Genetics of congenital heart defects: is it not all in the DNA?

Abstract

We read with great interest the paper by Wu et al1Wu G. Shan J. Pang S. Wei X. Zhang H. Yan B. Genetic analysis of the promoter region of GATA4 gene in patients with ventricular septal defects.Transl Res. 2012; 159: 376-382Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar on the genetic analysis of the promoter region of the GATA4 gene in patients with ventricular septal defect (VSD).The authors provide new important ideas about the potential role of genetic variants within regulatory region rather than the codifying sequences that may contribute to the etiology of VSD, the most common type of congenital heart defect (CHD). In this study, 5 heterozygous sequence variants were found within the promoter region of GATA4 gene in VSD patients but in none of the healthy controls. Although these variants do not interrupt the regulatory promoter regions, they seem to significantly alter the transcriptional activity of GATA4 gene promoter, which may contribute to the VSD.In another study published by the same authors,2Pang S. Shan J. Qiao Y. et al.Genetic and functional analysis of the NKX2-5 gene promoter in patients with ventricular septal defects.Pediatr Cardiol. 2012; ([Epub ahead of print])PubMed Google Scholar functional analysis showed that sequence variants within promoter regions significantly enhance the transcriptional activities of the NKX2-5 gene, which may lead to upregulated NKX2-5 gene expression, contributing to the VSD etiology.2Pang S. Shan J. Qiao Y. et al.Genetic and functional analysis of the NKX2-5 gene promoter in patients with ventricular septal defects.Pediatr Cardiol. 2012; ([Epub ahead of print])PubMed Google ScholarWe believe that these observations underlie that the causative factors and the molecular mechanisms involved in the CHD etiology still remain largely elusive.In recent years, several lines of evidence have highlighted the importance of GATA4, in association with a variety of binding partners like NKX2-5, in a specific transcriptional complex that confer tissue-specific gene expression during cardiogenesis and that can be altered during the development of CHD.3Ransom J. Srivastava D. The genetics of cardiac birth defects.Semin Cell Dev Biol. 2007; 18: 132-139Crossref PubMed Scopus (55) Google Scholar Indeed, mutations leading to gene haploinsufficiency in key cardiac transcription factors (TFs) are responsible for inherited and sporadic CHDs.3Ransom J. Srivastava D. The genetics of cardiac birth defects.Semin Cell Dev Biol. 2007; 18: 132-139Crossref PubMed Scopus (55) Google ScholarNevertheless, the study of genetic basis of CHDs is complicated by the fact that a given structural defect can be caused by more than one gene because TFs work in a synergic manner. In addition, the frequency of mutations in TF genes have been shown to be less than 3%, especially in the sporadic forms of CHD.4Posch M.G. Perrot A. Schmitt K. et al.Mutations in GATA4, NKX2.5, CRELD1, and BMP4 are infrequently found in patients with congenital cardiac septal defects.Am J Med Genet A. 2008; 15: 251-253Crossref Scopus (79) Google Scholar, 5Pulignani S. Foffa I. Cresci M. Vittorini S. Ait-Ali L. Andreassi M.G. Genetic screening of GATA4 and NKX2.5 mutations in hereditary congenital heart defects: 5 familial cases.Recenti Prog Med. 2011; 102: 120-125PubMed Google Scholar These observations suggest that the predisposition to the disease involves multiple factors, notably for isolated non-family CHDs, including complex gene interactions, several signaling pathways, and environmental influences as well as a combination of these factors.Furthermore, the hypothesis of somatic mutations has been also suggested as novel genetic mechanism for CHDs.6Reamon-Buettner S.M. Borlak J. Somatic mutations in cardiac malformations.J Med Genet. 2006; 43: e45Crossref PubMed Scopus (14) Google Scholar This theory still remains a controversial scientific matter that needs further investigations.7Draus Jr., J.M. Hauck M.A. Goetsch M. Austin III, E.H. Tomita-Mitchell A. Mitchell M.E. Investigation of somatic NKX2-5 mutations in congenital heart disease.J Med Genet. 2009; 46: 115-122Crossref PubMed Scopus (56) Google Scholar, 8Salazar M. Consoli F. Villegas V. et al.Search of somatic GATA4 and NKX2.5 gene mutations in sporadic septal heart defects.Eur J Med Gen. 2011; 54: 306-309Crossref PubMed Scopus (35) Google Scholar, 9Wang J. Lu Y. Chen H. Yin M. Yu T. Fu Q. Investigation of somatic NKX2.5, GATA4 and HAND1 mutations in patients with tetralogy of Fallot.Pathology. 2011; 43: 322-326Crossref PubMed Scopus (32) Google ScholarIt is also important to remember that, during cardiogenesis, there is a cooperative relationship between tissue-specific TFs and epigenetic variations to specify cell fate and promote terminal differentiation.Cytosine methylation at 5’-CpG-3’ dinucleotide is the most common base modification in the eukaryotic genome that influence gene expression. Generally, CpG islands in the gene promoter are protected from DNA methylation, whereas CpG sites in gene-coding or non-coding region are commonly methylated.10Movassagh M. Choy M.-K. Goddard M. Bennet M.R. Down T.A. Foo R.S. Differential DNA methylation correlates with differential expression of angiogenic factors in human heart failure.PloS ONE. 2010; 5: e8564Crossref PubMed Scopus (155) Google Scholar However, the methylation pattern could be disrupted in diseases, and methylated CpG islands can be silenced or downregulated.10Movassagh M. Choy M.-K. Goddard M. Bennet M.R. Down T.A. Foo R.S. Differential DNA methylation correlates with differential expression of angiogenic factors in human heart failure.PloS ONE. 2010; 5: e8564Crossref PubMed Scopus (155) Google Scholar Consequently, DNA methylation may be proposed as a potential mechanism involved in CHDs.Interestingly, histone deacetylases 1 and 2, key regulatory enzymes involved in the regulation of gene expression during development and throughout life, have mostly been characterized as having a role in cardiac morphogenesis, growth, and contractility.11Montgomery R.L. Davis C.A. Potthoff M.J. et al.Histone deacetylases 1 and 2 redundantly regulate cardiac morphogenesis, growth, and contractility.Genes Dev. 2007; 21: 1790-1802Crossref PubMed Scopus (533) Google Scholar Furthermore, the hearts of mutant mice displayed unusual morphologic abnormalities of the right ventricular chamber.11Montgomery R.L. Davis C.A. Potthoff M.J. et al.Histone deacetylases 1 and 2 redundantly regulate cardiac morphogenesis, growth, and contractility.Genes Dev. 2007; 21: 1790-1802Crossref PubMed Scopus (533) Google ScholarAnother potential mechanism on the basis of CHD is the microRNA (miRNA) post-transcriptional regulation that control key genetic programs in cardiovascular biology.12Chen J. Wang D.Z. microRNAs in cardiovascular development.J Mol Cell Cardiol. 2012; 52: 949-957Abstract Full Text Full Text PDF PubMed Scopus (74) Google Scholar One of the best examples of miRNA regulation in the heart involves the basic helix-loop-helix TF, Hand2, and its repression by miR-1 and miR-133a, leading to VSD.13Zhao Y. Samal E. Srivastava D. Serum response factor regulates a muscle-specific microRNA that targets Hand2 during cardiogenesis.Nature. 2005; 436: 214-220Crossref PubMed Scopus (1347) Google Scholar Indeed, miRNAs can inhibit translation and/or promote mRNA degradation depending on its degree of complementarity with the target.12Chen J. Wang D.Z. microRNAs in cardiovascular development.J Mol Cell Cardiol. 2012; 52: 949-957Abstract Full Text Full Text PDF PubMed Scopus (74) Google ScholarFinally, there is a recent evidence supporting the idea that common genetic variants, not necessarily disease-causing, may contribute to risk of CHD, especially interacting with environmental factors.Indeed, we recently showed that exposure to toxicants from both parents affect the risk of children with CHD, supporting a pivotal influence of the environmental risk factors in the pathogenesis of congenital malformations.14Cresci M. Foffa I. Ait-Ali L. et al.Maternal and paternal environmental risk factors, metabolizing GSTM1 and GSTT1 polymorphisms, and congenital heart disease.Am J Cardiol. 2011; 108: 1625-1631Abstract Full Text Full Text PDF PubMed Scopus (57) Google Scholar, 15Cresci M. Foffa I. Ait-Ali L. et al.Maternal environmental exposure, infant GSTP1 polymorphism and risk of isolated congenital heart disease.Pediatr Cardiol. 2012; ([Epub ahead of print])Google Scholar In addition, our gene-environment analyses suggested that specific and common genetic variants in genes involved in detoxification pathways can modify a person's risk of toxicant exposure-induced disease.14Cresci M. Foffa I. Ait-Ali L. et al.Maternal and paternal environmental risk factors, metabolizing GSTM1 and GSTT1 polymorphisms, and congenital heart disease.Am J Cardiol. 2011; 108: 1625-1631Abstract Full Text Full Text PDF PubMed Scopus (57) Google Scholar, 15Cresci M. Foffa I. Ait-Ali L. et al.Maternal environmental exposure, infant GSTP1 polymorphism and risk of isolated congenital heart disease.Pediatr Cardiol. 2012; ([Epub ahead of print])Google ScholarIn conclusion, many questions still remain open about the disease. What are the genetic and epigenetic bases of different forms of CHD? What is the recurrence risk for parents of a child with CHD? Which is the risk of disease transmission in grown-up CHD patients? Future studies and more research in this area are greatly needed to provide insight into the molecular basis CHD as well as to answer these questions (Fig 1).In the near future, it is expected that the power of next generation sequencing technologies may allow a more comprehensive analysis of genetic and epigenetic contributions to the pathogenesis of CHD.Furthermore, understanding the biologic impact of gene-environmental interactions may provide a key insight into the prevention of these congenital malformations in future generations. Understanding the genetic basis and the molecular mechanisms of CHD may allow the identification of family members at risk as well as to identify new possible therapeutic targets and appropriate preventive strategies because environmental factors can be modified in contrast to genetic factors. We read with great interest the paper by Wu et al1Wu G. Shan J. Pang S. Wei X. Zhang H. Yan B. Genetic analysis of the promoter region of GATA4 gene in patients with ventricular septal defects.Transl Res. 2012; 159: 376-382Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar on the genetic analysis of the promoter region of the GATA4 gene in patients with ventricular septal defect (VSD). The authors provide new important ideas about the potential role of genetic variants within regulatory region rather than the codifying sequences that may contribute to the etiology of VSD, the most common type of congenital heart defect (CHD). In this study, 5 heterozygous sequence variants were found within the promoter region of GATA4 gene in VSD patients but in none of the healthy controls. Although these variants do not interrupt the regulatory promoter regions, they seem to significantly alter the transcriptional activity of GATA4 gene promoter, which may contribute to the VSD. In another study published by the same authors,2Pang S. Shan J. Qiao Y. et al.Genetic and functional analysis of the NKX2-5 gene promoter in patients with ventricular septal defects.Pediatr Cardiol. 2012; ([Epub ahead of print])PubMed Google Scholar functional analysis showed that sequence variants within promoter regions significantly enhance the transcriptional activities of the NKX2-5 gene, which may lead to upregulated NKX2-5 gene expression, contributing to the VSD etiology.2Pang S. Shan J. Qiao Y. et al.Genetic and functional analysis of the NKX2-5 gene promoter in patients with ventricular septal defects.Pediatr Cardiol. 2012; ([Epub ahead of print])PubMed Google Scholar We believe that these observations underlie that the causative factors and the molecular mechanisms involved in the CHD etiology still remain largely elusive. In recent years, several lines of evidence have highlighted the importance of GATA4, in association with a variety of binding partners like NKX2-5, in a specific transcriptional complex that confer tissue-specific gene expression during cardiogenesis and that can be altered during the development of CHD.3Ransom J. Srivastava D. The genetics of cardiac birth defects.Semin Cell Dev Biol. 2007; 18: 132-139Crossref PubMed Scopus (55) Google Scholar Indeed, mutations leading to gene haploinsufficiency in key cardiac transcription factors (TFs) are responsible for inherited and sporadic CHDs.3Ransom J. Srivastava D. The genetics of cardiac birth defects.Semin Cell Dev Biol. 2007; 18: 132-139Crossref PubMed Scopus (55) Google Scholar Nevertheless, the study of genetic basis of CHDs is complicated by the fact that a given structural defect can be caused by more than one gene because TFs work in a synergic manner. In addition, the frequency of mutations in TF genes have been shown to be less than 3%, especially in the sporadic forms of CHD.4Posch M.G. Perrot A. Schmitt K. et al.Mutations in GATA4, NKX2.5, CRELD1, and BMP4 are infrequently found in patients with congenital cardiac septal defects.Am J Med Genet A. 2008; 15: 251-253Crossref Scopus (79) Google Scholar, 5Pulignani S. Foffa I. Cresci M. Vittorini S. Ait-Ali L. Andreassi M.G. Genetic screening of GATA4 and NKX2.5 mutations in hereditary congenital heart defects: 5 familial cases.Recenti Prog Med. 2011; 102: 120-125PubMed Google Scholar These observations suggest that the predisposition to the disease involves multiple factors, notably for isolated non-family CHDs, including complex gene interactions, several signaling pathways, and environmental influences as well as a combination of these factors. Furthermore, the hypothesis of somatic mutations has been also suggested as novel genetic mechanism for CHDs.6Reamon-Buettner S.M. Borlak J. Somatic mutations in cardiac malformations.J Med Genet. 2006; 43: e45Crossref PubMed Scopus (14) Google Scholar This theory still remains a controversial scientific matter that needs further investigations.7Draus Jr., J.M. Hauck M.A. Goetsch M. Austin III, E.H. Tomita-Mitchell A. Mitchell M.E. Investigation of somatic NKX2-5 mutations in congenital heart disease.J Med Genet. 2009; 46: 115-122Crossref PubMed Scopus (56) Google Scholar, 8Salazar M. Consoli F. Villegas V. et al.Search of somatic GATA4 and NKX2.5 gene mutations in sporadic septal heart defects.Eur J Med Gen. 2011; 54: 306-309Crossref PubMed Scopus (35) Google Scholar, 9Wang J. Lu Y. Chen H. Yin M. Yu T. Fu Q. Investigation of somatic NKX2.5, GATA4 and HAND1 mutations in patients with tetralogy of Fallot.Pathology. 2011; 43: 322-326Crossref PubMed Scopus (32) Google Scholar It is also important to remember that, during cardiogenesis, there is a cooperative relationship between tissue-specific TFs and epigenetic variations to specify cell fate and promote terminal differentiation. Cytosine methylation at 5’-CpG-3’ dinucleotide is the most common base modification in the eukaryotic genome that influence gene expression. Generally, CpG islands in the gene promoter are protected from DNA methylation, whereas CpG sites in gene-coding or non-coding region are commonly methylated.10Movassagh M. Choy M.-K. Goddard M. Bennet M.R. Down T.A. Foo R.S. Differential DNA methylation correlates with differential expression of angiogenic factors in human heart failure.PloS ONE. 2010; 5: e8564Crossref PubMed Scopus (155) Google Scholar However, the methylation pattern could be disrupted in diseases, and methylated CpG islands can be silenced or downregulated.10Movassagh M. Choy M.-K. Goddard M. Bennet M.R. Down T.A. Foo R.S. Differential DNA methylation correlates with differential expression of angiogenic factors in human heart failure.PloS ONE. 2010; 5: e8564Crossref PubMed Scopus (155) Google Scholar Consequently, DNA methylation may be proposed as a potential mechanism involved in CHDs. Interestingly, histone deacetylases 1 and 2, key regulatory enzymes involved in the regulation of gene expression during development and throughout life, have mostly been characterized as having a role in cardiac morphogenesis, growth, and contractility.11Montgomery R.L. Davis C.A. Potthoff M.J. et al.Histone deacetylases 1 and 2 redundantly regulate cardiac morphogenesis, growth, and contractility.Genes Dev. 2007; 21: 1790-1802Crossref PubMed Scopus (533) Google Scholar Furthermore, the hearts of mutant mice displayed unusual morphologic abnormalities of the right ventricular chamber.11Montgomery R.L. Davis C.A. Potthoff M.J. et al.Histone deacetylases 1 and 2 redundantly regulate cardiac morphogenesis, growth, and contractility.Genes Dev. 2007; 21: 1790-1802Crossref PubMed Scopus (533) Google Scholar Another potential mechanism on the basis of CHD is the microRNA (miRNA) post-transcriptional regulation that control key genetic programs in cardiovascular biology.12Chen J. Wang D.Z. microRNAs in cardiovascular development.J Mol Cell Cardiol. 2012; 52: 949-957Abstract Full Text Full Text PDF PubMed Scopus (74) Google Scholar One of the best examples of miRNA regulation in the heart involves the basic helix-loop-helix TF, Hand2, and its repression by miR-1 and miR-133a, leading to VSD.13Zhao Y. Samal E. Srivastava D. Serum response factor regulates a muscle-specific microRNA that targets Hand2 during cardiogenesis.Nature. 2005; 436: 214-220Crossref PubMed Scopus (1347) Google Scholar Indeed, miRNAs can inhibit translation and/or promote mRNA degradation depending on its degree of complementarity with the target.12Chen J. Wang D.Z. microRNAs in cardiovascular development.J Mol Cell Cardiol. 2012; 52: 949-957Abstract Full Text Full Text PDF PubMed Scopus (74) Google Scholar Finally, there is a recent evidence supporting the idea that common genetic variants, not necessarily disease-causing, may contribute to risk of CHD, especially interacting with environmental factors. Indeed, we recently showed that exposure to toxicants from both parents affect the risk of children with CHD, supporting a pivotal influence of the environmental risk factors in the pathogenesis of congenital malformations.14Cresci M. Foffa I. Ait-Ali L. et al.Maternal and paternal environmental risk factors, metabolizing GSTM1 and GSTT1 polymorphisms, and congenital heart disease.Am J Cardiol. 2011; 108: 1625-1631Abstract Full Text Full Text PDF PubMed Scopus (57) Google Scholar, 15Cresci M. Foffa I. Ait-Ali L. et al.Maternal environmental exposure, infant GSTP1 polymorphism and risk of isolated congenital heart disease.Pediatr Cardiol. 2012; ([Epub ahead of print])Google Scholar In addition, our gene-environment analyses suggested that specific and common genetic variants in genes involved in detoxification pathways can modify a person's risk of toxicant exposure-induced disease.14Cresci M. Foffa I. Ait-Ali L. et al.Maternal and paternal environmental risk factors, metabolizing GSTM1 and GSTT1 polymorphisms, and congenital heart disease.Am J Cardiol. 2011; 108: 1625-1631Abstract Full Text Full Text PDF PubMed Scopus (57) Google Scholar, 15Cresci M. Foffa I. Ait-Ali L. et al.Maternal environmental exposure, infant GSTP1 polymorphism and risk of isolated congenital heart disease.Pediatr Cardiol. 2012; ([Epub ahead of print])Google Scholar In conclusion, many questions still remain open about the disease. What are the genetic and epigenetic bases of different forms of CHD? What is the recurrence risk for parents of a child with CHD? Which is the risk of disease transmission in grown-up CHD patients? Future studies and more research in this area are greatly needed to provide insight into the molecular basis CHD as well as to answer these questions (Fig 1). In the near future, it is expected that the power of next generation sequencing technologies may allow a more comprehensive analysis of genetic and epigenetic contributions to the pathogenesis of CHD. Furthermore, understanding the biologic impact of gene-environmental interactions may provide a key insight into the prevention of these congenital malformations in future generations. Understanding the genetic basis and the molecular mechanisms of CHD may allow the identification of family members at risk as well as to identify new possible therapeutic targets and appropriate preventive strategies because environmental factors can be modified in contrast to genetic factors.