Factor structure and familiality of first-rank symptoms in sibling pairs with schizophrenia and schizoaffective disorder

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Abstract
Background: Since their introduction as diagnostic criteria by Schneider in 1937, nuclear symptoms have played a key role in concepts of schizophrenia, but their relationship to each other and to genetic predisposition has been unclear.Aims: To ascertain the factor structure and familiality of nuclear symptoms.Methods: Nuclear (Schneiderian) symptoms were extracted from case notes and interviews in a study of 103 sibling pairs with DSM–III–R schizophrenia or schizoaffective disorder.Results: Principal components analysis demonstrated two major factors: one, accounting for about 50% of the variance, groups thought withdrawal, insertion and broadcasting, with delusions of control; and the second, accounting for <20% of the variance, groups together third-person voices, thought echo and running commentary. Factor I was significantly correlated within sibling pairs.Conclusions: The correlation within sibling pairs suggests that, contrary to the conclusion of some previous studies, some nuclear symptoms do show a degree of familiality and therefore perhaps heritability.