Porous diagnostic boundaries: a new emphasis for the Bulletin.

There is much discussion of the overlap between schizophrenia and bipolar disorders, and this discussion will surely be extended to include a number of disorders. This will not only be mood disorders with psychotic features, but anxiety disorders, neurodevelopmental disorders, and others. It had been hoped that Diagnostic and Statistical Manual of Mental Disorders (DSM-5) could be extensively organized by psychopathology spectrum to at least suggest which disorders group together on variables important to pathophysiology such as associated genes, neuroimaging biomarkers, and epidemiological risk factors.1 Data is available to support some spectra such as autism spectrum including several neurodevelopmental disorders or schizophrenia spectrum including schizophrenia, schizoaffective, schizophreniform, schizotypal personality disorders, and attenuated psychoses syndrome.2 However, a review of evidence for including bipolar disorder in the DSM-5 psychosis chapter with schizophrenia was not compelling.3 Similarities in dependent measures between disorders are often viewed as evidence that the diagnostic classes are not distinctive. Perhaps, bipolar and schizophrenia are different versions of a similar core pathophysiological or etiological mechanism. Or, psychoses are viewed as a continuum without separate classes validated with points of rarity. As this issue is being addressed regarding the validity of current classification, general similarities should not always be viewed as evidence of porous boundaries. The overlap between disorders needs to be substantial and relevant to a core feature or a critical validator of diagnostic class. Consider the shared and unshared genetic variance between schizophrenia and bipolar disorders. To challenge current diagnostic concepts and establish new classes, we need to know: