Hypothesis: epigenetic effects will require a review of the genetics of child development.

The worldwide prevalence of developmental disorders in children including birth defects, mental dysfunctions, as well as early-life abnormalities leading to the predisposition for adult diseases is one of the major unsolved problems in medicine and societies. Child development is influenced by both genes and the environment; however, the role of the environment is more emphatic, since the genome is most vulnerable to environmental factors during early development due to the high cellular differentiation rate. This inherent characteristic of child development lays the stress on a probabilistic rather than a deterministic view with regard to the manifestation of developmental disorders. Therefore, the analysis of gene-environment interactions in child development, beyond providing information about the developmental disorders of children, has an additional value that contributes to the knowledge on epigenetics in general and the interface between the genome and the environment playing a significant part in causing a wide range of diseases, in particular. The present study, rather than attempting to give a complete overview on epigenetics, is intended to illustrate that the issue of child development is an attractive target to extend the scope of genetics both in health and disease. Since the results might be extrapolated to the understanding of the pathomechanism of many age-dependent multifactorial diseases, the importance of studying gene-environment interaction in child development also lies in identifying new and potentially modifiable risk factors for diseases that are, therefore, of public health significance.