We have used molecular genetic genome-wide case–control association data to compare the genetic association signals according to several different operational categories in the bipolar disorder spectrum. The participants meeting RDC criteria for schizoaffective disorder, bipolar type (a broad definition of schizoaffective disorder) received strongest support (i.e. this was the most genetically useful, and by this criterion, most biologically valid diagnostic subset). It is important for research, and may be important for clinical practice, that such individuals are better recognised and distinguished from other people with mood–psychosis disorders.
