Genetic mutation analysis in Japanese patients with non-syndromic congenital heart disease

Sequence variations in GATA4 and CITED2 gene among patients with cardiac septation defects from Xinjiang, China

Studies have shown that genetic factors play an important role in CHD's development. The mutations in GATA4 and CITED2 genes result in the failure of the heart to develop normally, thereby leading to septal defects. The present study investigated the underlying molecular aetiology of patients with cardiac septation defects from Xinjiang. We investigated variants of the GATA4 and CITED2 gene coding regions in 172 patients with cardiac septation defects by sequencing. Healthy controls (n = 200) were included. Three heterozygous variations (p.V380M, p.P394T, and p.P407Q) of the GATA4 gene were identified in three patients. p.V380M was discovered in a patient with atrial septal defect. p.P394T was noted in a patient with atrial septal defect. p.V380M and p.P407Q of the GATA4 gene were detected in one patient with ventricular septal defect. A novel homozygous variation (p. Sl92G) of the CITED2 gene was found in one patient with ventricular septal defect. Other patients and healthy individuals were normal. The limited prevalence of genetic variations observed in individuals with cardiac septal defects from Xinjiang provides evidence in favour of the hypothesis that CHD is a polygenic hereditary disorder. It is plausible that mutations in the GATA4 and CITED2 genes could potentially underlie the occurrence of idiopathic CHD in affected patients.

A Pilot Study of Multiplex Ligation-Dependent Probe Amplification Evaluation of Copy Number Variations in Romanian Children with Congenital Heart Defects

Congenital heart defects (CHDs) have had an increasing prevalence over the last decades, being one of the most common congenital defects. Their etiopathogenesis is multifactorial in origin. About 10-15% of all CHD can be attributed to copy number variations (CNVs), a type of submicroscopic structural genetic alterations. The aim of this study was to evaluate the involvement of CNVs in the development of congenital heart defects. We performed a cohort study investigating the presence of CNVs in the 22q11.2 region and GATA4, TBX5, NKX2-5, BMP4, and CRELD1 genes in patients with syndromic and isolated CHDs. A total of 56 patients were included in the study, half of them (28 subjects) being classified as syndromic. The most common heart defect in our study population was ventricular septal defect (VSD) at 39.28%. There were no statistically significant differences between the two groups in terms of CHD-type distribution, demographical, and clinical features, with the exceptions of birth length, weight, and length at the time of blood sampling, that were significantly lower in the syndromic group. Through multiplex ligation-dependent probe amplification (MLPA) analysis, we found two heterozygous deletions in the 22q11.2 region, both in patients from the syndromic group. No CNVs involving GATA4, NKX2-5, TBX5, BMP4, and CRELD1 genes were identified in our study. We conclude that the MLPA assay may be used as a first genetic test in patients with syndromic CHD and that the 22q11.2 region may be included in the panels used for screening these patients.

Total Anomalous Pulmonary Venous Connections, Human Genetics

Partial anomalous pulmonary venous connections (PAVC) have been found after abnormal gene expressions involving several syndromes. Total anomalous pulmonary venous connection (TAPVC) is found in conjunction with heterotaxia syndrome as well as several other syndromes. It has been reported with an autosomal dominance with variable expression and incomplete penetrance. The occurrence is also related to environmental factors which may superimpose on a familial susceptibility for TAPVC. Many pathways are involved in the normal development of the pulmonary venous connections and as a consequence disturbance of many genetic and epigenetic pathways lead to partial or total pulmonary venous misconnections. In this chapter, an overview of current knowledge regarding human genetics of anomalous venous connections is provided.

TBX5 pathogenic variant in a patient with congenital heart defect and tracheal stenosis

Congenital tracheal stenosis is a rare life-threatening disorder caused by narrow O-shaped tracheal ring without smooth muscle. Its underlying genetic cause has not been elucidated. We performed whole exome sequencing in a patient with congenital tracheal stenosis and congenital heart defect, and identified a de novo pathogenic TBX5 variant (NM_181486.4:c.680T>C, p.(Ile227Thr)). The Ile227Thr-TBX5 protein was predicted to have a decreased stability by in silico protein structural analyses, and was shown to have a significantly reduced activity for the NPPA promoter by luciferase assay. The results, together with the expression of mouse Tbx5 in the lung and trachea and the development of tracheal cartilage dysplasia in the lung-specific Tbx5 null mice, imply the relevance of TBX5 pathogenic variants to congenital tracheal stenosis.

Genetic Alterations of Transcription Factors and Signaling Molecules Involved in the Development of Congenital Heart Defects-A Narrative Review

Congenital heart defects (CHD) are the most common congenital abnormality, with an overall global birth prevalence of 9.41 per 1000 live births. The etiology of CHDs is complex and still poorly understood. Environmental factors account for about 10% of all cases, while the rest are likely explained by a genetic component that is still under intense research. Transcription factors and signaling molecules are promising candidates for studies regarding the genetic burden of CHDs. The present narrative review provides an overview of the current knowledge regarding some of the genetic mechanisms involved in the embryological development of the cardiovascular system. In addition, we reviewed the association between the genetic variation in transcription factors and signaling molecules involved in heart development, including TBX5, GATA4, NKX2-5 and CRELD1, and congenital heart defects, providing insight into the complex pathogenesis of this heterogeneous group of diseases. Further research is needed in order to uncover their downstream targets and the complex network of interactions with non-genetic risk factors for a better molecular-phenotype correlation.

A genetic and developmental biological approach for a family with complex congenital heart diseases-evidence of digenic inheritance

Objective

Congenital heart disease (CHD) is caused by cardiovascular developmental defects and has a global prevalence of ∼1%. The etiology of CHD is multifactorial and remains generally unknown, despite advances in analytical techniques based on next-generation sequencing (NGS). The aim of our study was to elucidate the multi-genetic origin and pathogenesis of an intriguing familial case with complex CHD.

Methods

We performed an original trio-based gene panel analysis using NGS of the family, including two siblings with CHD of single ventricular phenotype, and their unaffected parents. The pathogenicity of the detected rare variants was investigated in silico, and the functional effects of the variants were confirmed in vitro using luciferase assays. The combinatorial effect of gene alterations of the putative responsible genes was tested in vivo using genetically engineered mutant mice.

Results

NGS-based gene panel analyses revealed two heterozygous rare variants in NODAL and in TBX20 common to the siblings and to just one of parents. Both variants were suspected pathogenic in silico, and decreased transcriptional activities of downstream signaling pathways were observed in vitro. The analyses of Nodal and Tbx20 double mutant mice demonstrated that Nodal+/-Tbx20-/- embryos showed more severe defects than Nodal+/+Tbx20-/- embryos during early heart development. The expression of Pitx2, a known downstream target of Nodal, was downregulated in Tbx20-/- mutants.

Conclusions

Two rare variants on NODAL and TBX20 genes detected in this family were considered to be loss-of-function mutations. Our results suggest that NODAL and TBX20 may be complementary for the cardiac development, and a combinatorial loss-of-function of NODAL and TBX20 could be implicated in digenic inherence as the etiology of complex CHD associated with single ventricle defects in this family.

High-risk genes involved in common septal defects of congenital heart disease

The septation defect is one of the main categories of congenital heart disease (CHD). They can affect the septation of the atria leading to atrial septal defect (ASD), septation of ventricles leading to ventricular septal defect (VSD), and formation of the central part of the heart leading to atrioventricular septal defect (AVSD). Disruption of critical genetic factors involved in the proper development of the heart structure leads to CHD manifestation. Because of this, to identify the high-risk genes involved in common septal defects, a comprehensive search of the literature with the help of databases and the WebGestalt analysis tool was performed. The high-risk genes identified in the analysis were checked in 16 Indian whole-exome sequenced samples, including 13 VSD and three Tetralogy of Fallot for in silico validation. This data revealed three variations in GATA4, i.e., c.C1223A at exon 6: c.C602A and c.C1220A at exon 7; and one variation in MYH6, i.e., c.G3883C at exon 28 in two VSD cases. This study supports previously published studies that suggested GATA4 and MYH6 as the high-risk genes responsible for septal defects. Thus, this study contributes to a better understanding of the genes involved in heart development by identifying the high-risk genes and interacting proteins in the pathway.

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.

DNA Methylation Levels of the TBX5 Gene Promoter Are Associated with Congenital Septal Defects in Mexican Paediatric Patients

The TBX5 gene regulates morphological changes during heart development, and it has been associated with epigenetic abnormalities observed in congenital heart defects (CHD). The aim of this research was to evaluate the association between DNA methylation levels of the TBX5 gene promoter and congenital septal defects. DNA methylation levels of six CpG sites in the TBX5 gene promoter were evaluated using pyrosequencing analysis in 35 patients with congenital septal defects and 48 controls. Average methylation levels were higher in individuals with congenital septal defects than in the controls (p < 0.004). In five CpG sites, we also found higher methylation levels in patients than in the controls (p < 0.05). High methylation levels were associated with congenital septal defects (OR = 3.91; 95% CI = 1.02–14.8; p = 0.045). The analysis of Receiver Operating Characteristic (ROC) showed that the methylation levels of the TBX5 gene could be used as a risk marker for congenital septal defects (AUC = 0.68, 95% CI = 0.56–0.80; p = 0.004). Finally, an analysis of environmental factors indicated that maternal infections increased the risk (OR = 2.90; 95% CI = 1.01–8.33; p = 0.048) of congenital septal defects. Our data suggest that a high DNA methylation of the TBX5 gene could be associated with congenital septal defects.

In silico analysis of GATA4 variants demonstrates main contribution to congenital heart disease

Introduction: Congenital heart disease (CHD) is the most common congenital abnormality and the main cause of infant mortality worldwide. Some of the mutations that occur in the GATA4 gene region may result in different types of CHD. Here, we report our in silico analysis of gene variants to determine the effects of the GATA4 gene on the development of CHD.

Methods: Online 1000 Genomes Project, ExAC, gnomAD, GO-ESP, TOPMed, Iranome, GME, ClinVar, and HGMD databases were drawn upon to collect information on all the reported GATA4 variations.The functional importance of the genetic variants was assessed by using SIFT, MutationTaster, CADD,PolyPhen-2, PROVEAN, and GERP prediction tools. Thereafter, network analysis of the GATA4protein via STRING, normal/mutant protein structure prediction via HOPE and I-TASSER, and phylogenetic assessment of the GATA4 sequence alignment via ClustalW were performed.

Results: The most frequent variant was c.874T>C (45.58%), which was reported in Germany.Ventricular septal defect was the most frequent type of CHD. Out of all the reported variants of GATA4,38 variants were pathogenic. A high level of pathogenicity was shown for p.Gly221Arg (CADD score=31), which was further analyzed.

Conclusion: The GATA4 gene plays a significant role in CHD; we, therefore, suggest that it be accorded priority in CHD genetic screening.

CHDGKB: a knowledgebase for systematic understanding of genetic variations associated with non-syndromic congenital heart disease

Congenital heart disease (CHD) is one of the most common birth defects, with complex genetic and environmental etiologies. The reports of genetic variation associated with CHD have increased dramatically in recent years due to the revolutionary development of molecular technology. However, CHD is a heterogeneous disease, and its genetic origins remain inconclusive in most patients. Here we present a database of genetic variations for non-syndromic CHD (NS-CHD). By manually literature extraction and analyses, 5345 NS-CHD-associated genetic variations were collected, curated and stored in the public online database. The objective of our database is to provide the most comprehensive updates on NS-CHD genetic research and to aid systematic analyses of pathogenesis of NS-CHD in molecular level and the correlation between NS-CHD genotypes and phenotypes. Database URL: http://www.sysbio.org.cn/CHDGKB/.

TBX5-encoded T-box transcription factor 5 variant T223M is associated with long QT syndrome and pediatric sudden cardiac death

Long QT syndrome (LQTS) is a genetic disease resulting in a prolonged QT interval on a resting electrocardiogram, predisposing affected individuals to polymorphic ventricular tachycardia and sudden death. Although a number of genes have been implicated in this disease, nearly one in four individuals exhibiting the LQTS phenotype are genotype-negative. Whole-exome sequencing identified a missense T223M variant in TBX5 that cosegregates with prolonged QT interval in a family with otherwise genotype-negative LQTS and sudden death. The TBX5-T223M variant was absent among large ostensibly healthy populations (gnomAD) and predicted to be pathogenic by in silico modeling based on Panther, PolyPhen-2, Provean, SIFT, SNAP2, and PredictSNP prediction tools. The variant was located in a highly conserved region of TBX5 predicted to be part of the DNA-binding interface. A luciferase assay identified a 57.5% reduction in the ability of TBX5-T223M to drive expression at the atrial natriuretic factor promotor compared to wildtype TBX5 in vitro. We conclude that the variant is pathogenic in this family, and we put TBX5 forward as a disease susceptibility allele for genotype-negative LQTS. The identification of this familial variant may serve as a basis for the identification of previously unknown mechanisms of LQTS with broader implications for cardiac electrophysiology.

Association between congenital heart disease and NKX2.5 gene polymorphisms: systematic review and meta-analysis

Aim: To analyze the association of NKX2.5 gene with congenital heart disease (CHD), and to determine if the variants rs703752, rs3729753 and rs2277923 increase the risk for developing CHD. Materials & methods: PubMed, EBSCO and Web of Science databases were screened to identify eligible studies. Through a comprehensive meta-analysis software, the association between NKX2.5 gene variants and susceptibility of CHD was calculated by pooled odd ratio (ORs) and 95% CI. Results: We observed that the allelic model of rs703752 and rs2277923 increased the risk in the overall population: OR = 1.24; 95% CI: 1.00-1.55; Z p-value = 0.049; OR = 1.18; 95% CI: 0.01-1.37; Z p-value = 0.036; respectively. Conclusion: Our results suggested that the rs703752 and rs2277923 polymorphisms of the NKX2.5 gene are associated with CHD.

BVES downregulation in non-syndromic tetralogy of fallot is associated with ventricular outflow tract stenosis

BVES is a transmembrane protein, our previous work demonstrated that single nucleotide mutations of BVES in tetralogy of fallot (TOF) patients cause a downregulation of BVES transcription. However, the relationship between BVES and the pathogenesis of TOF has not been determined. Here we reported our research results about the relationship between BVES and the right ventricular outflow tract (RVOT) stenosis. BVES expression was significantly downregulated in most TOF samples compared with controls. The expression of the second heart field (SHF) regulatory network genes, including NKX2.5, GATA4 and HAND2, was also decreased in the TOF samples. In zebrafish, bves knockdown resulted in looping defects and ventricular outflow tract (VOT) stenosis, which was mostly rescued by injecting bves mRNA. bves knockdown in zebrafish also decreased the expression of SHF genes, such as nkx2.5, gata4 and hand2, consistent with the TOF samples` results. The dual-fluorescence reporter system analysis showed that BVES positively regulated the transcriptional activity of GATA4, NKX2.5 and HAND2 promoters. In zebrafish, nkx2.5 mRNA partially rescued VOT stenosis caused by bves knockdown. These results indicate that BVES downregulation may be associated with RVOT stenosis of non-syndromic TOF, and bves is probably involved in the development of VOT in zebrafish.

TBX5 R264K acts as a modifier to develop dilated cardiomyopathy in mice independently of T-box pathway

Background

TBX5 is a transcription factor that has an important role in development of heart. TBX5 variants in the region encoding the T-box domain have been shown to cause cardiac defects, such as atrial septal defect or ventricular septal defect, while TBX5 variants have also been identified in a few cardiomyopathy patients and considered causative. We identified a TBX5 variant (c.791G>A, p.Arg264Lys), that is over-represented in cardiomyopathy patients. This variant is located outside of the T-box domain, and its pathogenicity has not been confirmed by functional analyses.

Objective

To investigate whether the TBX5 R264K is deleterious and could contribute to the pathogenesis of cardiomyopathy.

Methods and results

We developed mice expressing Tbx5 R264K. Mice homozygous for this variant displayed compensated dilated cardiomyopathy; mild decreased fractional shortening, dilatation of the left ventricle, left ventricular wall thinning and increased heart weight without major heart structural disorders. There was no difference in activation of the ANF promotor, a transcriptional target of Tbx5, compared to wild-type. However, analysis of RNA isolated from left ventricular samples showed significant increases in the expression of Acta1 in left ventricle with concomitant increases in the protein level of ACTA1.

Conclusions

Mice homozygous for Tbx5 R264K showed compensated dilated cardiomyopathy. Thus, TBX5 R264K may have a significant pathogenic role in some cardiomyopathy patients independently of T-box domain pathway.

The Functional Polymorphism R129W in the BVES Gene Is Associated with Sporadic Tetralogy of Fallot in the Han Chinese Population

Background: Tetralogy of Fallot (TOF) accounts for ∼10% of congenital heart disease cases. The blood vessel epicardial substance (BVES) gene has been reported to play a role in the function of adult hearts. However, whether allelic variants in BVES contribute to the risk of TOF and its possible mechanism remains unknown. Methods: The open reading frame of the BVES gene was sequenced using samples from 146 TOF patients and 100 unrelated healthy controls. qRT-PCR and western blot assays were used to confirm the expression of mutated BVES variants in the TOF samples. The online software Polyphen2 and SIFT were used to predict the deleterious effects of the observed allelic variants. The effects of these allelic variants on the transcriptional activities of genes were examined using dual-fluorescence reporter assays. Results: We genotyped four single nucleotide polymorphisms (SNPs) in the BVES gene from each of the 146 TOF patients. Among them, the minor allelic frequencies of c.385C>T (p.R129W) were 0.035% in TOF, but ∼0.025% in 100 controls and the Chinese Millionome Database. This allelic variant was predicted to be a potentially harmful alteration by the Polyphen2 and SIFT softwares. qRT-PCR and western blot analyses indicated that the expression of BVES in the six right ventricular outflow tract samples with the c.385C>T allelic variant was significantly downregulated. A dual-fluorescence reporter system showed that the c.385C>T allelic variant significantly decreased the transcriptional activity of the BVES gene and also decreased transcription from the GATA4 and NKX2.5 promoters. Conclusions: c.385C>T (p.R129W) is a functional SNP of the BVES gene that reduces the transcriptional activity of BVES in vitro and in vivo in TOF tissues. This subsequently affects the transcriptional activities of GATA4 and NKX2.5 related to TOF. These findings suggest that c.385C>T may be associated with the risk of TOF in the Han Chinese population.

Navigating the non-coding genome in heart development and Congenital Heart Disease

Congenital Heart Disease (CHD) is characterised by a wide range of cardiac defects, from mild to life-threatening, which occur in babies worldwide. To date, there is no cure to CHD, however, progress in surgery has reduced its mortality allowing children affected by CHD to reach adulthood. In an effort to understand its genetic basis, several studies involving whole-genome sequencing (WGS) of patients with CHD have been undertaken and generated a great wealth of information. The majority of putative causative mutations identified in WGS studies fall into the non-coding part of the genome. Unfortunately, due to the lack of understanding of the function of these non-coding mutations, it is challenging to establish a causal link between the non-coding mutation and the disease. Thus, here we review the state-of-the-art approaches to interpret non-coding mutations in the context of CHD and address the following questions: What are the non-coding sequences important for cardiac function? Which technologies are used to identify them? Which resources are available to analyse them? What mutations are expected in these non-coding sequences? Learning from developmental process, what is their expected role in CHD?

CHD4 and the NuRD complex directly control cardiac sarcomere formation

Cardiac development relies on proper cardiomyocyte differentiation, including expression and assembly of cell-type-specific actomyosin subunits into a functional cardiac sarcomere. Control of this process involves not only promoting expression of cardiac sarcomere subunits but also repressing expression of noncardiac myofibril paralogs. This level of transcriptional control requires broadly expressed multiprotein machines that modify and remodel the chromatin landscape to restrict transcription machinery access. Prominent among these is the nucleosome remodeling and deacetylase (NuRD) complex, which includes the catalytic core subunit CHD4. Here, we demonstrate that direct CHD4-mediated repression of skeletal and smooth muscle myofibril isoforms is required for normal cardiac sarcomere formation, function, and embryonic survival early in gestation. Through transcriptomic and genome-wide analyses of CHD4 localization, we identified unique CHD4 binding sites in smooth muscle myosin heavy chain, fast skeletal α-actin, and the fast skeletal troponin complex genes. We further demonstrate that in the absence of CHD4, cardiomyocytes in the developing heart form a hybrid muscle cell that contains cardiac, skeletal, and smooth muscle myofibril components. These misexpressed paralogs intercalate into the nascent cardiac sarcomere to disrupt sarcomere formation and cause impaired cardiac function in utero. These results demonstrate the genomic and physiological requirements for CHD4 in mammalian cardiac development.

Genomics and Epigenomics of Congenital Heart Defects: Expert Review and Lessons Learned in Africa

Congenital heart defects (CHD) are structural malformations found at birth with a prevalence of 1%. The clinical trajectory of CHD is highly variable and thus in need of robust diagnostics and therapeutics. Major surgical interventions are often required for most CHDs. In Africa, despite advances in life sciences infrastructure and improving education of medical scholars, the limited clinical data suggest that CHD detection and correction are still not at par with the rest of the world. But the toll and genetics of CHDs in Africa has seldom been systematically investigated. We present an expert review on CHD with lessons learned on Africa. We found variable CHD phenotype prevalence in Africa across countries and populations. There are important gaps and paucity in genomic studies of CHD in African populations. Among the available genomic studies, the key findings in Africa were variants in GATA4 (P193H), MTHFR 677TT, and MTHFR 1298CC that were associated with atrial septal defect, ventricular septal defect (VSD), Tetralogy of Fallot (TOF), and patent ductus arteriosus phenotypes and 22q.11 deletion, which is associated with TOF. There were no data on epigenomic association of CHD in Africa, however, other studies have shown an altered expression of miR-421 and miR-1233-3p to be associated with TOF and hypermethylation of CpG islands in the promoter of SCO2 gene also been associated with TOF and VSD in children with non-syndromic CHD. These findings signal the urgent need to develop and implement genetic and genomic research on CHD to identify the hereditary and genome-environment interactions contributing to CHD. These projected studies would also offer comparisons on CHD pathophysiology between African and other populations worldwide. Genomic research on CHD in Africa should be developed in parallel with next generation technology policy research and responsible innovation frameworks that examine the social and political factors that shape the emergence and societal embedding of new technologies.

A Novel MEF2C Loss-of-Function Mutation Associated with Congenital Double Outlet Right Ventricle

Congenital heart defect (CHD) represents the most prevalent birth defect, and accounts for substantial morbidity and mortality in humans. Aggregating evidence demonstrates the genetic basis for CHD. However, CHD is a heterogeneous disease, and the genetic determinants underlying CHD in most patients remain unknown. In the present study, a cohort of 186 unrelated cases with CHD and 300 unrelated control individuals were recruited. The coding exons and flanking introns of the MEF2C gene, which encodes a transcription factor crucial for proper cardiovascular development, were sequenced in all study participants. The functional effect of an identified MEF2C mutation was characterized using a dual-luciferase reporter assay system. As a result, a novel heterozygous MEF2C mutation, p.R15C, was detected in an index patient with congenital double outlet right ventricle (DORV) as well as ventricular septal defect. Analysis of the proband's pedigree showed that the mutation co-segregated with CHD with complete penetrance. The missense mutation, which changed the evolutionarily conserved amino acid, was absent in 300 control individuals. Functional deciphers revealed that the mutant MEF2C protein had a significantly decreased transcriptional activity. Furthermore, the mutation significantly reduced the synergistic activation between MEF2C and GATA4, another transcription factor linked to CHD. This study firstly associates MEF2C loss-of-function mutation with DORV in humans, which provides novel insight into the molecular pathogenesis of CHD, suggesting potential implications for genetic counseling and personalized treatment of CHD patients.

Novel mutation of GATA4 gene in Kurdish population of Iran with nonsyndromic congenital heart septals defects

BACKGROUND

The mutations in GATA4 gene induce inherited atrial and ventricular septation defects, which is the most frequent forms of congenital heart defects (CHDs) constituting about half of all cases.

METHOD

We have performed High resolution melting (HRM) mutation scanning of GATA4 coding exons of nonsyndrome 100 patients as a case group including 39 atrial septal defects (ASD), 57 ventricular septal defects (VSD) and four patients with both above defects and 50 healthy individuals as a control group. Our samples are categorized according to their HRM graph. The genome sequencing has been done for 15 control samples and 25 samples of patients whose HRM analysis were similar to healthy subjects for each exon. The PolyPhen-2 and MUpro have been used to determine the causative possibility and structural stability prediction of GATA4 sequence variation.

RESULTS

The HRM curve analysis exhibit that 21 patients and 3 normal samples have deviated curves for GATA4 coding exons. Sequencing analysis has revealed 12 nonsynonymous mutations while all of them resulted in stability structure of protein 10 of them are pathogenic and 2 of them are benign. Also we found two nucleotide deletions which one of them was novel and one new indel mutation resulting in frame shift mutation, and 4 synonymous variations or polymorphism in 6 of patients and 3 of normal individuals. Six or about 50% of these nonsynonymous mutations have not been previously reported.

CONCLUSION

Our results show that there is a spectrum of GATA4 mutations resulting in septal defects.

A novel NR2F2 loss-of-function mutation predisposes to congenital heart defect

Congenital heart defect (CHD) is the most common type of birth defect in humans and a leading cause of infant morbidity and mortality. Previous studies have demonstrated that genetic defects play a pivotal role in the pathogenesis of CHD. However, the genetic basis of CHD remains poorly understood due to substantial genetic heterogeneity. In this study, the coding exons and splicing boundaries of the NR2F2 gene, which encodes a pleiotropic transcription factor required for normal cardiovascular development, were sequenced in 168 unrelated patients with CHD, and a novel mutation (c.247G > T, equivalent to p.G83X) was detected in a patient with double outlet right ventricle as well as ventricular septal defect. Genetic scanning of the mutation carrier's relatives available showed that the mutation was present in all affected family members but absent in unaffected family members. Analysis of the index patient's pedigree displayed that the mutation co-segregated with CHD, which was transmitted as an autosomal dominant trait with complete penetrance. The nonsense mutation was absent in 230 unrelated, ethnically-matched healthy individuals used as controls. Functional deciphers by using a dual-luciferase reporter assay system revealed that the mutant NR2F2 protein had no transcriptional activity as compared with its wild-type counterpart. Furthermore, the mutation abrogated the synergistic transcriptional activation between NR2F2 and GATA4, another core cardiac transcription factor associated with CHD. This study firstly associates NR2F2 loss-of-function mutation with an increased susceptibility to double outlet right ventricle in humans, which provides further significant insight into the molecular mechanisms underpinning CHD, suggesting potential implications for genetic counseling of CHD families and personalized treatment of CHD patients.

Functional mutant GATA4 identification and potential application in preimplantation diagnosis of congenital heart diseases

Congenital heart diseases (CHDs) affect nearly 1% of all neonates and show an increasing tendency. The complex inheritance patterns and multifactorial etiologies make these defects difficult to be identified before complete manifestation. Genetic screening has identified hundreds of specific mutant sites for CHDs based on cardiac transcriptional factors. GATA4 is a master regulator required for ventral morphogenesis and heart tube formation. Its mutation is most widely studied in CHDs. In the past decades, over 100 GATA4 mutant sites have been reported, but only a few functional sites have been identified. Thus, it is important to distinguish deleterious sites from neutral sites. In silico prediction of functional sites using bioinformatics tools can provide the valuable information, but it is not solid enough. Here, the roles of GATA4 in heart development is discussed in detail and its mutation sites in protein coding region are summarized systematically, providing an integrated resource for GATA4 mutations. Furthermore, we discussed the advantage and disadvantage of different methods for functional mutation identification. Especially, the disease model of induced pluripotent stem cell is emerging as a powerful tool to assess GATA4 mutations in human. In the recent years, single-cell based high-throughput sequencing is being applied in preimplantation diagnosis and assisted reproduction progressively, providing a new strategy for the prevention of congenital diseases as we discussed. Based on functional mutant sites identification, preimplantation diagnosis will contribute to CHDs prevention eventually.

TBX20 loss-of-function mutation responsible for familial tetralogy of Fallot or sporadic persistent truncus arteriosus

Congenital heart disease (CHD), the most common form of developmental abnormality in humans, remains a leading cause of morbidity and mortality in neonates. Genetic defects have been recognized as the predominant causes of CHD. Nevertheless, CHD is of substantial genetic heterogeneity and the genetic defects underlying CHD in most cases remain unclear. In the current study, the coding regions and splicing junction sites of the TBX20 gene, which encodes a T-box transcription factor key to cardiovascular morphogenesis, were sequenced in 175 unrelated patients with CHD, and a novel heterozygous TBX20 mutation, p.K274X, was identified in an index patient with tetralogy of Fallot (TOF). Genetic analysis of the proband's available family members showed that his father, elder brother and son had also TOF. In addition, his father and elder brother had also atrial septal defect, and his niece had persistent truncus arteriosus and ventricular septal defect. Analysis of the pedigree revealed that the mutation co-segregated with CHD transmitted in an autosomal dominant fashion, with complete penetrance. The nonsense mutation, which was absent in the 800 control chromosomes, was predicted to produce a truncated protein with only the amino terminus and partial T-box domain left. Functional analyses by using a dual-luciferase reporter assay system showed that the mutant TBX20 lost the ability to transactivate the target gene ANF. Furthermore, the mutation reduced the synergistic activation between TBX20 and NKX2.5 as well as GATA4, two other transcriptional factors previously associated with various CHD, encompassing TOF. This study firstly links TBX20 loss-of-function mutation to familial TOF or sporadic persistent truncus arteriosus, providing novel insight into the molecular pathogenesis of CHD.

HAND1 Loss-of-Function Mutation Causes Tetralogy of Fallot

As the most prevalent form of birth defect in humans worldwide, congenital heart disease (CHD) is responsible for substantial morbidity and is still the leading cause of birth defect-related demises. Increasing evidence demonstrates that genetic defects play an important role in the pathogenesis of CHD, and mutations in multiple genes, especially in those coding for cardiac core transcription factors, have been causally linked to various CHDs. Nevertheless, CHD is a genetically heterogeneous disease and the genetic determinants underpinning CHD in an overwhelming majority of patients remain elusive. In the current study, genomic DNA was extracted from venous blood samples of 165 unrelated patients with CHD, and the coding exons and splicing junction sites of the HAND1 gene, which encodes a basic helix-loop-helix transcription factor essential for cardiovascular development, were sequenced. As a result, a novel heterozygous mutation, p.R118C, was identified in a patient with tetralogy of Fallot (TOF). The missense mutation, which was absent in 600 referential chromosomes, altered the amino acid that was completely conserved evolutionarily. Biological assays with a dual-luciferase reporter assay system revealed that the R118C-mutant HAND1 protein had significantly reduced transcriptional activity when compared with its wild-type counterpart. Furthermore, the mutation significantly decreased the synergistic activation of a downstream target gene between HAND1 and GATA4, another cardiac core transcription factor associated with TOF. To our knowledge, this is the first report on the association of a HAND1 loss-of-function mutation with enhanced susceptibility to TOF in humans. The findings provide novel insight into the molecular etiology underlying TOF, suggesting potential implications for the improved prophylactic and therapeutic strategies for TOF.

CASZ1 loss-of-function mutation associated with congenital heart disease

As the most common form of birth defect in humans, congenital heart disease (CHD) is associated with substantial morbidity and mortality in both children and adults. Increasing evidence demonstrates that genetic defects play a pivotal role in the pathogenesis of CHD. However, CHD is of great heterogeneity, and in an overwhelming majority of cases, the genetic determinants underpinning CHD remain elusive. In the present investigation, the coding exons and flanking introns of the CASZ1 gene, which codes for a zinc finger transcription factor essential for the cardiovascular morphogenesis, were sequenced in 172 unrelated patients with CHD. As a result, a novel heterozygous CASZ1 mutation, p.L38P, was identified in an index patient with congenital ventricular septal defect (VSD). Genetic scanning of the mutation carrier's available family members revealed that the mutation was present in all affected patients but absent in unaffected individuals. Analysis of the proband's pedigree showed that the mutation co-segregated with VSD, which was transmitted as an autosomal dominant trait with complete penetrance. The missense mutation, which altered the amino acid that was highly conserved evolutionarily, was absent in 200 unrelated, ethnically-matched healthy subjects used as controls. Functional deciphers by using a dual-luciferase reporter assay system unveiled that the mutant CASZ1 had significantly reduced transcriptional activity as compared with its wild-type counterpart. To the best of our knowledge, the current study firstly identifies CASZ1 as a new gene predisposing to CHD in humans, which provides novel insight into the molecular mechanisms underlying CHD and a potential therapeutic target for CASZ1-associated CHD, suggesting potential implications for personalized prophylaxis and therapy of CHD.