The thalassemia syndromes are due to quantitative abnormalities of hemoglobin peptide synthesis. Thalassemia is manifested only by hypochromia and microcytosis, with little or no anemia in the heterozygous patient (minor form); however, it causes severe hypochromic, microcytic anemia with features of hemolysis in the homozygous patient (major form). Actually, thalassemia refers to a whole spectrum of genetically determined diseases of red blood cells (RBC).
The primary defect is in the rate of hemoglobin synthesis. When the genetic anomaly depresses only β-globin chain synthesis, the disorder is termed β thalassemia. This type of thalassemia is expressed in both heterozygous and homozygous forms and comprises more than 90% of all cases. β thalassemia in homozygous patients has been known as Cooley anemia.
From 5% to 10% of persons carrying the thalassemia trait have hemoglobin A2 levels affected. These patients have an abnormal synthesis of hemoglobin due to a-globin deficiency or abnormality. The
Danilevicius Z. α Thalassemia—Caused by Gene Deletion. JAMA. 1974;230(10):1437. doi:10.1001/jama.1974.03240100055033