Low levels of serum inhibin B do not exclude successful sperm recovery in men with nonmosaic Klinefelter syndrome

The Klinefelter Syndrome and Testicular Sperm Retrieval Outcomes

Klinefelter syndrome (KS), caused by the presence of an extra X chromosome, is the most prevalent chromosomal sexual anomaly, with an estimated incidence of 1:500/1000 per male live birth (karyotype 47,XXY). High stature, tiny testicles, small penis, gynecomastia, feminine body proportions and hair, visceral obesity, and testicular failure are all symptoms of KS. Endocrine (osteoporosis, obesity, diabetes), musculoskeletal, cardiovascular, autoimmune disorders, cancer, neurocognitive disabilities, and infertility are also outcomes of KS. Causal theories are discussed in addition to hormonal characteristics and testicular histology. The retrieval of spermatozoa from the testicles for subsequent use in assisted reproduction treatments is discussed in the final sections. Despite testicular atrophy, reproductive treatments allow excellent results, with rates of 40–60% of spermatozoa recovery, 60% of clinical pregnancy, and 50% of newborns. This is followed by a review on the predictive factors for successful sperm retrieval. The risks of passing on the genetic defect to children are also discussed. Although the risk is low (0.63%) when compared to the general population (0.5–1%), patients should be informed about embryo selection through pre-implantation genetic testing (avoids clinical termination of pregnancy). Finally, readers are directed to a number of reviews where they can enhance their understanding of comprehensive diagnosis, clinical care, and fertility preservation.

Role of treatment with human chorionic gonadotropin and clinical parameters on testicular sperm recovery with microdissection testicular sperm extraction and intracytoplasmic sperm injection outcomes in 184 Klinefelter syndrome patients

OBJECTIVE

To investigate whether preoperative human chorionic gonadotropin (hCG) treatment can help predict the outcomes of microdissection testicular sperm extraction (micro-TESE) and affect fertility outcomes in non-mosaic Klinefelter syndrome (KS) patients.

DESIGN

Retrospective cohort study.

SETTING

University-affiliated fertility center.

PATIENT(S)

A total of 184 non-mosaic KS patients who underwent micro-TESE with or without preoperative hCG treatment from January 2016 to July 2019.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Sperm retrieval rate (SRR) with and without hCG treatment, logistic models analysis.

RESULT(S)

Eighty KS patients (43.5%) had successful sperm retrievals after micro-TESE. There was no statistically significant difference in the SRR between the group who received hCG treatment and the group that did not (44.0% vs. 43.3%). Logistic regression analyses demonstrated that the hCG treatment had no statistically significant effect on successful sperm retrieval. However, higher preoperative testosterone (T) levels seemed to be associated with a higher probability of successful sperm retrieval (multivariate adjusted odds ratio 1.09; 95% confidence interval [CI], 1.04-1.16). The prediction model for SRR on KS patients had an area under the curve of 67.3% (95% CI, 59.3-75.3%). In the hCG treatment group, the data indicated that the three parameters of testicular volume, pretreatment T level, and alterations of T were associated with the probability of successful sperm retrieval. Moreover, hCG therapy did not affect intracytoplasmic sperm injection (ICSI) outcomes. No differences in the pregnancy rate or live-birth rate were observed between the two groups.

CONCLUSION(S)

Therapy with hCG does not affect SRR or ICSI outcomes of non-mosaic KS patients. However, preoperative T levels, whether treated with hCG or not, can predict the chance of sperm retrieval with micro-TESE.

Fertility management of Klinefelter syndrome

Introduction: Klinefelter syndrome (KS) represents the most common chromosomal abnormality in the general population, and one of the most common genetic etiologies of nonobstructive azoospermia (NOA) and in severe oligospermia. Once considered untreatable, men with KS and NOA now have a variety of treatment options to obtain paternity.Areas covered: The cornerstone of treatment for both KS and NOA patients remains the surgical retrieval of viable sperm, which can be used for intracytoplasmic sperm injection to obtain pregnancy. Although the field has advanced significantly since the early 1990s, approximately half of men with KS will ultimately fail fertility treatments. Presented is a critical review of the available evidence that has attempted to identify predictive factors for successful sperm recovery. To optimize surgical success, a variety of treatment modalities have also been suggested and evaluated, including hormonal manipulation and timing of retrieval.Expert opinion: Individuals with KS have a relatively good prognosis for sperm recovery compared to other men with idiopathic NOA. Surgical success is heavily dependent upon surgical technique and the experience of the andrology/embryology team tasked with the identification and use of testicular sperm.

Klinefelter Syndrome: Integrating Genetics, Neuropsychology, and Endocrinology

Although first identified over 70 years ago, Klinefelter syndrome (KS) continues to pose substantial diagnostic challenges, as many patients are still misdiagnosed, or remain undiagnosed. In fact, as few as 25% of patients with KS are accurately diagnosed and most of these diagnoses are not made until adulthood. Classic characteristics of KS include small testes, infertility, hypergonadothropic hypogonadism, and cognitive impairment. However, the pathophysiology behind KS is not well understood, although genetic effects are also thought to play a role. For example, recent developments in genetics and genomics point to a fundamental change in our understanding of KS, with global epigenetic and RNA expression changes playing a central role for the phenotype. KS is also associated with more general health markers, including higher morbidity and mortality rates and lower socioeconomic status (which likely affect both morbidity and mortality). In addition, hypogonadism is associated with greater risk of metabolic syndrome, type 2 diabetes, cardiovascular disease, breast cancer, and extragonadal germ cell tumors. Medical treatment typically focuses on testosterone replacement therapy (TRT), although the effects of this therapy have not been studied rigorously, and future studies need to evaluate the effects of TRT on metabolic risk and neurocognitive outcomes. This review presents a comprehensive interdisciplinary examination of recent developments in genetic, endocrine, and neurocognitive science, including the study of animal models. It provides a number of recommendations for improving the effectiveness of research and clinical practice, including neonatal KS screening programs, and a multidisciplinary approach to KS treatment from childhood until senescence.

Novel insights on testicular volume and testosterone replacement therapy in Klinefelter patients undergoing testicular sperm extraction. A retrospective clinical study

STUDY QUESTION

To investigate whether sperm recovery is related to clinical features, hormone parameters and testosterone replacement therapy (TRT) in patients with Klinefelter syndrome (KS).

SUMMARY ANSWER

This study provides three interesting insights: (i) the probability to retrieve sperm is not related to testicular volume; (ii) TRT does not affect sperm retrieval rate (SRR); and (iii) reduced levels of LH and FSH represent a negative predictor of sperm retrieval in patients with TRT.

WHAT IS KNOWN ALREADY

Classical KS shows a karyotype with one extra X chromosome in all of somatic cells and clinical manifestations characterized by hypergonadotropic hypogonadism and infertility.

STUDY DESIGN, SIZE AND DURATION

We performed a retrospective cohort study. Data from 111 consecutive KS azoospermic patients undergoing testicular sperm extraction (TESE) were collected from 2005 to 2016.

PARTICIPANTS/MATERIALS, SETTING AND METHODS

Data on anthropometric parameters, reproductive hormones and testicular volumes were collected. SRR was related to clinical characteristics and compared between TRT and untreated patients.

MAIN RESULTS AND THE ROLE OF CHANCE

A total of 38 patients (34.2%) had successful sperm recovery. The comparison of clinical characteristics did not differ between patients with and without sperm recovery. Sperm retrieval was successful also in subjects with smaller testes. The comparison of SRR in patients with or without TRT was not different (33.3% vs 34.6%). In TRT group, LH and FSH levels were significantly lower in subjects with no sperm retrieval (P values, respectively, <.05 and <.001).

LIMITATIONS AND REASONS FOR CAUTION

Well-designed controlled studies are necessary to confirm these data aimed to set the best therapeutic approach for fertility management in hypogonadal patients with nonmosaic KS.

WIDER IMPLICATIONS OF THE FINDINGS

Age at TESE, anthropometric measures, testis volume, sex hormones levels and semen parameters are not predictive parameters of SRR. Among TRT patients, reduced gonadotropin is related to failure in sperm retrieval.

Sperm recovery and ICSI outcomes in Klinefelter syndrome: a systematic review and meta-analysis

BACKGROUND

Specific factors underlying successful surgical sperm retrieval rates (SRR) or pregnancy rates (PR) after testicular sperm extraction (TESE) in adult patients with Klinefelter syndrome (KS) have not been completely clarified.

OBJECTIVE AND RATIONALE

The aim of this review was to meta-analyse the currently available data from subjects with KS regarding SRRs as the primary outcome. In addition, when available, PRs and live birth rates (LBRs) after the ICSI technique were also investigated as secondary outcomes.

SEARCH METHODS

An extensive Medline, Embase and Cochrane search was performed. All trials reporting SRR for conventional-TESE (cTESE) or micro-TESE (mTESE) and its specific determinants without any arbitrary restriction were included.

OUTCOMES

Out of 139 studies, 37 trials were included in the study, enrolling a total of 1248 patients with a mean age of 30.9 ± 5.6 years. The majority of the studies (n = 18) applied mTESE, 13 applied cTESE and in one case testicular sperm aspiration (TESA) was used. Additionally, four studies used a mixed approach and in one study, the method applied for sperm retrieval was not specified. Overall, a SRR per TESE cycle of 44[39;48]% was detected. Similar results were observed when mTESE was compared to cTESE (SRR 43[35;50]% vs 45[38;52]% for cTESE vs micro-TESE, respectively; Q = 0.20, P = 0.65). Meta-regression analysis showed that none of the parameters tested, including age, testis volume and FSH, LH and testosterone (T) levels at enrollment, affected the final SRR. Similarly, no difference was observed when a bilateral procedure was compared to a unilateral approach. No sufficient data were available to evaluate the effect of previous T treatment on SRR. Information on fertility outcome after ICSI was available for 29 studies. Overall a total of 218 biochemical pregnancies after 410 ICSI cycles were observed (PR = 43[36;50]%). Similar results were observed when LBR was analyzed (LBR = 43[34;53]%). Similar to what was observed for SRR, no influence of KS age, mean testis volume, LH, FSH or total T levels on either PR and LBR was observed. No sufficient data were available to test the effect of the women's age or other female fertility problems on PR and LBR. Finally, no difference in PR or LBR was observed when the use of fresh sperm was compared to the utilization of cryopreserved sperm.

WIDER IMPLICATIONS

The present data suggest that performing TESE/micro-TESE in subjects with KS results in SRRs of close to 50%, and then PRs and LBRs of close to 50%, with the results being independent of any clinical or biochemical parameters tested.

Outcome of intracytoplasmic sperm injection using fresh and cryopreserved-thawed testıcular spermatozoa in 83 azoospermic men with Klinefelter syndrome

AIM

To report the outcome of intracytoplasmic sperm injection (ICSI) cycles using fresh or cryopreserved-thawed testicular spermatozoa of men with Klinefelter syndrome (KS).

METHODS

Medical records of 83 azoospermic men with KS who underwent testicular sperm extraction (TESE) were reviewed. The clinical parameters for predicting sperm retrieval and fertilization, implantation, pregnancy and live birth rates of ICSI cycles in these patients were evaluated.

RESULTS

A total of 88 TESE procedures were performed with sperm retrieval rates of 39.8% per cycle (35/88) and 42.1% per patient (35/83). None of the studied clinical parameters were found to be informative in predicting successful sperm recovery. A total of 41 embryo transfer cycles were carried out using fresh testicular spermatozoa in 30, cryopreserved-thawed spermatozoa in 10 and cryopreserved-thawed embryo replacement in one. The fertilization and clinical pregnancy rates were comparable at 52.7% and 51.6% with fresh and 48.3% and 60% with cryopreserved-thawed testicular spermatozoa groups, respectively. Twenty-two clinical pregnancies were obtained, including 14 singletons, five twins, two triplets and one quadruplet and ended with the delivery of 13 singletons and six twins. In total, out of 25 delivered fetuses, four died (3 female, 1 male) following delivery and 21 newborns (14 female, 7 male) were healthy with a female to male ratio of 2:1. Conclusions We concluded that no clinical or laboratory parameter predicts the presence of spermatozoa in patients with KS, except the TESE procedure itself. The use of fresh or cryopreserved-thawed spermatozoa on ICSI cycle outcomes are equally successful in patients with KS.

Reproductive outcomes in men with karyotype abnormalities: Case report and review of the literature

Reciprocal translocations of autosomal chromosomes are present in about 1/625 men, yet often there are no symptoms except primary infertility. Abnormal segregation during meiosis often produces sperm and subsequent embryos with unbalanced translocations that often ultimately result in spontaneous abortions. We report on a 37-year-old man and his 39-year-old wife who complained of primary infertility. Previous in vitro fertilization (IVF) had resulted in pregnancy, but two spontaneous abortions. Upon chromosomal testing, the man was diagnosed with a reciprocal translocation and his wife was diagnosed with mosaic Turner's syndrome. Through testicular sperm extraction (TESE) and IVF with preimplantation genetic screening (PGS), they succeeded in having two healthy children. Since men with different karyotype abnormalities can have male infertility, we reviewed the literature and summarized the reproductive outcomes for men with both autosome and sex chromosomal karyotype abnormalities.

Testicular Sperm Sampling by Subcapsular Orchiectomy in Klinefelter Patients: A New Simplified Treatment Approach

OBJECTIVE

To evaluate subcapsular orchiectomy as a method to retrieve spermatozoa from minute testicular foci in men with Klinefelter syndrome (KS).

METHODS

Fourteen men with KS were consecutively recruited to unilateral subcapsular orchiectomy. Testicular tissue was dissected mechanically and enzymatically to identify possible sperm. Previous testosterone replacement therapy was interrupted for 10 months (range: 9-12 months) to minimize a possible effect on the spermatogenesis. Two men with high estrogen/testosterone ratios were treated with aromatase inhibitor (letrozol, 2.5 mg/d for 3 months) before operation.

RESULTS

Testicular sperm were detected in 5 of 14 KS men giving an overall success rate of 36%. The success rate was 50% (5 of 10 men) after exclusion of the 4 men previous treated with androgen substitution. So far, 3 (21%) clinical pregnancies and 2 live births or ongoing pregnancies (14%) have been obtained. Testicular sperm could not be detected in the 2 men treated with aromatase inhibitor before operation. The maximum operative time was 20 minutes, and none had surgical complications such as pain, fever, or hematomas. The mean testosterone level, measured 1-4 months after orchiectomy, decreased to 72% (7.9 ± 2.4 nmol/L) of the preoperative level.

CONCLUSION

Subcapsular orchiectomy appears to be easy and quick compared with conventional microtesticular sperm extraction. However, in this pilot study, it has not been possible to demonstrate pregnancy and live birth rates as high as that reported with microtesticular sperm extraction, and further studies are needed before the procedure should be used routinely for sperm retrieval in patients with KS.

Managing infertility in patients with Klinefelter syndrome

Klinefelter syndrome (KS) is the most frequent chromosomal abnormality with a prevalence of 150 per 100,000 males. It is now well known that the phenotype of Klinefelter adults varies from individual to individual and one registry study indicates that approximately 75% of KS subjects are not diagnosed probably because of very mild phenotypes. Due to seminiferous tubule fibrosis KS patients have small testes and are infertile because of azoospermia (>90%) or severe oligozoospermia (<10%). Adoption or heterologous insemination has been used in the past to achieve paternity. Currently it is well known that with TESE/micro-TESE (TESE = TEsticular Sperm Extraction) spermatozoa can be found in the testes of 28-67% of KS patients. Predictive factors of sperm retrieval success/failure, such as reproductive hormone plasma levels, testis volume and age, have been evaluated without any positive results. By combining TESE/micro-TESE with intracytoplasmic sperm injection an average of 50% of these patients have the possibility of fathering children and the birth of more than 150 children with normal karyotype has been reported in the last 20 years. However couples with a Klinefelter partner must be informed of the increased risk of autosomal/sex chromosomes aberrations in the sperm and embryos and of the possibility of preimplantation genetic diagnosis which is currently suggested by a minority of authors.

Klinefelter syndrome and TESE-ICSI

Until few years ago, Klinefelter syndrome with a homogenous 47,XXY karyotype was considered a model of absolute male sterility. We will discuss first the potential fertility following Testicular Sperm Injection, then the physiopathology of spermatogenic failure and the origin of focal spermatogenesis and risk of aneuploidy in offspring, and third the advantage of searching spermatozoa earlier instead of adult age. The rate of positive sperm extraction seems to be better for younger patients. During childhood, there is a low rate of spermatogonia. The spermagonia, which completes the spermatogenesis, seems resulting from a rare clone of 46,XY gonia, having lost their extra X chromosome. Several arguments suggest that this focal spermatogenesis decreases with age. In addition, androgen treatment, frequently prescribed in case of Klinefelter syndrome, carries a risk of decreasing focal spermatogenesis by lowering gonadotropins. The question arises if it is necessary to expect the sperm cryopreservation before introducing androgen treatment. Further studies are necessary to determine the best age of sperm retrieval in case of Klinefelter syndrome.

Testicular function and fertility in men with Klinefelter syndrome: a review

Klinefelter syndrome, 47,XXY (KS), is the most frequent sex chromosome aberration in males, affecting 1 in 660 newborn boys. The syndrome is characterized by testicular destruction with extensive fibrosis and hyalinization of the seminiferous tubules resulting in small testes, hypergonadotropic hypogonadism, and azoospermia in the majority of cases. Until recently, infertility was considered an untreatable condition in KS. However, with the development of new advanced assisted reproductive techniques such as testicular sperm extraction (TESE) combined with ICSI it seems that KS patients should no longer be labelled as infertile. Especially, microdissection (micro)-TESE has proved to be an advantageous procedure for the identification of testicular spermatozoa in KS. The aim of this review was to describe current knowledge on the testicular changes occurring in KS, the associated changes in reproductive hormones and spermatogenesis, and the existing possibilities of biological fatherhood in 47,XXY patients.

Klinefelter syndrome: an argument for early aggressive hormonal and fertility management

OBJECTIVE

To investigate the impact of early hormone replacement therapy (HT) on sperm retrieval rates in patients with Klinefelter syndrome (KS).

DESIGN

A systematic review of the relevant literature using the PubMed NLM database.

RESULT(S)

There are no randomized controlled trials evaluating the impact of HT on sperm retrieval or reproductive outcomes in men with KS. On average, surgical sperm retrieval rates in men with KS are around 51%, with a range of 28%-69%. Young patient age is the most consistent positive predictor of sperm retrieval. Lower retrieval rates have been reported in a small subset of KS adults who previously received exogenous T, although the nature, duration, and reason for such therapy in these patient subsets are unknown.

CONCLUSION(S)

Early HT is recommended in patients with KS, but its effect on fertility potential has not been definitively studied. Larger studies are needed to better answer this question. Cryopreservation of sperm-containing semen or testicular tissue from a significant proportion of affected adolescents is possible, even when containing very low numbers of spermatozoa, and should be considered to maximize future fertility potential.

[Fertility in patients with Klinefelter syndrome (47,XXY)]

In the past 10 years, our knowledge about fertility chances of patients with Klinefelter syndrome (KS, 47,XXY) has changed considerably, especially when regarding the possibility of IVF ICSI treatment (in vitro fertilisation, intracytoplasmic sperm injection) with single testicular spermatozoa. Thus, it is important to take this knowledge into consideration when counselling Klinefelter patients.Germ cell degeneration in the testicles of Klinefelter patients due to their additional X chromosome is an important phenomenon in this disease which is not yet fully understood. When entering puberty, the testicular volume of KS patients increases for a short time with rising testosterone and inhibin B levels at the same time. These decrease, however, and FSH increases during puberty. This seems to indicate a critical point in time when spermatogenetic function of the testicles could still be existent. Thus, in early puberty there could possibly be a time slot when spermatozoa could be detected in the ejaculate or-if not-at least in the testicular tissue. These could be extracted by testicular sperm extraction, cryopreserved and used for intracytoplasmic sperm injection therapy later on. In the literature, a total of 133 births of children from Klinefelter fathers have been reported. This early specific procedure could lead to a better acceptance of their diagnosis and also offer the option of not being incurably infertile.

Should non-mosaic Klinefelter syndrome men be labelled as infertile in 2009?

BACKGROUND

Klinefelter syndrome is a common genetic condition. Affected non-mosaic men are azoospermic and have been labelled as infertile. Despite reports that these men can have children using assisted reproduction techniques, it is not common practice in the UK to offer sperm retrieval to these men.

METHODS

Medline and EMBASE (1980-2009) were searched independently by two authors and all studies involving surgical sperm retrieval in non-mosaic Klinefelter syndrome were included. The primary outcome was success of surgical sperm retrieval and the secondary outcome was live birth rate.

RESULTS

The overall success rate for sperm retrieval was 44%, with a higher rate of success using micro-dissection testicular sperm aspiration (micro-TESE) (55%). This, along with ICSI, has led to the birth of 101 children. However, there are no known predictors for successful sperm retrieval. Although there are concerns about genetic risk to the offspring of non-mosaic Klinefelter patients, this risk has not been found to be greater than that of patients with non-obstructive azoospermia with normal karyotype.

CONCLUSIONS

It is possible for a man with non-mosaic Klinefelter to father a child. However, before these techniques are offered, some ethical issues need to be explored.

Low semen volume in 47 adolescents and adults with 47,XXY Klinefelter or 46,XX male syndrome

Klinefelter syndrome is characterized by progressive testicular failure causing androgen deficiency and azoospermia in most patients. The aim of this study was to evaluate semen quality in consecutive patients with an additional X chromosome as compared with healthy males. Forty-seven males with non-mosaic 47,XXY (n = 40) or SRY-positive 46,XX male (n = 7) karyotypes aged 26.1 (range: 15.0-51.7) years participated. Semen quality was compared with 2136 (control group I) men from the general population aged 18.9 (17.9-28.6) years and with 349 fertile men (control group II) aged 30.9 (22.0-43.8) years. Semen volume adjusted for duration of abstinence was significantly smaller in the patients [2.0 (0.2-5.7) mL] when compared with control group I [3.1 (0.3-12.5) mL, p < 0.0001] and group II [3.6 (0.6-12.5) mL, p < 0.0001]. There was no difference in semen volume between 47,XXY and 46,XX males. All patients had azoospermia except two 47,XXY males aged 29 years who had sperm concentrations of 0.5 and 1.6 million/mL, respectively. We found significantly smaller semen volume in the patients when compared with controls, and the presence of motile spermatozoa in two out of 47 patients. The small semen volume supports the notion of 47,XXY patients being androgen insufficient despite serum testosterone levels within the normal range.

Microdissection testicular sperm extraction: prediction, outcome, and complications

Testicular spermatozoa can be retrieved successfully by the testicular sperm extraction (TESE) procedure and used for intracytoplasmic sperm injection in cases of non-obstructive azoospermia (NOA). The successful application of TESE depends on the identification of seminiferous tubules containing spermatozoa; testicular tubules of patients with NOA are usually heterogeneous, and TESE may not always be successful in these patients. Microdissection TESE with an operative microscope is advantageous because larger, more opaque, and whitish tubules, presumably containing germ cells with active spermatogenesis, can be identified directly. This procedure is currently the best method for the certain identification of sperm, resulting in a high spermatozoa retrieval rate and minimal postoperative complications. The present review considers the surgical procedure, outcome, prediction for spermatozoa retrieval, and postoperative complications of microdissection TESE.

Sperm cryopreservation in male infertility due to genetic disorders

Certain chromosomal and genetic anomalies, such as Klinefelter syndrome (47,XXY) and Y chromosome microdeletions, have been reported as potential causes of a progressive impairment of spermatogenesis. In these cases cryoconservation of ejaculated or testicular sperm represent a valuable tool for the preservation of fertility. However, dealing with genetic disorders, the transmission of genetic anomalies has to be taken into consideration. It is therefore important to be aware about the clinical importance and the related genetic risks of these anomalies. In this article we describe the clinical significance of these diseases.

Natural history of seminiferous tubule degeneration in Klinefelter syndrome

Klinefelter syndrome (47,XXY) is characterized by small, firm testis, gynaecomastia, azoospermia and hypergonadotropic hypogonadism. Degeneration of the seminiferous tubules in 47,XXY males is a well-described phenomenon. It begins in the fetus, progresses through infancy and accelerates dramatically at the time of puberty with complete hyalinization of the seminiferous tubules, although a few tubules with spermatogenesis may be present in adult life. Activation of the pituitary-gonadal axis at 3 months of age is seen in Klinefelter boys similar to healthy boys. However, the level of testosterone in Klinefelter boys is significantly lower than in controls. After this 'minipuberty', the hormone levels decline to normal prepubertal levels until puberty. In puberty, an initial rise in testosterone, inhibin B, LH and FSH occurs in Klinefelter boys. However, the rise in testosterone levels off and ends at a low-normal level in young adults. Likewise, serum concentration of inhibin B exhibits a dramatic decline to a low, often undetectable level, concomitantly with a rise in FSH, reflecting the degeneration of the seminiferous tubules. Many hypotheses about the underlying mechanism of the depletion of the germ cells in Klinefelter males have been reported and include insufficient supranumerary X-chromosome inactivation, Leydig cell insufficiency and disturbed regulation of apoptosis of Sertoli and Leydig cells. However, at present, the exact mechanism remains unclear. In this article, we summarize current knowledge on the development of the classical endocrinological and histological features of 47,XXY males from fetus to adulthood and review the literature concerning the degeneration of the seminiferous tubules in this syndrome.