Sickle Cell Disease

Features and Management of a Genetic Red Blood Cell Disorder

Feb 7, 2009 Anthony Lee

Sickle cell disease can result in complications for individuals who inherit it.

Sickle cell disease refers to a genetic defect in the hemoglobin of red blood cells (RBCs). Individuals with the sickle cell gene are predominantly of African descent. This includes fewer than 10% of African-Americans and a larger proportion among native inhabitants in Africa.

Pathophysiology

Normal adult hemoglobin (Hb A) in RBCs is an aggregate of four amino acid chains: two alpha chains and two beta chains. Individuals with the sickle cell gene have a genetic defect that replaces the sixth amino acid of the beta chain, glutamic acid, with the amino acid valine. The result is hemoglobin S (Hb S), an abnormal hemoglobin with one or two beta chains altered this way.

In this context, hemoglobin is often described in terms of the composition of the structure. Because sickle cell disease is recessive, requiring two sickle cell genes for the disease to fully manifest itself (homozygosity), individuals with sickle cell disease are referred to as having Hb SS. Those with one sickle cell gene (heterozygosity), are said to have sickle cell trait with Hb AS, acting as carriers of sickle cell disease with very few clinical manifestations.

Under conditions of low oxygen, Hb S becomes less soluble and forms a gel-like substance. This causes the normally biconcave RBC to assume the sickle shape that gives the disease its name. These sickle cells adhere to the inner lining of arteries and capillaries, causing vascular obstruction, and rupture (hemolyze) due to instability of their structure.

Clinical Manifestations

Patients with sickle cell disease experience episodes of sickle cell crisis. These episodes involve severe pain in the arms, legs, abdomen, and/or other location depending on where sickle cell vascular obstruction occurs. In addition, sickle cell crisis results in anemia due to hemolysis of sickled RBCs. A variety of other complications may occur, such as bone and joint damage, stroke, bile stone formation, and kidney failure. A serious condition stemming from sickle cell disease is acute chest syndrome, a medical emergency that leads to lung damage and respiratory failure if left untreated.

Treatment

As much as the disease is well described, no curative treatment exists for sickle cell disease. Intravenous fluids are given to address vascular occlusion as well as opioid medications for pain. For anemia, blood transfusions are often indicated but have questionable efficacy and the risk of iron overload with multiple transfusions. Therefore, a more acceptable option is exchange transfusion with removal of sickled RBCs and introduction of donor RBCs. There are many other treatments that are offered to sickle cell disease patients, all of which manage symptoms and/or address any active complications.

References

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Sickle Cell