On testosterone, Klinefelter men had less limb lean mass than Kallmann
A single-center retrospective study of 50 men on testosterone replacement found men with Klinefelter syndrome had less limb lean mass than men with Kallmann syndrome. DXA scans showed low muscle mass with excess body fat in about 21 out of 100 men with Klinefelter syndrome and 5 out of 100 with Kallmann syndrome. Bone density did not differ significantly.
Key Findings
The study included 50 men, 29 with Klinefelter syndrome and 21 with Kallmann syndrome, all receiving testosterone replacement therapy.
Appendicular lean mass index was 8.37 ± 1.15 kg/m² in Kallmann syndrome and 7.28 ± 1.20 kg/m² in Klinefelter syndrome (P < .001).
Radiologic sarcopenic obesity affected 7 men (14%): 6 of 29 with Klinefelter syndrome and 1 of 21 with Kallmann syndrome. Osteosarcopenic obesity affected 2 men (4%), both with Klinefelter syndrome.
Reduced muscle mass appeared in 12 men (24%) and reduced bone mineral density in 13 men (26%). Bone mineral density showed no significant difference between the two syndromes.
Higher follicle-stimulating hormone (FSH) was associated with lower appendicular lean mass index, before and after adjustment for confounders (P = .002 in both models).
Interpretation
The study is a retrospective review of records at one hospital, so it shows associations only. Fifty men is a small group, which reflects how rare both syndromes are. Only White men were included, and the bone and fat cutoffs use White reference values, so the findings may not apply to other groups. All men were on testosterone replacement, which the authors say precluded assessing the direct effects of hypogonadism on bone and body composition. The authors describe a possible role for FSH and list other explanations, including estradiol and a Leydig cell hormone called INSL3, which they did not measure. The FSH association was small. Muscle strength was not tested, and only 4 men had vertebral deformities, too few to relate body composition to fractures.
RRM Context
Klinefelter and Kallmann syndromes are two genetic causes of low testosterone in men. Both bear on male fertility. Restorative reproductive medicine evaluates both partners, so the male hormone picture belongs in the evaluation from the start. The study reports body composition and bone outcomes. It reports no fertility, sperm, or pregnancy outcomes.
Our editorial summary of this paper, not the article's abstract.
Abstract
Context
Klinefelter syndrome and Kallmann syndrome are 2 rare genetic disorders characterized by reduced testosterone (T) levels but differing in their gonadotrophin profiles. To date, no studies have directly compared body composition in these 2 syndromes.
Objective
This work aimed to assess the prevalence of altered body composition parameters in patients with Klinefelter and Kallmann syndromes and to compare body composition between the 2 groups. Secondary objectives included evaluating associations between body composition, bone mineral density (BMD), and serum follicle-stimulating hormone (FSH) levels.
Methods
This single-center, retrospective observational study included 50 patients, 29 with Klinefelter and 21 with Kallmann syndrome receiving T replacement therapy. Body composition was evaluated using whole-body dual-energy x-ray absorptiometry (DXA), which provided measurements of appendicular lean mass (ALM), total body fat (TBF), visceral adipose tissue (VAT), the ALM-to-height² ratio (appendicular lean mass index, ALMI), and the ALM-to-weight ratio.
Results
Radiologic sarcopenic obesity was identified in 7 patients (14%; 6/29 Klinefelter, 1/21 Kallmann), while osteosarcopenic obesity was found in 2 patients (4%), both with Klinefelter syndrome. Patients with Kallmann syndrome had significantly higher ALMI values than those with Klinefelter syndrome (8.37 ± 1.15 vs 7.28 ± 1.20 kg/m²; P < .001). Univariable analysis revealed an inverse association between FSH levels and ALMI (B = -0.026; P = .002), which remained statistically significant after adjustment for confounders (B = -0.030; P = .0022).
Conclusion
This study demonstrated a significant difference in lean mass between Klinefelter and Kallmann syndromes, supporting a potential role for FSH in modulating muscle mass independently of T levels.
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.
Vena W et al., 2023·Journal of endocrinological investigation
Klinefelter syndrome (KS) frequently causes skeletal fragility characterized by profound alterations in bone microstructure with increased risk of fractures. Increased body fat mass associated with decreased body lean mass are frequent features of KS with possible detrimental effects on skeletal health. In this cross-sectional study, we evaluated the associations between body composition parameters, vertebral fractures (VFs) and trabecular bone score (TBS) in adult subjects with KS.
Seventy-one adult males (median age 41 years, range 18-64) with 47, XXY KS were consecutively enrolled by two Endocrinology and Andrology Units (IRCCS Humanitas Research Hospital in Milan and ASST Spedali Civili in Brescia). Dual-energy X-ray absorptiometry (DXA) was performed to assess bone mineral density (BMD) at lumbar spine, femoral neck and total hip, TBS and body composition. Prevalence of VFs was assessed by quantitative morphometry on lateral spine X-rays.
VFs were detected in 14 patients (19.7%), without significant association with low BMD (p = 0.912). In univariate logistic regression analysis, VFs were significantly associated with truncal/leg fat ratio (OR 2.32 per tertile; 95% CI 1.05-5.15; p = 0.038), whereas impaired TBS (detected in 23.4% of subjects) was associated with older age at study entry (p = 0.001) and at diagnosis of disease (p = 0.015), body mass index (BMI; p = 0.001), waist circumference (p = 0.007), fat mass index (FMI; p < 0.001), FMI/lean mass index (LMI) ratio (p = 0.001). Prevalence of VFs was not significantly different between subjects with impaired TBS as compared to those with normal TBS (26.7 vs. 18.4%; p = 0.485). Skeletal end-points were not significantly associated with duration of testosterone replacement therapy and serum testosterone and 25hydroxyvitamin D values.
Body composition might influence bone quality and risk of VFs in subjects with KS.
Grande G et al., 2023·Endocrine connections·Free full text on PubMed Central
Low bone mass is common in men with Klinefelter syndrome (KS), with a prevalence of 6-15% of osteoporosis and of 25-48% of osteopenia. Reduced bone mass has been described since adolescence and it might be related to both reduced bone formation and higher bone resorption. Although reduced testosterone levels are clearly involved in the pathogenesis, this relation is not always evident. Importantly, fracture risk is increased independently from bone mineral density (BMD) and testosterone levels. Here we discuss the pathogenesis of osteoporosis in patients with KS, with a particular focus on the role of testosterone and testis function. In fact, other hormonal mechanisms, such as global Leydig cell dysfunction, causing reduced insulin-like factor 3 and 25-OH vitamin D levels, and high follicle-stimulating hormone and estradiol levels, might be involved. Furthermore, genetic aspects related to the supernumerary X chromosome might be involved, as well as androgen receptor expression and function. Notably, body composition, skeletal mass and strength, and age at diagnosis are other important aspects. Although dual-energy x-ray absorptiometry is recommended in the clinical workflow for patients with KS to measure BMD, recent evidence suggests that alterations in the microarchitecture of the bones and vertebral fractures might be present even in subjects with normal BMD. Therefore, analysis of trabecular bone score, high-resolution peripheral quantitative computed tomography and vertebral morphometry seem promising tools to better estimate the fracture risk of patients with KS. This review also summarizes the evidence on the best available treatments for osteoporosis in men with KS, with or without hypogonadism.
Ferlin A et al., 2011·The Journal of clinical endocrinology and metabolism
Klinefelter syndrome (KS) is a chromosomal alteration characterized by supernumerary X-chromosome(s), primary hypogonadism, decreased pubertal peak bone mineral density (BMD), and accelerated bone loss during adulthood. Decreased bone mass has been traditionally related to low testosterone levels. However, testosterone replacement therapy does not necessarily increase bone mass in these patients, and low BMD can be observed also in patients with normal testosterone levels. The androgen receptor (AR) gene CAG polymorphism seems to modulate the sensitivity to testosterone and previous studies have related it to some clinical aspects of KS, to include BMD, gynecomastia, testes and prostate volume, and hemoglobin concentration.
To analyze the relation between bone mass, testosterone, and AR CAG polymorphism in men with KS.
Cross-sectional cohort study.
University department.
One hundred twelve consecutive treatment-naïve 47,XXY Klinefelter patients (mean age 33.5 ± 4.7 yr) and 51 age-matched normal male controls.
Dual-energy x-ray absorptiometry, CAG repeat length polymorphism, X-chromosome inactivation, and testosterone levels.
Forty-nine of 112 KS subjects (42.5%) had low bone mass (osteopenia or osteoporosis). Lumbar and/or femoral T-scores were lower in KS patients compared with controls. No significant relationship was observed between testosterone levels and bone parameters, and the prevalence of osteopenia/osteoporosis was similar in subjects with normal and low testosterone levels (43.7% and 40.5%, respectively). The mean CAG repeat length calculated after X-chromosome inactivation analysis showed no differences between patients with normal and low bone mass.
Testosterone levels and AR CAG polymorphism are not associated with bone mass phenotype in KS.
Klinefelter syndrome (KS) may induce skeletal fragility, but the studies so far published on this topic were mainly focused on the evaluation of bone mineral density (BMD) and bone microstructure, whereas data on fracture risk are still lacking.
To evaluate the prevalence and determinants of vertebral fractures (VFs), that is, the hallmark of osteoporosis, in subjects with KS.
Eighty-seven patients with KS (median age 41 years, range 18-64) were consecutively evaluated for radiological VFs (by quantitative morphometry) and lumbar spine and femoral neck BMD (by DXA). Fifty-five patients with KS were also evaluated by the fracture risk assessment (FRAX) tool.
Low BMD was found in 22/87 (25.3%) patients [12 with osteopenia, three with osteoporosis and seven with "low BMD per age" (subject < 50 years with Z-score ≤-2.0 SD)] and VFs in 13/87 (14.9%) patients. In patients with VFs, the median spine deformity index was 2 (range 1-9). Prevalence of VFs was similar between healthy and low-BMD patients (15.9% vs 13.6%; P = .80). Noteworthy, patients with VFs had significantly higher age at diagnosis of KS as compared to patients who did not fracture (P = .039), without significant differences in age at the time of observation (P = .162), body mass index (P = .234), testosterone replacement therapy (P = .432), duration of testosterone therapy (P = .409), vitamin D therapy (P = 681), and serum testosterone levels (P = .338). Moreover, patients with VFs were more likely to complain back pain in comparison with those without VFs (33.3% vs 7.4%; P = .047). In 55 cases evaluated by the FRAX® tool, no significant differences in 10-year risk of major fracture (P = .270) and hip fracture (P = .860) were found between fractured and non-fractured patients.
This study provides first evidence that KS may be associated with risk of VFs in close relationship with delay in disease diagnosis but independently of BMD values and serum testosterone levels or testosterone therapy.
Bone Health › Hormones and Bone › Estrogen and Bone
Caterina Buoso, Andrea Delbarba, Matteo Riva, Giulia Artifoni, Elisa Gatta, Davide Farina, Eugenia Quiros-Roldan, Carlo Cappelli
C Buoso, A Delbarba, M Riva, G Artifoni, E Gatta, D Farina, E Quiros-Roldan, C Cappelli
PMID 41073368 41073368 DOI 10.1210/clinem/dgaf565 10.1210/clinem/dgaf565 Buoso et al. 2026, Buoso 2026
00240q980