Genetic epidemiology is the discipline that studies the role of genetic and environmental factors in the origin of complex traits, behaviors and diseases. The major focus of genetic epidemiology is the analysis of the relative contribution of genes, environment and their interplay in human traits. Among others, twin studies have become an important tool to disentangle the different roles of genes and environment and to estimate heritability. Within the genetic epidemiology, the ecogenetics study the relationship between genetic and environmental factors and seek to understand both the vulnerability of different genotypes present in the population facing the same environmental risk factors (gene-environment interaction, GxE) and the influence of the individual's own genotype in the search of specific environments and/or risk factors (gene-environment correlation, rGE). There are numerous studies from quantitative genetics and molecular genetics that describe such GxE and rGE effects on the etiology of complex traits and disorders. However, it is important to consider the methodological requirements and limitations associated with these studies. Undoubtedly one of the challenges of genetic epidemiology in the coming years will be to combine the gene-environment studies (based on specific assumptions) with the huge amount of genomic data provided by new molecular approaches.
Keywords: Antisocial behaviour, Cannabis use, Childhood maltreatment, Complex traits, Environment, Friendship, Genes, Gene-environment correlation, Gene-environment interaction, Heritability, Obesity, Schizophrenia, Twins.