Abstract

Background: Gender Dysphoria (GD) is characterized by a marked incongruence between one‘s experienced gender and biological sex (DSM-5). Transsexuals are individuals who have undergone a transition from male-to-female (MtF) or female-to-male (FtM). Cross-sex hormone therapy (CHT) is critical for phenotypical and psychological transition, however, the impact of the CHT onto the epigenetic regulation has not been comprehensively addressed nowadays. We postulated that the CHT could change the methylation pattern at the estrogen receptor α (ESR1) promoter region. Methods: We analyzed the methylation degree on the Region III of the ESR1 promoter region in 5 FtMs, 7 MtFs, before and after six months of CHT; and 18 controls (10 females and 8 males). Genomic DNA was extracted from blood using the DNeasy Blood & Tissue Kit (Qiagen). The bisulfite reaction was carried out using the MethylCode TM Bisulfite convertion Kit (Invitrogen). The RIII covering the transcriptional regulatory region (-1297 to -731) of ESR1 gene was amplified by PCR using the primers described by Asada et al., (2008). The PCR products were cloned by T&A cloning Kit (Yeastern Biotech), 10 or more clones were randomly picked from each PCR, were sequenced with a 3130xl Genetic Analyzer (Applied Biosystems) and analyzed by QUMA (http://quma.cdb.riken.jp/). Results: There are sex differences in CpG methylation in RIII. Specifically, control males exhibit a higher methylation degree than females. FtMs before the CHT show statistical differences with respect to the female control group. The CpG positions 306, 372 and 405 were lower methylated in FtM0 vs. control XX group, and the global methylation was also lower, suggesting a higher expression of ESR1 in the FtM population before the CHT. After six months of treatment, FtM6m showed an increase in the global methylation degree. This increase in CpG methylation suggests that treatment with sex steroids can modify the pattern of methylation of the ESR1 and suggests a lower expression of ESR1 in FtM6m. With regard to MtFs, before the CHT the global methylation status was lower in MtF0 vs. the control XY group, suggesting a higher expression of ESR1 in the MtF population before the CHT with regard to the control XY group. After six months of CHT, the methylation degree increased, becoming more similar to the control group XY. Conclusions: CHT is associated to epigenetic changes in the RIII of the ESR1 promoter region in FtM and MtF populations. Six months of CHT produce an increase of the methylation in the FtM population. MtFs were lower methylated before the CHT but after six months of treatment, the global methylation was now similar to the control XY group. Key Words: estrogen receptor, female-to-male transsexuals, gender dysphoria, gender incongruence, male-to-female transsexuals, methylation. Funding Sources: This work was supported by grants from the Spanish Ministry of Science and Innovation [PSI2010- 15115 (EP) and PSI2014-58004-P (AG)] and the Xunta de Galicia (grant number ED431B 2016/013). J. Cortés-Cortés was supported by a doctoral fellowship FPU 15/02558.