Genetics: investigation of microdeletion: 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 · Genetics: investigation of microdeletion

Sample item

A 5-day-old infant has cyanosis with a truncus arteriosus, cleft palate and seizures with a serum calcium of 6.2 mg/dL. Which test confirms the suspected underlying genetic diagnosis?

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

The answer and the reasoning

B. FISH or chromosomal microarray for 22q11.2 deletion

The combination of conotruncal heart defect, hypocalcaemia from parathyroid hypoplasia, and palatal anomalies suggests 22q11.2 deletion syndrome (DiGeorge). The deletion is submicroscopic, so FISH with a TUPLE1 or N25 probe or chromosomal microarray is used. Immunological evaluation of T cells is also needed because of thymic hypoplasia.

Option by option

  • A. Triplet repeat PCR for FMR1

    FMR1 repeat testing is for fragile X syndrome.

  • B. FISH or chromosomal microarray for 22q11.2 deletion (correct)

    Correct. A targeted 22q11.2 FISH or microarray detects the microdeletion.

  • C. Methylation analysis of the 15q11-q13 region

    Methylation analysis is for Prader-Willi and Angelman syndromes.

  • D. G-banded karyotype alone

    G-banded karyotype cannot resolve a deletion of this size and is usually normal.

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 Anatomy question

What is the answer to this Anatomy question?

The best answer is B, FISH or chromosomal microarray for 22q11.2 deletion. The combination of conotruncal heart defect, hypocalcaemia from parathyroid hypoplasia, and palatal anomalies suggests 22q11.

Why is "Triplet repeat PCR for FMR1" not the answer?

FMR1 repeat testing is for fragile X syndrome.

Why is "Methylation analysis of the 15q11-q13 region" not the answer?

Methylation analysis is for Prader-Willi and Angelman syndromes.

Why is "G-banded karyotype alone" not the answer?

G-banded karyotype cannot resolve a deletion of this size and is usually normal.

What concept does this question test?

It tests Genetics: investigation of microdeletion in Anatomy. 2 deletion syndrome (DiGeorge). The deletion is submicroscopic, so FISH with a TUPLE1 or N25 probe or chromosomal microarray is used. Immunological evaluation of T cells is also needed because of thymic hypoplasia.

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 Genetics: investigation of microdeletion?

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.