Molecular genetics, reductionism, and disease concepts in psychiatry

The study of mental illness by the methods of molecular genetics is still in its infancy, but the use of genetic markers in psychiatry may potentially lead to a Virchowian revolution in the conception of mental illness. Genetic markers may define novel clusters of patients having diverse clinical presentations but sharing a common genetic and mechanistic basis. Such clusters may differ radically from the conventional classification schemes of psychiatric illness. However, the reduction of even relatively simple Mendelian phenomena to molecular genetics has been shown to be a surprisingly complex and problematic enterprise. Mental illnesses exist at many levels of including social, environmental, and developmental interactions. Reductionistic shifts in the classification of such a disease entity will have to address the interlevel dynamics that take place within the structure of theories of mental illness. The question of how molecular analysis of psychiatric disease will impact on the structure of existing theories and classification systems is the central topic of this paper.