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Sickle Cell Anemia

Sickle Cell Anemia Overview

Sickle cell anemia is an inherited blood disorder that affects the hemoglobin molecule in red blood cells. Hemoglobin is the part of the red blood cells that carries oxygen from the lungs and delivers it to the rest of the body.

How Cells Become "Sickled" or an Irregular Shape

In sickle cell anemia, the hemoglobin molecule is abnormal such that under conditions of low oxygen levels, neighboring hemoglobin molecules tend to stick together in long rods in a process called polymerization.

Polymerization distorts the shape of the red blood cell changing it from the usual biconcave disk shape to an irregular sickled shape. These sickled red blood cells have a tendency to stick to the walls of blood vessels causing the clogging of blood vessels known as vaso-occlusion, which compromises the blood supply to organs and tissues. This leads to the classic pain crisis for which sickle cell anemia is most recognized as well as chronic organ damage and other complications.

How Sickle Shaped Cells Cause Anemia

Red blood cells live about 120 days in the bloodstream, but sickled red cells die after about 10 to 20 days. Because they cannot be replaced fast enough, the blood is chronically short of red blood cells, leading to a condition called anemia. Anemia can lead to shortness of breath, fatigue, exercise intolerance, and delayed growth and development in children. The rapid breakdown of red blood cells is called hemolysis and may also cause yellowing of the eyes and skin, or jaundice.

Different Types of Sickle Cell Disease

Sickle cell anemia usually refers to homozygosity for sickle trait (2 sickle traits), while sickle cell disease is a broader term referring to any genetic disease that can lead to sickling. The most common cause of sickling is sickle cell anemia, but other sickling disorders such as sickle beta thalassemia and hemoglobin SC disease also exist as well as more rare sickle variants.

How Sickle Cell Disease is Inherited

Sickle Cell disease is a disorder that is inherited from parents and is not contagious. The inheritance pattern is autosomal recessive, which means that an individual needs two defective genes in order to have the disease. Here is how the inheritance pattern works:

Facts About Sickle Cell Anemia

Sickle cell anemia affects millions of people worldwide. It is particularly common among people whose ancestors come from Africa, Mediterranean countries (such as Greece, Turkey, and Italy), the Arabian peninsula, India, and Spanish-speaking regions (South America, Central America, and parts of the Caribbean).

USA sickle cell anemia is the most common inherited blood disorder in the United States, affecting 70,000 to 80,000 Americans. The disease occurs in approximately 1 in 500 African American newborns and 1 in 1,000 to 1,400 Hispanic American births. About 2 million Americans, or 1 in 12 African Americans, carry the sickle cell allele.

Other names for sickle cell anemia:

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Last Reviewed: Jul 10, 2009

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Professor of Hematology
College of Medicine
The Ohio State University

Formerly, Assistant Professor of Pediatrics
School of Medicine
Case Western Reserve University