Sickle Cell (cont.)
How is sickle cell anemia inherited?
Sickle cell anemia is inherited as an autosomal (meaning that the
gene is not linked to a sex chromosome) recessive condition whereas
sickle cell trait is inherited as an autosomal dominant trait. This
means that the gene can be passed on from a parent carrying it to
male and female children. In order for sickle cell anemia to occur, a
sickle cell gene must be inherited from both the mother and the
father, so that the child has two sickle cell genes.
The inheritance of just one sickle gene is called sickle cell trait
or the "carrier" state. Sickle cell trait does not cause sickle cell
anemia. Persons with sickle cell trait usually do not have many
symptoms of disease and have normal hospitalization rates and life
expectancies. Sickle cell trait is present in some two million
blacks in the United States (8% of the U.S. black population at
birth). When two carriers of sickle cell trait mate, their offspring
have a one in four chance of having sickle cell anemia. (In some
parts of Africa, one in five persons is a carrier for sickle cell
trait.)
What conditions promote the sickling (distortion) of the red
blood cells in sickle cell anemia?
Sickling of the red blood cells in patients with sickle cell anemia
results in cells of abnormal shape and flexibility. The sickling is
promoted by conditions which are associated with low oxygen levels,
increased acidity, or low volume (dehydration) of the blood. These
conditions can occur as a result of injury to the body's tissues,
dehydrating states, or anesthesia.
Even certain organs are predisposed to lower oxygen levels or
acidity, such as when blood moves slowly through the spleen, liver,
or kidney. Also, organs with particularly high metabolism rates
(such as the brain, muscles, and the placenta in a pregnant woman
with sickle cell anemia) promote sickling by extracting more oxygen
from the blood. These conditions make these organs susceptible to
injury from sickle cell anemia.
Next: How is sickle cell anemia diagnosed? »
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