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How does thalassemia affect adult hemoglobin production?

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blood disease Peripheral blood smear revealing histopathologic features indicative of a blast crisis in a case of chronic myelogenous leukemia (CML). Blast crisis occurs when one-fifth to one-third of the cells in the blood or bone marrow are immature blood cells, or blast cells. This phase of CML is characterized by fever, weakness, and an enlarged spleen.

Thalassemia is a group of inherited blood disorders characterized by genetically determined abnormalities in the synthesis of globin polypeptide chains, which are essential components of hemoglobin.12

In healthy individuals, normal adult hemoglobin (Hb A) consists of two alpha ( $α$ ) and two beta ( $β$ ) globin chains. Thalassemia disrupts this production by reducing or preventing the synthesis of specific chains, leading to an imbalance in chain pairs. This imbalance results in:21

Ineffective Erythropoiesis: The production of red blood cells is compromised, and the cells produced are often small (microcytosis) and prone to destruction (hemolysis).12
Deficient Hemoglobin: Because the chains are not produced in the correct ratios, the body cannot manufacture sufficient functional hemoglobin to transport oxygen effectively.1
Formation of Unstable Tetramers: In $α$ -thalassemia, the excess of non- $α$ chains may form unstable tetramers, such as $β_{4}$ (hemoglobin H), which are ineffective at oxygen delivery.12

While the body may attempt to compensate—such as through bone marrow expansion—the resulting red cells are often defective, leading to the clinical symptoms of anemia.12