Association of BDNF gene polymorphism with bipolar disorders in Han Chinese population

Recent data suggest that brain-derived neurotrophic factor (BDNF) plays an essential role in neuronal plasticity and etiology of bipolar disorders (BPD). However, results from different studies have been inconsistent. In present study, 342 patients who met DSM-IV (Diagnostic and Statistical Manual of Mental Disorders, 4th Edition) criteria for bipolar disorders type I (BPD-I) or type II (BPD-II) and 386 matched health controls were enrolled, and TaqMan(®) SNP Genotyping Assays (Applied Biosystems, Foster City, CA, USA) were applied to detect the functional polymorphism rs6265 (Val66Met) of BDNF gene. Treatment response to lithium and valproate was retrospectively determined. The association between Val66Met polymorphism and BPD, treatment response to mood stabilizers, was estimated. The genotype and allele distribution of Val66Met polymorphism between BPD patients and control subjects showed significant difference (genotype: χ(2) = 6.18, df = 2, P = 0.046; allele: χ(2) = 5.01, df = 1, P = 0.025) with Met allele as risk factor for disease susceptibility (OR = 0.79, 95%CI as 0.64-0.97). The post hoc analysis interestingly showed that Met allele had opposite effect on the treatment response for BPD-I and BPD-II separately. For BPD-I patients, the response score in Val/Val group was significantly lower than that in Met allele carriers (t = -2.27, df = 144, P = 0.025); for BPD-II patients, the response score in Val/Val group was significantly higher than that in Met allele carriers (t = 2.33, df = 26, P = 0.028). Although these results should be interpreted with caution because of the limited sample for Val/Val genotype in BPD-II patients (N = 5), these findings strengthen the hypothesis that BDNF pathway gets involved in the etiology and pharmacology of BPD and suggest the differences between BPD-I and BPD-II.