Based on the karyotype, which of the following statements is most likely true?

III.A Complete Androgen Insensitivity Syndrome

A 46,XY karyotype, testes and an unambiguously female habitus and psychosexual orientation characterize individuals with CAIS. Axillary and pubic hair are sparse or absent (hairless women) and the external genitalia are female. The female internal genitalia, the uterus and the fallopian tubes, are absent; the vagina is thus blind-ending. The testes are located in the abdomen, the inguinal canal, or in the labia majora. They contain normal Leydig cells and seminiferous tubules without spermatogenesis. In the adult, gonadotropin secretion and testosterone production are in the upper normal range for men or are elevated and estrogen production is increased. Adults tend to be tall, and bone age is normal. Bone mass is within the female range, which indicates that estrogens alone do not fully compensate for the loss of androgen receptor function. The underlying defects of the disorder are various mutations in the androgen receptor gene.

46,XY DSD

A 46,XY karyotype reveals that one is dealing with a genetic male who was undermasculinized during fetal development. Laboratory findings of normal or elevated testosterone and DHT indicate a diagnosis of AIS. If testosterone levels are normal but DHT levels are low, a diagnosis of steroid 5α-reductase deficiency can be made. Low levels of testosterone and DHT, along with marked elevation of some androgen precursors, indicate a deficiency of one of the enzymes required for androgen biosynthesis. For example, if the elevated precursors include androstenedione and 17-hydroxyprogesterone, then the defective enzyme is 17-ketosteroid reductase. In all cases of testosterone biosynthetic defects, MIH levels are similar to those observed in male infants not affected by DSD. Finally, when all androgens and their precursors are below normal levels, one is dealing with either gonadal dysgenesis or 46,XY ovotesticular DSD. In these cases, MIH values should also be low. In contrast, for babies affected by Leydig cell hypoplasia, androgens and their precursors are low, while MIH values should be in the normal male range. In patients with 46,XY DSD, it is also important to appreciate the risk for tumors in testes located in the abdomen. The consensus statement on management of DSD has outlined recommendations on timing of gonadectomy in these patients [1].

4.23.6.3 Sex Chromosome Effects in a Mouse Model of MS

The finding that the XY− sex chromosome complement, as compared to the XX, was relatively more stimulatory with respect to cytokine responses (IFNγ, TNFα, and IL10) during autoantigen-specific stimulation supported the concept of direct effects of sex chromosomes on autoimmunity, but the precise role in autoimmune disease remained unknown. IFNγ and TNFα may have either disease-promoting or disease-protective effects depending on the dose and timing of their production, while IL10 is generally considered to be protective in EAE. In addition, there are numerous other cytokines, chemokines, adhesion molecules, and costimulatory factors that play a role in EAE pathogenesis, and they too could theoretically be affected by sex chromosome complement. Thus, to directly assess the role of sex chromosome complement in disease, EAE was induced in mice with the informative sex chromosome complements. Specifically, both females and males were gonadectomized to remove any effects of circulating sex hormones that might mask effects of sex chromosomes (Palaszynski et al., 2005). SJL castrated male mice that were either XXSry or XY−Sry, had active EAE induced with PLP 139–151 peptide. Clinical disease course was significantly more severe in XXSry mice, as compared to XY−Sry mice. This significant difference in disease severity also occurred when comparing ovariectomized female XX versus XY− mice. Further, in adaptive EAE, CNS pathology revealed higher levels of inflammation in mice that had received autoantigen-specific cells derived from XX mice as compared to those from XY− mice, Figure 6(a) and 6(b). Together, these data showed that the XX sex chromosome complement, as compared to the XY−, was associated with a greater ability to induce EAE (Smith-Bouvier et al., 2008). Studies have also suggested that Y chromosome polymorphisms may confer protection against EAE (Spach et al., 2009; Teuscher et al., 2006).

Since it had been previously shown that no sex bias existed in EAE in the C57BL/6 strain of mice (Okuda et al., 2002; Palaszynski et al., 2004b; Papenfuss et al., 2004), it was then ascertained whether an effect of sex chromosomes could be found in this strain. Thus, the Sry-deficient Y chromosome from the original outbred MF1 mice (Mahadevaiah et al., 1998) was backcrossed onto the C57BL/6 strain. Both females and males were gonadectomized to remove any effects of sex hormones which might mask effects of sex chromosomes (Palaszynski et al., 2005). C57BL/6 castrated male mice that were either XXSry or XY−Sry had active EAE induced with MOG 35–55 peptide. In contrast to results in the SJL, clinical disease courses were no different when comparing XXSry mice with XY−Sry mice. There was also no difference in disease when comparing ovariectomized female XX versus XY− mice. Together, these data indicated that when a strain was used that was characterized by a female-to-male difference in EAE (the SJL), a sex chromosome effect was present. In contrast, when a strain was used that is not characterized by a female-to-male difference in EAE (the C57BL/6), a sex chromosome effect was not present. The presence of a sex chromosome effect in one strain, but not another, revealed an interaction between sex chromosome complement and genetic background. Notably, effects of sex hormones in EAE have also previously been shown to be dependent on genetic background (Palaszynski et al., 2004b), and some autosomal gene linkages to susceptibility to MS have been identified in one gender but not the other (Kantarci et al., 2005). Thus, in the outbred human population, the genetic background of some, but not all, individuals may be permissive to sex chromosome or sex hormone effects. Notably, since overall there is a sex difference in many autoimmune diseases in humans, we hypothesize that relatively permissive genetic backgrounds are likely to be prevalent, not rare, in occurrence.

Recent work on the potential role of sex chromosomes in the CNS response to immune-mediated injury in EAE used XX versus XY bone marrow chimeras reconstituted with a common immune system of one sex chromosomal type. EAE mice with an XY sex chromosome complement in the CNS, compared with XX, demonstrated greater clinical disease severity with more neuropathology in the spinal cord, cerebellum, and cerebral cortex. A candidate gene on the X chromosome, TLR7, was then examined. TLR7 expression in cortical neurons was higher in mice with XY compared with mice with XX CNS, consistent with the known neurodegenerative role for TLR7 in neurons. These results suggested that sex chromosome effects on neurodegeneration in the CNS run counter to effects on immune responses, and may bear relevance to the clinical enigma of greater MS susceptibility in women but faster disability progression in men. This work demonstrated a direct effect of sex chromosome complement on neurodegeneration in a neurological disease (Du et al., 2014).

SEX CHROMOSOME EFFECTS IN A MOUSE MODEL OF MULTIPLE SCLEROSIS

The finding that the XY− sex chromosome complement, compared with the XX, resulted in relatively more robust autoantigen-specific cytokine responses supported the concept of direct effects of sex chromosomes on autoimmunity. However, because these cytokines can have both pro-inflammatory and anti-inflammatory roles in EAE, the role of sex chromosome complement in disease remained unknown. To directly assess this question, EAE was induced in mice with the informative sex chromosome complements.143 SJL castrated male mice that were either XXSry or XY−Sry had active EAE induced with the PLP 139-151 peptide. The clinical disease course was significantly more severe in the XXSry mice than in the XY−Sry mice. This significant difference in disease severity also occurred in ovariectomized female XX versus XY− mice. Further, in adoptive EAE, CNS pathology revealed higher levels of inflammation in mice that had received autoantigen-specific cells derived from XX mice, compared with those derived from XY− mice. Together, these data showed that the XX sex chromosome complement, compared with XY−, was associated with greater encephalitogenicity.

Because it had been shown previously that no gender bias exists in EAE in the C57BL/6 strain of mice,37-39 we investigated whether an effect of sex chromosomes could be found in this strain.143 C57BL/6 castrated male mice that were either XXSry or XY−Sry had active EAE induced with the MOG 35-55 peptide. In contrast to results in the SJL mice, the clinical disease course was no different in XXSry compared with XY−Sry mice. Likewise, there was no difference in disease course in ovariectomized female XX versus XY− mice. Together, these data indicated the presence of a sex chromosome effect in a strain exhibiting gender difference in EAE (the SJL) but not in a strain characterized by no gender difference in EAE (the C57BL/6). This finding revealed an interaction between sex chromosome complement and genetic background. Significantly, the effects of sex hormones in EAE were also previously been shown to be dependent on genetic background,39 and some autosomal gene linkages to susceptibility to MS in humans have been identified in one gender but not the other.40 Therefore, in the outbred human population, the genetic background of some, but not all, individuals may be permissive to sex chromosome or sex hormone effects. Because there is a gender difference in many autoimmune diseases in humans, we hypothesize that relatively permissive genetic backgrounds are likely to be prevalent, not rare, in occurrence.

45,X/46,XY Mosaicism and Variants

A mosaic 45,X/46,XY karyotype, sometimes referred to as mixed gonadal dysgenesis, probably arises through anaphase lag during mitosis in the zygote, although Y chromosomal abnormalities are sometimes seen, and interchromosomal rearrangements with loss of structural abnormal Y material may be a common mechanism for variants of this con­dition. Although the classic form of this condition is associated with 45,X/46,XY mosaicism, 45,X/47,XYY or 45,X/46,XY/47,XYY mosaic karyotypes have also been reported.

The clinical phenotype associated with a 45,X/46,XY mosaicism is highly variable, and the true prevalence of this condition is unknown (see Table 23-4). Historically, individuals with the most severe forms of 45,X/46,XY mosaicism have been referred for further assessment, and most series of patients reported in the literature have probably reflected this bias, as studies based on nonselected prenatal karyotyping have shown that most children with 45,X/46,XY mosaicism appear male.209-211

Reported genital phenotypes associated with 45,X/46,XY mosaicism range from female external genitalia or mild clitoromegaly through all stages of ambiguous genitalia to hypospadias or a normal penis.209,212-215 Gonadal phenotypes range from streak gonads through dysgenetic testes to testes with normal histologic architecture. In rare cases, ovarian-like stroma and sparse primordial follicles may be present. The gonads may be positioned anywhere along the pathway of testicular descent, with streak gonads more likely to be intra-abdominal and well-formed testes more likely to be in the inguinoscrotal region. Müllerian structures may be present in the most severe cases because of impaired AMH production by Sertoli cells. Marked differences in gonadal development and histologic appearance can be seen between the right and the left sides or even within a single gonad (hence, the term mixed gonadal dysgenesis), often resulting in an asymmetry of the external genitalia.215 The presence of a hemiuterus and fallopian tube on the side of the most severely affected gonad in some cases provides important evidence for the paracrine actions of AMH on developing müllerian structures.

Somatic features associated with a 45,X/46,XY karyotype are highly variable and do not always correlate well with the gonadal phenotype.209,213-215 Approximately 40% of children have additional, clinical features reminiscent of Turner syndrome, such as short stature, nuchal folds, low-set hairline, and cardiac and renal abnormalities.215 Detailed evaluation and long-term follow-up of these patients may be warranted, as for Turner syndrome (see Chapter 10). In other cases, a reduction in predicted height may be the only somatic manifestation. Ongoing monitoring for features associated with Turner syndrome (e.g., thyroid function, hearing, cardiac anomalies) may be required for this group of individuals, and many families benefit from the psychological support and education that can be linked to specialist services.

Gender assignment can be difficult in individuals with 45,X/46,XY, and several factors should be considered, including genital appearance and urogenital anatomy, risk of gonadal malignancy, fertility and reproductive options, potential need for hormone replacement, and probable gender identity, sex role behavior, and psychosexual functioning.

Most infants with female or minimally androgenized genitalia are raised as female, and the presence of a uterus or hemiuterus allows the potential for pregnancy by ovum donation in the future, though predicting future function can be difficult. Intra-abdominal streak and dysgenetic gonads are thought to pose a significant risk of malignancy and should be removed because of a higher germ-cell tumor risk in dysgenetic structures.212,214,216 Estrogen replacement is required to induce breast and uterine development in adolescence, and the addition of progestins allows menstruation when a uterus is present. Growth-promoting agents have been used on an individual basis when short stature or Turner syndrome–like features are present. No large trials have been performed to assess this group of patients, although there can be a significant loss of growth during puberty and some studies have suggested use of GH from earlier in childhood may optimize growth potential if this is a concern.213,214,217 Similarly, no long-term outcome data on gender identity or psychosexual functioning are available.

Infants with hypospadias and reasonable phallic development are usually raised as male. Testosterone can sometimes be given to promote phallic growth in infancy, and hypospadias repair is usually offered as a two-stage procedure. Attempts should be made to perform orchidopexy as a one- or two-stage procedure, because there may be a significant risk of malignancy in these gonads, and careful monitoring of testes is necessary. Gonads that cannot be placed within the scrotum are usually removed.212,214 Gonads that can be secured within the scrotum need careful monitoring by palpation and biopsy in adolescence to assess for carcinoma in situ. Some studies have suggested that regular testicular ultrasound in adolescence can be used to detect changes such as microlithiasis.212,214 Puberty should be carefully monitored to ensure adequate endogenous testosterone production, and in some cases, testosterone supplementation is needed. Most boys enter puberty spontaneously but some then develop androgen insufficiency and are typically likely to undergo urogenital surgery.214 Reduced final height is invariable but there is beneficial response to growth hormone in some boys.213,214,217

Assignment of gender and management of a 45,X/46,XY child with highly ambiguous genitalia can be a difficult situation for parents and physicians, and long-term outcome data for this group are not available. Limited data suggest that approximately 60% of infants with this phenotype are raised female, but they are infertile, have no uterus, require gonadectomy, and are likely to undergo urogenital surgery. In contrast, those raised as male often undergo multiple hypospadias operations, may have poor corporal tissue, are infertile if dysgenetic gonads are present that need to be removed, and may have a significantly reduced height potential. Detailed assessment of each child is important and an individualized approach by an experienced multidisciplinary team is important for management and for long-term monitoring and support. Long-term outcome data from larger studies may provide better guidance on the management of this group of individuals in the future.

In addition to the most severe cases described earlier, a 45,X/46,XY mosaic karyotype can be associated with a male phenotype and apparently normal testis development. Initial cases of normal males with a 45,X/46,XY karyotype were described after screening of family members as potential bone marrow transplant donors, but later studies of amniocentesis showed that 90% of fetuses diagnosed as 45,X/46,XY by amniocentesis and confirmed as having this karyotype have normal male genitalia and apparently normal testes postnatally.210,211 Moreover, there seems to be limited correlation between the degree of mosaicism on peripheral blood sampling and gonadal or somatic phenotype. Follow-up data on this cohort are limited, HPG function has not been reported in detail, and fertility outcome and tumor risk are not known. Although a 45,X/46,XY karyotype is an uncommon finding in men presenting with testicular tumors or in the infertility clinic, more detailed long-term studies of the 45,X/46,XY male cohort are required to know whether extensive follow-up is necessary. It may seem prudent to monitor gonadal function in this cohort and to assess for evidence of testicular carcinoma in situ in adolescence, but evidence for the best approach is lacking.

Other Syndromes of Aberrant Sexual Differentiation

Several syndromes worth mentioning do not neatly fit into the described classification systems.

Vanishing testis syndrome is characterized by a 46,XY karyotype but absent testes bilaterally. This generally results in virilization to the point of normal external genitalia and internal duct structure but absent testes. The testes were thought to have produced androgen at some point, resulting in this masculinization, but subsequently vanished related to torsion or regression. Patients are generally raised as boys, and hormonal supplementation at puberty is required.51

Klinefelter’s syndrome is characterized by a male karyotype containing two or more X chromosomes (47,XXY; 48,XXXY; etc.). Although phenotypically male prepubertally, these patients acquire abnormal male secondary sexual characteristics (tall stature with disproportionately long legs, sparse facial hair, decreased muscle mass, and a feminine fat distribution) and infertility. The testes are small and hard, with decreased androgen production and elevated estradiol levels related to primary hypergonadotropic hypogonadism. Gynecomastia often occurs with an increased risk of breast cancer.52 Fertility has been reported but requires assisted means, such as intracytoplasmic sperm injection.53

46,XX Testicular DSD (XX sex reversal) is characterized by a male phenotype with a 46,XX karyotype. Most commonly this occurs from translocation of Y chromosomal material to the X chromosome, but it also can occur from mutation of the X chromosome or from mosaicism. The phenotype and management are similar to those of Klinefelter’s syndrome, with the exception of shorter stature.54

Mayer-Rokitansky-Küster-Hauser syndrome is characterized by a 46,XX karyotype with normal female external genitalia but a short, blind-ending vagina. Normal ovaries and fallopian tubes are present, but the uterus is generally rudimentary. Patients are seen initially with primary amenorrhea but may have cyclical pain related to functioning endometrium. Treatment is geared toward vaginal reconstruction to allow menses or intercourse, or both.55

Y Chromosome Disorder – Swyer Syndrome

Phenotypic females with ovarian failure can have a pure 46,XY karyotype without a coexistent 45,X cell line – Swyer syndrome. In this case, women will have bilateral streak gonads, normal stature, and a normal uterus and vagina without sexual ambiguity. These patients have the highest risk of developing tumors in their dysgenetic gonads (up to 25%); therefore, extirpating the gonads should be performed after the diagnosis.12

The gene for the sex-determining region of the Y chromosome (SRY) resides on the distal short arm of the Y chromosome (Fig. 30.4). When SRY is present the undifferentiated gonad will develop into a testis, which will first elaborate anti-Müllerian hormone (AMH) to remove the Müllerian system, and then testosterone for sexual differentiation. In Swyer syndrome, the gonad is dysfunctional (and replaced by fibrous streaks) so that AMH and testosterone are not produced. The lack of AMH leads to the retention of the uterus and vagina, while the reduction in normal Leydig cell function results in low testosterone and absent male sexual development. Therefore, the patient presents as a phenotypic female without breast development. Most cases of Swyer syndrome are sporadic and thought to be caused by SRY mutations, which is a single-exon gene on Yp encoding a transcription factor with a conserved HMG (high mobility group) domain. However, only about 15% of these patients actually have SRY mutations, suggesting that other genes must be involved.12 Certainly, other genes may cause disorders of sexual development resulting in sexual ambiguity, but they will be covered in Chapter 27. Swyer syndrome is detailed here because it results in gonadal failure in phenotypic females (genetic males).

Growth

Girls and boys who have a 45,X/46,XY karyotype are at high risk for adult short stature, similar to girls who have 45,X monosomy. Short stature may be the only physical sign in affected children, both boys and girls. Growth failure in association with a history of hypospadias or undescended testes should always prompt karyotyping. Although commonly administered nowadays, growth hormone therapy seems to result in improved height gain mainly on the short term, while adult height is disappointing and apparently with no better outcomes in treated as compared to untreated individuals. No differences have been observed between girls and boys, or those who entered puberty spontaneously or after hormonal stimulation. These data need confirmation in a larger sample (Richter-Unruh et al., 2004; Martinerie et al., 2012; Lindhardt Johansen et al., 2012; Bertelloni et al., 2015).

Complete Androgen Insensitivity

Children afflicted with androgen insensitivity syndrome (AIS) have a 46,XY karyotype and testes as gonads17-19 (see Chapter 138). Because the external genitalia have a normal female appearance, the disorder is often unnoticed at birth. Surgical repair of an inguinal hernia containing a testis may reveal the condition. Hormonal puberty is, without intervention, feminizing due to the aromatization of endogenous androgens to estrogens. In cases of complete AIS, sex assignment and rearing are almost invariably female. The differentiation of gender identity/role is feminine.17-19 This fact is theoretically important in showing that the nature of the chromosomes and gonads per se does not dictate gender identity and role. And further, that the virtual absence of androgen exposure is associated with a female gender identity and sexual orientation toward men. Apparently, the high levels of estradiol, derived from their elevated levels of testosterone production, do not defeminize as has been found in lower mammals.20

In adulthood, gender identity/role and sexuality conform almost universally to typical heterosexual feminine expectations. Removal of the testis is warranted because of the risk for malignant degeneration of (cryptorchid) testis, though the optimal age for this intervention has not been determined. Hereafter, hormone replacement is required.21,22

5.101.3.4 Diagnosis and Treatment

The diagnosis is established by demonstrating a 45,X/46,XY karyotype in peripheral blood and/or skin fibroblast culture and/or gonadal tissue (Grumbach et al., 2003). As stated above, a low threshold to perform blood karyotyping or eventually fibroblast or gonadal karyotyping is appropriate, even in isolated hypospadias or clitoral hypertrophy. Hypospadias associated with cryptorchidism must always be further examined for the presence of hidden mosaicism. The presence of functional testicular tissue can be demonstrated by an hCG test for the evaluation of Leydig cell function, whereas plasma AMH and inhibin B levels are indicative of Sertoli cell function. Obtained serum levels of AMH, inhibin B, and testosterone must be interpreted in view of the patient's age (Crofton et al., 2002; Grumbach et al., 2003; Rey et al., 1999). Ultrasonography is indicative for the presence or absence of Müllerian structures but the sensitivity of this technique is highly dependent on the examinator's experience. Laparoscopic exploration of internal gonadal structures is usually mandatory. The decision on sex of rearing must be made after a thorough evaluation of prenatal androgen exposure, the possibility to make genitalia consistent with the chosen sex, gonadal function, and fertility chances (Hughes et al., 2006).

In case of male gender assignment, testicles should be brought into a palpable, if possible low scrotal position, to allow follow-up for the development of malignancy by physical examination and ultrasound. In this context, the presence of bilateral microlithiasis might be a specific point of interest. If it is impossible to bring the testes into a scrotal position, they should be removed and testicular prostheses should be placed. Hypospadias should be corrected. The possibility of phalloplastic surgery, analogous to phalloplasty in female-to-male transsexuals, offers new perspectives for patients with micropenis (Hoebeke et al., 2003; Selvaggi et al., 2007).

In case of female gender assignment, removal of a testis, ovotestis, or streak is mandatory to avoid malignancy and eventually the production of cross-sex hormones. Clitoris reduction should be performed by an experienced surgeon, only in cases of severe clitoromegaly. The ideal timing for vaginoplasty (early in life vs. during puberty) is controversial. Vaginal dilatation should not be undertaken until puberty (Bondy and Turner Syndrome Study, 2007; Grumbach et al., 2003; Hughes et al., 2006). Detailed analysis of gonadal biopsy material for the presence of premalignant changes in DSD gonads (Cools et al., 2006a,b,c, 2005; Honecker et al., 2004; Kersemaekers et al., 2005; Stoop et al., 2005) allowed avoidance of gonadectomy in some cases. However, this technique is limited due to the fact that a biopsy is only partially representative for the gonad as a whole. We observed a case of 46,XX/47,XXY mosaicism, born with ambiguous genitalia, who was assigned a female gender. Laparoscopy and bilateral gonadal biopsies at 2 years of age revealed the likely presence of a normal ovary and hemiuterus on one side and a testicle on the other. After removal of the testicle, which turned out to be an ovotestis after complete evaluation, we performed hCG testing in combination with AMH and inhibin B screening. The results confirmed the absence of remaining functional testicular tissue; hence, it was decided to leave the ovary in place. However, based on this information, we are unable to exclude the presence of undifferentiated parts in the remaining gonad, containing a high risk for the development of gonadoblastoma. The need for hormonal replacement therapy (androgens or estrogens) depends on the capacity of the remaining gonad(s) to produce sex hormones.