Reproduction: 5-alpha reductase deficiency: 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 · Reproduction: 5-alpha reductase deficiency

Sample item

A 46,XY child raised as a girl virilises at puberty, with a deeper voice, phallic growth and muscle development. Testes are present, serum testosterone is normal, dihydrotestosterone is low, and a blind vaginal pouch is seen. Which defect is most likely?

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

The answer and the reasoning

D. 5-alpha reductase type 2 deficiency

Dihydrotestosterone, made from testosterone by 5-alpha reductase type 2, masculinises the external genitalia, prostate and urethra in fetal life. Testosterone alone masculinises the Wolffian ducts. With the enzyme deficient, external genitalia are ambiguous or female at birth, but the rise in testosterone at puberty virilises the body. The testosterone to DHT ratio is raised.

Option by option

  • A. 17-beta hydroxysteroid dehydrogenase type 3 deficiency

    17-beta HSD3 deficiency also virilises at puberty but gives low testosterone with raised androstenedione.

  • B. 21-hydroxylase deficiency

    21-hydroxylase deficiency virilises a 46,XX fetus, and in a 46,XY infant it gives normal male genitalia with salt wasting or raised 17-hydroxyprogesterone.

  • C. Androgen receptor defect (complete androgen insensitivity)

    Complete androgen insensitivity causes breast development and no virilisation, with high testosterone.

  • D. 5-alpha reductase type 2 deficiency (correct)

    Testosterone that is normal with low DHT, and virilisation at puberty, fits 5-alpha reductase deficiency.

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 D, 5-alpha reductase type 2 deficiency. Dihydrotestosterone, made from testosterone by 5-alpha reductase type 2, masculinises the external genitalia, prostate and urethra in fetal life.

Why is "17-beta hydroxysteroid dehydrogenase type 3 deficiency" not the answer?

17-beta HSD3 deficiency also virilises at puberty but gives low testosterone with raised androstenedione.

Why is "21-hydroxylase deficiency" not the answer?

21-hydroxylase deficiency virilises a 46,XX fetus, and in a 46,XY infant it gives normal male genitalia with salt wasting or raised 17-hydroxyprogesterone.

Why is "Androgen receptor defect (complete androgen insensitivity)" not the answer?

Complete androgen insensitivity causes breast development and no virilisation, with high testosterone.

What concept does this question test?

It tests Reproduction: 5-alpha reductase deficiency in Physiology. Testosterone alone masculinises the Wolffian ducts. With the enzyme deficient, external genitalia are ambiguous or female at birth, but the rise in testosterone at puberty virilises the body. The testosterone to DHT ratio is raised.

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 Reproduction: 5-alpha reductase deficiency?

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.