A twin study of clinical variables in psychotic disorders

Abstract

Background: Psychotic disorders show considerable clinical heterogeneity. However, little is known about the genetic basis of most clinical variables. Methods: 224 proband-wise twin pairs (106 MZ, 118 same-sex DZ) where probands had a lifetime history of psychosis were ascertained from the Maudsley Hospital Twin Register in London. Familial aggregation for a range of subtypes, symptoms, illness history and comorbidity variables was investigated in twin pairs concordant for RDC psychotic disorders. Relationships between clinical variables and genetic liability to psychoses, as measured by risk of psychoses in co-twins, were assessed using logistic regression analysis. Results: Familial aggregation was greater in MZ than DZ pairs and/ or previous sib-pair studies for age of onset; hebephrenic vs other subtypes of schizophrenia; inappropriate affect, and positive formal thought disorder; and for illness course, life-time marital status and premorbid social adjustment in schizophrenia and all psychoses combined (and delusions of influence and catatonia in schizophrenia). There was a modest relationship between familial liability to psychoses and younger age of illness onset; positive formal thought disorder, and catatonia; and poor premorbid social adjust-ment and never marrying. Conclusions: On the basis of this and previous studies there is strong evidence for a genetic contribution to age of onset in psychotic disorders, and some evidence of a genetic contribution to other clinically relevant variables.