Pigmentary disorders: congenital erythropoietic porphyria: practice question

A Dermatology 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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Dermatology · Pigmentary disorders: congenital erythropoietic porphyria

Sample item

A newborn has red-stained urine in the diaper and, over months, blistering of sun-exposed skin with mutilating scarring. The teeth fluoresce red under Wood lamp, and he has haemolytic anaemia. Which enzyme is deficient?

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

The answer and the reasoning

D. Uroporphyrinogen III synthase

Congenital erythropoietic (Günther) porphyria results from deficiency of uroporphyrinogen III synthase. It causes severe photosensitivity, erythrodontia, red urine and haemolysis.

Option by option

  • A. Uroporphyrinogen decarboxylase

    Uroporphyrinogen decarboxylase deficiency causes porphyria cutanea tarda in adults.

  • B. Ferrochelatase

    Ferrochelatase deficiency causes erythropoietic protoporphyria, with painful photosensitivity without blisters.

  • C. Porphobilinogen deaminase

    Porphobilinogen deaminase deficiency causes acute intermittent porphyria, which is not photosensitive.

  • D. Uroporphyrinogen III synthase (correct)

    Correct. Uroporphyrinogen III synthase deficiency causes Günther disease.

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 Dermatology question

What is the answer to this Dermatology question?

The best answer is D, Uroporphyrinogen III synthase. Congenital erythropoietic (Günther) porphyria results from deficiency of uroporphyrinogen III synthase.

Why is "Uroporphyrinogen decarboxylase" not the answer?

Uroporphyrinogen decarboxylase deficiency causes porphyria cutanea tarda in adults.

Why is "Ferrochelatase" not the answer?

Ferrochelatase deficiency causes erythropoietic protoporphyria, with painful photosensitivity without blisters.

Why is "Porphobilinogen deaminase" not the answer?

Porphobilinogen deaminase deficiency causes acute intermittent porphyria, which is not photosensitive.

What concept does this question test?

It tests Pigmentary disorders: congenital erythropoietic porphyria in Dermatology. It causes severe photosensitivity, erythrodontia, red urine and haemolysis.

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 Pigmentary disorders: congenital erythropoietic porphyria?

Learn each condition by its primary lesion, site and signature sign. Then use the flashcards and the other Dermatology 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.