Heritability of Schneider's first-rank symptoms

Background Schneider's first-rank symptoms are given particular weight when making a diagnosis of schizophrenia, but the nuclear syndrome, characterised by one or more first-rank symptoms, has been found previously to have no heritability. Aims To estimate the heritability of the nuclear syndrome. Method A total of 224 twin pairs (106 monozygotic, 118 same-gender dizygotic) were ascertained from the Maudsley Twin Register in London via probands with any psychosis. Lifetime-ever first-rank symptoms were rated using the OPCRIT checklist. Probandwise concordance rates were calculated for the nuclear syndrome and a heritability estimate was derived from biometric model fitting. Results Probandwise concordance rates were 13/49 (26.5%) for monozygotic and 0/45 to 2146 (0.0-4.3%) for dizygotic pairs. The heritability estimate for the best-fitting model was 71% (95% Cl 57-82). Conclusions These results indicate that the nuclear syndrome shows substantial heritability, although this is slightly lower than that for schizophrenia as defined by the DSM and ICD systems. Declaration of interest None. Funding from the National Institute of Mental Health and the Stanley Foundation.