Sickle cell anemia is the most common inherited blood disorder in the United States. Approximately 72,000 Americans have sickle cell anemia, and an additional two million Americans have the sickle cell trait. The disorder primarily affects people of African ancestry, but also occurs in other ethnic groups, including people who are of Mediterranean and Middle Eastern descent. It is characterized by episodes of pain, chronic anemia and severe infections, usually beginning in early childhood.

The underlying problem stems from the production of an abnormal form of hemoglobin (HbS) produced by those with sickle cell anemia. Red blood cells with normal hemoglobin (HbA) flow easily through the bloodstream, delivering oxygen to all of the cells of the body. Normal red blood cells are soft and flexible, and are shaped like doughnuts. In contrast, HbS molecules tend to clump together, making red blood cells sticky, stiff, and causing them to assume a curved or sickled shape. Unlike normal red cells, the sickled cells cannot squeeze through small blood vessels. Instead, they stack

As the red blood cells cycle through the body delivering oxygen, they repeatedly spring in and out of the sickle shape until the cells get stuck in the sickle shape. The stress of the shape changes also damages the cells and the cells die after ten to twenty days instead of living out their normal lifespan of 120 days. The premature death of the red blood cells causes a shortage of red blood cells, a condition called anemia. The shortage lowers the amount of oxygen delivered to the body’s tissues and causes the fatigue, shortness of breath, and the slow rate of growth seen in people with sickle cell disease. For reasons not completely understood, sickled cells and even normally shaped cells are more likely to adhere to the walls of the blood vessels in a person with the disease. The stiff sickled cells cannot squeeze past the blockage and they start piling up, creating a larger barrier that prevents even normally-shaped cells from passing by.

Lungs can also be damaged by blocked vessels, a bacterial or viral infection, or fatty pieces of bone marrow that dislodge from the bone and get stuck in the lung. Red blood cells cannot pick up oxygen, and less oxygen causes more cells to sickle. The whole process can spiral into lung failure. Blockages in the brain’s blood vessels can cause a stroke if brain cells are killed. Usually, a person who has a stroke loses some ability to think; perceive sights, sounds, or smells; and walk or move easily.

· If one parent has sickle cell anemia and the other has the sickle cell trait, with each pregnancy, there is a 50% chance of bearing a child with sickle cell disease and a 50% chance of bearing a child who carries the sickle cell trait.

The painful crises, anemia, and organ damage of the disease can be traced back to the structure of an important blood protein called beta globin. Beta globin proteins are found inside red blood cells. The protein’s job is to carry another molecule called heme. Inside the cells, beta and alpha globins combine to form hemoglobin, the molecule that delivers oxygen to all the body’s cells. Two beta globins plus two alpha globins and each globin’s heme group make one molecule of hemoglobin. The heme of each globin binds the oxygen molecule. The instructions for making beta globin are encoded inside a gene located on chromosome 11. Most people have two chromosome 11’s, with two beta globin genes. Inside the gene, the bases code for the cell to construct the protein. Through the process of protein sythesis, the code is translated and the appropriate amino acids are placed in their proper positions. In people with sickle cell, the code inside both beta globin genes is different from usual. Instead of containing the letters GAG standing near the beginning of the gene, the adenine i

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