Sickle Cell Disease (SCD)
Sickle Cell: Synopsis
Sickle Cell Anemia affects millions throughout the world. We know that sickle cell trait is related to malaria and geography and not by race. It is particularly common among people whose ancestors come from sub-Saharan Africa; Spanish-speaking regions (South America, Cuba, Central America); Saudi Arabia; India; and Mediterranean countries such as Turkey, Greece, and Italy.
In the Unites States, you may be shocked to learn that there are over 2,000 babies born with Sickle Cell Disease each year. Approximately 80,000 Americans have the disease. More carry the genetic trait, which can be passed on to children. The disease occurs in about one in every 500 African-American births and 1 in every 1000 to 1400 Hispanic-American births. About 2 million Americans or 1 in 12 African Americans carry the sickle cell trait. Throughout the world, sickle cell trait is seen in 1 in 4 West Africans; 1 in 10 African-Caribbean's; 1 in 50 Asians; 1 in 100 Greeks and occasionally in Northern Europeans.
Sickle Cell Disease is a group of inherited disorders that affect the hemoglobin protein found in red blood cells. This disease causes the red blood cells to be hard, sticky, and shaped like a sickle (like a crooked banana). Normal red blood cells are soft, smooth, and round and last about 120 days. Sickle red blood cells only last about 20 days.
Usually, individuals receive two copies of the Hemoglobin A gene, one from each parent. Individuals with Sickle Cell Disease do not have any copies of the Hemoglobin A gene. Instead, these individuals have received two copies of an alternative form of the hemoglobin gene. At least one of those two alternative genes must be hemoglobin S in order to result in Sickle Cell Disease. The following section describes the various types of sickle cell disease and what genes those individuals carry.
Types of Sickle Cell Disease
There are three main types of sickle cell disease:
- Hemoglobin SS disease (HbSS): Individuals have received two copies of the hemoglobin S gene.
- Hemoglobin SC disease (HbSC): Individuals have received one copy of the hemoglobin S gene and one copy of the hemoglobin C gene.
- Hemoglobin SB (beta) Thalassemia disease including SB0 (beta zero) and SB+ Thalassemia disease (HbS beta thalassemia): Individuals have received one copy of the hemoglobin S gene and one copy of the hemoglobin beta- thalassemia gene. The beta-thalassemia genes result in reduced (B+) or lack of expression (B0) of normal hemoglobin A, resulting in a person either having only hemoglobin S or mostly hemoglobin S with a small percent of normal hemoglobin A.
Rarely, a person has one gene for hemoglobin S and another rarer form of hemoglobin, such as hemoglobin O.
What is Sickle Cell Trait?
When an individual receives a copy of hemoglobin A from one parent and a copy of hemoglobin S from the other parent, the result is Sickle Cell Trait. Sickle Cell Trait is not a disease and does not change into Sickle Cell Disease later on in life. However, if two individuals with Sickle Cell Trait have a child together, that child is at risk (25%) for having Sickle Cell Disease.
