The origins of hypertrophic cardiomyopathy-causing mutations in two South African subpopulations: a unique profile of both independent and founder events

Missense variants in phospholamban and cardiac myosin binding protein identified in patients with a family history and clinical diagnosis of dilated cardiomyopathy

As the genetic landscape of cardiomyopathies continues to expand, the identification of missense variants in disease-associated genes frequently leads to a classification of variant of uncertain significance (VUS). For the proper reclassification of such variants, functional characterization is an important contributor to the proper assessment of pathogenic potential. Several missense variants in the calcium transport regulatory protein phospholamban have been associated with dilated cardiomyopathy. However, >40 missense variants in this transmembrane peptide are currently known and most remain classified as VUS with little clinical information. Similarly, missense variants in cardiac myosin binding protein have been associated with hypertrophic cardiomyopathy. However, hundreds of variants are known and many have low penetrance and are often found in control populations. Herein, we focused on novel missense variants in phospholamban, an Ala15-Thr variant found in a 4-year-old female and a Pro21-Thr variant found in a 60-year-old female, both with a family history and clinical diagnosis of dilated cardiomyopathy. The patients also harbored a Val896-Met variant in cardiac myosin binding protein. The phospholamban variants caused defects in the function, phosphorylation, and dephosphorylation of this calcium transport regulatory peptide, and we classified these variants as potentially pathogenic. The variant in cardiac myosin binding protein alters the structure of the protein. While this variant has been classified as benign, it has the potential to be a low-risk susceptibility variant because of the structural change in cardiac myosin binding protein. Our studies provide new biochemical evidence for missense variants previously classified as benign or VUS.

MYH7 in cardiomyopathy and skeletal muscle myopathy

Myosin heavy chain gene 7 (MYH7), a sarcomeric gene encoding the myosin heavy chain (myosin-7), has attracted considerable interest as a result of its fundamental functions in cardiac and skeletal muscle contraction and numerous nucleotide variations of MYH7 are closely related to cardiomyopathy and skeletal muscle myopathy. These disorders display significantly inter- and intra-familial variability, sometimes developing complex phenotypes, including both cardiomyopathy and skeletal myopathy. Here, we review the current understanding on MYH7 with the aim to better clarify how mutations in MYH7 affect the structure and physiologic function of sarcomere, thus resulting in cardiomyopathy and skeletal muscle myopathy. Importantly, the latest advances on diagnosis, research models in vivo and in vitro and therapy for precise clinical application have made great progress and have epoch-making significance. All the great advance is discussed here.

Associations of Race and Ethnicity With Presentation and Outcomes of Hypertrophic Cardiomyopathy: JACC Focus Seminar 6/9

Significant racial and ethnicity-based disparities in clinical presentation, management, and outcome of hypertrophic cardiomyopathy (HCM) are reported. Black patients with HCM are more likely to present with heart failure but are less commonly referred for symptom management, sudden cardiac death stratification, surgical septal myectomy, or for implantable cardioverter-defibrillators, all interventions that increase survival. Prevalence of bystander cardiopulmonary resuscitation is lower for Black patients than for White patients. Black patients with HCM have decreased survival after hospital discharge following out-of-hospital cardiac arrest. Biomedical and social interventions are urgently needed to reduce ethnicity-based disparities, which have an impact on outcomes in HCM and other cardiovascular diseases. There is also a need to focus on implementation science to support durable adoption of evidence-based therapies in Black patients and communities.

MYBPC3 Haplotype Linked to Hypertrophic Cardiomyopathy in Rhesus Macaques (Macaca mulatta)

In humans, abnormal thickening of the left ventricle of the heart clinically defines hypertrophic cardiomyopathy (HCM), a common inherited cardiovascular disorder that can precede a sudden cardiac death event. The wide range of clinical presentations in HCM obscures genetic variants that may influence an individual's susceptibility to sudden cardiac death. Although exon sequencing of major sarcomere genes can be used to detect high-impact causal mutations, this strategy is successful in only half of patient cases. The incidence of left ventricular hypertrophy (LVH) in a managed research colony of rhesus macaques provides an excellent comparative model in which to explore the genomic etiology of severe HCM and sudden cardiac death. Because no rhesus HCM-associated mutations have been reported, we used a next-generation genotyping assay that targets 7 sarcomeric rhesus genes within 63 genomic sites that are orthologous to human genomic regions known to harbor HCM disease variants. Amplicon sequencing was performed on 52 macaques with confirmed LVH and 42 unrelated, unaffected animals representing both the Indian and Chinese rhesus macaque subspecies. Bias-reduced logistic regression uncovered a risk haplotype in the rhesus MYBPC3 gene, which is frequently disrupted in both human and feline HCM; this haplotype implicates an intronic variant strongly associated with disease in either homozygous or carrier form. Our results highlight that leveraging evolutionary genomic data provides a unique, practical strategy for minimizing population bias in complex disease studies.

Genetics of inherited cardiomyopathies in Africa

In sub-Saharan Africa (SSA), the burden of noncommunicable diseases (NCDs) is rising disproportionately in comparison to the rest of the world, affecting urban, semi-urban and rural dwellers alike. NCDs are predicted to surpass infections like human immunodeficiency virus, tuberculosis and malaria as the leading cause of mortality in SSA over the next decade. Heart failure (HF) is the dominant form of cardiovascular disease (CVD), and a leading cause of NCD in SSA. The main causes of HF in SSA are hypertension, cardiomyopathies, rheumatic heart disease, pericardial disease, and to a lesser extent, coronary heart disease. Of these, the cardiomyopathies deserve greater attention because of the relatively poor understanding of mechanisms of disease, poor outcomes and the disproportionate impact they have on young, economically active individuals. Morphofunctionally, cardiomyopathies are classified as dilated, hypertrophic, restrictive and arrhythmogenic; regardless of classification, at least half of these are inherited forms of CVD. In this review, we summarise all studies that have investigated the incidence of cardiomyopathy across Africa, with a focus on the inherited cardiomyopathies. We also review data on the molecular genetic underpinnings of cardiomyopathy in Africa, where there is a striking lack of studies reporting on the genetics of cardiomyopathy. We highlight the impact that genetic testing, through candidate gene screening, association studies and next generation sequencing technologies such as whole exome sequencing and targeted resequencing has had on the understanding of cardiomyopathy in Africa. Finally, we emphasise the need for future studies to fill large gaps in our knowledge in relation to the genetics of inherited cardiomyopathies in Africa.

Hypertrophic Cardiomyopathy: An Overview of Genetics and Management

Hypertrophic cardiomyopathy (HCM) is a genetically heterogeneous cardiac muscle disorder with a diverse natural history, characterized by unexplained left ventricular hypertrophy (LVH), with histopathological hallmarks including myocyte enlargement, myocyte disarray and myocardial fibrosis. Although these features can cause significant cardiac symptoms, many young individuals with HCM are asymptomatic or mildly symptomatic. Sudden cardiac death (SCD) may occur as the initial clinical manifestation. Over the past few decades, HCM has been considered a disease of sarcomere, and typically as an autosomal dominant disease with variable expressivity and incomplete penetrance. Important insights into the genetic landscape of HCM have enhanced our understanding of the molecular pathogenesis, empowered gene-based diagnostic testing to identify at-risk individuals, and offered potential targets for the development of therapeutic agents. This article reviews the current knowledge on the clinical genetics and management of HCM.

Hypertrophic Cardiomyopathy: An Overview of Genetics and Management

Hypertrophic cardiomyopathy (HCM) is a genetically heterogeneous cardiac muscle disorder with a diverse natural history, characterized by unexplained left ventricular hypertrophy (LVH), with histopathological hallmarks including myocyte enlargement, myocyte disarray and myocardial fibrosis. Although these features can cause significant cardiac symptoms, many young individuals with HCM are asymptomatic or mildly symptomatic. Sudden cardiac death (SCD) may occur as the initial clinical manifestation. Over the past few decades, HCM has been considered a disease of sarcomere, and typically as an autosomal dominant disease with variable expressivity and incomplete penetrance. Important insights into the genetic landscape of HCM have enhanced our understanding of the molecular pathogenesis, empowered gene-based diagnostic testing to identify at-risk individuals, and offered potential targets for the development of therapeutic agents. This article reviews the current knowledge on the clinical genetics and management of HCM.

FRET-based analysis of the cardiac troponin T linker region reveals the structural basis of the hypertrophic cardiomyopathy-causing Δ160E mutation

Mutations in the cardiac thin filament (TF) have highly variable effects on the regulatory function of the cardiac sarcomere. Understanding the molecular-level dysfunction elicited by TF mutations is crucial to elucidate cardiac disease mechanisms. The hypertrophic cardiomyopathy-causing cardiac troponin T (cTnT) mutation Δ160Glu (Δ160E) is located in a putative "hinge" adjacent to an unstructured linker connecting domains TNT1 and TNT2. Currently, no high-resolution structure exists for this region, limiting significantly our ability to understand its role in myofilament activation and the molecular mechanism of mutation-induced dysfunction. Previous regulated in vitro motility data have indicated mutation-induced impairment of weak actomyosin interactions. We hypothesized that cTnT-Δ160E repositions the flexible linker, altering weak actomyosin electrostatic binding and acting as a biophysical trigger for impaired contractility and the observed remodeling. Using time-resolved FRET and an all-atom TF model, here we first defined the WT structure of the cTnT-linker region and then identified Δ160E mutation-induced positional changes. Our results suggest that the WT linker runs alongside the C terminus of tropomyosin. The Δ160E-induced structural changes moved the linker closer to the tropomyosin C terminus, an effect that was more pronounced in the presence of myosin subfragment (S1) heads, supporting previous findings. Our in silico model fully supported this result, indicating a mutation-induced decrease in linker flexibility. Our findings provide a framework for understanding basic pathogenic mechanisms that drive severe clinical hypertrophic cardiomyopathy phenotypes and for identifying structural targets for intervention that can be tested in silico and in vitro.

Hypertrophic cardiomyopathy mutations in MYBPC3 dysregulate myosin

The mechanisms by which truncating mutations in MYBPC3 (encoding cardiac myosin-binding protein C; cMyBPC) or myosin missense mutations cause hypercontractility and poor relaxation in hypertrophic cardiomyopathy (HCM) are incompletely understood. Using genetic and biochemical approaches, we explored how depletion of cMyBPC altered sarcomere function. We demonstrated that stepwise loss of cMyBPC resulted in reciprocal augmentation of myosin contractility. Direct attenuation of myosin function, via a damaging missense variant (F764L) that causes dilated cardiomyopathy (DCM), normalized the increased contractility from cMyBPC depletion. Depletion of cMyBPC also altered dynamic myosin conformations during relaxation, enhancing the myosin state that enables ATP hydrolysis and thin filament interactions while reducing the super relaxed conformation associated with energy conservation. MYK-461, a pharmacologic inhibitor of myosin ATPase, rescued relaxation deficits and restored normal contractility in mouse and human cardiomyocytes with MYBPC3 mutations. These data define dosage-dependent effects of cMyBPC on myosin that occur across the cardiac cycle as the pathophysiologic mechanisms by which MYBPC3 truncations cause HCM. Therapeutic strategies to attenuate cMyBPC activity may rescue depressed cardiac contractility in patients with DCM, whereas inhibiting myosin by MYK-461 should benefit the substantial proportion of patients with HCM with MYBPC3 mutations.

Heterozygous junctophilin-2 (JPH2) p.(Thr161Lys) is a monogenic cause for HCM with heart failure

During the last two decades, mutations in sarcomere genes have found to comprise the most common cause for hypertrophic cardiomyopathy (HCM), but still significant number of patients with dominant HCM in the family are left without molecular genetic diagnosis. Next generation sequencing (NGS) does not only enable evaluation of established HCM genes but also candidate genes for cardiomyopathy are frequently tested which may lead to a situation where conclusive interpretation of the variant requires extensive family studies. We aimed to characterize the phenotype related to a variant in the junctophilin-2 (JPH2) gene, which is less known non-sarcomeric candidate gene. In addition, we did extensive review of the literature and databases about JPH2 variation in association with cardiac disease. We characterize nine Finnish index patients with HCM and heterozygous for JPH2 c.482C>A, p.(Thr161Lys) variant were included and segregation studies were performed. We identified 20 individuals affected with HCM with or without systolic heart failure and conduction abnormalities in the nine Finnish families with JPH2 p.(Thr161Lys) variant. We found 26 heterozygotes with the variant and penetrance was 71% by age 60 and 100% by age 80. Co-segregation of the variant with HCM phenotype was observed in six families. Main clinical features were left ventricular hypertrophy, arrhythmia vulnerability and conduction abnormalities including third degree AV-block. In some patients end-stage severe left ventricular heart failure with normal or mildly enlarged diastolic dimensions was detected. In conclusion, we propose that the heterozygous JPH2 p.(Thr161Lys) variant is a new Finnish mutation causing atypical HCM.

Aggregate penetrance of genomic variants for actionable disorders in European and African Americans

In populations that have not been selected for family history of disease, it is unclear how commonly pathogenic variants (PVs) in disease-associated genes for rare Mendelian conditions are found and how often they are associated with clinical features of these conditions. We conducted independent, prospective analyses of participants in two community-based epidemiological studies to test the hypothesis that persons carrying PVs in any of 56 genes that lead to 24 dominantly inherited, actionable conditions are more likely to exhibit the clinical features of the corresponding diseases than those without PVs. Among 462 European American Framingham Heart Study (FHS) and 3223 African-American Jackson Heart Study (JHS) participants who were exome-sequenced, we identified and classified 642 and 4429 unique variants, respectively, in these 56 genes while blinded to clinical data. In the same participants, we ascertained related clinical features from the participants' clinical history of cancer and most recent echocardiograms, electrocardiograms, and lipid measurements, without knowledge of variant classification. PVs were found in 5 FHS (1.1%) and 31 JHS (1.0%) participants. Carriers of PVs were more likely than expected, on the basis of incidence in noncarriers, to have related clinical features in both FHS (80.0% versus 12.4%) and JHS (26.9% versus 5.4%), yielding standardized incidence ratios of 6.4 [95% confidence interval (CI), 1.7 to 16.5; P = 7 × 10^-4) in FHS and 4.7 (95% CI, 1.9 to 9.7; P = 3 × 10^-4) in JHS. Individuals unselected for family history who carry PVs in 56 genes for actionable conditions have an increased aggregated risk of developing clinical features associated with the corresponding diseases.

A One Health Approach to Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiac disease in humans and results in significant morbidity and mortality. Research over the past 25 years has contributed enormous insight into this inherited disease particularly in the areas of genetics, molecular mechanisms, and pathophysiology. Our understanding continues to be limited by the heterogeneity of clinical presentations with various genetic mutations associated with HCM. Transgenic mouse models have been utilized especially studying the genotypic and phenotypic interactions. However, mice possess intrinsic cardiac and hemodynamic differences compared to humans and have limitations preventing their direct translation. Other animal models of HCM have been studied or generated in part to overcome these limitations. HCM in cats shows strikingly similar molecular, histopathological, and genetic similarities to human HCM, and offers an important translational opportunity for the study of this disease. Recently, inherited left ventricular hypertrophy in rhesus macaques was identified and collaborative investigations have been conducted to begin to develop a non-human primate HCM model. These naturally-occurring large-animal models may aid in advancing our understanding of HCM and developing novel therapeutic approaches to this disease. This review will highlight the features of HCM in humans and the relevant available and developing animal models of this condition.

Prevalence and Phenotypic Expression of Mutations in the MYH7, MYBPC3 and TNNT2 Genes in Families with Hypertrophic Cardiomyopathy in the South of Brazil: A Cross-Sectional Study

Background:

Mutations in sarcomeric genes are found in 60-70% of individuals with familial forms of hypertrophic cardiomyopathy (HCM). However, this estimate refers to northern hemisphere populations. The molecular-genetic profile of HCM has been subject of few investigations in Brazil, particularly in the south of the country.

Objective:

To investigate mutations in the sarcomeric genes MYH7, MYBPC3 and TNNT2 in a cohort of HCM patients living in the extreme south of Brazil, and to evaluate genotype-phenotype associations.

Methods:

Direct DNA sequencing of all encoding regions of three sarcomeric genes was conducted in 43 consecutive individuals of ten unrelated families.

Results:

Mutations for CMH have been found in 25 (58%) patients of seven (70%) of the ten study families. Fourteen (56%) individuals were phenotype-positive. All mutations were missense, four (66%) in MYH7 and two (33%) in MYBPC3. We have not found mutations in the TNNT2 gene. Mutations in MYH7 were identified in 20 (47%) patients of six (60%) families. Two of them had not been previously described. Mutations in MYBPC3 were found in seven (16%) members of two (20%) families. Two (5%) patients showed double heterozygosis for both genes. The mutations affected different domains of encoded proteins and led to variable phenotypic expression. A family history of HCM was identified in all genotype-positive individuals.

Conclusions:

In this first genetic-molecular analysis carried out in the south of Brazil, we found mutations in the sarcomeric genes MYH7 and MYBPC3 in 58% of individuals. MYH7-related disease was identified in the majority of cases with mutation.

Fundamento:

Mutações em genes do sarcômero são encontradas em 60-70% dos indivíduos com formas familiares de cardiomiopatia hipertrófica. (CMH). Entretanto, essa estimativa refere-se a populações de países do hemisfério norte. O perfil genético-molecular da CMH foi tema de poucos estudos no Brasil, particularmente na região sul do país.

Objetivo:

Realizar a pesquisa de mutações dos genes sarcoméricos MYH7, MYBPC3 e TNNT2 numa coorte de CMH estabelecida no extremo sul do Brasil, assim como avaliar as associações genótipo-fenótipo.

Métodos:

Sequenciamento direto do DNA de todas as regiões codificantes dos três genes sarcoméricos foi realizada em 43 indivíduos consecutivos de dez famílias não-relacionadas.

Resultados:

Mutações para CMH foram encontradas em 25 (58%) indivíduos de sete (70%) das dez famílias estudadas, sendo 14 (56%) deles fenótipo-positivos. Todas as mutações eram missense, quatro (66%) no gene MYH7 e duas (33%) no gene MYBPC3. Não foram encontradas mutações no gene TNNT2. Mutações em MYH7 foram identificadas em 20 (47%) indivíduos de seis (60%) famílias. Duas delas não haviam sido previamente relatadas. Mutações de MYBPC3 foram detectadas em sete (16%) membros de duas (20%) famílias. Dois (5%) indivíduos apresentaram dupla heterozigose com mutações em ambos os genes. As mutações acometeram distintos domínios das proteínas codificadas e produziram expressão fenotípica variável. História familiar de CMH foi identificada em todos os indivíduos genótipo-positivos.

Conclusões:

Nessa primeira análise genético-molecular da CMH realizada no sul do Brasil, foram encontradas mutações nos genes sarcoméricos MYH7 e MYBPC3 em 58% dos indivíduos. Doença relacionada ao gene MYH7 foi identificada na maioria dos casos com mutação.

Clinical features, spectrum of causal genetic mutations and outcome of hypertrophic cardiomyopathy in South Africans

BACKGROUND

Little is known about the clinical characteristics, spectrum of causal genetic mutations and outcome of hypertrophic cardiomyopathy (HCM) in Africans. The objective of this study was to delineate the clinical and genetic features and outcome of HCM in African patients.

METHODS

Information on clinical presentation, electrocardiographic and echocardiographic findings, and outcome of cases with HCM was collected from the Cardiac Clinic at Groote Schuur Hospital over a mean duration of follow up of 9.1 ± 3.4 years. Genomic DNA was screened for mutations in 15 genes that cause HCM, i.e. cardiac myosin-binding protein C (MYBPC3), cardiac β-myosin heavy chain (MYH7), cardiac troponin T2 (TNNT2), cardiac troponin I (TNNI3), regulatory light chain of myosin (MYL2), essential light chain of myosin (MYL3), tropomyosin 1 (TPM1), phospholamban (PLN), α-actin (ACTC1), cysteine and glycine-rich protein 3 (CSRP3), AMP-activated protein kinase (PRKAG2), α-galactosidase (GLA), four-and-a-half LIM domains 1 (FHL1), lamin A/C (LMNA) and lysosome-associated membrane protein 2 (LAMP2). Survival and its predictors were analysed using the Kaplan-Meier and Cox proportional hazards regression methods, respectively.

RESULTS

Forty-three consecutive patients [mean age 38.5 ± 14.3 years; 25 (58.1%) male; and 13 (30.2%) black African] were prospectively enrolled in the study from January 1996 to December 2012. Clinical presentation was similar to that reported in other studies. The South African founder mutations that cause HCM were not found in the 42 probands. Ten of 35 index cases (28.6%) tested for mutations in 15 genes had disease-causing mutations in MYH7 (six cases or 60%) and MYBPC3 (four cases or 40%). No disease-causing mutation was found in the other 13 genes screened. The annual mortality rate was 2.9% per annum and overall survival was 74% at 10 years, which was similar to the general South African population. Cox's proportional hazards regression showed that survival was predicted by New York Heart Association (NYHA) functional class at last visit (p equals; 0.026), but not by the presence of a disease-causing mutation (p = 0.474).

CONCLUSIONS

Comprehensive genetic screening was associated with a 29% yield of causal genetic mutations in South African HCM cases, all in MYH7 and MBPC3 genes. A quarter of the patients had died after a decade of follow up, with NYHA functional class serving as a predictor of survival.

The genetic basis of hypertrophic cardiomyopathy in cats and humans

Mutations in genes that encode for muscle sarcomeric proteins have been identified in humans and two breeds of domestic cats with hypertrophic cardiomyopathy (HCM). This article reviews the history, genetics, and pathogenesis of HCM in the two species in order to give veterinarians a perspective on the genetics of HCM. Hypertrophic cardiomyopathy in people is a genetic disease that has been called a disease of the sarcomere because the preponderance of mutations identified that cause HCM are in genes that encode for sarcomeric proteins (Maron and Maron, 2013). Sarcomeres are the basic contractile units of muscle and thus sarcomeric proteins are responsible for the strength, speed, and extent of muscle contraction. In people with HCM, the two most common genes affected by HCM mutations are the myosin heavy chain gene (MYH7), the gene that encodes for the motor protein β-myosin heavy chain (the sarcomeric protein that splits ATP to generate force), and the cardiac myosin binding protein-C gene (MYBPC3), a gene that encodes for the closely related structural and regulatory protein, cardiac myosin binding protein-C (cMyBP-C). To date, the two mutations linked to HCM in domestic cats (one each in Maine Coon and Ragdoll breeds) also occur in MYBPC3 (Meurs et al., 2005, 2007). This is a review of the genetics of HCM in both humans and domestic cats that focuses on the aspects of human genetics that are germane to veterinarians and on all aspects of feline HCM genetics.

Spectrum of Mutations in Hypertrophic Cardiomyopathy Genes Among Tunisian Patients

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is a common cardiac genetic disorder associated with heart failure and sudden death. Mutations in the cardiac sarcomere genes are found in approximately half of HCM patients and are more common among cases with a family history of the disease. Data about the mutational spectrum of the sarcomeric genes in HCM patients from Northern Africa are limited. The population of Tunisia is particularly interesting due to its Berber genetic background. As founder mutations have been reported in other disorders.

METHODS

We performed semiconductor chip (Ion Torrent PGM) next generation sequencing of the nine main sarcomeric genes (MYH7, MYBPC3, TNNT2, TNNI3, ACTC1, TNNC1, MYL2, MYL3, TPM1) as well as the recently identified as an HCM gene, FLNC, in 45 Tunisian HCM patients.

RESULTS

We found sarcomere gene polymorphisms in 12 patients (27%), with MYBPC3 and MYH7 representing 83% (10/12) of the mutations. One patient was homozygous for a new MYL3 mutation and two were double MYBPC3 + MYH7 mutation carriers. Screening of the FLNC gene identified three new mutations, which points to FLNC mutations as an important cause of HCM among Tunisians.

CONCLUSION

The mutational background of HCM in Tunisia is heterogeneous. Unlike other Mendelian disorders, there were no highly prevalent mutations that could explain most of the cases. Our study also suggested that FLNC mutations may play a role on the risk for HCM among Tunisians.

Cryo-EM structure of a human cytoplasmic actomyosin complex at near-atomic resolution

The interaction of myosin with actin filaments is the central feature of muscle contraction and cargo movement along actin filaments of the cytoskeleton. The energy for these movements is generated during a complex mechanochemical reaction cycle. Crystal structures of myosin in different states have provided important structural insights into the myosin motor cycle when myosin is detached from F-actin. The difficulty of obtaining diffracting crystals, however, has prevented structure determination by crystallography of actomyosin complexes. Thus, although structural models exist of F-actin in complex with various myosins, a high-resolution structure of the F-actin–myosin complex is missing. Here, using electron cryomicroscopy, we present the structure of a human rigor actomyosin complex at an average resolution of 3.9 Å. The structure reveals details of the actomyosin interface, which is mainly stabilized by hydrophobic interactions. The negatively charged amino (N) terminus of actin interacts with a conserved basic motif in loop 2 of myosin, promoting cleft closure in myosin. Surprisingly, the overall structure of myosin is similar to rigor-like myosin structures in the absence of F-actin, indicating that F-actin binding induces only minimal conformational changes in myosin. A comparison with pre-powerstroke and intermediate (Pi-release) states of myosin allows us to discuss the general mechanism of myosin binding to F-actin. Our results serve as a strong foundation for the molecular understanding of cytoskeletal diseases, such as autosomal dominant hearing loss and diseases affecting skeletal and cardiac muscles, in particular nemaline myopathy and hypertrophic cardiomyopathy.

Exome Sequencing Identifies a Novel LMNA Splice-Site Mutation and Multigenic Heterozygosity of Potential Modifiers in a Family with Sick Sinus Syndrome, Dilated Cardiomyopathy, and Sudden Cardiac Death

The goals are to understand the primary genetic mechanisms that cause Sick Sinus Syndrome and to identify potential modifiers that may result in intrafamilial variability within a multigenerational family. The proband is a 63-year-old male with a family history of individuals (>10) with sinus node dysfunction, ventricular arrhythmia, cardiomyopathy, heart failure, and sudden death. We used exome sequencing of a single individual to identify a novel LMNA mutation and demonstrated the importance of Sanger validation and family studies when evaluating candidates. After initial single-gene studies were negative, we conducted exome sequencing for the proband which produced 9 gigabases of sequencing data. Bioinformatics analysis showed 94% of the reads mapped to the reference and identified 128,563 unique variants with 108,795 (85%) located in 16,319 genes of 19,056 target genes. We discovered multiple variants in known arrhythmia, cardiomyopathy, or ion channel associated genes that may serve as potential modifiers in disease expression. To identify candidate mutations, we focused on ~2,000 variants located in 237 genes of 283 known arrhythmia, cardiomyopathy, or ion channel associated genes. We filtered the candidates to 41 variants in 33 genes using zygosity, protein impact, database searches, and clinical association. Only 21 of 41 (51%) variants were validated by Sanger sequencing. We selected nine confirmed variants with minor allele frequencies <1% for family studies. The results identified LMNA c.357-2A>G, a novel heterozygous splice-site mutation as the primary mutation with rare or novel variants in HCN4, MYBPC3, PKP4, TMPO, TTN, DMPK and KCNJ10 as potential modifiers and a mechanism consistent with haploinsufficiency.

MYBPH acts as modifier of cardiac hypertrophy in hypertrophic cardiomyopathy (HCM) patients

Left ventricular hypertrophy is a risk factor for cardiovascular morbidity and mortality. Hypertrophic cardiomyopathy (HCM) is considered a model disease to study causal molecular factors underlying isolated cardiac hypertrophy. However, HCM manifests with various clinical symptoms, even in families bearing the same genetic defects, suggesting that additional factors contribute to hypertrophy. The gene encoding the cardiac myosin binding protein C (cMYBPC) is one of the most frequently implicated genes in HCM. Recently another myosin binding protein, myosin binding protein H (MYBPH) was shown to function in concert with cMYBPC in regulating cardiomyocyte contraction. Given the similarity in sequence, structure and the critical role MYBPH plays in sarcomere contraction, we proposed that MYBPH may be involved in HCM pathogenesis. Family-based genetic association analysis was employed to investigate the contribution of MYBPH in modifying hypertrophy. Seven single nucleotide polymorphisms and haplotypes in MYBPH were investigated for hypertrophy modifying effects in 388 individuals (27 families), in which three unique South African HCM-causing founder mutations (p.R403W and pA797T in β-myosin heavy chain gene (MYH7) and p.R92W in the cardiac troponin T gene (TNNT2)) segregate. We observed a significant association between rs2250509 and hypertrophy traits in the p.A797T MYH7 mutation group. Additionally, haplotype GGTACTT significantly affected hypertrophy within the same mutation group. MYBPH was for the first time assessed as a candidate hypertrophy modifying gene. We identified a novel association between MYBPH and hypertrophy traits in HCM patients carrying the p.A797T MYH7 mutation, suggesting that variation in MYBPH can modulate the severity of hypertrophy in HCM.

Using whole exome sequencing and bioformatics in the molecular autopsy of a sudden unexplained death syndrome (SUDS) case

Whole exome sequencing (WES) and bioinformatics analysis were used to investigate potential disease-causing gene mutations in a sudden unexplained death syndrome (SUDS) case after autopsy and pathology tests failed to suggest an obvious disease mechanism. Following whole exome sequencing, a 3-step bioinformatics filtering procedure was carried out to identify possible pathogenic genomic features. Single nucleotide variations (SNVs) were analyzed and ranked by likely mutation impact using various open online tools. After screening, we identified G643S as a putative causative heterozygous mutation in the KCNQ1 gene. This mutation has been reported in abnormalities consistent with SUDS, such as IKs in cardiac myocytes, a condition that predisposes for arrhythmias. Our work demonstrates the application of sequencing technology at the whole exome level for determining potential causes of an otherwise unexplained death.

Compound heterozygosity deteriorates phenotypes of hypertrophic cardiomyopathy with founder MYBPC3 mutation: evidence from patients and zebrafish models

Although most founder mutation carriers of hypertrophic cardiomyopathy (HCM), such as the cardiac myosin-binding protein C gene (MYBPC3), arose from a common ancestor exhibit favorable clinical phenotypes, there still remain small fractions of these carriers associated with increased cardiovascular events. However, few data exist regarding the defining factors that modify phenotypes of these patients, particularly in terms of multiple gene mutations. Therefore, we assessed genotype-phenotype correlations and investigated factors that contribute to phenotypic diversities of mutation carriers from 488 unrelated HCM probands. A prevalent founder mutation (Val762Asp) in MYBPC3 was identified in 33 subjects from 19 families. Among them, 28 carriers harbored an isolated Val762Asp mutation and exhibited a late onset of overt HCM compared with other MYBPC3 mutation carriers (62.8 ± 3.0 vs 50.1 ± 2.6 yr, P < 0.05). In contrast, the remaining five carriers had additional sarcomere gene mutations (3 carriers in MYBPC3 and 2 carriers in the cardiac troponin T gene). Of these five carriers, two carriers showed early disease onset and one carrier exhibited end-stage HCM. These phenotypes were recapitulated in zebrafish models; injection of MYBPC3 Val762Asp alone did not alter ventricular size or function, but ventricular dimension was significantly increased when MYBPC3 Val762Asp mRNA was coinjected with MYBPC3 Arg820Gln mRNA. These results demonstrate that MYBPC3 Val762Asp may be associated with unfavorable HCM phenotypes in some cases when combined with another MYBPC3 mutation.

A new common mutation in the cardiac beta-myosin heavy chain gene in Finnish patients with hypertrophic cardiomyopathy

BACKGROUND

In the nationwide FinHCM Study including 306 Finnish patients with hypertrophic cardiomyopathy (HCM), we have previously identified two founder mutations in the alpha-tropomyosin (TPM1-D175N) and myosin-binding protein C (MYBPC3-Q1061X) genes, accounting for 18% of all cases. Objective. To screen additional mutations, previously identified in eastern Finnish cohorts with HCM, in the FinHCM Study population.

PATIENTS AND METHODS

Ten mutations in the beta-myosin heavy chain gene (MYH7), TPM1, and MYBPC3 were screened.

RESULTS

MYH7-R1053Q was found in 17 of 306 patients (5.6%). No carriers of MYH7-R719W or N696S were found. A novel TPM1-D175G mutation was found in a single patient. MYBPC3 mutations were found in 14 patients: IVS5-2A-C in two, IVS14-13G-A in two, K811del in six, and A851insT in four patients. Altogether, a HCM-causing mutation was identified in 32 patients, accounting for 10.5% of all cases. In addition, two MYBPC3 variants R326Q and V896M with uncertain pathogenicity were found in eight and in 10 patients, respectively.

CONCLUSION

Combining the present findings with our previous results, a causative mutation was identified in 28% of the FinHCM cohort. MYH7-R1053Q was the third most common mutation, and should be screened in all new cases of HCM in Finland.

Nationwide study on hypertrophic cardiomyopathy in Iceland: evidence of a MYBPC3 founder mutation

BACKGROUND

The geographic isolation and homogeneous population of Iceland are ideally suited to ascertain clinical and genetic characteristics of hypertrophic cardiomyopathy (HCM) at the population level.

METHODS AND RESULTS

Medical records and cardiac imaging studies obtained between 1997 and 2010 were reviewed to identify Icelandic patients with HCM. Surviving patients were recruited for clinical and genetic studies. A previously identified Icelandic mutation, MYBPC3 c.927-2A>G, was genotyped, and mutation-negative samples were sequenced for HCM genes and other hypertrophic genes. Record review identified 180 patients with HCM. Genetic analyses of 151 patients defined pathogenic mutations in 101 (67%), including MYBPC3 c.927-2A>G (88 patients, 58%), 4 other MYBPC3 or MYH7 mutations (5 patients, 3.3%), and 2 GLA mutations (8 patients, 5.3%). Haplotype and genetic genealogical data defined MYBPC3 c.927-2A>G as a founder mutation, introduced into the Icelandic population in the 15th century, with a current population prevalence of 0.36%. MYBPC3 c.927-2A>G mutation carriers exhibited phenotypic diversity but were younger at diagnosis (42 versus 49 years; P=0.001) and sustained more adverse events (15% versus 2%; P=0.02) than mutation-negative patients. All-cause mortality for patients with HCM was similar to that of an age-matched Icelandic population (hazard ratio, 0.98; P=0.9). HCM-related mortality (0.78%/y) occurred at a mean age of 68 compared with 81 years for non-HCM-related mortality (P=0.02).

CONCLUSIONS

A founder MYBPC3 mutation that arose >550 years ago is the predominant cause of HCM in Iceland. The MYBPC3 c.927-2A>G mutation is associated with low adverse event rates but earlier cardiovascular mortality, illustrating the impact of genotype on outcomes in HCM.

Genetic biomarkers in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy is a common inherited heart muscle disorder associated with sudden cardiac death, arrhythmias and heart failure. Genetic mutations can be identified in approximately 60% of patients; these are commonest in genes that encode proteins of the cardiac sarcomere. Similar to other Mendelian diseases these mutations are characterized by incomplete penetrance and variable clinical expression. Our knowledge of this genetic diversity is rapidly evolving as high-throughput DNA sequencing technology is now used to characterize an individual patient's disease. In addition, the genomic basis of several multisystem diseases associated with a hypertrophic cardiomyopathy phenotype has been elucidated. Genetic biomarkers can be helpful in making an accurate diagnosis and in identifying relatives at risk of developing the condition. In the clinical setting, genetic testing and genetic screening should be used pragmatically with appropriate counseling. Here we review the current role of genetic biomarkers in hypertrophic cardiomyopathy, highlight recent progress in the field and discuss future challenges.

Screening of MYH7, MYBPC3, and TNNT2 genes in Brazilian patients with hypertrophic cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HC) is the most prevalent genetic cardiac disease caused by a mutation in sarcomeres, Z-disks, or calcium-handling genes and is characterized by unexplained left ventricular hypertrophy. The aim of this study was to determine the genetic profile of Brazilian patients with HC and correlate the genotype with the phenotype.

METHODS

We included 268 index patients from São Paulo city and 3 other cities in Brazil and extracted their DNA from whole blood. We amplified the coding sequencing of MYH7, MYBPC3, and TNNT2 genes and sequenced them with an automatic sequencer.

RESULTS

We identified causal mutations in 131 patients (48.8%). Seventy-eight (59.5%) were in the MYH7 gene, 50 (38.2%) in the MYBPC3 gene, and 3 (2.3%) in the TNNT2 gene. We identified 69 mutations, 24 not previously described. Patients with an identified mutation were younger at diagnosis and at current age, had a higher mean heart rate and higher nonsustained ventricular tachycardia frequency compared with those without a mutation. Patients with MYH7 gene mutations had a larger left atrium and higher frequency of atrial fibrillation than did patients with MYBPC3 gene mutations.

CONCLUSION

The presence of a mutation in one of the genes suggests a worse prognosis. Mutations in the MYH7 gene, rather than in the MYBPC3 gene, were also related to a worse prognosis. This is the first work characterizing HC molecular epidemiology in the Brazilian population for the 3 most important genes.

Recent advances in the epidemiology, pathogenesis and prognosis of acute heart failure and cardiomyopathy in Africa

This review addresses recent advances in the epidemiology, pathogenesis and prognosis of acute heart failure and cardiomyopathy based on research conducted in Africa. We searched Medline/PubMed for publications on acute decompensated heart failure and cardiomyopathy in Africa for the past 5 years (ie, 1 January 2008 to 31 December 2012). This was supplemented with personal communications with colleagues from Africa working in the field. A large prospective registry has shown that acute decompensated heart failure is caused by hypertension, cardiomyopathy and rheumatic heart disease in 90% of cases, a pattern that is in contrast with the dominance of coronary artery disease in North America and Europe. Furthermore, acute heart failure is a disease of the young with a mean age of 52 years, occurs equally in men and women, and is associated with high mortality at 6 months (∼18%), which is, however, similar to that observed in non-African heart failure registries, suggesting that heart failure has a dire prognosis globally, regardless of aetiology. The molecular genetics of dilated cardiomyopathy, hypertrophic cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy in Africans is consistent with observations elsewhere in the world; the unique founder effects in the Afrikaner provide an opportunity for the study of genotype-phenotype correlations in large numbers of individuals with cardiomyopathy due to the same mutation. Advances in the understanding of the molecular mechanisms of peripartum cardiomyopathy have led to promising clinical trials of bromocriptine in the treatment of peripartum heart failure. The key challenges of management of heart failure are the urgent need to increase the use of proven treatments by physicians, and the control of hypertension in primary care and at the population level.

Heart failure in sub-Saharan Africa

The heart failure syndrome has been recognized as a significant contributor to cardiovascular disease burden in sub-Saharan African for many decades. Seminal knowledge regarding heart failure in the region came from case reports and case series of the early 20th century which identified infectious, nutritional and idiopathic causes as the most common. With increasing urbanization, changes in lifestyle habits, and ageing of the population, the spectrum of causes of HF has also expanded resulting in a significant burden of both communicable and non-communicable etiologies. Heart failure in sub-Saharan Africa is notable for the range of etiologies that concurrently exist as well as the healthcare environment marked by limited resources, weak national healthcare systems and a paucity of national level data on disease trends. With the recent publication of the first and largest multinational prospective registry of acute heart failure in sub-Saharan Africa, it is timely to review the state of knowledge to date and describe the myriad forms of heart failure in the region. This review discusses several forms of heart failure that are common in sub-Saharan Africa (e.g., rheumatic heart disease, hypertensive heart disease, pericardial disease, various dilated cardiomyopathies, HIV cardiomyopathy, hypertrophic cardiomyopathy, endomyocardial fibrosis, ischemic heart disease, cor pulmonale) and presents each form with regard to epidemiology, natural history, clinical characteristics, diagnostic considerations and therapies. Areas and approaches to fill the remaining gaps in knowledge are also offered herein highlighting the need for research that is driven by regional disease burden and needs.

Mutations in the cardiac troponin T gene show various prognoses in Japanese patients with hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant disorder resulting from mutations in genes for at least 15 various sarcomere-related proteins including cardiac β-myosin heavy chain, cardiac myosin-binding protein C, and cardiac troponin T. The troponin T gene (TNNT2) mutation has the third incidence of familial HCM, and the genotype–phenotype correlation of this gene still remains insufficient in Japanese familial HCM. Therefore, in the present study, we focused on screening the TNNT2 mutation in 173 unrelated Japanese patients with familial HCM, and found three reported mutations and a new mutation of TNNT2 in 11 individuals from four families. In these families, two individuals from one family had double mutations, Arg130Cys and Phe110Ile, six individuals from two other families had an Arg92Trp mutation, and one individual of another family had a new mutation, Ile79Thr, of TNNT2. The phenotype of each family was often different from reported cases, even if they had the same genetic mutation. In addition, families with the same genetic mutation showed a similar trend in the phenotype, but it was not exactly the same. However, sudden death in youth was observed in all of these families. Although the type of genetic mutation is not useful for predicting prognosis in HCM, the possibility of sudden cardiac death remains. Therefore, the prognosis of individuals bearing the TNNT2 mutation with familial HCM should be more carefully observed from birth.

Two founder mutations in the alpha-tropomyosin and the cardiac myosin-binding protein C genes are common causes of hypertrophic cardiomyopathy in the Finnish population

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is predominantly caused by a large number of various mutations in the genes encoding sarcomeric proteins. However, two prevalent founder mutations for HCM in the alpha-tropomyosin (TPM1-D175N) and myosin-binding protein C (MYBPC3-Q1061X) genes have previously been identified in eastern Finland.

OBJECTIVE

To assess the prevalence of these founder mutations in a large population of patients with HCM from all over Finland. Patients and methods. We screened for two founder mutations (TPM1-D175N and MYBPC3-Q1061X) in 306 unrelated Finnish patients with HCM from the regions covering a population of ∼4,000,000.

RESULTS

The TPM1-D175N mutation was found in 20 patients (6.5%) and the MYBPC3-Q1061X in 35 patients (11.4%). Altogether, the two mutations accounted for 17.9% of the HCM cases. In addition, 61 and 59 relatives of the probands were found to be carriers of TPM1-D175N and MYBPC3-Q1061X, respectively. The mutations showed regional clustering. TPM1-D175N was prevalent in central and western Finland, and MYBPC3-Q1061X in central and eastern Finland.

CONCLUSION

The TPM1-D175N and MYBPC3-Q1061X mutations account for a substantial part of all HCM cases in the Finnish population, indicating that routine genetic screening of these mutations is warranted in Finnish patients with HCM.

Early results of sarcomeric gene screening from the Egyptian National BA-HCM Program

The present study comprised sarcomeric genotyping of the three most commonly involved sarcomeric genes: MYBPC3, MYH7, and TNNT2 in 192 unrelated Egyptian hypertrophic cardiomyopathy (HCM) index patients. Mutations were detected in 40 % of cases. Presence of positive family history was significantly (p = 0.002) associated with a higher genetic positive yield (49/78, 62.8 %). The majority of the detected mutations in the three sarcomeric genes were novel (40/62, 65 %) and mostly private (47/62, 77 %). Single nucleotide substitution was the most frequently detected mutation type (51/62, 82 %). Over three quarters of these substitutions (21/27, 78 %) involved CpG dinucleotide sites and resulted from C > T or G > A transition in the three analyzed genes, highlighting the significance of CpG high mutability within the sarcomeric genes examined. This study could aid in global comparative studies in different ethnic populations and constitutes an important step in the evolution of the integrated clinical, translational, and basic science HCM program.

Founder mutations in hypertrophic cardiomyopathy patients in the Netherlands

In this part of a series on cardiogenetic founder mutations in the Netherlands, we review the Dutch founder mutations in hypertrophic cardiomyopathy (HCM) patients. HCM is a common autosomal dominant genetic disease affecting at least one in 500 persons in the general population. Worldwide, most mutations in HCM patients are identified in genes encoding sarcomeric proteins, mainly in the myosin-binding protein C gene (MYBPC3, OMIM #600958) and the beta myosin heavy chain gene (MYH7, OMIM #160760). In the Netherlands, the great majority of mutations occur in the MYBPC3, involving mainly three Dutch founder mutations in the MYBPC3 gene, the c.2373_2374insG, the c.2864_2865delCT and the c.2827C>T mutation. In this review, we describe the genetics of HCM, the genotype-phenotype relation of Dutch founder MYBPC3 gene mutations, the prevalence and the geographic distribution of the Dutch founder mutations, and the consequences for genetic counselling and testing. (Neth Heart J 2010;18:248-54.).

Comorbid obsessive-compulsive personality disorder in obsessive-compulsive disorder (OCD): a marker of severity

INTRODUCTION

Comorbid obsessive-compulsive personality disorder (OCPD) is well-described in obsessive-compulsive disorder (OCD). It remains unclear, however, whether OCPD in OCD represents a distinct subtype of OCD or whether it is simply a marker of severity in OCD.

MATERIALS AND METHODS

The aim of this study was to compare a large sample of OCD subjects (n=403) with and without OCPD on a range of demographic, clinical and genetic characteristics to evaluate whether comorbid OCPD in OCD represents a distinct subtype of OCD, or is a marker of severity.

RESULTS

Our findings suggest that OCD with and without OCPD are similar in terms of gender distribution and age at onset of OC symptoms. Compared to OCD-OCPD (n=267, 66%), those with OCD+OCPD (n=136, 34%) are more likely to present with the OC symptom dimensions which reflect the diagnostic criteria for OCPD (e.g., hoarding), and have significantly greater OCD severity, comorbidity, functional impairment, and poorer insight. Furthermore there are no differences in distribution of gene variants, or response to treatment in the two groups.

CONCLUSION

The majority of our findings suggest that in OCD, patients with OCPD do not have a highly distinctive phenomenological or genetic profile, but rather that OCPD represents a marker of severity.

Identifying sarcomere gene mutations in hypertrophic cardiomyopathy: a personal history

This review provides an historical and personal perspective on the discovery of genetic causes for hypertrophic cardiomyopathy (HCM). Extraordinary insights by physicians who initially detailed remarkable and varied manifestations of the disorder, collaboration among multidisciplinary teams with skills in clinical diagnostics and molecular genetics, and hard work by scores of trainees solved the etiologic riddle of HCM and unexpectedly demonstrated mutations in sarcomere protein genes as the cause of disease. In addition to celebrating 20 years of genetic research in HCM, this article serves as an introductory overview to a thematic review series that will present contemporary advances in the field of hypertrophic heart disease. Through the continued application of advances in genetic methodologies, combined with biochemical and biophysical analyses of the consequences of human mutations, fundamental knowledge about HCM and sarcomere biology has emerged. Expanding research to elucidate the mechanisms by which subtle genetic variation in contractile proteins remodel the human heart remains an exciting opportunity, one with considerable promise to provide new strategies to limit or even prevent HCM pathogenesis.

Genetic variation in angiotensin II type 2 receptor gene influences extent of left ventricular hypertrophy in hypertrophic cardiomyopathy independent of blood pressure

Introduction. Hypertrophic cardiomyopathy (HCM), an inherited primary cardiac disorder mostly caused by defective sarcomeric proteins, serves as a model to investigate left ventricular hypertrophy (LVH). HCM manifests extreme variability in the degree and distribution of LVH, even in patients with the same causal mutation. Genes coding for renin—angiotensin—aldosterone system components have been studied as hypertrophy modifiers in HCM, with emphasis on the angiotensin (Ang) II type 1 receptor (AT1R). However, Ang II binding to Ang II type 2 receptors (AT2R) also has hypertrophy-modulating effects.

Methods. We investigated the effect of the functional +1675 G/A polymorphism (rs1403543) and additional single nucleotide polymorphisms in the 3’ untranslated region of the AT2R gene ( AGTR2) on a heritable composite hypertrophy score in an HCM family cohort in which HCM founder mutations segregate.

Results. We find significant association between rs1403543 and hypertrophy, with each A allele decreasing the average wall thickness by ~0.5 mm, independent of the effects of the primary HCM causal mutation, blood pressure and other hypertrophy covariates ( p = 0.020).

Conclusion. This study therefore confirms a hypertrophy-modulating effect for AT2R also in HCM and implies that +1675 G/A could potentially be used in a panel of markers that profile a genetic predisposition to LVH in HCM.

Serial observations and mutational analysis of an adoptee with family history of hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is an inherited cardiac disease with an autosomal dominant mode of transmission. Comprehensive genetic screening of several genes frequently found mutated in HCM is recommended for first-degree relatives of HCM patients. Genetic testing provides the means to identify those at risk of developing HCM and to institute measures to prevent sudden cardiac death (SCD). Here, we present an adoptee whose natural mother and maternal relatives were known be afflicted with HCM and SCD. The proband was followed closely from age 6 to 17 years, revealing a natural history of the progression of clinical findings associated with HCM. Genetic testing of the proband and her natural mother, who is affected by HCM, revealed that they were heterozygous for both the R719Q and T1513S variants in the cardiac beta-myosin heavy chain (MYH7) gene. The proband's ominous family history indicates that the combination of the R719Q and T1513S variants in cis may be a "malignant" variant that imparts a poor prognosis in terms of the disease progression and SCD risk.

Of founder populations, long QT syndrome, and destiny

Founder populations, characterized by a single ancestor affected by long QT syndrome (LQTS) and by a large number of individuals and families who all are related to the ancestor and thereby carry the same disease-causing mutation, represent the ideal human model for studying the role of "modifier genes" in LQTS. This article reviews some of the fundamental concepts related to founder populations and provides the necessary historical background to understand why so many can be found in South Africa. The focus then moves to a specific LQT1 founder population, carrier of the A341V mutation, that has been studied extensively during the last 10 years and has provided a significant amount of previously unforeseen information. These novel findings range from an unusually high clinical severity not explained by the electrophysiologic characteristics of the mutation, to the importance of tonic and reflex control of heart rate for risk stratification, to the identification of the first modifier genes for clinical severity of LQTS.

Clinical features, survival experience, and profile of plakophylin-2 gene mutations in participants of the arrhythmogenic right ventricular cardiomyopathy registry of South Africa

Little is known about arrhythmogenic right ventricular cardiomyopathy (ARVC) in Africa. The objective of this study was to delineate the clinical characteristics, survival, and genetics of ARVC in South Africa. Information on clinical presentation, electrocardiographic and cardiac imaging findings, histology, and outcome of cases with suspected ARVC was collected using the standardised form of the ARVC Registry of South Africa. Genomic DNA was screened for mutations in plakophylin-2 (PKP2) gene. Survival and its predictors were analyzed using the Kaplan-Meier and Cox proportional hazards regression methods, respectively. Fifty unrelated cases who met the diagnostic criteria for ARVC were enrolled between January 2004 and April 2009. Clinical presentation was similar to that reported in other studies. Annual mortality rate was 2.82%, five-year cumulative mortality rate 10%, and mean age at death 36.9 +/- 14.7 years. Overall survival was similar to the general South African population (P = 0.25). Independent risk factors for death were syncope (Hazard Ratio [HR] 10.73, 95% Confidence Interval [CI] 1.88-61.18, P = 0.008) and sustained ventricular tachycardia (HR = 22.97, 95%CI 2.33-226.18, P = 0.007). Seven PKP2 gene mutations were found in 9/36 (25%) unrelated participants, five being novel. The novel C1162T mutation occurred in four white South Africans sharing a common haplotype, suggesting a founder effect. Compound heterozygotes exhibited a severe phenotype signifying an allele dose effect. ARVC is associated with early mortality that is no different to the general South Africa population whose lifespan is shortened by HIV/AIDS. PKP2 gene mutations are common, have an allele dose effect, and a novel founder effect in white South Africans.

Abnormal blood pressure response to exercise occurs more frequently in hypertrophic cardiomyopathy patients with the R92W troponin T mutation than in those with myosin mutations

Abnormal blood pressure response to exercise is reported to occur in up to a third of hypertrophic cardiomyopathy (HCM) cases and is associated with an increased risk of death, particularly in the young, but it is not known whether the HCM-causing mutation influences blood pressure response to exercise. The purpose of this article is to ascertain whether the blood pressure response to exercise differs among carriers of the R92W mutation in the cardiac troponin T gene (TNNT2), which has been associated with an increased risk of sudden cardiac death in young males; carriers of mutations in the cardiac β-myosin heavy chain gene (MYH7); and their noncarrier relatives. Thirty R92W_TNNT2 carriers, 51 MYH7 mutation carriers, and 68 of their noncarrier relatives were subjected to bicycle ergonometric exercise testing to assess blood pressure response to, as well as heart rate recovery after, exercise. Additional echocardiographic and demographic details were documented for all participants. R92W_TNNT2 carriers demonstrated significantly more abnormal blood pressure responses to exercise (P = .021; odds ratio 3.03; confidence interval 1.13–8.12) and smaller increases in systolic blood pressure than MYH7 mutation carriers or related noncarrier control individuals. Although abnormal blood pressure response occurred at similar frequencies in males in all groups (23%–26%), the percentage of R92W_TNNT2 females with abnormal blood pressure response was 64%, compared with 25% for MYH7 and 22% for noncarriers. Therefore, these results show that blood pressure response to exercise is influenced by genotype and gender in patients with HCM.

Diagnostic, prognostic, and therapeutic implications of genetic testing for hypertrophic cardiomyopathy

Over the last 2 decades, the pathogenic basis for the most common heritable cardiovascular disease, hypertrophic cardiomyopathy (HCM), has been investigated extensively. Affecting approximately 1 in 500 individuals, HCM is the most common cause of sudden death in young athletes. In recent years, genomic medicine has been moving from the bench to the bedside throughout all medical disciplines including cardiology. Now, genomic medicine has entered clinical practice as it pertains to the evaluation and management of patients with HCM. The continuous research and discoveries of new HCM susceptibility genes, the growing amount of data from genotype-phenotype correlation studies, and the introduction of commercially available genetic tests for HCM make it essential that the modern-day cardiologist understand the diagnostic, prognostic, and therapeutic implications of HCM genetic testing.

Alternative exon 9-encoded relay domains affect more than one communication pathway in the Drosophila myosin head

We investigated the biochemical and biophysical properties of one of the four alternative regions within the Drosophila myosin catalytic domain: the relay domain encoded by exon 9. This domain of the myosin head transmits conformational changes in the nucleotide-binding pocket to the converter domain, which is crucial to coupling catalytic activity with mechanical movement of the lever arm. To study the function of this region, we used chimeric myosins (IFI-9b and EMB-9a), which were generated by exchange of the exon 9-encoded domains between the native embryonic body wall (EMB) and indirect flight muscle isoforms (IFI). Kinetic measurements show that exchange of the exon 9-encoded region alters the kinetic properties of the myosin S1 head. This is reflected in reduced values for ATP-induced actomyosin dissociation rate constant (K(1)k(+2)) and ADP affinity (K(AD)), measured for the chimeric constructs IFI-9b and EMB-9a, compared to wild-type IFI and EMB values. Homology models indicate that, in addition to affecting the communication pathway between the nucleotide-binding pocket and the converter domain, exchange of the relay domains between IFI and EMB affects the communication pathway between the nucleotide-binding pocket and the actin-binding site in the lower 50-kDa domain (loop 2). These results suggest an important role of the relay domain in the regulation of actomyosin cross-bridge kinetics.

Diagnostic yield, interpretation, and clinical utility of mutation screening of sarcomere encoding genes in Danish hypertrophic cardiomyopathy patients and relatives

The American Heart Association (AHA) recommends family screening for hypertrophic cardiomyopathy (HCM). We assessed the outcome of family screening combining clinical evaluation and screening for sarcomere gene mutations in a cohort of 90 Danish HCM patients and their close relatives, in all 451 persons. Index patients were screened for mutations in all coding regions of 10 sarcomere genes (MYH7, MYL3, MYBPC3, TNNI3, TNNT2, TPM1, ACTC, CSRP3, TCAP, and TNNC1) and five exons of TTN. Relatives were screened for presence of minor or major diagnostic criteria for HCM and tracking of DNA variants was performed. In total, 297 adult relatives (>18 years) (51.2%) fulfilled one or more criteria for HCM. A total of 38 HCM-causing mutations were detected in 32 index patients. Six patients carried two disease-associated mutations. Twenty-two mutations have only been identified in the present cohort. The genetic diagnostic yield was almost twice as high in familial HCM (53%) vs. HCM of sporadic or unclear inheritance (19%). The yield was highest in families with an additional history of HCM-related clinical events. In relatives, 29.9% of mutation carriers did not fulfil any clinical diagnostic criterion, and in 37.5% of relatives without a mutation, one or more criteria was fulfilled. A total of 60% of family members had no mutation and could be reassured and further follow-up ceased. Genetic diagnosis may be established in approximately 40% of families with the highest yield in familial HCM with clinical events. Mutation-screening was superior to clinical investigation in identification of individuals not at increased risk, where follow-up is redundant, but should be offered in all families with relatives at risk for developing HCM.

Familial hypertrophic cardiomyopathy: basic concepts and future molecular diagnostics

Familial hypertrophic cardiomyopathies (FHC) are the most common genetic heart diseases in the United States, affecting nearly 1 in 500 people. Manifesting as increased cardiac wall thickness, this autosomal dominant disease goes mainly unnoticed as most affected individuals are asymptomatic. Up to 1-2% of children and adolescents and 0.5-1% adults with FHC die of sudden cardiac death, making it critical to quickly and accurately diagnose FHC to institute therapy and potentially reduce mortality. However, due to the heterogeneity of the genetic defects in mainly sarcomere proteins, this is a daunting task even with current diagnostic methods. Exciting new methods utilizing high-throughput microarray technology to identify FHC mutations by a method known as array-based resequencing has recently been described. Additionally, next generation sequencing methodologies may aid in improving FHC diagnosis. In this review, we discuss FHC pathophysiology, the rationale for testing, and discuss the limitations and advantages of current and future diagnostics.

Mendelian-inherited heart disease: a gateway to understanding mechanisms in heart disease Update on work done at the University of Stellenbosch

The presence of founder effects in South Africa for many single-gene diseases, which include heart diseases such as progressive familial heart block types I and II, hypertrophic cardiomyopathy and the long QT syndromes, afforded us the opportunity to identify causal genes and associated mutations through genetic mapping and positional cloning. From finding the genes, the emphasis has shifted to elucidating how primary defects cause disease and recognising factors that could explain the often pronounced phenotypic variability seen in persons carrying the same inherited defect. In some of these diseases, sudden unexpected death has been a frequent occurrence in young, apparently healthy individuals who had not been aware that they had inherited an underlying risk. Herein, we review progress in identifying genes, mutations and risk factors associated with the diseases mentioned.

Investigating the role of the brain-derived neurotrophic factor (BDNF) val66met variant in obsessive-compulsive disorder (OCD)

Although evidence from family studies suggest that genetic factors play an important role in mediating obsessive-compulsive disorder (OCD), results from genetic case-control association analyses have been inconsistent. Discrepant findings may be attributed to the lack of phenotypic resolution, and population stratification. The aim of the present study was to investigate the role that the val66met variant within the gene encoding brain-derived neurotrophic factor (BDNF) may play in mediating the development of selected OCD subtypes accounting for the aforementioned confounding factors. One hundred and twelve OCD subjects and 140 controls were selected from the South African Afrikaner population. A significant association was observed in the male subgroup, with the met66 allele implicated as the risk allele in the development of OCD. This allele was also found to be associated with an earlier age at onset of OCD in males. On the other hand, the val66val genotype was associated with more severe OCD in the female population. No evidence of population stratification was observed in Afrikaner control subjects. These preliminary results point towards genetically distinct characteristics of OCD mediated by dysfunctions in BDNF. The present investigation forms part of ongoing research to elucidate the genetic components involved in the aetiology of OCD and OCD-related characteristics.