Sickle Cell Anemia
Thousands of genetic disorders are known to be inherited as simple recessive traits. These disorders range in severity from relatively mild, such as albinism (lack of pigmentation, which results in susceptibility to skin cancers and vision problems), to life-threatening, such as cystic fibrosis. The most common inherited disorder among people of African descent is sickle-cell disease, which affects one out of 400 African-Americans.
Sickle-cell disease also known as sickle-cell anemia, is a hereditary blood disorder, characterized by an abnormality in the oxygen-carrying protein hemoglobin found in red blood cells. When the oxygen content of an affected individual’s blood is low (at high altitudes or under physical stress, for instance), the sickle-cell hemoglobin molecules aggregate into long rods to deform the red cells into a sickle shape. Sickled cells may clump and clog small blood vessels, often leading to other symptoms throughout the body, including physical weakness, attacks of severe pain (“sickle-cell crisis”), organ damage, paralysis, stroke, and there is an increased risk of death.
Normal Red Cells and Sickle Red Cells
Sickle-cell disease occurs when a person inherits two abnormal copies of the hemoglobin gene, one from each parent. Several subtypes exist, depending on the exact mutation in each hemoglobin gene. Although two sickle-cell alleles are necessary for an individual to manifest full-blown sickle-cell disease, the presence of one sickle-cell allele can affect the phenotype. Thus, at the organism level, the normal allele is incompletely dominant to the sickle-cell allele. A person with a single abnormal copy may suffer some sickle-cell symptoms, and is said to have sickle-cell trait. Such people are also referred to as carriers.
Almost 300,000 children are born with a form of sickle-cell disease every year, mostly in sub-Saharan Africa, but also in other parts of the world such as the...