Identification and Functional Characterization of an ISL1 Mutation Predisposing to Dilated Cardiomyopathy

Genetic and functional variants of the TBX20 gene promoter in dilated cardiomyopathy

BACKGROUND

Dilated cardiomyopathy (DCM) is a major cause of heart failure and sudden cardiac death. As DCM is a genetically heterogeneous disease, genetic variants of cardiac transcription factor genes may play an important role. Transcription factor TBX20, an indispensable factor in normal heart development, is involved in the regulation of cardiac structure and function. Although the TBX20 gene is associated with the occurrence and development of DCM, the influence of genetic variants of the TBX20 gene promoter region on DCM has not been reported.

METHODS

We conducted a case-control study consisting of 107 DCM patients and 210 healthy controls. Genetic variants within TBX20 gene promoter region were identified using sequencing techniques and were functionally analyzed by dual-luciferase reporting assay. Electrophoretic mobility shift assay (EMSA) was used to investigate DNA-protein interactions.

RESULTS

In this study cohort (n = 317), we identified eight variants within TBX20 gene promoter. One novel DNA sequence variants (DSV) (g.4275G>T) and four single-nucleotide polymorphisms (SNPs) [g.4169G>A (rs1263874255), g.4949C>T (rs1191745927), g.5114G>A (rs112076877), g.5252C>T (rs1356932911)] were identified in DCM patients, but in none of controls. Among them, the DSV (g.4275G>T) and three SNPs [g.4949C>T (rs1191745927), g.5114G>A (rs112076877) and g.5252C>T (rs1356932911)] significantly altered the transcription activity of TBX20 gene promoter by dual-luciferase reporting assay (p < 0.05). Further, EMSA assay indicated that the DSV (g.4275G>T) and three SNPs [g.4949C>T (rs1191745927), g.5114G>A (rs112076877) and g.5252C>T (rs1356932911)] affected the binding of transcription factors.

CONCLUSIONS

These data indicate that the DSV (g.4275G>T) and three SNPs [g.4949C>T (rs1191745927), g.5114G>A (rs112076877) and g.5252C>T (rs1356932911)] increase transcription activity of TBX20 gene promoter in both HEK-293 and neonatal rat cardiomyocytes (NRCMs) cell lines by affecting the binding of transcription factors. But the mechanism remains to be verified in vivo.

Genetic Variants of ISL1 Gene Promoter Identified from Congenital Tetralogy of Fallot Patients Alter Cellular Function Forming Disease Basis

Tetralogy of Fallot (TOF) is the most common cyanotic congenital heart disease in newborns. ISL1 is a master transcription factor in second heart field development, whereas the roles of ISL1 gene promoter variants in TOF patients have not been genetically investigated. Total DNA extraction from 601 human subjects, including 308 TOF patients and 293 healthy controls, and Sanger sequencing were performed. Four variants (including one novel heterozygous variant) within the ISL1 gene promoter were only found in TOF patients. Functional analysis of DNA sequence variants was performed by using the dual-luciferase reporter assay and demonstrated that three of the four variants significantly decreased the transcriptional activity of ISL1 gene promoter in HL-1 cells (p < 0.05). Further, the online JASPAR database and electrophoretic mobility shift assay showed that the three variants affected the binding of transcription factors and altered ISL1 expression levels. In conclusion, the current study for the first time demonstrated that the variants identified from the ISL1 gene promoter region are likely involved in the development of TOF by affecting the transcriptional activity and altering the ISL1 expression level. Therefore, these findings may provide new insights into the molecular etiology and potential therapeutic strategy of TOF.

Identification of a novel missense mutation in the TPM1 gene via exome sequencing in a Chinese family with dilated cardiomyopathy: A case report and literature review

RATIONALE

Dilated cardiomyopathy (DCM) is a cardiovascular disorder characterized by consecutive ventricular dilation and contractile dysfunction, often leading to congestive heart failure. DCM type 1Y (DCM1Y) is caused by a mutation in the TPM1 (tropomyosin 1) gene. To date, about thirty TPM1 gene mutations have been reported to be related to DCM1Y. However, mutational screening of the TPM1 gene is still far from being complete. Identification of TPM1 mutation is particularly important in the diagnosis of DCM1Y and will give more insights into the molecular pathogenesis of DCM1Y.

PATIENT CONCERNS

A Chinese Han family with DCM phenotypes was examined.

DIAGNOSIS

A novel missense mutation, c.340G > C in exon 3 of the TPM1 gene, was identified.

INTERVENTIONS

Next-generation sequencing (NGS) of DNA samples was performed to detect the gene mutation in the proband, which was confirmed by Sanger sequencing.

OUTCOMES

This novel heterozygous mutation results in the substitution of glutamic acid with glutamine (p.E114Q). Based on this finding and clinical manifestations, a final diagnosis of DCM1Y was made.

LESSONS

We present evidence that p.E114Q mutation represents a novel TPM1 mutation in a Chinese Han family with DCM. Our data expand the mutation spectrum of the TPM1 gene and may facilitate the clinical diagnosis of DCM1Y.

Heart failure risk estimation based on novel biomarkers

Introduction: Despite advances in medical care, heart failure (HF)-associated morbidity and mortality remains high. Consequently, there is increased effort to find better ways for predicting, screening, and prognosticating HF in order to facilitate effective primary and secondary prevention.Areas covered: In this review, we describe the various biomarkers associated with different etiologic pathways implicated in HF, and discuss their roles in screening, diagnosing, prognosticating and predicting HF. We explore the emerging role of multi-omic approaches. We performed electronic searches in databases (PubMed and Google Scholar) through December 2020, using the following key terms: biomarker, novel, heart failure, risk, prediction, and estimation.Circulating BNP and troponin concentrations have been established in clinical care as key biomarkers for diagnosing and prognosticating HF. Emerging biomarkers (such as galectin-3 and ST-2) have gained further recognition for use in evaluating prognosis of HF patients. Promising biomarkers that are yet to be part of clinical recommendations include biomarkers of cardiorenal disease.Expert opinion: Increasing recognition of the complex and interdependent nature of pathophysiological pathways of HF has led to the application of multi-marker approaches including multi-omic high throughput assays. These newer approaches have the potential for new therapeutic discoveries and improving precision medicine in HF.

SOX17 Loss-of-Function Mutation Underlying Familial Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) refers to a rare, progressive disorder that is characterized by occlusive pulmonary vascular remodeling, resulting in increased pulmonary arterial pressure, right-sided heart failure, and eventual death. Emerging evidence from genetic investigations of pediatric-onset PAH highlights the strong genetic basis underpinning PAH, and deleterious variants in multiple genes have been found to cause PAH. Nevertheless, PAH is of substantial genetic heterogeneity, and the genetic defects underlying PAH in the overwhelming majority of cases remain elusive. In this investigation, a consanguineous family suffering from PAH transmitted as an autosomal-dominant trait was identified. Through whole-exome sequencing and bioinformatic analyses as well as Sanger sequencing analyses of the PAH family, a novel heterozygous SOX17 mutation, NM_022454.4: c.379C>T; p. (Gln127*), was found to co-segregate with the disease in the family, with complete penetrance. The nonsense mutation was neither observed in 612 unrelated healthy volunteers nor retrieved in the population genetic databases encompassing the Genome Aggregation Database, the Exome Aggregation Consortium database, and the Single Nucleotide Polymorphism database. Biological analyses using a dual-luciferase reporter assay system revealed that the Gln127*-mutant SOX17 protein lost the ability to transcriptionally activate its target gene NOTCH1. Moreover, the Gln127*-mutant SOX17 protein exhibited no inhibitory effect on the function of CTNNB1-encode β-catenin, which is a key player in vascular morphogenesis. This research firstly links SOX17 loss-of-function mutation to familial PAH, which provides novel insight into the molecular pathogenesis of PAH, suggesting potential implications for genetic and prognostic risk evaluation as well as personalized prophylaxis of the family members affected with PAH.

SOX17 loss-of-function variation underlying familial congenital heart disease

As the most prevalent form of human birth defect, congenital heart disease (CHD) contributes to substantial morbidity, mortality and socioeconomic burden worldwide. Aggregating evidence has convincingly demonstrated that genetic defects exert a pivotal role in the pathogenesis of CHD, and causative mutations in multiple genes have been causally linked to CHD. Nevertheless, CHD is of pronounced genetic heterogeneity, and the genetic components underpinning CHD in the overwhelming majority of patients remain obscure. In this research, a four-generation consanguineous family suffering from CHD transmitted in an autosomal dominant mode was recruited. By whole-exome sequencing and bioinformatics analyses as well as Sanger sequencing analyses of the family members, a new heterozygous SOX17 variation, NM_022454.4: c.553G > T; p.(Glu185*), was identified to co-segregate with CHD in the family, with complete penetrance. The nonsense variation was neither detected in 310 unrelated healthy volunteers used as controls nor retrieved in such population genetics databases as the Exome Aggregation Consortium database, Genome Aggregation Database, and the Single Nucleotide Polymorphism database. Functional assays by utilizing a dual-luciferase reporter assay system unveiled that the Glu185*-mutant SOX17 protein had no transcriptional activity on its two target genes NOTCH1 and GATA4, which have been reported to cause CHD. Furthermore, the mutation abrogated the synergistic transactivation between SOX17 and NKX2.5, another established CHD-causing transcription factor. These findings firstly indicate SOX17 loss-of-function mutation predisposes to familial CHD, which adds novel insight to the molecular mechanism of CHD, implying potential implications for genetic risk appraisal and individualized prophylaxis of the family members affected with CHD.

Cardiomyopathies in China: A 2018-2019 state-of-the-art review

Cardiomyopathies are diseases of the cardiac muscle and are often characterized by ventricular dilation, hypertrophy, and cardiac arrhythmia. Patients with cardiomyopathies often experience sudden death and cardiac failure and require cardiac transplantation during the course of disease progression. Early diagnosis, differential diagnosis, and genetic consultation depend on imaging techniques, genetic testing, and new emerging diagnostic tools such as serum biomarkers. The molecular genetics of cardiomyopathies has been widely studied recently. The discovery of mechanisms underlying heterogeneity and overlapping of the phenotypes of cardiomyopathies has revealed the existence of disease modifiers, and this has led to the emergence of novel disease-modifying therapy. This 2018-2019 state-of-the-art review outlines the pathogenesis, diagnosis, and treatment of cardiomyopathies in China.

Detection and functional characterization of a novel MEF2A variation responsible for familial dilated cardiomyopathy

OBJECTIVES

Dilated cardiomyopathy (DCM) represents the most frequent form of cardiomyopathy, leading to heart failure, cardiac arrhythmias and death. Accumulating evidence convincingly demonstrates the crucial role of genetic defects in the pathogenesis of DCM, and over 100 culprit genes have been implicated with DCM. However, DCM is of substantial genetic heterogeneity, and the genetic determinants underpinning DCM remain largely elusive.

METHODS

Whole-exome sequencing and bioinformatical analyses were implemented in a consanguineous Chinese family with DCM. A total of 380 clinically annotated control individuals and 166 more DCM index cases then underwent Sanger sequencing analysis for the identified genetic variation. The functional characteristics of the variant were delineated by utilizing a dual-luciferase assay system.

RESULTS

A heterozygous variation in the MEF2A gene (encoding myocyte enhancer factor 2A, a transcription factor pivotal for embryonic cardiogenesis and postnatal cardiac adaptation), NM_001365204.1: c.718G>T; p. (Gly240*), was identified, and verified by Sanger sequencing to segregate with autosome-dominant DCM in the family with complete penetrance. The nonsense variation was neither detected in 760 control chromosomes nor found in 166 more DCM probands. Functional analyses revealed that the variant lost transactivation on the validated target genes MYH6 and FHL2, both causally linked to DCM. Furthermore, the variation nullified the synergistic activation between MEF2A and GATA4, another key transcription factor involved in DCM.

CONCLUSIONS

The findings firstly indicate that MEF2A loss-of-function variation predisposes to DCM in humans, providing novel insight into the molecular mechanisms of DCM and suggesting potential implications for genetic testing and prognostic evaluation of DCM patients.

A novel TBX5 mutation predisposes to familial cardiac septal defects and atrial fibrillation as well as bicuspid aortic valve

TBX5 has been linked to Holt-Oram syndrome, with congenital heart defect (CHD) and atrial fibrillation (AF) being two major cardiac phenotypes. However, the prevalence of a TBX5 variation in patients with CHD and AF remains obscure. In this research, by sequencing analysis of TBX5 in 178 index patients with both CHD and AF, a novel heterozygous variation, NM_000192.3: c.577G>T; p.(Gly193*), was identified in one index patient with CHD and AF as well as bicuspid aortic valve (BAV), with an allele frequency of approximately 0.28%. Genetic analysis of the proband's pedigree showed that the variation co-segregated with the diseases. The pathogenic variation was not detected in 292 unrelated healthy subjects. Functional analysis by using a dual-luciferase reporter assay system showed that the Gly193*-mutant TBX5 protein failed to transcriptionally activate its target genes MYH6 and NPPA. Moreover, the mutation nullified the synergistic transactivation between TBX5 and GATA4 as well as NKX2-5. Additionally, whole-exome sequencing analysis showed no other genes contributing to the diseases. This investigation firstly links a pathogenic variant in the TBX5 gene to familial CHD and AF as well as BAV, suggesting that CHD and AF as well as BAV share a common developmental basis in a subset of patients.

ISL1 loss-of-function variation causes familial atrial fibrillation

Atrial fibrillation (AF) represents the most frequent form of sustained cardiac rhythm disturbance, affecting approximately 1% of the general population worldwide, and confers a substantially enhanced risk of cerebral stroke, heart failure, and death. Increasing epidemiological studies have clearly demonstrated a strong genetic basis for AF, and variants in a wide range of genes, including those coding for ion channels, gap junction channels, cardiac structural proteins and transcription factors, have been identified to underlie AF. Nevertheless, the genetic pathogenesis of AF is complex and still far from completely understood. Here, whole-exome sequencing and bioinformatics analyses of a three-generation family with AF were performed, and after filtering variants by multiple metrics, we identified a heterozygous variant in the ISL1 gene (encoding a transcription factor critical for embryonic cardiogenesis and postnatal cardiac remodeling), NM_002202.2: c.481G > T; p.(Glu161*), which was validated by Sanger sequencing and segregated with autosome-dominant AF in the family with complete penetrance. The nonsense variant was absent from 284 unrelated healthy individuals used as controls. Functional assays with a dual-luciferase reporter assay system revealed that the truncating ISL1 protein lost transcriptional activation on the verified target genes MEF2C and NKX2-5. Additionally, the variant nullified the synergistic transactivation between ISL1 and TBX5 as well as GATA4, two other transcription factors that have been implicated in AF. The findings suggest ISL1 as a novel gene contributing to AF, which adds new insight to the genetic mechanisms underpinning AF, implying potential implications for genetic testing and risk stratification of the AF family members.

Homozygous damaging SOD2 variant causes lethal neonatal dilated cardiomyopathy

BACKGROUND

Idiopathic dilated cardiomyopathy (DCM) is recognised to be a heritable disorder, yet clinical genetic testing does not produce a diagnosis in >50% of paediatric patients. Identifying a genetic cause is crucial because this knowledge can affect management options, cardiac surveillance in relatives and reproductive decision-making. In this study, we sought to identify the underlying genetic defect in a patient born to consanguineous parents with rapidly progressive DCM that led to death in early infancy.

METHODS AND RESULTS

Exome sequencing revealed a potentially pathogenic, homozygous missense variant, c.542G>T, p.(Gly181Val), in SOD2. This gene encodes superoxide dismutase 2 (SOD2) or manganese-superoxide dismutase, a mitochondrial matrix protein that scavenges oxygen radicals produced by oxidation-reduction and electron transport reactions occurring in mitochondria via conversion of superoxide anion (O₂ ^-·) into H₂O₂. Measurement of hydroethidine oxidation showed a significant increase in O₂ ^-· levels in the patient's skin fibroblasts, as compared with controls, and this was paralleled by reduced catalytic activity of SOD2 in patient fibroblasts and muscle. Lentiviral complementation experiments demonstrated that mitochondrial SOD2 activity could be completely restored on transduction with wild type SOD2.

CONCLUSION

Our results provide evidence that defective SOD2 may lead to toxic increases in the levels of damaging oxygen radicals in the neonatal heart, which can result in rapidly developing heart failure and death. We propose SOD2 as a novel nuclear-encoded mitochondrial protein involved in severe human neonatal cardiomyopathy, thus expanding the wide range of genetic factors involved in paediatric cardiomyopathies.

Human Induced Pluripotent Stem-Cell-Derived Cardiomyocytes as Models for Genetic Cardiomyopathies

In the last few decades, many pathogenic or likely pathogenic genetic mutations in over hundred different genes have been described for non-ischemic, genetic cardiomyopathies. However, the functional knowledge about most of these mutations is still limited because the generation of adequate animal models is time-consuming and challenging. Therefore, human induced pluripotent stem cells (iPSCs) carrying specific cardiomyopathy-associated mutations are a promising alternative. Since the original discovery that pluripotency can be artificially induced by the expression of different transcription factors, various patient-specific-induced pluripotent stem cell lines have been generated to model non-ischemic, genetic cardiomyopathies in vitro. In this review, we describe the genetic landscape of non-ischemic, genetic cardiomyopathies and give an overview about different human iPSC lines, which have been developed for the disease modeling of inherited cardiomyopathies. We summarize different methods and protocols for the general differentiation of human iPSCs into cardiomyocytes. In addition, we describe methods and technologies to investigate functionally human iPSC-derived cardiomyocytes. Furthermore, we summarize novel genome editing approaches for the genetic manipulation of human iPSCs. This review provides an overview about the genetic landscape of inherited cardiomyopathies with a focus on iPSC technology, which might be of interest for clinicians and basic scientists interested in genetic cardiomyopathies.

Importance of Genetic Testing in Dilated Cardiomyopathy: Applications and Challenges in Clinical Practice

Dilated cardiomyopathy (DCM) is a clinical syndrome characterized by left ventricular dilatation and contractile dysfunction. It is the most common cause of heart failure in young adults. The advent of next-generation sequencing has contributed to the discovery of a large amount of genomic data related to DCM. Mutations involving genes that encode cytoskeletal proteins, the sarcomere, and ion channels account for approximately 40% of cases previously classified as idiopathic DCM. In this scenario, geneticists and cardiovascular genetics specialists have begun to work together, building knowledge and establishing more accurate diagnoses. However, proper interpretation of genetic results is essential and multidisciplinary teams dedicated to the management and analysis of the obtained information should be considered. In this review, we approach genetic factors associated with DCM and their prognostic relevance and discuss how the use of genetic testing, when well recommended, can help cardiologists in the decision-making process.