Brain-derived neurotrophic factor and neurocognitive profiles in the psychosis spectrum: Findings in bipolar disorder and schizophrenia

Background: There has been recent interest in the role of brain-derived neurotrophic factor (BDNF) in the pathophysiology and treatment of bipolar disorder and schizophrenia. BDNF plays a role in neuroplasticity by promoting neuronal growth, survival, differentiation, neurostructure, and neurofunction in several brain areas. Its specific neuroplasticity-related role in affective and non-affective psychoses has shown several commonalities that cast doubts on traditional Kraepelinian distinctions between bipolar disorder and schizophrenia. Method: We review relevant studies of BDNF gene polymorphisms and expression in people with bipolar disorder and schizophrenia compared to healthy controls that suggest its putative role in etiology, mechanism, and phenotypic expression in both disorders. Results: Studies suggest that peripheral BDNF is low in people with bipolar disorder and schizophrenia and BDNF concentrations are inversely correlated with symptom severity. At the DNA level, studies of the Val66Met single nucleotide polymorphisms (SNP) of the BDNF gene suggests that the Met allele is associated with neurocognitive deficits present in both disorders. In contrast, several studies suggest that the Val allele may be associated with symptom severity and the incidence of both bipolar disorder and schizophrenia. Conclusions: BDNF appears to be a shared biomarker of bipolar disorder and schizophrenia with demonstrable associations with incidence, clinical symptoms, and neurocognitive phenotypes. This state of affairs supports a latent dimension or spectrum model of affective and non-affective psychoses rather than the traditional categorical distinctions. Despite growing evidence of BDNF's role in the psychosis spectrum, questions remain about its reliability and validity as a clinical biomarker and predictor of bipolar disorder and schizophrenia.