Genetic factors involved in the development of premature ovarian insufficiency

Premature ovarian Insufficiency (POI) is the cessation of the ovarian function before the age of 40, defined by high serum gonadotrophins, low estradiol and amenorrhea for at least 4 months. The etiology may be iatrogenic after a surgery, chemotherapy or radiotherapy treatment, environmental, autoimmune or genetic. However, in most of the cases the cause remains unknown. Clinical and family studies suggest a strong heritability of age at menopause and POI, but the number of genetic causes and genes identified to be involved in human POI remains very small. In POI patients, the two crucial functions of the ovary, hormonal secretion and reproduction, are absent. In the last decades, however, new advances in assisted reproduction techniques have allowed the possibility of carrying pregnancies to POI women, thanks to oocyte donation. The aim of this study was to identify new genetic factors implicated in the development of POI women and to analyse the reproductive possibilities and outcome of women with a genetic cause of POI. For the first part of the study, the DNA of a cohort of POI women recruited in the Fertility Clinic of the Hôpital Erasme of the Université Libre de Bruxelles was used to sequence five candidate genes (FSHR, GDF9, BMP15, AMH and AMHR2) known to be implicated in the ovarian folliculogenesis. The most important findings were two very rare variants and one unknown variant in the AMH gene. The functional study performed with these variants suggested a diminished function of the mutant protein. Furthermore, one of the variants was found in the mother of one of the patients, who was also diagnosed of POI at 32 years old. These arguments strongly suggest that a defective AMH could play a role in the development of POI. This is supported by previous studies with knock out mice models, which show an earlier depletion of the ovarian follicle pool due to a faster recruitment of the primordial follicles that constitute the ovarian reserve. The sequencing of the BMP15 gene led to the identification of two new variants not identified among controls but not predicted to be deleterious. Interestingly, one variant previously reported in POI women and predicted to be deleterious for the protein function, was found in a Sub-Saharan African POI patient as well as in our control cohort. This variant was already studied functionally and shown to have a reduced biological activity. However, we identified this variant in 6% of the Sub-Saharan African control population, which suggests that this is a more prevalent variant in the African genotype and raises up the importance of the ethnicity when studying genetic variants.The sequencing of the other genes (FSHR, GDF9 and AMHR2) did not lead to any association with POI.In the second part of the study, 24 women with Turner syndrome and POI were analysed in terms of reproductive, obstetrical and perinatal outcome after oocyte donation. This specific group of patients was chosen because of their specific systemic anomalies that could interfere with pregnancy outcome and because very few reports have been published on this subject. In the 23 patients finally transferred, the pregnancy rate was similar to that obtained after oocyte donation in other cohorts. There was a miscarriage rate of 23% and a rate of complications of pregnancy as high as 50%, mainly caused by pregnancy-induced hypertensive diseases. Four women at risk of genetic POI were included in the fertility preservation program in order to vitrify their oocytes. Three of them have already vitrified successfully their oocytes but none of them has yet used them.Oocyte vitrification represents a new hope for those women with genetic risk of POI to be able to carry a pregnancy with their own oocytes.In conclusion, three variants of the AMH gene could be implicated in the development of POI as demonstrated by the reduced in vitro bioactivity of the variants and the familial segregation of the cases. Since then, it sounds plausible to propose AMH sequencing in the case of familial POI and secondary amenorrhea.In the BMP15 gene, 2 new variants were predicted to be tolerated. A potentially deleterious variant of the BMP15 gene (L148P) previously associated to POI, was also found in 6% of the Sub-Saharan African controls which suggests that it is a common variant in the African ethnic. No clear association was found between the other tested candidate genes and our POI cohort.Regarding Turner’s Syndrome pregnancies, we can conclude that they are high-risk pregnancies that need of a multidisciplinary follow-up before and during pregnancy.Oocyte cryopreservation represents a new tool to be offered to women at risk of genetic POI to preserve their fertility, but not without previous genetic counselling.Doctorat en Sciences médicales (Médecine)