Sporadic Congenital Heart Disease Research Articles

Implication of GATA4 synonymous variants in congenital heart disease: A comprehensive in-silico approach

Synonymous variations, previously considered as neutral, are recently shown to have a significant impact on mRNA structure and stability thereby affecting protein expression and function. Their role in disease pathogenesis is also emerging. GATA4 is an important transcription factor involved in cardiac development and a well-known candidate gene associated with congenital heart disease (CHD). In the present study, we sought to conduct molecular screening of GATA4 gene in 285 sporadic and non-syndromic CHD cases. We identified four synonymous (c.27C>A, c.822C>T, c.1233G>A and c.1263C>T) and two intronic variants (g.83217T>G & g.85012T>A) in GATA4. Extensive computational analysis using widely acceptable tools i.e., Mfold, Human Splicing Finder (HSF) and Codon Usage bias was performed with a view to understand their putative downstream effects on GATA4 function. Mfold, a mRNA structure prediction tool showed the alterations of the mRNA structure and stability due to synonymous variants. Similarly, HSF also confidently predicted effect on the cis-acting regulatory elements of splicing due to four synonymous and one donor site intronic variants. Additionally, a significant change in ‘Relative Synonymous Codon usage (RSCU) frequencies’ and ‘log ratio of codon usage frequencies’ of variant codon was also noted that might affect the rate of translation. This study establishes that the synonymous variants are possibly associated with disease phenotype in CHD patients. Comprehensive computational analysis, using well-established web based tools, is suggestive of their potential downstream molecular effects on the structure, stability and expression of GATA4 protein.

The Role of Immune Interactions on HLA in the Maternal – Fetal System in Implementation of the Risk of Forming Sporadic Septal Congenital Heart Diseases without Chromosomal Diseases in the Following Generation

The Role of Immune Interactions on HLA in the Maternal – Fetal System in Implementation of the Risk of Forming Sporadic Septal Congenital Heart Diseases without Chromosomal Diseases in the Following Generation

Copy number variations in the GATA4, NKX2-5, TBX5, BMP4 CRELD1, and 22q11.2 gene regions in Chinese children with sporadic congenital heart disease.

Congenital heart disease (CHD) is a common birth defect originating from both environmental and genetic factors. An overabundance of copy number variations (CNVs) affecting cardiac-related genes has previously been detected in individuals with CHD. To evaluate if the presence of CNVs in the 22q11.2 region, and to determine whether GATA4, NKX2-5, TBX5, BMP, and CRELD1 genes contributed toward the pathogenesis of isolated incidences of CHDs in southwest China. In total 167 patients from southwest China with sporadic CHD were studied, including 121 patients with ventricular septal defect (VSD), 24 with atrial septal defect (ASD), 12 with tetralogy of fallot (TOF), six VSD cases with TOF, two cases with patent ductus arteriosus (PDA), and two VSD cases with ASD. 22q11.2, GATA4, NKX2-5, TBX5, BMP4, and CRELD1 regions were screened using MLPA and copy number variation sequencing (CNV-Seq). A 2.5-2.8Mb deletion in the 22q11.2 region was identified in 5 patients with CHD. Two of these patients were diagnosed with VSD, while two had VSD and ASD, and the other had TOF. 5 patients correspond to the same classical DiGeorge syndrome. A 0.86Mb duplication in the 22q11.2 region was identified in a PDA patient, whom was without extracardiac symptoms. These data suggest that copy number variation in the 22q11.2 region is common in CHD patients in southwest China. Regardless of the presence or absence of extracardiac symptoms, results also indicate that it is necessary to perform prenatal screening for CHD.

Search of Somatic Mutations of NKX2-5 and GATA4 Genes in Chinese Patients with Sporadic Congenital Heart Disease.

Congenital heart disease (CHD) usually occurs sporadically, with only a minority of cases associated with a known genetic mechanism. Cardiac-specific transcription factors NKX2-5 and GATA4 play key roles in the mammalian heart development, and the affected cardiac tissues of CHD patients are prone to somatic mutations which thus participate in the pathogenesis of CHD. We collected 98 patients with sporadic CHD, extracted genomic DNA from cardiac tissues and blood, and then screened NKX2-5 and GATA4 genes using PCR-direct sequence analysis. A novel heterozygous missense mutation (c.907G>A, p.V303I) of NKX2-5 gene was identified in a patient with tetralogy of Fallots. Functional assay revealed that this mutant was associated with significantly reduced transcriptional activity. In addition, we found two known single-nucleotide polymorphisms (SNPs) (rs2277923, rs3729753) in NKX2-5 and two known SNPs (rs56166237, rs3729856) in GATA4. All variations identified in cardiac tissues were consistent with those of peripheral blood, and no somatic mutations were found in cardiac tissues. Our study shows no evidence of NKX2-5 and GATA4 somatic mutations playing a role in the pathogenesis of sporadic CHD.

Prevalence of 22q11.2 Deletion and Genetic Characterization in Chinese Patients with Congenital Heart Disease

BackgroundThe 22q11.2 deletion syndrome, resulted from the rearrangements in the 22q11.2 chromosomal region, is the most common microdeletion syndrome. Most patients share a common 3Mb or 1.5Mb hemizygous deletion of 22q11.2 in the low copy repeats (LCRs). The remaining patients include smaller deletions that are nested within the 3Mb typically deleted region (TDR) and a few rare deletions that have no overlap with the TDR. The present work aimed to identify the prevalence and the detailed genetic characterization of 22q11.2 deletion or amplification in the children with any sporadic congenital heart disease (CHD), and to explore the genotype‐phenotype relationship between deletion/amplification type and clinical data.MethodsA total of 354 CHD patients were screened by multiplex ligation‐dependent probe amplification and capillary electrophoresis methods. Universal Probe Library technology was applied to validate the screening results.ResultsWe found 40 patients in 354 CHD (11.3%) carried different levels of deletions or amplifications. The phenotypes of the 40 patients included ventricular septal defect (15), atrial septal defect (12), patent ductus arteriosus (12), tetralogy of Fallot (6), right ventricular outflow tract stenosis (4), pulmonary stenosis (2), pulmonary hypertension (18), and Down's syndrome (2). Two patients with ventricular septal defect carried the 3Mb TDR from CLTCL1 to HIC2 (LCR A–D) and 1.5Mb deletions from CLTCL1 to MED15 (LCR A–B) respectively; all the others carried atypical deletions or amplifications nested within the LCRs. Based on the gene analysis, CDC45 (15), TBX1 (8), USP18 (8), RTDR1 (7), SNAP29 (6), and ZNF74 (4) exhibited a higher incidence among the 40 individuals; in addition, 6 patients presented a amplification in TOP3B gene.ConclusionsThis study revealed 3Mb TDR, smaller deletions, rare deletions, and segmental amplifications of chromosome 22q11.2 in Chinese CHD patients. The genotype‐phenotype relationship analysis indicated that those gene abnormalities may cause various types of CHD. Our data also suggest that genetic detection should be performed routinely in CHD patients and the unique deletions or amplifications may provide useful insight into individual analysis.Support or Funding InformationSupported by grants from the National Natural Science Foundation of China (81170148 & 81641017), Zhejiang Provincial Natural Science Foundation (LY15H020008), & Tianjin Binhai Key Platform for Creative Research Program (2012‐BK110004), Binhai New Area Health Bureau (2012BWKZ008, 2016BWKY007, 2016BWKZ003).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Influence of the social, medicinal and environmental factors upon the development of sporadic congenital heart diseases

The epidemiological studies have shown an increase of congenital heart diseases in the industrial regions of the Russian Federation. The etiology and pathogenesis of most congenital heart defects are still unknown despite high achievements in cardiology and cardiac surgery. The purpose of this review is to analyze the literature data devoted to the influence of a complex of exogenous and endogenous factors, including the genetic ones, upon the development of the sporadic congenital heart diseases, which are not associated with the chromosomal abnormalities. It isshown that the sporadic congenital heart diseases associate with the women's social factors such as a low social status and level of education, smoking, and alcohol. The air pollution with nanoparticles smaller than 10 µm is a risk factor for the development of the congenital heart diseases and other pathological conditions of the cardiovascular system. It has been proven that the alleles and genotypes of polymorphic variants of genes GATA6, NPPB (rs198388 and rs198389), CYP1A1, CYP1B1, and NAT2 have the associative links with the congenital heart disease in the children.

A Rare Rs139365823 Polymorphism in Pre-miR-138 Is Associated with Risk of Congenital Heart Disease in a Chinese Population.

miR-138 modulates cardiac morphogenesis in zebrafish. We explored whether a genetic polymorphism in miR-138 might contribute to the occurrence of sporadic congenital heart disease (CHD) and the potential mechanism. We performed a case-control study consisting of 857 CHD cases and 938 non-CHD controls by genotyping miR-138 in a Chinese population. Two SNPs, including rare rs139365823 located in the pre-miR-138 sequence and rs76987351 located in the pri-miR-138 sequence, were identified by sequencing miR-138. The results demonstrated that the genotypes and allele frequencies of the rs139365823 minor allele A were significantly associated with the increased risk of CHD cases overall or in the Tetralogy of Fallot (TOF) subtype, but not with the rs76987351 A/G allele. Real-time PCR data showed that the rs139365823 minor allele A significantly increased the expression of mature miR-138, whereas the rs76987351 minor allele A had the opposite effect. As TOF is caused by severe outflow tract (OFT) development and an alignment defect, we identified Dvl2, involved in OFT development, as a direct target of miR-138. Further, the rs139365823 minor allele A enhanced the miR-138-mediated inhibitory regulation of Dvl2. Taken together, our results demonstrated for the first time that the functional variant rs139365823 in pre-miR-138 altered the expression of mature miR-138 and its inhibitory effect on target genes and conferred the risk for CHD in the population studied here.

Peculiarities of alleles and genotypes distribution of genes CRELD1 and GATA6 in mothers of children with sporadic congenital heart diseases

Peculiarities of alleles and genotypes distribution of genes CRELD1 and GATA6 in mothers of children with sporadic congenital heart diseases

RCAN1 Mutation and Functional Characterization in Children with Sporadic Congenital Heart Disease.

Congenital heart disease (CHD) is the most frequent birth defect. RCAN1 (regulator of calcineurin 1) contributes to CHD in Down syndrome. However, whether RCAN1 is also associated with nonsyndromic CHD remains unclear. This study sequenced the exons and flanking region of RCAN1 in 128 sporadic CHD patients and 150 normal controls. We identified six novel heterozygous mutations in CHD patients. Functional assay showed that the g.482G>T could obviously raise the promoter activity of RCAN1.4 in vitro; However, we failed to detect the expression of RCAN1 in the right auricle, which made it confused to evaluate the pathogenicity of this mutation. In addition, we demonstrated that c.290T>C and g.1056+58C>A had no effect on the alternative splicing of RCAN1. The *196C>T, *790G>A, and *1278C>G did not influence the translation of RCAN1 post transcription. In conclusion, a novel mutation of g.482G>T in RCAN1 may be related to CHD by causing overexpression of RCAN1.4.

Association of genetic polymorphisms of de novo nucleotide biosynthesis with increased CHD susceptibility in the northern Chinese population

Congenital heart disease (CHD) is one of most prevalent birth defects in the world. However, the underlying molecular mechanism(s) have not been fully understood. Here we report that increased CHD susceptibility is associated with genetic polymorphisms for de novo nucleotide biosynthesis in northern Chinese population, which has been reported with lower plasma folate levels. Nine tagSNPs of four genes (GART, ATIC, MTHFD1 and SHMT1) in de novo nucleotide biosynthesis were sequenced in 802 sporadic CHD patients and 1093 controls from two Han Chinese populations, located in north China (Shandong) and South China (Shanghai), respectively. Six SNPs were found to be significantly associated with CHDs or septation defects only in the Shandong population dataset, but none displayed significant association with any CHDs in the Shanghai population dataset as well as in the combined dataset. We also showed that the minor A allele of rs7279549 in GART reduced transcriptional activity and displayed lower affinity for unknown transcription factor(s), demonstrating the allele is a functional risk factor for CHD in Shandong population. Our study indicates that dysregulation of de novo nucleotide biosynthesis pathway may conditionally contribute to CHD pathogenesis in northern Chinese.

Association Between Sequence Variations in RCAN1 Promoter and the Risk of Sporadic Congenital Heart Disease in a Chinese Population.

The pathogenesis of congenital heart disease (CHD) is unclear. There is a high incidence of CHD in Down syndrome, in which RCAN1 (regulator of calcineurin 1) overexpression is observed. However, whether RCAN1 plays an important role in non-syndromic CHD is unknown. This study investigates the relationship between sequence variations in the RCAN1 promoter and sporadic CHD. This was a case-control study in which the RCAN1 promoter was cloned and sequenced in 128 CHD patients (median age 1.1 year) and 150 normal controls (median age 3.0 year). No mutation sites had been identified in this research. Three single-nucleotide (C to T) polymorphisms were detected: rs193289374, rs149048873 and rs143081213. The polymorphisms were not associated with CHD risk according to a logistic regression analysis. Functional assays in vitro showed that compared with the wild-type genotype, the rs149048873 polymorphism decreased, and the rs143081213 increased, the RCAN1 promoter activity, though the rs193289374 polymorphism had no effect. In conclusion, the sequence variations in RCAN1 promoter are not major genetic factors involved in sporadic CHD, at least in the current research population.

Genetic Pathways in Congenital Heart Development

Congenital heart disease (CHD) is the most common birth defect in newborns. Although insights into the genes and pathways involved that cause CHD have been identified by targeted perturbations of molecules that function in the developmental pathways involved in myocyte specification, differentiation or cardiac morphogenesis, the direct role of these or other perturbations in humans has remained poorly understood. Researchers have tried to bridge this knowledge gap through conventional genome‐wide analyses of rare Mendelian CHD families and by sequencing candidate genes in CHD cohorts. While these discoveries have yield highly penetrant inherited mutations in families with mild to moderately severe CHD, analyses of these genes rarely defines a pathogenic mutation in severe forms of CHD that occurs as a sporadic event, the most common presentation of CHD. The advent of contemporary genomic technologies including SNP arrays, next‐generation sequencing, and CNV analyses are accelerating the discovery of genetic causes of severe and sporadic CHD. Remarkably, emerging genomic data have validated and extended earlier observations leaned from the experimental CHD models and monogenic CHD families. Together these dataset have begun to define the genetic architecture of CHD: CHD gene encode molecules that orchestrate cardiac development; CHD mutations alter gene/protein dosage; comparable CHD mutations yield many distinct malformations, implying that higher order interactions account for particular CHD phenotypes.

Association of aminoacyl-tRNA synthetases gene polymorphisms with the risk of congenital heart disease in the Chinese Han population.

Aminoacyl-tRNA synthetases (ARSs) are in charge of cellular protein synthesis and have additional domains that function in a versatile manner beyond translation. Eight core ARSs (EPRS, MRS, QRS, RRS, IRS, LRS, KRS, DRS) combined with three nonenzymatic components form a complex known as multisynthetase complex (MSC).We hypothesize that the single-nucleotide polymorphisms (SNPs) of the eight core ARS coding genes might influence the susceptibility of sporadic congenital heart disease (CHD). Thus, we conducted a case-control study of 984 CHD cases and 2953 non-CHD controls in the Chinese Han population to evaluate the associations of 16 potentially functional SNPs within the eight ARS coding genes with the risk of CHD. We observed significant associations with the risk of CHD for rs1061248 [G/A; odds ratio (OR) = 0.90, 95% confidence interval (CI) = 0.81–0.99; P = 3.81×10−2], rs2230301 [A/C; OR = 0.73, 95%CI = 0.60–0.90, P = 3.81×10−2], rs1061160 [G/A; OR = 1.18, 95%CI = 1.06–1.31; P = 3.53×10−3] and rs5030754 [G/A; OR = 1.39, 95%CI = 1.11–1.75; P = 4.47×10−3] of EPRS gene. After multiple comparisons, rs1061248 conferred no predisposition to CHD. Additionally, a combined analysis showed a significant dosage-response effect of CHD risk among individuals carrying the different number of risk alleles (P trend = 5.00×10−4). Compared with individuals with “0–2” risk allele, those carrying “3”, “4” or “5 or more” risk alleles had a 0.97-, 1.25- or 1.38-fold increased risk of CHD, respectively. These findings indicate that genetic variants of the EPRS gene may influence the individual susceptibility to CHD in the Chinese Han population.

No association of pri-miR-143 rs41291957 polymorphism with the risk of congenital heart disease in a Chinese population.

MiR-143 plays an important role in the heart development of zebra fish. The rs41291957 variant located in the pri-miR-143 sequence is associated with colorectal carcinogenesis. Therefore, the authors hypothesized that rs41291957 in pri-miR-143 might be involved in the risk of sporadic congenital heart disease (CHD). The authors conducted a case-control study of CHD in a Chinese population to test their hypothesis by genotyping pri-miR-143 rs41291957 in 1,109 CHD cases and 915 non-CHD control subjects. Logistic regression analyses showed no significant association of genotype or allele frequencies of pri-miR-143 rs41291957 A/G polymorphism with the CHD cases in overall or various subtypes compared with the control group. To the authors' knowledge, this is the first study to investigate the relationship between miR-143 and CHD cases. The results demonstrated that rs41291957 in pri-miR-143 has no major role in genetic susceptibility to sporadic CHD, at least in the current study population.

Uncovering the rare variants of DLC1 isoform 1 and their functional effects in a Chinese sporadic congenital heart disease cohort.

Congenital heart disease (CHD) is the most common birth defect affecting the structure and function of fetal hearts. Despite decades of extensive studies, the genetic mechanism of sporadic CHD remains obscure. Deleted in liver cancer 1 (DLC1) gene, encoding a GTPase-activating protein, is highly expressed in heart and essential for heart development according to the knowledge of Dlc1-deficient mice. To determine whether DLC1 is a susceptibility gene for sporadic CHD, we sequenced the coding region of DLC1 isoform 1 in 151 sporadic CHD patients and identified 13 non-synonymous rare variants (including 6 private variants) in the case cohort. Importantly, these rare variants (8/13) were enriched in the N-terminal region of the DLC1 isoform 1 protein. Seven of eight amino acids at the N-terminal variant positions were conserved among the primates. Among the 9 rare variants that were predicted as “damaging”, five were located at the N-terminal region. Ensuing in vitro functional assays showed that three private variants (Met360Lys, Glu418Lys and Asp554Val) impaired the ability of DLC1 to inhibit cell migration or altered the subcellular location of the protein compared to wild-type DLC1 isoform 1. These data suggest that DLC1 might act as a CHD-associated gene in addition to its role as a tumor suppressor in cancer.

Congenital Heart Disease

Congenital heart disease (CHD) remains a leading cause of morbidity and mortality in childhood and is the most common human birth defect, affecting nearly 1% of all live births worldwide. The morphogenetic events that are disrupted during cardiogenesis that lead to CHD are now partially understood, as are many of the molecular networks that guide normal heart development. Studies of rare Mendelian forms of familial CHD, as well as CHD associated with stereotypic syndromes, have revealed numerous single-gene mutations that cause CHD. However, mutations in these genes are infrequent in the more common sporadic form of CHD. Despite epidemiological evidence for an inherited component in sporadic CHD, the contribution of inherited variants or de novo mutations in the setting of CHD has been unclear. A recent landmark article in Nature begins to tackle this question by using modern genetic approaches and suggests that roughly 10% of sporadic CHD cases have de novo mutations that contribute significantly to the disease process.

Genetic variants of the endothelial NO synthase gene (eNOS) may confer increased risk of sporadic congenital heart disease.

The endothelial NO synthase (eNOS) enzyme is expressed during the early stages of cardiogenesis and plays an important role in normal heart development. Genetic variations of eNOS G894T have been shown to influence individual susceptibility to some phenotypes of congenital heart disease (CHD) in different populations. We conducted a case-control study comprised of 945 CHD patients and 972 non-CHD individuals in a Chinese population. Two functional single nucleotide polymorphisms (SNPs) (T-786C: rs2070744 and G894T: rs1799983) and one tagging SNP (rs7830) were evaluated in our study, and we assessed their association with the risk of CHD. Compared with the rs7830 CC/AC genotypes, the eNOS rs7830 AA genotype showed a significantly increased risk of CHD (adjusted odds radio (OR) = 1.45, 95% confidence interval (CI = 1.13-1.85). A stratified analysis was performed and showed that the association between the rs7830 AA genotype and CHD risk was stronger in patients with perimembranous ventricular septal defects (adjusted OR = 1.62, 95%CI = 1.20-2.20). Our results suggest that the eNOS rs7830 polymorphism may contribute to the susceptibility of sporadic CHD in a Chinese population.

Association of Two Variants in SMAD7 with the Risk of Congenital Heart Disease in the Han Chinese Population

SMAD7 is a general antagonist of TGF-β signaling and has been found to be involved in cardiogenesis in mouse models, but its role in human congenital heart disease (CHD) has yet to be investigated. To examine if SMAD7 is associated with CHD, we conducted a case-control study in the Han Chinese population. Exon1 and exon4 of SMAD7, which encode the functional MH1 and MH2 domains, were directly sequenced in 1,201 sporadic CHD patients and 1,116 control individuals. A total of 18 sequence variations were identified. Two common variants rs3809922 and rs3809923 are located at exon4 of SMAD7, and were found in strong linkage disequilibrium with each other (r 2 = 0.93). We analyzed the association of these two loci with CHD in 3 independent subgroup case-control studies, and found that in some subgroups, rs3809922 and rs3809923 were significantly associated with CHD through genetic model analysis. In the combined data set, TT genotype in rs3809922 significantly increased the risk of CHD compared with CC and CT, while GG genotype in rs3809923 significantly increased the risk of CHD compared with CC and CG, particularly in the recessive model. In addition, haplotype analyses showed that haplotype TG significantly increased the risk of CHD (P = 6.9×10−6); this finding supports the results from the analyses based on single locus. According to data from the 1000 Genomes Project, the frequencies of the two risk alleles varied greatly between populations worldwide, which indicate the identified associations might have a population difference. To our knowledge, this is the first report that genetic variants in SMAD7 influence susceptibility to CHD risk.

R25C mutation in the NKX2.5 gene in Italian patients affected with non-syndromic and syndromic congenital heart disease

Heterozygous mutations in the transcription factor Nkx2.5 indicate a genetic cause for congenital heart diseases (CHDs) in human beings. The present study aimed to assess the prevalence of NKX2.5 mutations in Italian patients with sporadic non-syndromic and syndromic CHD, as well as to appraise any genotype-phenotype correlations. One hundred Italian patients affected with CHD (90 had sporadic non-syndromic CHD and 10 had syndromic CHD) were screened for NKX2.5 mutations. The coding region and flanking regions involved in gene splicing of the CSX/NKX2.5 gene were amplified from genomic DNA by PCR, and mutational analysis was performed using denaturing high performance liquid chromatography and DNA sequencing. One previously reported NKX2.5 mutation (c.73C>T, p.R25C) was identified in two of the 100 CHD patients (2%). We have detected the p.R25C alteration in a woman showing aneurysm of the membranous septum, aortic coarctation and bicuspid aortic valve, that was a different phenotype from those previously reported, and for the first time in a patient with syndromic CHD with Down's syndrome (posterior ventricular septal defect, atrial septal defect, left superior cava vein ' sinus, and patent ductus arteriosus). Our results confirm that NKX2.5 mutations are not a common cause of CHD; furthermore, the p.R25C variation may increase susceptibility to development of CHD in patients with and without chromosomal abnormalities.

Identification of functional mutations in GATA4 in patients with congenital heart disease.

Congenital heart disease (CHD) is one of the most prevalent developmental anomalies and the leading cause of noninfectious morbidity and mortality in newborns. Despite its prevalence and clinical significance, the etiology of CHD remains largely unknown. GATA4 is a highly conserved transcription factor that regulates a variety of physiological processes and has been extensively studied, particularly on its role in heart development. With the combination of TBX5 and MEF2C, GATA4 can reprogram postnatal fibroblasts into functional cardiomyocytes directly. In the past decade, a variety of GATA4 mutations were identified and these findings originally came from familial CHD pedigree studies. Given that familial and sporadic CHD cases allegedly share a basic genetic basis, we explore the GATA4 mutations in different types of CHD. In this study, via direct sequencing of the GATA4 coding region and exon-intron boundaries in 384 sporadic Chinese CHD patients, we identified 12 heterozygous non-synonymous mutations, among which 8 mutations were only found in CHD patients when compared with 957 controls. Six of these non-synonymous mutations have not been previously reported. Subsequent functional analyses revealed that the transcriptional activity, subcellular localization and DNA binding affinity of some mutant GATA4 proteins were significantly altered. Our results expand the spectrum of GATA4 mutations linked to cardiac defects. Together with the newly reported mutations, approximately 110 non-synonymous mutations have currently been identified in GATA4. Our future analysis will explore why the evolutionarily conserved GATA4 appears to be hypermutable.