Medical genetics: chromosomal abnormalities: 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 · Medical genetics: chromosomal abnormalities

Sample item

A newborn has midline facial clefting, scalp cutis aplasia and postaxial polydactyly. MRI shows a single fused cerebral ventricle, and karyotype shows trisomy 13. What is the brain malformation and its developmental basis?

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

The answer and the reasoning

A. Holoprosencephaly from incomplete cleavage of the prosencephalon

Patau syndrome is classically associated with holoprosencephaly, in which the forebrain fails to divide into two hemispheres, with midline facial defects such as cleft lip and palate, and in severe cases cyclopia. Defects relate to impaired sonic hedgehog signalling. Survival beyond infancy is poor.

Option by option

  • A. Holoprosencephaly from incomplete cleavage of the prosencephalon (correct)

    Correct. Failure of prosencephalic cleavage gives a single ventricle and midline facial defects.

  • B. Hydrocephalus from aqueduct stenosis

    Aqueduct stenosis gives obstructive hydrocephalus and not a fused single ventricle.

  • C. Spina bifida from failure of the posterior neuropore to close

    Spina bifida is a defect of the posterior neuropore and is unrelated to the forebrain.

  • D. Anencephaly from failure of anterior neuropore closure

    Anencephaly results from failure of anterior neuropore closure and absence of the forebrain vault.

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.

More Anatomy questions

Questions about this Anatomy question

What is the answer to this Anatomy question?

The best answer is A, Holoprosencephaly from incomplete cleavage of the prosencephalon. Patau syndrome is classically associated with holoprosencephaly, in which the forebrain fails to divide into two hemispheres, with midline facial defects such as cleft lip and palate, and in severe cases cyclopia.

Why is "Hydrocephalus from aqueduct stenosis" not the answer?

Aqueduct stenosis gives obstructive hydrocephalus and not a fused single ventricle.

Why is "Spina bifida from failure of the posterior neuropore to close" not the answer?

Spina bifida is a defect of the posterior neuropore and is unrelated to the forebrain.

Why is "Anencephaly from failure of anterior neuropore closure" not the answer?

Anencephaly results from failure of anterior neuropore closure and absence of the forebrain vault.

What concept does this question test?

It tests Medical genetics: chromosomal abnormalities in Anatomy. Defects relate to impaired sonic hedgehog signalling. Survival beyond infancy is poor.

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 Medical genetics: chromosomal abnormalities?

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.