Schizotypal personality disorder in parents and the risk for schizophrenia in siblings.

With on exception, previous studies examining the familial relationship between schizotypal personality disorder (SPD) and schizophrenia have compared rates of SPD in relatives of probands with schizophrenia versus control probands. In the Roscommon Family Study, an epidemiologically based family study of major psychiatric disorders conducted in the west of Ireland, we used a Cox proportional hazards model to examine the impact of a parental diagnosis of SPD on the risk for psychiatric disorders in siblings of probands with schizophrenia or schizophrenia spectrum disorders. In siblings of probands with schizophrenia or schizophrenia spectrum, a parental diagnosis of SPD significantly increased the risk for schizophrenia and schizophrenia spectrum disorders, but not for affective illness or anxiety disorders. These findings replicate our previous results from the Roscommon Family Study, further supporting the hypothesis that SPD has a substantial familial relationship with schizophrenia and other schizophrenia spectrum disorders, but not with affective illness.