Background: Continuous rather than categorical measures of psychopathology may provide greater statistical power to detect susceptibility loci for schizophrenia. However, it has not been established that the dimensions of schizophrenic symptomatology and personality traits in nonpsychotic individuals share etiological factors. We therefore sought to clarify the relationship between positive and negative symptoms of schizophrenic probands and dimensions of schizotypy in their first-degree relatives.
Methods: In the Roscommon Family Study, we examined the ability of positive and negative symptoms in probands to predict 7 factors of schizotypy in nonpsychotic relatives using regression analysis. These consisted of positive, negative, and avoidant symptoms; odd speech; suspicious behavior; social dysfunction; and symptoms of borderline personality disorder. We examined 3 proband groups: schizophrenia (n = 127); schizophrenia, simple schizophrenia, and schizoaffective disorder (n = 178); and all nonaffective psychoses (n = 216), and their nonpsychotic relatives (n = 309, 477, and 584, respectively).
Results: Positive symptoms in all nonaffective psychoses probands predicted positive schizotypy (beta = 0.1972, P =.0004), social dysfunction (beta = 0.0719, P =.0489), and borderline personality disorder symptoms (beta = 0.1327, P =.0084) in relatives, while negative symptoms predicted negative schizotypy (beta = 0.2069, P =.0002), odd speech (beta = 0.2592, P =.0001), suspicious behavior (beta = 0.2749, P =.0001), and social dysfunction (beta =.2398, P =.0002). Proband negative symptoms and borderline personality disorder symptoms in relatives in the schizophrenia, simple schizophrenia, and schizoaffective disorder group were inversely related (beta = -0.1185, P =.05).
Conclusions: Positive and negative symptoms in schizophrenia predict corresponding schizotypal symptoms in relatives. This provides evidence that these schizophrenic symptom factors (1) are etiologically distinct from each other and (2) occur on an etiological continuum with their personality-based counterparts.