Tinnitus is a prevalent and potentially disabling disorder characterised by the perception of sound in the absence of an external sound source. Like other chronic health problems, tinnitus can be regarded as a chronic stressor, leading to a dysregulation of the hypothalamo-hypopituitary-adrenal (HPA) axis. More specifically, a hypersuppression of cortisol is seen in tinnitus patients after administration of a low dose of dexamethasone, suggesting an enhanced HPA axis feedback sensitivity. The mechanism responsible for this enhanced negative feedback remains unclear, but epigenetic phenomena such as hypomethylation of the 1F exon of the glucocorticoid receptor gene (NR3C1), an important component of the HPA axis feedback system, might be involved.
The current study aims to investigate the methylation percentage of the NR3C1-1F exon, as well as its effect on glucocorticoid feedback in tinnitus patients as compared to healthy controls. In tinnitus patients, lower methylation percentages of the NR3C1-1F exon and an associated hypersuppression of cortisol secretion in response to a 0.5mg dexamethasone challenge are expected. Given the frequent co-morbidity of and the clinical overlap between tinnitus and panic disorder, characterised by recurrent and unexpected panic attacks, the effect of panic attacks on NR3C1-1F methylation and its impact on negative HPA axis feedback in tinnitus patients will also be investigated. NR3C1-1F methylation percentages are expected to be higher in the group with panic attacks, and associated with a higher cortisol secretion following the dexamethasone suppression test, due to the normal to low cortisol suppression rates reported in PD.
60 patients with tinnitus for which insufficient medical cause was found, will be recruited at the Department of Otorhinolaryngology of the Antwerp University Hospital, among them 30 patients with and 30 without panic attacks. Exclusion criteria are a current diagnosis of major depressive or post-traumatic stress disorder, active substance abuse or a past or current diagnosis of bipolar or psychotic disorder, pregnancy or lactation, treatment with corticosteroids or hormonal replacement therapy (with the exception of contraception). 30 healthy controls will be matched for age and gender. DNA will be isolated from peripheral blood and analyzed through quantitative pyrosequencing to determine methylation percentages of the NR3C1-1F exon. mRNA will be isolated from whole blood and expression levels will then be determined by Two-Step real-time PCR. DNA methylation percentages and mRNA expression levels will then be correlated to functional measures of HPA axis function, namely the cortisol awakening response and cortisol suppression rates after administration of a low dose (0.5mg) of dexamethasone, measured in the same study subjects for another study protocol.