INTRODUCTION

Sickle cell hemoglobinopathy results from the substitution of a valine for glutamic acid as the sixth amino acid of the beta globin chain. Sickle cell disease (SCD) includes the most severe and most common form, homozygous sickle cell anemia (Hb SS), as well as the heterozygous condition of intermediate severity, S combined with hemoglobin C (Hb SC). Hemoglobin S is also seen in combination with beta thalassemia producing the more severe form, HbS-β0 thalassemia, and the less severe HbS-β+ thalassemia. The heterozygous (carrier) form in which hemoglobin S combines with normal hemoglobin A (Hb AS) is usually asymptomatic.

The sickling of erythrocytes that results from the deoxygenation-induced deformation of the hemoglobin S molecule causes erythrostasis, thrombosis, and ultimately infarction in the spleen of affected patients. SCD patients develop early functional asplenia, usually by 2–4 years of age, which leads to susceptibility to encapsulated organisms: Streptococcus pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae, Chlamydia pneumoniae. Prophylactic penicillin, given as 125 mg orally twice a day until 2–3 years of age and 250 mg twice daily until at least 5 years of age, is recommended as prevention against invasive pneumococcal disease.

EPIDEMIOLOGY

According to a World Health Organization report from 2005, “Sickle cell anemia affects millions throughout the world. In the United States, it affects around 72,000 people.