Follicle development in Turner syndrome ovaries: consideration of the somatic cells

Turner syndrome (TS) is characterized by the absence of one X chromosome and affects approximately 1 in 2,500 newborn women. Most cases show a mosaicism pattern, i.e., cells with a normal pattern of 46XX mixed with cells of altered karyotype. This is associated with accelerated depletion of follicles: <30% of patients with TS have spontaneous puberty, and premature ovarian insufficiency occurs at a mean (±SD) age of 29 years. Some will conceive naturally, but this may occur in only approximately 5% of women with TS, and pregnancy carries an increased risk of miscarriage and potentially life-threatening complications, notably aortic dissection. This very truncated reproductive lifespan with limited opportunity for having a family is a major concern for girls and women with TS and their parents (1Oktay K. Bedoschi G. Berkowitz K. Bronson R. Kashani B. McGovern P. et al.Fertility preservation in women with Turner syndrome: A comprehensive review and practical guidelines.J Pediatr Adolesc Gynecol. 2016; 29: 409Abstract Full Text Full Text PDF PubMed Scopus (105) Google Scholar). Although oocyte donation is the only established medical therapy to enhance the chances of pregnancy in women with TS and premature ovarian insufficiency, the possibility of ovarian tissue cryopreservation (OTC) and subsequent reimplantation offers a fertility preservation option because this can be performed in childhood or adolescence and provides the possibility to store primordial follicles within the ovarian tissue before their premature disappearance. It is generally accepted that OTC is an option mostly suited to patients with mosaic TS rather than those with monosomic karyotypes because patients with mosaic TS are more likely to have a greater number of follicles present (1Oktay K. Bedoschi G. Berkowitz K. Bronson R. Kashani B. McGovern P. et al.Fertility preservation in women with Turner syndrome: A comprehensive review and practical guidelines.J Pediatr Adolesc Gynecol. 2016; 29: 409Abstract Full Text Full Text PDF PubMed Scopus (105) Google Scholar, 2Mamsen L.S. Charkiewicz K. Anderson R.A. Telfer E.E. McLaughlin M. Kelsey T.W. et al.Characterization of follicles in girls and young women with Turner syndrome who underwent ovarian tissue cryopreservation.Fertil Steril. 2019; 111: 1217Abstract Full Text Full Text PDF PubMed Scopus (48) Google Scholar). However, the patient’s karyotype is generally determined from peripheral blood lymphocytes and may not accurately reflect all tissues or indeed all cell types within a tissue, such as the ovary. It is known that granulosa cells in TS ovarian tissue can be monosomic (45X), although surrounding oocytes have the normal complement of two X chromosomes. However, it is not known how common this might be or how this somatic cell composition affects oocyte and follicle development. This study by Peek et al. (3Peek R. Nadesapillai S. Thi Nguyen T.Y. Vassart S. Smeets D. van de Zande G. et al.Assessment of folliculogenesis in ovarian tissue from young patients with Turner syndrome using a murine xenograft model.Fertil Steril. 2023; 120: 371-381Abstract Full Text Full Text PDF Scopus (1) Google Scholar), published in Fertility and Sterility, examines the impact of aneuploid granulosa and stromal cells on the development of immature ovarian follicles containing normal oocytes using a mouse xenograft model with ovarian tissue from patients with mosaic TS. Tissue from 18 patients with mosaic TS aged 5–19 years and 13 similarly aged control patients was prepared and xenografted for five months (3Peek R. Nadesapillai S. Thi Nguyen T.Y. Vassart S. Smeets D. van de Zande G. et al.Assessment of folliculogenesis in ovarian tissue from young patients with Turner syndrome using a murine xenograft model.Fertil Steril. 2023; 120: 371-381Abstract Full Text Full Text PDF Scopus (1) Google Scholar). Using fluorescence in situ hybridization on histologic sections to detect X chromosomes and chromosome 18 as a somatic control, samples taken from nongrafted TS tissue revealed that 97% of oocytes examined were XX but surrounded by predominantly aneuploid (monosomy X) somatic cells. After grafting, it was demonstrated that the composition of the somatic cells did not significantly affect follicle development. Follicles at all stages of development, including antral stages, were present after grafting, but interestingly, the proportion of monosomy X granulosa cells within the growing follicles was significantly reduced, suggesting that as the granulosa cells proliferate, 46XX cells preferentially divide; this is consistent with evidence that 45X cells are more susceptible to apoptosis and have a longer cell cycle (3Peek R. Nadesapillai S. Thi Nguyen T.Y. Vassart S. Smeets D. van de Zande G. et al.Assessment of folliculogenesis in ovarian tissue from young patients with Turner syndrome using a murine xenograft model.Fertil Steril. 2023; 120: 371-381Abstract Full Text Full Text PDF Scopus (1) Google Scholar). This is novel and important information that will be valuable to factor into the analysis of tissue before transplantation. These observations will form the basis of further detailed investigations on how somatic cell composition affects cell communication, the regulation of proliferation and differentiation of these cells, and oocyte quality. The investigators also commented on reduced antimüllerian hormone (AMH) expression (by immunohistochemistry) in granulosa cells from these TS samples, although it increased toward control levels as follicles grew. This observation is at variance with increased AMH concentrations in follicular fluid detected in some TS samples (2Mamsen L.S. Charkiewicz K. Anderson R.A. Telfer E.E. McLaughlin M. Kelsey T.W. et al.Characterization of follicles in girls and young women with Turner syndrome who underwent ovarian tissue cryopreservation.Fertil Steril. 2019; 111: 1217Abstract Full Text Full Text PDF PubMed Scopus (48) Google Scholar) but may reflect analysis of different stages of follicular development. This may be important to consider in the assessment of the potential suitability of such patients for OTC (1Oktay K. Bedoschi G. Berkowitz K. Bronson R. Kashani B. McGovern P. et al.Fertility preservation in women with Turner syndrome: A comprehensive review and practical guidelines.J Pediatr Adolesc Gynecol. 2016; 29: 409Abstract Full Text Full Text PDF PubMed Scopus (105) Google Scholar) as it suggests that the relationship between serum AMH and follicle number may differ from that in normal ovaries. Ultimately, the key to the success of OTC and reimplantation is the number of follicles present at the time of tissue cryopreservation. This article highlights the variability in follicle numbers and the correlation with pubertal stage, and the investigators argue that OTC should be performed before puberty to optimize success. A previous study published in Fertility and Sterility by Mamsen et al. (2Mamsen L.S. Charkiewicz K. Anderson R.A. Telfer E.E. McLaughlin M. Kelsey T.W. et al.Characterization of follicles in girls and young women with Turner syndrome who underwent ovarian tissue cryopreservation.Fertil Steril. 2019; 111: 1217Abstract Full Text Full Text PDF PubMed Scopus (48) Google Scholar) analyzed 15 patients with TS aged 5–22 years who had undergone OTC and showed that 9 of 15 ovarian sample biopsies contained ovarian follicles. Furthermore, where follicles were present, many showed abnormal morphology, which is likely to limit their development. It would be interesting to know whether some of the unusual morphology observed in the Mamsen et al. (2Mamsen L.S. Charkiewicz K. Anderson R.A. Telfer E.E. McLaughlin M. Kelsey T.W. et al.Characterization of follicles in girls and young women with Turner syndrome who underwent ovarian tissue cryopreservation.Fertil Steril. 2019; 111: 1217Abstract Full Text Full Text PDF PubMed Scopus (48) Google Scholar) article was linked to the ploidy composition of the somatic cells; this article by Peek et al. (3Peek R. Nadesapillai S. Thi Nguyen T.Y. Vassart S. Smeets D. van de Zande G. et al.Assessment of folliculogenesis in ovarian tissue from young patients with Turner syndrome using a murine xenograft model.Fertil Steril. 2023; 120: 371-381Abstract Full Text Full Text PDF Scopus (1) Google Scholar) provides a good base for these types of analyses. Although OTC is increasingly performed on young girls with TS, its effectiveness and efficiency in this patient group remain unknown, with no successful pregnancies reported. In a series of 100 patients with TS considering OTC, the majority chose to have the procedure, but only two autotransplantations were recorded, and neither achieved restoration of endocrine ovarian function (4Rodriguez-Wallberg K.A. Sergouniotis F. Nilsson H.P. Lundberg F.E. Trends and outcomes of fertility preservation for girls, adolescents and young adults with Turner syndrome: A prospective cohort study.Front Endocrinol. 2023; 14113524Crossref PubMed Scopus (2) Google Scholar). This contrasts with the very high rate of restoration of ovarian function after OTC and replacement in women who have normal ovaries but are facing exogenous gonadotoxic treatment, generally for cancer. That situation differs markedly from conditions such as TS, where the pathological process is within the ovary and will therefore continue when the cryopreserved ovarian tissue is replaced, with the further insults of cryopreservation and engraftment (the timepoint when most follicles are lost from normal ovaries) superimposed. Current guidelines therefore regard as “research only” the clinical application of OTC for fertility preservation in conditions such as TS (5Anderson R.A. Amant F. Braat D. D’Angelo A. Chuva de Sousa Lopes S.M. et al.ESHRE Guideline Group on Female Fertility PreservationESHRE guideline: Female fertility preservation.Hum Reprod Open. 2020; 2020hoaa052Crossref Google Scholar). There are few studies focused on detailing the developmental potential of this tissue, and other options to use this tissue may also need to be explored, such as harvesting immature oocytes (2Mamsen L.S. Charkiewicz K. Anderson R.A. Telfer E.E. McLaughlin M. Kelsey T.W. et al.Characterization of follicles in girls and young women with Turner syndrome who underwent ovarian tissue cryopreservation.Fertil Steril. 2019; 111: 1217Abstract Full Text Full Text PDF PubMed Scopus (48) Google Scholar) and in vitro growth of immature follicles within this tissue. This study by Peek et al. (3Peek R. Nadesapillai S. Thi Nguyen T.Y. Vassart S. Smeets D. van de Zande G. et al.Assessment of folliculogenesis in ovarian tissue from young patients with Turner syndrome using a murine xenograft model.Fertil Steril. 2023; 120: 371-381Abstract Full Text Full Text PDF Scopus (1) Google Scholar) advances the field and provides important information that should be added to the decision-making process for fertility preservation in girls and young women with TS.