding the cardiac sodium channel Nav1.5, are associated with both rare forms of ventricular arrhythmia, as well as the most frequent form of arrhythmia, atrial fibrillation (AF). In this comprehensive review, we describe the functional role of Nav1.5 and its associated proteins in propagation and depolarization both in a normal‐ and in a pathophysiological setting. Furthermore, several of the arrhythmogenic diseases, such as long‐QT syndrome, Brugada syndrome, and AF, reported to be associated with mutations in SCN5A, are thoroughly described. (J Cardiovasc Electrophysiol, Vol. 21, pp. 107–115, January 2010)

Role of common and rare variants in SCN10A: results from the Brugada syndrome QRS locus gene discovery collaborative study

AIMS Brugada syndrome (BrS) remains genetically heterogeneous and is associated with slowed cardiac conduction. We aimed to identify genetic variation in BrS cases at loci associated with QRS duration. METHODS AND RESULTS A multi-centre study sequenced seven candidate genes (SCN10A, HAND1, PLN, CASQ2, TKT, TBX3, and TBX5) in 156 Caucasian SCN5A mutation-negative BrS patients (80% male; mean age 48) with symptoms (64%) and/or a family history of sudden death (47%) or BrS (18%). Forty-nine variants were identified: 18 were rare (MAF <1%) and non-synonymous; and 11/18 (61.1%), mostly in SCN10A, were predicted as pathogenic using multiple bioinformatics tools. Allele frequencies were compared with the Exome Sequencing and UK10K Projects. SKAT methods tested rare variation in SCN10A finding no statistically significant difference between cases and controls. Co-segregation analysis was possible for four of seven probands carrying a novel pathogenic variant. Only one pedigree (I671V/G1299A in SCN10A) showed co-segregation. The SCN10A SNP V1073 was, however, associated strongly with BrS [66.9 vs. 40.1% (UK10K) OR (95% CI) = 3.02 (2.35-3.87), P = 8.07 × 10-19]. Voltage-clamp experiments for NaV1.8 were performed for SCN10A common variants V1073, A1073, and rare variants of interest: A200V and I671V. V1073, A200V and I671V, demonstrated significant reductions in peak INa compared with ancestral allele A1073 (rs6795970). CONCLUSION Rare variants in the screened QRS-associated genes (including SCN10A) are not responsible for a significant proportion of SCN5A mutation negative BrS. The common SNP SCN10A V1073 was strongly associated with BrS and demonstrated loss of NaV1.8 function, as did rare variants in isolated patients.

New Exome Data Question the Pathogenicity of Genetic Variants Previously Associated With Catecholaminergic Polymorphic Ventricular Tachycardia

Background—Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a lethal, rare hereditary disease with an estimated prevalence of 1:10 000. The genetic variants that cause CPVT are usually highly penetrant. To date, about 189 variants in 5 genes (RYR2, CASQ2, CALM1, TRND, and KCNJ2) have been associated with CPVT pathogenesis. Methods and Results—The Exome Sequencing Project database (ESP; n= 6503) was systematically searched for previously published missense and nonsense CPVT–associated variants reported in several comprehensive reviews and in 2 databases: The Human Gene Mutation Database and The Inherited Arrhythmias Database. We used 4 different prediction tools to assess all missense variants previously associated with CPVT and compared the prediction of protein damage between CPVT-associated variants identified in the ESP and those variants not identified in the ESP. We identified 11% of the variants previously associated with CPVT in the ESP population. In the literature, 57% of these variants were reported as novel disease-causing variants absent in the healthy control subjects. These putative CPVT variants were identified in 41 out of 6131 subjects in the ESP population, corresponding to a prevalence of CPVT of up to 1:150. Using an agreement of ≥3, in silico prediction tools showed a significantly higher frequency of damaging variants among the CPVT-associated variants not identified in the ESP database (83%) compared with those variants identified in the ESP (50%; P=0.021). Conclusions—We identified a substantial overrepresentation of CPVT-associated variants in a large exome database, suggesting that these variants are not necessarily the monogenic cause of CPVT.

Sports-related sudden cardiac death in a competitive and a noncompetitive athlete population aged 12 to 49 years: Data from an unselected nationwide study in Denmark

BACKGROUND Preparticipation screening programs have been suggested to reduce the numbers of sports-related sudden cardiac deaths (SrSCD). OBJECTIVE The purpose of this study was to identify and characterize all SrSCD aged 12-49 years and to address the difference in incidence rates between competitive and noncompetitive athletes. METHODS All deaths among persons aged 12-49 years from 2007-2009 were included. Death certificates were reviewed. History of previous admissions to hospital was assessed, and discharge summaries and autopsy reports were read. Sudden cardiac deaths (SCDs) and SrSCD cases were identified. RESULTS In the 3-year period, there were 881 SCDs, of which we identified 44 SrSCD. In noncompetitive athletes aged 12-35 years, the incidence rate of SrSCD was 0.43 (95% confidence interval [CI] 0.16-0.94) per 100,000 athlete person-years vs 2.95 (95% CI 1.95-4.30) in noncompetitive athletes aged 36-49 years. In competitive athletes, the incidence rate of SrSCD was 0.47 (95% CI 0.10-1.14) and 6.64 (95% CI 2.86-13.1) per 100,000 athlete person-years in those aged 12-35 years and 36-49 years, respectively. The incidence rate of SCD in the general population was 10.7 (95% CI 10.0-11.5) per 100.000 person-years. CONCLUSION The incidence rates of SrSCD in noncompetitive and competitive athletes are not different. The study showed an increase in the incidence rate of SrSCD in persons aged 36-49 years in both noncompetitive and competitive athletes compared to those aged 12-35 years. Importantly, SCD in the general population is much more prevalent than is SrSCD in all age groups.