Jann-Frederik Cremers

University of Münster | WWU · Centre of Reproductive Medicine and Andrology

The vasectomy is a safe and effective method of contraception for men. Up to 6% of men who underwent vasectomy have a renewed child wish. Microsurgical vasectomy reversal (VR) in men, microsurgical epididymal sperm aspiration (MESA), or testicular sperm extraction (TESE) in men plus assisted reproductive technology (ART) in the female partner as we...

Aim This official guideline was published and coordinated by the DGGG, OEGGG and SGGG with the involvement of other medical societies. The aim was to provide a consensus-based overview of non-hormonal forms of contraception based on an evaluation of the relevant literature. The first part of these summarized statements and recommendations presents...

Aim This official guideline was published and coordinated by the DGGG, OEGGG and SGGG with the involvement of other medical societies. The aim was to provide a consensus-based overview of non-hormonal forms of contraception based on an evaluation of the relevant literature. The first part of these summarized statements and recommendations presents...

The sterilization of men (vasectomy) is so far the only contraceptive method apart from the use of condoms that is available to men. It is based on a permanent surgical bilateral severance of the vas deferens and should therefore be reserved for men who do not (or no longer) want children. The contraceptive safety is classified as very good with a...

Background and objective: While international guidelines advocate for a multifaceted approach to treating erectile dysfunction (ED) involving physical activities, psychological support, and education, structured programs are infrequent. To address this gap, an appbased therapy was developed, offering a systematic approach. This randomized, singlebl...

This study examines spermatogonial numbers in testicular samples from 43 prepubertal patients undergoing haematopoietic stem cell transplantation (HSCT). High‐dose chemotherapy and/or radiation during HSCT can impact spermatogenesis requiring fertility preservation. Results show that 49% of patients have decreased and 19% severely depleted spermato...

Sperm production and function require the correct establishment of DNA methylation patterns in the germline. Here, we examined the genome-wide DNA methylation changes during human spermatogenesis and its alterations in disturbed spermatogenesis. We found that spermatogenesis is associated with remodeling of the methylome, comprising a global declin...

Background and objective The longitudinal efficacy and clinical utility of Testosterone Therapy (TTh) in ameliorating functional hypogonadism (FH) remain contentious, with long‐term data being scarce. To address this lacuna, a comprehensive long‐term registry study, stratifying patients across a spectrum of hypogonadal etiologies, offers a robust i...

STUDY QUESTION Are there subgroups among patients with cryptozoospermia pointing to distinct etiologies? SUMMARY ANSWER We reveal two distinct subgroups of cryptozoospermic (Crypto) patients based on testicular tissue composition, testicular volume, and FSH levels. WHAT IS KNOWN ALREADY Cryptozoospermic patients present with a sperm concentration...

Plastic induration of the penis (PIP, Peyronie’s disease) is an acquired and chronic disease of the penis, which is characterized by penile pain, distortion and deformation of the penis as well as the resulting impairments in sexual activity of the patient. The most probable causes are microtrauma and macrotrauma within the tunica albuginea of the...

Sperm production and function require the correct establishment of DNA methylation patterns in the germline. Here, we examined the genome-wide DNA methylation changes during human spermatogenesis and its alterations in disturbed spermatogenesis. We found that spermatogenesis is associated with remodeling of the methylome, comprising a global-declin...

Background Little is known about patients’ pre‐treatment expectations in Peyronie's disease (PD). Objective To evaluate in detail patients’ expectations of conservative therapy and surgery. Patients and methods This multi‐center study prospectively enrolled 317 PD patients, who were scheduled to receive conservative therapy or surgery between 201...

The process of spermatogenesis—when germ cells differentiate into sperm—is tightly regulated, and misregulation in gene expression is likely to be involved in the physiopathology of male infertility. The testis is one of the most transcriptionally rich tissues; nevertheless, the specific gene expression changes occurring during spermatogenesis are...

Study question Can cryptozoospermic patients be sub classified based on clinical parameters? Summary answer Cryptozoospermic patients can be subdivided in two subgroups based on the histological phenotype of their testicular tissues, testicular volume and FSH levels. What is known already Cryptozoospermia is a severe form of oligozoospermia in wh...

Background Crypto- and azoospermia (very few/no sperm in the semen) are main contributors to male factor infertility. Genetic causes for spermatogenic failure (SPGF) include Klinefelter syndrome and Y-chromosomal azoospermia factor microdeletions, and CFTR mutations for obstructive azoospermia (OA). However, the majority of cases remain unexplained...

Background: Transrectal ultrasound(TRUS) parameters are not standardized, especially in men of reproductive age. Hence, the European Academy of Andrology(EAA) promoted a multicenter study to assess the TRUS characteristics of healthy-fertile men(HFM) to establish normative parameters. Objectives: To report and discuss the prostate and seminal ve...

Context Testosterone (T) therapy of hypogonadal men requires stable kinetics, tolerance and attenuation of symptoms. Both intramuscular injections of the long-acting ester T undecanoate (TU) and transdermal application of T gel offer a proven efficacy. As T has marked effects on hematopoiesis, an elevation of hematocrit has to be considered during...

Cell differentiation processes are highly dependent on cell stage-specific gene expression, including timely production of alternatively spliced transcripts. One of the most transcriptionally rich tissues is the testis, where the process of spermatogenesis, or generation of male gametes, takes place. To date, germ cell-specific transcriptome dynami...

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...

Background Several studies have reported an association between male infertility and aberrant sperm DNA methylation patterns, in particular in imprinted genes. In a recent investigation based on whole methylome and deep bisulfite sequencing, we have not found any evidence for such an association, but have demonstrated that somatic DNA contamination...

Study question Do DNA methylation changes occur in testicular germ cells (TGCs) from patients with impaired spermatogenesis? Summary answer TGCs from men with cryptozoospermia exhibit altered DNA methylation levels at several genomic regions, many of which are associated with genes involved in spermatogenesis. What is known already In the last 15...

Study question: Do males with the rare lysosomal storage disease infantile nephropathic cystinosis (INC) have a chance of biological fatherhood? Summary answer: Cryostorage of semen could be an option for approximately 20% of young males with INC, with surgical sperm retrieval from the centre of the testes providing additional opportunities for...

Despite the high incidence of male infertility, about 70% of infertile men do not receive a causative diagnosis. To gain insights into the regulatory mechanisms governing human germ cell function in normal and impaired spermatogenesis (cryptozoospermic patients, crypto), we combined single cell RNA sequencing (>30.000 cells), proteome, and histomor...

Background Scrotal colour‐Doppler ultrasound(CDUS) still suffers from lack of standardization. Hence, the European Academy of Andrology(EAA) has promoted a multicenter study to assess the CDUS characteristics of healthy‐fertile men(HFM) to obtain normative parameters. Objectives To report and discuss the scrotal organs CDUS reference ranges and ch...

Life-long sperm production leads to the assumption that male fecundity remains unchanged throughout life. However, recently it was shown that paternal age has profound consequences for male fertility and offspring health. Paternal age effects are caused by an accumulation of germ cell mutations over time, causing severe congenital diseases. Apart f...

Background Infertility affects 7‐12% of men and its etiology is unknown in half of cases. To fill this gap, use of the male genital tract colour‐Doppler ultrasound (MGT‐CDUS) has progressively expanded. However, MGT‐CDUS still suffers from lack of standardization. Hence, the European Academy of Andrology(EAA) has promoted a multicenter study (“EAA...

Children of older fathers have higher risk for certain diseases. Nevertheless, how ageing specifically affects male germ cells is so far not completely understood. In a cohort of 197 healthy men (18-84 years), we found that semen and reproductive parameters remained normal over six decades. Along with an age-dependent increase in telomere length in...

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 technique...

Purpose: Previous studies suggested that serum levels of microRNA (miR)-371a-3p (so-called M371 test) have a much higher sensitivity and specificity than the classic markers of testicular germ cell tumors (GCTs) and are applicable toward both seminoma and nonseminoma. We sought to confirm the usefulness of this test as a novel biomarker for GCT....

Context Testicular sperm extraction (TESE) followed by assisted reproductive techniques often remains the only therapeutic option for men presenting with azoospermia due to spermatogenic failure. Reproductive parameters, such as gonadotropin levels, testicular volume or histopathology, contribute to the prediction of sperm retrieval rate (SRR) in T...

Klinefelter syndrome (KS) and undescended testes (UDT) are known etiologies for non‐obstructive azoospermia (NOA), and coexistence of both etiologies is not uncommon. Patients with both KS and a history of UDT are therefore considered to have extremely reduced chances for paternity. We aimed to analyze the impact of previous surgically corrected un...

Purpose: Diagnosing germ cell neoplasia in situ (GCNis) can detect germ cell tumours (GCTs) at the pre-invasive stage. To date, testicular biopsy with the potential of surgical complications is the only way of safely diagnosing GCNis. Recently, microRNAs (miRs) 371-3, and miR 367 were shown to be valuable serum biomarkers of GCTs. We explored the...