Sickle Cell Anemia Health Article

Sickle cell anemia

Genes are inherited in pairs, one copy from each parent. Therefore, each person has two copies of the gene that makes beta-globin. As long as a person inherits one normal beta-globin gene, the body can produce sufficient quantities of normal beta-globin. A person who inherits a copy of each of the normal and abnormal beta-globin genes is referred to as a carrier of the sickle cell trait. Generally, carriers do not have symptoms, but their red blood cells contain some hemoglobin S.

A child who inherits the sickle cell trait from both parents—a 25% possibility if both parents are carriers—will develop sickle cell anemia. These cells have a decreased life span in comparison to normal red blood cells. Normal red blood cells survive for approximately 120 days in the bloodstream; sickle cells last only 10-12 days. As a result, the bloodstream is chronically short of red blood cells and the affected individual develops anemia.

The sickle cells can create other complications. Due to their shape, they do not fit well through small blood vessels. As an aggravating factor, the outside surfaces of sickle cells may have altered chemical properties that increase

the cell's "stickiness." These sticky sickle cells are more likely to adhere to the inside surfaces of small blood vessels as well as to other blood cells. As a result of the sickle cells' shape and stickiness, blockages occasionally form in small blood vessels. Such blockages prevent oxygenated blood from reaching areas where it is needed, causing extreme pain as well as organ and tissue damage.

The severity of the symptoms cannot be predicted based solely on the person's genetic inheritance. Some individuals with sickle cell anemia develop health- or life-threatening problems in infancy but others may have only mild symptoms throughout their lives. For example, genetic factors, such as the continued production of fetal hemoglobin after birth can modify the course of the disease. Fetal hemoglobin contains gamma-globin in place of beta-globin; if enough of it is produced, the potential interactions between hemoglobin S molecules are reduced.

Definition

Sickle cell anemia, which is also known as meniscocytosis or sicklemia, is an inherited blood disorder that arises from a gene mutation. As a result, affected hemoglobin molecules have a tendency to stick to one another, forming abnormal strands of hemoglobin within the red blood cells. The cells that contain these strands become stiff and elongated—sickle-shaped.

Because sickle cell anemia is characterized by the rapid loss of red blood cells as they enter the circulation, it is classified as a hemolytic anemia, "hemolytic" referring to the destruction of the cell membrane of red blood cells, resulting in the release of hemoglobin.

Description

Sickle-shaped cells die much more rapidly than normal red blood cells and the body cannot create replacements fast enough. Anemia develops due to the chronic shortage of red blood cells. Further complications arise because sickle cells do not fit well through small blood vessels, and can become trapped. The trapped sickle cells form blockages that prevent oxygenated blood from reaching associated tissues and organs. The damaged tissues and organs cause considerable pain and can lead to serious complications, including stroke and an impaired immune system. Sickle cell anemia primarily affects people with African, Mediterranean, Middle Eastern, and Indian ancestry. In the United States, one in 12 African Americans are carriers. An additional 72,000 Americans have sickle cell anemia, meaning they have inherited the trait from both parents. Among African Americans, approximately one in every 500 babies is diagnosed with sickle cell anemia. Hispanic Americans are also heavily affected; sickle cell anemia occurs in one of every 1,000-1,400 births. Worldwide, it has been estimated that 250,000 children are born each year with sickle cell anemia.

Hemoglobin structure

Normal hemoglobin is composed of a heme molecule and two pairs of proteins called globins. Humans have the genes to create six different types of globins—alpha, beta, gamma, delta, epsilon, and zeta—but do not use all of them at once. The type of genes expressed depends upon the stage of development: embryonic, fetal, or adult. Virtually all of the hemoglobin produced in humans from ages 2-3 months and onward contains a pair of alpha-globin and beta-globin molecules.