The aim of the present study was to identify key genes that may be involved in the pathogenesis of Tetralogy of Fallot (TOF) using bioinformatics methods. The GSE26125 microarray dataset, which includes cardiovascular tissue samples derived from 16 children with TOF and five healthy age‑matched control infants, was downloaded from the Gene Expression Omnibus database. Differential expression analysis was performed between TOF and control samples to identify differentially expressed genes (DEGs) using Student's t‑test, and the R/limma package, with a log2 fold‑change of >2 and a false discovery rate of <0.01 set as thresholds. The biological functions of DEGs were analyzed using the ToppGene database. The ReactomeFIViz application was used to construct functional interaction (FI) networks, and the genes in each module were subjected to pathway enrichment analysis. The iRegulon plugin was used to identify transcription factors predicted to regulate the DEGs in the FI network, and the gene‑transcription factor pairs were then visualized using Cytoscape software. A total of 878 DEGs were identified, including 848 upregulated genes and 30 downregulated genes. The gene FI network contained seven function modules, which were all comprised of upregulated genes. Genes enriched in Module 1 were enriched in the following three neurological disorder‑associated signaling pathways: Parkinson's disease, Alzheimer's disease and Huntington's disease. Genes in Modules 0, 3 and 5 were dominantly enriched in pathways associated with ribosomes and protein translation. The Xbox binding protein 1 transcription factor was demonstrated to be involved in the regulation of genes encoding the subunits of cytoplasmic and mitochondrial ribosomes, as well as genes involved in neurodegenerative disorders. Therefore, dysfunction of genes involved in signaling pathways associated with neurodegenerative disorders, ribosome function and protein translation may contribute to the pathogenesis of TOF.

Tetralogy of Fallot (TOF) is the most common cyanotic congenital heart malformation accounting for ~10% of cases. Although the pathogenesis of TOF is complex and largely unknown, epigenetics plays a huge role, specifically DNA methylation. The protein δ like non‑canonical Notch ligand 1 (DLK1) gene encodes a non‑canonical ligand of the Notch signaling pathway, which is involved in heart development. However, the epigenetic mechanism of DLK1 in the pathogenesis of TOF is yet to be elucidated. Therefore, the present study aimed to clarify its specific mechanism. In this study, immunohistochemistry was used to detect the protein expression of DLK1 and the methylation status of the DLK1 promoter was measured via bisulfite sequencing PCR. Dual‑luciferase reporter assays were performed to examine the influence of transcription factor ETS proto‑oncogene 1 (ETS1) on DLK1 gene expression. The electrophoretic mobility shift assay and chromatin immunoprecipitation assay, both in vivo and in vitro, were used to verify the binding of the ETS1 transcription factor to the DLK1 promoter as well as the influence of methylation status of DLK1 promoter on this binding affinity. The expression of DLK1 in the right ventricular outflow tract was significantly lower in patients with Tetralogy of Fallot (TOF) than that in controls (P<0.001). Moreover, the methylation level of CpG site 10 and CpG site 11 in the DLK1_R region was significantly decreased in TOF cases compared with controls (P<0.01). The integral methylation levels of DLK1_R and the methylation status of the CpG site 11 were both positively associated with DLK1 protein expression in TOF cases. ETS1 was found to inhibit DLK1 transcriptional activity by binding to the CpG site 11 and this affinity could be influenced by the methylation level of the DLK1 promoter. These findings demonstrated that the hypomethylation of the DLK1 promoter could increase the binding affinity of ETS1 transcription factor, which in turn inhibited DLK1 gene transcriptional activity and contributed to the development of TOF.

Tetralogy of Fallot (TOF) is the most common form of cyanotic congenital heart disease (CHD). Although a lower methylation level of whole genome has been demonstrated in TOF patients, little is known regarding the DNA methylation changes in specific gene and its associations with TOF development. NOTCH4 is a mediator of the Notch signalling pathway that plays an important role in normal cardiac development. However, the role of epigenetic regulation of the NOTCH4 gene in the pathogenesis of TOF remains unclear. Considering the NOTCH4 low mutation frequency and reduced expression in the TOF patients, we hypothesized that abnormal DNA methylation change of NOTCH4 gene may influence its expression and responsible for TOF development. In this study, we measured the promoter methylation status of NOTCH4 and was measured and its regulation mechanism was explored, which may be related to TOF disease. Additionally, the promoter methylation statuses of NOTCH4 was measured in order to further understand epigenetic mechanisms that may serve a role in the development of TOF. Immunohistochemical analysis was used to examine NOTCH4 expression in right ventricular outflow tract myocardial tissues in patients with TOF. Compared with healthy controls, patients with TOF displayed significantly reduced in NOTCH4 expression (P=0.0055). Moreover, bisulphite sequencing suggested that the methylation levels of CpG site 2 in the NOTCH4 promoter was significantly higher in the patients than in the controls (P=0.0459). NOTCH4 expression was negatively associated with CpG site 2 methylation levels (r=‑0.51; P=0.01). ETS1 transcription factor can serve as transcriptional activators by binding to specific DNA sequences of target genes, such as DLL4 and NOTCH4, which serves an important role in normal heart development. Dual‑luciferase reporter and electrophoretic mobility shift assays indicated that the ETS1 transcription factor could bind to the NOTCH4 promoter region. However, binding of ETS1 to the NOTCH4 promoter was abrogated by methylation at the putative ETS1 binding sites. These findings suggested that decreased NOTCH4 expression in patients with TOF may be associated with hypermethylation of CpG site 2 in the NOTCH4 promoter region, due to impaired binding of ETS1.

Triphalangeal thumb‑polysyndactyly syndrome (TPT‑PS) is an autosomal dominant disorder with complete penetrance and a variable expression consisting of opposable triphalangeal thumbs, duplication of the distal thumb phalanx, pre‑axial polydactyly and duplication of the big toes (hallux). The causative gene of TPT‑PS has been mapped to 7q36.3. Sonic hedgehog (SHH) expressed in the zone of polarizing activity (ZPA) has an important role in defining the anterior‑posterior axis and numbers of digits in limb bud development. Point mutation or duplication in the ZPA regulatory sequence (ZRS), a cis‑regulator of SHH, will lead to TPT‑PS. The present study describes a 1‑year‑old female congenital heart disease (CHD) patient with TPT‑PS phenotype. In this Han Chinese family with TPT‑PS, high resolution single nucleotide polymorphism array technology identified a novel 0.29 Mb duplication comprising ZRS at 7q36.3 where LMBR1 is located. Additionally, a novel deletion of 22q11.21 was detected in the proband with Tetralogy of Fallot. However, the parents and other relatives of the patient did not harbor this genomic lesion nor CHD. The findings supported the hypothesis that an increased copy number variation of ZRS is the genetic mechanism underlying the phenotype of TPT‑PS, and corroborated that 22q11.21 deletion is a genetic cause of CHD.

Chronic hypoxia can be observed in the heart under physiological or pathophysiological states, including embryonic development or cyanotic congenital heart disease. The aim of the present study was to examine gene expression profiles of chronically hypoxic myocardium and to explore the pathophysiological mechanisms by which the heart adapts to chronic hypoxia. Raw data from the next‑generation sequencing data set GSE36761 were downloaded from the Gene Expression Omnibus database. The data set comprised 30 specimens, including 8 healthy myocardia and 22 tetralogy of Fallot (TOF) congenital cardiac malformations; only 7 original data sets of healthy myocardia were obtained, and 5/22 TOFs were excluded. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses of differentially expressed genes (DEGs) were performed. Furthermore, network analysis of DEGs using Cytoscape software based on protein‑protein interaction (PPI) data was also conducted. A total of 1,260 DEGs were selected, of which 926 DEGs were enriched in 83 GO biological process terms, including extracellular matrix organization, regeneration and monocyte chemotaxis. Furthermore, 406 DEGs were enriched in 13 KEGG pathways, including cytokine‑cytokine receptor interaction, focal adhesion and apoptosis. PPI network analysis indicated that six hub genes with correlated degree scores >25 among nodes were identified, including G protein subunit β4, C‑C motif chemokine receptor (CCR)1, CCR2, platelet factor 4, catenin β1 and Jun proto‑oncogene (JUN). Of these, JUN was enriched in GO terms of regeneration and neuron projection regeneration, and in KEGG pathways of focal adhesion, apoptosis and Chagas disease (American trypanosomiasis). The present bioinformatics analysis of these DEGs and hub genes may provide a molecular insight to the role of diverse genes in the pathophysiology of chronically hypoxic myocardium and in myocardial adaptation to chronic hypoxia.