Morbidity risks for mental illness were determined in 750 first-degree
relatives of chronic schizophrenic and normal control probands. Psychiatric
disorders that were more frequent in relatives of schizophrenic probands
than in relatives of normal control probands were chronic schizophrenia
(5.8% versus 0.6%), schizotypal personality disorder (definite, 14.6%
versus 2.1%; probable, 12.1% versus 6.5%), and paranoid personality
disorder (7.3% versus 2.3%). The data suggest that schizotypal and paranoid
personality disorders are genetically related to schizophrenia. The
implications for schizophrenia research are discussed.Abstract Teaser