Question
Every individual carries four alpha gene alleles. Deletion of three alleles leads to development of:
The correct answer is
Haemoglobin H disease
Alpha Gene Allele Deletion and Haemoglobin H Disease
Alpha gene alleles are essential for synthesizing the alpha-globin chains that form a part of normal adult haemoglobin (HbA).
Each person typically inherits four alpha gene alleles (two on each chromosome 16).
The number of deleted alpha gene alleles determines the clinical presentation, often referred to as alpha-thalassemia:
- Deletion of one allele: Usually asymptomatic (silent carrier).
- Deletion of two alleles: Causes alpha-thalassemia trait, typically mild anaemia.
- Deletion of three alleles: Leads to the formation of excess beta-globin chains, which associate to form Haemoglobin H (HbH). This results in Haemoglobin H disease, characterized by moderate to severe anaemia.
- Deletion of all four alleles: Causes hydrops fetalis, a severe condition usually resulting in stillbirth or neonatal death.
Consequently, the deletion of three alpha gene alleles directly causes the development of Haemoglobin H disease.
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