Background: Although schizotypal personality disorder aggregates in relatives of schizophrenic probands, the criteria for this disorder may not be optimal either in describing the dimensions of schizotypal phenomena or in identifying those with a high familial liability to schizophrenia.
Methods: In the Roscommon Family Study, an epidemiologically based family study of major psychiatric disorders conducted in the west of Ireland, we examined 25 individual schizotypal symptoms and signs, assessed by structured personal interview, in 1544 first-degree relatives (without chronic psychosis or mental retardation) of five proband groups: schizophrenia; other nonaffective psychoses; psychotic affective illness; nonpsychotic affective illness; and matched, unscreened controls.
Results: We obtained seven meaningful schizotypal factors: negative schizotypy, positive schizotypy, borderline symptoms, social dysfunction, avoidant symptoms, odd speech, and suspicious behavior. Taken individually, all of these factors, except borderline symptoms, significantly discriminated relatives of schizophrenic probands from relatives of controls; in descending order of the odds ratios, they were odd speech, social dysfunction, suspicious behavior, negative schizotypy, avoidant symptoms, and positive schizotypy. In a multivariate analysis, four of these factors remained significant: odd speech, negative symptoms, social dysfunction, and avoidant symptoms. These schizotypal factors differed in their specificity. Three of the four most predictive schizotypal factors also significantly discriminated relatives of probands with other nonaffective psychoses from relatives of controls.
Conclusion: "Schizotypy" is a complex, multidimensional clinical construct, whose various dimensions differ widely both in the degree and specificity with which they reflect the familial liability to schizophrenia. Subpsychotic thought disorder; negative schizotypal signs, such as poor rapport and odd behavior; deficient occupational functioning; and social isolation/avoidance best characterized relatives of schizophrenic probands compared with relatives of matched controls.