The boundaries of schizophrenia: Overlap with bipolar disorders

The extent to which schizophrenia and bipolar disorder converge or diverge across a range of domains is a fundamental construct in psychiatric nosology and neuroscience. Both conditions share overlapping symptomatology and the Kraepelinian dichotomy that course of illness helps define and separate each condition longitudinally is, at best, contentious. Schizophrenia and bipolar disorders both show high rates of heritability, with recent whole genome linkage studies providing some evidence for shared genetic liability. On the other hand, the available evidence suggests a greater influence of nongenetic factors in schizophrenia than in bipolar disorders. There are also subtle differences in structural brain abnormalities and in cellular architecture between these conditions. In the area where perhaps heretofore there was the greatest divergence, emerging information suggests an overlap in therapeutic efficacy between medications used for the treatment of schizophrenia and those agents used for treating mood disorders. Pertinent aspects of etiopathogenesis as well as recent publications that address overlapping domains between schizophrenia and mood disorders are reviewed.