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 Sickle Cell Anemia (SCA) is the most common inherited
blood disorder in the United States, affecting about 72,000 Americans or 1
in 500 African Americans. SCA is characterized by episodes of pain,
chronic hemolytic anemia and severe infections, usually beginning in early
childhood.
SCA is an autosomal recessive disease caused by
a point mutation in the hemoglobin beta gene (HBB) found on
chromosome 11p15.4. Carrier frequency of HBB varies significantly
around the world, with high rates associated with zones of high malaria
incidence, since carriers are somewhat protected against malaria. About 8%
of the African American population are carriers. A mutation in HBB
results in the production of a structurally abnormal hemoglobin (Hb),
called HbS. Hb is an oxygen carrying protein that gives red blood cells
(RBC) their characteristic color. Under certain conditions, like low
oxygen levels or high hemoglobin concentrations, in individuals who are
homozygous for HbS, the abnormal HbS clusters together, distorting the
RBCs into sickled shapes. These deformed and rigid RBCs become trapped
within small blood vessels and block them, producing pain and eventually
damaging organs.
Though, as yet, there is no cure for SCA,
a combination of fluids, painkillers, antibiotics and transfusions are
used to treat symptoms and complications. Hydroxyurea, an antitumor drug,
has been shown to be effective in preventing painful crises. Hydroxyurea
induces the formation of fetal Hb (HbF) - a Hb normally found in the fetus
or newborn - which, when present in individuals with SCA, prevents
sickling. A mouse model of SCA has been developed and is being used to
evaluate the effectiveness of potential new therapies for SCA.
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