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Thalassemias are inherited blood disorders that result in abnormal hemoglobin. [7] Symptoms depend on the type of thalassemia and can vary from none to severe. [1] Often there is mild to severe anemia (low red blood cells or hemoglobin) as thalassemia can affect the production of red blood cells and also affect how long the red blood cells live. [1]
The pathogen that causes the disease spends part of its cycle in the red blood cells and triggers an abnormal drop in oxygen levels in the cell. In carriers, this drop is sufficient to trigger the full sickle-cell reaction, which leads to infected cells being rapidly removed from circulation and strongly limiting the infection's progress.
This would be similar to the hemoglobin allele which is responsible for sickle-cell disease, but solely in people with two copies; those with just one copy of the allele have a sickle cell trait and gain partial immunity to malaria as a result. This effect is called heterozygote advantage. [27]
Sickle-cell disease was the genetic disorder to be linked to a mutation of a specific protein. Pauling introduced his fundamentally important concept of sickle cell anemia as a genetically transmitted molecular disease. [20] This vein (4) shows the interaction between the malaria sporozoites (6) with sickle cells (3) and regular cells (1).
Sickle cell disease exhibits characteristics of either homozygous hemoglobin S, also known as Hb S, or Hb S paired with another hemoglobin variant. In diagnosing patients with sickle cell, HbA2 is taken into account alongside a complete blood count, family history, and clinical data. [4]
The test uses the principles of gel electrophoresis to separate out the various types of hemoglobin and is a type of native gel electrophoresis.After the sample has been treated to release the hemoglobin from the red cells, it is introduced into a porous gel (usually made of agarose or cellulose acetate) and subjected to an electrical field, most commonly in an alkaline medium.
In persons with sickle cell disease, high levels of fetal hemoglobin as found in a newborn or as found abnormally in persons with hereditary persistence of fetal hemoglobin, the HbF causes the sickle cell disease to be less severe. In essence the HbF inhibits polymerization of HbS. A similar mechanism occurs with persons who have sickle cell trait.
In addition, there is sickle cell trait (HbAS) which is defined by having HbA and HbS. This makes the individual heterozygous for sickle cell. Of the world population, it is estimated that there are about 300 million individuals with the sickle cell trait and about 100 million of those are in sub-Saharan Africa. [18]