Why are some patients with 45,X Turner syndrome fertile? A young girl with classical 45,X Turner syndrome and a cryptic mosaicism in the ovary

Objective: To report a case of a young girl initially diagnosed with exclusively 45,X Turner syndrome (TS), but with a cryptic mosaicism in the ovary.

Design: Case report.

Setting: Radboud University Medical Center in the Netherlands.

Patient(s): A 14-year-old girl with TS showing an exclusively 45,X cell line in lymphocytes, buccal cells, and urine cells in the presence of ovarian follicles.

Intervention(s): Laparoscopic unilateral oophorectomy was performed to obtain ovarian cortex tissue for fertility preservation purposes. One cortex fragment was used to determine the number of follicles by serial sectioning and staining, to perform fluorescence in situ hybridization (FISH) analysis and an in vitro growth (IVG) assay.

Main outcome measure(s): FISH analysis of ovarian cells and the capacity of unilaminar follicles to develop to secondary follicles.

Result(s): FISH analysis revealed that most oocytes had a normal tetraploid X chromosomal content, the stromal cell compartment had both 45,X and 47,XXX cell lines, and all follicular granulosa cells had a 45,X karyotype. IVG assay showed that unilaminar follicles were capable of maturing to secondary follicles, but that the granulosa layers and membrana granulosa were distorted.

Conclusion(s): We report a case where follicles were found in a girl with monosomic TS, in the presence of a cryptic mosaicism. Karyotyping of extraovarian cells was not predictive of the karyotype of ovarian cells in the same patient. Despite the presence of normal oocytes, our observation that all analyzed follicles contained exclusively 45,X granulosa cells embedded in mosaic 45,X/47,XXX stromal tissue may have functional consequences for follicular development.

Clinical trial registration number: NCT03381300.