Endocrinology: adrenal steroidogenesis: 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: adrenal steroidogenesis

Sample item

A 46,XY infant has female-appearing genitalia and salt wasting. Cortisol, aldosterone and sex steroids are all low, ACTH and renin are high, and imaging shows enlarged adrenals loaded with lipid. Which step in steroid synthesis is defective?

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

The answer and the reasoning

A. Transport of cholesterol into mitochondria by StAR

All steroid hormones start with cholesterol, and the rate-limiting step is its transfer into mitochondria by steroidogenic acute regulatory protein, after which side-chain cleavage makes pregnenolone. When this fails, every adrenal and gonadal steroid is low, cholesterol esters accumulate and the XY fetus is undervirilised.

Option by option

  • A. Transport of cholesterol into mitochondria by StAR (correct)

    Correct. A StAR defect blocks the first step, so all adrenal and gonadal steroids are deficient and lipid accumulates.

  • B. Conversion of testosterone to dihydrotestosterone

    A 5-alpha-reductase defect spares cortisol and aldosterone, so there would be no salt wasting.

  • C. 11-beta-hydroxylation of 11-deoxycortisol

    11-beta-hydroxylase deficiency gives hypertension from excess deoxycorticosterone and does not cause salt wasting.

  • D. 21-hydroxylation of progesterone

    21-hydroxylase deficiency impairs cortisol and aldosterone but raises androgens, and does not make an XY infant female.

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 A, Transport of cholesterol into mitochondria by StAR. All steroid hormones start with cholesterol, and the rate-limiting step is its transfer into mitochondria by steroidogenic acute regulatory protein, after which side-chain cleavage makes pregnenolone.

Why is "Conversion of testosterone to dihydrotestosterone" not the answer?

A 5-alpha-reductase defect spares cortisol and aldosterone, so there would be no salt wasting.

Why is "11-beta-hydroxylation of 11-deoxycortisol" not the answer?

11-beta-hydroxylase deficiency gives hypertension from excess deoxycorticosterone and does not cause salt wasting.

Why is "21-hydroxylation of progesterone" not the answer?

21-hydroxylase deficiency impairs cortisol and aldosterone but raises androgens, and does not make an XY infant female.

What concept does this question test?

It tests Endocrinology: adrenal steroidogenesis in Physiology. When this fails, every adrenal and gonadal steroid is low, cholesterol esters accumulate and the XY fetus is undervirilised.

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: adrenal steroidogenesis?

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.