Background

The functional psychoses “schizophrenia,” “schizoaffective disorders,” “psychotic depression,” “bipolar illness,” and “atypical psychosis” are distinct diagnostic entities sharing a considerable overlap in their underlying clinical syndromes (Stassen et al., 1988; Maier et al., 1993; 1999; 2005; Faraone et al., 1995; Maziade et al., 1995, 2001; Scharfetter and Stassen, 1995; Loftus et al., 1998; Wildenauer et al., 1999; Berrettini, 2000; Pulver et al., 2000; Vogt et al., 2000; Vuoristo et al., 2000; Bailer et al., 2002; Glatt et al., 2003; Kendler, 2003; Schurhoff et al., 2003; Craddock et al., 2005). Across ethnicities, schizophrenia and bipolar illness each affect about one percent of the general population, causing the loss of the ability to work, to have close relationships, and to have a fulfilling life. Population frequencies appear to be largely independent of ethnicity and social factors, as suggested by numerous epidemiologic studies including the World Health Organization (WHO) program on the outcome of severe mental disorders (Jablensky et al., 1992), and the Epidemiologic Catchment Area (ECA) program on psychiatric epidemiology (Weissmann et al., 1988). However, physical and sociocultural environments may modify the course of functional psychoses since patients in developing countries have a more benign course than patients in developed countries (Leff et al., 1992).