Sickle Cell Disease & Malaria Resistance

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Sickle Cell Disease & Malaria Resistance

Sickled erythrocytes are found intermixed with normal erythrocytes in the blood of people with both sickle cell disease and sickle cell trait. Image courtesy of the National Institute of Health's Heart, Lung, and Blood Institute.

http://www.nlm.nih.gov/medlineplus/sicklecellanemia.html

Sickle cell disease, or sickle cell anemia is an autosomal recessive disease caused by hemoglobin S, an oxygen-carrying protein in blood cells. A single point mutation in the nucleobase sequence of chromosome 11 causes the sixth amino acid in the hemoglobin protein, glutamic acid, to be replaced by valine, changing standard hemoglobin beta into hemoglobin S.[2]The sickle shape is caused by hemoglobin’s resulting structural change, and it is from this structure that the disease gets its name.[1]
People with either HbAS (heterozygous with hemoglobin A and hemoglobin S) or HbSS (homozygous with hemoglobin S) are considered to have sickle cell trait and can show symptoms of sickle cell disease. However, when an individual is homozygous recessive for hemoglobin S, severe symptoms start to occur. The most infamous being anemia, which can, in turn, cause shortness of breath, jaundice, and high blood pressure. This biggest problem is blood clotting in vessels, which could lead to damaged tissues that rely on the clotted vessels. Individuals heterozygous for the trait are not prone to the same severity of symptoms as homozygous recessive individuals.[1]
Despite the disease’s lethal symptoms, it protects the carrier from malaria, which is why sickle cell alleles are most common in people of African descent (about 7% of people of African descent carry an allele), and other areas where malaria is prevalent.[3]Sickle cell trait is hypothesized to have evolved because of the vital protection from malaria it provides.[9]Furthermore, individuals with HbAS tend to survive better than individuals with HbSS as they are not exposed to the same severity of risks yet still receive protection from malaria.

Directions: Answer the questions below in at least one paragraph (> 5 sentences).

1)  How does sickle cell disease relate to malaria resistance?

2)  If you could choose, which genotype for the hemoglobin gene would you want? Why?

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