Ambiguous genitalia


Ambiguous genitalia




Chapter outline



INTRODUCTION


AMBIGUOUS GENITALIA: TALKING WITH THE PARENTS


TERMINOLOGY


SEX DETERMINATION


DEVELOPMENT OF THE REPRODUCTIVE SYSTEM



MOUSE MODELS


DISORDERS OF GONADAL DIFFERENTIATION



OVOTESTICULAR DISORDER


46,XX TESTICULAR DISORDER


46,XX DISORDER OF OVARIAN DEVELOPMENT



DISORDERS OF CHOLESTEROL AND STEROID BIOSYNTHESIS



MATERNAL HYPERANDROGENISM


DISORDERS OF ANDROGEN ACTION



MULLERIAN DUCT ABNORMALITIES



HYPOGONADOTROPIC HYPOGONADISM


ROBINOW SYNDROME


WARBURG-MICRO SYNDROME


MAMLD1


EXSTROPHY OF THE BLADDER


ENDOCRINE ENVIRONMENTAL DISRUPTORS


DIAGNOSIS



TREATMENT



CONCLUSIONS



Introduction


Normal gonadal differentiation and sex development depend on the meticulous choreography and synchrony of a network of endocrine, paracrine, and autocrine signaling pathways reflecting the actions and interactions of specific genes, transcription factors, and hormones. Perturbations of this intricate network of gene regulation and gene expression governing fetal gonadal development result in disorders of sex development (DSD). Approximately 1 in 4000 infants is born with a DSD.1


These disorders include a spectrum of abnormalites in which chromosomal, genetic, gonadal, hormonal, or anatomic aspects of sex are atypical. Understanding the developmental biology and embryology of the urogenital system is crucial to categorizing and identifying the molecular basis of the disorder, and its treatment where possible in an individual patient. Knowledge of the many genes, proteins, and hormones involved in gonadal sex determination and sexual differentiation is rapidly increasing. Clarity in terminology provides a framework to approach the differential diagnosis in a patient. The pediatric endocrinologist’s role in the care of a child with ambiguous genitalia begins at diagnosis or earlier for infants identified through prenatal testing. In such circumstances the physician’s responsibility for the management of this child is only starting and will continue until transition to adult care providers is deemed appropriate.



Talking with the parents


For parents, the birth of their child is a long-anticipated and exciting event. Due to the increased frequency of prenatal ultrasound examinations, parents have usually been told the sex of their child and have selected their infant’s name. In some instances, abnormal genital development has been identified through ultrasound and the parents have been informed of this situation and educated regarding the likely diagnostic and treatment plans. In the absence of prior knowledge, the parents are suddenly confronted with a newborn with a birth defect involving the external genitalia and uncertainty regarding their infant’s gender. The apprehension regarding the baby’s health and gender are particularly traumatic if the parents had no prior awareness of the abnormal genital development.


Initially, the parents need to be congratulated on the birth of their child. They need to hear that their child has a problem of sex development and that this condition will be carefully and completely addressed. They need to learn that abnormalities of sex development involve the complex system that directs the development of reproductive system including external genital development. Explanation that it may be impossible to tell the sex of their child simply by examining the external genitalia is essential. It is important to emphasize that the atypical development is not the parents’ fault and that they should not feel guilty. Physician and healthcare professionals should not offer guesses or presumptive diagnoses. The parents can be reassured that necessary studies will be obtained to provide information to ascertain their child’s gender. These studies may also identify the etiology of the DSD. The infant’s care should involve a multidisciplinary team that includes pediatric endocrinologists, pediatric urologists/surgeons, geneticists, neonatalogists, radiologists, behavioral health providers, and pediatric endocrine nurse educators. One team member needs to serve as the prinicipal communicator with the family.


Although contemporary society includes overt references to sex and sexuality, parents may have difficulty thinking of their child as a sexual being and feel embarrassed discussing their child’s sex and future sexuality. Cultural attitudes, preexisting expectations, and family support systems impact the parent’s responses. The medical team needs to promote an open and caring network to provide support for the parents and engage the parents in the medical decision-making process progressively as information becomes available.


The initial treatment goal is to determine if there is an underlying or associated life-threatening condition that requires specific urgent treatment. If the child’s gender remains unclear, information needs to be obtained to assist the parents in determining the most appropriate sex of rearing. Usually, this can be accomplished within a matter of hours or days. In more complex instances, the diagnostic process may take longer. In situations in which it is impossible to identify the specific etiology, the general DSD category (see later) provides a basis for decision making.


Factors to be considered in the medical decision-making process include the extent of external and internal reproductive system development, evidence of gonadal functionality (potential for pubertal hormone secretion and fertility), and hormone responsiveness. In some instances, these factors are more relevant than the karyotype. Genes and gene products mapped to diverse autosomal areas of the genome influence the sex development of the developing fetus and child. When consensus has been reached regarding a diagnostic category, available outcome information for that diagnosis should be reviewed. Knowledge of the specific etiology, including details of the diagnosis, enables planning therapeutic interventions and genetic counseling for future pregnancies. Although the exact details are unclear, the extent, timing, and duration of prenatal androgen exposure likely influences CNS differentiation and affects multiple functions. Hence, healthcare providers need to be cognizant that available outcome data to assist in the decision-making processes are limited. Currently accessible information in published reports is largely based on retrospective studies obtained using diverse methodologies.2


The first interview with the parents should set a positive and optimistic tone to promote parental bonding with their infant. Indeed, the emotional tone of this initial interaction is usually more meaningful than the factual information provided and is recalled by parents for many years. Respect for the family and individual perspectives together with a willingness to repeat or defer detailed explanations are crucial. In the midst of the emotional distress associated with the uncertainty of their infant’s gender, parents cannot be expected to assimilate the vast amount of information that eventually needs to be shared. Repeated discussions with the parents will enable them to deal emotionally and intellectually with their concerns regarding their infant and to allow them to appropriately interact with their infant, family members, friends, and colleagues.


Factual explanations regarding the process of sexual differentiation with a focus on their infant’s situation should be initially outlined. The primary goal at this point is to provide the parents with a basic understanding that the internal and external genital structures for both boys and girls develop from the same primordial tissues. It is also helpful to explain that there are not exclusively male and female hormones. Rather, the environments in which male and female fetuses develop are characterized by differing relative amounts of these hormones. The use of simple sketches and provision of pictures and diagrams can be helpful to explain the embryology of genital development to the parents. Some parents may benefit from practicing the words they will use to discuss the infant’s health with other family members. Detailed explanations and discussion can be repeated multiple times as the child ages.


During the early dialogues, examining the infant with the parents to identify the specific physical findings of their infant is often beneficial. This can reduce their apprehension, increase their comfort when viewing their infant’s genitalia, and reinforce their perception that their infant’s needs are similar to those of all infants. Information can be presented in a manner that will minimize anxiety and better equip parents to participate in the decision-making process. To provide the best support for their infant, each parent must reach an individual resolution with a commitment to a positive perspective concerning this situation. Discussion of the many concerns (particularly those related to gender identity, pubertal development, sexual orientation, sexual function, and fertility) may be helpful. Honest discussions will engender positive feelings that enhance positive interactions and enable the parents to promote their child’s self-esteem.


Unless the gender assignment is clear at this point, the healthcare team should recommend that the parents delay naming the infant, announcing the baby’s birth, and registering the birth until more information becomes available. The message should be clear that they will be involved in deciding the appropriate gender of rearing for their child since it is their privilege and responsibility to participate in the process leading to a gender assignment. Until sex of rearing is established, it is best to refer to the infant as “your baby” or “your child.” Terms such as he, she, and it should be avoided.



Terminology


Under the auspices of the Pediatric Endocrine Society (North America) and the European Society for Pediatric Endocrinology, an international consensus statement was formulated that recommended a revised classification of the medical terminology used for disorders of sex development to avoid confusing and derogatory terms.1 This descriptive classification attempts to be sensitive to concerns of parents and flexible enough to incorporate novel molecular genetic information. The updated classification system integrates molecular genetic considerations into the nomenclature for “disorders of sexual differentiation (DSD)”1 and provides an approach to the diagnostic evaluation.


Terms such as pseudohermaphrodite, intersex, and gender labeling in the diagnosis should be avoided.3 To accommodate all types of DSD, the classification system is broad and includes some conditions that do not present with obvious abnormalities of genital development (Box 5-1). The primary goal of this classification system is to provide a framework for diagnosis, assessment, and care management based largely on sex chromosome status. Currently, microarray and candidate gene analyses are increasingly available and utilized.The DSD categories include sex chromosome DSDs such as 45,X/46,XY (formerly mixed gonadal dysgenesis); ovotesticular DSD (formerly true hermaphroditism); 46,XY DSDs such as disorders of testicular development, disorders of androgen synthesis and action (replacing and expanding the former category of male pseudohermaphroditism), and XY sex reversal; and 46,XX DSDs such as masculinization of the XX individual (replacing female pseudohermaphrodite) and XX sex reversal. Because of the complexities of chromosomal and gonadal development, some diagnoses can be included in more than one of the three major categories. The number of genes identified to be involved in sex development continues to increase. Nevertheless, despite many recent advances the specific molecular etiology of the genital ambiguity in an individual cannot always be identified.



BOX 5-1   Summary of Disorders Associated with Ambiguous Genitalia















Sex determination


Sex determination is the binary switch that launches the developmental destiny of the embryonic gonads to become testes or ovaries. Sexual differentiation refers to the process through which male or female phenotype develops. The gonads, internal genital ducts, and external genital structures all develop from bipotential embryologic tissues. Each cell in the developing gonad has the potential to differentiate into either a testicular or ovarian cell. How the transcriptome of the undifferentiated cell realizes its pathway to develop into an ovary or testis provides an opportunity to elucidate cell fate decision making. However, “the fate decisions in individual cells are highly coordinated such that cells of discordant fate are rarely seen.”4 Thus, male and female development depends on the regulated orchestration of the expression and interaction of specific genes and gene products. Sex determination is largely influenced through transcriptional regulation whereas secreted hormone and hormone receptors influence sex differentiation.


Through Alfred Jost’s experiments with fetal rabbits in the 1940s and 1950s, the critical requirements for a testis and testosterone for male sexual differentiation were established.5 Chromosomal composition of the human embryo, XX or XY, determines gonadal sex. The genetic locus primarily responsible for this binary switch, the sex-determining region on the Y (SRY) gene on the Y chromosome, was identified through studies of patients with disorders of sexual differentiation. Studies involving creation of transgenic SRY+ mice confirmed the essential role of SRY and provided further molecular understanding of testicular differentiation.6,7


In the usual situation, the karyotype (46,XY or 46,XX) of the primordial gonad determines whether it differentiates into a testis or ovary, respectively. Local factors (such as hormones secreted by the developing gonads or tissue-specific transcription factors) influence the ensuing differentiation of the internal and external genital structures. This process integrates sex-specific pathway signals that appear to antagonize each other. Divergence from the normal sequence of events leads to disorders of sex differentiation that can manifest as abnormal gonadal differentiation, inconsistent internal genital differentiation, or ambiguity of the external genitalia. Although genital ambiguity is usually not considered to be a medical emergency, it may be highly distressing to the parents and extended family. Hence, prompt referral and evaluation by a multidisciplinary team with expertise in disorders of sex differentiation is strongly recommended. Information regarding our current knowledge of sex determination is presented, followed by a discussion of the various causes and treatments for ambiguous genital development.



Development of the reproductive system



Urogenital development


The gonads are derived from intermediate mesoderm. In humans, at 4 to 6 weeks of gestation, the urogenital ridges develop as paired outgrowths of coelomic epithelium (mesothelium). The gonads, adrenal cortex, kidney, and reproductive tract derive from the urogenital ridge (Figure 5-1). Several genes are requisite for the development of the bipotential gonad. The Wilms tumor (WT1) gene codes a zinc transcription factor that is expressed in embryonic mesodermal tissues and appears to influence mesodermal-epithelial interactions.8 GATA4 is expressed in the somatic cells of the urogenital ridge and bipotential gonad before showing sex specific expression. Chromobox homolog 2 (CBX2) appears to play a role in early gonadal development and may promote transactivation of steroidogenic factor-1 (NR5A1), which is encoded by NR5A1/SF1. NR5A1 is expressed in the urogenital ridge and appears to upregulate SRY expression. In addition to transcription factors and specific secreted factors (hormones), physical contact with the mesonephros appears to be important for subsequent gonadal differentiation.9



Due to their origin as part of the developing urogenital system, ovaries and testes are initially located high in the abdomen near the kidneys. One of the earliest morphologic changes is increased proliferation and size of developing 46,XY gonads. The bipotential gonad consists of at least four cell lineages, which are germ cells, supportive cells, steroidogenic cells, and connective tissue. Although sex determination has been equated with testis differentiation, recent data challenge this dogma. Rather, specific signaling molecules activate or repress gonadal determination for both testes and ovaries. Competition between specific genes and proteins influences cell fate decisions in gonadal development.10 Specific examples include Forkhead transcription factor 2 (FOXL2) vs. SRY-box 9 (SOX9) and SOX9 vs. Wingless-type MMMTV integration site family member (WNT)/β-catenin, which are discussed later.11



Germ cell development


Germ cells are not required for the initial development of ovaries or testes. Rather, the local environment directs the fate of the primordial germ cells. Until approximately 6 weeks of gestation in the human, primordial germ cells proliferate and migrate from the hindgut to colonize the genital ridges. This migration depends on intrinsic motility and external guidance cues as specified by attractive and repulsive signals.12 When this migration process goes awry, the gonadal germ cell population is lacking. Factors important for germ cell migration and colonization of the genital ridges include WNT5A, NANOG, stromal cell–derived factor 1 (SDF1, also known as CXCL12) and its receptor CXCR4.


Meiosis is a sexually dimorphic regulated step governing terminal differentiation of germ cells with meiosis favoring oocytes and active inhibition of meiosis being essential for male germ cells.13 The RNA binding protein Deleted in azoospermia-like (DAZL) plays a role in this branding of germ cells as male or female.14 Factor in germline alpha (FIGLA) and newborn ovary homeobox (NOBOX) are oocyte-specific proteins that appear to repress male specific genes.15 Subsequent stages of germ cell differentiation into a sperm or an egg are closely linked to the cell cycle decision between mitosis and meiosis.16 Meiosis is dependent on retinoic acid, a morphogen, primarily synthesized in the developing gonad.17 Expression of Stimulated by Retinoic Acid (STRA8) increases in the human fetal ovary concomitant with the initiation of meiosis in this tissue, but remains low in the testis. STRA8 is required for pre-meiotic DNA replication and progression through meiosis. In mice, the expression of CYP26B1, a cytochrome P450 enzyme that degrades retinoic acid, prevents meiosis in male germ cells. In human male fetuses, expression of CYP26B1 does not fully account of inhibition of meiosis in the germ cell.18 Expression for NANO2 appears to be restricted to fetal testes.


The Sertoli cells envelope the germ cells to form seminiferous cords at approximately 7 to 9 weeks of gestation in the human XY gonad. The germ cells in the developing testis enter a state of mitotic arrest. In a human XX gonad, germ cell meiosis begins at 10 to 11 weeks of gestation. In the developing ovary, the germ cells initially form clusters connected by intracellular bridges. Selected oogonia enter meiosis and progress through meiotic prophase I (MPI) to arrest at the diplotene stage. The fetal ovary is characterized by the existence of multiple subpopulations of germ cells at different developmental stages. By approximately 20 weeks of gestation, the oogonia clusters break down to form primordial follicles. Primordial follicles destined for future ovulation remain quiescent. By the 24th week of gestation, most oogonia are surrounded by supporting cells. However, apoptosis is the fate for many oogonia. From a peak of 6.8 million oocytes at approximately 5 months of gestation, approximately 2 million are present at birth due to follicular atresia.19 Accelerated follicular atresia contributes to the follicular depletion characteristic of streak gonads in X monosomy.


The internal environment throughout fetal ovary development has the potential to directly influence the fertility of the developing fetus (controlling the size of the ovarian reserve) and the quality of the oocyte that will eventually become her child (by influencing the extent of selection and apoptosis).20 Although not associated with genital ambiguity, mutations in genes governing oocyte and ovarian development cause disorders of sex development characterized by delayed puberty or premature ovarian failure.


During gestation, maternal and paternal alleles are differentially imprinted such that monoallelic expression of specific genes occurs. During this process of imprinting, mature oocytes and sperm are differentially marked reflecting “parent-of-origin” specific methylation patterns. In the primordial immature germ cells, inherited imprints are erased shortly after the germ cells enter the gonadal ridge. Sexually dimorphic methylation imprinting is subsequently reestablished in male and female gametes. This process occurs late in fetal development in the male and postnatally in female germ cells.21,22 The importance of this imprinting process has been elucidated through study of parent-of-origin–dependent gene disorders such as Beckwith-Wiedemann, Prader-Willi, and Angelman syndromes and some forms neonatal diabetes mellitus.



Human testicular development


Testicular differentiation occurs earlier than ovarian development. The testis consists of five cell types: supporting or Sertoli cells, endothelial cells, peritubular myoid cells, steroid-secreting Leydig cells, and germ cells. The first evidence of testicular differentiation is the appearance of primitive Sertoli cells at 6 to 7 weeks gestation in the human fetal testis. Cells, mostly endothelial cells, migrate from the mesonephros and interact with the pre-Sertoli cells to promote development of the testicular cords.23 The testicular cords are precursors of the seminiferous tubules that will contain Sertoli and germ cells. Interactions between endothelial and mesenchymal cells appear to influence development of the testicular cords.24


The binary switch responsible for testicular development is the SRY gene located on the short arm of the Y chromosome. The SRY protein contains a high-mobility group (HMG) domain and is encoded by a single exon gene. Two nuclear localization signals are located in the HMG domain. The SRY protein is expressed in pre-Sertoli cells, where it triggers a molecular switch to induce Sertoli cell differentiation, thus, initiating the process of male sexual differentiation. The HMG domain of the SRY protein binds to the minor DNA groove, where it functions as a transcription factor by bending DNA to presumably permit other proteins access to regulatory regions and to promote assembly of nucleoprotein transcription complexes. A threshold SRY level must be achieved at a critical time during gestation to establish male sexual differentiation. otherwise, the ovarian differentiation pathway is activated.25 Available data suggest that NR5A1 promotes SRY expression.


SRY expression is independent of the presence of germ cells. SRY increases the expression of the SRY-related HMG box-containing-9 (SOX9) gene. Phenotype-genotype studies of humans and mice demonstrate that SOX9 expression is a crucial step, downstream of SRY, in testis development. Upstream from the SOX9 transcription start site, there appears to be a testis specific enhancer element (hTES). Available data suggest that initially phosphorylated NR5A1 and SRY cooperate to activate the hTES leading to increased SOX9 expression; subsequently SRY, NR5A1, and SOX9 maintain SOX9 expression through actions at hTES.26 In addition to SRY, SOX9, and NR5A1, sequential expression of several other genes is required for normal male sexual differentiation. These genes include fibroblast growth factor 9 (FGF9), anti-Mullerian hormone (AMH), dosage-sensitive sex reversal adrenal hypoplasia congenita critical region on X (DAX1),GATA-binding-4 (GATA4), desert hedgehog (DHH), patched (PTCH1), and WNT7A.


Using immunohistochemistry, NR5A1 and SOX9 proteins can be detected in human embryonic gonadal tissue at 6 to 7 weeks of gestation. At this time, SOX9 expression becomes limited to nuclei of Sertoli cells in a 46,XY fetus but remains cytosolic in a 46,XX fetus. NR5A1 and SOX9 protein expression precede AMH expression. After AMH protein expression increases, Wilms tumor (WT1) and GATA-4 protein expression increase in the fetal testis.27 GATA4 belongs to a family of zinc finger transcription factors known as GATA-binding proteins because they bind to a consensus sequence in the promoter and enhancer regions of target genes. Sexually dimorphic expression of Doublesex- and MAB3-Related Transcription Factor 1 (DMRT1) was found in 6- and 7-week-old human fetuses, with expression limited to male fetuses.28


SOX9 induces expression of prostaglandin D synthase (Pgds), an enzyme involved in prostaglandin synthesis.29 In a positive feedback loop, developing Sertoli cells secrete prostaglandin D2, which binds to its cognate receptor to up-regulate SOX9 expression and recruit additional Sertoli cells.30 In addition, SOX9 promotes expression of fibroblast growth factor 9 (FGF9). FGF9 acting through the its receptor, FGFR2, helps to maintain SOX9 expression and promote Sertoli cell differentiation.31 Normal testicular development appears to involve diffusion of FGF9 from the center to the poles of the undifferentiated gonad.32 Through direct and indirect mechanisms, SOX9 interferes with genes promoting ovarian differentiation.


Vascular development in the gonad is sexually dimorphic with the endothelial cells in the developing testis, forming a characteristic pattern consisting of a prominent coelomic vessel on the antimesonephric surface with branches between the testis cords. This blood vessel is absent in the ovary. Peritubular myoid cells are testis-specific smooth muscle–like cells important to structural integrity and development of the testis cords. Factors relevant to peritubular myoid cell differentiation include desert hedgehog (DHH), which is secreted by Sertoli cells and its receptor Patched (Ptch1).33 The peritubular myoid cells surround the Sertoli cells, separating them from the Leydig cells, which are then sequestered in the interstitium. Downstream of SRY, hedgehog signaling plays a role in cell-cell communication and cell fate determination to influence sex dimorphic development in gonads, reproductive tracts, and external genitalia.33


Leydig cell differentiation depends on paracrine signals, including platelet-derived growth factor receptor-alpha (PDGFR-α), DHH, PTCH1, and Aristaless-related homeobox (ARX). NR5A1 is expressed in Leydig cells to promote steroidogenic enzyme genes expression. The number of fetal Leydig cells reflects gonadotropin stimulation because the number is decreased in anencephalic male fetuses and increased in 46,XY fetuses, with elevated gonadotropin concentrations secondary to complete androgen insensitivity.34 Differentiation of adult Leydig cells occurs postnatally.34


By 11 weeks of gestation, the testicular compartments, tubular and interstitial components, and the cell types of interest (Leydig, Sertoli, and germ cells) can be visualized. In human fetal testes, HSD17B3, CYP11A1, and PTCH1 mRNA levels increased significantly through the second trimester without significant changes in CYP17A1, LHR, or INSL3 levels. The most rapid growth in Sertoli cell number appears to occur during the latter half of the first trimester and the second trimester.35



Human ovary development


Although ovarian differentiation has long been considered the default pathway that occurs in the absence of SRY gene expression, accumulating evidence indicates that specific genes influence ovarian differentiation. Genes implicated in ovarian differentiation include wingless-related MMTV integration site 4 (WNT4), forkhead L2 (FOXL2), follistatin (FST), Iroquois-3 (IRX3), bone morphogenic protein-2 (BMP2), and R-spondin-1 (RSPO1).36 FOXL2 functions to repress male-specific genes especially SOX9 beginning in the fetus and continuing through adulthood. FOXL2 and SOX9 expression appear to be mutually exclusive in developing gonads and in gonadal tissue obtained from patients with DSD conditions.37


In the absence of SRY, between 6 to 9 weeks of gestation, R-spondin-1(RSPO1) expression increases in the developing human ovary. RSPO1 is a secreted factor that activates the β-catenin WNT signaling pathway.38 WNT4 expression also increases. RSPO1 and WNT4 appear to stabilize and amplify β-catenin signaling to activate target gene transcription.39 LIN28A, an RNA-binding protein is differentially expressed in the fetal ovary particularly in the germ cells; its expression appears to be restricted to primordial and premeiotic germ cells.40 LIN28 blocks the production of mature let-7, which is a microRNA that interferes with translation of cell cycle regulators and metabolic pathway components.41,42 In the absence of LIN28, let-7 inhibits production of BLIMP1, a factor involved with primordial germ cell development.41 Expression of both let-7 and LIN28A decreases when germ cells transition from the stem cell state to meiosis.41


Persistent DAX1 expression appears to play a role in ovarian differentiation. The functions of WNT4 include suppression of the androgen-secreting interstitial cells, inhibition of coelomic vascularization, and support of Mullerian derivatives. FOXL2 is a forkhead transcription factor expressed in the ovary.


Two genes, factor in FIGLA and NOBOX, are expressed in fetal or neonatal germ cells where they recruit developing granulosa cells to form primordial and primary follicles. As noted previously, many oocytes degenerate through apoptosis. GATA 4 is expressed in the granulosa cells and is speculated to prevent granulosa cell apoptosis.43 The second trimester human fetal ovary expresses proteins necessary to synthesize and respond to estrogenic, progestogenic, and androgenic signaling.44



Development of internal genital structures


The Wolffian duct originates as the excretory duct of the mesonephros and develops into the epididymis, vas deferens, ejaculatory duct, and seminal vesicle. The epididymis consists of four functional portions: initial segment, caput, corpus, and cauda. Sperm mature in the caput and corpus, whereas the cauda is primarily for storage. The Mullerian or paramesonephric duct originates as an invagination of the coelomic epithelium and develops into the Fallopian tubes, uterus, and upper third of the vagina.


In the male fetus, the Sertoli cells secrete anti- Mullerian hormone (AMH), also known as Mullerian inhibitory hormone (MIH). In human 46,XY fetuses, AMH expression can be detected by 7 weeks of gestation, is not dependent on the presence of germ cells within the testis, and promotes regression of the Mullerian ducts. AMH, a member of the transforming growth factor-β (TGF-β) family, undergoes proteolytic cleavage to become biologically active. AMH binds to its receptor, AMH-RII, on the surface of the Mullerian duct mesenchymal cells to induce increased matrix metalloproteinase 2 expression.45,46 The net result is degeneration and loss of basement membrane integrity of the epithelial and mesenchymal Mullerian cells, leading to regression of the Mullerian ducts.


AMH expression is highly regulated because inappropriate expression in a 46,XX fetus would lead to uterine agenesis. In the 46,XX fetus with absence of both AMH and testosterone, the Mullerian duct derivatives persist and the Wolffian ducts regress. When a female fetus is inappropriately exposed to AMH (as in freemartin cattle), Mullerian duct regression and ovarian masculinization occur. By 12 weeks in the XX fetus, the uterine corpus and cervix have begun to differentiate.47


The fetal hypothalamic-pituitary-gonadal (HPG) axis is active by mid-gestation, with peak fetal testosterone concentrations occurring at approximately 15 to 16 weeks of gestation. Prior to this time, placental hCG stimulates testosterone production by the fetal Leydig cells. Secretion of testosterone by the fetal Leydig cells stabilizes the Wolffian ducts in 46,XY fetuses. Region-specific signaling molecules such as bone morphogenic proteins (BMPs), homeobox genes (HOXA10 and HOXA11), growth differentiation factor 7 (GDF7), relaxin, an orphan G-protein–coupled receptor (LGR4), platelet-derived growth factor A (PDGFA), and its cognate receptor (PDGFRA) influence the development of the epididymis and seminal vesicle.


The prostate, a male accessory sex gland, contributes to seminal fluid plasma and develops from the urogenital sinus. After the initial testosterone-dependent induction of prostate differentiation, subsequent development involves epithelial-mesenchymal interactions that lead to cell differentiation and branching morphogenesis. The requisite signaling molecules FGFs, sonic hedgehog (SHH), BMPs, HOXA13, and HOXD13 are similar to those required for external genital differentiation.48,49



Development of external genital structures


The genital tubercle, urethral folds, and labioscrotal swellings give rise to the external genitalia. Under the influence of circulating androgens that are converted to dihydrotestosterone in target tissues, the urethral folds fuse to form the corpus spongiosum and penile urethra, the genital tubercle develops into the corpora cavernosa of the penis, and the labioscrotal folds fuse to form the scrotum.


In the normal 46,XY human fetus, a cylindrical 2-mm phallus with genital swellings has developed by 9 weeks of gestation. By 12 to 14 weeks of gestation, the urethral folds have fused to form the cavernous urethra and corpus spongiosum. By 14 weeks, the external genitalia are clearly masculine apart from testicular location. The high incidence of hypospadias in humans suggests that urethral fusion is a delicate and finely regulated process.


In the 46,XX fetus, in the absence of androgens the urethral folds and labioscrotal swellings do not fuse and develop into the labia minora and labia majora, respectively. The genital tubercle forms the clitoris, and canalization of the vaginal plate creates the lower portion of the vagina. By 11 weeks of gestation, the clitoris is prominent and the lateral boundaries of the urogenital sulcus have separated. Minimal clitoral growth, well- defined labia majora, hypoplastic labia minora, and separate vaginal and urethral perineal openings are present by 20 weeks of gestation.


By 33 days’ postconception, the human fetal adrenal cortex is distinct from the developing gonad. Due to its role as the source of DHEAS for placental estrogen biosynthesis, the fetal adrenal cortex grows rapidly. By 50 to 52 days’ postconception, expression of several steroidogenic enzymes, steroidogenic acute regulatory protein (StAR), 11β-hydroxylase (CYP11B1), 17α-hydroxylase/ 17,20-lyase (CYP17), and 21-hydroxylase (CYP21) in the fetal adrenal cortex have been demonstrated immunohistochemically.50 Recent data indicate that transitory cortisol biosynthesis peaks at 8 to 9 weeks’ gestation.50 This early cortisol biosynthesis coincides with transient adrenal expression of both nerve growth factor IB-like (NGFI-B) and 3β-hydroxysteroid dehydrogenase-2 (HSD3B2).50 At the same time, ACTH can be detected in the anterior pituitary—suggesting the presence of negative feedback inhibition during the first trimester.50 During the time male sexual differentiation begins, this negative feedback inhibition may serve to prevent virilization of female fetuses to ensure normal female sexual differentiation.50,51



Anogenital distance


The anogenital distance (AGD), the distance from the posterior aspect of the scrotum to the anal verge, shows sexually dimorphism. Longitudinal assessment of AGD defined as measurement from the center of the anus to the base of the scrotum in males and to the posterior fourchette in females showed that mean AGD (+/- SD) at birth was 19.8 +/- 6.1 mm in males and 9.1 +/- 2.8 mm in females. In both sexes, AGD increased up to 12 months and maintained the sex dimorphic pattern. AGD also showed positive correlation with penile length at birth and with the increase in AGD from birth to 3 months.52 AGD provides an index of early fetal androgen exposure and masculinization.


Androgens play a time-dependent role in formation, differentiation, and growth of the fetal external genitalia; a role that is especially relevant for male reproductive organ development. Studies among rats suggest that there is a limited time during early fetal development known as the masculinization programming window (MPW). During the MPW the potential for masculinization is determined. Deficiency of androgen or androgen action in the MPW results in reduced penis length, which can not be rescued by postnatal T therapy.53 The MPW predetermines potential organ size, while post-natal androgen action is required to realize normal potential.54

Only gold members can continue reading. Log In or Register to continue

Related posts:

Overview and principles of pediatric endocrinology Neonatal diabetes mellitus Thyroid disorders in children and adolescents Laboratory methods in pediatric endocrinology Receptor transduction pathways mediating hormone action Adrenal cortex and its disorders

Stay updated, free articles. Join our Telegram channel
Tags:
Jun 4, 2016 | Posted by in ENDOCRINOLOGY | Comments Off on Ambiguous genitalia

Full access? Get Clinical Tree
Get Clinical Tree app for offline access