Disorders of Sexual Development

Steroidogenic enzyme defects (autosomal recessive)

• **21-hydroxylase deficiency (CYP21A2)**: the dominant cause of 46,XX DSD; cortisol/aldosterone block shunts precursors into androgens
• 11β-hydroxylase deficiency: virilization plus hypertension and hypokalemia from accumulated 11-deoxycorticosterone (a mineralocorticoid agonist)
• 17α-hydroxylase/17,20-lyase deficiency: undervirilized 46,XY with hypertension and hypokalemia — androgens are absent, mineralocorticoid precursors accumulate
• 3β-hydroxysteroid dehydrogenase deficiency: mild virilization in XX (peripheral DHEA conversion), undervirilization in XY
• **P450 oxidoreductase and StAR (lipoid CAH) defects**: rarer, may include skeletal anomalies (Antley–Bixler)

Androgen action defects

• **Androgen insensitivity (X-linked AR mutation)**: receptor cannot transduce testosterone/DHT signal despite normal or high hormone levels
• 5α-reductase type 2 deficiency (autosomal recessive): testosterone normal, DHT low, so external genitalia (DHT-dependent) are undervirilized while wolffian structures (testosterone-dependent) are intact

Gonadal determination/differentiation defects

• Sex chromosome aneuploidy: 45,X (Turner), 47,XXY (Klinefelter), 45,X/46,XY mosaicism (mixed gonadal dysgenesis)
• Gene-level defects: SRY deletion or autosomal translocation, NR5A1, DHH, WT1 (Denys–Drash, Frasier), SOX9 (campomelic dysplasia)
• AMH or AMH receptor mutation: persistent müllerian duct syndrome in an otherwise virilized 46,XY male

Non-modifiable risk factors examiners plant

• Consanguinity or affected sibling: the tip-off for any autosomal recessive enzyme block
• Ashkenazi Jewish, Hispanic, or Yupik ancestry: enriched CYP21A2 carrier frequency (nonclassic and classic CAH)
• Advanced maternal age: meiotic nondisjunction underlying 47,XXY
• Prematurity/small-for-gestational-age: associated with hypospadias and cryptorchidism

Modifiable/exposure-related risk factors

• Maternal androgens or androgenic progestins/danazol: exogenous virilization of a 46,XX fetus
• Maternal virilizing tumor or luteoma of pregnancy, and placental aromatase deficiency: maternal virilization during gestation plus a virilized XX newborn
• Poorly controlled maternal CAH: excess maternal androgen crossing the placenta

• Chromosomal DSD (46,XX and 46,XY with sex chromosome anomalies) — Results from aneuploidy or structural abnormalities of sex chromosomes (e.g., Turner syndrome 45,X; Klinefelter syndrome 47,XXY); altered gene dosage disrupts normal gonadal development and sex-specific hormone production

• 46,XX DSD (virilization of genotypic female) — Most commonly caused by congenital adrenal hyperplasia (CAH), predominantly 21-hydroxylase deficiency (90% of cases); enzymatic block prevents cortisol synthesis, causing accumulation of precursors shunted to androgen pathway, resulting in excess fetal androgen exposure and masculinization of external genitalia; other causes include 11β-hydroxylase and 3β-hydroxysteroid dehydrogenase deficiencies, or maternal androgen exposure

• 46,XY DSD (undervirilization of genotypic male) — Results from defects in androgen synthesis (Leydig cell dysfunction, 17α-hydroxylase deficiency, 17,20-lyase deficiency), androgen receptor dysfunction (androgen insensitivity syndrome), abnormal anti-müllerian hormone (AMH) signaling (persistent müllerian duct syndrome), or gonadal dysgenesis; causes range from complete female phenotype (complete androgen insensitivity syndrome, cAIS) to mild hypospadias

• Gonadal dysgenesis — Results from defective migration, proliferation, or differentiation of primordial germ cells; mutations in genes like SRY, DHH, DMRT1, or NR5A1; presents as streak gonads with absent germ cells and insufficient sex hormone production

• True gonadal hermaphroditism — Presence of both ovarian and testicular tissue (most commonly 46,XX); often associated with SRY translocation to autosomes or low-level mosaicism

• Ambiguous external genitalia at birth — The cardinal presentation prompting immediate evaluation; ranges from mild clitoromegaly in 46,XX CAH to severe hypospadias with undescended testes in 46,XY androgen insensitivity; degree of virilization depends on timing and degree of androgen exposure/action

• Discordance between prenatal imaging/ultrasound findings and postnatal examination — May reveal unexpected internal reproductive structures (e.g., uterus present in 46,XY individual, or absent in 46,XX with severe virilization); important diagnostic clue

• Neonatal hypoglycemia, hyponatremia, and shock (adrenal crisis) — Occurs in salt-wasting form of 21-hydroxylase CAH deficiency (classic CAH); presents days to weeks of life with vomiting, poor feeding, and cardiovascular collapse if not recognized emergently

• Delayed or absent puberty — May present in adolescence if DSD not previously recognized; primary amenorrhea in genetic females with gonadal dysgenesis or müllerian agenesis; cryptorchidism and micropenis in undervirilized 46,XY individuals

• Infertility or reduced fertility — Gonadal dysgenesis causes azoospermia in males and premature ovarian failure in females; patients with androgen insensitivity syndrome are phenotypic females but genotypically XY with streak gonads

• Psychological distress and gender incongruence — Particularly when sex of rearing chosen at birth does not align with patient's gender identity later in life; emphasizes importance of careful interdisciplinary evaluation and family counseling

• Clinical history and physical examination — Document timing of genital ambiguity recognition, family history of DSD/consanguinity, maternal medication/exposure history, and presence of signs of adrenal insufficiency; carefully examine external genitalia (measure clitoral/penile width and length), palpate gonads (location and consistency), assess for müllerian structures, and evaluate for hyperpigmentation or signs of adrenal crisis

• Karyotype (46,XX vs. 46,XY) and fluorescence in situ hybridization (FISH) or chromosomal microarray — Establishes chromosomal sex; detects mosaicism and structural abnormalities; essential first-tier test

• Pelvic and abdominal ultrasound — Visualizes presence/absence of uterus, ovaries, and intra-abdominal testes; determines gonadal size, echogenicity, and location; non-invasive assessment of internal genitalia

• 17-hydroxyprogesterone (17-OHP) level — Elevated (>1000 ng/dL in neonates) in 21-hydroxylase CAH; perform on dried blood spot from newborn screening; most common cause of 46,XX DSD

• Hormonal assessment panel — Measure testosterone, androstenedione, DHEA-S, LH, FSH, and 17-OHP under standardized conditions (morning, supine); assess adrenal and gonadal function; ACTH stimulation test may be used if enzyme deficiency suspected

• Müllerian duct assessment — Presence of uterus on imaging or MRI confirms müllerian duct development; absence suggests defective AMH signaling or insufficient müllerian-inhibiting substance in 46,XY individuals

• Androgen receptor gene sequencing — Identifies pathogenic variants in AR gene in suspected androgen insensitivity syndrome; confirms diagnosis in genetic males with female or partially virilized phenotype and normal testosterone levels

• Gonadal biopsy or histology — Reserved for cases of true gonadal hermaphroditism or when gonadal dysgenesis severity unclear; reveals presence of testicular versus ovarian tissue

• Genetic testing for genes involved in gonadal development — Next-generation sequencing of SRY, DHH, DMRT1, NR5A1, GATA4, and others in cases of gonadal dysgenesis with no clear etiology

• MRI of pelvis and adrenals — Superior soft-tissue resolution for evaluating complex internal anatomy; identify adrenal hyperplasia in CAH; assess for wolffian versus müllerian duct development

General Principles

• Multidisciplinary team approach — Involves pediatric endocrinology, urology/gynecology, psychology, genetics, and social work; emphasizes shared decision-making with family and, when developmentally appropriate, the patient

• Deferred sex assignment in some cases — Historically, sex of rearing was assigned immediately; current best practice allows time for chromosomal, gonadal, and hormonal evaluation before irreversible surgical decisions in ambiguous cases; avoids gender dysphoria later in life

Treatment by Diagnosis

46,XX CAH (21-hydroxylase deficiency) — Classic Salt-Wasting Form

• Hydrocortisone replacement — 15-20 mg/m²/day divided into 2-3 doses (morning dose 8-10 mg/m², afternoon 5-7 mg/m², evening 2-3 mg/m²); most critical therapy; suppresses excess ACTH and abnormal androgen production; requires dose adjustment with stress, illness, and growth
• Mineralocorticoid (fludrocortisone) replacement — 0.1-0.2 mg daily in salt-wasting form; replaces deficient aldosterone; maintains sodium balance and prevents vascular collapse
• IV normal saline (0.9%) bolus — Acute treatment during adrenal crisis: 20 mL/kg over 30 minutes followed by continuous infusion and high-dose hydrocortisone (50-100 mg IV

Emergencies

• Salt-wasting adrenal crisis (classic 21-hydroxylase deficiency) — EMERGENCY: absent cortisol and aldosterone produce hypotension unresponsive to fluids alone; signaled by vomiting, poor feeding, and weight loss at 1–3 weeks of life with hyponatremia, hyperkalemia, hypoglycemia, and non-anion-gap metabolic acidosis. Treat before confirmatory labs return
• Hyperkalemic arrhythmia — EMERGENCY: peaked T waves and widened QRS from mineralocorticoid deficiency
• Aortic dissection or rupture in Turner syndrome — EMERGENCY: bicuspid valve and coarctation predispose; sudden chest/back pain in a short-statured woman with primary amenorrhea. The international Turner Syndrome Clinical Practice Guidelines mandate baseline and serial cardiac imaging
• Hypertensive emergency: in 11β-hydroxylase and 17α-hydroxylase deficiency from deoxycorticosterone excess

Disease complications

• Germ cell malignancy (gonadoblastoma → dysgerminoma/seminoma): risk is highest in dysgenetic gonads containing Y chromosome material, which is why gonadectomy is recommended in that group; risk in complete androgen insensitivity is comparatively low and prepubertal, allowing gonadectomy to be deferred until after spontaneous pubertal feminization
• Short adult stature: androgen excess accelerates bone age and causes premature epiphyseal fusion despite early tall stature
• Infertility: testicular adrenal rest tumors in poorly controlled males with CAH obstruct seminiferous tubules; anovulation and a PCOS-like picture in females; azoospermia with hyalinized tubules in Klinefelter
• Osteoporosis and metabolic syndrome: sex-steroid deficiency in gonadal dysgenesis, Klinefelter, or post-gonadectomy patients
• Gender dysphoria, depression, and suicidality: driven historically by early irreversible surgery and non-disclosure

Treatment complications

• Glucocorticoid over-replacement: iatrogenic Cushing syndrome, growth suppression, and further loss of adult height — signaled by weight gain with falling growth velocity
• Under-replacement: recurrent virilization, precocious pseudopuberty, advancing bone age
• Fludrocortisone excess: hypertension and hypokalemia
• Testosterone therapy (Klinefelter): erythrocytosis and suppression of any residual spermatogenesis — check hematocrit; sperm cryopreservation before starting, per Endocrine Society hypogonadism guidance
• Genitoplasty: vaginal stenosis, urethral fistula, and impaired sexual sensation

• Ambiguous genitalia in a newborn is a social and medical urgency, not a surgical one: the single best next step is karyotype plus serum 17-OHP and electrolytes — do not assign sex or operate before results, per the LWPES/ESPE (Chicago) consensus
• Markedly elevated 17-OHP = 21-hydroxylase deficiency: the most common cause of ambiguous genitalia in a 46,XX newborn. Salt-wasting labs are hyponatremia + hyperkalemia + hypoglycemia; give IV saline, dextrose, and stress-dose hydrocortisone before the diagnosis is confirmed
• Use blood pressure to sort the CAH enzymes: hypertension + virilized XX = 11β-hydroxylase; hypertension + undervirilized XY with absent puberty = 17α-hydroxylase; hypotension/salt-wasting = 21-hydroxylase. All three hinge on whether deoxycorticosterone accumulates
• Complete androgen insensitivity: 46,XY phenotypic female with primary amenorrhea, normal breasts (peripheral aromatization), scant pubic and axillary hair, blind-ending vaginal pouch, no uterus (AMH from Sertoli cells worked), and testosterone in the normal male range with elevated LH
• **The classic distractor is müllerian agenesis (MRKH)**: also primary amenorrhea with a blind vaginal pouch, but 46,XX with normal pubic hair, ovaries present, and female testosterone. Pubic hair and karyotype separate them
• 5α-reductase deficiency: "penis at 12" — virilization at puberty from a testosterone surge; normal testosterone with an elevated testosterone:DHT ratio; wolffian structures present because they need testosterone, not DHT
• The association examiners love: Y chromosome material in a dysgenetic gonad → gonadoblastoma; streak gonads in a 46,XY female (Swyer syndrome) warrant gonadectomy
• Klinefelter (47,XXY): tall stature with long limbs, small firm testes, gynecomastia, low testosterone with high LH and FSH; testosterone replacement treats symptoms but does not restore fertility, so discuss sperm retrieval first