Knowledge about Klinefelter syndrome (KS) has increased substantially since its first description almost 80 years ago. A variety of treatment options concerning the spectrum of symptoms associated with KS exists, also regarding aspects beyond testicular dysfunction. Nevertheless, the diagnostic rate is still low in relation to prevalence and no international guidelines are available for KS.
Objective
To create the first European Academy of Andrology (EAA) guidelines on KS.
Methods
An expert group of academicians appointed by the EAA generated a consensus guideline according to the GRADE (Grading of Recommendations, Assessment, Development and Evaluation) system.
Results
Clinical features are highly variable among patients with KS, although common characteristics are severely attenuated spermatogenesis and Leydig cell impairment, resulting in azoospermia and hypergonadotropic hypogonadism. In addition, various manifestations of neurocognitive and psychosocial phenotypes have been described as well as an increased prevalence of adverse cardiovascular, metabolic and bone-related conditions which might explain the increased morbidity/mortality in KS. Moreover, compared to the general male population, a higher prevalence of dental, coagulation and autoimmune disorders is likely to exist in patients with KS. Both genetic and epigenetic effects due to the supernumerary X chromosome as well as testosterone deficiency contribute to this pathological pattern. The majority of patients with KS is diagnosed during adulthood, but symptoms can already become obvious during infancy, childhood or adolescence. The paediatric and juvenile patients with KS require specific attention regarding their development and fertility.
Conclusion
These guidelines provide recommendations and suggestions to care for patients with KS in various developmental stages ranging from childhood and adolescence to adulthood. This advice is based on recent research data and respective evaluations as well as validations performed by a group of experts.
Grande G et al., 2026·The Journal of clinical endocrinology and metabolism·Free to read
Male factor infertility (MFI) is frequently labelled idiopathic when evaluation relies primarily on semen analysis, potentially overlooking endocrine and pathophysiological mechanisms relevant for targeted management.
To phenotypically define MFI and develop a pathophysiology-based classification aimed at reducing idiopathic infertility following comprehensive evaluation.
Prospective monocentric cohort study conducted at a tertiary referral academic centre.
Eight hundred male partners of infertile couples evaluated between October 2024 and January 2026 after exclusion of isolated female factor infertility.
Prevalence of MFI categories, hormonal patterns across phenotypes, and proportion of idiopathic infertility after comprehensive work-up.
All patients underwent standardized clinical evaluation, hormonal assessment (total testosterone, FSH, LH), testicular ultrasound, and complete semen analysis. Microbiological testing, transrectal ultrasound, and genetic analyses were performed according to guidelines.
Primary spermatogenic failure was the most prevalent category (56.0%), followed by infection/inflammation (22.4%) and hypogonadotropic hypogonadism (8.5%). Idiopathic infertility was identified in only 5.3% of cases. Distinct endocrine profiles were observed, with high-FSH spermatogenic failure representing the dominant phenotype.
Comprehensive phenotyping markedly reduces the proportion of patients classified as having idiopathic infertility and identifies clinically relevant subgroups. This prospective study provides validation of a pathophysiology-based classification and supports a shift toward endocrine-integrated diagnostic strategies in male infertility, with potential implications for targeted management.
Rocca MS et al., 2026·Journal of translational medicine·Free to read
Standard semen analysis has little prognostic value in distinguishing fertile from infertile men. Furthermore, in men with semen parameters within the reference ranges, it cannot distinguish fertile men from infertile men, i.e. partners of couples with idiopathic infertility. Oxidative stress, mitochondrial dysfunction, sperm telomere shortening, and DNA fragmentation have been proposed as contributors to impaired male fertility. However, these biomarkers have not been evaluated as a whole in subjects with normal semen parameters, partners of fertile and infertile couples.
To characterise a multidimensional panel of sperm biomarkers-including sperm telomere length (STL), mitochondrial DNA copy number (mtDNAcn), reactive oxygen species (ROS), lipid peroxidation (LP), sperm chromatin dispersion (SCD), and respiratory control ratio (RCR)-and to identify whether these parameters might discriminate, in men with normal semen parameters, infertile men from fertile controls.
A total of 150 men with semen parameters within the normal ranges were enrolled: 47 male partners of couples with idiopathic infertility and 103 fertile controls. STL and mtDNAcn were quantified by qPCR; ROS were assessed using OxiSperm®II with semiquantitative imaging; LP was measured spectrophotometrically in seminal plasma; SCD was used to determine DNA fragmentation; and mitochondrial function was evaluated by oxygen consumption and RCR. Correlations between biomarkers and semen parameters were analysed using Pearson or Spearman coefficients, and intergroup comparisons were adjusted for age.
Semen parameters did not differ significantly between male partners of fertile and infertile couples. compared to men of fertile couples, men of infertile couples exhibited significantly shorter STL (0.57 ± 0.59 vs 1.21 ± 1.13, p_adj = 0.001) and higher oxidative stress, with both ROS (8300.9 ± 4214.8 vs 6555.3 ± 3394.3, p_adj = 0.027) and LP (88.33 ± 55.50 vs 40.29 ± 46.98, p_adj < 0.001) markedly elevated. mtDNAcn, SCD, and RCR showed no difference between the groups. Across the entire cohort, STL correlated negatively with ROS and LP and positively with RCR. ROS correlated negatively with total sperm count, motility and RCR, and positively with LP. LP displayed the strongest pattern of associations, correlating negatively with concentration, total count, motility, STL and RCR, and positively with age and volume.
Among men with normal semen analysis, partners of couples with idiopathic infertility exhibit a distinct sperm molecular profile characterised by telomere shortening and oxidative imbalance. STL, ROS and LP emerged as age-independent biomarkers associated with infertility status and showed promising discriminatory ability in this cohort, supporting their integration as second-level tests to complement routine semen analysis in cases of normozoospermia.
Ponce MR et al., 2026·Andrology·Free full text on PubMed Central
Transgender individuals assigned male at birth (AMAB) may choose to preserve their fertility prior to starting gender-affirming hormone therapy (GAHT). However, limited data exist regarding the baseline reproductive and hormonal characteristics of this population before and after GAHT.
To characterize semen quality and hormonal profiles in transgender AMAB individuals prior to GAHT and compare findings with cisgender men and with transgender individuals who discontinued GAHT for at least 3 months.
This retrospective study included transgender AMAB individuals from two tertiary andrology centers who underwent sperm cryopreservation before GAHT initiation (treatment-naïve group). Clinical evaluation included anthropometric measures, testicular volume assessment, varicocele detection, and sex hormone measures. Semen parameters were analyzed according to WHO criteria and compared with those of cisgender men and previously treated transgender individuals.
Thirty-two treatment-naïve transgender AMAB individuals were included. Hormonal parameters were generally within reference ranges. Only 46.9% of treatment-naïve individuals met WHO criteria for normozoospermia, compared with 75.5% of cisgender controls. Compared with nine previously treated individuals, estradiol levels were higher and seminal volume lower. A higher frequency of seminal abnormalities was observed, although not statistically significant.
A substantial proportion of treatment-naïve transgender AMAB individuals exhibited impaired semen parameters prior to GAHT initiation. Prior GAHT exposure showed a trend toward poorer semen quality. These findings support early fertility counseling and preservation in transgender individuals prior to GAHT initiation.
Delbarba A et al., 2026·Reviews in endocrine & metabolic disorders·Free full text on PubMed Central
Male hypogonadism is associated with significant alterations in body composition, including reduced lean body mass (LBM), increased fat body mass (FBM), particularly visceral adiposity, and impaired muscle function, contributing to frailty and cardiometabolic risk. These changes reflect the disruption of a complex endocrine crosstalk among bone, muscle, and adipose tissue, mediated by cytokines such as osteokines, myokines, and adipokines. This dysregulation promotes the development of osteosarcopenic obesity, a condition characterized by the coexistence of low bone mass, sarcopenia, and excess adiposity. Testosterone (T) plays a central role in maintaining body composition by stimulating muscle protein synthesis, inhibiting adipogenesis, and preserving bone health. Its deficiency, irrespective of etiology, leads to rapid impairment of anabolic pathways, resulting in decreased lean mass and increased fat accumulation. Evidence from clinical and experimental models demonstrates that these alterations are partially reversible with T replacement therapy (TRT), although variability exists depending on the underlying cause of hypogonadism. Dual-energy X-ray absorptiometry (DXA) represents the gold standard for assessing bone mineral density (BMD) and a key tool for evaluating body composition through a three-compartment model. It allows precise quantification of fat and lean mass, as well as their regional distribution, with minimal radiation exposure. In this review, we provide a comprehensive and clinically oriented overview of body composition alterations in male hypogonadism, focusing on underlying pathophysiological mechanisms and the practical application of DXA across different clinical scenarios. We discuss evidence from conditions such as Klinefelter syndrome, Kallmann syndrome, androgen deprivation therapy, HIV infection, and transgender care, aiming to offer a pragmatic framework for integrating body composition assessment into routine practice and improving patient management.
Related research
Guidelines by Clinical Area · Bone and Endocrine Guidelines
Zitzmann M et al., 2025·The aging male : the official journal of the International Society for the Study of the Aging Male·Free to read
This is the inaugural recommendation for the management of the Aging Male with Klinefelter Syndrome (KS), a demographic characterized by primary hypogonadism in the presence of one or more supernumerary X-chromosomes with irregular gene-inactivation, and metabolic dysregulation, contributing a component of functional hypogonadism as aging in these men progresses. The unique constellation of symptoms spanning multiple organ systems and health domains necessitates specialized diagnostic and therapeutic strategies. Neglecting the specific needs of this population can precipitate a considerable decline in quality of life and overall health outcomes. Our recommendations advocate for a multidisciplinary approach involving endocrinologists, urologists, geneticists, mental health professionals, and other specialists, to address the complex interplay of hormonal imbalances, metabolic disorders, cardiovascular risk factors including arrhythmia, bone health concerns, psychological and sexual challenges, ophthalmological problems, and dental issues. By providing a structured framework for comprehensive and individualized care, these recommendations aim to bridge existing healthcare gaps, optimize well-being, and enhance the overall quality of life for aging men with KS.
Pasquali D et al., 2022·Journal of endocrinological investigation·Free full text on PubMed Central
Klinefelter syndrome (KS) is frustratingly under-diagnosed. KS have a broad spectrum of clinical features, making it difficult to identify. We describe KS clinical presentation in a large Italian cohort.
This is the first observational cohort study within a national network, the Klinefelter ItaliaN Group (KING). Primary outcomes were to describe the basic clinical features and the actual phenotype of KS in Italy. Secondary outcomes were to determine age at diagnosis and geographical distribution.
We performed a basic phenotyping and evaluation of the hormonal values of 609 adult KS patients.
Mean age at diagnosis was 37.4 ± 13.4 years. The overall mean testicular size was 3 ml, and 2.5 ml in both testes in untreated KS group. BMI was 26.6 ± 5.8 kg/m2, and 25.5% of KS had metabolic syndrome (MetS). LH and FSH were increased, and mean total testosterone were 350 ± 9.1 ng/dl. A descriptive analysis showed that 329 KS patients were evaluated in Northern Italy, 76 in Central and 204 in Southern Italy. Analysis of variance demonstrated significant statistical differences (p < 0001) between the age at diagnosis of the three geographical groups. Compared with the expected number among male patients matched for age in Italy, only 16% of KS patients received a diagnosis.
These data are the results of the only national database available that collects the clinical and hormonal data of the KS patients, currently referred at the KING centers. In Italy the typical KS patient is overweight, with small testes, and elevated LH and FSH. Only 25.5% of them are diagnosed with MetS. Early detection and timely treatment are mandatory.
Male Endocrine and Genetic Factors · Genetic Causes of Male Infertility
Klinefelter syndrome (KS) is a common genetic disorder characterized by an additional X chromosome in males. A deficient androgen production and a varied observed response of end-organs to testosterone can lead to delayed progression of puberty with reduction in muscle development and facial/body hair, osteoporosis, and gynecomastia. Medical management during puberty focuses on the preservation of fertility and testosterone replacement treatment (TRT) to reduce the current or future consequences of testicular fibrosis. However, more research is needed to establish the need and conditions for TRT in adolescence, as well as the opportunity and timing for sperm recovery in adolescents and young boys with KS. Furthermore, screening for associated diseases such as metabolic syndrome, osteoporosis, and malignancies should be guaranteed during this lifetime. Preventive care should be provided by diagnosis, ideally through a multidisciplinary approach.
Male Endocrine and Genetic Factors · Genetic Causes of Male Infertility
Selice R et al., 2010·Journal of endocrinological investigation
Klinefelter syndrome (KS) (47,XXY) is the most common sex chromosomal disorder, and it is a frequent form of male hypogonadism and infertility. Although the majority of these patients are azoospermic, they might have severe oligozoospermia or residual single-residual foci with spermatogenesis in the testis.
We report our experience on sperm retrieval in the ejaculate and testis, and evaluate the frequency of chromosome abnormalities in sperm of KS.
Eighty-four 47,XXY KS were evaluated with seminal analysis, body hair distribution, reproductive hormones, ultrasonographic scanning of the testis and prostate, bilateral testicular sperm extraction (TESE), sperm or testicular cells sex chromosomes aneuploidies.
Out of 84 patients, 7 (7/84; 8.3%) had sperm in the ejaculate. Out of the 77 azoospermic patients, 24 underwent TESE and 9 (9/24; 37.5%) had successful sperm recovery. The comparison of reproductive hormones, age and testicular volume did not show significant differences between patients with and without successful sperm recovery in semen or TESE . Patients without successful sperm recovery in semen analysis or TESE had signs of hypoandrogenism more evident than patients with successful sperm recovery. Patients with KS produced a higher number of sperm aneuploidy with respect to normozoospermic fertile controls and non-genetic severely oligozoospermic men.
Men with KS are not always sterile. In some of these patients sperm can be found in semen or in the testis, but the proportion of sperm aneuploidy is high. Signs of hypoandrogenism seem to be associated with low sperm recovery rate.
Clinical Guidelines and Standards › Guidelines by Clinical Area › Fertility and Infertility Guidelines · Male Fertility › Male Endocrine and Genetic Factors › Genetic Causes of Male Infertility · Genetics and Immunology › Reproductive Genetics › Chromosomal Abnormalities
Michael Zitzmann, Lise Aksglaede, Andrea M Isidori, Anders Juul, Guy T'Sjoen, Sabine Kliesch, Kathleen D'Hauwers, Jorma Toppari, Jolanta Słowikowska-Hilczer, Frank Tüttelmann
Mike Zitzmann, M Zitzmann, L Aksglaede, A Isidori, A Juul, G T'Sjoen, S Kliesch, K D'Hauwers, J Toppari, J Słowikowska-Hilczer, F Tüttelmann
PMID 32959490 32959490 DOI 10.1111/andr.12909 10.1111/andr.12909 Zitzmann et al. 2021, Zitzmann 2021
