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mutation triggers erythropoietin hypersensitivity

Beta-thalassemia minor (trait) occurs in heterozygotes (beta/beta + or beta/beta 0), who are usually asymptomatic with mild to moderate microcytic anemia. This phenotype may also occur in mild cases of beta +/beta +.

Beta-thalassemia intermedia is a variable clinical picture that is intermediate between thalassemia major or minor, caused by inheritance of 2 beta thalassemia alleles (beta +/beta 0 or severe cases of beta +/beta +).

Beta-thalassemia major (or Cooley anemia) occurs in homozygotes (beta 0/beta 0) or severe compound heterozygotes (beta 0/beta +) and results from severe beta globin deficiency. These patients develop severe anemia and bone marrow hyperactivity. Beta-thalassemia major manifests by age 1 to 2 years with symptoms of severe anemia and transfusional and absorptive iron overload. Patients are jaundiced, and leg ulcers and cholelithiasis occur (as in sickle cell disease). Splenomegaly, often massive, is common. Splenic sequestration may develop, accelerating destruction of transfused normal red blood cells. Bone marrow hyperactivity causes thickening of the cranial bones and malar eminences. Long bone involvement predisposes to pathologic fractures and impairs growth, possibly delaying or preventing puberty.

With iron overload, iron deposits in heart muscle may cause heart failure. Hepatic siderosis is typical, leading to functional impairment and cirrhosis. Iron chelation is usually necessary.