In Search for Biomarkers in Obsessive-Compulsive Disorder: New Evidence on Saliva as a Practical Source of DNA to Assess Epigenetic Regulation

Background: Brain-Derived Neurotrophic Factor (BDNF) is a promising candidate biomarker in both the development and aetiology of different neuropsychiatric conditions, including obsessive-compulsive disorder (OCD). Most of the studies in the field have been carried out in blood cells, including peripheral blood mononucleated cells (PBMCs), although DNA of high quality can be easily isolated from saliva. Objective: The objective of this study was to evaluate the epigenetic regulation of the BDNF gene in the saliva of a clinical sample of OCD patients in order to assess this source as an alternative to blood. Methods: We first analyzed DNA methylation levels at BDNF in the saliva of subjects suffering from OCD (n= 50) and healthy controls (n=50). Then, we compared these data with the results previously obtained for the same genomic region in blood samples from the same patients and controls (CTRL). Results: Our preliminary data showed a significant reduction of 5mC levels at BDNF gene (OCD: 1.23 } 0.45; CTRL: 1.85 } 0.64; p < 0.0001) and a significant correlation between DNA methylation in PBMCs and saliva (Spearman r = 0.2788). Conclusion: We support the perspective that saliva could be a possible, reliable source, and a substitute for blood, in search of epigenetic biomarkers in OCD.