Genetic and metabolic disorders: xeroderma pigmentosum: practice question

A Pediatrics 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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Pediatrics · Genetic and metabolic disorders: xeroderma pigmentosum

Sample item

A 3-year-old has severe sunburn and blistering after minimal sun exposure, freckle-like pigmentation of exposed skin, photophobia and a squamous cell carcinoma on the lip. Which cellular process is defective?

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

The answer and the reasoning

C. Nucleotide excision repair of ultraviolet-induced damage

Xeroderma pigmentosum is an autosomal recessive defect of nucleotide excision repair, so ultraviolet-induced pyrimidine dimers are not removed. Children develop early skin cancers, ocular surface disease and sometimes neurological degeneration. Strict sun protection is essential.

Option by option

  • A. Base excision repair of oxidative DNA damage

    Base excision repair handles oxidative damage and is not the pathway affected by ultraviolet light.

  • B. Homologous recombination repair of double-strand breaks

    Homologous recombination defects underlie BRCA-related cancers and some chromosomal instability disorders, not ultraviolet sensitivity.

  • C. Nucleotide excision repair of ultraviolet-induced damage (correct)

    Correct. Failure of nucleotide excision repair leaves ultraviolet photoproducts unrepaired and drives skin cancer.

  • D. Mismatch repair of DNA replication errors

    Mismatch repair defects cause Lynch syndrome and colorectal cancer, without photosensitivity.

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 Pediatrics question

What is the answer to this Pediatrics question?

The best answer is C, Nucleotide excision repair of ultraviolet-induced damage. Xeroderma pigmentosum is an autosomal recessive defect of nucleotide excision repair, so ultraviolet-induced pyrimidine dimers are not removed.

Why is "Base excision repair of oxidative DNA damage" not the answer?

Base excision repair handles oxidative damage and is not the pathway affected by ultraviolet light.

Why is "Homologous recombination repair of double-strand breaks" not the answer?

Homologous recombination defects underlie BRCA-related cancers and some chromosomal instability disorders, not ultraviolet sensitivity.

Why is "Mismatch repair of DNA replication errors" not the answer?

Mismatch repair defects cause Lynch syndrome and colorectal cancer, without photosensitivity.

What concept does this question test?

It tests Genetic and metabolic disorders: xeroderma pigmentosum in Pediatrics. Children develop early skin cancers, ocular surface disease and sometimes neurological degeneration. Strict sun protection is essential.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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 Genetic and metabolic disorders: xeroderma pigmentosum?

Memorise milestones and the vaccine schedule as tables and revise them often. Then use the flashcards and the other Pediatrics 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.