The spectrum concept of schizophrenia: evidence for a genetic-environmental continuum

Family data from 84 chronic schizophrenic, 11 schizotypal and 90 normal control probands were analyzed by multivariate-multifactorial genetic models using morbid risk statistics. The results were consistent with multifactorial inheritance whereby chronic schizophrenia and schizotypal personality disorder represent different phenotypic manifestations of the same underlying process; that is, the two disorders were found to have different thresholds on a single continuum of genetic-environmental liability. When subclassified according to Taylor and Abrams' criteria, chronic schizophrenic subjects who met these criteria (narrow schizophrenia) had a higher threshold of liability than those who did not (broad schizophrenia). The hypothesis of separate liabilities for the different disease states was rejected. Overall, the results suggest a gradation in multifactorial liability from schizotypal personality disorder (mild) to broad schizophrenia (moderate) to narrow schizophrenia (severe).