Classic genetics research in psychiatric disorders has provided an abundance of data but a paucity of insight. Things will only get worse in terms of this ratio, as massive sequencing of genomes becomes routine.
The reasons are four-fold. First, psychiatric disorders are genetically complex, with many (hundreds, if not thousands) genes involved. We first proposed that over a decade ago, based on our pioneering gene expression work cross-matched with human genetic data (Convergent Functional Genomics). Second, psychiatric disorders are genetically heterogeneous, with different mutations in the same gene present in different individuals. Many of these mutations are in fact common variants present in non-psychiatrically ill individuals as well. Third, psychiatric disorders as currently defined by DSM are overlapping and interdependent, with genes and biological pathways shared among disorders. Fourth, the environment plays a major role in modulating gene expression and the development or not of illness.
The key to progress is to acknowledge reality in the four areas mentioned above. Illness or lack of illness are the result of cumulative combinatorics of common gene variants and environmental stressors (or favorable factors). Genetic context and environmental context are important to whether a mutation contributes or not to the illness. Gene expression studies are more informative than classic genetics, as they reflect the actual results of the interaction between genes and environment, and underlie the subsequent patho-physiological outcomes. Biological pathways and mechanistic-level analyses will show more commonality and reproducibility across individuals, and from study to study. A dimensional approach to psychiatric profiling of individuals will eliminate the confusion and overlap of DSM, as well as permit a better mapping and tracking of biological reality. Our group has provided comprehensive proof and solutions over the years in all these areas, and we will continue to do our bit.
Alexander B. Niculescu, III, MD, PhD