The possible role of AMH in shortening the gubernacular cord in testicular descent: A reappraisal of the evidence

Anti-Müllerian hormone, testicular descent and cryptorchidism

Anti-Müllerian hormone (AMH) is a Sertoli cell-secreted glycoprotein involved in male fetal sex differentiation: it provokes the regression of Müllerian ducts, which otherwise give rise to the Fallopian tubes, the uterus and the upper part of the vagina. In the first trimester of fetal life, AMH is expressed independently of gonadotropins, whereas from the second trimester onwards AMH testicular production is stimulated by FSH and oestrogens; at puberty, AMH expression is inhibited by androgens. AMH has also been suggested to participate in testicular descent during fetal life, but its role remains unclear. Serum AMH is a well-recognized biomarker of testicular function from birth to the first stages of puberty. Especially in boys with nonpalpable gonads, serum AMH is the most useful marker of the existence of testicular tissue. In boys with cryptorchidism, serum AMH levels reflect the mass of functional Sertoli cells: they are lower in patients with bilateral than in those with unilateral cryptorchidism. Interestingly, serum AMH increases after testis relocation to the scrotum, suggesting that the ectopic position result in testicular dysfunction, which may be at least partially reversible. In boys with cryptorchidism associated with micropenis, low AMH and FSH are indicative of central hypogonadism, and serum AMH is a good marker of effective FSH treatment. In patients with cryptorchidism in the context of disorders of sex development, low serum AMH is suggestive of gonadal dysgenesis, whereas normal or high AMH is found in patients with isolated androgen synthesis defects or with androgen insensitivity. In syndromic disorders, assessment of serum AMH has shown that Sertoli cell function is preserved in boys with Klinefelter syndrome until mid-puberty, while it is affected in patients with Noonan, Prader-Willi or Down syndromes.

[Hormonal and genetic causes of cryptorchidism]

Cryptorchidism is the most frequent congenital disorders of the reproductive system, is present in 2-3% of term newborn boys. Genes involved in embryonic testicular migration are known but their role in cryptorchidism development are not investigated enough. Genetical causes of cryptorchidism are identified in 5-7% of patients. The article contains data on the role of insulin-like peptide 3 and its receptor, anti-Müllerian hormone, gonadotropins, androgens in embryonic testicular migration. INSL3 and AMH are presented as markers of testicular dysfunction associated with cryptorchidism. Hypogonadotropic hypogonadism is also associated with cryptorchidism and can be diagnosed based on it. Results of modern investigations determine the necessary of hormonal and genetical examination of patients with isolated cryptorchidism to detect causes of cryptorchidism and manage of patients.

Two novel AMHR2 gene variants in monozygotic twins with persistent Müllerian duct syndrome: A case report and functional study

Background

Persistent Müllerian duct syndrome (PMDS) is an autosomal recessive congenital abnormality in which Müllerian derivatives, uterus, cervix, upper two‐thirds of the vagina, and fallopian tubes persist in otherwise normally virilized males. Mutations in anti‐Müllerian hormone (AMH) and AMH receptor type II (AMHR2) genes have been identified as causative. However, functional experimental analysis of AMHR2 or AMH variants that cause PMDS is still lacking.

Materials and Methods

A Chinese Han family affected by PMDS was identified. To assess the history and clinical manifestations of PMDS, physical, operational, ultrasonographical, pathological, and other examinations were performed on family members. The variant screening was conducted using trio whole‐exome sequencing (trio WES) and Sanger sequencing. Complementation‐based NanoLuciferase Binary Technology (NanoBiT) was used to examine the interaction between AMH and AMHR2 variants in vivo. The effect of the two variants on the transcriptional activity of the TGFβ/BMP pathway was evaluated using a luciferase assay.

Results

Classic phenotypic manifestations of PMDS in a pair of identical twins were described and confirmed by genetic sequence analysis. Molecular studies revealed two novel variants c.118G > C [p.(Gly40Arg)], c.1222G > C [p.(Ala408Pro)] in the AMHR2 gene. The AMHR2 p.Gly40Arg variant reduces its ability to bind to AMH, while the p.Ala408Pro variant alters the kinase domain structure. Both variants significantly reduce TGFβ/BMP signaling.

Conclusion

Two missense AMHR2 variants associated with PMDS were identified. These findings provide novel insights toward better clinical evaluation and further understanding of the molecular basis of PMDS.

Testicular descent: A review of a complex, multistaged process to identify potential hidden causes of UDT

BACKGROUND/PURPOSE

What causes normal descent of the testis in a fetus, and what goes wrong with this complex process to cause undescended testes (UDT), or cryptorchidism? Over the last 2 decades, most authors searching for the cause(s) of UDT have looked at the 2 main hormones involved, insulin-like hormone 3 (Insl3) and testosterone (T)/ dihydrotestosterone (DHT), and their known upstream (hypothalamic-pituitary axis) and intracellular 'downstream' pathways. Despite these detailed searches, the genetic causes of UDT remain elusive, which suggest the aetiology is multifactorial, and/or we are looking in the wrong place.

METHODS

In this review we highlight the intricate morphological steps involved in testicular descent, which we propose may contain the currently 'idiopathic' causes of UDT. By integrating decades of research, we have underlined many areas that have been overlooked in the search for causes of UDT.

RESULTS

It is quite likely that the common causes of UDT are still hidden in these areas, and we suggest examining these processes is worthwhile in the hope of finding the common genetic anomalies that lead to cryptorchidism. Given the fact that a fibrous barrier preventing descent is often described at orchidopexy, examination of the extracellular matrix enzymes needed to allow gubernacular migration may be a fruitful place to start.

CONCLUSION

This review of the complex anatomical steps and hormonal regulation of testicular descent highlights many areas of morphology and signalling pathways that have been overlooked in the search for causes of UDT.

Genetics of cryptorchidism and testicular regression

Cryptorchidism, i.e., undescended testis, is one of the most common genital malformations in newborn male babies. The birth rate of cryptorchidism varies from 1.6 to 9.0 %. Etiology of disrupted testicular descent is complex and predisposing causes include genetic, hormonal, environmental, lifestyle and maternal factors. Testicular descent occurs in two major steps and testicular hormones and normal function of hypothalamic-pituitary-testicular axis are important for normal descent. Several gene mutations are associated with syndromic cryptorchidism but they are rarely found in boys with isolated undescended testis. Testicular regression can also cause an empty scrotum. Normal male genital phenotype indicates that the boy has had functioning testis during development. Torsion of the testis can cause testicular regression but in many cases the reason for vanishing testis remains elusive. In this narrative review we discuss genetics of cryptorchidism and testicular regression.

Association of antimullerian hormone with the size of the appendix testis, the androgen and estrogen receptors and their expression in the appendix testis, in congenital cryptorchidism

OBJECTIVES

Antimullerian hormone (AMH) causes regression of the mullerian ducts in the male fetus. The appendix testis (AT) is a vestigial remnant of mullerian duct origin, containing both androgen (AR) and estrogen (ER) receptors. The role of both AMH and AT in testicular descent is yet to be studied. We investigated the possible association of AMH with AT size, the AR and ER, and their expression in the AT, in congenital cryptorchidism.

METHODS

A total of 26 patients with congenital unilateral cryptorchidism and 26 controls with orthotopic testes were investigated, and 21 ATs were identified in each group. AMH and insulin-like three hormone (INSL3) concentrations were measured with spectrophotometry. AR and ER receptor expression was assessed with immunohistochemistry using monoclonal antibodies R441 for AR and MAB463 for ER. For the estimation of receptor expression, the Allred Score method was used.

RESULTS

AMH concentrations did not present significant differences between patients with congenital cryptorchidism and the controls. Also, no correlation was found between AMH, INSL3, and AT length. Allred scores did not present significant differences. However, expression percentiles and intensity for both receptors presented significant differences. Three children with cryptorchidism and the highest AMH levels also had the highest estrogen receptor scores in the AT.

CONCLUSIONS

No association was found between AMH and the studied major parameters. However, higher AMH concentrations, in combination with higher estrogen receptor scores in the AT, may play a role in cryptorchidism in some children. Larger population samples are needed to verify this observation.

Late-onset vanishing testis-like syndrome in a 38,XX/38,XY agonadic pig (Sus scrofa)

Here we describe the case of a pig with intersex traits including ambiguous external genitalia, sex chromosome abnormalities and a late-onset vanishing testis-like syndrome. It was identified shortly after birth by presenting a predominantly female phenotype with two large scrotal masses resembling testes. The karyotype is 38,XX (53%)/38,XY (47%). Sex steroid levels were undetectable at 1 and 7 months old, whereas circulating cortisol levels were typical. DNA studies excluded gene alterations in sex-determining region Y (SRY), dosage-sensitive sex reversal-congenital adrenal hypoplasia critical region on the X chromosome protein 1 (DAX1), SRY-related high mobility group-box gene 9 (SOX9), nuclear receptor subfamily 5, group a, member 1 (NR5A1), nuclear receptor subfamily 3, group c, member 4 (NR3C4) and steroid 5-alpha-reductase 2 (SRD5A2). At 8 months of age the XX/XY pig evinced delayed growth; however, the most striking phenotypic change was that the testes-like structures completely vanished in a 2-3-week period. The internal genitalia were found to consist of a portion of a vagina and urethra. No fallopian tubes, uterus or remnants of Wolffian derivatives were observed. More importantly, no testes, ovaries, ovotestis or gonadal streaks could be identified. The XX/XY sex chromosome dosage and/or overexpression of the DAX1 gene on the X chromosome in the presence of a wild-type SRY gene may have caused this predominantly female phenotype. This specimen represents an atypical case of 38,XX/38,XY chimeric, ovotesticular disorder of sex development associated with agonadism.

Diagnosis and treatment of the intra-abdominal gonad in the pediatric population: Testes, ovaries, dysgenetic gonads, streaks, and ovotestes

BACKGROUND/PURPOSE

Pediatric surgical specialists are often confronted with the difficult task of identifying, diagnosing and managing intra-abdominal gonads in children. Ranging from the intra-abdominal cryptorchid testis to normal or pathologic ovaries and gonads in disorders of sexual development, all intra-abdominal gonads in the pediatric population pose different diagnosis and management challenges. Understanding the hormonal and fertility potential of the gonad and knowing its potential cancer risk is essential when deciding how to manage these patients. In addition, the ideal surgical management for each one of these patients is often debated.

METHODS

Descriptive literature review.

RESULTS/CONCLUSION

Herein, we reviewed gonadal formation, common etiologies, diagnosis and management of intra-abdominal testes, pathologic ovaries and gonads in disorders of sexual development. Fertility potential and cancer risk for each were also reviewed and how both affect surgical management of the gonad.

TYPE OF STUDY/LEVEL OF EVIDENCE

Review Article, Level V.

AMH and AMHR2 mutations: A spectrum of reproductive phenotypes across vertebrate species

Anti-Müllerian hormone (AMH) is a member of the Transforming Growth Factor-β family of secreted signaling proteins. AMH is expressed in Sertoli cells of the fetal and adult testes and granulosa cells of the postnatal ovary. AMH is required for the regression of the Müllerian ducts in mammalian fetuses during male differentiation. AMH signals through its Type II receptor, AMHR2. AMHR2 is expressed in mesenchyme adjacent to the Müllerian ducts, and in Sertoli, Leydig, and granulosa cells. Although AMH and AMHR2 genes have been identified in numerous vertebrate species, spontaneous or engineered mutations or variants have been found or created in only a few mammals and teleost fishes. AMH or AMHR2 mutations in mammals lead to the development of Persistent Müllerian Duct Syndrome (PMDS), a recessive condition in which affected males are fully virilized but retain Müllerian duct-derived tissues, including a uterus and oviducts, and in human and dog, undescended testes. Amh mutant female mice had accelerated ovarian primordial follicle recruitment, suggesting a role for AMH in regulating germ cells. amh and amhr2 mutations have also been experimentally generated in various teleost fishes. Depending on the fish species, loss of AMH signaling results in infertility, germ cell tumors, or male-to-female sex reversal. Here we compare the spectrum of phenotypes caused by AMH and AMHR2 mutations in a variety of vertebrate species. There are both common and unique phenotypes between species, highlighting the range of biological processes regulated by AMH signaling.

Testis Development

Production of sperm and androgens is the main function of the testis. This depends on normal development of both testicular somatic cells and germ cells. A genetic program initiated from the Y chromosome gene sex-determining region Y (SRY) directs somatic cell specification to Sertoli cells that orchestrate further development. They first guide fetal germ cell differentiation toward spermatogenic destiny and then take care of the full service to spermatogenic cells during spermatogenesis. The number of Sertoli cells sets the limits of sperm production. Leydig cells secrete androgens that determine masculine development. Testis development does not depend on germ cells; that is, testicular somatic cells also develop in the absence of germ cells, and the testis can produce testosterone normally to induce full masculinization in these men. In contrast, spermatogenic cell development is totally dependent on somatic cells. We herein review germ cell differentiation from primordial germ cells to spermatogonia and development of the supporting somatic cells. Testicular descent to scrota is necessary for normal spermatogenesis, and cryptorchidism is the most common male birth defect. This is a mild form of a disorder of sex differentiation. Multiple genetic reasons for more severe forms of disorders of sex differentiation have been revealed during the last decades, and these are described along with the description of molecular regulation of testis development.

Hypogonadism and Cryptorchidism

Congenital cryptorchidism (undescended testis) is one of the most common congenital urogenital malformations in boys. Prevalence of cryptorchidism at birth among boys born with normal birth weight ranges from 1.8 to 8.4%. Cryptorchidism is associated with a risk of low semen quality and an increased risk of testicular germ cell tumors. Testicular hormones, androgens and insulin-like peptide 3 (INSL3), have an essential role in the process of testicular descent from intra-abdominal position into the scrotum in fetal life. This explains the increased prevalence of cryptorchidism among boys with diseases or syndromes associated with congenitally decreased secretion or action of androgens, such as patients with congenital hypogonadism and partial androgen insensitivity syndrome. There is evidence to support that cryptorchidism is associated with decreased testicular hormone production later in life. It has been shown that cryptorchidism impairs long-term Sertoli cell function, but may also affect Leydig cells. Germ cell loss taking place in the cryptorchid testis is proportional to the duration of the condition, and therefore early orchiopexy to bring the testis into the scrotum is the standard treatment. However, the evidence for benefits of early orchiopexy for testicular endocrine function is controversial. The hormonal treatments using human chorionic gonadotropin (hCG) or gonadotropin-releasing hormone (GnRH) to induce testicular descent have low success rates, and therefore they are not recommended by the current guidelines for management of cryptorchidism. However, more research is needed to assess the effects of hormonal treatments during infancy on future male reproductive health.

Evaluation of testicular function in prepubertal children

INTRODUCTION

The assessment of testicular function is not currently performed in childhood. The aim of this review was to address the usefulness of serum Anti-Müllerian Hormone (AMH), inhibin B, and testicular volume (TV) evaluation in children.

REVIEW

Serum AMH and inhibin B levels reflect Sertoli cells (SCs) health and number, SCs maturation degree and their exposure to FSH and to intra-tubular testosterone (T). These hormones might be helpful in discriminating between congenital central hypogonadism (cHH) and constitutional delay in growth and puberty (CDGP) and in case of clinical suspicious of precocious puberty. Furthermore, low AMH and/or inhibin B levels have been observed in children with primary testicular disorders, suggesting the existence of SC dysfunction. TV also provides useful information on testicular health. Recently, a medical calculator, requiring testis length and the stage of genital development, has been developed to easily derive TV.

CONCLUSIONS

The evidence supports the usefulness of AMH, inhibin B and TV evaluation for the early diagnosis of puberty disorders and primary testicular damage. We suggest the measurement of TV by using the medical calculator in all children and to reserve AMH and inhibin B measurements to those cases of no testicular growth, clinical suspicious of puberty disorders or in children at risk for spermatogenesis damage. This work-up might allow the early detection of testicular tubular damage which, in turn, may be useful to prevent the oncoming male infertility in adulthood.

An immunohistochemical analysis of the effects of androgen receptor knock out on gubernacular differentiation in the mouse

AIM

Cryptorchidism affects 2%-4% of newborn boys and causes infertility and cancer. While normal androgen function is required for successful inguinoscrotal descent, its exact role on gubernacular morphology remains unidentified. We aimed to decipher the effect of androgen blockade on the gubernaculum and surrounding structures.

METHODS

Genetically modified mice with androgen receptor knock out (ARKO) were sectioned at ages E17, D0, and D2 for immunohistochemical analysis and D4 for morphological analysis (with ethical approval; A644). Mutants and control littermates were labeled with Ki67, Desmin, and Pax7 to identify the degree of gubernaculuar eversion and the composition of the growth center in the gubernaculum, using light or confocal microscopy.

RESULTS

Androgen blockade prevented gubernacular eversion in all animals aged between E17 and D2 when compared to wild types. Furthermore, a growth center was visible, as indicated by a 'swirl' of immature fibroblasts, in D2 animals but was absent in ARKO mice. Moreover, the gubernacular cord was seen to increase in ARKO mice when compared to wild types and increased in size with age. There were no labeling differences in the antibodies tested for gubernacular differentiation.

CONCLUSION

Gubernacular eversion in rodents prior to inguinoscrotal migration was androgen dependent, as well as maintenance of gubernacular cord length. This study shows that androgen blockade causes cryptorchidism in mice by preventing gubernacular eversion and possibly by preventing shortening of the gubernacular cord. Altering the morphology of the gubernaculum in response to androgen clearly contributes to the clinical problem of cryptorchidism.

Anti-Müllerian Hormone and Testicular Function in Prepubertal Boys With Cryptorchidism

INTRODUCTION

The functional capacity of the testes in prepubertal boys with cryptorchidism before treatment has received very little attention. The assessment of testicular function at diagnosis could be helpful in the understanding of the pathophysiology of cryptorchidism and in the evaluation of the effect of treatment. Anti-Müllerian hormone is a well-accepted Sertoli cell biomarker to evaluate testicular function during childhood without the need for stimulation tests.

OBJECTIVE

The aim of the study was to assess testicular function in prepubertal children with cryptorchidism before orchiopexy, by determining serum anti-Müllerian hormone (AMH). We also evaluated serum gonadotropins and testosterone and looked for associations between testicular function and the clinical characteristics of cryptorchidism.

MATERIALS AND METHODS

We performed a retrospective, cross-sectional, analytical study at a tertiary pediatric public hospital. All clinical charts of patients admitted at the outpatient clinic, and recorded in our database with the diagnosis of cryptorchidism, were eligible. The main outcome measure of the study was the serum concentration of AMH. Secondary outcome measures were serum LH, FSH, and testosterone. For comparison, serum hormone levels from a normal population of 179 apparently normal prepubertal boys were used.

RESULTS

Out of 1,557 patients eligible in our database, 186 with bilateral and 124 with unilateral cryptorchidism were selected using a randomization software. Median AMH standard deviation score was below 0 in both the bilaterally and the unilaterally cryptorchid groups, indicating that testicular function was overall decreased in patients with cryptorchidism. Serum AMH was significantly lower in boys with bilateral cryptorchidism as compared with controls and unilaterally cryptorchid patients between 6 months and 1.9 years and between 2 and 8.9 years of age. Serum AMH below the normal range reflected testicular dysfunction in 9.5-36.5% of patients according to the age group in bilaterally cryptorchid boys and 6.3-16.7% in unilaterally cryptorchid boys. FSH was elevated in 8.1% and LH in 9.1% of boys with bilateral cryptorchidism, most of whom were anorchid. In patients with present testes, gonadotropins were only mildly elevated in less than 5% of the cases. Basal testosterone was mildly decreased in patients younger than 6 months old, and uninformative during childhood.

CONCLUSION

Prepubertal boys with cryptorchidism, especially those with bilaterally undescended gonads, have decreased AMH production. Although serum AMH may fall within the normal range, there is a considerable prevalence of testicular dysfunction during childhood in this frequent condition.

On the descent of the epididymo-testicular unit, cryptorchidism, and prevention of infertility

This comprehensive review provides in-depth coverage of progress made in understanding the molecular mechanisms underlying cryptorchidism, a frequent pathology first described in about 1786 by John Hunter. The first part focuses on the physiology, embryology, and histology of epididymo-testicular descent. In the last 20 years epididymo-testicular descent has become the victim of schematic drawings with an unjustified rejection of valid histological data. This part also includes discussion on the roles of gonadotropin-releasing hormone, fibroblast growth factors, Müllerian inhibiting substance, androgens, inhibin B, and insulin-like 3 in epididymo-testicular descent. The second part addresses the etiology and histology of cryptorchidism as well as the importance of mini-puberty for normal fertility development. A critical view is presented on current clinical guidelines that recommend early orchidopexy alone as the best possible treatment. Finally, by combining classical physiological information and the output of cutting-edge genomics data into a complete picture the importance of hormonal treatment in preventing cryptorchidism-induced infertility is underscored.