The RDC schizoaffective disorder, bipolar type describes individuals that, in addition to clear-cut episodes of mania, display psychotic symptoms (delusions and/or hallucinations) that are not easily understood as being the result of extreme mood change and that are often seen also in individuals diagnosed with schizophrenia. It does not include all the people with bipolar disorder with psychosis. An analysis using the set of participants with bipolar disorder who had experienced psychotic symptoms during their lifetime did not reveal significantly more independent hits (data not shown). Thus, we can be confident that our finding does not simply relate to a subset of people with bipolar disorder having psychotic features. It is of interest that we did not observe evidence for increased hits in the DSM–IV schizoaffective disorder, bipolar type subset of individuals. It is possible that this may simply reflect the smaller sample size (n = 98) or it may be an indication that the RDC definition of schizoaffective disorder, bipolar type is more biologically useful than that of DSM–IV (at least with respect to identifying the contribution of common
