Brain-derived Neurotrophic Factor Level and Gene Polymorphism as Risk Factors for Depression in Patients with type 2 Diabetes Mellitus- A Case-Controlled Study

Background: Diabetes mellitus and depression are comorbidities that can be caused by each other. Brain-derived neurotrophic factor (BDNF) functions as a neuronal growth factor. It maintains the functional integrity of the nervous system. Aim: To study the possible association between BDNF levels and gene polymorphism with depression in patients diagnosed with type 2 diabetes mellitus. Methods: The Elisa technique measured BDNF, and rs6265 gene polymorphism was detected using real-time PCR. Depression was assessed utilizing a clinical interview tool designed to establish the diagnosis of depression and differentiate it from other psychiatric diseases. Results: BDNF levels were significantly lower in patients with type 2 diabetes mellitus and symptoms of depression than in patients with type 2 diabetes mellitus and no symptoms of depression (82.6 +/- 16.1. vs. 122 +/- 17.47, P< 0.001). There was a statistically significant difference in BDNF levels in patients with diabetes among the three genotypes of the BDNF gene (P-value < 0.001). Val/ Val carriers had the highest serum BDNF levels, and Met/ Met carriers had the lowest serum BDNF levels. Subgroup analysis showed statistically significant genotype-related differences in serum BDNF levels among the three subgroups in the Depression group. Val/ Val carriers had the highest serum BDNF levels, and Met/ Met carriers had the lowest serum BDNF levels. BDNF Val66Met polymorphism had no significant association with the presence of depression, yet there was a trend towards significance (p = 0.05). Conclusion: In this pilot, Low levels of BDNF were associated with depression in patients with type 2 diabetes. Carriers of the Met/ Met allele have the lowest serum BDNF levels. Multi-center studies with more participants are required.