Correlation and familial aggregation of dimensions of psychosis in affected sibling pairs

We measured the familial aggregation of clinical and demographic features and symptom dimensions of schizophrenia in 136 families with two or more affected members. Each affected member was assessed for lifetime worst positive and negative symptoms, general psychopathology, aggression, premorbid schizotypy and schizoid traits, type of onset, global functioning and developmental and demographic variables. We used two analytical methods: calculation of an intraclass correlation coefficient and evaluation of components of variance using the QTDT program. With either method, we found that global functioning, positive symptoms and global psychopathology, premorbid schizotypal and schizoid traits and premorbid social adjustment all showed significant evidence of familial aggregation. We found close correlation between clinical measures: 1) Worse pre-morbid social adjustment and pre-morbid schizoid and schizotypal traits were correlated with more severe symptoms, worse general psychopathology, poorer global functioning, more severe negative symptoms, and delayed early motor development; 2) Less severe pre-morbid schizoid and schizotypal trait scores were associated with more positive symptoms and 3) Chronic onset of illness was associated with more negative symptoms.