The HBB gene encodes for the β-globin chain of hemoglobin, an essential protein found in red blood cells. Mutations in the HBB gene lead to blood disorders, including β-thalassemia. β-thalassemia is an autosomal recessive disorder, which means two defective copies of HBB are necessary to be affected by the disease. HBB mutations are referred to as either beta-zero (β0), where no β-globin is produced, or beta-plus (β+), where some β-globin is still produced. The severity of β-thalassemia symptoms varies depending on the nature of these inherited genetic change:
- β-thalassemia minor – These individuals have only one defective copy of HBB (either β0 or β+) and are known as carriers of β-thalassemia.
- β-thalassemia intermedia – A condition where individuals have two defective copies of HBB, but at least one copy has a β+ mutation, hence some β-globin is still produced. Symptoms range from mild to severe depending on the amount of β-globin produced.
- β-thalassemia major – Affected individuals have two defective copies of the HBB gene, both with β0 mutations, hence no β-globin is produced. These people experience the life-threatening symptoms of beta thalassemia, including severe anemia, hypochromic (paler than normal) and microcytic (smaller) red blood cells.
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