Germ cell loss in Klinefelter syndrome: When and why?

X-Linked Gene Dosage and SOX2 Act as Key Roadblocks for Human Germ Cell Specification in Klinefelter Syndrome

Klinefelter syndrome (KS), characterized by the presence of at least one extra X-chromosome, is a common cause of male infertility. However, the mechanism underlying the failure of germline specification is not well studied. Intriguingly, the differentiation efficiency of female human pluripotent stem cells (hPSCs) is often lower than that of male. This study investigates how X-linked gene dosage affects human primordial germ cell-like cells (hPGCLCs) specification in both healthy and diseased conditions. This work reveals that X-linked genes play a multifaceted role against the fate competency to hPGCLCs, with escape genes IGSF1 and CHRDL1 inhibiting the TGF-beta/Activin A and BMP pathways, respectively. Notably, this work identifies a previously unrecognized role of SOX2, upregulated by the escape gene USP9X, elucidating a species-specific function in the mammalian germline. The USP9X-SOX2 regulatory axis profoundly influenced cellular metabolism, mitochondrial morphology, and progenitor competence in hPGCLCs specification. Furthermore, the inability to downregulate SOX2 and upregulate SOX17 in response to BMP signaling impedes downstream gene activation due to motif binding competition. These findings shed novel insights into the human germline specification by elucidating the divergent roles of SOX2 versus SOX17 in mammals, influenced by X-linked gene dosage effects. These results offer potential applications for improving the induction efficiency of hPGCLCs, facilitating disease mechanistic studies.

Testicular mosaicism in non-mosaic postpubertal Klinefelter patients with focal spermatogenesis and in non-mosaic prepubertal Klinefelter boys

STUDY QUESTION

Do testis-specific cells have a normal karyotype in non-mosaic postpubertal Klinefelter syndrome (KS) patients with focal spermatogenesis and in non-mosaic prepubertal KS boys?

SUMMARY ANSWER

Spermatogonia have a 46, XY karyotype, and Sertoli cells surrounding these spermatogonia in postpubertal patients also have a 46, XY karyotype, whereas, in prepubertal KS boys, Sertoli cells surrounding the spermatogonia still have a 47, XXY karyotype.

WHAT IS KNOWN ALREADY

A significant proportion of patients with non-mosaic KS can have children by using assisted reproductive techniques thanks to focal spermatogenesis. However, the karyotype of the cells that are able to support focal spermatogenesis has not been revealed.

STUDY DESIGN, SIZE, DURATION

Testicular biopsy samples from non-mosaic KS patients were included in the study. Karyotyping for sex chromosomes in testis-specific cells was performed by immunohistochemical analysis of inactive X (Xi) chromosome and/or fluorescent in situ hybridization (FISH) analysis of chromosomes 18, X, and Y.

PARTICIPANTS/MATERIALS, SETTING, METHODS

A total of 22 KS patients (17 postpubertal and 5 prepubertal) who were non-mosaic according to lymphocyte karyotype analysis, were included in the study. After tissue processing, paraffin embedding, and sectioning, the following primary antibodies were used for cell-specific analysis and Xi detection; one section was stained with MAGE A4 for spermatogonia, SOX9 for Sertoli cells, and H3K27me3 for Xi; the other one was stained with CYP17A1 for Leydig cells, ACTA2 for peritubular myoid cells, and H3K27me3 for Xi. Xi negative (Xi-) somatic cells (i.e. Sertoli cells, Leydig cells, and peritubular myoid cells) were evaluated as having the 46, XY karyotype; Xi positive (Xi+) somatic cells were evaluated as having the 47, XXY. FISH stain for chromosomes 18, X, and Y was performed on the same sections to investigate the karyotype of spermatogonia and to validate the immunohistochemistry results for somatic cells.

MAIN RESULTS AND THE ROLE OF CHANCE

According to our data, all spermatogonia in both postpubertal and prepubertal non-mosaic KS patients seem to have 46, XY karyotype. However, while the Sertoli cells surrounding spermatogonia in postpubertal samples also had a 46, XY karyotype, the Sertoli cells surrounding spermatogonia in prepubertal samples had a 47, XXY karyotype. In addition, while the Sertoli cells in some of the Sertoli cell-only tubules had 46, XY karyotype, the Sertoli cells in some of the other Sertoli cell-only tubules had 47, XXY karyotype in postpubertal samples. In contrast to the postpubertal samples, Sertoli cells in all tubules in the prepubertal samples had the 47, XXY karyotype. Our data also suggest that germ cells lose the extra X chromosome during embryonic, fetal, or neonatal life, while Sertoli cells lose it around puberty. Peritubular myoid cells and Leydig cells may also be mosaic in both postpubertal patients and prepubertal boys, but it requires further investigation.

LIMITATIONS, REASONS FOR CAUTION

The number of prepubertal testicle samples containing spermatogonia is limited, so more samples are needed for a definitive conclusion. The fact that not all the cell nuclei coincide with the section plane limits the accurate detection of X chromosomes by immunohistochemistry and FISH in some cells. To overcome this limitation, X chromosome analysis could be performed by different techniques on intact cells isolated from fresh tissue. Additionally, there is no evidence that X chromosome inactivation reoccurs after activation of the Xi during germ cell migration during embryogenesis, limiting the prediction of X chromosome content in germ cells by H3K27me3.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings will lay the groundwork for new clinically important studies on exactly when and by which mechanism an extra X chromosome is lost in spermatogonia and Sertoli cells.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by The Scientific and Technological Research Council of Türkiye (TUBITAK) (2219 - International Postdoctoral Research Fellowship Program for Turkish Citizens) and the Strategic Research Program (SRP89) from the Vrije Universiteit Brussel. The authors declare no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Klinefelter syndrome: etiology and clinical considerations in male infertility†

Klinefelter syndrome (KS) is the most prevalent chromosomal disorder occurring in males. It is defined by an additional X chromosome, 47,XXY, resulting from errors in chromosomal segregation during parental gametogenesis. A major phenotype is impaired reproductive function, in the form of low testosterone and infertility. This review comprehensively examines the genetic and physiological factors contributing to infertility in KS, in addition to emergent assisted reproductive technologies, and the unique ethical challenges KS patients face when seeking infertility treatment. The pathology underlying KS is increased susceptibility for meiotic errors during spermatogenesis, resulting in aneuploid or even polyploid gametes. Specific genetic elements potentiating this susceptibility include polymorphisms in checkpoint genes regulating chromosomal synapsis and segregation. Physiologically, the additional sex chromosome also alters testicular endocrinology and metabolism by dysregulating interstitial and Sertoli cell function, collectively impairing normal sperm development. Additionally, epigenetic modifications like aberrant DNA methylation are being increasingly implicated in these disruptions. We also discuss assisted reproductive approaches leveraged in infertility management for KS patients. Application of assisted reproductive approaches, along with deep comprehension of the meiotic and endocrine disturbances precipitated by supernumerary X chromosomes, shows promise in enabling biological parenthood for KS individuals. This will require continued multidisciplinary collaboration between experts with background of genetics, physiology, ethics, and clinical reproductive medicine.

In Vitro Generation of Haploid Germ Cells from Human XY and XXY Immature Testes in a 3D Organoid System

Increasing survival rates of children following cancer treatment have resulted in a significant population of adult survivors with the common side effect of infertility. Additionally, the availability of genetic testing has identified Klinefelter syndrome (classic 47,XXY) as the cause of future male infertility for a significant number of prepubertal patients. This study explores new spermatogonia stem cell (SSC)-based fertility therapies to meet the needs of these patients. Testicular cells were isolated from cryopreserved human testes tissue stored from XY and XXY prepubertal patients and propagated in a two-dimensional culture. Cells were then incorporated into a 3D human testicular organoid (HTO) system. During a 3-week culture period, HTOs maintained their structure, viability, and metabolic activity. Cell-specific PCR and flow cytometry markers identified undifferentiated spermatogonia, Sertoli, Leydig, and peritubular cells within the HTOs. Testosterone was produced by the HTOs both with and without hCG stimulation. Upregulation of postmeiotic germ cell markers was detected after 23 days in culture. Fluorescence in situ hybridization (FISH) of chromosomes X, Y, and 18 identified haploid cells in the in vitro differentiated HTOs. Thus, 3D HTOs were successfully generated from isolated immature human testicular cells from both euploid (XY) and Klinefelter (XXY) patients, supporting androgen production and germ cell differentiation in vitro.

Individuals with numerical and structural variations of sex chromosomes: interdisciplinary management with focus on fertility potential

Diagnosis and management of individuals who have differences of sex development (DSD) due to numerical or structural variations of sex chromosomes (NSVSC) remains challenging. Girls who have Turner syndrome (45X) may present with varying phenotypic features, from classical/severe to minor, and some remain undiagnosed. Boys and girls who have 45,X/46,XY chromosomal mosaicism may have Turner syndrome-like features and short stature; therefore, unexplained short stature during childhood requires karyotype analysis in both sexes, particularly if characteristic features or atypical genitalia are present. Many individuals with Klinefelter syndrome (47XXY) remain undiagnosed or are only diagnosed as adults due to fertility problems. Newborn screening by heel prick tests could potentially identify sex chromosome variations but would have ethical and financial implications, and in-depth cost-benefit analyses are needed before nationwide screening can be introduced. Most individuals who have NSVSC have lifelong co-morbidities and healthcare should be holistic, personalized and centralized, with a focus on information, psychosocial support and shared decision-making. Fertility potential should be assessed individually and discussed at an appropriate age. Oocyte or ovarian tissue cryopreservation is possible in some women who have Turner syndrome and live births have been reported following assisted reproductive technology (ART). Testicular sperm cell extraction (TESE) is possible in some men who have 45,X/46,XY mosaicism, but there is no established protocol and no reported fathering of children. Some men with Klinefelter syndrome can now father a child following TESE and ART, with multiple reports of healthy live births. Children who have NSVSC, their parents and DSD team members need to address possibilities and ethical questions relating to potential fertility preservation, with guidelines and international studies still needed.

The Klinefelter Syndrome and Testicular Sperm Retrieval Outcomes

Klinefelter syndrome (KS), caused by the presence of an extra X chromosome, is the most prevalent chromosomal sexual anomaly, with an estimated incidence of 1:500/1000 per male live birth (karyotype 47,XXY). High stature, tiny testicles, small penis, gynecomastia, feminine body proportions and hair, visceral obesity, and testicular failure are all symptoms of KS. Endocrine (osteoporosis, obesity, diabetes), musculoskeletal, cardiovascular, autoimmune disorders, cancer, neurocognitive disabilities, and infertility are also outcomes of KS. Causal theories are discussed in addition to hormonal characteristics and testicular histology. The retrieval of spermatozoa from the testicles for subsequent use in assisted reproduction treatments is discussed in the final sections. Despite testicular atrophy, reproductive treatments allow excellent results, with rates of 40–60% of spermatozoa recovery, 60% of clinical pregnancy, and 50% of newborns. This is followed by a review on the predictive factors for successful sperm retrieval. The risks of passing on the genetic defect to children are also discussed. Although the risk is low (0.63%) when compared to the general population (0.5–1%), patients should be informed about embryo selection through pre-implantation genetic testing (avoids clinical termination of pregnancy). Finally, readers are directed to a number of reviews where they can enhance their understanding of comprehensive diagnosis, clinical care, and fertility preservation.

Examining potential mechanisms of testicular fibrosis in Klinefelter Syndrome: A review of current understanding

BACKGROUND

Men with Klinefelter Syndrome develop some degree of seminiferous tubule degeneration, hyalinization, and fibrosis by adulthood. However, the pathophysiology surrounding testicular fibrosis in Klinefelter Syndrome patients remains incompletely understood.

OBJECTIVES

To perform a systematic review of literature studying the mechanisms of fibrosis initiation or propagation in Klinefelter Syndrome testes.

MATERIALS/METHODS

PubMed was searched systematically for articles specific to Klinefelter Syndrome and the process of fibrosis. Articles that did not contain original data or specifically addressed the target material were excluded. Additional references were extracted when pertinent from the reference lists of included studies.

RESULTS

Primary search yielded 139 articles for abstract review, which was narrowed to 16 for full-text review. Following full-text review, eight contained original data and met topic criteria, with one paper added from reference review for a total of nine papers.

DISCUSSION

The date range for included papers was 1992-2022. The proposed mechanisms of fibrosis mainly were centered around the impact of altered Sertoli cells on germ cells, the hormonal impact on Leydig cells, the inflammation mediated by mast cells, or the fibrous extracellular matrix deposition by peritubular myoid cells. Additionally, discussions of the role of the altered microvasculature and the specific proteins involved in the blood-testis barrier or the seminiferous tubule architecture are reviewed. Recent papers have incorporated advanced sequencing and offer future directions for targeted gene expression analysis. Still, much of the published data consists solely of immunohistological assessment by age range, creating difficulties in extrapolating causality.

CONCLUSION

The specific initiating factors of fibrosis of the seminiferous tubules and the propagation mechanisms unique to Klinefelter Syndrome remain incompletely understood with a relative paucity of data. Nonetheless, academic interest is increasing in this field as it may further elucidate the pathophysiology behind Klinefelter syndrome.

Testicular microlithiasis in paediatric patients with Klinefelter syndrome from infancy till adolescence: early start of degenerative process in the testes-preliminary results

To present the results of testicular ultrasonography supported by clinical and hormonal aspects in paediatric patients with Klinefelter syndrome (KS). Prospective analysis of medical files of 20 patients diagnosed with KS between 2016 and 2022. Assessed data included analysis of causes of referral, ultrasound, and clinical characterisation with hormonal evaluation of serum FSH, LH, testosterone, inhibin B, and anti-Müllerian hormone. Non-mosaic Klinefelter syndrome (47, XXY) was diagnosed in 65% of cases (13/20) by the geneticist (including 7 cases prenatally), in 25% (5/20) by the endocrinologist and in 10% (2/20) by the hematologist. Ultrasound assessment revealed bilateral testicular microlithiasis (TM) in all patients. The youngest KS patient with TM was 3 months old. TM patterns have not changed during follow-ups of up to 6 years in any of the patients. In all KS patients markedly reduced echogenicity and in pubertal KS patients, also irregular echostructure of the testes was observed. The hormonal patterns observed in the study group were typical for those already described in KS. Sertoli and Leydig cell function was intact in prepubertal patients and deteriorated after the start of puberty.

CONCLUSION

Although the degenerative process in the testicular tissue starts very early in the testes in KS and is reflected in morphological changes seen in ultrasonography, Sertoli and Leydig cell hormonal function is normal in prepubertal KS patients.

WHAT IS KNOWN

• So far, normal Leydig and Sertoli cell function was observed in infants and prepubertal KS patients.

WHAT IS NEW

• The morphological changes in the testes in KS may already be seen in early infancy.

Transcriptomic differences between fibrotic and non-fibrotic testicular tissue reveal possible key players in Klinefelter syndrome-related testicular fibrosis

Klinefelter syndrome (KS; 47,XXY) affects 1-2 in 1000 males. Most men with KS suffer from an early germ cell loss and testicular fibrosis from puberty onwards. Mechanisms responsible for these processes remain unknown. Previous genomics studies on testis tissue from men with KS focused on germ cell loss, while a transcriptomic analysis focused on testicular fibrosis has not yet been performed. This study aimed to identify factors involved in the fibrotic remodelling of KS testes by analysing the transcriptome of fibrotic and non-fibrotic testicular tissue. RNA sequencing was performed to compare the genes expressed in testicular samples with (KS and testis atrophy) and without (Sertoli cell-only syndrome and fertile controls) fibrosis (n = 5, each). Additionally, differentially expressed genes (DEGs) between KS and testis atrophy samples were studied to reveal KS-specific fibrotic genes. DEGs were considered significant when p < 0.01 and log2FC > 2. Next, downstream analyses (GO and KEGG) were performed. Lastly, RNA in situ hybridization was performed to validate the results. The first analysis (fibrotic vs non-fibrotic) resulted in 734 significant DEGs (167 up- and 567 down-regulated). Genes involved in the extracellular structure organization (e.g. VCAM1) were found up-regulated. KEGG analysis showed an up-regulation of genes involved in the TGF-β pathway. The KS vs testis atrophy analysis resulted in 539 significant DEGs (59 up- and 480 down-regulated). Chronic inflammatory response genes were found up-regulated. The overlap of X-linked DEGs from the two analyses revealed three genes: matrix-remodelling associated 5 (MXRA5), doublecortin (DCX) and variable charge X-Linked 3B (VCX3B). RNA in situ hybridization showed an overexpression of VCAM1, MXRA5 and DCX within the fibrotic group compared with the non-fibrotic group. To summarize, this study revealed DEGs between fibrotic and non-fibrotic testis tissue, including VCAM1. In addition, X-linked fibrotic genes were revealed, e.g. MXRA5, DCX and VCX3B. Their potential role in KS-related testicular fibrosis needs further study.

Testicular Tissue Banking for Fertility Preservation in Young Boys: Which Patients Should Be Included?

Due to the growing number of young patients at risk of germ cell loss, there is a need to preserve spermatogonial stem cells for patients who are not able to bank spermatozoa. Worldwide, more and more clinics are implementing testicular tissue (TT) banking programs, making it a novel, yet indispensable, discipline in the field of fertility preservation. Previously, TT cryopreservation was predominantly offered to young cancer patients before starting gonadotoxic chemo- or radiotherapy. Nowadays, most centers also bank TT from patients with non-malignant conditions who need gonadotoxic conditioning therapy prior to hematopoietic stem cell (HSCT) or bone marrow transplantation (BMT). Additionally, some centers include patients who suffer from genetic or developmental disorders associated with prepubertal germ cell loss or patients who already had a previous round of chemo- or radiotherapy. It is important to note that the surgical removal of TT is an invasive procedure. Moreover, TT cryopreservation is still considered experimental as restoration methods are not yet clinically available. For this reason, TT banking should preferably only be offered to patients who are at significant risk of becoming infertile. In our view, TT cryopreservation is recommended for young cancer patients in need of high-risk chemo- and/or radiotherapy, regardless of previous low-risk treatment. Likewise, TT banking is advised for patients with non-malignant disorders such as sickle cell disease, beta-thalassemia, and bone marrow failure, who need high-risk conditioning therapy before HSCT/BMT. TT retrieval during orchidopexy is also proposed for patients with bilateral cryptorchidism. Since patients with a medium- to low-risk treatment generally maintain their fertility, TT banking is not advised for this group. Also for Klinefelter patients, TT banking is not recommended as it does not give better outcomes than a testicular sperm extraction later in life.

Infertility considerations in klinefelter syndrome: From origin to management

Klinefelter syndrome (KS) is defined as the presence of one or more extra "X" chromosome in a male patient. It affects approximately 1 in 600 newborn males and the most common chromosomal abnormality, leading to male hypogonadism and infertility. There is a lack of data supporting best practices for KS patients' care. In this paper we review controversial issues in KS research ranging from mechanisms of variation in KS phenotype to abnormalities resulting in reduced sperm production to successful sperm retrieval disparities after testicular sperm extraction (TESE). Translation to live birth and offspring health is also examined. Finally, medical therapies used to optimize the hormonal status and chances of fertility in KS patients are reviewed. We will also discuss the experimental spermatogonial stem cell (SSC) treatments, which are considered the future for TESE negative patients.