Embryology: pharyngeal pouches and neural crest: 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: pharyngeal pouches and neural crest

Sample item

A newborn has hypocalcaemic seizures, persistent truncus arteriosus, a cleft palate and an absent thymic shadow. Which embryological explanation and genetic abnormality fit best?

AEctodermal defect of the second pharyngeal cleft, with 45,XBNeural crest defect affecting the third and fourth pharyngeal pouches and the outflow tract, with 22q11.2 deletionCMesodermal defect of the sixth arch, with trisomy 18DEndodermal defect of the first pharyngeal pouch, with trisomy 21

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

The answer and the reasoning

B. Neural crest defect affecting the third and fourth pharyngeal pouches and the outflow tract, with 22q11.2 deletion

In DiGeorge syndrome, 22q11.2 deletion disrupts neural crest cells that migrate into the pharyngeal arches and the outflow tract. The third pouch forms the thymus and inferior parathyroids and the fourth pouch the superior parathyroids, so hypocalcaemia and T cell deficiency result. The outflow anomalies include truncus arteriosus and interrupted aortic arch.

Option by option

A. Ectodermal defect of the second pharyngeal cleft, with 45,X
The second cleft is normally obliterated, and 45,X causes Turner syndrome.
B. Neural crest defect affecting the third and fourth pharyngeal pouches and the outflow tract, with 22q11.2 deletion (correct)
Correct. Neural crest failure explains the combination of pouch derivative loss and conotruncal anomalies.
C. Mesodermal defect of the sixth arch, with trisomy 18
Trisomy 18 gives a different pattern of anomalies and the sixth arch forms the pulmonary arteries and ductus.
D. Endodermal defect of the first pharyngeal pouch, with trisomy 21
The first pouch forms the middle ear and auditory tube, not the thymus or parathyroids.

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 B, Neural crest defect affecting the third and fourth pharyngeal pouches and the outflow tract, with 22q11.2 deletion. In DiGeorge syndrome, 22q11.

Why is "Ectodermal defect of the second pharyngeal cleft, with 45,X" not the answer?

The second cleft is normally obliterated, and 45,X causes Turner syndrome.

Why is "Mesodermal defect of the sixth arch, with trisomy 18" not the answer?

Trisomy 18 gives a different pattern of anomalies and the sixth arch forms the pulmonary arteries and ductus.

Why is "Endodermal defect of the first pharyngeal pouch, with trisomy 21" not the answer?

The first pouch forms the middle ear and auditory tube, not the thymus or parathyroids.

What concept does this question test?

It tests Embryology: pharyngeal pouches and neural crest in Anatomy. 2 deletion disrupts neural crest cells that migrate into the pharyngeal arches and the outflow tract. The third pouch forms the thymus and inferior parathyroids and the fourth pouch the superior parathyroids, so hypocalcaemia and T cell deficiency result. The outflow anomalies include truncus arteriosus and interrupted aortic arch.

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 Embryology: pharyngeal pouches and neural crest?

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.