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Difficulty: Very hardEndocrinology and Metabolism

A 17-year-old girl is brought to the physician by her mother for evaluation of primary amenorrhea. She has never had a menstrual period. The patient has no significant past medical history and takes no medications. Her blood pressure is 162/100 mmHg162/100\text{ mmHg} and pulse is 78/min78/\text{min}. Physical examination shows a tall, thin adolescent with Tanner stage 1 breast development and absent pubic and axillary hair. A pelvic ultrasound reveals a small, prepubertal uterus and bilateral ovaries. Laboratory studies show a serum sodium of 145 mEq/L145\text{ mEq/L}, potassium of 2.8 mEq/L2.8\text{ mEq/L}, and bicarbonate of 32 mEq/L32\text{ mEq/L}. Which of the following additional laboratory findings is most likely present in this patient?

  1. Decreased serum aldosterone and elevated serum corticosteroneAnswer
  2. B
    Elevated serum testosterone and elevated 11-deoxycortisol
  3. C
    Decreased serum luteinizing hormone and decreased serum follicle-stimulating hormone
  4. D
    Elevated serum aldosterone and decreased plasma renin activity
  5. E
    Elevated 17-hydroxyprogesterone and elevated plasma renin activity

Answer

The correct answer is decreased serum aldosterone and elevated serum corticosterone.
This patient's presentation is pathognomonic for 17α17\alpha-hydroxylase deficiency, a rare form of Congenital Adrenal Hyperplasia. The enzyme 17α17\alpha-hydroxylase is required to convert pregnenolone and progesterone into 1717-hydroxypregnenolone and 1717-hydroxyprogesterone, respectively. A deficiency completely blocks the synthesis of both glucocorticoids (cortisol) and sex steroids (androgens and estrogens). The lack of estrogen causes primary amenorrhea and absent breast development, while the lack of androgens causes absent pubic and axillary hair. Because cortisol synthesis is impaired, loss of negative feedback increases ACTH, which continuously drives the only unblocked adrenal pathway: mineralocorticoid synthesis. This results in massive overproduction of 11-deoxycorticosterone (DOC) and corticosterone. DOC is a potent mineralocorticoid that causes sodium retention (hypertension) and potassium/hydrogen excretion (hypokalemic metabolic alkalosis). Crucially, this intravascular volume expansion suppresses the juxtaglomerular apparatus, leading to low plasma renin activity. The low renin subsequently fails to stimulate aldosterone synthase, resulting in paradoxical decreased true serum aldosterone levels despite the profound mineralocorticoid effect.

Step-by-Step Solution

1
Analyze the clinical triad.
The patient has primary amenorrhea with sexual infantilism (Tanner stage 1 breasts, absent pubic hair), severe hypertension, and hypokalemic metabolic alkalosis.
Identifying these three distinct physiological abnormalities is required to localize a single unifying enzymatic defect.
2
Differentiate the causes of Congenital Adrenal Hyperplasia (CAH).
The combination of hypertension and sexual infantilism points specifically to 17α17\alpha-hydroxylase deficiency.
Other CAH forms cause virilization (11β11\beta-hydroxylase, 2121-hydroxylase) or hypotension (2121-hydroxylase).
3
Trace the biochemical consequences of a 17α17\alpha-hydroxylase block.
The block prevents conversion of progesterone to 1717-hydroxyprogesterone, halting the synthesis of cortisol and sex steroids (estrogens/androgens), while shunting all precursors into the mineralocorticoid pathway.
Understanding the steroidogenesis pathway predicts the exact serum hormone levels.
4
Determine the downstream effects on the renin-angiotensin-aldosterone system.
Excess 11-deoxycorticosterone (DOC) and corticosterone act as potent mineralocorticoids, causing sodium retention, hypertension, and hypokalemia. This volume expansion suppresses renin release, which in turn leads to decreased synthesis of true aldosterone.
This explains the paradoxical finding of high mineralocorticoid effect with low actual serum aldosterone.

Key Concept

Congenital Adrenal Hyperplasia (17α17\alpha-hydroxylase deficiency)
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Topics

Endocrinology and Metabolism

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