In the typical developing gonad, cells with XY chromosomes become masculinised into Sertoli cells, leading to the development of the bipotential gonad into testes. Disruptions to sex determining genes and transcription factors, or XX chromosome complement, typically leads to failure of Sertoli cell development. In the study of sex determination, upregulation of specific genes in animal models has sucessfully led to male factor expression in XX cells in some animals but not in others. There have been no previous reports of XX cells expressing male factors or Sertoli characteristics in the human.
We report a phenotypically normal boy with a 46,XX/46,XY tetragametic chimeric karyotype. Chromosomal microarray confirmed four distinct SNP profiles in the one individual, ie. fusion of four disctinct gametes (X, X, Y, Y). He commenced puberty at age 13, and spontaneously reached Tanner stage 3 puberty with 10 mL testes. Unfortunately he began to show testicular failure from age 15, with FSH rising to 28 u/L and testes reducing to 6mL bilaterally.
Ejaculate was collected for semen analysis and storage, but found azoospermia. The patient then underwent microdissection testicular sperm extraction (microTESE) as the most advanced technique currently available to optimise preservation of any remaining fertility, along with testicular biopsy for gonadal analysis. MicroTESE surgery is becoming the gold standard for sperm retrieval in azoospermia, with key applications in individuals with disorders of sex development, and was successful in finding sperm for storage.
Histologic and FISH cytogenetic analysis of the testicular biopsy revealed very interesting results, confirming for the first time the ability of XX cells to masculinise into Sertoli cells in the human testis. As the peripheral blood XX cells had a normal profile on microarray, it was assumed the testicular XX cells also contained a normal genetic complement. This suggests possible endocrine or other epigenetic influences on the fundamental mechanism of sex determination, as opposed to a process solely dependent on the endogenous DNA profile of the individual cell nucleus. RNA analysis of the XX Sertoli cells is underway.
Here we show for the first time that that XX cells are able to masculinise into phenotypically normal Sertoli cells in the human testis, illuminating new possible mechanisms of paracrine or epigenetic effects on sex determination. We also show that paediatric use of microTESE surgery can be successful in cases of azoospermia, and may significantly improve the fertility prospects for many young people with DSD.
19 Sep 2019 - 21 Sep 2019