The first criteria-based definition of this disorder was proposed by the RDC. This disorder was shown to aggregate in families, but not in a specific manner.7 Some variants of this disorder also occurred

more commonly than would be expected by chance in families of probands with schizophrenia and other variants in families of probands with affective disorders, and vice versa. The clinical characterization of these variants demonstrated that cosegregation with schizophrenia was preferentially associated with the more chronic, schizophrenia-like schizoaffective Inhibitors,research,lifescience,medical disorder, whereas other subtypes coaggregated preferentially with affective disorders.8 As a consequence, the schizophrenia-like Inhibitors,research,lifescience,medical schizoaffective disorders were distinguished from other schizoaffective disorders, which were subsequently considered to belong to the affective disorders in DSM-III-R and DSM-IV and likewise in ICD-10. Diagnostic definitions ignoring familial-genetic evidence Several studies were recently conducted applying one of the aforementioned criteria of validity to competing diagnostic definitions or diagnostic criteria, particularly with regard to the definition of schizophrenia and psychotic disorders. Twin and family studies focused primarily on the positive/Tasocitinib negative distinction. It was demonstrated that the complex of negative symptoms was fairly consistently associated Inhibitors,research,lifescience,medical with a high familial

similarity, a higher familial loading with psychotic disorders, and a higher genetic load than positive symptoms.9 One twin study even found no genetic influence at all on the occurrence Inhibitors,research,lifescience,medical of positive symptoms (first-rank Schneiderian symptoms), whereas other definitions, including positive and negative symptoms in Inhibitors,research,lifescience,medical the definition of schizophrenia, were associated with at least a moderate degree

of heritability.10 If a classification system relies on the specificity and magnitude of underlying genetic determinants, a redefinition of the concepts of schizophrenia and other psychotic disorders should result from these findings. In contrast to this empirical evidence, Mephenoxalone even the most recent definitions of schizophrenia and psychotic disorders in DSM-III-R, DSM-IV, and ICD-10 give priority to positive symptoms. As an exception, ICD-10 proposes the residual category of latent schizophrenia (schizophrenia simplex), which is only defined by the presence of negative symptoms, in the absence of positive symptoms. The familial-genetic nature of this condition is not widely known, as most research into the genetics of schizophrenia is based on cases with a mixture of positive and negative symptoms. The most distinctive difference between the DSM-III-R, DSM-IV, and ICD-10 classification of schizophrenia is the minimal duration of the disease episodes. ICD-10 requires the presence of symptoms for just 1 month.