Evaluation of polymorphism in the SYCP2L gene in infertile women and its correlation with assisted reproduction results

Abstract

In assisted human reproduction the response to controlled ovarian hyperstimulation with exogenous gonadotrophins is the first and crucial step of the treatment, which aims to obtain a sufficient number of mature oocytes to allow the selection of the most viable embryo for transfer. The response to ovulation induction is variable and difficult to predict. In young ovulatory women undergoing in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI), the standard protocol may result in both a satisfactory response and an inadequate response, which includes the low production or no oocytes, requiring the adjusting of the dose of recombinant FSH, or in the ovarian hyperstimulation syndrome (OHSS); a potentially serious complication of IVF/ICSI if not adequately managed, characterized by increased ovaries and extravasation of fluid in the abdominal cavity, resulting in ascites, hypovolemia, and hemoconcentration. Thus, the identification of patients with potential to develop hyper or poor response to standard treatment would be of great clinical assistance. Several biomarkers of the ovarian response have already been proposed in order to predict a possible response of the patient to ovulation induction, allowing the individualized protocol in determining the exact amount of exogenous gonadotrophin to obtain the optimal response of each patient. The most frequently used markers in clinical practice are follicle-stimulating hormone (FSH), anti-mullerian hormone (AMH) and antral follicle counting (AFC), however, they provide only limited information to predict individual response to ovarian stimulation in IVF/ICSI cycles because they are indirect measures or because of intra- and inter-cycle variability. In addition, the ovarian reserve is also influenced by age and genetic variants. It has been suggested that the ovarian response to ovulation induction depends on the combination of genetic and environmental factors. Genes with specific effects on the reproductive system and presenting polymorphisms that affect gene function or expression are targets of pharmacogenetic studies regarding the response to controlled ovarian stimulation as a complementary strategy for the individualization of protocols in IVF/ICSI treatments. Studies have shown that the Ala307Thr and Asn680Ser polymorphisms in the FSHR gene can cause follicular growth arrest leading to decreased ovarian reserve by affecting ovarian sensitivity to FSH in women submitted to ovulation induction for assisted reproduction, with conflicting results. However, other polymorphisms seem to influence the ovarian response. Laisk-Podar et al., in 2015, investigated 36 genetic markers of ovarian function, response to ovulation induction and IVF/ICSI outcomes in 306 women. The authors observed that the polymorphism rs2153157 of the SYCP2L gene was associated with the amount of FSHr required to obtain an oocyte and the chances of biochemical and clinical gestation. Thus, small variations in candidate genes can determine the variability of the follicular pool and thus be responsible by the variability of ovarian response to stimulation and assisted reproduction outcomes. Investigating the predictive factors of ovarian reserve can help to individualize ovulation induction protocols to reduce cancellation rates, financial costs, risk of developing OHSS and ensure better pregnancy rates in fewer cycles of assisted reproduction treatment. The objective of the present study was to evaluate the frequency of the polymorphism rs2153157 of the SYCP2L gene in 180 women underwent to assisted reproduction treatment and to correlate the genotypes with ovarian reserve markers (FSH, AMH and CFA), ovarian response to ovulation induction, and IVF/ICSI outcomes (MII, number of embryos and biochemical gestation rate).