Impact of complex genetic conditions on public health

Complex genetic diseases are often common: in most common diseases liability is influenced by genetic variation. The ways in which this variation is analyzed are discussed using diabetes, affective disorders and schizophrenia as examples. Molecular biology has opened new paths for a more incisive analysis of genetic heterogeneity and biological mechanisms. However, important population genetic aspects such as mutation and selection are largely unexplored. Therefore, predictions regarding possible increases or decreases in frequencies of susceptibility genes are hardly feasible. In many cases, however, the public health impact of such diseases can be alleviated and the quality of life of the individual can be improved, by appropriate adaptation of relevant environmental factors.