Dimensions of psychosis in affected sibling pairs

Factor analytical studies of schizophrenia symptoms have consistently sugge sted three or more symptom dimensions, but it is not known whether any of t hese dimensions have a genetic basis. The purpose of this study was to inve stigate to what extent the dimensions show familial aggregation. Symptom ra tings were made using the SAPS and SANS and the OPCRIT checklist on the mem bers of 109 sibling pairs with DSM-IV schizophrenia or schizoaffective diso rder, Factor analyses were performed on the ratings of both instruments, an d correlations were made of within-pair factor scores. Analyses were also p erformed on the 89 pairs in which both members had a diagnosis of schizophr enia. Factor analysis of SAPS and SANS ratings resulted in positive, negati ve, and disorganization factors; analysis of OPCRIT ratings resulted in pos itive, negative, disorganization, and first-rank delusion factors. Only the disorganization dimension showed significant within-pair correlations, but these were of modest size and not significantly greater than the correlati ons for the other dimensions. None of the dimensions showed sufficient fami lial aggregation to suggest that they are close markers of genetic or commo n environmental factors that contribute liability to schizophrenia. They ma y be weakly associated with such factors and with factors that do not contr ibute liability to schizophrenia but do influence the form taken by the ill ness.