Diagnostics · Hormone Testing
Abstract
This article reviews the role of INSL3 as biomarker of Leydig cell function and its systemic action in testis-bone-skeletal muscle crosstalk in adult men. Insulin-like factor 3 (INSL3) is a peptide hormone secreted constitutively in a differentiation-dependent mode by testicular Leydig cells. Besides the role for the testicular descent, this hormone has endocrine anabolic functions on the bone-skeletal muscle unit. INSL3 levels are low in many conditions of undifferentiated or altered Leydig cell status, however the potential clinical utility of INSL3 measurement is not yet well defined. INSL3 levels are modulated by the long-term cytotropic effect of the hypothalamicpituitary- gonadal axis, unlike testosterone that is acutely sensitive to the stimulus by luteinizing hormone (LH). INSL3 directly depends on the number and differentiation state of Leydig cells and therefore it represents the ideal marker of Leydig cell function. This hormone is more sensitive than testosterone to Leydig cell impairment, and the reduction of INSL3 in adult men can precociously detect an endocrine testicular dysfunction. Low INSL3 levels could cause or contribute to some symptoms and signs of male hypogonadism, above all sarcopenia and osteoporosis. The measurement provided suggested that the measurement of INSL3 levels should be considered in the clinical management of male hypogonadism and in the evaluation of testicular endocrine function. The monitoring of INSL3 levels could allow an early detection of Leydig cell damage, even when testosterone levels are still in the normal range.
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By this author
Semen Analysis · Sperm Function Testing
Preimplantation genetic testing for male factor infertility: lights and shadows
Mazzilli R et al., 2026 · Journal of endocrinological investigation
Male factor could contribute, alone or in combination with female factor, to the inability to conceive in a couple in more than half of cases. The effect of male factor infertility (MFI) on embryological assisted reproductive technology (ART) outcomes remains an ongoing discussion. to evaluate the impact of MFI on embryo aneuploidy rates, to better understand the role and possible indication for Preimplantation genetic testing for aneuploidies (PGT-A), considering the role of sperm characteristics, paternal age, sperm DNA fragmentation and sperm aneuploidies. this narrative review included all available articles, published up to January 2026. Available evidence, often based on heterogeneous and old-fashioned methodologies, suggests that MFI may impair embryonic development, particularly in terms of fertilization rate and blastulation rate, more than embryo euploidy; however, a comprehensive evaluation of MFI should be integrated into clinical practice in the context of couple infertility, to also optimize the efficiency and outcomes of ART. Promising results emerged from sperm DNA fragmentation as a tool to predict embryo euploidy, but further investigations involving larger sample sizes and improved standardization are required.
Neoplastic Risk in Patients With Klinefelter Syndrome
Graziani A et al., 2026 · Andrology · Free to read
Besides gonadal involvement (hypogonadism, male factor infertility, and testicular hypotrophy), patients with Klinefelter syndrome (KS) may suffer from several extra-gonadic complications, including neoplastic events. The aim of this review is to summarize all major clinical evidence dealing with the association between KS and neoplastic diseases and provide practical suggestions for the management of patients with KS regarding neoplastic risk. This narrative review was conducted through a comprehensive search of the PubMed database, using combinations of the following keywords: "Klinefelter syndrome," "cancer," "neoplasm," "breast cancer," "germ cell tumor," "lymphoma," and "testosterone replacement therapy". KS is associated with a higher risk of breast cancer and mediastinal germ cell tumors and an apparent higher risk of hematological malignancies, in particular non-Hodgkin lymphoma and leukemia. Evidence on testicular cancer is limited, with no clear increase in risk attributable to KS, while prostate cancer has a lower risk and lower mortality rate. Given the complexity of the syndrome and the limited available evidence, regular clinical follow-up with targeted investigations when clinically indicated may facilitate early diagnosis and management of associated comorbidities.
Bone Mineral Density · Measurement
Impact of reference gender on bone mineral density and fracture risk assessment in transgender adults
Scala A et al., 2026 · Osteoporosis international : a journal established as result of cooperation between the European Foundation for Osteoporosis and the National Osteoporosis Foundation of the USA · Free full text on PubMed Central
In transgender adults, reference-gender choice alters Z-scores and fracture-risk estimates. Z-scores differ by 0.4-0.6 SD, with male references identifying more individuals with low BMD for age, especially in those assigned male at birth. Dual-reference reporting is advisable until further evidence becomes available. Transgender individuals, especially those assigned male at birth (AMAB), exhibit lower bone mineral density (BMD) compared with the cisgender population. Interpretation of densitometric data is challenging, as the choice of reference gender can significantly influence Z-scores and fracture risk scores. This study aims to evaluate the impact of the gender reference database (male or female) on the assessment of BMD and fracture risk in transgender adults prior to gender-affirming hormone therapy (GAHT). We conducted a cross-sectional analysis of 249 transgender individuals (153 assigned female at birth - AFAB and 96 AMAB) aged 18-43 years, recruited in the Hospitals of Padua and Brescia (Italy). Z-scores were calculated using both male and female reference databases and FRAX scores were computed using both gender inputs. Associations with anthropometric, biochemical, and hormonal parameters were explored. Z-scores differed systematically depending on the reference gender, with mean ΔZ ranging 0.4-0.6 SD across skeletal sites. Switching reference databases frequently led to reclassification of BMD status. AMAB individuals showed a higher prevalence of low BMD for age, particularly when assessed against male references (27.1%), whereas AFAB participants generally maintained normal BMD. However, FRAX scores remained low. BMI and 25-OH vitamin D levels were independent predictors of BMD and Z-scores in AMAB individuals. The choice of reference gender significantly influences densitometric interpretation in young transgender adults. Until further evidence becomes available, calculating Z-scores using both male and female reference databases is advisable. Early preventive interventions remain essential to preserve bone health.
Male Factor Treatment · Surgical Management
Predictive parameters of semen outcome improvement after varicocele treatment by scleroembolization: a retrospective study
De Toni L et al., 2026 · Journal of endocrinological investigation · Free full text on PubMed Central
Varicocele is a recognized male factor of infertility. Surgical/microsurgical correction represents a therapeutical option to improve fertility outcomes but predictive parameters for the identification who can actually benefit from varicocele correction are under investigated. Here we aimed to identify baseline predictors of semen outcome improvement after varicocele treatment by scleroembolization approach. 85 patients receiving varicocele treatment by anterograde scleroembolization (ASE, N = 42) or retrograde scleroembolization (RSE, N = 43) were retrospectively recruited. Basal and 6-months follow-up evaluation of semen, hormonal and ultrasound parameters (US) were performed to address the respective effect of varicocele treatment. In addition, basal parameters were assessed as clinical outcome predictors. Varicocele grade reduction was observed in more than 90% of patients (P < 0.001). Compared to basal, significant increase of sperm concentration (10.0 ± 9.2 × 106cells/mL vs. 23.4 ± 26.9 × 106cells/mL; P < 0.001), total sperm count (TSC 39.0 ± 54.5 × 106cells vs. 70.3 ± 90.6 × 106cells, P < 0.001) and total motile sperm count (TMS, 9.8 ± 12.8 × 106cells vs. 36.7 ± 58.1 × 106cells, P < 0.001), was observed, with no differences between RSE or ASE. All US parameters were also improved (all P < 0.001). Logistic regression analysis of basal semen and ultrasound parameters showed that basal sperm motility and left testis-mean transit time (L-MTT) were associated with TSC and TMS doubling at follow-up. However, Receiver Operating Characteristic curve analysis showed that only basal L-MTT basal sperm was consistently associated with TSC and TMS doubling at follow-up (respectively: AUC = 0.834, CI: 0.747-0.921 and AUC = 0.805, CI: 0.708-0.901; both P < 0.001). Baseline sperm count and US parameters represent useful clinical descriptors to address those subjects eligible for varicocele correction.
Related research
Hormone Testing · Serum Panels
Insulin-like factor 3: a novel circulating hormone of testicular origin in humans
Ferlin A et al., 2005 · Annals of the New York Academy of Sciences
Insulin-like factor 3 (INSL3) affects testicular descent. Mutations in the INSL3 gene or its receptor, LGR8/GREAT, can cause cryptorchidism. Expression of LGR8/GREAT in different tissues and production of INSL3 by adult-type Leydig cells suggest additional roles for this hormonal system in adults. We used a novel radioimmunoassay kit to measure INSL3 concentrations in the serum of normal men and those with different testicular pathologies. We demonstrate that INSL3 circulates in adult men and is almost exclusively of testicular origin. Subjects with severe testicular damage (infertility) produce small amounts of INSL3, and concentrations of this hormone seem to reflect the functional status of the Leydig cells. Analysis of men treated with different combinations of hormones of the hypothalamus-pituitary-testis axis suggests that the production of INSL3 is related to the luteinizing hormone.
Hormone Testing · Serum Panels
A novel circulating hormone of testis origin in humans
Foresta C et al., 2004 · The Journal of clinical endocrinology and metabolism
Insulin-like factor 3 (INSL3) is a member of the relaxin-insulin family, and it is expressed in pre- and postnatal Leydig cells of the testis. This peptide affects testicular descent during embryonic development, and mutations in INSL3 gene or its receptor LGR8 (leucine-rich repeat-containing G protein-coupled receptor 8)/GREAT (G protein-coupled receptor affecting testicular descent) cause cryptorchidism in humans. The expression of LGR8/GREAT in different tissues and the production of INSL3 also by adult-type Leydig cells suggest additional roles of this hormonal system in adulthood. In this preliminary report we performed the first analysis in humans of INSL3 using a novel RIA kit to measure INSL3 concentrations in serum of normal men and with different testicular pathologies. The results show that INSL3 is circulating in adult men, and it is almost exclusively of testicular origin. Subjects with severe testicular damage, such as men with severe infertility, produce low amount of INSL3, and the concentrations of this hormone seem to reflect the functional status of the Leydig cells. In particular, INSL3 concentrations may be an even more sensitive marker of Leydig cell function than testosterone itself. Analysis of men treated with different combinations of hormones of the hypothalamus-pituitary-testis axis suggests that the production of INSL3 is related to LH in a manner similar to that of the LH-testosterone axis.
Hormone Testing · Serum Panels
Effects of acute hCG stimulation on serum INSL3 and 25-OH vitamin D in Klinefelter syndrome
Santi D et al., 2020 · Andrology
It has recently been suggested that the hypergonadotropic hypogonadism characterizing Klinefelter syndrome (KS) might not be due to a steroidogenic dysfunction per se, but mainly to an altered testosterone (T) secretion into the bloodstream. However, the Leydig cell functionality remains incompletely studied in KS, and new markers should be considered. Previous data indicated that chronic hCG stimulation influences the production of both insulin-like peptide 3 (INSL3) and 25-hydroxy-vitamin D (25-VD) in eugonadal men. To evaluate INSL3 and 25-VD serum levels, as markers of Leydig cell functionality, in association with sex steroids, after an acute hCG test in a group of KS patients and healthy volunteers. A retrospective analysis of a prospective case-control clinical trial was carried out. KS patients (n = 11) and age-matched healthy controls (n = 11) provided a basal blood sample (V0) immediately followed by a single intramuscular injection of hCG 5000 IU. Blood samples were taken in the following five days (V1-V5). At baseline, INSL3 was lower in KS patients compared with controls (P = .007). When adjusted for INSL3 levels, the production of steroids was similar between KS patients and controls. 25-VD was in the insufficient range both in KS patients and in controls and was not different (P = .064). Acute hCG stimulation increased neither INSL3 nor 25-VD in both KS patients and controls. In controls, an inverse correlation was detected between INSL3 levels and body mass index (P = .020) and waist circumference (P = .020). INSL3 secretion is independent from steroidogenesis, and its production is mostly not influenced by acute hCG stimulation both in KS men and in controls. INSL3 serum levels should be considered as a marker of Leydig cell differentiation and numbers rather than steroidogenesis. 25-VD serum levels are also not increased by a single acute hCG administration, which was not able to restore the normal concentrations of 25-VD.
Ovarian Hormones · Androgens
Paracrine and endocrine roles of insulin-like factor 3
Ferlin A et al., 2006 · Journal of endocrinological investigation
Insulin-like factor 3 (INSL3) is expressed in Leydig cells of the testis and theca cells of the ovary. This peptide affects testicular descent by acting on gubernaculum via its specific receptor leucine-rich repeat-containing G protein-coupled receptor 8 (LGR8). From initial animal data showing the cryptorchid phenotype of Insl3/Lgr8 mutants, an extensive search for mutations in INSL3 and LGR8 genes was undertaken in human patients with cryptorchidism, and a frequency of mutation of 4-5% has been detected. However, definitive proofs of a causative role for some of these mutations are still lacking. More recent data suggest additional paracrine (in the testis and ovary) and endocrine actions of INSL3 in adults. INSL3 circulates at high concentrations in serum of adult males and its production is dependent on the differentiation effect of LH. Therefore, INSL3 is increasingly used as a specific marker of Leydig cell differentiation and function.
Diagnostics › Hormone Testing › Serum Panels · Bone Health › Hormones and Bone › Estrogen and Bone
PMID 32981493 32981493 DOI 10.2174/0929866527666200925105739 10.2174/0929866527666200925105739 Facondo et al. 2020, Facondo 2020