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

Chromosomal Location and Identification of TBX20 as a New Gene Responsible for Familial Bicuspid Aortic Valve

Background/Objectives: Congenital bicuspid aortic valve (BAV) signifies the most frequent category of congenital cardiovascular anomaly globally, occurring in approximately 0.5-2% of the general population worldwide. BAV is a major cause of thoracic aortopathy, encompassing aortic stenosis, aortic root dilation with regurgitation, aortic dissection, and aortic aneurysms, consequently leading to substantial late-onset morbidity and mortality. Accumulating evidence convincingly demonstrates the strong genetic basis underpinning BAV, though the inheritable reasons responsible for BAV in most patients remain largely obscure. Methods: A genome-wide genotyping with 400 polymorphic genetic markers followed by linkage analysis, haplotype assay, and sequencing analysis of candidate genes was conducted in a 4-generation BAV kindred of 47 individuals. Biochemical assays were performed to evaluate the functional effect of the identified mutation on TBX20. Results: A novel BAV-causative locus was mapped to chromosome 7p14. A sequencing assay of the genes within the mapped chromosomal region (locus) unveiled that only the c.656T>G (p.Ile219Arg) variation of TBX20 was in co-segregation with BAV in the entire pedigree. The missense mutation was not uncovered in 322 healthy persons employed as control individuals. Functional deciphers revealed that the mutation significantly decreased the transcriptional activation of the representative target gene ANP and the binding ability to the ANP promoter and impaired the intranuclear distribution of TBX20. Conclusions: This investigation maps a new genetic locus (chromosome 7p14) linked to BAV and uncovers TBX20 as a novel causative gene for familial BAV, adding more insight into the mechanisms underlying BAV and providing a molecular target for the individualized management of BAV.

Dimethomorph induces heart and vascular developmental defects by disrupting thyroid hormone in zebrafish embryos

Dimethomorph (DMT) is a widely-used selective active fungicide that effectively controls downy mildew, crown rot, and late blight in crops. The extensive application of DMT raises concerns about its ecological impact on non-target organisms in the environment. However, there is limited understanding of the toxicological properties of DMT on these organisms. In this study, we utilized zebrafish as an animal model to assess the toxicity of DMT induced by exposure 5.5-72 hours post-fertilization (hpf). During this period, we monitored and evaluated the development of the zebrafish heart and vascular system. Additionally, embryo samples were collected to perform molecular-level detection of PCNA, oxidative stress, and related genes. The results showed a concentration-dependent decrease in survival rate and hatching rate, shortened body length, slowed heart rate, and pericardial edema, body curvature and reduced eye size as DMT exposure concentration increased. Furthermore, DMT exposure led to impairments in the development of the heart, vascular, along with change in the expression levels of relevant genes. It also caused a decrease in cell proliferation and an increase in oxidative stress levels. Moreover, DMT disrupts the normal development of thyroid follicular cells, leading to a reduction in T3 levels. Thyroid hormone supplementation partially reverses the toxicity induced by DMT, increasing eye size, restoring body length, reducing spine curvature, and reducing pericardial edema. Therefore, we speculate that DMT likely affects the development of zebrafish embryos by disrupting normal thyroid follicle development.

Bicuspid Aortic Valve, from the Unknown till the Perfection of the Species

The bicuspid aortic valve (BAV) is the most common congenital cardiac abnormality. Though most often isolated, BAV may be associated with other cardiovascular malformations. BAV-related aortopathy is the most common, sharing genetic alterations and phenotypic heterogeneity characteristics. Sometimes silent for a lifetime, BAV may manifest as aortic valve dysfunction, aortic aneurysm, or more emergent situations, such as endocarditis or aortic dissection. Its embryological origin and the characterization of the genes involved, as well as the histopathological and hemodynamic aspects of its natural history, are becoming increasingly clear. In addition, emerging evidence of rhythm disorders associated with BAV has been identified. A new international nomenclature and classification has been introduced to interpret all the advances made in recent years for the comprehension of this condition. In the guidelines, more attention has been paid to the diagnosis of BAV and related aortopathy, together with surveillance, and family screening. Surgical treatment remains the gold standard, especially in young low-risk patients, and valve repair techniques have been shown to be effective and durable. Finally, the new era of transcatheter techniques is also being applied to dysfunctional BAV, allowing the treatment of patients at high surgical risk, with increasingly promising results, and the possibility of expanding indications through the introduction of more advanced devices. This review aims to comprehensively describe the BAV conundrum, focusing on anatomy, pathophysiology, genetics, diagnosis of BAV-related disorders, and the different treatment options available in the transcatheter era.

Somatic GATA4 mutation contributes to tetralogy of Fallot

Tetralogy of Fallot (TOF) is the most prevalent cyanotic congenital heart pathology and causes infant morbidity and mortality worldwide. GATA-binding protein 4 (GATA4) serves as a pivotal transcriptional factor for embryonic cardiogenesis and germline GATA4 mutations are causally linked to TOF. However, the effects of somatic GATA4 mutations on the pathogenesis of TOF remain to be ascertained. In the present study, sequencing assay of GATA4 was performed utilizing genomic DNA derived from resected heart tissue specimens as well as matched peripheral blood specimens of 62 patients with non-familial TOF who underwent surgical treatment for TOF. Sequencing of GATA4 was also performed using the heart tissue specimens as well as matched peripheral venous blood samples of 68 sporadic cases who underwent heart valve displacement because of rheumatic heart disorder and the peripheral venous whole blood samples of 216 healthy subjects. The function of the mutant was explored by dual-luciferase activity analysis. Consequently, a new GATA4 mutation, NM_002052.5:c.708T>G;p.(Tyr236*), was found in the heart tissue of one patient with TOF. No mutation was detected in the heart tissue of the 68 cases suffering from rheumatic heart disorder or in the venous blood samples of all 346 individuals. GATA4 mutant failed to transactivate its target gene, myosin heavy chain 6. Additionally, this mutation nullified the synergistic transactivation between GATA4 and T-box transcription factor 5 or NK2 homeobox 5, two genes causative for TOF. Somatic GATA4 mutation predisposes TOF, highlighting the significant contribution of somatic variations to the molecular pathogenesis underpinning TOF.

Whole exome sequencing reveals genetic landscape associated with left ventricular outflow tract obstruction in Chinese Han population

Left ventricular outflow tract obstruction (LVOTO), a major form of outflow tract malformation, accounts for a substantial portion of congenital heart defects (CHDs). Unlike its prevalence, the genetic architecture of LVOTO remains largely unknown. To unveil the genetic mutations and risk genes potentially associated with LVOTO, we enrolled a cohort of 106 LVOTO patients and 100 healthy controls and performed a whole-exome sequencing (WES). 71,430 rare deleterious mutations were found in LVOTO patients. By using gene-based burden testing, we further found 32 candidate genes enriched in LVOTO patient including known pathological genes such as GATA5 and GATA6. Most variants of 32 risk genes occur simultaneously rather exclusively suggesting polygenic inherence of LVOTO and 14 genes out of 32 risk genes interact with previously discovered CHD genes. Single cell RNA-seq further revealed dynamic expressions of GATA5, GATA6, FOXD3 and MYO6 in endocardium and neural crest lineage indicating the mutations of these genes lead to LVOTO possibly through different lineages. These findings uncover the genetic architecture of LVOTO which advances the current understanding of LVOTO genetics.

Nkx2.5: a crucial regulator of cardiac development, regeneration and diseases

Cardiomyocytes fail to regenerate after birth and respond to mitotic signals through cellular hypertrophy rather than cellular proliferation. Necrotic cardiomyocytes in the infarcted ventricular tissue are eventually replaced by fibroblasts, generating scar tissue. Cardiomyocyte loss causes localized systolic dysfunction. Therefore, achieving the regeneration of cardiomyocytes is of great significance for cardiac function and development. Heart development is a complex biological process. An integral cardiac developmental network plays a decisive role in the regeneration of cardiomyocytes. During this process, genetic epigenetic factors, transcription factors, signaling pathways and small RNAs are involved in regulating the developmental process of the heart. Cardiomyocyte-specific genes largely promote myocardial regeneration, among which the Nkx2.5 transcription factor is one of the earliest markers of cardiac progenitor cells, and the loss or overexpression of Nkx2.5 affects cardiac development and is a promising candidate factor. Nkx2.5 affects the development and function of the heart through its multiple functional domains. However, until now, the specific mechanism of Nkx2.5 in cardiac development and regeneration is not been fully understood. Therefore, this article will review the molecular structure, function and interaction regulation of Nkx2.5 to provide a new direction for cardiac development and the treatment of heart regeneration.

Comparison of Outcome in Patients With Familial Versus Spontaneous Atrial Septal Defect

Patients with atrial septal defects (ASDs) have increased mortality and morbidity. This can only partly be explained by hemodynamic changes caused by the ASD, suggesting additional underlying causes. Patients with an ASD have an increased burden of pathogenic gene variants in ASD-related genes, indicating genetics as an important factor in etiology. Inheritance of genetic variants with high impact can cause ASD in relatives (familial ASD). This study aimed to investigate whether lifelong outcomes were different in patients with familial ASD compared with patients with sporadic ASD. We used health registries and a nationwide cohort of 2,151 patients with ASD to compare the incidences of atrial fibrillation or flutter (together abbreviated as AF), heart failure, and mortality between patients with familial and sporadic ASD using Cox proportional hazard ratio and Fine and Gray analysis. Patients with familial ASD experienced AF and heart failure earlier in life than patients with sporadic ASD, with hazard ratios of 1.6 and 1.7, respectively. Subdistribution hazard ratios showed an increased risk of AF and heart failure in patients with familial ASD compared with patients with sporadic ASDs (2.3 and 3.1, respectively). Our results suggest that genetic variants with high impact may influence the outcomes of patients with ASD. In conclusion, patients with familial ASD have an increased risk and an earlier onset of AF and heart failure compared with patients with sporadic ASD, hence clinical awareness of arrhythmias and heart failure in patients with familial ASD may lead to timely treatment.

TBX5 variant with the novel phenotype of mixed‑type total anomalous pulmonary venous return in Holt‑Oram Syndrome and variable intrafamilial heart defects

Variants in T‑box transcription factor 5 (TBX5) can result in a wide phenotypic spectrum, specifically in the heart and the limbs. TBX5 has been implicated in causing non‑syndromic cardiac defects and Holt‑Oram syndrome (HOS). The present study investigated the underlying molecular etiology of a family with heterogeneous heart defects. The proband had mixed‑type total anomalous pulmonary venous return (mixed‑type TAPVR), whereas her mother had an atrial septal defect. Genetic testing through trio‑based whole‑exome sequencing was used to reveal the molecular etiology. A nonsense variant was identified in TBX5 (c.577G>T; p.Gly193*) initially showing co‑segregation with a presumably non‑syndromic presentation of congenital heart disease. Subsequent genetic investigations and more complete phenotyping led to the correct diagnosis of HOS, documenting the novel association of mixed‑type TAPVR with HOS. Finally, protein modeling of the mutant TBX5 protein that harbored this pathogenic nonsense variant (p.Gly193*) revealed a substantial drop in the quantity of non‑covalent bonds. The decrease in the number of non‑covalent bonds suggested that the resultant mutant dimer was less stable compared with the wild‑type protein, consequently affecting the protein's ability to bind DNA. The present findings extended the phenotypic cardiac defects associated with HOS; to the best of our knowledge, this is the first association of mixed‑type TAPVR with TBX5. Prior to the current analysis, the molecular association of TAPVR with HOS had never been documented; hence, this is the first genetic investigation to report the association between TAPVR and HOS. Furthermore, it was demonstrated that the null‑variants reported in the T‑box domain of TBX5 were associated with a wide range of cardiac and/or skeletal anomalies on both the inter‑and intrafamilial levels. In conclusion, genetic testing was highlighted as a potentially powerful approach in the prognostication of the proper diagnosis.

SOX7 loss-of-function variation as a cause of familial congenital heart disease

INTRODUCTION

As the most frequent type of birth defect in humans, congenital heart disease (CHD) leads to a large amount of morbidity and mortality as well as a tremendous socioeconomic burden. Accumulating studies have convincingly substantiated the pivotal roles of genetic defects in the occurrence of familial CHD, and deleterious variations in a great number of genes have been reported to cause various types of CHD. However, owing to pronounced genetic heterogeneity, the hereditary components underpinning CHD remain obscure in most cases. This investigation aimed to identify novel genetic determinants underlying CHD.

METHODS AND RESULTS

A four-generation pedigree with high incidence of autosomal-dominant CHD was enrolled from the Chinese Han race population. Using whole-exome sequencing and Sanger sequencing assays of the family members available, a novel SOX7 variation in heterozygous status, NM_031439.4: c.310C>T; p.(Gln104*), was discovered to be in co-segregation with the CHD phenotype in the whole family. The truncating variant was absent in 500 unrelated healthy subjects utilized as control individuals. Functional measurements by dual-luciferase reporter analysis revealed that Gln104*-mutant SOX7 failed to transactivate its two important target genes, GATA4 and BMP2, which are both responsible for CHD. In addition, the nonsense variation invalidated the cooperative transactivation between SOX7 and NKX2.5, which is another recognized CHD-causative gene.

CONCLUSION

The present study demonstrates for the first time that genetically defective SOX7 predisposes to CHD, which sheds light on the novel molecular mechanism underpinning CHD, and implies significance for precise prevention and personalized treatment in a subset of CHD patients.

Update in Biomolecular and Genetic Bases of Bicuspid Aortopathy

Bicuspid aortic valve (BAV) associated with aortopathy is the most common congenital heart disease in the general population. Far from being a simple harmless valve malformation, it can be a complex and heterogeneous disease and a source of chronic and acute pathology (early valvular disease, aneurysm, dissection). In the previous years, intense research has been carried out to find out and understand its mechanisms, but the pathophysiology of the disease is still not fully understood and many questions remain open. Recent studies have discovered several genetic mutations involved in the development of valvular and aortic malformations, but still cannot explain more than 5–10% of cases. Other studies have also focused on molecular alterations and cellular processes (TGF-β pathway, microRNAs, degradation of the extracellular matrix, metalloproteinases, etc.), being a field in constant search and development, looking for a therapeutic target to prevent the development of the disease. Increased knowledge about this multifaceted disorder, derived from both basic and clinical research, may influence the diagnosis, follow-up, prognosis, and therapies of affected patients in the near future. This review focuses on the latest and outstanding developments on the molecular and genetic investigations of the bicuspid aortopathy.

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.