MURRAY ET AL (2004) REVISITED: IS BIPOLAR DISORDER SCHIZOPHRENIA WITHOUT DEVELOPMENTAL IMPAIRMENT?

Abstract

In 2004, Murray and colleagues suggested that the main difference between bipolar disorder (BPD) and schizophrenia (Sz) was a larger prevalence of developmental impairments in the latter. What is the actual status is of the prediction offered byMurray and colleaguesmore than five years ago? These issues are particularly important given the upcoming revisions of diagnostic systems in psychiatry: how should bipolar disorder and schizophrenia be classified in DSM-V and ICD-11? Here we review studies relevant to this issue, with a special focus on work published in the last 10 years. Both Sz and BPD have onset in adolescence and young adulthood, with an earlier onset in men. The incidenceof bothdisorders is lowandassociatedwithahighprevalence: incidence ratio, indicative of a high rate of chronicity. Schizophrenia patients have high rates of affective symptoms, although lower than in BPD, and bipolar patients have negative symptoms and cognitive impairment, although lower than in Sz. The diagnostic contrast between Sz and BPD is high for affective symptoms, but this is mostly due to artificial diagnostic exclusioncriteria. Sz andBPDhave correlatedgenetic liabilities, some of which is becoming substantiated in recent genomewide molecular genetic association studies. Of interest, however, is the fact that genetic risk for Sz is strongly expressed as neurocognitive impairmentwhereas genetic risk forBPD is onlyweaklyexpressed in the neurocognitive domain. Danish studies have shown that BPD and Sz have a high population comorbidity index; general population studies have shown that both BPD and Sz phenotypes are associated with psychometric risk states in healthy individuals, and that BPD and Sz psychometric risk states are similarly highly comorbid with each other. Risk factors representing social stress and defeat as well as early emotional alterations are associatedwith both BPD and Sz whereas risk factors reflecting early motor and cognitive alterations appear specific for schizophrenia. Interesting is thedifferential associationwithgrowing up in an urban environment (not associated with bipolar disorder), suggesting that this exposure impacts on specific developmental alterations associated with schizophrenia. Acknowledgement: Nil Kaymaz is supported by the Netherlands Organisation for Scientific Research (NWO) under project number: 017.002.048.