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Patient Story

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A 4-year-old boy with known sickle cell disease is brought to the emergency department with worsening pain in his thighs, lower back, abdomen, and chest. He developed pain in both thighs 2 days ago, and was treated with ibuprofen without improvement. His chest pain began today and he refused to walk or eat. In the emergency department, he was tachypneic and had an oxygen saturation by pulse oximetry of 84 percent on room air, which increased to 95 percent on 2 liters oxygen by nasal canula. A chest x-ray showed bilateral infiltrates (Figure 211-1). He was diagnosed with acute chest syndrome and admitted to the pediatric intensive care unit, where he was treated with intravenous fluids, pain medications, and antibiotics, and made a full recovery.

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FIGURE 211-1

Acute chest syndrome on chest x-ray in a young child with sickle cell disease. (Used with permission from Arunkumar Modi, MD, MPH.)

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Introduction

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Sickle cell diseases (SCD) are a group of genetic disorders in which the affected individual has at least one copy of the genes that encode b-globin chains affected by the sickle cell mutation. This mutation causes sickling of red blood cells with resultant hypoxia and acidosis leading to a chronic progressive multisystem disorder. Sickle cell trait (SCT) is a condition in which affected individuals have one normal copy of the β chain gene and one sickle mutated copy. These individuals are generally unaffected. Hemoglobin SS disease (SCD-SS) is a condition in which affected individuals are homozygous for the sickle mutated β chain gene.1

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Synonyms

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  • Sickle cell disease (SCD), Sickle cell anemia, Hemoglobin SS disease (SCD-SS).

  • Hemoglobin SC disease (SCD-SC) and Hemoglobin S β-thalassemia (SCD-S-β Thalassemia) are types of sickle cell disease with different mutations than SCD-SS.

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Epidemiology

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  • SCD affects 90,000 to 100,000 Americans.

  • SCD occurs in approximately 1 out of every 500 Black or African-American births.

  • SCD occurs in approximately 1 out of every 36,000 Hispanic-American births.

  • SCT occurs in approximately 1 in 12 Blacks or African-Americans.2

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Etiology and Pathophysiology

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  • Sickle cell disease is caused by a hemoglobin structural defect that results from the substitution of valine for glutamic acid at the 6th position on the gene coding for β globin.

  • The mutation causes sickling in deoxygenated cells and leads to red cell membrane rigidity, increased red blood cell adhesion to the vascular endothelium, venous occlusion, and a decreased red cell life span of 10 to 20 days.

  • The point mutation in Hemoglobin C disease results from a hemoglobin structural defect that results from the substitution of lysine for glutamic acid at the 6th position on the gene coding for β globin.

  • This mutation results in persistent cellular potassium loss and ...

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