Evidence of associations between brain-derived neurotrophic factor (BDNF) gene polymorphisms and serum BDNF levels with tinnitus

Tinnitus is a common symptom of hearing system and defined as perception of sound in the ear or any part of the head without any external stimuli. Still very little is known about the pathophysiology of tinnitus. Brain-derived neurotrophic factor(BDNF) is one of the neurotrophic factors which play key role in growth, differentiation, survival of neurons and developing auditory pathway including the sensory epithelium of the inner ear. BDNF gene polymorphisms [rs6265 (Val66Met), rs2030324 ve rs1491850] is associated with abnormalites of regulated secretion of BDNF and there are studies which associated with changes in brainstem auditory evoked potentials (BAER) test results and furthermore BDNF levels are reduced tinnitus and psychiatric disorders and cases such as depression, dysthymic disorder that may be associated with stress, conversion disorder and suicide attempts due to crises of life. Tinnitus is often closely associated with mood disorders such as depression. All these data suggest may be correlation between tinnitus with BDNF gene polimorhpysm and BDNF serum levels. This purpose, we investigated whether there is any role of BDNF changes in the pathophysiology of tinnitus. In this study, we will examine the possible effects of BDNF variants in individuals with a diagnosis of tinnitus continuing for more than 3 months. We will select 52 subjects for examination between the ages of 18-55 and as control group at the same age group, 42 subjects which were free of any otorhinolaryngology and systemic disease. Patients which selected appropriately with these characteristics will be evaluated and examine. The severities of tinnitus and depression will be measured using the tinnitus handicap inventory (THI) and the differential diagnosis of psychiatric diagnoses made using the Structured Clinical Interview(SCID-I) for DSM-IV in the psychiatry department. Genomic DNA will be extracted from the venous blood and BDNF gene single nucleotide polymorphism will be analyzed in the DNA samples and the serum levels of BDNF will be measured. As a result, level of serum BDNF was found lower in the patients with tinnitus than controls and appeared to have no correlation between BDNF gene polimorfizm and disorder. Keywords: Tinnitus, BDNF gene, polimorfizm, serum BDNF