Thalassemia is a genetic disorder in which there is decreased production of one of the globin chains found in hemoglobin . If the body fails to produce enough of any one type of globin, a deficiency of hemoglobin can result, causing anemia. Sometimes the body manufactures abnormal hemoglobin, containing yet another combination of chains. Such abnormal hemoglobins often do not transport oxygen efficiently and may also be unstable. In the case of sickle cell disease , the problem is the characteristic behavior of abnormal sickle hemoglobin.
Thalassemias differ in severity and in the type of globin chain that is deficient.
The most common type in the United States is b thalassemia, also known as Mediterranean anemia in its mild form or Cooley's anemia in its severe form. A pair of genes controls the production of the b globin chain. Other hemoglobins such as A2 and fetal hemoglobin that do not contain b chains will be made. After the first few months of life, however, the quantity of these other hemoglobins diminishes. A person with b thalassemia major , in which both genes are affected, develops severe anemia starting at a few months of age.