Brain-Derived Neurotrophic Factor Val66Met Polymorphism and Its Synergism with L/S Polymorphism in the Promoter Region of Serotonin Transporter in Bipolar I Disorder Patients in Western Iran

Brain-derived neurotrophic factor (BDNF) might involve in the pathogenesis of mental disorders. There are inconsistent reports related to the role of BDNF Val66Met in susceptibility to bipolar disorder (BD).
The aim of the present study was to investigate the role of BDNF Val66Met and its synergism with 5-HTT gene-linked polymorphic region (5-HTTLPR) variants in susceptibility to bipolar I disorder (BP-I) in Western Iran.
In this case-control study, 153 patients with BP-I and 146 age- and gender-matched healthy individuals were investigated for BDNF and 5-HTTLPR variants using PCR-RFLP method.
The frequency of BDNF A (Met) allele in patients (17.7%) was slightly lower than that in controls (19.9%, P = 0.5). The concomitant presence of BDNF G (Val) and 5-HTTLPR S alleles tended to increase the risk of BP-I by 1.41 times (P = 0.064) compared to the combined presence of BDNF G and 5-HTTLPR L alleles. Also, interaction between BDNF G (Val) and 5-HTTLPR S tended to increase the risk of BP-I by 1.28-fold (P = 0.062) compared to the concomitant presence of BDNF A and 5-HTTLPR S alleles.
This study, conducted for the first time on Kurdish population in Western Iran, did not indicate any association between BDNF Val66Met with BP-I. However, the interaction between BDNF and 5-HTTLPR variants tended to increase the susceptibility to BP-I.