A comprehensive twin study on genetic and nongenetic traits related to the etiologies of schizophrenia.

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1. A new schizophrenic twin sample, found during the term of research, consists of 22 monozygotic (Mz) and 14 dizygotic (Dz) twins. Thirty two pairs of them were born in Nagasaki prefecture.2. Epidemiological investigation demonstrated (1) a new twin concordance for DSM-III-R schizophrenia(Sz), 50.0% by probandwise method very close to those from U.K.and Norway, (2) second-born Mz twins were more vulnerable to Sz and dysfunctioned than the first-borns, and (3) a decreased developmental buffer capacity revealed by hjgh fluctuating dermatoglyphic asymmetry in Mz twins concordant for Sz (conc-Mz) while plausible environmental insults in prenatal period resulting in an increase of thumbs' ridge counts in Mz twins discordant for Sz (dise Mz).3. Brain morphological study by magnetic resonance imaging (MRI) revealed ventricular enlargement in conc-Mz while smaller size the left hippocampus in affected member of disc-Mz than the non-affected. These results suggested the involvement of genetic and non-genetic factors such as pre-or perinatal damage in the development of Sz traits.4. Twin sample, especially disc-Mz, can serve as an assay system to test whether only geneomic DNA can cause or disease. Candidate gene mutations such as D2DR missense mutation and triplet repeats expansion as well as entire pair genomes are going to be compared between affected and non-affected members in disc-Mz pairs applying new molecular genetic techniques.