Immunodeficiency: DiGeorge syndrome: practice question

A Pathology 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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Pathology · Immunodeficiency: DiGeorge syndrome

Sample item

A 3-day-old neonate has seizures with a serum calcium of 6.2 mg/dL, a cleft palate and a conotruncal cardiac defect. The chest radiograph shows no thymic shadow. Which test best confirms the underlying disorder?

ASequencing of the BTK geneBNitroblue tetrazolium testCConventional G-banded karyotype aloneDFluorescence in situ hybridisation for 22q11.2 deletion

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

The answer and the reasoning

D. Fluorescence in situ hybridisation for 22q11.2 deletion

DiGeorge syndrome results from a 22q11.2 microdeletion causing maldevelopment of the third and fourth pharyngeal pouches, with thymic and parathyroid hypoplasia, so it presents with hypocalcaemia, T-cell deficiency and cardiac defects. The microdeletion is too small for a routine karyotype, so FISH or chromosomal microarray is needed.

Option by option

A. Sequencing of the BTK gene
BTK sequencing diagnoses X-linked agammaglobulinaemia, which does not have these features.
B. Nitroblue tetrazolium test
The nitroblue tetrazolium test screens for chronic granulomatous disease.
C. Conventional G-banded karyotype alone
A standard karyotype usually misses this microdeletion.
D. Fluorescence in situ hybridisation for 22q11.2 deletion (correct)
Correct. FISH detects the 22q11.2 microdeletion.

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 Pathology question

What is the answer to this Pathology question?

The best answer is D, Fluorescence in situ hybridisation for 22q11.2 deletion. DiGeorge syndrome results from a 22q11.

Why is "Sequencing of the BTK gene" not the answer?

BTK sequencing diagnoses X-linked agammaglobulinaemia, which does not have these features.

Why is "Nitroblue tetrazolium test" not the answer?

The nitroblue tetrazolium test screens for chronic granulomatous disease.

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

A standard karyotype usually misses this microdeletion.

What concept does this question test?

It tests Immunodeficiency: DiGeorge syndrome in Pathology. 2 microdeletion causing maldevelopment of the third and fourth pharyngeal pouches, with thymic and parathyroid hypoplasia, so it presents with hypocalcaemia, T-cell deficiency and cardiac defects. The microdeletion is too small for a routine karyotype, so FISH or chromosomal microarray is needed.

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 Immunodeficiency: DiGeorge syndrome?

Learn each disease as a bundle: cause, key histology, markers, and the clinical hallmark. Then use the flashcards and the other Pathology 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.