Familial relatedness of schizophrenia and schizotypal states.

The types and expectancy of mental disorders in the siblings of 74 probands with chronic schizophrenia were examined. The siblings were classified according to whether 1) both parents had schizotypal personality disorder, 2) one parent had the disorder and one was normal, or 3) both parents were normal. Siblings whose parents both had the disorder were at significantly greater risk for schizophrenia and schizotypal personality disorder than siblings with at least one normal parent. Similarly, the expectancy of schizotypal personality disorder alone and combined with schizophrenia was higher among siblings with one parent with the disorder than in siblings with two normal parents. The data suggest that schizotypal traits may be genetically related to schizophrenia.