(See also Overview of Hemolytic Anemia Overview of Hemolytic Anemia At the end of their normal life span (about 120 days), red blood cells (RBCs) are removed from the circulation. Hemolysis is defined as premature destruction and hence a shortened RBC life span... read more .)
Because of the increased frequency of both hemoglobin (Hb) S (the abnormal hemoglobin that is responsible for sickle cell disease Sickle Cell Disease Sickle cell disease (a hemoglobinopathy) causes a chronic hemolytic anemia occurring almost exclusively in people with African ancestry. It is caused by homozygous inheritance of genes for hemoglobin... read more ) and beta-thalassemia genes in people with African, Mediterranean, or Southeast Asian ancestry, inheritance of both defects is relatively common. Beta-thalassemia Beta-thalassemia Thalassemias are a group of inherited microcytic, hemolytic anemias characterized by defective hemoglobin synthesis. Alpha-thalassemia is particularly common among people with African, Mediterranean... read more results from decreased production of the beta-polypeptide chains of hemoglobin due to either mutations or deletions in the beta globin gene, leading to impaired production of hemoglobin A (see also Thalassemias Thalassemias Thalassemias are a group of inherited microcytic, hemolytic anemias characterized by defective hemoglobin synthesis. Alpha-thalassemia is particularly common among people with African, Mediterranean... read more ).
Beta globin mutations may result in partial loss (beta + allele) or complete loss (beta 0 allele) of beta globin function. Thus, manifestations of S-beta-thalassemia depend on whether the patient has a beta + or beta 0 allele. Those with beta + produce varying amounts of beta globin (and thus have varying amounts of Hb A). Those with beta 0 produce no beta globin and thus have no Hb A.
Clinically, manifestations depend on the amount of Hb A. Thus, Hb-S-beta 0 thalassemia manifests similarly to sickle cell disease (Hb SS), whereas Hb S–beta+ thalassemia causes symptoms of moderate anemia and some signs of sickle cell disease Symptoms and Signs Sickle cell disease (a hemoglobinopathy) causes a chronic hemolytic anemia occurring almost exclusively in people with African ancestry. It is caused by homozygous inheritance of genes for hemoglobin... read more , which are usually less frequent and less severe than those of pure sickle cell disease. Mild to moderate microcytic anemia is usually present along with some sickled red blood cells on stained blood smears.
Diagnosis requires quantitative hemoglobin studies. Hb S predominates on electrophoresis and is always greater than 50%. Hb A is decreased in Hb-S-beta + or absent in Hb-S-beta 0. Hb F increase is variable.
Treatment, if necessary (eg, for symptomatic anemia, painful crises, end-organ disease), is the same as treatment of sickle cell disease Treatment Sickle cell disease (a hemoglobinopathy) causes a chronic hemolytic anemia occurring almost exclusively in people with African ancestry. It is caused by homozygous inheritance of genes for hemoglobin... read more .