Embryology: Treacher Collins syndrome: practice question

A Anatomy 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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Anatomy · Embryology: Treacher Collins syndrome

Sample item

A child has downslanting palpebral fissures, malar and mandibular hypoplasia, microtia and conductive deafness, with normal intelligence. The primary defect is in which embryonic cells?

ANeural crest cells migrating to the first and second pharyngeal archesBSurface ectoderm cells forming the frontonasal prominenceCEndodermal cells lining the pharyngeal pouchesDParaxial mesoderm cells migrating to the pharyngeal arches

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

The answer and the reasoning

A. Neural crest cells migrating to the first and second pharyngeal arches

Treacher Collins syndrome (mandibulofacial dysostosis) results from deficient migration or survival of neural crest cells to the first and second arches. The result is hypoplasia of the malar bones, mandible and external and middle ear.

Option by option

A. Neural crest cells migrating to the first and second pharyngeal arches (correct)
Correct. Reduced neural crest contribution explains the first and second arch hypoplasia.
B. Surface ectoderm cells forming the frontonasal prominence
The frontonasal prominence is not the principal site of the defect.
C. Endodermal cells lining the pharyngeal pouches
Pouch endoderm gives thymus, parathyroid and tubotympanic structures but not the facial skeleton.
D. Paraxial mesoderm cells migrating to the pharyngeal arches
Paraxial mesoderm forms arch muscle and not the skeletal and connective tissue of the face.

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 Anatomy question

What is the answer to this Anatomy question?

The best answer is A, Neural crest cells migrating to the first and second pharyngeal arches. Treacher Collins syndrome (mandibulofacial dysostosis) results from deficient migration or survival of neural crest cells to the first and second arches.

Why is "Surface ectoderm cells forming the frontonasal prominence" not the answer?

The frontonasal prominence is not the principal site of the defect.

Why is "Endodermal cells lining the pharyngeal pouches" not the answer?

Pouch endoderm gives thymus, parathyroid and tubotympanic structures but not the facial skeleton.

Why is "Paraxial mesoderm cells migrating to the pharyngeal arches" not the answer?

Paraxial mesoderm forms arch muscle and not the skeletal and connective tissue of the face.

What concept does this question test?

It tests Embryology: Treacher Collins syndrome in Anatomy. The result is hypoplasia of the malar bones, mandible and external and middle ear.

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 Embryology: Treacher Collins syndrome?

Learn every nerve by its route, its muscles and what a lesion looks like at the bedside. That one habit answers a large share of questions. Then use the flashcards and the other Anatomy 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.