Biomolecules and enzymes: intermediate filament markers: practice question

A Biochemistry 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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Biochemistry · Biomolecules and enzymes: intermediate filament markers

Sample item

A 6-year-old child has a rapidly growing orbital mass. Biopsy shows small round cells with some elongated strap-shaped cells showing cross-striations. Immunostaining for which intermediate filament protein best confirms the muscle lineage?

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

The answer and the reasoning

C. Desmin

Desmin is the intermediate filament protein of muscle cells and is positive in rhabdomyosarcoma, the likely diagnosis here. GFAP marks astrocytes, cytokeratins mark epithelial cells and neurofilament proteins mark neurons. Choosing the filament by cell type is a standard way to classify poorly differentiated tumours.

Option by option

  • A. Glial fibrillary acidic protein

    GFAP is the intermediate filament of astrocytes and is used for glial tumours.

  • B. Cytokeratin

    Cytokeratins mark epithelial cells and carcinomas, not muscle tumours.

  • C. Desmin (correct)

    Correct. Desmin is the intermediate filament of skeletal and smooth muscle and marks rhabdomyoblasts.

  • D. Neurofilament protein

    Neurofilament proteins mark neurons and neuroblastic tumours.

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 Biochemistry question

What is the answer to this Biochemistry question?

The best answer is C, Desmin. Desmin is the intermediate filament protein of muscle cells and is positive in rhabdomyosarcoma, the likely diagnosis here.

Why is "Glial fibrillary acidic protein" not the answer?

GFAP is the intermediate filament of astrocytes and is used for glial tumours.

Why is "Cytokeratin" not the answer?

Cytokeratins mark epithelial cells and carcinomas, not muscle tumours.

Why is "Neurofilament protein" not the answer?

Neurofilament proteins mark neurons and neuroblastic tumours.

What concept does this question test?

It tests Biomolecules and enzymes: intermediate filament markers in Biochemistry. GFAP marks astrocytes, cytokeratins mark epithelial cells and neurofilament proteins mark neurons. Choosing the filament by cell type is a standard way to classify poorly differentiated tumours.

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 Biomolecules and enzymes: intermediate filament markers?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry 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.