Gynaecological endocrinology: 5-alpha reductase deficiency: practice question

A OBG 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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OBG · Gynaecological endocrinology: 5-alpha reductase deficiency

Sample item

A child raised as a girl with ambiguous genitalia at birth develops deepening of the voice, muscle mass and phallic enlargement at puberty. Karyotype is 46,XY, testosterone is normal for male puberty and dihydrotestosterone is low. What is the diagnosis?

AComplete androgen insensitivity syndromeBSwyer syndromeC5-alpha reductase deficiencyDMullerian agenesis

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

The answer and the reasoning

C. 5-alpha reductase deficiency

Failure to convert testosterone to dihydrotestosterone causes poor virilisation of the external genitalia in fetal life, while normal testosterone produces virilisation at puberty. Testes are present and Mullerian structures are absent. Complete androgen insensitivity gives a female phenotype with breast development at puberty.

Option by option

A. Complete androgen insensitivity syndrome
Complete androgen insensitivity does not virilise at puberty and breasts develop.
B. Swyer syndrome
Swyer syndrome gives streak gonads and a female phenotype without virilisation.
C. 5-alpha reductase deficiency (correct)
Correct. Low DHT with normal testosterone and pubertal virilisation is characteristic.
D. Mullerian agenesis
Mullerian agenesis occurs in 46,XX females with normal external genitalia.

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.

Questions about this OBG question

What is the answer to this OBG question?

The best answer is C, 5-alpha reductase deficiency. Failure to convert testosterone to dihydrotestosterone causes poor virilisation of the external genitalia in fetal life, while normal testosterone produces virilisation at puberty.

Why is "Complete androgen insensitivity syndrome" not the answer?

Complete androgen insensitivity does not virilise at puberty and breasts develop.

Why is "Swyer syndrome" not the answer?

Swyer syndrome gives streak gonads and a female phenotype without virilisation.

Why is "Mullerian agenesis" not the answer?

Mullerian agenesis occurs in 46,XX females with normal external genitalia.

What concept does this question test?

It tests Gynaecological endocrinology: 5-alpha reductase deficiency in OBG. Testes are present and Mullerian structures are absent. Complete androgen insensitivity gives a female phenotype with breast development at puberty.

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 Gynaecological endocrinology: 5-alpha reductase deficiency?

Learn management algorithms as steps: PPH, eclampsia, ectopic pregnancy. Then use the flashcards and the other OBG 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.