Question:medium
Hemoglobin H (HbH) disease is seen in which of the following?
Hemoglobin H (HbH) disease is seen in which of the following?
Show Hint
HbH is beta4 tetramer from severe alpha chain shortage, one step short of hydrops fetalis.
Updated On: Jun 24, 2026
- Deletion of 3 alpha genes
- Deletion of all 4 alpha genes
- Deletion of 3 beta genes
- Deletion of all 4 beta genes
Show Solution
The Correct Option is A
Solution and Explanation
Alpha thalassemia is graded by the number of functional alpha globin genes lost out of the normal four. Think of it as a sliding scale: lose one gene and the person is a clinically silent carrier; lose two and they have the mild alpha thalassemia trait; lose three and the imbalance becomes large enough that surplus beta chains accumulate; lose all four and no alpha chains are made at all, producing Hb Bart and fatal hydrops fetalis in utero.
Hemoglobin H is specifically the tetramer formed by four beta chains ($\beta_4$) when there is a severe shortage of alpha chains to pair with them. This degree of shortage occurs only when three of the four alpha genes are deleted, leaving a single working alpha gene. That single gene cannot supply enough alpha chains, so the leftover beta chains self-associate into HbH.
Matching the options: 4-gene deletion is hydrops fetalis (not HbH), and beta gene deletions cause beta thalassemia, not alpha-related HbH. Only the 3 alpha gene deletion fits.\[\boxed{\text{Deletion of 3 alpha genes}}\]
Hemoglobin H is specifically the tetramer formed by four beta chains ($\beta_4$) when there is a severe shortage of alpha chains to pair with them. This degree of shortage occurs only when three of the four alpha genes are deleted, leaving a single working alpha gene. That single gene cannot supply enough alpha chains, so the leftover beta chains self-associate into HbH.
Matching the options: 4-gene deletion is hydrops fetalis (not HbH), and beta gene deletions cause beta thalassemia, not alpha-related HbH. Only the 3 alpha gene deletion fits.\[\boxed{\text{Deletion of 3 alpha genes}}\]
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