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Alpha thalassemia
Last reviewed: 06.07.2025
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Alpha thalassemia is a group of diseases common in Southeast Asia, China, Africa, and the Mediterranean. Two nearly identical copies of the alpha globin gene are found on chromosome 16. In 80 to 85 percent of cases of alpha thalassemia, one or more of these four genes are lost. In the remaining patients, these genes are retained but do not function.
The clinical manifestations of alpha-thalassemia correlate with the degree of impairment of alpha-globin chain synthesis, but are usually less pronounced than in β-thalassemia. This is due, firstly, to the fact that the presence of four alpha-globin genes promotes the formation of an adequate number of alpha chains until three or four genes are lost. A significant imbalance of hemoglobin chains occurs only if three of the four genes are affected. Secondly, β-chain aggregates (β1-tetramers are formed with alpha-chain deficiency) are more soluble than alpha4 - tetramers, and therefore even in patients with significantly impaired alpha-globin synthesis in alpha-thalassemia, hemolysis is much weaker and erythropoiesis is more effective than in β-thalassemia.
Alpha-Thalassemia (alpha-thal) is a hemolytic anemia caused by a deficiency in the synthesis of alpha-globin as a result of loss or damage to one or more alpha-globin genes. Decreased synthesis of alpha chains leads to the accumulation of free γ- and β-chains and the formation of tetramers-γ 4 (Hb Bart's) and unstable β 4 (Hb H) from them with subsequent acceleration of the destruction of red blood cells. Having a very high affinity for oxygen, these tetramers cannot perform the function of oxygen transport. Thus, the clinical picture of severe alpha-thal is characterized by a combination of hypochromic anemia, hemolysis and defective oxygen transport due to varying amounts of physiologically ineffective hemoglobin in red blood cells. As a result, the degree of tissue hypoxia significantly exceeds that expected for the corresponding degree of anemia.
There are 4 groups of clinical alpha-thal syndromes:
- silent carriage;
- minimal change alpha thalassemia;
- hemoglobinopathy H;
- alpha thalassemic hydrops fetalis.
The severity of the phenotypic manifestation of alpha-thal is directly proportional to the decrease in alpha-globin synthesis.
Silent carriage (alpha-thal-2 heterozygotes)
Phenotypically, silent carriers of alpha-thal differ little from healthy children. MCV is usually within 78-80 fL, while MCH may correspond to the lower limit of normal. All other hematological parameters are normal. Some silent carriers may even have normal MCV values in the range of 80-85 fL. In the blood of some of them, small amounts of Hb Bart's (<2%) are detected in the neonatal period, which disappears during the first months of life.
Minor alpha-thalassemia-2 (asymptomatic carrier) - is caused by the loss of two alpha-globin genes on different chromosomes (trans-form). It is found in residents of Asia, Africa, and the Mediterranean. Hematological parameters do not differ from the norm; there are no clinical manifestations. In the neonatal period, an increased amount of Hb Bart is determined - 0.8-5%. In adults with a-thalassemia-2, pathological fractions of HbH hemoglobin H Bart are not detected, the content of HbA 2 and HbF are normal.
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