GATA4 loss-of-function mutations underlie familial tetralogy of fallot

Conotruncal Heart Defects: A Narrative Review of Molecular Genetics, Genomics Research and Innovation

Congenital heart defects (CHDs) are most prevalent cardiac defects that occur at birth, leading to significant neonatal mortality and morbidity, especially in the developing nations. Among the CHDs, conotruncal heart defects (CTDs) are particularly noteworthy, comprising a significant portion of congenital cardiac anomalies. While advances in imaging and surgical techniques have improved the diagnosis, prognosis, and management of CTDs, their molecular genetics and genomic substrates remain incompletely understood. This expert review covers the recent advances from January 2016 onward and examines the complexities surrounding the genetic etiologies, prevalence, embryology, diagnosis, and clinical management of CTDs. We also emphasize the known copy number variants and single nucleotide variants associated with CTDs, along with the current planetary health research efforts aimed at CTDs in large cohort studies. In all, this comprehensive narrative review of molecular genetics and genomics research and innovation on CTDs draws from and highlights selected works from around the world and offers new ideas for advances in CTD diagnosis, precision medicine interventions, and accurate assessment of prognosis and recurrence risks.

In-Depth Genomic Analysis: The New Challenge in Congenital Heart Disease

The use of next-generation sequencing has provided new insights into the causes and mechanisms of congenital heart disease (CHD). Examinations of the whole exome sequence have detected detrimental gene variations modifying single or contiguous nucleotides, which are characterised as pathogenic based on statistical assessments of families and correlations with congenital heart disease, elevated expression during heart development, and reductions in harmful protein-coding mutations in the general population. Patients with CHD and extracardiac abnormalities are enriched for gene classes meeting these criteria, supporting a common set of pathways in the organogenesis of CHDs. Single-cell transcriptomics data have revealed the expression of genes associated with CHD in specific cell types, and emerging evidence suggests that genetic mutations disrupt multicellular genes essential for cardiogenesis. Metrics and units are being tracked in whole-genome sequencing studies.

Somatic GATA4 mutation contributes to tetralogy of Fallot

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

Human Genetics of Tetralogy of Fallot and Double-Outlet Right Ventricle

Tetralogy of Fallot (TOF) and double-outlet right ventricle (DORV) are conotruncal defects resulting from disturbances of the second heart field and the neural crest, which can occur as isolated malformations or as part of multiorgan syndromes. Their etiology is multifactorial and characterized by overlapping genetic causes. In this chapter, we present the different genetic alterations underlying the two diseases, which range from chromosomal abnormalities like aneuploidies and structural mutations to rare single nucleotide variations affecting distinct genes. For example, mutations in the cardiac transcription factors NKX2-5, GATA4, and HAND2 have been identified in isolated TOF cases, while mutations of TBX5 and 22q11 deletion, leading to haploinsufficiency of TBX1, cause Holt-Oram and DiGeorge syndrome, respectively. Moreover, genes involved in signaling pathways, laterality determination, and epigenetic mechanisms have also been found mutated in TOF and/or DORV patients. Finally, genome-wide association studies identified common single nucleotide polymorphisms associated with the risk for TOF.

Gene editing and cardiac disease modelling for the interpretation of genetic variants of uncertain significance in congenital heart disease

BACKGROUND

Genomic sequencing in congenital heart disease (CHD) patients often discovers novel genetic variants, which are classified as variants of uncertain significance (VUS). Functional analysis of each VUS is required in specialised laboratories, to determine whether the VUS is disease causative or not, leading to lengthy diagnostic delays. We investigated stem cell cardiac disease modelling and transcriptomics for the purpose of genetic variant classification using a GATA4 (p.Arg283Cys) VUS in a patient with CHD.

METHODS

We performed high efficiency CRISPR gene editing with homology directed repair in induced pluripotent stem cells (iPSCs), followed by rapid clonal selection with amplicon sequencing. Genetic variant and healthy matched control cells were compared using cardiomyocyte disease modelling and transcriptomics.

RESULTS

Genetic variant and healthy cardiomyocytes similarly expressed Troponin T (cTNNT), and GATA4. Transcriptomics analysis of cardiomyocyte differentiation identified changes consistent with the patient's clinical human phenotype ontology terms. Further, transcriptomics revealed changes in calcium signalling, and cardiomyocyte adrenergic signalling in the variant cells. Functional testing demonstrated, altered action potentials in GATA4 genetic variant cardiomyocytes were consistent with patient cardiac abnormalities.

CONCLUSIONS

This work provides in vivo functional studies supportive of a damaging effect on the gene or gene product. Furthermore, we demonstrate the utility of iPSCs, CRISPR gene editing and cardiac disease modelling for genetic variant interpretation. The method can readily be applied to other genetic variants in GATA4 or other genes in cardiac disease, providing a centralised assessment pathway for patient genetic variant interpretation.

Genetic Variants of ISL1 Gene Promoter Identified from Congenital Tetralogy of Fallot Patients Alter Cellular Function Forming Disease Basis

Tetralogy of Fallot (TOF) is the most common cyanotic congenital heart disease in newborns. ISL1 is a master transcription factor in second heart field development, whereas the roles of ISL1 gene promoter variants in TOF patients have not been genetically investigated. Total DNA extraction from 601 human subjects, including 308 TOF patients and 293 healthy controls, and Sanger sequencing were performed. Four variants (including one novel heterozygous variant) within the ISL1 gene promoter were only found in TOF patients. Functional analysis of DNA sequence variants was performed by using the dual-luciferase reporter assay and demonstrated that three of the four variants significantly decreased the transcriptional activity of ISL1 gene promoter in HL-1 cells (p < 0.05). Further, the online JASPAR database and electrophoretic mobility shift assay showed that the three variants affected the binding of transcription factors and altered ISL1 expression levels. In conclusion, the current study for the first time demonstrated that the variants identified from the ISL1 gene promoter region are likely involved in the development of TOF by affecting the transcriptional activity and altering the ISL1 expression level. Therefore, these findings may provide new insights into the molecular etiology and potential therapeutic strategy of TOF.

Functional characterization of GATA6 genetic variants associated with mild congenital heart defects

Damaging GATA6 variants can cause moderate congenital heart defects. With the application of next-generation sequencing approaches, various novel GATA6 variants with unknown significance have been identified from a broad spectrum of congenital heart defects. However, functional assessment for distinct GATA6 variants from different severity of congenital heart defects, especially from mild defects, is lacking, which hinders our understanding of the genotype-phenotype correlations and underlying mechanisms. Here, we assessed the functional consequences of nine rare GATA6 variants, which had been implicated as the most significant variants associated with mild congenital heart defects using the largest case and control cohort. We examined the effects of these variants on subcellular localization, transcriptional activity, and protein interactions in 293T or AC16 cells and their ability to rescue heart malformation in gata6 zebrafish mutant. We found that two of these nine variants, Q120X and S424I, significantly decreased transcriptional activity. Additionally, Q120X altered subcellular localization. Consistent with the in vitro results, the in vivo results showed that Q120X and S424I lost their potency to rescue ventricular malformation in gata6 -/- embryos. The results indicated that Q120X and S424I are pathogenic in mild congenital heart defects. Further, the inconsistence of severely impaired Q120X function and mild CHDs phenotype suggested the complexity of the genotype-phenotype correlation between the GATA6 variant and heart phenotype, which may help to inform prenatal genetic counseling and pre-implantation genotyping for congenital heart defects.

A novel causative functional mutation in GATA6 gene is responsible for familial dilated cardiomyopathy as supported by in silico functional analysis

Dilated cardiomyopathy (DCM), one of the most common types of cardiomyopathies has a heterogeneous nature and can be seen in Mendelian forms. Next Generation Sequencing is a powerful tool for identifying novel variants in monogenic disorders. We used whole-exome sequencing (WES) and Sanger sequencing techniques to identify the causative mutation of DCM in an Iranian pedigree. We found a novel variant in the GATA6 gene, leading to substituting Histidine by Tyrosine at position 329, observed in all affected family members in the pedigree, whereas it was not established in any of the unaffected ones. We hypothesized that the H329Y mutation may be causative for the familial pattern of DCM in this family. The predicted models of GATA6 and H329Y showed the high quality according to PROCHECK and ERRAT. Nonetheless, simulation results revealed that the protein stability decreased after mutation, while the flexibility may have been increased. Hence, the mutation led to the increased compactness of GATA6. Overall, these data indicated that the mutation could affect the protein structure, which may be related to the functional impairment of GATA6 upon H329Y mutation, likewise their involvement in pathologies. Further functional investigations would help elucidating the exact mechanism.

Endocardial Regulation of Cardiac Development

The endocardium is a specialized form of endothelium that lines the inner side of the heart chambers and plays a crucial role in cardiac development. While comparatively less studied than other cardiac cell types, much progress has been made in understanding the regulation of and by the endocardium over the past two decades. In this review, we will summarize what is currently known regarding endocardial origin and development, the relationship between endocardium and other cardiac cell types, and the various lineages that endocardial cells derive from and contribute to. These processes are driven by key molecular mechanisms such as Notch and BMP signaling. These pathways in particular have been well studied, but other signaling pathways and mechanical cues also play important roles. Finally, we will touch on the contribution of stem cell modeling in combination with single cell sequencing and its potential translational impact for congenital heart defects such as bicuspid aortic valves and hypoplastic left heart syndrome. The detailed understanding of cellular and molecular processes in the endocardium will be vital to further develop representative stem cell-derived models for disease modeling and regenerative medicine in the future.

Diverse Molecular Mechanisms Underlying Pathogenic Protein Mutations: Beyond the Loss-of-Function Paradigm

Most known disease-causing mutations occur in protein-coding regions of DNA. While some of these involve a loss of protein function (e.g., through premature stop codons or missense changes that destabilize protein folding), many act via alternative molecular mechanisms and have dominant-negative or gain-of-function effects. In nearly all cases, these non-loss-of-function mutations can be understood by considering interactions of the wild-type and mutant protein with other molecules, such as proteins, nucleic acids, or small ligands and substrates. Here, we review the diverse molecular mechanisms by which pathogenic mutations can have non-loss-of-function effects, including by disrupting interactions, increasing binding affinity, changing binding specificity, causing assembly-mediated dominant-negative and dominant-positive effects, creating novel interactions, and promoting aggregation and phase separation. We believe that increased awareness of these diverse molecular disease mechanisms will lead to improved diagnosis (and ultimately treatment) of human genetic disorders. Expected final online publication date for the Annual Review of Genomics and Human Genetics, Volume 23 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Accelerated Growth, Differentiation, and Ploidy with Reduced Proliferation of Right Ventricular Cardiomyocytes in Children with Congenital Heart Defect Tetralogy of Fallot

The myocardium of children with tetralogy of Fallot (TF) undergoes hemodynamic overload and hypoxemia immediately after birth. Comparative analysis of changes in the ploidy and morphology of the right ventricular cardiomyocytes in children with TF in the first years of life demonstrated their significant increase compared with the control group. In children with TF, there was a predominantly diffuse distribution of Connexin43-containing gap junctions over the cardiomyocytes sarcolemma, which redistributed into the intercalated discs as cardiomyocytes differentiation increased. The number of Ki67-positive cardiomyocytes varied greatly and amounted to 7.0–1025.5/10⁶ cardiomyocytes and also were decreased with increased myocytes differentiation. Ultrastructural signs of immaturity and proliferative activity of cardiomyocytes in children with TF were demonstrated. The proportion of interstitial tissue did not differ significantly from the control group. The myocardium of children with TF under six months of age was most sensitive to hypoxemia, it was manifested by a delay in the intercalated discs and myofibril assembly and the appearance of ultrastructural signs of dystrophic changes in the cardiomyocytes. Thus, the acceleration of ontogenetic growth and differentiation of the cardiomyocytes, but not the reactivation of their proliferation, was an adaptation of the immature myocardium of children with TF to hemodynamic overload and hypoxemia.

Genomic frontiers in congenital heart disease

The application of next-generation sequencing to study congenital heart disease (CHD) is increasingly providing new insights into the causes and mechanisms of this prevalent birth anomaly. Whole-exome sequencing analysis identifies damaging gene variants altering single or contiguous nucleotides that are assigned pathogenicity based on statistical analyses of families and cohorts with CHD, high expression in the developing heart and depletion of damaging protein-coding variants in the general population. Gene classes fulfilling these criteria are enriched in patients with CHD and extracardiac abnormalities, evidencing shared pathways in organogenesis. Developmental single-cell transcriptomic data demonstrate the expression of CHD-associated genes in particular cell lineages, and emerging insights indicate that genetic variants perturb multicellular interactions that are crucial for cardiogenesis. Whole-genome sequencing analyses extend these observations, identifying non-coding variants that influence the expression of genes associated with CHD and contribute to the estimated ~55% of unexplained cases of CHD. These approaches combined with the assessment of common and mosaic genetic variants have provided a more complete knowledge of the causes and mechanisms of CHD. Such advances provide knowledge to inform the clinical care of patients with CHD or other birth defects and deepen our understanding of the complexity of human development. In this Review, we highlight known and candidate CHD-associated human genes and discuss how the integration of advances in developmental biology research can provide new insights into the genetic contributions to CHD.

Sequencing of a Chinese tetralogy of fallot cohort reveals clustering mutations in myogenic heart progenitors

Tetralogy of Fallot (TOF) is the most common cyanotic heart defect, yet the underlying genetic mechanisms remain poorly understood. Here, we performed whole-genome sequencing analysis on 146 nonsyndromic TOF parent-offspring trios of Chinese ethnicity. Comparison of de novo variants and recessive genotypes of this data set with data from a European cohort identified both overlapping and potentially novel gene loci and revealed differential functional enrichment between cohorts. To assess the impact of these mutations on early cardiac development, we integrated single-cell and spatial transcriptomics of early human heart development with our genetic findings. We discovered that the candidate gene expression was enriched in the myogenic progenitors of the cardiac outflow tract. Moreover, subsets of the candidate genes were found in specific gene coexpression modules along the cardiomyocyte differentiation trajectory. These integrative functional analyses help dissect the pathogenesis of TOF, revealing cellular hotspots in early heart development resulting in cardiac malformations.

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.

Rare variants in KDR, encoding VEGF Receptor 2, are associated with tetralogy of Fallot

PURPOSE

Rare genetic variants in KDR, encoding the vascular endothelial growth factor receptor 2 (VEGFR2), have been reported in patients with tetralogy of Fallot (TOF). However, their role in disease causality and pathogenesis remains unclear.

METHODS

We conducted exome sequencing in a familial case of TOF and large-scale genetic studies, including burden testing, in >1,500 patients with TOF. We studied gene-targeted mice and conducted cell-based assays to explore the role of KDR genetic variation in the etiology of TOF.

RESULTS

Exome sequencing in a family with two siblings affected by TOF revealed biallelic missense variants in KDR. Studies in knock-in mice and in HEK 293T cells identified embryonic lethality for one variant when occurring in the homozygous state, and a significantly reduced VEGFR2 phosphorylation for both variants. Rare variant burden analysis conducted in a set of 1,569 patients of European descent with TOF identified a 46-fold enrichment of protein-truncating variants (PTVs) in TOF cases compared to controls (P = 7 × 10-11).

CONCLUSION

Rare KDR variants, in particular PTVs, strongly associate with TOF, likely in the setting of different inheritance patterns. Supported by genetic and in vivo and in vitro functional analysis, we propose loss-of-function of VEGFR2 as one of the mechanisms involved in the pathogenesis of TOF.

Whole-Exome Sequencing Reveals a Novel Mutation of FLNA Gene in an Iranian Family with Nonsyndromic Tetralogy of Fallot

OBJECTIVE

Tetralogy of Fallot (TOF) is one of the most common congenital abnormalities that need early intervention. Here, for the first time, we report a nonsyndromic form of TOF caused by a novel variant in the FLNA gene in 2 siblings of an Iranian family.

METHODS

The family underwent a complete workup, including karyotyping, sequencing of 6 common genes in congenital heart diseases (GATA4, NKX2-5, ZIC3, FOXH1, NODAL, and GJA1), array comparative genomic hybridization, multiplex ligation-dependent probe amplification, and whole-exome sequencing. Segregation and in silico analysis were also conducted for the identified variant.

RESULTS

A variant, c.3415C>T, in the FLNA gene was found in both affected brothers in this family; this variant was heterozygous in their mother. Bioinformatics tools predicted the variant as a pathogenic one.

CONCLUSION

Many allelic disorders have been reported for FLNA mutations. Mutations in this gene may cause a nonsyndromic congenital form of TOF.

Is There Any Clinical Utility to Genetic Testing for Patients With Congenital Heart Disease?

Genetic diagnosis is becoming increasingly sophisticated, with the ability to identify even fine differences in patients with a wide variety of congenital heart lesions. Although we have an incomplete understanding of the clinical consequences of most genetic findings, some categories of mutations can have important implications for disease recurrence and prognosis. Consideration of the biology underlying a genetic deficiency, when known, can be useful in the clinical management of some patients.

Common Genetic Variants Modulate the Electrocardiographic Tpeak-to-Tend Interval

Sudden cardiac death is responsible for half of all deaths from cardiovascular disease. The analysis of the electrophysiological substrate for arrhythmias is crucial for optimal risk stratification. A prolonged T-peak-to-Tend (Tpe) interval on the electrocardiogram is an independent predictor of increased arrhythmic risk, and Tpe changes with heart rate are even stronger predictors. However, our understanding of the electrophysiological mechanisms supporting these risk factors is limited. We conducted genome-wide association studies (GWASs) for resting Tpe and Tpe response to exercise and recovery in ∼30,000 individuals, followed by replication in independent samples (∼42,000 for resting Tpe and ∼22,000 for Tpe response to exercise and recovery), all from UK Biobank. Fifteen and one single-nucleotide variants for resting Tpe and Tpe response to exercise, respectively, were formally replicated. In a full dataset GWAS, 13 further loci for resting Tpe, 1 for Tpe response to exercise and 1 for Tpe response to exercise were genome-wide significant (p ≤ 5 × 10^-8). Sex-specific analyses indicated seven additional loci. In total, we identify 32 loci for resting Tpe, 3 for Tpe response to exercise and 3 for Tpe response to recovery modulating ventricular repolarization, as well as cardiac conduction and contraction. Our findings shed light on the genetic basis of resting Tpe and Tpe response to exercise and recovery, unveiling plausible candidate genes and biological mechanisms underlying ventricular excitability.

Identification and analysis of KLF13 variants in patients with congenital heart disease

Background

The protein Kruppel-like factor 13 (KLF13) is a member of the KLF family and has been identified as a cardiac transcription factor that is involved in heart development. However, the relationship between KLF13 variants and CHDs in humans remains largely unknown. The present study aimed to screen the KLF13 variants in CHD patients and genetically analyze the functions of these variants.

Methods

KLF13 variants were sequenced in a cohort of 309 CHD patients and population-matched healthy controls (n = 200) using targeted sequencing. To investigate the effect of variants on the functional properties of the KLF13 protein, the expression and subcellular localization of the protein, as well as the transcriptional activities of downstream genes and physical interactions with other transcription factors, were assessed.

Results

Two heterozygous variants, c.487C > T (P163S) and c.467G > A (S156N), were identified in two out of 309 CHD patients with tricuspid valve atresia and transposition of the great arteries, respectively. No variants were found among healthy controls. The variant c.467G > A (S156N) had increased protein expression and enhanced functionality compared with the wild type, without affecting the subcellular localization. The other variant, c.487C > T (P163S), did not show any abnormalities in protein expression or subcellular localization; however, it inhibited the transcriptional activities of downstream target genes and physically interacted with TBX5, another cardiac transcription factor.

Conclusion

Our results show that the S156N and P163S variants may affect the transcriptional function of KLF13 and physical interaction with TBX5. These results identified KLF13 as a potential genetic risk factor for congenital heart disease.

Familial co-occurrence of congenital heart defects follows distinct patterns

Aims

Congenital heart defects (CHD) affect almost 1% of all live born children and the number of adults with CHD is increasing. In families where CHD has occurred previously, estimates of recurrence risk, and the type of recurring malformation are important for counselling and clinical decision-making, but the recurrence patterns in families are poorly understood. We aimed to determine recurrence patterns, by investigating the co-occurrences of CHD in 1163 families with known malformations, comprising 3080 individuals with clinically confirmed diagnosis.

Methods and results

We calculated rates of concordance and discordance for 41 specific types of malformations, observing a high variability in the rates of concordance and discordance. By calculating odds ratios for each of 1640 pairs of discordant lesions observed between affected family members, we were able to identify 178 pairs of malformations that co-occurred significantly more or less often than expected in families. The data show that distinct groups of cardiac malformations co-occur in families, suggesting influence from underlying developmental mechanisms. Analysis of human and mouse susceptibility genes showed that they were shared in 19% and 20% of pairs of co-occurring discordant malformations, respectively, but none of malformations that rarely co-occur, suggesting that a significant proportion of co-occurring lesions in families is caused by overlapping susceptibility genes.

Conclusion

Familial CHD follow specific patterns of recurrence, suggesting a strong influence from genetically regulated developmental mechanisms. Co-occurrence of malformations in families is caused by shared susceptibility genes.

Functional analysis of rare variants of GATA4 identified in Chinese patients with congenital heart defect

Congenital heart defect (CHD) is one of the most common cardiovascular diseases, affecting approximately 0.8% of live births. The transcription factor GATA4 has been known to play a key role in cardiac development. In this study, we performed whole exome sequencing in nine unrelated CHD patients and found two rare deleterious missense variants in the GATA4 gene (c.C487T,p.P163S and c.C1223A,p.P408Q) (ExAC <0.001 and CADD >15) in three cases that were confirmed by Sanger sequencing. Subsequently, these two variants were screened for in an additional 226 patients with CHD and 206 healthy controls by Sanger sequencing, and no variants were observed. These two variants were predicted to be damaging to protein function using a functional prediction program. Co-IP indicated that both of the GATA4 variants (P163S and P408Q) blocked heterodimer formation between GATA4 and ZFPM2 protein. Immunofluorescence showed that the two GATA4 variants diminished the colocalization formation between GATA4 and ZFPM2 protein compared to that of WT protein. These findings indicate that the two rare variants of GATA4 might disturb its interaction with ZFPM2 and influence corresponding downstream gene activity, suggesting that the GATA4 variants may be associated with the pathogenesis of CHD.

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.

Functional analysis of the congenital heart disease‑associated GATA4 H436Y mutation in vitro

Congenital heart disease (CHD) is the most common type of developmental defect, with high rates of morbidity in infants. The transcription factor GATA‑binding factor 4 (GATA4) has been reported to serve a critical role in embryogenesis and cardiac development. Our previous study reported a heterozygous GATA4 c.1306C>T (p.H436Y) mutation in four Chinese infants with congenital heart defects. In the present study, functional analysis of the GATA4 H436Y mutation was performed in vitro. The functional effect of GATA4 mutation was compared with GATA4 wild‑type using a dual‑luciferase reporter assay system and immunofluorescence. Electrophoretic mobility‑shift assays were performed to explore the binding affinity of the mutated GATA4 to the heart and neural crest derivatives expressed 2 (HAND2) gene. The results revealed that the mutation had no effect on normal nuclear localization, but resulted in diminished GATA‑binding affinity to HAND2 and significantly decreased gene transcriptional activation. These results indicated that this GATA4 mutation may not influence cellular localization in transfected cells, but may affect the affinity of the GATA‑binding site on HAND2 and decrease transcriptional activity, thus suggesting that the GATA4 mutation may be associated with the pathogenesis of CHD.

The Contribution of Gene Mutations to the Pathogenesisof Tetralogy of Fallot

Congenital heart disease (CHD) is considered as an important and developing area in the medical community. Since these patients can reach maturity and have children, the role of genetic determinants in increasing risk of CHD is extremely evident among children of these patients. Because genetic studies related to CHD are increasing, and each day the role of new genetic markers is more and more clarified, this review re-examined the effects of gene mutations in the pathogenesis of tetralogy of Fallot (TOF) as an important pathological model among other CHDs. Due to the complexity of heart development, it is not astonishing that numerous signaling pathways and transcription factors, and many genes are involved in pathogenesis of TOF. This review focuses on the jag1, nkx2.5, gata4, zfpm2/fog2 and cited2 genes previously reported to be involved in TOF.

Gata4 regulates hedgehog signaling and Gata6 expression for outflow tract development

Dominant mutations of Gata4, an essential cardiogenic transcription factor (TF), were known to cause outflow tract (OFT) defects in both human and mouse, but the underlying molecular mechanism was not clear. In this study, Gata4 haploinsufficiency in mice was found to result in OFT defects including double outlet right ventricle (DORV) and ventricular septum defects (VSDs). Gata4 was shown to be required for Hedgehog (Hh)-receiving progenitors within the second heart field (SHF) for normal OFT alignment. Restored cell proliferation in the SHF by knocking-down Pten failed to rescue OFT defects, suggesting that additional cell events under Gata4 regulation is important. SHF Hh-receiving cells failed to migrate properly into the proximal OFT cushion, which is associated with abnormal EMT and cell proliferation in Gata4 haploinsufficiency. The genetic interaction of Hh signaling and Gata4 is further demonstrated to be important for OFT development. Gata4 and Smo double heterozygotes displayed more severe OFT abnormalities including persistent truncus arteriosus (PTA). Restoration of Hedgehog signaling renormalized SHF cell proliferation and migration, and rescued OFT defects in Gata4 haploinsufficiency. In addition, there was enhanced Gata6 expression in the SHF of the Gata4 heterozygotes. The Gata4-responsive repressive sites were identified within 1kbp upstream of the transcription start site of Gata6 by both ChIP-qPCR and luciferase reporter assay. These results suggested a SHF regulatory network comprising of Gata4, Gata6 and Hh-signaling for OFT development.

Gata4 is an important transcription factor that regulates the development of the heart. Human possessing a single copy of Gata4 mutation display congenital heart defects (CHD), including double outlet right ventricle (DORV). DORV is an alignment problem in which both the Aorta and Pulmonary Artery originate from the right ventricle, instead of originating from the left and the right ventricles, respectively. In this study, a Gata4 mutant mouse model was used to study how Gata4 mutations cause DORV. We showed that Gata4 is required in the cardiac precursor cells for the normal alignment of the great arteries. Although Gata4 mutations inhibit the rapid increase in the cardiac precursor cell numbers, resolving this problem does not recover the normal alignment of the great arteries. It indicates that there is a migratory issue of the cardiac precursor cells as they navigate to the great arteries during development. The study further showed that a specific molecular signaling, Hh-signaling and Gata6 are responsible to the Gata4 action in the cardiac precursor cells. Importantly, over-activation of the Hh-signaling pathways rescues the DORV in the Gata4 mutant embryos. This study provides a molecular model to explain the ontogeny of a subtype of CHD.

[Ultrastructural features of cardiomyocytes in infants with tetralogy of Fallot in the first year of life]

OBJECTIVE

To analyze cardiomyocyte (CMC) ultrastructural changes in the right ventricle outflow tract (RVOT) of infants with tetralogy of Fallot (TF) in the first years of life and to compare the findings with clinical parameters in these patients.

MATERIAL AND METHODS

Intraoperative RVOT myocardial biopsy specimens obtained from 51 patients aged 3-33 months with TF during radical correction of defect were investigated. CMC diameter and length were measured using the semithin myocardial sections stained with periodic acid-Schiff. The ultrathin sections were examined in the electron microscope.

RESULTS

The diameter of CMCs in the RVOT of infants with TF varied significantly (7.3-17.0 µm) and averaged 10.8±2.2 µm; a large number of multinucleated CMCs were observed. There were ultrastructural signs of incomplete differentiation of CMCs: active myofibril assembly in the free sarcoplasmic region; gap junctions on the lateral surfaces of CMCs; and centrioli in their sarcoplasm. Myofibrillogenesis in babies under 6 months increased in response to hemodynamic overload and hypoxemia. In addition, organelles suggestive of the synthetic activity of CMCs, such as cisterns and vesicles of the Golgi complex and granular endoplasmic reticulum, were detected in the sarcoplasm of a number of CMCs. TF infants' myocardium also displayed focal disorders of CMC interposition; the change in the shape of myocytes was accompanied by the appearance of additional lateral insert discs. Some CMCs showed the abnormal localization of the nucleus beneath the sarcolemma, sarcoplasmic bulging areas, and dystrophic changes.

CONCLUSION

There were ultrastructural features characteristic for the myocardium that was at the state of active growth and differentiation (increases in the diameter and length of CMCs and in the number of nuclei; myofibrillogenesis; signs of synthetic and proliferative activity along with insignificant dystrophic changes) in the CMCs of myocardial RVOT in infants with TF in the first years of life.

A loss-of-function mutation p.T52S in RIPPLY3 is a potential predisposing genetic risk factor for Chinese Han conotruncal heart defect patients without the 22q11.2 deletion/duplication

Background

Conotruncal heart defect (CTD) is a complex congenital heart disease with a complex and poorly understood etiology. The transcriptional corepressor RIPPLY3 plays a pivotal role in heart development as a negative regulator of the key cardiac transcription factor TBX1. A previous study showed that RIPPLY3 contribute to cardiac outflow tract development in mice, however, the relationship between RIPPLY3 and human cardiac malformation has not been reported.

Methods

615 unrelated CTD Chinese Han patients were enrolled, we excluded the 22q11.2 deletion/duplication using a modified multiplex ligation-dependent probe amplification method—CNVplex^®, and investigated the variants of RIPPLY3 in 577 patients without the 22q11.2 deletion/duplication by target sequencing. Functional assays were performed to testify the potential pathogenicity of nonsynonymous variants found in these CTD patients.

Results

Four rare heterozygous nonsynonymous variants (p.P30L, p.T52S, p.D113N and p.V179D) were identified in four CTD patients, the variant NM_018962.2:c.155C>G (p.T52S) is referred as rs745539198, and the variant NM_018962.2:c.337G>A (p.D113N) is referred as rs747419773. However, variants p.P30L and p.V179D were not found in multiple online human gene variation databases. Western blot analysis and immunofluorescence showed that there were no significant difference between wild type RIPPLY3 and these four variants. Luciferase assays revealed that the p.T52S variant altered the inhibition of TBX1 transcriptional activity in vitro, and co-immunoprecipitation assays showed that the p.T52S variant reduced the physical interaction of RIPPLY3 with TBX1. In addition to the results from pathogenicity prediction tools and evolutionary protein conservation, the p.T52S variant was thought to be a potentially deleterious variant.

Conclusion

Our results provide evidence that deleterious variants in RIPPLY3 are potential molecular mechanisms involved in the pathogenesis of human CTD.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1633-1) contains supplementary material, which is available to authorized users.

Identification of TBX2 and TBX3 variants in patients with conotruncal heart defects by target sequencing

Background

Conotruncal heart defects (CTDs) are heterogeneous congenital heart malformations that result from outflow tract dysplasia; however, the genetic determinants underlying CTDs remain unclear. Increasing evidence demonstrates that dysfunctional TBX2 and TBX3 result in outflow tract malformations, implying that both of them are involved in CTD pathogenesis. We screened for TBX2 and TBX3 variants in a large cohort of CTD patients (n = 588) and population-matched healthy controls (n = 300) by target sequencing and genetically analyzed the expression and function of these variants.

Results

The probably damaging variants p.R608W, p.T249I, and p.R616Q of TBX2 and p.A192T, p.M65L, and p.A562V of TBX3 were identified in CTD patients, but none in controls. All altered amino acids were highly conserved evolutionarily. Moreover, our data suggested that mRNA and protein expressions of TBX2 and TBX3 variants were altered compared with those of the wild-type. We screened PEA3 and MEF2C as novel downstream genes of TBX2 and TBX3, respectively. Functional analysis revealed that TBX2R608W and TBX2R616Q variant proteins further activated HAS2 promoter but failed to activate PEA3 promoter and that TBX3A192T and TBX3A562V variant proteins showed a reduced transcriptional activity over MEF2C promoter.

Conclusions

Our results indicate that the R608W and R616Q variants of TBX2 as well as the A192T and A562V variants of TBX3 contribute to CTD etiology; this was the first association of variants of TBX2 and TBX3 to CTDs based on a large population.

Electronic supplementary material

The online version of this article (10.1186/s40246-018-0176-0) contains supplementary material, which is available to authorized users.

Potential Role of Exosomes in Mending a Broken Heart: Nanoshuttles Propelling Future Clinical Therapeutics Forward

Stem cell transplantation therapy is a promising adjunct for regenerating damaged heart tissue; however, only modest improvements in cardiac function have been observed due to poor survival of transplanted cells in the ischemic heart. Therefore, there remains an unmet need for therapies that can aid in attenuating cardiac damage. Recent studies have demonstrated that exosomes released by stem cells could serve as a potential cell-free therapeutic for cardiac repair. These exosomes/nanoshuttles, once thought to be merely a method of waste disposal, have been shown to play a crucial role in physiological functions including short- and long-distance intercellular communication. In this review, we have summarized studies demonstrating the potential role of exosomes in improving cardiac function, attenuating cardiac fibrosis, stimulating angiogenesis, and modulating miRNA expression. Furthermore, exosomes carry an important cargo of miRNAs and proteins that could play an important role as a diagnostic marker for cardiovascular disease post-myocardial infarction. Although there is promising evidence from preclinical studies that exosomes released by stem cells could serve as a potential cell-free therapeutic for myocardial repair, there are several challenges that need to be addressed before exosomes could be fully utilized as off-the-shelf therapeutics for cardiac repair.

Protein-altering and regulatory genetic variants near GATA4 implicated in bicuspid aortic valve

Bicuspid aortic valve (BAV) is a heritable congenital heart defect and an important risk factor for valvulopathy and aortopathy. Here we report a genome-wide association scan of 466 BAV cases and 4,660 age, sex and ethnicity-matched controls with replication in up to 1,326 cases and 8,103 controls. We identify association with a noncoding variant 151 kb from the gene encoding the cardiac-specific transcription factor, GATA4, and near-significance for p.Ser377Gly in GATA4. GATA4 was interrupted by CRISPR-Cas9 in induced pluripotent stem cells from healthy donors. The disruption of GATA4 significantly impaired the transition from endothelial cells into mesenchymal cells, a critical step in heart valve development.

A HAND to TBX5 Explains the Link Between Thalidomide and Cardiac Diseases

Congenital heart disease is the leading cause of death in the first year of life. Mutations only in few genes have been linked to some cases of CHD. Thalidomide was used by pregnant women for morning sickness but was removed from the market because it caused severe malformations including CHDs. We used both in silico docking software, and in vitro molecular and biochemical methods to document a novel interaction involving Thalidomide, TBX5, and HAND2. Thalidomide binds readily to TBX5 through amino acids R81, R82, and K226 all implicated in DNA binding. It reduces TBX5 binding to DNA by 40%, and suppresses TBX5 mediated activation of the NPPA and VEGF promoters by 70%. We documented a novel interaction between TBX5 and HAND2, and showed that a p.G202V HAND2 variant associated with CHD and coronary artery diseases found in a large Lebanese family with high consanguinity, drastically inhibited this interaction by 90%. Similarly, thalidomide inhibited the TBX5/HAND2 physical interaction, and the in silico docking revealed that the same amino acids involved in the interaction of TBX5 with DNA are also involved in its binding to HAND2. Our results establish a HAND2/TBX5 pathway implicated in heart development and diseases.

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.

A Novel Missense Mutation of GATA4 in a Chinese Family with Congenital Heart Disease

Background

Congenital heart disease (CHD) is the most prevalent type of birth defect in human, with high morbidity in infant. Several genes essential for heart development have been identified. GATA4 is a pivotal transcription factor that can regulate the cardiac development. Many GATA4 mutations have been identified in patients with different types of CHD.

Aims

In this study, the NKX2-5, HAND1 and GATA4 coding regions were sequenced in a family spanning three generations in which seven patients had CHD. Disease-causing potential variation in this family was evaluated by bioinformatics programs and the transcriptional activity of mutant protein was analyzed by the dual luciferase reporter assay.

Results

A novel GATA4 mutation, c.C931T (p.R311W), was identified and co-segregated with the affected patients in this family. The bioinformatics programs predicted this heterozygous mutation to be deleterious and the cross-species alignment of GATA4 sequences showed that the mutation occurred within a highly conserved amino acid. Even though it resided in the nuclear localization signal domain, the mutant protein didn’t alter its intracellular distribution. Nevertheless, further luciferase reporter assay demonstrated that the p.R311W mutation reduced the ability of GATA4 to activate its downstream target gene.

Conclusions

Our study identified a novel mutation in GATA4 that likely contributed to the CHD in this family. This finding expanded the spectrum of GATA4 mutations and underscored the pathogenic correlation between GATA4 mutations and CHD.

HAND1 loss-of-function mutation associated with familial dilated cardiomyopathy

The basic helix-loop-helix transcription factor HAND1 is essential for cardiac development and structural remodeling, and mutations in HAND1 have been causally linked to various congenital heart diseases. However, whether genetically compromised HAND1 predisposes to dilated cardiomyopathy (DCM) in humans remains unknown.

The whole coding region and splicing junctions of the

A novel heterozygous HAND1 mutation, p.R105X, was identified in a family with DCM transmitted as an autosomal dominant trait, which co-segregated with DCM in the family with complete penetrance. The nonsense mutation was absent in 520 control chromosomes. Functional analyses unveiled that the mutant HAND1 had no transcriptional activity. Furthermore, the mutation abolished the synergistic activation between HAND1 and GATA4, another crucial cardiac transcription factors that has been associated with various congenital cardiovascular malformations and DCM.

This study firstly reports the association of HAND1 loss-of-function mutation with increased susceptibility to DCM in humans, which provides novel insight into the molecular mechanisms underpinning DCM.

Nuclear Receptor-Like Structure and Interaction of Congenital Heart Disease-Associated Factors GATA4 and NKX2-5

AIMS

Transcription factor GATA4 is a dosage sensitive regulator of heart development and alterations in its level or activity lead to congenital heart disease (CHD). GATA4 has also been implicated in cardiac regeneration and repair. GATA4 action involves combinatorial interaction with other cofactors such as NKX2-5, another critical cardiac regulator whose mutations also cause CHD. Despite its critical importance to the heart and its evolutionary conservation across species, the structural basis of the GATA4-NKX2-5 interaction remains incompletely understood.

METHODS AND RESULTS

A homology model was constructed and used to identify surface amino acids important for the interaction of GATA4 and NKX2-5. These residues were subjected to site-directed mutagenesis, and the mutant proteins were characterized for their ability to bind DNA and to physically and functionally interact with NKX2-5. The studies identify 5 highly conserved amino acids in the second zinc finger (N272, R283, Q274, K299) and its C-terminal extension (R319) that are critical for physical and functional interaction with the third alpha helix of NKX2-5 homeodomain. Integration of the experimental data with computational modeling suggests that the structural arrangement of the zinc finger-homeodomain resembles the architecture of the conserved DNA binding domain of nuclear receptors.

CONCLUSIONS

The results provide novel insight into the structural basis for protein-protein interactions between two important classes of transcription factors. The model proposed will help to elucidate the molecular basis for disease causing mutations in GATA4 and NKX2-5 and may be relevant to other members of the GATA and NK classes of transcription factors.

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

Congenital heart disease (CHD) is the most prevalent type of birth defect in humans and is the leading non-infectious cause of infant death worldwide. There is a growing body of evidence demonstrating that genetic defects play an important role in the pathogenesis of CHD. However, CHD is a genetically heterogeneous disease and the genetic basis underpinning CHD in an overwhelming majority of patients remains unclear. In this study, the coding exons and splice junction sites of the TBX1 gene, which encodes a T-box homeodomain transcription factor essential for proper cardiovascular morphogenesis, were sequenced in 230 unrelated children with CHD. The available family members of the index patient carrying an identified mutation and 200 unrelated ethnically matched healthy individuals used as controls were subsequently genotyped for TBX1. The functional effect of the TBX1 mutation was predicted by online program MutationTaster and characterized by using a dual-luciferase reporter assay system. As a result, a novel heterozygous TBX1 mutation, p.Q277X, was identified in an index patient with double outlet right ventricle (DORV) and ventricular septal defect (VSD). Genetic analysis of the proband's available relatives showed that the mutation co-segregated with CHD transmitted in an autosomal dominant pattern with complete penetrance. The nonsense mutation, which was absent in 400 control chromosomes, altered the amino acid that was completely conserved evolutionarily across species and was predicted to be disease-causing by MutationTaster. Biochemical analysis revealed that Q277X-mutant TBX1 lost transcriptional activating function when compared with its wild-type counterpart. This study firstly associates TBX1 loss-of-function mutation with enhanced susceptibility to DORV and VSD in humans, which provides novel insight into the molecular mechanism underlying CHD and suggests potential implications for the development of new preventive and therapeutic strategies for CHD.

A novel TBX5 loss-of-function mutation associated with sporadic dilated cardiomyopathy

Dilated cardiomyopathy (DCM) represents the most prevalent form of primary cardiomyopathy, and is the most common reason for heart transplantation and a major cause of congestive heart failure. Aggregating evidence demonstrates that genetic defects are associated with DCM, and a great number of mutations in >50 genes have been linked to DCM. However, DCM is a genetically heterogeneous disorder and the genetic components underpinning DCM in a significant proportion of patients remain unknown. In the present study, the coding exons and flanking exon‑intron boundaries of the T-Box 5 (TBX5) gene, which encodes a T‑box transcription factor required for normal cardiac development, were sequenced in 146 unrelated patients with sporadic DCM. The functional characteristics of the mutant TBX5 were assayed in contrast to its wild‑type counterpart by using a dual‑luciferase reporter assay system. As a result, a novel heterozygous TBX5 mutation, p.A143T, was identified in a patient with sporadic DCM. The missense mutation, which was absent in 400 control chromosomes, altered the amino acid that was completely conserved evolutionarily among species. Biological analyses revealed that the A143T mutation of TBX5 was associated with significantly decreased transcriptional activity on the promoter of the target gene atrial natriuretic factor (ANF), when compared to its wild‑type counterpart. Furthermore, the A143T mutation abolished the synergistic activation of the ANF promoter between TBX5 and GATA binding protein 4 (GATA4), another crucial transcriptional factor for heart development. To the best of our knowledge, this is the first report on the association of a TBX5 loss‑of‑function mutation with an enhanced susceptibility to sporadic DCM, providing novel insight into the molecular mechanisms of the pathogenesis of DCM and suggesting potential implications for the prenatal prophylaxis and personalized treatment of this commonest primary myocardial disease.

PITX2 Loss-of-Function Mutation Contributes to Congenital Endocardial Cushion Defect and Axenfeld-Rieger Syndrome

Congenital heart disease (CHD), the most common type of birth defect, is still the leading non-infectious cause of infant morbidity and mortality in humans. Aggregating evidence demonstrates that genetic defects are involved in the pathogenesis of CHD. However, CHD is genetically heterogeneous and the genetic components underpinning CHD in an overwhelming majority of patients remain unclear. In the present study, the coding exons and flanking introns of the PITX2 gene, which encodes a paired-like homeodomain transcription factor 2essential for cardiovascular morphogenesis as well as maxillary facial development, was sequenced in 196 unrelated patients with CHD and subsequently in the mutation carrier's family members available. As a result, a novel heterozygous PITX2 mutation, p.Q102X for PITX2a, or p.Q148X for PITX2b, or p.Q155X for PITX2c, was identified in a family with endocardial cushion defect (ECD) and Axenfeld-Rieger syndrome (ARS). Genetic analysis of the pedigree showed that the nonsense mutation co-segregated with ECD and ARS transmitted in an autosomal dominant pattern with complete penetrance. The mutation was absent in 800 control chromosomes from an ethnically matched population. Functional analysis by using a dual-luciferase reporter assay system revealed that the mutant PITX2 had no transcriptional activity and that the mutation eliminated synergistic transcriptional activation between PITX2 and NKX2.5, another transcription factor pivotal for cardiogenesis. To our knowledge, this is the first report on the association of PITX2 loss-of-function mutation with increased susceptibility to ECD and ARS. The findings provide novel insight into the molecular mechanisms underpinning ECD and ARS, suggesting the potential implications for the antenatal prophylaxis and personalized treatment of CHD and ARS.

Duplication of HEY2 in cardiac and neurologic development

HEY2 is a basic helix-loop-helix (bHLH) transcription factor that plays an important role in the developing mammalian heart and brain. In humans, nonsynonymous mutations in HEY2 have been described in patients with atrial ventricular septal defects, and a subset of individuals with chromosomal deletions involving HEY2 have cardiac defects and cognitive impairment. Less is known about the potential effects of HEY2 overexpression. Here, we describe a female child with tetralogy of Fallot who developed severe right ventricular outflow tract obstruction due to a combination of infundibular and valvular pulmonary stenosis. She was also noted to have hypotonia, lower extremity weakness, fine motor delay and speech delay. A copy number variation (CNV) detection analysis followed by real-time quantitative PCR analysis revealed a single gene duplication of HEY2. This is the only duplication involving HEY2 identified in our database of over 70,000 individuals referred for CNV analysis. In the developing heart, overexpression of HEY2 is predicted to cause decreased expression of the cardiac transcription factor GATA4 which, in turn, has been shown to cause tetralogy of Fallot. In mice, misexpression of Hey2 in the developing brain leads to inhibition of neurogenesis and promotion of gliogenesis. Hence, duplication of HEY2 may be a contributing factor to both the congenital heart defects and the neurodevelopmental problems evident in our patient. These results suggest that individuals with HEY2 duplications should be screened for congenital heart defects and monitored closely for evidence of developmental delay and/or cognitive impairment.

GATA5 loss-of-function mutation in familial dilated cardiomyopathy

Dilated cardiomyopathy (DCM), the most common form of primary myocardial disease, is an important cause of sudden cardiac death and heart failure and is the leading indication for heart transplantation in children and adults worldwide. Recent studies have revealed a strong genetic basis for idiopathic DCM, with many distinct genes causally implicated. Nevertheless, DCM is a genetically heterogeneous disorder and the genetic determinants underlying DCM in a substantial proportion of patients remain unclear. In this study, the whole coding exons and flanking introns of the GATA binding protein 5 (GATA5) gene, which codes for a zinc-finger transcription factor essential for cardiovascular development and structural remodeling, were sequenced in 130 unrelated patients with idiopathic DCM. The available relatives of the index patient carrying an identified mutation and 200 unrelated ethnically matched healthy individuals used as the controls were genotyped for GATA5. The functional characteristics of the mutant GATA5 were analyzed in contrast to its wild-type counterpart by using a dual-luciferase reporter assay system. As a result, a novel heterozygous GATA5 mutation, p.G240D, was identified in a family with DCM inherited in an autosomal dominant pattern, which co-segregated with DCM in the family with complete penetrance. The missense mutation was absent in 400 reference chromosomes and the altered amino acid was completely conserved evolutionarily across species. Functional analyses revealed that the GATA5 mutant was associated with significantly diminished transcriptional activity. This study firstly links GATA5 mutation to DCM, which provides novel insight into the molecular mechanisms of DCM, suggesting a potential molecular target for the prenatal prophylaxis and allele-specific treatment of DCM.

A novel NKX2.6 mutation associated with congenital ventricular septal defect

Congenital heart disease (CHD) is the most common birth defect and is the most prevalent non-infectious cause of infant death. Aggregating evidence demonstrates that genetic defects are involved in the pathogenesis of CHD. However, CHD is genetically heterogeneous and the genetic determinants for CHD in an overwhelming majority of patients remain unknown. In this study, the coding regions and splice junctions of the NKX2.6 gene, which encodes a homeodomain transcription factor crucial for cardiovascular development, were sequenced in 210 unrelated CHD patients. As a result, a novel heterozygous NKX2.6 mutation, p.K152Q, was identified in an index patient with ventricular septal defect (VSD). Genetic analysis of the proband's available family members showed that the mutation cosegregated with VSD transmitted as an autosomal dominant trait with complete penetrance. The missense mutation was absent in 400 control chromosomes and the altered amino acid was completely conserved evolutionarily across species. Due to unknown transcriptional targets of NKX2.6, the functional characteristics of the identified mutation at transcriptional activity were analyzed by using NKX2.5 as a surrogate. Alignment between human NKX2.6 and NKX2.5 proteins displayed that K152Q-mutant NKX2.6 was equivalent to K158Q-mutant NKX2.5, and introduction of K158Q into NKX2.5 significantly reduced its transcriptional activating function when compared with its wild-type counterpart. This study firstly links NKX2.6 loss-of-function mutation with increased susceptibility to isolated VSD, providing novel insight into the molecular mechanism underpinning VSD and contributing to the development of new preventive and therapeutic strategies for this common form of CHD.

c.620C>T mutation in GATA4 is associated with congenital heart disease in South India

BACKGROUND

Congenital heart diseases (CHDs) usually refer to abnormalities in the structure and/or function of the heart that arise before birth. GATA4 plays an important role in embryonic heart development, hence the aim of this study was to find the association of GATA4 mutations with CHD among the south Indian CHD patients.

METHOD

GATA4 gene was sequenced in 100 CHD patients (ASD, VSD, TOF and SV) and 200 controls. Functional significance of the observed GATA4 mutations was analyzed using PolyPhen, SIFT, PMut, Plink, Haploview, ESE finder 3.0 and CONSITE.

RESULTS

We observed a total of 19 mutations, of which, one was in 5' UTR, 10 in intronic regions, 3 in coding regions and 5 in 3' UTR. Of the above mutations, one was associated with Atrial Septal Defect (ASD), two were found to be associated with Tetralogy of Fallot (TOF) and three (rs804280, rs4841587 and rs4841588) were strongly associated with Ventricular Septal Defect (VSD). Interestingly, one promoter mutation (-490 to 100 bp) i.e., 620 C>T (rs61277615, p-value = 0.008514), one splice junction mutation (G>A rs73203482; p-value = 9.6e-3, OR = 6.508) and one intronic mutation rs4841587 (p-value = 4.6e-3, OR = 4.758) were the most significant findings of this study. In silico analysis also proves that some of the mutations reported above are pathogenic.

CONCLUSION

The present study found that GATA4 genetic variations are associated with ASD, TOF and VSD in South Indian patients. In silico analysis provides further evidence that some of the observed mutations are pathogenic.