Blood and immunity: hydrops fetalis and haemoglobin Bart's: practice question

A Physiology 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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Physiology · Blood and immunity: hydrops fetalis and haemoglobin Bart's

Sample item

A fetus has hydrops, severe anaemia and a haemoglobin that is almost entirely made of four gamma chains. Which genetic defect underlies this?

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

The answer and the reasoning

B. Deletion of all four alpha globin genes

With deletion of all four alpha genes no alpha chains are made, so excess gamma chains form tetramers (haemoglobin Bart's), which carry oxygen very poorly because of their high affinity. This causes hydrops fetalis, usually fatal in utero or soon after birth.

Option by option

  • A. Homozygous beta globin mutation

    Beta globin defects present after birth, when haemoglobin F is replaced by adult haemoglobin.

  • B. Deletion of all four alpha globin genes (correct)

    Correct. Absence of all four alpha genes gives gamma tetramers and hydrops fetalis.

  • C. Deletion of both gamma globin genes

    Fetal haemoglobin needs gamma chains, so deleting them would not produce gamma tetramers.

  • D. Deletion of one alpha globin gene

    Loss of one alpha gene is a silent carrier state with no anaemia.

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 Physiology question

What is the answer to this Physiology question?

The best answer is B, Deletion of all four alpha globin genes. With deletion of all four alpha genes no alpha chains are made, so excess gamma chains form tetramers (haemoglobin Bart's), which carry oxygen very poorly because of their high affinity.

Why is "Homozygous beta globin mutation" not the answer?

Beta globin defects present after birth, when haemoglobin F is replaced by adult haemoglobin.

Why is "Deletion of both gamma globin genes" not the answer?

Fetal haemoglobin needs gamma chains, so deleting them would not produce gamma tetramers.

Why is "Deletion of one alpha globin gene" not the answer?

Loss of one alpha gene is a silent carrier state with no anaemia.

What concept does this question test?

It tests Blood and immunity: hydrops fetalis and haemoglobin Bart's in Physiology. This causes hydrops fetalis, usually fatal in utero or soon after birth.

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 Blood and immunity: hydrops fetalis and haemoglobin Bart's?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology 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.