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An inherited blood disorder characterized by episodes of pain, chronic hemolytic anemia, and severe infections, usually beginning in early childhood. As a result of the vasoocclusive nature of the disease, in the worst situation, patients may present with congestive heart failure, cerebral infarction, kidney damage with bloody urine, splenomegaly, hepatomegaly and jaundice, eye damage, and bone marrow defects.

There are four different types: Sickle Cell Trait; Hemoglobin SS; Hemoglobin SC Disease; Hemoglobin Sickle Beta-Thalassemia.

Sickle Cell Anemia is the most common inherited blood disorder in the United States, affecting 1 in 375 to 500 African Americans. Eight percent of African Americans are affected. Homozygous HbS disease occurs in 0.2% of African Americans, while heterozygous sickle cell trait occurs in 8%. Globally, a quarter of a million children are born every year with the disease. At least five haplotypes of sickle cell disease are recognized based upon their origin: Senegal, Cameron, Benin, Central African Republic, and India. Among these, patients from the Central African Republic have the most severe disease and those from Senegal the least severe. Other nationalities with sickle cell include Arabs, Greeks, Italians (mostly southern), and Latin Americans.

Autosomal recessive inheritance caused by a point mutation in the hemoglobin beta gene (HBB) found on chromosome 11p15.4.

HbS is characterized by the substitution of valine for glutamic acid in the sixth position of the B chain. When deoxygenated, the red cells change conformation, forming a sickle shape that rheologically favors vascular stasis and subsequently ischemia. While the red cells of patients with sickle cell trait have less than 50% HbS, the red cells of homozygotes may have upwards of 70 to 90% HbS. Clinical severity improves with increased levels of fetal hemoglobin (HbF). Other Sickle Cell Diseases include Hemoglobin SC Disease, Sickle Cell Beta-Thalassemia, and Hemoglobin SD Disease. These diseases are often, but not always, milder than Hemoglobin SS Disease. Sickle Trait is usually asymptomatic, although hematuria and inability to concentrate urine may occur.

Sickle Cell Trait suggests a person who carries a sickle hemoglobin-producing gene inherited from one parent with a normal (HbA) and an abnormal (HbS) gene leading to Hb AS on the electrophoresis. This form does not cause HbSS Disease. Fetal diagnosis is via chorionic villus biopsy. Electrophoresis of umbilical cord blood is also indicated to establish the diagnosis in neonates. Peripheral smear with sickled cells, target cells, and reticulocytosis is characteristic. Hydroxyurea, an antitumor, is effective in preventing painful crises because it induces the formation of fetal Hb (HbF), preventing sickling.

Vasoocclusive (painful) crises (bones, abdomen, chest) are characteristic of this disease and caused by sickling red cells leading to ischemia. Aplastic crisis (associated with parvovirus B19 infection) can also be seen. Sequestration crisis (usually children, though can affect adults with Hemoglobin SC Disease and Sickle Cell Beta-Thalassemia) is another mode of clinical presentation. Hemolytic crisis, growth retardation, bone defects/osteomyelitis (salmonella), renal papillary necrosis, ...

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