(60) Kleinfelter Mosaicism in a Phenotypic Female: A Case Report

Background: Kleinfelter Mosaicism is a rare phenomenon, with only about 20 cases of 47, XXY/ 46, XX mosaicism reported in the literature. Of these, only two patients were phenotypically female, lending little data to predict the risk of germ cell tumors or the status of future fertility for our phenotypically female patient. This poster aims to review the recorded cases of 47, XXY/ 46, XX mosaicism to increase awareness of this rare condition and to discuss the relationship of this condition to other differences in sexual development in order to assess the specific health risks our patient may face.

Case: Our patient presented as a 10 month old female who had an abnormal NIPT indicating an abnormality of the Y chromosome. A karyotype analysis at age 4 weeks revealed 47, XXY [5] / 46, XX [45] and subsequent FISH analysis for the SRY gene revealed the presence of the Y chromosome in 11.5% of nuclei. The patient had normal appearing external female genitalia on physical exam and had no other concerns with health or development. Labs at age 6 months revealed normal hormone levels and U/S identified a small uterus and a candidate for a right ovary, but did not visualize a left ovary. Parents opted for no intervention at this time and they were advised to request that her pediatrician provide biannual abdominal exams to assess for masses and to return to the Differences in Sexual Development clinic every 3-4 years for further evaluation.

Comments: Kleinfelter Syndrome as a whole is associated with higher rates of germ cell tumors than the general population. The other reported cases of 47, XXY / 46, XX type of Kleinfelter mosaicism share similarities with both ovotesticular DSD (OT-DSD) and complete gonadal dysgenesis (OT-DSD). Both of these conditions have different risks associated with germ cell tumors and different fertility profiles. All but two of these cases, however, developed as phenotypic males, leaving a gap in the medical community's understanding of how our patient might develop.