Sickle cell disease:
Chapter: 20a
Hemoglobinopathy in which sickling of red cells occurs, and chronic hemolytic anemia is present. The abnormal hemoglobin is termed Hemoglobin S, and is due to a substitution of valine for glutamic acid at position 6 of the beta-globin chain, due to a point mutation from adenine to thymine. Patients with sickle cell anemia are homozygous for the hemoglobin SS gene, which is the result of inheriting one gene from each parent, and occurs in one in 650 African-Americans. Sickle cell crises can be aplastic, infarctive or sequestration in pathogenesis, and are often precipitated by infection. Many organs are affected, with notable disease affects as follows: splenic infarcts with eventual autosplenectomy, renal papillary necrosis, osteomyelitis, avascular necrosis of the femoral head, gallstones, and iron overload. Sickle cell trait is the heterozygous form of sickle cell disease, occurring in 8-10% of African Americans.