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A single point mutation in this polypeptide chain, which is 147 amino acids long, results in the disease known as Sickle Cell Anemia. [18] Sickle-cell anemia is an autosomal recessive disorder that affects 1 in 500 African Americans, and is one of the most common blood disorders in the United States. [17]
The mutation which causes sickle cell disease results in an abnormal hemoglobin known as hemoglobin S (HbS), which replaces HbA in adults. [20] The human genome contains a pair of genes for β-globin; in people with sickle cell disease, both genes are affected and the erythropoietic cells in the bone marrow will only create HbS.
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.
P – Point mutation, or any insertion/deletion entirely inside one gene; D – Deletion of a gene or genes; Dup - Duplication of a gene or genes; C – Whole chromosome extra, missing, or both (see chromosome abnormality) T – Trinucleotide repeat disorders: gene is extended in length
The most common is HbS, which causes sickle cell disease. HbS is produced by a point mutation in HBB in which the codon GAG is replaced by GTG. This results in the replacement of hydrophilic amino acid glutamic acid with the hydrophobic amino acid valine at the seventh position (β6Glu→Val). This substitution creates a hydrophobic spot on the ...
In the most common variant of sickle-cell disease, the 20th nucleotide of the gene for the beta chain of hemoglobin is altered from the codon GAG to GTG. Thus, the 6th amino acid glutamic acid is substituted by valine—notated as an "E6V" mutation—and the protein is sufficiently altered to cause the sickle-cell disease. [7]
Hemoglobin D is a result of a mutation in the one or both of the Beta-chains that make up hemoglobin molecules. Having one gene effected is referred to as trait; having two is referred to as homozygous "disease" although the symptoms of this disease are mild.
Photomicrograph of normal-shaped and sickle-shape red blood cells from a patient with sickle cell disease. Sickle cell anemia is a genetic disease that causes deformed red blood cells with a rigid, crescent shape instead of the normal flexible, round shape. [29] It is caused by a change in one nucleotide, a point mutation [30] in the HBB gene.