Thalassemia is an inherited disease of faulty synthesis of hemoglobin. The name is derived from the Greek word "thalassa" meaning "the sea" because the condition was first described in populations living near the Mediterranean Sea.
Alpha-thalassemias are characterized by decreased hemoglobin alpha chain synthesis; alpha-zero-thalassemia being the condition where no normal alpha globin is produced, and alpha-plus-thalassemia being the condition where there is reduced globin production. There are two alpha globin genes per haploid genome, and alpha thalassemia abnormalities can result from one to four gene deletions. A single alpha gene mutation leads to the silent carrier state (alpha-plus). The two gene mutation is a minor clinical condition, with mild hypochromic, microcytic anemia.
Mutation of three of the alpha genes leads to Hemoglobin H disease, characterized by microcytic hypochromic hemolytic anemia, hepatosplenomegaly, mild jaundice, and sometimes thalassemia-like bone changes. Mutation of all four alpha genes results in Hb Bart hydrops fetalis (Hb Bart) syndrome, typified by fetal onset of generalized edema, pleural and pericardial effusions, and severe hypochromic anemia. Death usually occurs in the neonatal period. No effective treatment is available for Hb Bart syndrome. Occasional RBCs transfusion may be required for patients with HbH disease.