Normal pregnancy and antenatal care: steroid sulfatase 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 · Normal pregnancy and antenatal care: steroid sulfatase deficiency

Sample item

A second-trimester screen shows markedly low maternal unconjugated oestriol with normal AFP and hCG. The male fetus is structurally normal, the fetal adrenals are normal, and the mother is not virilised. After birth the boy develops dry, scaly skin and corneal opacities. Which enzyme deficiency explains the low oestriol?

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

The answer and the reasoning

C. Placental sulfatase deficiency

Fetal adrenal DHEA sulphate must be desulphated by placental steroid sulfatase before aromatisation to oestrogen. Deficiency of this X-linked enzyme gives very low maternal oestriol and, in the male child, X-linked ichthyosis with corneal opacities. Aromatase deficiency would instead virilise the mother.

Option by option

  • A. Fetal 21-hydroxylase deficiency

    21-hydroxylase deficiency causes adrenal hyperplasia with ambiguous genitalia in girls, not this skin and oestriol picture.

  • B. Placental aromatase deficiency

    Aromatase deficiency causes maternal virilisation from unconverted androgens, which is absent here.

  • C. Placental sulfatase deficiency (correct)

    Correct. Without sulfatase, fetal DHEA sulphate cannot be converted, so oestriol is low; the same gene defect causes X-linked ichthyosis.

  • D. Fetal 17-alpha-hydroxylase deficiency

    17-alpha-hydroxylase deficiency causes hypertension and failed sexual development, not ichthyosis.

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 OBG question

What is the answer to this OBG question?

The best answer is C, Placental sulfatase deficiency. Fetal adrenal DHEA sulphate must be desulphated by placental steroid sulfatase before aromatisation to oestrogen.

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

21-hydroxylase deficiency causes adrenal hyperplasia with ambiguous genitalia in girls, not this skin and oestriol picture.

Why is "Placental aromatase deficiency" not the answer?

Aromatase deficiency causes maternal virilisation from unconverted androgens, which is absent here.

Why is "Fetal 17-alpha-hydroxylase deficiency" not the answer?

17-alpha-hydroxylase deficiency causes hypertension and failed sexual development, not ichthyosis.

What concept does this question test?

It tests Normal pregnancy and antenatal care: steroid sulfatase deficiency in OBG. Deficiency of this X-linked enzyme gives very low maternal oestriol and, in the male child, X-linked ichthyosis with corneal opacities. Aromatase deficiency would instead virilise the mother.

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 Normal pregnancy and antenatal care: steroid sulfatase 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.