Sex Development¶
Chapter 402 | Part 12: Endocrinology and Metabolism
KEY CLINICAL POINTS¶
- Differences of sex development (DSDs) encompass chromosomal, gonadal, and phenotypic sex variations, with classifications including 46,XY and 46,XX DSDs.
- SRY gene on the Y chromosome initiates testis development, while WNT4 and RSPO1 promote ovarian development. Disruption of these pathways leads to DSDs.
- Klinefelter syndrome (47,XXY) and Turner syndrome (45,X) are common DSDs with distinct clinical features, requiring multidisciplinary management.
- Congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency is the most common cause of androgenization in 46,XX fetuses, presenting with ambiguous genitalia.
- Management of DSDs involves hormone replacement, surgical interventions, and long-term monitoring, with emphasis on patient autonomy and psychological support.
1. DEFINITION & OVERVIEW¶
Sex development involves chromosomal sex (karyotype), gonadal sex (testis/ovary differentiation), and phenotypic sex (external genitalia). DSDs arise from disruptions at any stage of this process.
Table 402-1: Classification of Differences (Disorders) of Sex Development (DSDs)¶
| SEX CHROMOSOME DSD | 46,XY DSD | 46,XX DSD |
|---|---|---|
| 47,XXY (Klinefelter syndrome) | Gonadal (testis) development | Gonadal (ovary) development |
| 45,X (Turner syndrome) | Complete or partial gonadal dysgenesis | Gonadal dysgenesis |
| 45,X/46,XY mosaicism | Impaired fetal Leydig cell function | Ovotesticular DSD |
| 46,XX/46,XY (chimerism/mosaicism) | Ovotesticular DSD | Testicular DSD |
| Testis regression | Disruption in androgen synthesis or action | Androgen excess |
| Disruption of androgen biosynthesis | LH receptor (LHCGR) | Fetal 3b-Hydroxysteroid dehydrogenase II (HSD3B2) |
| Smith-Lemli-Opitz syndrome (DHCR7) | Steroidogenic acute regulatory (StAR) protein | 21-Hydroxylase (CYP21A2) |
| Cholesterol side-chain cleavage (CYP11A1) | 17a-Hydroxylase/17,20-lyase (CYP17A1) | P450 oxidoreductase (POR) |
| 3b-Hydroxysteroid dehydrogenase II (HSD3B2) | 11b-Hydroxylase (CYP11B1) | Fetoplacental aromatase deficiency (CYP19A1) |
| 17a-Hydroxylase/17,20-lyase (CYP17A1) | P450 oxidoreductase (POR) | Maternal virilizing tumors (e.g., luteomas) |
| SEX CHROMOSOME DSD | 46,XY DSD | 46,XX DSD |
|---|---|---|
| P450 oxidoreductase (POR) | Cytochrome b5 (CYB5A) | Androgenic drugs |
| Cytochrome b5 (CYB5A) | 17b-Hydroxysteroid dehydrogenase III (HSD17B3) | Others include: syndromic associations, Müllerian agenesis, uterine abnormalities |
1.1 Chromosomal Sex¶
Defined by karyotype (46,XX/46,XY). Chromosomal abnormalities (e.g., 45,X, 47,XXY) lead to gonadal dysgenesis or testicular/ovarian development.
1.2 Gonadal Sex¶
Embryonic gonads are bipotential. SRY gene (Y chromosome) drives testis development; WNT4/R-spondin-1 promote ovarian development.
1.3 Phenotypic Sex¶
External genitalia and secondary sex characteristics develop under hormonal influence (testosterone/AMH for male, estrogen for female).
2. EPIDEMIOLOGY¶
DSDs affect ~1 in 5000 newborns. Klinefelter syndrome (47,XXY) has an incidence of ~1 in 1000 men, while Turner syndrome (45,X) occurs in ~1 in 2500 women. CAH (21-hydroxylase deficiency) is the most common cause of ambiguous genitalia in 46,XX infants.
Table 402-2: Presentation of DSDs at Different Life Stages¶
| PRESENTATION | FEATURES | PROFESSIONAL | EXAMPLES |
|---|---|---|---|
| Prenatal | Karyotype-phenotype discordance | Obstetrician; fetal medicine | Many |
| Atypical genitalia | Obstetrician; neonatal medicine | ||
| Salt-losing crisis | Pediatrician | CAH (CYP21A2) | |
| Childhood | Hernia | Surgeon | CAIS |
| Androgenization | Endocrinologist | CAH (CYP21A2, CYP11B1) | |
| Poor growth | Pediatrician | Turner, 45,X/46,XY | |
| Associated features | Oncologist/nephrologist | Wilms’ tumor | |
| Puberty | Androgenization | Endocrinologist | 17b-HSD, 5a-reductase, SF1 |
| Estrogenization | Endocrinologist | Ovotestis | |
| Absent puberty | Endocrinologist | Gonadal dysgenesis, CAH (CYP17A1), Turner | |
| Amenorrhea | Gynecologist | ||
| Adult | Infertility | Andrologist | Klinefelter, 45,X/46,XY, SF1 |
2.1 Risk Factors¶
Chromosomal abnormalities (e.g., 45,X/46,XY mosaicism), genetic mutations (e.g., SRY, WNT4), and maternal factors (e.g., virilizing tumors).
2.2 Demographics¶
Turner syndrome is more common in females; Klinefelter syndrome in males. CAH is more prevalent in females due to androgenization.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
DSDs arise from disruptions in SRY gene (testis development), WNT4/R-spondin-1 (ovarian development), or androgen synthesis/action pathways. Genetic mutations (e.g., SF1, SRY, CYP21A2) and chromosomal abnormalities (e.g., 45,X, 47,XXY) are key mechanisms.
Table 402-4: Genetic Causes of 46,XY DSDs¶
| GENE | INHERITANCE | GONAD | UTERUS | EXTERNAL GENITALIA | ASSOCIATED FEATURES |
|---|---|---|---|---|---|
| WT1 | AD | Dysgenetic testis | +/– | Female or ambiguous | Wilms’ tumor, renal abnormalities |
| SF1/NR5A1 | AR/AD (SL) | Dysgenetic testis/Leydig dysfunction | +/– | Female, ambiguous or male | Primary adrenal failure, hyposplenia |
| SRY | Y | Dysgenetic testis or ovotestis | +/– | Female or ambiguous | |
| SOX9 | AD | Dysgenetic testis or ovotestis | +/– | Female or ambiguous | Campomelic dysplasia |
| DHX37 | AD | Dysgenetic testis | +/– | Female, ambiguous or male | Testicular regression syndrome |
| CYP21A2 | AR | Ovary | + | Ambiguous | CAH, hypertension, salt-losing crisis |
| CYP11B1 | AR | Ovary | + | Ambiguous | CAH, hypertension due to 11-deoxy corticosterone |
| HSD3B2 | AR | Ovary | + | Ambiguous | CAH, primary adrenal insufficiency |
| CYP17A1 | AR | Ovary | + | Ambiguous | CAH, hypertension, 17a-hydroxylase deficiency |
| POR | AR | Ovary | + | Ambiguous or female | Mixed 21-hydroxylase and 17a-hydroxylase deficiency |
| HSD17B3 | AR | Ovary | + | Ambiguous | Partial androgenization at puberty |
| GENE | INHERITANCE | GONAD | UTERUS | EXTERNAL GENITALIA | ASSOCIATED FEATURES |
|---|---|---|---|---|---|
| SRD5A2 | AR | Ovary | + | Ambiguous or male | Partial androgenization at puberty |
| AKR1C2 | AR | Ovary | + | Ambiguous | Decreased fetal DHT production |
3.1 Testis Development¶
SRY gene initiates testis differentiation via SOX9, leading to AMH secretion and Müllerian duct regression. Disruption causes gonadal dysgenesis or testicular regression.
3.2 Ovarian Development¶
WNT4 and R-spondin-1 suppress testis development. Mutations in these genes lead to ovotesticular DSDs or female pseudohermaphroditism.
3.3 Androgen Pathway¶
Defects in CYP21A2, CYP17A1, or AR cause CAH or androgen insensitivity syndrome (AIS).
4. CLINICAL FEATURES¶
Clinical manifestations vary by DSD type. Klinefelter syndrome presents with small testes, infertility, and gynecomastia. Turner syndrome features short stature, lymphedema, and cardiac defects. CAH causes ambiguous genitalia and adrenal crises.
Table 402-3: Clinical Features of Sex Chromosome Variations¶
| DISORDER | COMMON CHROMOSOMAL COMPLEMENT | GONAD | GENITALIA | BREAST DEVELOPMENT |
|---|---|---|---|---|
| Klinefelter syndrome | 47,XXY or 46,XY/47,XXY | Hyalinized testes | Male | Increased gynecomastia |
| Turner syndrome | 45,X or 45,X/46,XX | Streak gonad or immature ovary | Female | Immature female |
| 45,X/46,XY mosaicism | 45,X/46,XY | Testis or streak gonad | Variable | Usually male |
| Ovotesticular DSD | 46,XX/46,XY | Testis and ovary or ovotestis | Variable | Gynecomastia |
4.1 Klinefelter Syndrome (47,XXY)¶
Small testes, infertility, gynecomastia, tall stature, and increased risk of breast cancer. Most diagnosed post-puberty.
4.2 Turner Syndrome (45,X)¶
Short stature, webbed neck, lymphedema, cardiac defects, and ovarian dysgenesis. Most diagnosed prepubertally.
4.3 Congenital Adrenal Hyperplasia (CAH)¶
Ambiguous genitalia in 46,XX infants, hypertension, and adrenal crises. 21-hydroxylase deficiency is the most common cause.
5. DIFFERENTIAL DIAGNOSIS¶
Differential diagnoses include congenital adrenal hyperplasia, androgen insensitivity syndrome, androgen excess disorders, and genetic syndromes (e.g., Turner, Klinefelter).
5.1 Ambiguous Genitalia¶
Consider CAH, AIS, 46,XX testicular DSD, or maternal virilizing tumors.
5.2 Primary Amenorrhea¶
Evaluate for Turner syndrome, androgen insensitivity, or ovarian dysgenesis.
6. INVESTIGATIONS & DIAGNOSIS¶
Diagnostic workup includes karyotype, hormone assays (testosterone, AMH, FSH), imaging (ultrasound, MRI), and genetic testing (SRY, CYP21A2, SF1).
Table 402-5: Genetic Causes of 46,XX DSDs¶
| GENE | INHERITANCE | GONAD | UTERUS | EXTERNAL GENITALIA | ASSOCIATED FEATURES |
|---|---|---|---|---|---|
| SRY | Translocation | Testis or ovotestis | - | Male or ambiguous | |
| SF1/NR5A1 (codon 92) | AD | Testis or ovotestis | +/– | Male or ambiguous | |
| CYP21A2 | AR | Ovary | + | Ambiguous | CAH, hypertension, salt-losing crisis |
| CYP11B1 | AR | Ovary | + | Ambiguous | CAH, hypertension due to 11-deoxy corticosterone |
| POR | AR | Ovary | + | Ambiguous or female | Mixed 21-hydroxylase and 17a-hydroxylase deficiency |
| HSD3B2 | AR | Ovary | + | Ambiguous | CAH, primary adrenal insufficiency |
| CYP19 | AR | Ovary | + | Ambiguous | Maternal virilization, absent breast development |
6.1 Laboratory Tests¶
Measure testosterone, AMH, FSH, LH, and cortisol. Test for 17-hydroxyprogesterone in CAH suspicion.
6.2 Imaging¶
Ultrasound for gonadal assessment; MRI for aortic root dilation in Turner syndrome.
7. MANAGEMENT & TREATMENT¶
Management includes hormone replacement (estrogen/testosterone), surgical interventions (genitoplasty), and monitoring for complications. Multidisciplinary care is essential.
7.1 Hormone Replacement¶
Estrogen for females, testosterone for males. Monitor bone density and cardiovascular health.
7.2 Surgical Options¶
Vaginoplasty for 46,XX DSDs; orchidopexy for cryptorchidism. Consider genitoplasty with patient assent.
7.3 Fertility Considerations¶
In vitro fertilization (IVF) with donor eggs for Turner syndrome. Testicular sperm extraction for 46,XX DSDs.
8. PROGNOSIS & COMPLICATIONS¶
Prognosis varies by DSD type. Complications include infertility, cardiovascular disease, osteoporosis, and psychological challenges. Long-term follow-up is critical.
8.1 Klinefelter Syndrome¶
Increased risk of breast cancer, osteoporosis, and cardiovascular disease. Early testosterone replacement improves outcomes.
8.2 Turner Syndrome¶
Risk of aortic dissection, infertility, and osteoporosis. Regular cardiac and renal monitoring required.
9. SPECIAL CONSIDERATIONS¶
Considerations include gender identity, fertility preservation, and pregnancy risks. Genetic counseling is recommended for families.
9.1 Pregnancy¶
Turner syndrome females may require donor eggs. 46,XX DSDs with gonadal tissue may have fertility potential.
9.2 Pediatric Management¶
Early intervention for ambiguous genitalia. Avoid unnecessary surgeries without patient consent.
10. KEY POINTS & CLINICAL PEARLS¶
- DSDs require multidisciplinary care and patient autonomy.
- SRY gene is critical for testis development; WNT4 for ovarian development.
- CAH is the most common cause of ambiguous genitalia in 46,XX infants.
- Hormone replacement and long-term monitoring are essential for optimal outcomes.
- Genetic counseling is vital for families with DSDs.