Twin study of symptom dimensions in psychoses

Background Symptomatology in psychoses can be summarised as quantitative sy mptom dimensions. but their genetic basis is unknown. Aims To investigate whether genes make an important contribution to symptom dimensions. Method A total of 224 probandwise twin pairs (106 monozygotic, 118 same-gen der dizygotic) where probands had psychosis were ascertained from the Mauds ley Twin Register in London. Factor analysis was performed on lifetime symp toms rated on the Operational Checklist for Psychotic Disorders (OPCRIT). C orrelations of dimension scores within monozygotic and dizygotic pairs conc ordant for Research Diagnostic Criteria psychoses were performed. Relations hips between dimension scores and genetic loading for psychoses were assess ed using logistic regression. Results Patterns of familial aggregation consistent with a genetic effect w ere found for the disorganised dimension and for some measures of the negat ive, manic and general psychotic dimensions. Disorganised dimension scores were related significantly to genetic loading for psychoses. Conclusions The disorganised dimension, and possibly other symptom dimensio ns. may be useful phenotypes for molecular genetic studies of psychoses.