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Sickle Cell Disease: Overview and Risk Factors

Sickle cell disease (SCD) is an autosomal recessive condition, in which red blood cells become sickle shaped and fragile. This results in hemolytic anemia and recurrent vaso-occlusion in the microvasculature due to increased red blood cell adhesion and retention. Sickle cell crises, caused by acute vaso-occlusion, are characterized by severe pain in the musculoskeletal system, abdomen, and other areas. Other acute vaso-occlusive complications include splenic sequestration and/or infarct and the acute chest syndrome associated with pulmonary infarcts. Large vessel stroke occurs in the setting of stenotic blood vessels due to chronic vessel wall injury.

Hemoglobin S (HbS) is characterized by a single change in the amino acid sequence of the β-globin chain and is responsible for creating the abnormal red cell morphology. Individuals who are heterozygous for the HbS gene generally have no symptoms or sequelae of SCD, but they and are said to have sickle cell trait; ie, they are carriers of the HbS gene. Their offspring could be affected if the other parent is heterozygous or homozygous for the gene, or carries another abnormal hemoglobin gene.

Other SCD variants include hemoglobin SC, a heterozygous combination of HbS and hemoglobin C, and hemoglobin S and β-thalassemia (hemoglobin Sβ+- thalassemia or Sβo-thalassemia). These conditions cause SCD, although the symptoms and complications may be less severe than those in the homozygous condition. The remainder of this chapter will focus on SCD that results from homozygous HbS.

Acute signs and symptoms may include pain in the hands and feet, fever, immunocompromise due to splenic sequestration/infarction, priapism, chest pain, shortness of breath, fatigue, pallor, tachycardia, jaundice, and urinary symptoms. Chronic complications include delayed growth/puberty, retinopathy, chronic lung and kidney disease, avascular necrosis of the hips and shoulders, bone infarcts, and leg ulcers.

Risk Factors

The disease occurs most often among people whose ancestry can be linked to sub-Saharan Africa, South and Central America, the Caribbean, India, and the Middle East and Mediterranean regions. A Texas study showed the disease to be about 300 times more common in African Americans (approximately 3 per 1,000) than in whites, and 3 times more common in individuals of Hispanic ethnicity than in non-Hispanic whites.1 Approximately 1 in 12 African Americans carry sickle cell trait.


Sickle Cell Disease: Diagnosis >>