BACKGROUND Infertility is an important side effect of treatments used for cancer and other non-malignant conditions in males. This may be due to the loss of spermatogonial stem cells (SSCs) and/or altered functionality of testicular somatic cells (e.g. Sertoli cells, Leydig cells). Whereas sperm cryopreservation is the first-line procedure to preserve fertility in post-pubertal males, this option does not exist for prepubertal boys. For patients unable to produce sperm and at high risk of losing their fertility, testicular tissue freezing is now proposed as an alternative experimental option to safeguard their fertility. OBJECTIVE AND RATIONALE With this review, we aim to provide an update on clinical practices and experimental methods, as well as to describe patient management inclusion strategies used to preserve and restore the fertility of prepubertal boys at high risk of fertility loss. SEARCH METHODS Based on the expertise of the participating centres and a literature search of the progress in clinical practices, patient management strategies and experimental methods used to preserve and restore the fertility of prepubertal boys at high risk of fertility loss were identified. In addition, a survey was conducted amongst European and North American centres/networks that have published papers on their testicular tissue banking activity. OUTCOMES Since the first publication on murine SSC transplantation in 1994, remarkable progress has been made towards clinical application: cryopreservation protocols for testicular tissue have been developed in animal models and are now offered to patients in clinics as a still experimental procedure. Transplantation methods have been adapted for human testis, and the efficiency and safety of the technique are being evaluated in mouse and primate models. However, important practical, medical and ethical issues must be resolved before fertility restoration can be applied in the clinic.Since the previous survey conducted in 2012, the implementation of testicular tissue cryopreservation as a means to preserve the fertility of prepubertal boys has increased. Data have been collected from 24 co-ordinating centres worldwide, which are actively offering testis tissue cryobanking to safeguard the future fertility of boys. More than 1033 young patients (age range 3 months to 18 years) have already undergone testicular tissue retrieval and storage for fertility preservation. LIMITATIONS, REASONS FOR CAUTION The review does not include the data of all reproductive centres worldwide. Other centres might be offering testicular tissue cryopreservation. Therefore, the numbers might be not representative for the entire field in reproductive medicine and biology worldwide. The key ethical issue regarding fertility preservation in prepubertal boys remains the experimental nature of the intervention. WIDER IMPLICATIONS The revised procedures can be implemented by the multi-disciplinary teams offering and/or developing treatment strategies to preserve the fertility of prepubertal boys who have a high risk of fertility loss. STUDY FUNDING/COMPETING INTEREST(S) The work was funded by ESHRE. None of the authors has a conflict of interest.

Summary Despite the high incidence of male infertility, only 30% of infertile men receive a causative diagnosis. To explore the regulatory mechanisms governing human germ cell function in normal and impaired spermatogenesis (crypto), we performed single-cell RNA sequencing (>30,000 cells). We find major alterations in the crypto spermatogonial compartment with increased numbers of the most undifferentiated spermatogonia (PIWIL4 + ). We also observe a transcriptional switch within the spermatogonial compartment driven by increased and prolonged expression of the transcription factor EGR4. Intriguingly, the EGR4-regulated chromatin-associated transcriptional repressor UTF1 is downregulated at transcriptional and protein levels. This is associated with changes in spermatogonial chromatin structure and fewer A dark spermatogonia, characterized by tightly compacted chromatin and serving as reserve stem cells. These findings suggest that crypto patients are disadvantaged, as fewer cells safeguard their germline’s genetic integrity. These identified spermatogonial regulators will be highly interesting targets to uncover genetic causes of male infertility.

Male infertility affects $7% of men, but its causes remain poorly understood. The most severe form is non-obstructive azoospermia (NOA), which is, in part, caused by an arrest at meiosis. So far, only a few validated disease-associated genes have been reported. To address this gap, we performed whole-exome sequencing in 58 men with unexplained meiotic arrest and identified the same homozygous frameshift variant c.676dup (p.Trp226LeufsTer4) in M1AP, encoding meiosis 1 associated protein, in three unrelated men. This variant most likely results in a truncated protein as shown in vitro by heterologous expression of mutant M1AP. Next, we screened four large cohorts of infertile men and identified three additional individuals carrying homozygous c.676dup and three carrying combinations of this and other likely causal variants in M1AP. Moreover, a homozygous missense variant, c.1166C>T (p.Pro389Leu), segregated with infertility in five men from a consanguineous Turkish family. The common phenotype between all affected men was NOA, but occasionally spermatids and rarely a few spermatozoa in the semen were observed. A similar phenotype has been described for mice with disruption of M1ap. Collectively, these findings demonstrate that mutations in M1AP are a relatively frequent cause of autosomal recessive severe spermatogenic failure and male infertility with strong clinical validity.

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Introduction Cross-sex hormone treatment of gender dysphoria (GD) patients changing from male to female a prerequisite for sex reassignment. For initial physical adaptation, a combined treatment of anti-androgens and estrogens is used. Provided that patients fulfill specific criteria, sex reassignment surgery (SRS) presents the final step toward physical adaptation. However, systematic studies analyzing effects of hormone treatment regimens are lacking. Aim The aim of this study was to compare the effects of three different hormonal treatment strategies regarding endocrinological parameters and testicular histology. Methods Testicular tissues were obtained in a multicenter study from 108 patients on the day of SRS from three clinics following different treatment strategies. Patients either discontinued treatment 6 weeks (clinic A) or 2 weeks (clinic B) prior to SRS or not at all (clinic C). Testicular tissues, ethylenediaminetetraacetic acid blood and questionnaires were obtained on the day of SRS. Main Outcome Measures Blood hormone and intratesticular testosterone (ITT) levels were measured. Testicular weight and histology were evaluated and the percentage of luteinizing hormone/choriogonadotropin receptor (LHCGR) positive cells was determined. Results According to the questionnaires, patients showed desired phenotypical changes including breast growth (75%) and smooth skin (32%). While patients from clinics A and B presented with rather virilized hormonal levels, patients from clinic C showed generally feminized blood serum levels. Histological evaluation revealed highly heterogeneous results with about 24% of patients presenting with qualitatively normal spermatogenesis. In accordance with serum endocrine profile, ITT levels were lowest in clinic C and correlated with testosterone and free testosterone, but not with the spermatogenic state. The percentage of LHCGR-positive cells and ITT levels did not correlate. Conclusion Only patients that did not discontinue hormonal treatment showed feminized blood levels on the day of SRS. The ones who stopped re-virilized quickly. Interestingly, testicular histology was highly heterogeneous irrespective of the treatment strategy, a phenomenon that requires further investigation.

Background The most common sex chromosomal aneuploidy in males is Klinefelter syndrome, which is characterized by at least one supernumerary X chromosome. While these men have long been considered infertile, focal spermatogenesis can be observed in some patients, and sperm can be surgically retrieved and used for artificial reproductive techniques. Although these gametes can be used for fertility treatments, little is known about the molecular biology of the germline in Klinefelter men. Specifically, it is unclear if germ cells in Klinefelter syndrome correctly establish the androgenetic DNA methylation profile and transcriptome. This is due to the low number of germ cells in the Klinefelter testes available for analysis. Results Here, we overcame these difficulties and successfully investigated the epigenetic and transcriptional profiles of germ cells in Klinefelter patients employing deep bisulfite sequencing and single-cell RNA sequencing. On the transcriptional level, the germ cells from Klinefelter men clustered together with the differentiation stages of normal spermatogenesis. Klinefelter germ cells showed a normal DNA methylation profile of selected germ cell-specific markers compared with spermatogonia and sperm from men with normal spermatogenesis. However, germ cells from Klinefelter patients showed variations in the DNA methylation of imprinted regions. Conclusions These data indicate that Klinefelter germ cells have a normal transcriptome but might present aberrant imprinting, showing impairment in germ cell development that goes beyond mere germ cell loss. Electronic supplementary material The online version of this article (10.1186/s13148-019-0720-3) contains supplementary material, which is available to authorized users.

Patients with gender dysphoria are offered cross-sex hormone therapy and sex reassignment surgery to achieve the transition between the sex assigned at birth and gender identity. According to international guidelines, cross-sex hormone therapy in trans-women should lead to a psychologically and physiologically healthy body with feminized serum hormone levels, resulting in suppression of spermatogenesis. However, in a recently published multi-center study, we discovered a high proportion of patients with male serum hormone levels and qualitatively intact spermatogenesis on the day of sex reassignment surgery. The objective of this study was to review the content of 11 publications that focus on the influence of cross-sex hormone therapy on testicular morphology. These publications were identified based on a PubMed search for the key words transgender/transsexual/gender dysphoria in male-to-female persons, cross-sex hormone therapy, and testicular tissues. Whereas three publications described a marked reduction of the spermatogenic level in all patients examined, eight publications reported inconsistent results. Histological analyses showed highly variable outcomes from qualitatively normal spermatogenesis and undisturbed Leydig/Sertoli cell morphology to full testicular regression with severe cellular damage and hyalinization. Explanations for these heterogeneous findings include insufficient cross-sex hormone therapy regarding dosage or duration. As complete spermatogenesis is associated with virilized serum hormone levels, these patients may face challenges especially after sex reassignment surgery in adjusting to the abruptly established hypogonadal state following removal of the testes. These findings also suggest that contraception should be discussed, and fertility preservation should be offered during/prior to cross-sex hormone therapy. There is a need for more individualized and better-controlled cross-sex hormone therapy and post-treatment regimens. Evidence-based guidelines for attending clinicians need to be established in order to deliver the most appropriate care.

Background In the past 15 years, numerous studies have described aberrant DNA methylation of imprinted genes (e.g. MEST and H19) in sperm of oligozoospermic men, but the prevalence and genomic extent of abnormal methylation patterns have remained unknown. Results Using deep bisulfite sequencing (DBS), we screened swim-up sperm samples from 40 normozoospermic and 93 patients diagnosed as oligoasthenoteratozoospermic, oligoteratozoospermic or oligozoospermic, which are termed OATs throughout the manuscript, for H19 and MEST methylation. Based on this screening, we defined three patient groups: normal controls (NC), abnormally methylated oligozoospermic (AMO; n = 7) and normally methylated oligozoospermic (NMO; n = 86). Whole-genome bisulfite sequencing (WGBS) of five NC and five AMO samples revealed abnormal methylation levels of all 50 imprinting control regions in each AMO sample. To investigate whether this finding reflected epigenetic germline mosaicism or the presence of residual somatic DNA, we made a genome-wide inventory of soma-germ cell-specific DNA methylation. We found that > 2000 germ cell-specific genes are promoter-methylated in blood and that AMO samples had abnormal methylation levels at these genes, consistent with the presence of somatic cell DNA. The comparison between the five NC and six NMO samples revealed 19 differentially methylated regions (DMRs), none of which could be validated in an independent cohort of 40 men. Previous studies reported a higher incidence of epimutations at single CpG sites in the CTCF-binding region 6 of H19 in infertile patients. DBS analysis of this locus, however, revealed an association between DNA methylation levels and genotype (rs2071094), but not fertility phenotype. Conclusions Our results suggest that somatic DNA contamination and genetic variation confound methylation studies in sperm of infertile men. While we cannot exclude the existence of rare patients with slightly abnormal sperm methylation at non-recurrent CpG sites, the prevalence of aberrant methylation in swim-up purified sperm of infertile men has likely been overestimated, which is reassuring for patients undergoing assisted reproduction.