Sickle cell anemia is a genetic disease, passed on from parents to children along the generations. It is a condition which causes severe pain and anemia. It happens when the body lacks healthy red blood cells to circulate oxygen in the body. The usual shape of the red blood cells is round, and they are flexible so they can pass through the narrow blood vessels of the body. However, sickle cell anemia causes them to become sickle-shaped, like tiny crescents, which are sticky and inflexible. This restricts their movement in the blood vessels causing them to get stuck in the blood vessels, and they can restrict and even block the flow of an ample supply of oxygen to the various parts of the body. The signs and symptoms of sickle cell anemia are not visible until an infant is about 4 months of age. These symptoms include anemia. The sickle-shaped cells are weak and fragile, and they break easily. Normal red blood cells have a lifespan of 120 days. The breakage of the cells causes a lack of red cells which cannot circulate enough oxygen which causes fatigue. Fatigue is symptomatic of anemia. It also causes episodic pain, which is called a crisis. The pain occurs when the tiny, sickle cells block the flow of blood to the chest, joints, abdomen, and even the bones. The pain can last from a few hours to a few weeks, and if severe enough, it can cause hospitalization. Swollen hands and feet are another symptoms, which is a result of lowered blood flow. Recurrent infections are also common because sickle cells damage the spleen, a major organ that fights infections. It can also cause delayed growth because of a shortage of oxygen and nutrients. There is currently no cure for the disease, and its signs and symptoms can only be prevented by medication. Bone marrow transplant is the only option. (Mayo Clinic).
Sickle cell anemia is inherited in an autosomal recessive pattern, where both sets of genes have mutations in each cell. Both parents of the individual carry an autosomal recessive condition of the mutated gene, but they usually don’t show any symptoms of the disease. It mostly affects people, whose ancestors belong to Africa, the Mediterranean countries such as Greece, Turkey, Italy and the Arabian Peninsula and mostly the Spanish-speaking areas of Latin America, Central America and certain regions of the Caribbean. (Harris and Malyango).
The Hemoglobin molecule (Hb) is a complex molecule consisting of four protein chains and four smaller, non-protein chains, termed ‘heme.’ These carry oxygen from the lungs to the rest of the body. Hb has two forms; one with the oxygen molecule attached the other with its dissociation. Sickle cell anemia is caused by the replacement of one acidic amino acid ßGlu6 to Val. This amino acid is present on the surface of the protein. When a sickle cell Hb called the HbS loses its oxygen, a hydrophobic area is exposed to Hb and HbS. The newly formed hydrophobic Val then is in a position to interact with it. Therefore large, fibrous clumps of Hb, consisting of thousands of molecules cause distortion of the shape of the red blood cell, making it sickle-shaped. . (Mayo Clinic).
Studying the evolutionary implications of the disease, research has found sickle cell anemia as a disease which can prove beneficial as well. Malaria is a disease known to correlate with it. The HbS in Africa almost matches the distribution of malaria which is heterozygous for hemoglobin in the forms HbS and HbA. Here the infected people will be resistant to the disease because malaria will affect the infected cells. The homozygous individuals with hemoglobin HbA/HbA have higher mortality rates for malaria. (Harris and Malyango). Hence, the sickle cell allele is prevalent because the heterozygotes have a better reproductive rate than homozygotes. This evolutionary concept is called balancing selection which keeps two or more favorable alleles at a higher frequency. (Harris and Malyango).
Work Cited
Harris, E. Eugene and Malyango, A. Avelin. Evolutionary explanations in medical and
health profession courses: are you answering your students' "why" questions? BMC Medical Education. 2005. Web. 23 Mar 2016.
Mayo Clinic. Sickle Cell Anemia. 2016. Web. 23 Mar 2016.
