Endocrine System, Congenital Adrenal Hyperplasia, and Disorders of Sex Development

Apparent Mineralocorticoid Excess and Liddle Syndrome

Apparent Mineralocorticoid Excess (AME)

• Hypertension and hypervolemia in this condition are independent of aldosterone concentrations.
• Serum cortisol and ACTH levels are generally within normal limits.
• The serum half-life of cortisol is increased, though testing for this requires a radioactive tracer and is not clinically available.
• Total urinary excretion of cortisol metabolites is markedly decreased.
• Biochemical markers include an elevated urinary ratio of free cortisol to free cortisone, and an elevated ratio of urinary tetrahydrocortisol plus allotetrahydrocortisol to tetrahydrocortisone.
• Differential Diagnosis:
  • Includes other forms of severe childhood hypertension such as renal artery anomalies.
  • Relately few conditions present with suppressed renin and aldosterone levels.
  • Liddle syndrome has a similar presentation but no steroid profile abnormalities.
  • Hypertensive forms of Congenital Adrenal Hyperplasia (CAH), such as $11\beta$-hydroxylase deficiency and $17\alpha$-hydroxylase deficiency, also show suppressed renin and aldosterone, but present with signs of androgen excess or deficiency.
  • Severe Cushing syndrome (often ectopic ACTH syndrome) can mimic AME because high cortisol levels overwhelm renal $HSD11B2$, leading to hypertension and altered cortisol-to-cortisone ratios.
• Treatment:
  • Low-salt diet.
  • Potassium supplementation.
  • Mineralocorticoid receptor blockade: $Spironolactone$ or $Eplerenone$.
  • Sodium channel blockers: $Amiloride$ or $Triamterene$ (may work at least as well).
  • Suppression of cortisol with $Dexamethasone$ is theoretically sound but often less effective in practice.

Liddle Syndrome

• A form of hypertension and hypokalemia clinically similar to AME but inherited in an autosomal dominant manner.
• Pathogenesis: Caused by activating pathogenic variants in the $\beta$ ($SCNN1B$) or $\gamma$ ($SCNN1G$) subunits of the epithelial sodium channel (ENaC).
• Mutations typically prevent channel subunits from being ligated to ubiquitin and targeted to the proteasome for degradation, a process normally regulated indirectly by aldosterone.
• The net effect is an increased number of open channels at the apical surface of renal collecting duct epithelial cells, facilitating sodium resorption and potassium excretion.
• Clinical Manifestations:
  • Severe early-onset hypertension.
  • Hypokalemia (may not be persistent).
  • Suppressed aldosterone and renin levels.
  • Normal levels of all steroid hormones.
• Treatment:
  • Low-salt diet.
  • Potassium supplementation.
  • Sodium channel blockers such as $Amiloride$ or $Triamterene$.
  • Mineralocorticoid receptor antagonists ($Spironolactone$) are ineffective.

Congenital Adrenal Hyperplasia (CAH) Overview

• CAH refers to a family of autosomal recessive disorders of cortisol biosynthesis.
• Cortisol deficiency leads to increased secretion of corticotropin (ACTH), resulting in adrenocortical hyperplasia and overproduction of intermediate metabolites.
• Clinical presentation varies based on the enzymatic deficiency and can include mineralocorticoid deficiency or excess, incomplete virilization, precocious puberty, or sexual infantilism.

21-Hydroxylase Deficiency

• Accounts for more than $90\%$ of CAH cases.
• Caused by a deficiency in the P450 enzyme $CYP21A2$ ($P450c21$), which hydroxylates progesterone and $17$-hydroxyprogesterone to yield $11$-deoxycorticosterone and $11$-deoxycortisol, respectively.
• Epidemiology:
  • Classic form occurs in $1$ in $14,000$ to $18,000$ births.
  • Roughly $70\%$ have the salt-losing form; $30\%$ have the simple virilizing form.
  • In the U.S., incidence is lower in African Americans ($1:42,000$) compared to White children ($1:15,500$).
  • Nonclassic disease prevalence is $1$ in $1,000$, occurring more frequently in Ashkenazi Jews and Hispanics.
• Genetics:
  • The active gene is $CYP21$ ($CYP21A2$).
  • $CYP21P$ ($CYP21A1P$) is a pseudogene with $98\%$ sequence identity.
  • More than $90\%$ of abnormal alleles result from recombinations between $CYP21$ and $CYP21P$.
  • Approximately $20\%$ of alleles are deletions from unequal meiotic crossing-over; others are nonreciprocal transfers (gene conversion).
  • Compound heterozygotes are frequent; severity is determined by the less severely affected allele.
  • Deletions extending into the tenascin-X ($TNX$) gene cause a contiguous gene syndrome of CAH and Ehlers-Danlos syndrome.
• Pathogenesis of Salt-Wasting Form:
  • Deficiency in both cortisol and aldosterone.
  • Manifests at $10$ to $14$ days of age with weight loss, anorexia, vomiting, dehydration, hypotension, hypoglycemia, hyponatremia, and hyperkalemia.
  • Progesterone and other metabolites may act as mineralocorticoid receptor antagonists, worsening salt wasting.
• Prenatal Androgen Excess:
  • $17$-hydroxyprogesterone is shunted into androgen biosynthesis, leading to high testosterone levels in utero by $8$ to $10$ weeks gestation.
  • Females present with masculinized external genitalia: clitoral enlargement, labial fusion, and a urogenital sinus.
  • Internal female organs (ovaries, uterus) are normal as there is no antim<llerian hormone (AMH) production.
• Postnatal Androgen Excess:
  • Rapid somatic growth and accelerated skeletal maturation.
  • Patients are tall as children but stunted as adults due to premature epiphyseal closure.
  • Males: Enlarged penis and scrotum, but prepubertal-sized testes. Potential for Testicular Adrenal Rest Tumors (TARTs).
  • Females: Further clitoral enlargement, potential for Primary Ovarian Insufficiency (POI) if untreated.
• Adrenomedullary Dysfunction:
  • Adrenal medulla development requires high local cortisol.
  • Patients show blunted epinephrine responses, decreased blood glucose, and lower heart rates during exercise.
• Laboratory Diagnosis:
  • Markedly elevated blood levels of $17$-hydroxyprogesterone.
  • Elevated androstenedione and testosterone (in females).
  • Elevated plasma renin with inappropriately low aldosterone.
  • Standard Test: Measurement of $17$-hydroxyprogesterone before and $30$ to $60$ minutes after an IV bolus of $0.125$ to $0.25\,mg$ of cosyntropin (ACTH 1-24).
• Treatment:
  • Glucocorticoids: $Hydrocortisone$ is preferred in children ($12$ to $15\,mg/m^2/24\,hr$ orally in $3$ divided doses). Higher doses for stress (infection, surgery).
  • Mineralocorticoids: $Fludrocortisone$ ($0.1$ to $0.3\,mg$ daily for infants; $0.05$ to $0.1\,mg$ for older children).
  • Sodium Supplementation: $Sodium\,chloride\,8\,mmol/kg$ for salt-wasting infants.
  • Monitoring: Periodic linear growth tracking, bone age radiographs, and hormone levels (early morning $17$-hydroxyprogesterone and androstenedione).
  • Experimental/Adjuvant Therapies: Antiandrogens ($Flutamide$), aromatase inhibitors ($Anastrozole$, $Letrozole$), CRH receptor antagonists ($Crinecerfont$, $Tildacerfont$), or absolute suppression with $Abiraterone\,acetate$.
• Surgical Management: Vaginoplasty and clitoral reduction for virilized females usually performed at $2$ to $6$ months.
• Prenatal Treatment: Mothers may be given $Dexamethasone$ ($20\,\mu g/kg$ daily) starting by $6$ weeks gestation to prevent female virilization.

Other Forms of Congenital Adrenal Hyperplasia

$11\beta$-Hydroxylase Deficiency

• Caused by variants in $CYP11B1$ (Chromosome $8q21-q22$).
• Biochemical markers: Accumulation of $11$-deoxycortisol and deoxycorticosterone (DOC).
• Clinical Manifestations:
  • Androgen excess signs similar to $21$-OH deficiency.
  • Hypertension (in $65\%$ of patients) due to DOC activity.
  • Suppressed renin and low aldosterone (though aldosterone synthesis capability is intact).
  • Hypokalemic alkalosis.
• Treatment: $Hydrocortisone$. Hypertension usually resolves but may require calcium channel blockers.

$3\beta$-Hydroxysteroid Dehydrogenase (3$\beta$-HSD) Deficiency

• Deficiency in $HSD3B2$ (Chromosome $1p13.1$).
• Impairs conversion of $\Delta^5$ steroids (pregnenolone, DHEA) to $\Delta^4$ steroids (progesterone, androstenedione).
• Clinical Manifestations:
  • Salt-wasting crises.
  • Males: Incomplete virilization (hypospadias) due to low testosterone.
  • Females: Mild virilization (clitoromegaly) due to elevated weak androgen DHEA.
• Laboratory Findings: Markedly elevated $\Delta^5$ steroids (e.g., $17$-hydroxypregnenolone, DHEA).
• Treatment: $Hydrocortisone$ and $Fludrocortisone$. Males may receive depot testosterone injections in infancy to increase phallus size.

$17\alpha$-Hydroxylase Deficiency

• Caused by variants in $CYP17A1$ (Chromosome $10q24.3$).
• The enzyme catalyzes both $17$-hydroxylase and $17,20$-lyase reactions.
• Clinical Manifestations:
  • Cortisol deficiency (compensated by corticosterone).
  • DOC excess leading to hypertension and hypokalemia.
  • Deficient sex hormones.
  • Males present as phenotypic females or with sexual ambiguity.
  • Females present with failure of sexual development/primary hypogonadism.
• Treatment: $Hydrocortisone$. Sex hormone replacement at puberty. Genetic males require gonadectomy if reared as female to prevent malignant transformation of abdominal testes.

Lipoid Adrenal Hyperplasia

• Severe impairment of all steroidogenesis with massive adrenal cholesterol accumulation.
• Caused by variants in $StAR$ (Steroidogenic Acute Regulatory protein) or $CYP11A1$ (cholesterol side-chain cleavage enzyme).
• Clinical Manifestations: Salt-losing crises, phenotypic female appearance in both genetic sexes (though genetic males have testes). Adrenal glands appear massively enlarged on imaging.

P450 Oxidoreductase Deficiency (Antley-Bixler Syndrome)

• Deficiency in $POR$ (Chromosome $7q11.3$), required for the activity of all microsomal P450 enzymes ($CYP17$, $CYP21$, $CYP19$).
• Clinical Manifestations: Disordered steroidogenesis and skeletal anomalies (Antley-Bixler: craniosynostosis, midface hypoplasia, humeroradial synostosis).
• Biochemical markers: Elevated pregnenolone and progesterone; decreased urinary cortisol metabolites.

Aldosterone Synthase Deficiency

• Impaired conversion of corticosterone to aldosterone.
• Caused by variants in $CYP11B2$. Classified into Corticosterone Methyloxidase deficiency types I and II.
• Manifestations: Hyponatremia, hyperkalemia, failure to thrive.
• Diagnosis: Increased plasma renin, low aldosterone, potentially markedly elevated $18$-hydroxycorticosterone (in Type II).
• Treatment: $Fludrocortisone$ and/or sodium chloride.

Glucocorticoid-Remediable Aldosteronism (GRA)

• Autosomal dominant low-renin hypertension.
• Caused by a chimeric gene combining the regulatory region of $CYP11B1$ with the coding sequence of $CYP11B2$.
• Aldosterone secretion is regulated by ACTH rather than renin-angiotensin.
• Clinical Signs: Early-onset hypertension, strong family history of early strokes.
• Laboratory Findings: Suppressed renin, elevated aldosterone, markedly increased urinary $18$-oxocortisol and $18$-hydroxycortisol.
• Treatment: Daily low-dose glucocorticoids (e.g., $Dexamethasone\,25\,\mu g/kg/day$).

Adrenocortical Tumors and Cushing Syndrome

Adrenocortical Tumors

• Rare in childhood ($0.3$ to $0.5$ cases per $1$ million child-years).
• Genetics: Associated with $TP53$ variants (Li-Fraumeni syndrome), Beckwith-Wiedemann syndrome ($IGF2$ overexpression), $MEN1$, and Lynch syndrome.
• Symptoms: Virilization ($50$ to $80\%$), Cushing syndrome ($15$ to $40\%$), or feminization (<$10\%$ due to aromatase overexpression).
• Treatment: Surgical removal (transperitoneal). Postoperative glucocorticoid coverage is essential to manage atrophy of the contralateral gland.

Cushing Syndrome

• Result of abnormally high blood levels of cortisol.
• Etiology:
  • Iatrogenic: Exogenous glucocorticoid administration (most common cause).
  • Endogenous:
  • Cushing Disease: Pituitary ACTH-secreting adenoma (most common over age $7$).
  • Adrenal Tumors: Predominant cause in infants.
  • Ectopic ACTH secretion (rare in children; associated with islet cell carcinoma, neuroblastoma, etc.).
• Genetic Syndromes: Carney Complex (pathogenic variants in $PRKAR1A$), McCune-Albright (somatic $GNAS$ variants), PPNAD.
• Clinical Manifestations:
  • Round facies (moon facies), flushed appearance.
  • Central obesity, decelerating linear growth.
  • Purplish striae, hirsutism, acne.
  • Hypertension, glucose intolerance, osteoporosis.
• Laboratory Diagnosis:
  • Lost circadian rhythm: Midnight serum or salivary cortisol $\gt 4.4\,\mu g/dL$.
  • Elevated $24$-hour urinary free cortisol.
  • Dexamethasone suppression tests ($25$ to $30\,\mu g/kg$ at $11\,pm$ results in 8 am cortisol $\gt 5\,\mu g/dL$).
• Treatment:
  • Transsphenoidal surgery for Cushing disease.
  • Adrenalectomy for adrenal tumors.
  • Medical options: $Mitotane$, $Osilodrostat$, $Pasireotide$, or steroidogenesis inhibitors ($Metyrapone$, $Ketoconazole$).

Primary Aldosteronism and Pheochromocytoma

Primary Aldosteronism

• Excessive aldosterone secretion independent of renin-angiotensin.
• Causes: Aldosterone-producing adenomas (linked to activating variants in $KCNJ5$, $CACNA1D$, $ATP1A1$) or bilateral hyperplasia.
• Symptoms: Hypertension, hypokalemia, polyuria, paralysis/tetany if hypokalemia is severe.
• Laboratory Diagnosis: High plasma aldosterone concentration to plasma renin activity ratio (ARR).
• Treatment: Laparoscopic adrenalectomy for adenomas; $Spironolactone$ or $Eplerenone$ for bilateral hyperplasia.

Pheochromocytoma

• Catecholamine-secreting tumors from chromaffin cells ($90\%$ in adrenal medulla).
• Genetics: Frequently associated with $VHL$, $MEN2A/2B$, $NF1$, and $SDHB/C/D$ variants.
• Symptoms: Sustained hypertension in children, headache, palpitations, sweating, pallor, and weight loss.
• Diagnosis: Measurement of plasma free metanephrines and urinary fractionated metanephrines. Imaging via CT, MRI, $^{123}I$-MIBG scan, or PET-CT with $^{68}Ga$-DOTATATE.
• Treatment: Surgical removal. Preoperative $\alpha$- and $\beta$-adrenergic blockade is mandatory (e.g., $Phenoxybenzamine$, $Doxazosin$).

Gonadal Development and Function

Genetic Control

• Male differentiation: Requires the $SRY$ gene on the Y chromosome, which upregulates $SOX9$, $SF-1$, and $WT1$. Sertoli cells produce AMH; Leydig cells produce testosterone.
• Ovarian development: Requires $XX$ complement, $R\text{-}spondin1$, $WNT4$, and $\beta\text{-}catenin$ signaling. $FOXL2$ and $DAX1$ are necessary to preserve ovarian stability.

Function of the Testes

• Fetal testosterone secretion is stimulated by placental hCG ($8$ to $12$ weeks) and later by fetal pituitary LH.
• Standard pathway to DHT: Testosterone converted by $5\alpha$-reductase type 2 ($SRD5A2$).
• Alternative "backdoor" pathway: DHT synthesis from androstanediol.
• Minipuberty: Neonatal surge of LH and testosterone peaks at $1$ to $2$ months, declining by $4$ to $6$ months.
• Peptide regulators: Inhibin B (marker of Sertoli cell function), Activins (stimulate FSH), and Follistatin (inhibits FSH).

Function of the Ovaries

• Oocytes reach peak number ($7$ million) at $5$ months gestation.
• FSH surge is more dominant than LH surge in female infants.
• Estradiol production peaks at $2$ to $6$ months of life during female minipuberty.

Male Hypogonadism

Hypergonadotropic (Primary)

• Klinefelter Syndrome ($47,XXY$): Incidence $1:500$ to $1:1,000$. Characterized by small firm testes, long legs, gynecomastia ($50$ to $80\%$), and language-based learning disabilities.
• Testicular Regression Syndrome (Vanishing Testes): Absence of testes in a phenotypic male with a $46,XY$ karyotype; implies loss of testes after $14$ weeks gestation.
• Acquired causes: Chemotherapy (alkylating agents), radiation (azoospermia at $\gt 2\,Gy$), mumps orchitis.
• Noonan Syndrome: Associated with cryptorchidism and delayed puberty.

Hypogonadotropic (Secondary)

• Kallmann Syndrome: HH associated with anosmia. Caused by variants in $ANOS1$ (X-linked), $FGFR1$, $PROKR2$, or $CHD7$.
• Normosmic Idiopathic HH: Caused by variants in $GNRH1/GNRHR$, $KISS1/KISS1R$, or $TAC3/TACR3$.
• Prader-Willi Syndrome: Common syndromic cause of HH.
• Treatment: Testosterone replacement ($testosterone\,enanthate/cypionate$ starting at $25$ to $50\,mg$ monthly). Gonadotropins ($hCG$ and $human\,menopausal\,gonadotropin$) for fertility.

Gynecomastia

• Physiologic: Neonatal (maternal estrogen) and pubertal (up to $70\%$ of males at Tanner stage 3-4).
• Pathologic:
  • Disorders: Klinefelter, androgen insensitivity, feminizing adrenal/testicular tumors.
  • Drugs: $Spironolactone$, $Ketoconazole$, marijuana, anabolic steroids, antipsychotics.
• Management: Reassurance for physiologic cases. Persistent cases may require medical ($Raloxifene$, $Tamoxifen$) or surgical removal.

Female Hypogonadism

Turner Syndrome ($45,X$)

• Pathogenesis: Complete or partial absence of the second X chromosome. Short stature linked to $SHOX$ haploinsufficiency.
• Clinical Manifestations: Webbed neck, shield chest, lymphedema of hands/feet, bicuspid aortic valve ($30$ to $50\%$), coarctation of the aorta ($20\%$), horseshoe kidney.
• Laboratory Findings: Markedly elevated FSH in infancy and after age $10$.
• Treatment: Growth hormone therapy starting in early childhood; Estrogen replacement starting at age $12$ to $13$.

Other Ovarian Disorders

• Pure Gonadal Dysgenesis ($46,XX$): Normal phenotype and height but streak ovaries and primary amenorrhea.
• $45,X/46,XY$ Mixed Gonadal Dysgenesis: Extreme phenotypic variability (Turner-like to male); high risk ($25\%$) for gonadoblastoma.
• Autoimmune Ovarian Failure: Associated with type I autoimmune polyendocrinopathy (APECED).

Disorders of Sex Development (DSD)

$46,XX$ DSD

• Primarily caused by CAH ($21$-OH deficiency).
• Other causes: Aromatase deficiency, maternal virilizing tumors, exposure to androgenic drugs during pregnancy.

$46,XY$ DSD

• Testicular Differentiation Defects: $SRY$ mutations, Swyer syndrome ($XY$ pure gonadal dysgenesis), Denys-Drash/Frasier/WAGR syndromes ($WT1$ mutations).
• Testicular Hormone Deficiency: Leydig cell aplasia ($LHCGR$ mutations), $17\alpha$-hydroxylase/$17,20$-lyase deficiency, $17\beta$-HSD deficiency.
• Androgen Action Defects: Complete or Partial Androgen Insensitivity Syndrome (CAIS/PAIS due to AR variants), $5\alpha$-reductase deficiency ($SRD5A2$ mutations).
• Persistent M Presence of uterus/tubes in a virilized male due to $AMH$ or $AMH\,receptor$ variants.

Diagnostic Approach to Atypical Genitalia

1. Rapid karyotype/FISH for X/Y chromosomes.
2. Adrenal/Androgen steroid profiling ($17$-OHP, testosterone, DHT).
3. Pelvic ultrasound/MRI to identify internal structures (uterus presence indicates lack of AMH action).
4. hCG stimulation test to assess Leydig cell function.
5. Molecular testing/Gene panels.