An independent analysis of the Copenhagen sample of the Danish adoption study of schizophrenia. II. The relationship between schizotypal personality disorder and schizophrenia.

To assess the relationship between schizophrenia and schizotypal personality disorder (SPD) as defined in DSM-III, the interviews of relatives from the Danish Adoption Study of Schizophrenia were independently and blindly reevaluated. The prevalence of SPD was significantly higher in the biologic relatives of the schizophrenic adoptees than in the biologic relatives of matched controls and was low and equal in the two groups of adoptive relatives. Compared with "borderline" and uncertain borderline schizophrenia as defined by Kety and co-workers, the criteria for SPD were more specific but less sensitive in identifying biologic relatives of schizophrenics. In this sample, SPD has a strong genetic, but no familial-environmental, relationship to schizophrenia. These results replicate the findings of Kety and co-workers on borderline schizophrenia and support the validity of the diagnosis of SPD.