Association between chronic tinnitus and brain-derived neurotrophic factor antisense RNA polymorphisms linked to the Val66Met polymorphism in BDNF.

Tinnitus is the sound heard in the ear or head of a person in the absence of external stimuli. Its etiopathogenesis is still not fully understood and the etiological causes responsible for tinnitus are quite variable. Brain-derived neurotrophic factor (BDNF) is one of the key neurotrophic factors in the growth, differentiation, and survival of neurons and in the developing auditory pathway, including the inner ear sensory epithelium. The regulation of BDNF gene is known to be managed by BDNF antisense (BDNF-AS) gene. BDNF-AS is located downstream of the BDNF gene and transcribes a long non-coding RNA. Inhibition of BDNF-AS upregulates BDNF mRNA, which increases protein levels and stimulates neuronal development and differentiation. Thus, BDNF and BDNF-AS both may play roles in the auditory pathway. Polymorphisms in both genes may have impact on hearing performance. A link was suggested between tinnitus and BDNF Val66Met polymorphism. However, there is no study questioning the relationship of tinnitus with BDNF-AS polymorphisms linked with BDNF Val66Met polymorphism. Therefore, this study aimed to scrutinize the role of BDNF-AS polymorphisms showing linkage with the BDNF Val66Met polymorphism in the course of tinnitus pathophysiology. Six BDNF-AS polymorphisms were analyzed on the tinnitus patients (n = 85) and the control subjects (n = 60) by Fluidigm Real-Time PCR using the Fluidigm Biomark microfluidic platform. When BDNF-AS polymorphisms were compared between the groups in terms of genotype and gender distribution, statistically significant differences were detected in rs925946, rs1519480, and rs10767658, polymorphisms (p less than 0.05). When the polymorphisms were compared by the duration of tinnitus, significant differences were found in rs925946, rs1488830, rs1519480, and rs10767658 polymorphisms (p less than 0.05). According to genetic inheritance model analysis, 2.33 and 1.53-fold risks were found for the rs10767658 polymorphism in the recessive and the additive models, respectively. For the rs1519480 polymorphism, a 2.25 fold risk was observed in the additive model. For the rs925946 polymorphism, 2.44 fold protective effect in dominant model, and 0.62 fold risk was found in the additive model. In conclusion, four of the polymorphisms in BDNF-AS gene (rs955946, rs1488830, rs1519480, and rs10767658) are potential gene loci that may play a role in the auditory pathway and affect auditory performance.