Sickle Cell Disease

Peter J. Paganussi Thom Mayer Maybelle Kou

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Sickle cell disease (SCD) is among the most common inherited disorders worldwide. It is the most common pediatric genetic condition encountered in emergency medicine, especially in urban settings. This genetic condition is found primarily in people of African, Mediterranean, Indian, or Middle Eastern heritage.

In the United States about 8 percent of the African-American population carries the hemoglobin (HgbS) gene and about 0.15 percent (approximately 1/500) are homozygous (HgbSS). These individuals have a predominance of "sickled" hemoglobin, thus resulting in symptomatic SCD. Patients with this hemoglobinopathy have both sickle (A2) and fetal hemoglobin. The most frequently encountered heterozygous sickle genotypes are HgbSA (sickle cell trait), Hgb-beta thalassemia (sickle beta thalassemia), and HgbSC (sickle cell-hemoglobin SCD). These less common variants of the homozygous disorder have similar, but far less severe, clinical manifestations. Patients with sickle cell trait have a normal life expectancy. However, SCD is associated with a significant mortality rate: 20 to 30 percent of all deaths from SCD occur before 5 years, with a mean age at death of 14 years of age. Current survival has been greatly improved as a result of more aggressive infection prophylaxis and advances in therapy. Nonetheless, the highest mortality occurs in children between 1 and 3 years of age, with sepsis being the leading cause of death.

The end-organ pathology created by sickle cell anemia can be found in every organ system. Clinical effects of the disorder can begin in infancy but usually are not seen until 5 to 6 months of age, because high levels of fetal hemoglobin are present following birth, and the beta-Hgb subunit is not predominant until about 3 months of age. SCD is characterized by abnormal sickle-shaped cells that are less deformable than normal red blood cells. Aggregation of these less pliant, abnormally shaped cells leads to obstruction and thrombosis of small vessels, resulting in ischemia and tissue infarction, leading to end-organ dysfunction.

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