Objectives: We sought to clarify the familial relationship between five putative schizophrenia-related personality disorders (schizotypal [SPD], paranoid, schizoid, avoidant, and borderline) and schizophrenia, other nonaffective psychoses, and affective illness.
Design: A case-controlled epidemiologic family study using DSM-III-R criteria.
Participants: Five hundred thirty-four probands selected from a psychiatric case register or electoral register, of whom 415 were personally interviewed, and 2043 living and traceable relatives, of whom 1753 were personally interviewed.
Results: Compared with relatives of unscreened controls, relatives of probands with schizophrenia had a highly significantly increased prevalence of SPD, and modest, but significant, increased prevalences of paranoid, schizoid, and avoidant personality disorders. Borderline personality disorder was rare, with a modest clustering of cases in relatives of affective disorder probands. The prevalence of SPD was also significantly elevated in relatives of probands with SPD and with other nonaffective psychoses but not in relatives of probands with psychotic or nonpsychotic affective illness. In contrast to the pattern seen for schizophrenia, the prevalence rate of SPD was substantially greater in parents than in siblings of schizophrenic probands.
Conclusions: Schizotypal personality disorder has a strong familial relationship with schizophrenia. Paranoid, schizoid, and avoidant, but not borderline, personality disorders may have a significant familial relationship with schizophrenia. Schizotypal personality disorder also reflects the familial liability to other psychotic disorders but probably not to affective illness. Fitness effects may substantially influence the pattern of schizophrenia-related personality disorders in relatives.