**3. Strategies and future perspectives**

The molecular mechanisms of congenital heart defects are so complex that we have to use diverse strategies to explore them. **Animal Models** Biomedical models have been defined as ''surrogates for a human being, or a human biologic system, that can be used to understand normal and abnormal function from gene to phenotype and to provide a basis for preventive or therapeutic intervention in human diseases'' . Because of the striking homology between mammalian genomes and the many similarities in anatomy, cell biology, and physiology, rat is an excellent animal model for studying of cardiac development and identifying novel genes that could contribute to human disease. The Human Genome Initiative is providing genetic information not only from humans, but also from animals traditionally used as models. In addition, related enabling technologies in transgenesis and animal cloning provide new approaches for designing and performing experiments to dissect complex biological systems. Because of these new technologies (e.g., transgenesis), scientists are no longer limited to the traditional methods of choosing naturally occurring models. Researchers can utilize genomic knowledge and available tools to create appropriate animal models. This approach is referred to as reverse genetics. In contrast to forward genetics in which the gene or genes responsible for a particular phenotype are identified by positional cloning (phenotype to genotype), the reverse genetics approach determines the function of a gene and predicts the phenotype of a cell, tissue, or organism (genotype to phenotype). **Genome-Wide Studies** Considerable progress has been made in understanding the pathophysiology of perioperative stress responses and their impact on the cardiovascular system; however, researchers are just beginning to unravel genetic and molecular determinants that predispose to increased risk for CHD. Recent improvements in genotyping technology and in our knowledge of human genetic variation have made it possible to carry out genome-wide genetic association studies to identify susceptibility genes for common disease. Multistage designs involving large numbers of coding sequence variants (300,000) and relatively large samples sizes (several hundred cases and control subjects) will be essential to reliably detect alleles with appreciable effect sizes (2-fold increase in relative risk). Direct sequencing of candidate genes in cases and control subjects provides an alternative approach that can reveal low-frequency alleles that influence disease susceptibility [88,89]. **Gene Expression (Microarrays)** Microarray analysis is a useful tool to obtain a gene expression profile of CHD. However, current estimates suggest that greater than 60% of human genes have more than one isoform. Alternatively, spliced isoforms from the same gene can produce proteins with different properties and distinct functions. The specific roles of gene expression and their splicing variants necessary for development need to be further delineated. **MicroRNA** Current research has revealed that the influence of RNA molecules on gene expression reaches beyond the realm of protein synthesis back into the nucleus, where it not only dictates the transcriptional activity of genes, but also shapes

Molecular Mechanisms of Congenital Heart Disease 135

(cadherin-associated protein), beta 1; TGF-ß= transforming growth factor, beta 1; EGF= epidermal growth factor (beta-urogastrone) ; erbB= v-erb-b2 erythroblastic leukemia viral oncogene homolog 2, neuro/glioblastoma derived oncogene homolog; NF1= neurofibromin 1;MEF2= myocyte enhancing factor 2; Hand= transcription factor protein; RUNX2= runtrelated transcription factor 2; NOTCH= Notch homolog; Hesr1/Hey1= hairy/enhancer-ofsplit related with YRPW motif 1; BAF60C= a subunit of chromatin-remodelling complex

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**7. References** 

the chromatin architecture of extensive regions of DNA. Non-coding RNA, in the context of this review, refers to transcripts expressed and processed in the nucleus much like any protein coding gene, but lacking an open reading frame and often transcribed antisense to bona fide protein coding genes. Dysregulation of miRNAs might result in congenital heart disease in humans. Further studies of miRNAs in CHD are required. **Epigenetics** There is increasing evidence that epigenetic modifications, arising primarily through DNA methylation and histone modifications may have as important a role as genetics in certain diseases, such as cancer, birth defects, developmental disorders, and psychiatric disorders. **Bioinformatics** Unprecedented growth in the interdisciplinary domain of biomedical informatics reflects the recent advancements in genomic sequence availability, high-content biotechnology screening systems, as well as the expectations of computational biology to command a leading role in drug discovery and disease characterization. These forces have moved much of life sciences research almost completely into the computational domain. Human genome project has succeeded, and postgenome era is following. Human genome comprises 30, 000-40, 000 genes, but their functions, relation, interaction, and regulation remain unknown. Bioinformatics is a powerful and indispensable tool in exploring the molecular mechanisms of CHD [90, 91].
