Sickle cell anemia is a genetic disorder where the body produces an abnormal hemoglobin called hemoglobin S. Hemoglobin is the protein in red blood cells that carries oxygen. Red blood cells are normally flexible and round, but when the hemoglobin is defective, blood cells take on a “sickle” or crescent shape. This causes the red blood cells to get stuck inside blood vessels and block blood flow and oxygen transport to some parts of the body, thereby causing sickle cell anemia.
Mutations leading to sickle cell anemia
Hemoglobin is made up of four different protein subunits, which includes two subunits called alpha-globin and two called beta-globin. Sickle cell anemia is caused by mutations in a gene called HBB, which is the gene that provides instructions for the production of beta-globin.
There are multiple mutations that can occur in the HBB gene. One of these leads to the production of hemoglobin S.
Inheritance of sickle cell anemia
Sickle cell anemia is an autosomal recessive disease, meaning that it only occurs if both the maternal and paternal copies of the HBB gene are defective.
In other words, if an individual receives just one copy of the defective HBB gene, either from their mother or their father, they do not have sickle cell anemia but have what is called “sickle cell trait”. People with sickle cell trait usually do not have any symptoms or problems but they can pass the mutated gene onto their children.
There are three inheritance scenarios that can lead to a child having sickle cell anemia:
Both parents have sickle cell trait
If both parents have sickle cell trait, then there is a 25 percent risk of the child having sickle cell anemia and a 50 percent risk of them having sickle cell trait. There is also a 25 percent chance that the child will not inherit either copy of the mutated gene.
One parent has sickle cell anemia and the other has sickle cell trait
If one parent has sickle cell anemia and the other has sickle cell trait, there is a 50 percent risk that their children will have sickle cell anemia and 50 percent risk they will have sickle cell trait.
Both parents have sickle cell anemia
If both parents have sickle cell anemia, then their children will also definitely have the disease.
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