Endocrinology: congenital adrenal enzyme defects: practice question

A Physiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Physiology · Endocrinology: congenital adrenal enzyme defects

Sample item

A 16-year-old 46,XX girl has hypertension, hypokalaemia, absent breast development and primary amenorrhoea. Cortisol and sex steroids are low, ACTH is high, deoxycorticosterone and corticosterone are raised and renin is low. Which enzyme is deficient?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. 17-alpha-hydroxylase

Without 17-alpha-hydroxylase the adrenal cannot make cortisol or sex steroids, so ACTH rises and drives the mineralocorticoid pathway. Excess deoxycorticosterone and corticosterone cause sodium retention, hypertension and hypokalaemia with low renin. Absence of sex steroids gives sexual infantilism.

Option by option

  • A. 3-beta-hydroxysteroid dehydrogenase

    3-beta-HSD deficiency blocks all three pathways and typically causes salt wasting, not hypertension.

  • B. 11-beta-hydroxylase

    11-beta-hydroxylase deficiency also causes hypertension, but androgens are raised and cause virilisation.

  • C. 17-alpha-hydroxylase (correct)

    Correct. Cortisol and sex steroids are blocked while mineralocorticoid precursors accumulate, giving hypertension and sexual infantilism.

  • D. 21-hydroxylase

    21-hydroxylase deficiency causes salt loss or virilisation, not hypertension with absent sex steroids.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is C, 17-alpha-hydroxylase. Without 17-alpha-hydroxylase the adrenal cannot make cortisol or sex steroids, so ACTH rises and drives the mineralocorticoid pathway.

Why is "3-beta-hydroxysteroid dehydrogenase" not the answer?

3-beta-HSD deficiency blocks all three pathways and typically causes salt wasting, not hypertension.

Why is "11-beta-hydroxylase" not the answer?

11-beta-hydroxylase deficiency also causes hypertension, but androgens are raised and cause virilisation.

Why is "21-hydroxylase" not the answer?

21-hydroxylase deficiency causes salt loss or virilisation, not hypertension with absent sex steroids.

What concept does this question test?

It tests Endocrinology: congenital adrenal enzyme defects in Physiology. Excess deoxycorticosterone and corticosterone cause sodium retention, hypertension and hypokalaemia with low renin. Absence of sex steroids gives sexual infantilism.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Endocrinology: congenital adrenal enzyme defects?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.