What is it?
Sickle-cell anemia is a disease in which red blood cells
form irregular crescent-like shapes. It
often results in painful episodes in the back or chest. Other symptoms include fatigue, paleness,
rapid heart rate, shortness of breath, and yellowing of the eyes and skin known
as jaundice.
How do you get it?
Sickle-cell anemia is an inherited disease. It is autosomal recessive and is more common
amoung people of African and Mediterranean descent. People can have the sickle-cell trait but not
express the characteristics of sickle-cell anemia.
What Causes it?
Our bodies are in constant need of oxygen. Red Blood cells are responsible for 98% of
the oxygen transport in the blood. Normal
red blood cells are shaped sort of like a jelly-filled doughnut. This unique structure is due to a complex arrangement
of filaments that make up its cytoskeleton.
Despite its structure it is extremely flexible. This flexibility is useful when going through
narrow capillaries. The shape also gives
it more surface area for more rapid oxygen and carbon dioxide exchange. In sickle-cell anemia, oxygen carrying
structures in the blood cells, called hemoglobin, are deformed due to a defect
in their amino acid chain, this deformed hemoglobin is called hemoglobin S
(HbS). This defect causes the hemoglobin
to crystallize when it releases oxygen pulling the cell into a crescent
shape. This crescent shape may cause the
cells to become tangled when passing through capillaries, forming blockages and
hypoxia (lack of oxygen). This hypoxia
is often what causes intense episodes of pain and shortness of breath. The fragile nature of the cells causes them
to rupture more often, which can cause a buildup of waste material (called
bilirubin) in the body causing discoloration known as jaundice.
Prognosis?
Usually symptoms of the disease are not manifested until
four months after birth. This is likely
due to the fetal hemoglobin getting replaced by adult hemoglobin and in this
case HbS. In the past patients with
sickle-cell anemia died between the ages of 20 and 40. Now, however, most patients live past 50. Most causes of death include infections and
organ failure.
Treatment?
- The only cure possible so far for sickle-cell anemia is a bone marrow or stem cell transplant. Pluripotent hematopoietic stem cells found in bone marrow are responsible for producing blood cells. If these can be replaced then curing the disease is possible. However, most patients do not have this option because they are unable to find well-matched donors. Complications or other side effects to these transplants may be risky and could lead to death. Research is being done limit these risks.
- One treatment is the administration of hydroxyurea, a compound that inhibits DNA synthesis. This compound alters the function of bone marrow (where most red blood cells are made) so that they produce fetal hemoglobin instead of adult hemoglobin. Fetal hemoglobin interferes with the crystallization that occurs to form sickle cells. Some studies with this drug show improvements in symptoms even before fetal hemoglobin levels increase. This may be because hydroxyurea breaks down into Nitric Oxide, which is a vasodilator (it makes blood vessels wider) which allows sickle cells to pass through easier. Research is being done with inhaled nitric oxide as a possible treatment as well.
- Folic Acid supplements are given to aid in red blood cell formation
- Blood transfusions may occur periodically to help prevent stroke
- Pain medications
- Patients are instructed to drink lots of fluids to keep their blood volume high so that blood cells can pass through blood vessels more easily.
- Research is being done in areas of gene therapy and other medications that increase the amount of oxygen red blood cells can carry or help reduce pain.
Sources:
Silverthorn, D. Human physiology an integrated approach. 6th. Pearson,
2012. Print.
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