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Sickle cell disease (SCD), also simply called sickle cell, is a group of hemoglobin-related blood disorders typically inherited. The most common type is known as sickle cell anemia. It results in an abnormality in the oxygen-carrying protein haemoglobin found in red blood cells.
Sickle cell trait describes a condition in which a person has one abnormal allele of the hemoglobin beta gene (is heterozygous), but does not display the severe symptoms of sickle cell disease that occur in a person who has two copies of that allele (is homozygous).
Sickle-cell anemia (SCA) is a genetic disorder caused by the presence of two incompletely recessive alleles. When a sufferer's red blood cells are exposed to low- oxygen conditions, the cells lose their healthy round shape and become sickle-shaped.
Sickle cell anemia – most common in those of African, Hispanic, and Mediterranean origin – leads to sickle cell crisis when the circulation of blood vessels is obstructed by sickled red blood cells, causing ischemic injuries.
Sickle cell anemia occurs when the HBB gene mutation causes both beta-globin subunits of hemoglobin to change into hemoglobin S (HbS). Sickle cell anemia is a pleiotropic disease because the expression of a single mutated HBB gene produces numerous consequences throughout the body.
Causes of increased breakdown include genetic disorders such as sickle cell anemia, infections such as malaria, and certain autoimmune diseases. Anemia can also be classified based on the size of the red blood cells and amount of hemoglobin in each cell.
When clinical consequences occur, they may include anemia due to hemolysis or polycythemia due to alterations in the oxygen affinity of the abnormal Hb. Common examples of hemoglobin variants associated with hemolysis include sickle Hb (HbS) and HbC.
The acute chest syndrome is a vaso-occlusive crisis of the pulmonary vasculature commonly seen in people with sickle cell anemia. This condition commonly manifests with a new opacification of the lung(s) on a chest x-ray.
It is possible for a person to have both the gene for hemoglobin S (the form associated with sickle cell anemia) and the gene for hemoglobin C; this state is called hemoglobin SC disease, and is generally more severe than hemoglobin C disease, but milder than sickle cell anemia.
Sickle cell disease. Sickle hemoglobin (HbS) is the most common variant of hemoglobin and arises due to an amino acid substitution in the beta-globin subunit at the sixth residue from glutamic acid to valine. There are different forms of sickle cell disease. HB SS which is the most common and severe form of sickle cell.