**2.3 Schizophrenia as a low fitness disease**

It has been well documented that the fertility of patients with schizophrenia, particularly of males, is remarkably reduced compared to healthy individuals (Böök, 1953; Larson & Nyman, 1973; Ødegård, 1980; Nanko & Moridaira, 1993; Fãnanás & Bertranpetit, 1995; Nimgaonkar, 1998; McGrath et al., 1999; Haukka et al., 2003; Svensson et al., 2007). The latest meta-analysis (Bundy et al., 2011) shows that fertility ratio (patients/controls) is ~0.39 and that the reduction of fertility is more pronounced in males (male/female ratio is ~0.54).

Because schizophrenia is an early onset disease (late adolescence ~ early adulthood), psychotic symptoms of the disease such as autistic way of life and abnormal behaviors may make mating unsuccessful. This tendency may be more pronounced in males because the age at onset is significantly lower in males than in females (Jablensky, 1995; Kulkarni & Fink, 2000). Thus, unsuccessful mating, coupled with an increased mortality (McGrath et al., 2008), may remarkably reduce the fertility of patients with schizophrenia.
