A Novel TBX1 Loss-of-Function Mutation Associated with Congenital Heart Disease

Human Genetics of Ventricular Septal Defect

Ventricular septal defects (VSDs) are recognized as one of the commonest congenital heart diseases (CHD), accounting for up to 40% of all cardiac malformations, and occur as isolated CHDs as well as together with other cardiac and extracardiac congenital malformations in individual patients and families. The genetic etiology of VSD is complex and extraordinarily heterogeneous. Chromosomal abnormalities such as aneuploidy and structural variations as well as rare point mutations in various genes have been reported to be associated with this cardiac defect. This includes both well-defined syndromes with known genetic cause (e.g., DiGeorge syndrome and Holt-Oram syndrome) and so far undefined syndromic forms characterized by unspecific symptoms. Mutations in genes encoding cardiac transcription factors (e.g., NKX2-5 and GATA4) and signaling molecules (e.g., CFC1) have been most frequently found in VSD cases. Moreover, new high-resolution methods such as comparative genomic hybridization enabled the discovery of a high number of different copy number variations, leading to gain or loss of chromosomal regions often containing multiple genes, in patients with VSD. In this chapter, we will describe the broad genetic heterogeneity observed in VSD patients considering recent advances in this field.

The TBX1/miR-193a-3p/TGF-β2 Axis Mediates CHD by Promoting Ferroptosis

Congenital heart disease (CHD) is the most common noninfectious cause of death during the neonatal stage. T-box transcription factor 1 (TBX1) is the main genetic determinant of 22q11.2 deletion syndrome (22q11.2DS), which is a common cause of CHD. Moreover, ferroptosis is a newly discovered kind of programmed cell death. In this study, the interaction among TBX1, miR-193a-3p, and TGF-β2 was tested using quantitative reverse transcription polymerase chain reaction (qRT-PCR), Western blotting, and dual-luciferase reporter assays. TBX1 silencing was found to promote TGF-β2 messenger ribonucleic acid (mRNA) and protein expression by downregulating the miR-193a-3p levels in H9c2 cells. In addition, the TBX1/miR-193a-3p/TGF-β2 axis was found to promote ferroptosis based on assessments of lipid reactive oxygen species (ROS) levels, Fe²⁺ concentrations, mitochondrial ROS levels, and malondialdehyde (MDA) contents; Cell Counting Kit-8 (CCK-8) assays and transmission electron microscopy; and Western blotting analysis of glutathione peroxidase 4 (GPX4), nuclear factor erythroid 2-related factor 2 (NRF2), heme oxygenase-1 (HO-1), NADPH oxidase 4 (NOX4), and acyl-CoA synthase long-chain family member 4 (ACSL4) protein expression. The protein expression of NRF2, GPX4, HO-1, NOX4, and ACSL4 and the level of MDA in human CHD specimens were also detected. In addition, TBX1 and miR-193a-3p expression was significantly downregulated and TGF-β2 levels were high in human embryonic CHD tissues, as indicated by the H9c2 cell experiments. In summary, the TBX1/miR-193a-3p/TGF-β2 axis mediates CHD by inducing ferroptosis in cardiomyocytes. TGF-β2 may be a target gene for CHD diagnosis and treatment in children.

Post-Transcriptional Regulation of Molecular Determinants during Cardiogenesis

Cardiovascular development is initiated soon after gastrulation as bilateral precardiac mesoderm is progressively symmetrically determined at both sides of the developing embryo. The precardiac mesoderm subsequently fused at the embryonic midline constituting an embryonic linear heart tube. As development progress, the embryonic heart displays the first sign of left-right asymmetric morphology by the invariably rightward looping of the initial heart tube and prospective embryonic ventricular and atrial chambers emerged. As cardiac development progresses, the atrial and ventricular chambers enlarged and distinct left and right compartments emerge as consequence of the formation of the interatrial and interventricular septa, respectively. The last steps of cardiac morphogenesis are represented by the completion of atrial and ventricular septation, resulting in the configuration of a double circuitry with distinct systemic and pulmonary chambers, each of them with distinct inlets and outlets connections. Over the last decade, our understanding of the contribution of multiple growth factor signaling cascades such as Tgf-beta, Bmp and Wnt signaling as well as of transcriptional regulators to cardiac morphogenesis have greatly enlarged. Recently, a novel layer of complexity has emerged with the discovery of non-coding RNAs, particularly microRNAs and lncRNAs. Herein, we provide a state-of-the-art review of the contribution of non-coding RNAs during cardiac development. microRNAs and lncRNAs have been reported to functional modulate all stages of cardiac morphogenesis, spanning from lateral plate mesoderm formation to outflow tract septation, by modulating major growth factor signaling pathways as well as those transcriptional regulators involved in cardiac development.

Association Between miR-143/145 rs4705343 Polymorphism and Risk of Congenital Heart Disease in a Chinese Tibetan Population

Objective: Congenital heart disease (CHD) is the most common birth defect worldwide and is caused by both genetic and environmental factors. The microRNA (miR)-143/145 cluster is involved in various biological processes related to cardiovascular development. The functional single nucleotide polymorphism (SNP) rs4705343 of miR-143/145 may influence the expression of these miRNAs. In this study, we aimed to estimate the association between miR-143/145 rs4705343 and the risk of CHD in a Chinese Tibetan population. Methods: Matrix-assisted laser desorption ionization time-of-flight mass spectrometry assays were performed to genotype the miRNA-143/145 rs4705343 SNP in 510 CHD Tibetan patients and 681 unrelated Tibetan healthy controls. The associations between the SNP frequencies and the CHD risk were analyzed by χ² test/Fisher's test and assessed by odds ratios (ORs) and 95% confidence intervals (95% CIs). Results: We successfully genotyped 1165 subjects with a SNP call rate of 97.8%. Under the allelic model we found that rs4705343 was not associated with the risk of CHD (p = 0.082), but under the recessive model the CC genotype at this locus was associated with a significantly increased risk of CHD compared with the other genotypes (CC vs TT+TC: OR = 1.60, 95% CI = 1.08-2.37, p = 0.017). Conclusion: The present study suggests that the rs4705343 CC genotype of miR-143/145 is associated with CHD risk in a Chinese Tibetan population.

Association of NFKB1, NKX2-5, GATA4 and RANKL Gene Polymorphisms with Sporadic Congenital Heart Disease in Greek Patients

Congenital heart disease (CHD) is a group of structural defects of the heart and the great vessels, and one of the leading causes of death among infants and young adults. Several gene variants are involved in diverse mechanisms of cardiac and vessel development and could thus be considered candidate mutated genes for a congenital heart defect or a specific variant could predispose a person to CHD. In the present study, variants in four such genes are investigated for the first time in a group of young Greek CHD patients: the NFKB1 gene polymorphism (-94ins/ delATTG), rs28362491, NKX2-5 gene polymorphism rs2277923, GATA4 gene polymorphism rs11785481 and RANKL gene polymorphism rs4531631. A total of 43 CHD patients and 100 healthy adults were included in the study. The polymerase chain reaction-restriction fragment length polymorphism (PRC-RFLP) method was used to genotype the aforementioned polymorphisms of NFKB1, NKX2-5, GATA4 and RANKL. The association analysis identified that there was a protective association between CHD and the A allele of rs2277923 polymorphism (p = 0.004). The D allele of the rs28362491 polymorphism is also a likely risk factor for causing CHD (p = 0.006). The differences of the rs4531631 and rs11785481 variant contribution had no statistical significance between the groups (p >0.05). In conclusion, our results revealed that the rs28362491 and rs2277923 gene polymorphisms, but not the rs4531631 and rs11785481 polymorphisms, may contribute to CHD risk in a cohort of Greek CHD patients.

Variants in a cis-regulatory element of TBX1 in conotruncal heart defect patients impair GATA6-mediated transactivation

Background

TBX1 (T-box transcription factor 1) is a major candidate gene that likely contributes to the etiology of velo-cardio-facial syndrome/DiGeorge syndrome (VCFS/DGS). Although the haploinsufficiency of TBX1 in both mice and humans results in congenital cardiac malformations, little has been elucidated about its upstream regulation. We aimed to explore the transcriptional regulation and dysregulation of TBX1.

Methods

Different TBX1 promoter reporters were constructed. Luciferase assays and electrophoretic mobility shift assays (EMSAs) were used to identify a cis-regulatory element within the TBX1 promoter region and its trans-acting factor. The expression of proteins was identified by immunohistochemistry and immunofluorescence. Variants in the cis-regulatory element were screened in conotruncal defect (CTD) patients. In vitro functional assays were performed to show the effects of the variants found in CTD patients on the transactivation of TBX1.

Results

We identified a cis-regulatory element within intron 1 of TBX1 that was found to be responsive to GATA6 (GATA binding protein 6), a transcription factor crucial for cardiogenesis. The expression patterns of GATA6 and TBX1 overlapped in the pharyngeal arches of human embryos. Transfection experiments and EMSA indicated that GATA6 could activate the transcription of TBX1 by directly binding with its GATA cis-regulatory element in vitro. Furthermore, sequencing analyses of 195 sporadic CTD patients without the 22q11.2 deletion or duplication identified 3 variants (NC_000022.11:g.19756832C > G, NC_000022.11:g.19756845C > T, and NC_000022.11:g. 19756902G > T) in the non-coding cis-regulatory element of TBX1. Luciferase assays showed that all 3 variants led to reduced transcription of TBX1 when incubated with GATA6.

Conclusions

Our findings showed that TBX1 might be a direct transcriptional target of GATA6, and variants in the non-coding cis-regulatory element of TBX1 disrupted GATA6-mediated transactivation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-01981-4.

Connection of GLI1 variants to congenital heart disease susceptibility: A case-control study

The purpose of this study was to investigate the relationship between glioma-associated oncogene homolog 1 (GLI1) rs2228226 and rs10783826 polymorphisms and congenital heart disease (CHD) risk in a Chinese Han population.Genotyping for our interested polymorphisms was performed using polymerase chain reaction-restriction fragment length polymorphism in 106 CHD patients and 112 healthy controls. Hardy-Weinberg equilibrium status in the control group was also checked via χ test. Differences in genotype and allele frequencies between the case and control groups were analyzed adopting Chi-Squared test as well, and the relative risk of CHD resulting from GLI1 genetic variants was checked via calculating odds ratio (OR) and 95% confidence interval (95%CI).CC genotype of rs2228226 showed significantly higher frequency in CHD patients than in controls (P = .011), indicating that it increased the disease risk (OR = 3.257, 95%CI = 1.280-8.287). Similarly, C allele of the polymorphism elevated CHD incidence by 1.609 folds, compared with G allele (OR = 1.609, 95%CI = 1.089-2.376). However, rs10783826 was not correlated with the occurrence of CHD.GLI1 rs2228226 polymorphism may be a risk factor for CHD in Chinese Han population, but not rs10783826.

Molecular genetics of 22q11.2 deletion syndrome

The 22q11.2 deletion syndrome (22q11.2DS) is a congenital malformation and neuropsychiatric disorder caused by meiotic chromosome rearrangements. One of the goals of this review is to summarize the current state of basic research studies of 22q11.2DS. It highlights efforts to understand the mechanisms responsible for the 22q11.2 deletion that occurs in meiosis. This mechanism involves the four sets of low copy repeats (LCR22) that are dispersed in the 22q11.2 region and the deletion is mediated by nonallelic homologous recombination events. This review also highlights selected genes mapping to the 22q11.2 region that may contribute to the typical clinical findings associated with the disorder and explain that mutations in genes on the remaining allele can uncover rare recessive conditions. Another important aspect of 22q11.2DS is the existence of phenotypic heterogeneity. While some patients are mildly affected, others have severe medical, cognitive, and/or psychiatric challenges. Variability may be due in part to the presence of genetic modifiers. This review discusses current genome-wide efforts to identify such modifiers that could shed light on molecular pathways required for normal human development, cognition or behavior.

HNRNPR Variants that Impair Homeobox Gene Expression Drive Developmental Disorders in Humans

The heterogeneous nuclear ribonucleoprotein (HNRNP) genes code for a set of RNA-binding proteins that function primarily in the spliceosome C complex. Pathogenic variants in these genes can drive neurodegeneration, through a mechanism involving excessive stress-granule formation, or developmental defects, through mechanisms that are not known. Here, we report four unrelated individuals who have truncating or missense variants in the same C-terminal region of hnRNPR and who have multisystem developmental defects including abnormalities of the brain and skeleton, dysmorphic facies, brachydactyly, seizures, and hypoplastic external genitalia. We further identified in the literature a fifth individual with a truncating variant. RNA sequencing of primary fibroblasts reveals that these HNRNPR variants drive significant changes in the expression of several homeobox genes, as well as other transcription factors, such as LHX9, TBX1, and multiple HOX genes, that are considered fundamental regulators of embryonic and gonad development. Higher levels of retained intronic HOX sequences and lost splicing events in the HOX cluster are observed in cells carrying HNRNPR variants, suggesting that impaired splicing is at least partially driving HOX deregulation. At basal levels, stress-granule formation appears normal in primary and transfected cells expressing HNRNPR variants. However, these cells reveal profound recovery defects, where stress granules fail to disassemble properly, after exposure to oxidative stress. This study establishes an essential role for HNRNPR in human development and points to a mechanism that may unify other "spliceosomopathies" linked to variants that drive multi-system congenital defects and are found in hnRNPs.

Dysregulation of TBX1 dosage in the anterior heart field results in congenital heart disease resembling the 22q11.2 duplication syndrome

Non-allelic homologous recombination events on chromosome 22q11.2 during meiosis can result in either the deletion (22q11.2DS) or duplication (22q11.2DupS) syndrome. Although the spectrum and frequency of congenital heart disease (CHD) are known for 22q11.2DS, there is less known for 22q11.2DupS. We now evaluated cardiac phenotypes in 235 subjects with 22q11.2DupS including 102 subjects we collected and 133 subjects that were previously reported as a confirmation and found 25% have CHD, mostly affecting the cardiac outflow tract (OFT). Previous studies have shown that global loss or gain of function (LOF; GOF) of mouse Tbx1, encoding a T-box transcription factor mapping to the region of synteny to 22q11.2, results in similar OFT defects. To further evaluate Tbx1 function in the progenitor cells forming the cardiac OFT, termed the anterior heart field, Tbx1 was overexpressed using the Mef2c-AHF-Cre driver (Tbx1 GOF). Here we found that all resulting conditional GOF embryos had a persistent truncus arteriosus (PTA), similar to what was previously reported for conditional Tbx1 LOF mutant embryos. To understand the basis for the PTA in the conditional GOF embryos, we found that proliferation in the Mef2c-AHF-Cre lineage cells before migrating to the heart, was reduced and critical genes were oppositely changed in this tissue in Tbx1 GOF embryos versus conditional LOF embryos. These results suggest that a major function of TBX1 in the AHF is to maintain the normal balance of expression of key cardiac developmental genes required to form the aorta and pulmonary trunk, which is disrupted in 22q11.2DS and 22q11.2DupS.

Heterozygous Mutations in TBX1 as a Cause of Isolated Hypoparathyroidism

CONTEXT

Most cases of autosomal dominant isolated hypoparathyroidism are caused by gain-of-function mutations in CASR or GNA11 or dominant negative mutations in GCM2 or PTH.

OBJECTIVE

To identify the genetic etiology for dominantly transmitted isolated hypoparathyroidism in two multigenerational families with 14 affected family members.

METHODS

We performed whole exome sequencing of DNA from two families and examined the consequences of mutations by minigene splicing assay.

RESULTS

We discovered disease-causing mutations in both families. A splice-altering mutation in TBX1 (c.1009+1G>C) leading to skipping of exon 8 (101 bp) was identified in 10 affected family members and five unaffected subjects of family A, indicating reduced penetrance for this point mutation. In a second family from France (family B), we identified another splice-altering mutation (c.1009+2T>C) adjacent to the mutation identified in family A that results in skipping of the same exon; two subjects in family B had isolated hypoparathyroidism, whereas a third subject manifested the clinical triad of the 22q11.2 deletion syndrome, indicative of variable expressivity.

CONCLUSIONS

We report evidence that heterozygous TBX1 mutations can cause isolated hypoparathyroidism. This study adds knowledge to the increasingly expanding list of causative and candidate genes in isolated hypoparathyroidism.

The correlation of TGFβ1 gene polymorphisms with congenital heart disease susceptibility

OBJECTIVE

The aim of this study was to investigate the relationship between single nucleotide polymorphisms (SNPs) in transforming growth factor beta 1 (TGFβ1) gene (rs1982073 and rs1800471) and congenital heart disease (CHD) susceptibility.

METHODS

Totally, 145 CHD patients and 140 healthy controls were enrolled in this case-control study. The case and control groups were matched in age and gender. Genotyping for TGFβ1 gene SNPs rs1982073 and rs1800471 was conducted via polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) approach. Chi-square test was used to analyze the association of TGFβ1 polymorphisms with CHD risk. The results were presented as odds ratios (ORs) and 95% confidence intervals (CIs).

RESULTS

The frequencies of the CT genotype and T allele of TGFβ1 gene SNP rs1982073 were significantly different between cases and controls (P < 0.05), revealing their associations with reduced susceptibility to CHD (OR = 0.521, 95%CI = 0.302-0.897; OR = 0.706, 95%CI = 0.507-0.983). Nevertheless, TGFβ1 gene SNP rs1800471 had no significant association with CHD susceptibility (P > 0.05).

CONCLUSION

TGFβ1 gene SNP rs1982073 might be correlated with CHD susceptibility, and the T allele might decrease the disease risk. However, TGFβ1 gene polymorphism rs1800471 was not related to CHD risk.

Genetic Imbalances in Argentinean Patients with Congenital Conotruncal Heart Defects

Congenital conotruncal heart defects (CCHD) are a subset of serious congenital heart defects (CHD) of the cardiac outflow tracts or great arteries. Its frequency is estimated in 1/1000 live births, accounting for approximately 10–30% of all CHD cases. Chromosomal abnormalities and copy number variants (CNVs) contribute to the disease risk in patients with syndromic and/or non-syndromic forms. Although largely studied in several populations, their frequencies are barely reported for Latin American countries. The aim of this study was to analyze chromosomal abnormalities, 22q11 deletions, and other genomic imbalances in a group of Argentinean patients with CCHD of unknown etiology. A cohort of 219 patients with isolated CCHD or associated with other major anomalies were referred from different provinces of Argentina. Cytogenetic studies, Multiplex-Ligation-Probe-Amplification (MLPA) and fluorescent in situ hybridization (FISH) analysis were performed. No cytogenetic abnormalities were found. 22q11 deletion was found in 23.5% of the patients from our cohort, 66% only had CHD with no other major anomalies. None of the patients with transposition of the great vessels (TGV) carried the 22q11 deletion. Other 4 clinically relevant CNVs were also observed: a distal low copy repeat (LCR)D-E 22q11 duplication, and 17p13.3, 4q35 and TBX1 deletions. In summary, 25.8% of CCHD patients presented imbalances associated with the disease.

Novel heterozygous mutation in TBX1 in an infant with hypocalcemic seizures

Patients with 22q11.2 deletion syndrome have characteristic facial appearance, palate abnormalities, hypoparathyroidism, thymic hypoplasia, and congenital heart disease. The 22q11.2 region includes TBX1 and 30 other genes. Analysis of Tbx1 transgenic mice showed that TBX1 was associated with the 22q11.2 deletion syndrome. In humans, TBX1 mutations have been reported in 22q11.2 deletion-negative patients with velocardiofacial syndrome or DiGeorge syndrome. Genotype-phenotype correlations are not fully understood in these patients. We report the case of an infant with a novel heterozygous TBX1 mutation who experienced hypocalcemic seizures. This patient had no palate abnormalities, cardiac anomalies, or the typical facial appearance observed in 22q11.2 deletion syndrome. The presence of thymic hypoplasia prompted us to perform G-banding, fluorescent in situ hybridization, and subsequent TBX1 analysis. We emphasize the importance of diagnosing thymic hypoplasia in hypocalcemic infants without 22q11.2 deletion for detecting TBX1 mutations.

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.

Whole exome sequencing identifies mutations in 10% of patients with familial non-syndromic cleft lip and/or palate in genes mutated in well-known syndromes

Background

Oral clefts, that is, clefts of the lip and/or cleft palate (CL/P), are the most common craniofacial birth defects with an approximate incidence of ~1/700. To date, physicians stratify patients with oral clefts into either syndromic CL/P (syCL/P) or non-syndromic CL/P (nsCL/P) depending on whether the CL/P is associated with another anomaly or not. In general, patients with syCL/P follow Mendelian inheritance, while those with nsCL/P have a complex aetiology and, as such, do not adhere to Mendelian inheritance. Genome-wide association studies have identified approximately 30 risk loci for nsCL/P, which could explain a small fraction of heritability.

Methods

To identify variants causing nsCL/P, we conducted whole exome sequencing on 84 individuals with nsCL/P, drawn from multiplex families (n=46).

Results

We identified rare damaging variants in four genes known to be mutated in syCL/P: TP63 (one family), TBX1 (one family), LRP6 (one family) and GRHL3 (two families), and clinical reassessment confirmed the isolated nature of their CL/P.

Conclusion

These data demonstrate that patients with CL/P without cardinal signs of a syndrome may still carry a mutation in a gene linked to syCL/P. Rare coding and non-coding variants in syCL/P genes could in part explain the controversial question of ‘missing heritability’ for nsCL/P. Therefore, gene panels designed for diagnostic testing of syCL/P should be used for patients with nsCL/P, especially when there is at least third-degree family history. This would allow a more precise management, follow-up and genetic counselling. Moreover, stratified cohorts would allow hunting for genetic modifiers.

TBX1 loss-of-function mutation contributes to congenital conotruncal defects

Conotruncal defects (CTDs) account for ~30% of all types of congenital heart disease and contribute to increased morbidity and mortality rates. Increasing evidence suggests that genetic risk factors are involved in the pathogenesis of CTDs. Mutations in a number of genes, including the TBX1 gene that codes for a T-box transcription factor essential for normal cardiovascular development, may contribute to the development of CTD. CTDs are genetically heterogeneous and the genetic defects responsible for CTDs in the majority of patients remain unknown. The present study sequenced the coding regions and splicing junction boundaries of TBX1 in 136 patients with CTDs and 300 matched healthy individuals. The disease-causing potential of the identified TBX1 sequence variation was evaluated using MutationTaster, PolyPhen-2, SIFT and PROVEN software. The functional characteristics of the mutant TBX1 gene were defined using a dual-luciferase reporter assay system. A novel heterozygous TBX1 mutation, p.S233Y, was identified in a patient with transposition of the great arteries (TGA) and a ventricular septal defect. This mutation was absent in the 300 controls and altered the amino acid produced, serine, which is evolutionarily conserved across several species, and was predicted to be pathogenic in silico. Luciferase assays conducted in COS-7 cells demonstrated that the newly identified TBX1 mutation was associated with significantly diminished transcriptional activation of the ANF promoter compared with the wild-type TBX1. To the best of our knowledge, the present study is the first to associate a TBX1 loss-of-function mutation with enhanced susceptibility to TGA, which adds significant insight to the molecular mechanism of TGA.

MEF2C loss-of-function mutation contributes to congenital heart defects

Congenital heart disease (CHD) is the most common type of developmental abnormality in humans, and is a leading cause for substantially increased morbidity and mortality in affected individuals. Increasing studies demonstrates a pivotal role of genetic defects in the pathogenesis of CHD, and presently mutations in more than 60 genes have been associated with CHD. Nevertheless, CHD is of pronounced genetic heterogeneity, and the genetic basis underpinning CHD in a large proportion of patients remains unclear. In the present study, the whole coding exons and splicing donors/acceptors of the MEF2C gene, which codes for a transcription factor essential for normal cardiovascular development, were sequenced in 200 unrelated patients affected with CHD, and a novel heterozygous missense mutation, p.L38P, was identified in an index patient with patent ductus arteriosus (PDA) and ventricular septal defect (VSD). Genetic scan of the mutation carrier's family members available showed that the mutation was present in all affected family members but absent in unaffected family members. Analysis of the proband's pedigree revealed that the mutation co-segregated with PDA, which was transmitted as an autosomal dominant trait with complete penetrance. The mutation changed the amino acid that was completely conserved evolutionarily, and did not exist in 300 unrelated, ethnically-matched healthy individuals used as controls. Functional deciphers by using a dual-luciferase reporter assay system unveiled that the mutant MEF2C protein had a significantly reduced transcriptional activity. Furthermore, the mutation significantly diminished the synergistic activation between MEF2C and GATA4, another cardiac core transcription factor that has been causally linked to CHD. In conclusion, this is the first report on the association of a MEF2C loss-of-function mutation with an increased vulnerability to CHD in humans, which provides novel insight into the molecular mechanisms underlying CHD, implying potential implications for early diagnosis and timely prophylaxis of CHD.

Histone lysine methylation and congenital heart disease: From bench to bedside (Review)

Histone post-translational modifications (PTM) as one of the key epigenetic regulatory mechanisms that plays critical role in various biological processes, including regulating chromatin structure dynamics and gene expression. Histone lysine methyltransferase contributes to the establishment and maintenance of differential histone methylation status, which can recognize histone methylated sites and build an association between these modifications and their downstream processes. Recently, it was found that abnormalities in the histone lysine methylation level or pattern may lead to the occurrence of many types of cardiovascular diseases, such as congenital heart disease (CHD). In order to provide new theoretical basis and targets for the treatment of CHD from the view of developmental biology and genetics, this review discusses and elaborates on the association between histone lysine methylation modifications and CHD.

Pulmonary endothelial cell DNA methylation signature in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a severe and incurable pulmonary vascular disease. One of the primary origins of PAH is pulmonary endothelial dysfunction leading to vasoconstriction, aberrant angiogenesis and smooth muscle cell proliferation, endothelial-to-mesenchymal transition, thrombosis and inflammation. Our objective was to study the epigenetic variations in pulmonary endothelial cells (PEC) through a specific pattern of DNA methylation. DNA was extracted from cultured PEC from idiopathic PAH (n = 11), heritable PAH (n = 10) and controls (n = 18). DNA methylation was assessed using the Illumina HumanMethylation450 Assay. After normalization, samples and probes were clustered according to their methylation profile. Differential clusters were functionally analyzed using bioinformatics tools. Unsupervised hierarchical clustering allowed the identification of two clusters of probes that discriminates controls and PAH patients. Among 147 differential methylated promoters, 46 promoters coding for proteins or miRNAs were related to lipid metabolism. Top 10 up and down-regulated genes were involved in lipid transport including ABCA1, ABCB4, ADIPOQ, miR-26A, BCL2L11. NextBio meta-analysis suggested a contribution of ABCA1 in PAH. We confirmed ABCA1 mRNA and protein downregulation specifically in PAH PEC by qPCR and immunohistochemistry and made the proof-of-concept in an experimental model of the disease that its targeting may offer novel therapeutic options. In conclusion, DNA methylation analysis identifies a set of genes mainly involved in lipid transport pathway which could be relevant to PAH pathophysiology.

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.

Association Between DSCR1 Variations and Congenital Heart Disease Susceptibility

Background

The objective of this study was aimed to detect the association of Down syndrome critical region 1 (DSCR1) gene polymorphisms (rs149048873 and rs143081213) and congenital heart disease (CHD) susceptibility.

Material/Methods

This case-control study included 102 CHD patients and 113 healthy controls. Cases and controls were matched in age and gender. Genotypes of DSCR1 gene polymorphisms were detected by TaqMan method in cases and controls. Hardy-Weinberg equilibrium (HWE) examination was performed by PLINK 1.0 software. Chi square test was utilized to assess the distribution of the genotypes and the alleles. Relative risk of CHD was presented by odds ratios (ORs) with 95% confidence intervals (CIs). All of the calculations were implemented using SPSS 18.0.

Results

Variant genotype distribution of rs149048873 and rs143081213 mutations were higher in cases than in controls, but the differences were not statistically obvious (P>0.05). Additionally, frequencies of mutant allele of the two polymorphisms were also significantly different in case and control groups (P>0.05).

Conclusions

No significant associations existed between DSCR1 gene rs149048873 and rs143081213 polymorphisms and CHD susceptibility.