Subtypes of schizophrenia--evidence from a twin-family study

In a combined twin-family study, the concordance for subtype of schizophrenia was investigated. The sample included 31 monozygotic (MZ) and 28 dizygotic (DZ) twin probands fulfilling the criteria of DSM-III-R schizophrenia. Their co-twins and first-degree relatives were personally interviewed and diagnosed in accordance with DSM-III-R. Any twin or relative diagnosed as schizophrenic was subclassified as either paranoid or nonparanoid. Schizophrenia was more often observed in co-twins of MZ probands with nonparanoid schizophrenia than in MZ probands with paranoid schizophrenia, indicating a stronger genetic influence in nonparanoid schizophrenia. Fifteen MZ pairs were concordant for schizophrenia, and 13 of these pairs were also concordant for subtype. Such a relationship was not observed in the first-degree relatives with schizophrenia. Our results indicate a complex etiology of subtypes in schizophrenia, and to some extent the etiology of subtypes may differ from the etiology of schizophrenia.