Thalassemia is the name of a group of inherited blood disorders. Hemoglobin, the part of red blood cells that carries oxygen, is made up of two different proteins, called alpha and beta. If the body has an imbalance in the two proteins the red blood cells cannot carry enough oxygen.
Two pairs of polypeptide chains - alpha and beta chains - make up hemoglobin. In thalassemia, diminished synthesis can affect either pair. Structurally, the chains are normal, but the genetic defect decreases their number. In alpha-thalassemia, alpha chain synthesis slows; in beta-thalassemia, beta chain synthesis slows. Some patients with beta-thalassemia have no normal hemoglobin - only hemoglobin S and the minor hemoglobins.
In the most severe form of alpha-thalassemiahydrops fetalis - severe anemia and heart failure render the fetus hydropic. The fetus is stillborn or dies shortly after birth. Prenatal testing can be used to detect the condition.
Beta-thalassemia (the most common form of this disorder) occurs in three clinical forms: thalassemia major, intermedia, and minor. The severity of the resulting anemia depends on whether the patient is homozygous or heterozygous for the thalassemic trait. The prognosis for beta-thalassemia varies. Patients with thalassemia major seldom survive to adulthood; children with thalassemia intermedia develop normally into adulthood, although puberty is usua1ly delayed; patients with thalassemia minor can expect a normal life span.
Thalassemia major and thalassemia intermedia result from homozygous inheritance of the partially dominant autosomal gene responsible for this trait. Thalassemia minor is caused by heterozygous inheritance of the same gene. In all three types of thalassemia, total or partial deficiency of beta polypeptide chain production impairs hemoglobin synthesis and results in continual production of fetal hemoglobin, even after the neonatal period has passed.
The diagnosis of thalassemia trait and thalassemia major is made from microscopic examination of the blood, which shows many small, pale red blood cells, and from other blood tests that show reduced levels of adult hemoglobin in the blood.
Treatment of thalassemia major is essentially supportive. For example, infections require prompt treatment with appropriate antibiotics. Folic acid supplements help maintain folic acid levels despite increase requirements. Transfusions of packed RBCs raise hemoglobin levels but must be used judiciously to minimize iron overload. Splenectomy and bone marrow uansplantation have been tried, but their effectiveness has not been confirmed.
Thalassemia intermedia and thalassemia minor generally don't require treatment. Iron supplements are contraindicated in all forms of thalassemia.
Treatment of children is more difficult. Regular blood transfusions may minimize physical and mental retardation, but transfusions increase the risk of deadly hemosiderosis and iron overload. Continuous subcutaneous infusion of iron-chelating agents may help produce a negative overall iron balance. If rapid splenic sequestration of transfused RBCs necessitates more transfusions, a splenectomy may be performed.
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