Screening and evaluation of TBX20 and CITED2 mutations in children with congenital cardiac septal defects: Correlation with cardiac troponin T and caspase-3

Congenital cardiac septal defect (CCSD) is the main type of congenital heart disease and owns a very high mortality rate among newborns. CCSD is controlled by specific transcription factors, including T-box transcription factor 20 (TBX20) and Cbp/P300 interacting transactivator with Glu/Asp rich carboxy-terminal domain 2 (CITED2) which are key molecular actors in heart development. Here, we screened for mutations in TBX20 and CITED2 genes in Egyptian children with CCSD and assessed their association with CCSD susceptibility and with cardiac troponin T (cTnT) and the apoptotic marker caspase-3 as biochemical markers for CCSD. Thirty unrelated newborns and children affected with CCSD and 30 matched healthy controls with no personal history of cardiac diseases were recruited. Selection criteria were children (<18 years) with any age diagnosed with CCSD using ECHO. Mutational analysis and genotyping were done using PCR-Sanger DNA sequencing technique. Serum cTnT and caspase-3 were analyzed using ELISA. Sequencing analysis identified 2 TBX20 variants (c.766T>C and c.39T>C) in the CCSD and control groups and 2 CITED2 variants (c.12T>C and c.9C>T) in one CCSD patient, while were absent in controls. In silico analysis identified TBX20 c.766T>C (rs3999941) as a missense (F256L) pathogenic variant and the other three variants as synonymous and benign. Compared with controls, TBX20 c.766T>C TC genotype and minor C allele were candidate high-risk factors for CCSD. Besides, serum cTnT and caspase-3 were dramatically elevated in CCSD children compared to controls. TBX20 c.766T>C TC genotype was associated with high cTnT in CCSD children. Conclusively, we advocate TBX20 c.766T>C variant as a potential genetic marker for CCSD which might associate with high cTnT levels. CITED2 genetic variants might have rare incidence among Egyptian CCSD children. Serum cTnT and caspase-3 are useful markers for ascertaining CCSD in children. These data could be exploited in prenatal genetic counseling, pre-implantation genotyping, and therapy of CCSD.

Discovery of TBX20 as a Novel Gene Underlying Atrial Fibrillation

Atrial fibrillation (AF), the most prevalent type of sustained cardiac dysrhythmia globally, confers strikingly enhanced risks for cognitive dysfunction, stroke, chronic cardiac failure, and sudden cardiovascular demise. Aggregating studies underscore the crucial roles of inherited determinants in the occurrence and perpetuation of AF. However, due to conspicuous genetic heterogeneity, the inherited defects accounting for AF remain largely indefinite. Here, via whole-genome genotyping with genetic markers and a linkage assay in a family suffering from AF, a new AF-causative locus was located at human chromosome 7p14.2-p14.3, a ~4.89 cM (~4.43-Mb) interval between the markers D7S526 and D7S2250. An exome-wide sequencing assay unveiled that, at the defined locus, the mutation in the TBX20 gene, NM_001077653.2: c.695A>G; p.(His232Arg), was solely co-segregated with AF in the family. Additionally, a Sanger sequencing assay of TBX20 in another family suffering from AF uncovered a novel mutation, NM_001077653.2: c.862G>C; p.(Asp288His). Neither of the two mutations were observed in 600 unrelated control individuals. Functional investigations demonstrated that the two mutations both significantly reduced the transactivation of the target gene KCNH2 (a well-established AF-causing gene) and the ability to bind the promoter of KCNH2, while they had no effect on the nuclear distribution of TBX20. Conclusively, these findings reveal a new AF-causative locus at human chromosome 7p14.2-p14.3 and strongly indicate TBX20 as a novel AF-predisposing gene, shedding light on the mechanism underlying AF and suggesting clinical significance for the allele-specific treatment of AF patients.

A novel de novo TBX20 variant in a 6-year-old Chinese girl with left ventricular noncompaction: a case report

Left ventricular noncompaction (LVNC) is a particular type of cardiomyopathy with an excessively prominent trabecular meshwork and deep intertrabecular recesses in the left ventricle (LV). The clinical manifestation of LVNC is highly variable, ranging from no symptom to congestive heart failure, arrhythmia, thrombosis, and potentially sudden cardiac death. Approximately half of LVNC cases are hereditary. TBX20 is expressed in human embryonic and vertebrate hearts. In this article, we report on a case of pediatric LVNC with a novel de novo TBX20 [c.859C>T, p.(Arg287Trp)] gene variant, which appears to be pathogenic and had not been previously reported in LVNC. The 6-year-old girl was admitted to our hospital for unexplained syncope. 2D-echocardiography revealed a dilated LV with numerous prominent trabeculations, and a two-layered structure, comprising a compacted thin epicardial band and a thicker non-compacted endocardial layer, with deep endomyocardial spaces and intertrabecular recesses in LV. During the follow-up, the child has not shown any obvious clinical signs or symptoms. In this case report, the de novo variant of TBX20 in LVNC expands the spectrum of variants that cause LVNC and contributes to the genetic counseling and individualized treatment of patients. Clinicians should focus on exploring the clinical and genetic characteristics of LVNC to provide therapies and follow-up to improve the outcome.

The Double Mutation DSG2-p.S363X and TBX20-p.D278X Is Associated with Left Ventricular Non-Compaction Cardiomyopathy: Case Report

Left ventricular non-compaction cardiomyopathy (LVNC) is a rare heart disease, with or without left ventricular dysfunction, which is characterized by a two-layer structure of the myocardium and an increased number of trabeculae. The study of familial forms of LVNC is helpful for risk prediction and genetic counseling of relatives. Here, we present a family consisting of three members with LVNC. Using a next-generation sequencing approach a combination of two (likely) pathogenic nonsense mutations DSG2-p.S363X and TBX20-p.D278X was identified in all three patients. TBX20 encodes the cardiac T-box transcription factor 20. DSG2 encodes desmoglein–2, which is part of the cardiac desmosomes and belongs to the cadherin family. Since the identified nonsense variant (DSG2-p.S363X) is localized in the extracellular domain of DSG2, we performed in vitro cell transfection experiments. These experiments revealed the absence of truncated DSG2 at the plasma membrane, supporting the pathogenic relevance of DSG2-p.S363X. In conclusion, we suggest that in the future, these findings might be helpful for genetic screening and counseling of patients with LVNC.

Maternal Folic Acid Intake and Methylation Status of Genes Associated with Ventricular Septal Defects in Children: Case-Control Study

Background: DNA methylation is the best epigenetic mechanism for explaining the interactions between nutrients and genes involved in intrauterine growth and development programming. A possible contributor of methylation abnormalities to congenital heart disease is the folate methylation regulatory pathway; however, the mechanisms and methylation patterns of VSD-associated genes are not fully understood. Objective: To determine if maternal dietary intake of folic acid (FA) is related to the methylation status (MS) of VSD-associated genes (AXIN1, MTHFR, TBX1, and TBX20). Methods: Prospective case–control study; 48 mothers and their children were evaluated. The mothers’ dietary variables were collected through a food frequency questionnaire focusing on FA and the consumption of supplements with FA. The MS of promoters of genes was determined in the children. Results: The intake of FA supplements was significantly higher in the control mothers. In terms of maternal folic acid consumption, significant differences were found in the first trimester of pregnancy. Significant differences were observed in the MS of MTHFR and AXIN1 genes in VSD and control children. A correlation between maternal FA supplementation and MS of AXIN1 and TBX20 genes was found in control and VSD children, respectively. Conclusions: A lower MS of AXIN1 genes and a higher MS of TBX20 genes is associated with FA maternal supplementation.

Association between the promoter methylation of the TBX20 gene and tetralogy of fallot

OBJECTIVES

To investigate the association between promoter methylation of the TBX20 gene and tetralogy of Fallot (TOF)． Methods. The methylation level of TBX20 promoter regions in 23 patients with TOF and five controls were analyzed through bisulfite sequencing polymerase chain reaction. Meanwhile, the expression of TBX20 mRNA was measured using real time fluorescence quantitative polymerase chain reaction.

RESULTS

The region -400 to -48 in the TBX20 promoter consisting of 42 CpG sites was predicted to contain multiple transcription factor binding sites. In this study, the overall methylation level in this region was lower in patients with TOF than in the controls (P = .035). Among the 42 CpG sites, the methylation percentages of the CpG 26 site in the TOF cases were lower than those in the controls (P = .016). The mRNA expression of TBX20 in the right ventricular outflow tract myocardium was increased in TOF cases in contrast to those in the controls (P < .001). The methylation levels in TOF cases were correlated with mRNA expression values (r = -0.81, P < .001).

CONCLUSION

The downregulated methylation level at TBX20 promoter may be responsible for the elevated mRNA expression levels in patients with TOF. The abnormal methylation status of the TBX20 promoter may contribute to the pathogenesis of TOF.

Association Analysis of Nonsyndromic Congenital Heart Disease and Tag Single Nucleotide Polymorphisms of TBX20 and Genes in the Ras-MAPK Pathway

AIMS

The present study was performed to determine whether there are variants in TBX20 and genes of the Ras-MAPK pathway associated with nonsyndromic congenital heart disease (ns-CHD).

MATERIALS AND METHODS

A total of 223 ns-CHD patients and 273 healthy controls from China were selected as study subjects to perform an association analysis using 22 tag single-nucleotide polymorphisms (tag SNPs) located either in one of three genes in the Ras-MAPK pathway (MAP2K2, BRAF, and RAF1) or the TBX20 gene that have previously been associated with syndromic congenital heart disease.

RESULTS

The results showed that none of these tag SNPs are associated with ns-CHD.

CONCLUSIONS

The results suggested that these disease-causing genes, which were previously discovered in familial cases, might not be the major genetic factors causing the development of ns-CHD in Chinese.

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.

Role of cardiac TBX20 in dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is an important cause of heart failure and sudden cardiac death worldwide. Transcription factor TBX20 has been shown to play a crucial role in cardiac development and maintenance of adult mouse heart. Recent studies suggest that TBX20 may have a role in pathophysiology of DCM. In the present study, we examined TBX20 expression in idiopathic DCM patients and in an animal model of cardiomyopathy, and studied its correlation with echocardiographic indices of LV function. Endomyocardial biopsies (EMBs) from intraventricular septal from the right ventricle region were obtained from idiopathic DCM patients (IDCM, n = 30) and from patients with ventricular septal defect (VSD, n = 14) with normal LVEF who served as controls. An animal model of DCM was developed by right renal artery ligation in Wistar rats. Cardiac TBX20 mRNA levels were measured by real-time PCR in IDCM, controls, and in rats. The role of DNA promoter methylation and copy number variation (CNVs) in regulating TBX20 gene expression was also investigated. Cardiac TBX20 mRNA levels were significantly increased (8.9 fold, p < 0.001) in IDCM patients and in RAL rats as compared to the control group. Cardiac TBX20 expression showed a negative correlation with LVEF (r = -0.71, p < 0.001) and a positive correlation with left ventricular end-systolic volume (r = 0.39, p = 0.038). No significant difference in TBX20 CNVs and promoter methylation was observed between IDCM patients and control group. Our results suggest a potential role of TBX20 in pathophysiology of DCM.

A novel variant in TBX20 (p.D176N) identified by whole-exome sequencing in combination with a congenital heart disease related gene filter is associated with familial atrial septal defect

Congenital heart disease (CHD) is the leading cause of birth defects, and its etiology is not completely understood. Atrial septal defect (ASD) is one of the most common defects of CHD. Previous studies have demonstrated that mutations in the transcription factor T-box 20 (TBX20) contribute to congenital ASD. Whole-exome sequencing in combination with a CHD-related gene filter was used to detect a family of three generations with ASD. A novel TBX20 mutation, c.526G>A (p.D176N), was identified and co-segregated in all affected members in this family. This mutation was predicted to be deleterious by bioinformatics programs (SIFT, Polyphen2, and MutationTaster). This mutation was also not presented in the current Single Nucleotide Polymorphism Database (dbSNP) or National Heart, Lung, and Blood Institute (NHLBI) Exome Sequencing Project (ESP). In conclusion, our finding expands the spectrum of TBX20 mutations and provides additional support that TBX20 plays important roles in cardiac development. Our study also provided a new and cost-effective analysis strategy for the genetic study in small CHD pedigree.