Meta-analysis reveals no association of the Val66Met polymorphism of brain-derived neurotrophic factor with either schizophrenia or bipolar disorder

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Abstract
A long-term controversy exists on whether or not major psychotic disorders can be discretely divided into two groups, for example, schizophrenia and bipolar disorder. Many genes and polymorphisms have been studied for a role in both disorders, including the Val66Met (also known as rs 6265 or G196A) variant of brain-derived neurotrophic factor (BDNF). Many case-control association studies have been performed to see if BDNF could serve as a useful clinical diagnostic biomarker for schizophrenia or bipolar disorder, but results have been equivocal.To determine, by meta-analysis, if the Val66Met polymorphism of BDNF influences risk for either schizophrenia, bipolar disorder, or both.We searched Pubmed, Medline, and PsycInfo using keywords including Val66Met, Rs6265, G196A, BDNF, schizophrenia, and bipolar disorder. A total of 13 studies for schizophrenia and 11 studies for bipolar disorder were combined by random-effects meta-analysis.The pooled results from the schizophrenia sample (2955 patients; 4035 controls) and the bipolar disorder sample (3143 patients; 6347 controls) indicated lack of significance with either of the two psychoses, with pooled odds ratios of 1.00 (P=0.944) and 0.95 (P=0.161), respectively.Although there are some limitations on the study, our results indicate there is a lack of association between the Val66Met polymorphism and either of the two psychoses. A larger sample size, and evaluation of more single-nucleotide polymorphisms are needed to obtain more robust and conclusive findings regarding the relationship between the BDNF gene and psychosis.