Alpha-thalassemia The thalassemias are a diverse group of genetic blood diseases characterized by decreased production of normal hemoglobin. In the α-thalassemias it is production of the α-globin chains that is specifically affected. Humans have two α-globin genes. Patients homozygous for a mutated poly(A) signal in the first of these two genes suffer a loss of α-chain production, not only from the mutated gene but also from the normal gene downstream. As a result, the excess β-chains (that are unable to find α-chains) form homotetramers called HbH. This abnormal hemoglobin has an extremely high affinity for oxygen and no Bohr effect, and is useless for the transport of oxygen. |