**4.1 Ovarian development**

There are two types of abnormal development that can cause XX sex reversal:


Loss of function mutations in genes coding for ovarian formation and function are associated with ovarian dysgenesis and/or accelerated loss of primordial follicles. This can cause premature ovarian failure (POF) and/or premature menopause.

The gene responsible for the differentiation of the bipotential gonad into ovaries is the *WNT4* gene (**Figure 4**). The *WNT4* gene is a member of the WNT family of secreted molecules. This family of genes function in a paracrine manner. The WNT proteins are ligands to members of the Frizzled (FZ) family of cell surface receptors. They are also possibly ligands to the single-pass transmembrane protein LDL-receptor-related proteins 5 and 6 (*LRP5* and *LRP6*) [40]. The binding of WNT to FZ leads to reduced degradation of β-catenin. This causes β-catenin-dependent activation of T-cell factor/lymphocyte enhancer factor transcription factors that lead to the induction of WNT – responsive genes [41]. *WNT4* is produced in ovarian pre-granulosa cells. *WNT4* up-regulates the gene *DAX1* [42], which antagonizes *NR5A1*, and inhibits steroidogenic enzymes. *WNT4* – knockout XX mice have been shown to have no Müllerian ducts derivatives, have present Wolffian ducts and masculinized with the expression of the steroidogenic enzymes, namely 3β hydroxy steroid dehydrogenase and 17α hydroxylase. They are critically important in the production of testosterone. Conversely, they are normally suppressed in the developing female ovary. Mice models showed ovaries with a decreased number of oocytes. This demonstrates the important role of *WNT4* in maintaining the female

germ cells and thus normal ovarian function [43]. This is contrasted by testicular function which continues in the absence of sperm.

In humans, duplication of chromosome 1p31-p35 causes a duplication of the *WNT4* gene. This duplication has been associated with male to female sex reversal exhibiting ambiguous genitalia, severe hypospadias, streak gonads and remnants of both Müllerian and Wolffian ducts [42] . Homozygotes with pathogenic variants in *WNT4* results in SERKAL (SEx Reversion, Kidneys, Adrenal and Lung dysgenesis) syndrome [44]. Pathogenic variants in this gene have also been found in women with absent Müllerian structures with clinical signs of androgen excess. Pathogenic variants have also presented with findings resembling Mayer-Rokitansky-Küster-Hauser syndrome [45].

Another important gene is the *FOXL2* gene which is responsible in the formation and function of the ovaries. Pathogenic variants in this gene result in BPES (blepharophimosis, ptosis, and epicanthus inversus) syndrome (OMIM # 110100). There are two types of the condition; in BPES I it is associated with premature ovarian failure (POF) and in BPES type II it is not associated with POF.

In mice models the continued expression of *FOXL2* is essential in maintaining ovarian function. Loss of gene expression leads to reprogramming of granulosa and theca cells into cells that are similar to Sertoli and Leydig cells, respectively [4, 46–49]. *FOXL2* also stimulates the expression of the gonadotropin releasing hormone (GnRH) receptor. This expression precedes glycoprotein hormone α-subunit, this is a common subunit to FSH, LH, and TSH in the pituitary gland [50].

*RSPO1* [roof plate-specific spondin-1] is an important gene in ovarian development. It's role is to act as a regulator of female sex differentiation by activating the canonical WNT/β-catenin pathway. This pathway opposes testis formation, with *WNT4* playing a prominent role as a key ligand [51, 52]. During sex differentiation significantly higher expression of *RSPO1* was detected in the ovaries compared to testis [52], supporting the genes importance in female sex differentiation.

Other genes associated with ovarian dysgenesis and premature ovarian failure include: *LHX8*, *MCM8*, *MCM9*, *NOBOX*, and *FSHR* [46–48].

#### **4.2 Exposure or overproduction of androgens**

In 46,XX female, increased fetal androgen synthesis or prenatal exposure to androgen leads to musculinization of the female external genitalia (**Figure 6**) [26].

#### *4.2.1 Exposure to androgens of non-fetal origin*

Maternal androgen producing tumors can cause virilization of a female infant. These include adrenal tumors and ovarian tumors. There have been reports including a maternal luteoma of pregnancy which caused virilization of both mother and child [53]. There are also various drugs with androgenic activity. These include androgens, danazol, progestins and potassium sparing diuretics that are known to cause virilization [17, 53].

Placental Aromatase Deficiency is another cause of virilization in a female. This is a rare autosomal recessive condition caused by mutations in *CYP19A1* on chromosome 15q21.2 and less than 20 cases have been described in literature. Aromatase converts androstenedione to estrone in the female ovaries (**Figure 6**) providing protection for the fetus from high circulating levels of androgens. Sources of androgens include the fetal adrenal glands and androgens of maternal origin [54]. Cases present with maternal virilization in the 3rd trimester and abnormal genitalia in the affected females [54, 55]. Biochemically cases have intact cortisol and aldosterone production and are not at risk for salt wasting.

**71**

adulthood [54].

**Figure 6.**

hirsutism and irregular menses.

*Approach to the Newborn with Disorders of Sex Development*

*4.2.2 Steroid synthesis defects – overproduction of androgens*

*21-hydroxylase; 11*β*-OH: 11*β*-hydroxylase (adapted from [17]).*

Steroid synthesis defects leading to congenital adrenal hyperplasia with androgen excess cause clitoral enlargement, partial or complete fusion of the labia

*Steroid hormone synthesis pathway in 46, XX DSD. 3*β*-HSD: 3*β*-hydroxysteroid dehydrogenase; 21-OH:* 

Patients with classic 21(OH) deficiency are at high risk (approximately

17α-hydroxyprogesterone, androstenedione and testosterone levels (**Figure 6**) and decreased sodium, elevated potassium and elevated renin at the end of the first week of life [17]. The high androgens levels result in virilization of the female external genitalia in female fetuses. This can be seen as early as 12 weeks gestation [54] and varies from mild clitoromegaly to complete male external genitalia with

Non-classic 21(OH) deficiency is more common than the classic form. The world

11β-OH is present in the adrenals and coded by the CYP11B1 gene. Defects lead to congenital adrenal hyperplasia which present with a similar picture to classical CAH. This is the second most common cause of congenital adrenal hyperplasia

wide incidence is 1:300, the Ashkenazi Jewish population has a higher incidence described as 1:27 [54]. They generally present in adolescence with a presentation is similar to Polycystic Ovarian Syndrome, namely premature pubarche, acne,

70%) for neonatal salt wasting [17]. These patients present with high

rugated and pigmented labioscrotal folds and a phallic structure [17].

majora and a short vagina [26] with virilization Prader stage above III [55]. The most common cause of 46, XX disorders of sexual differentiation (**Figure 6**) is 21-hydroxylase (21-OH) deficiency. This occurs in 90% of cases [55] and has a prevalence of 1:14,000–1:15,000 worldwide [54, 55]. This autosomal recessive condition is caused by mutations in the 21-OH gene (*CYP21A2*) on chromosome 6p21.1. The severity of the disease correlates generally to the degree of enzyme activity with classic 21(OH) deficiency having less than 5% activity. These patients present with congenital adrenal hyperplasia and in utero virilization of the external genitalia in females. Non-classic 21(OH) deficiency have >15% residual activity. These patients present with androgen excess in adolescence and early

*DOI: http://dx.doi.org/10.5772/intechopen.94570*

**Figure 6.**

*Congenital Anomalies in Newborn Infants - Clinical and Etiopathological Perspectives*

function which continues in the absence of sperm.

failure (POF) and in BPES type II it is not associated with POF.

Hauser syndrome [45].

germ cells and thus normal ovarian function [43]. This is contrasted by testicular

In humans, duplication of chromosome 1p31-p35 causes a duplication of the *WNT4* gene. This duplication has been associated with male to female sex reversal exhibiting ambiguous genitalia, severe hypospadias, streak gonads and remnants of both Müllerian and Wolffian ducts [42] . Homozygotes with pathogenic variants in *WNT4* results in SERKAL (SEx Reversion, Kidneys, Adrenal and Lung dysgenesis) syndrome [44]. Pathogenic variants in this gene have also been found in women with absent Müllerian structures with clinical signs of androgen excess. Pathogenic variants have also presented with findings resembling Mayer-Rokitansky-Küster-

Another important gene is the *FOXL2* gene which is responsible in the formation and function of the ovaries. Pathogenic variants in this gene result in BPES (blepharophimosis, ptosis, and epicanthus inversus) syndrome (OMIM # 110100). There are two types of the condition; in BPES I it is associated with premature ovarian

In mice models the continued expression of *FOXL2* is essential in maintaining ovarian function. Loss of gene expression leads to reprogramming of granulosa and

[4, 46–49]. *FOXL2* also stimulates the expression of the gonadotropin releasing hormone (GnRH) receptor. This expression precedes glycoprotein hormone α-subunit,

*RSPO1* [roof plate-specific spondin-1] is an important gene in ovarian development. It's role is to act as a regulator of female sex differentiation by activating the canonical WNT/β-catenin pathway. This pathway opposes testis formation, with *WNT4* playing a prominent role as a key ligand [51, 52]. During sex differentiation significantly higher expression of *RSPO1* was detected in the ovaries compared to

Other genes associated with ovarian dysgenesis and premature ovarian failure

In 46,XX female, increased fetal androgen synthesis or prenatal exposure to androgen leads to musculinization of the female external genitalia (**Figure 6**) [26].

Maternal androgen producing tumors can cause virilization of a female infant. These include adrenal tumors and ovarian tumors. There have been reports including a maternal luteoma of pregnancy which caused virilization of both mother and child [53]. There are also various drugs with androgenic activity. These include androgens, danazol, progestins and potassium sparing diuretics that are known to

Placental Aromatase Deficiency is another cause of virilization in a female. This is a rare autosomal recessive condition caused by mutations in *CYP19A1* on chromosome 15q21.2 and less than 20 cases have been described in literature. Aromatase converts androstenedione to estrone in the female ovaries (**Figure 6**) providing protection for the fetus from high circulating levels of androgens. Sources of androgens include the fetal adrenal glands and androgens of maternal origin [54]. Cases present with maternal virilization in the 3rd trimester and abnormal genitalia in the affected females [54, 55]. Biochemically cases have intact cortisol and aldosterone

theca cells into cells that are similar to Sertoli and Leydig cells, respectively

this is a common subunit to FSH, LH, and TSH in the pituitary gland [50].

testis [52], supporting the genes importance in female sex differentiation.

include: *LHX8*, *MCM8*, *MCM9*, *NOBOX*, and *FSHR* [46–48].

**4.2 Exposure or overproduction of androgens**

*4.2.1 Exposure to androgens of non-fetal origin*

production and are not at risk for salt wasting.

cause virilization [17, 53].

**70**

*Steroid hormone synthesis pathway in 46, XX DSD. 3*β*-HSD: 3*β*-hydroxysteroid dehydrogenase; 21-OH: 21-hydroxylase; 11*β*-OH: 11*β*-hydroxylase (adapted from [17]).*
