= 279), bipolar II disorder (n = 171) and manic disorder (n = 102). The diagnoses according to DSM–IV for the same set of participants were: bipolar I disorder (n = 1594), schizoaffective disorder, bipolar type (n = 98), bipolar II disorder (n = 134), bipolar disorder, not otherwise specified (n = 42). (Each individual has a diagnosis according to both RDC and DSM–IV. The joint distribution of diagnoses is shown in online Table DS1. Diagnostic reliability as measured by mean kappa (κ) coefficients for a set of 20 individuals was 0.86 for RDC and 0.84 for DSM–IV.) With the exception of DSM–IV bipolar disorder, not otherwise specified (n = 42), all definitions of diagnosis were of large enough sample size to warrant further investigation. The controls, who were not screened for psychiatric illness, came from two sources: the UK 1958 birth cohort longitudinal epidemiological sample (n = 1458) and the UK Blood Donor Service (n = 1480). It has previously been shown that it is valid to combine these two control samples for use as controls in genetic association studies using UK disease samples, including the current bipolar disorder sample.3
