The concept of endophenotypes in psychiatric diseases meeting the expectations?

Although the prominent role of genetics in psychiatric diseases has been established in various family, twin and adoption studies over the last decades, the identification of concrete contributing genes has been demanding. The reasons for this are manifold, including inconsistencies in psychiatric classification systems, complexity and heterogeneity of psychiatric disorders, epistatic effects and intervening environmental factors. In recent years interest has focused increasingly on the concept of endophenotypes. Genetic analyses have concentrated on discrete phenotypes supposedly linked to a particular psychiatric disorder by common neurobiological pathways, instead of studying the complex disease itself. Several endophenotypes have been established for psychiatric diseases including electrophysiological abnormalities and alterations in structural and functional brain imaging. Although results seem to be getting more consistent and reliable, several concerns have also emerged with the experience gained on the topic. This review will give an overview of the prospects and limitations related to endophenotypes in psychiatric diseases. We will also summarize essential prerequisites for successful endophenotypes in the future as well as applications for psychiatric diseases which have been envisioned.