Definition
Sickle cell anaemia is a genetic disease of the blood or more precisely of the red blood cells (erythrocytes). There are two different forms depending on the inheritance: a so-called heterozygous and homozygous form. The forms are based on a disturbed form of the erythrocytes. In the absence of oxygen, they take on a sickle-like form, which gives the disease its name.
Causes
The cause of sickle cell anemia is genetic inheritance. It is an autosomal codominant hereditary disease, i.e. its genetic equivalents are not located on the sex chromosomes, so even one affected parent is sufficient to pass the disease on to their child. The exact cause lies in the exchange (more precisely: point mutation) of a single amino acid: the amino acid glutamate is replaced by the amino acid valine.
Glutamate, along with many other amino acids, is a component of the protein hemoglobin, which is known to be the oxygen carrier on the red blood cells (erythrocytes). The intended spatial form of hemoglobin is therefore not achieved by using the “wrong” amino acid valine. An altered hemoglobin is formed, called HbS (hemoglobin of sickle cell anemia).
Alternatively, another hemoglobin is also formed: HbF (fetal hemoglobin), which is actually only formed during the foetal period of an unborn child. It has a higher affinity for oxygen and serves as a compensatory substitute oxygen transport. The hemoglobin molecules of sickle cell patients consist of 20% HbF and 80% HbS at the end of production.
This leads to a loss of elasticity of the erythrocytes, but their flexibility is essential for passage through the smallest blood vessels. If a person has the disease from both parents, both copies of their corresponding gene for hemoglobin are affected. It is a so-called homozygous carrier.
In these people, 100% of all hemoglobins are altered and even minimal oxygen changes in the blood cause them to assume a sickle shape. In a heterozygous carrier, only one parent was sick or passed on the disease. Here, a severe lack of oxygen is required for the hemoglobin and thus the erythrocytes to change.
Regardless of whether it is a homozygous or heterozygous carrier, the disease mechanism is the same: as soon as a molecule takes on the wrong form, it is broken down. This can happen in the blood vessels or in the spleen (see hemolysis). As a result, there are fewer erythrocytes in the blood (anemia), so the supply of oxygen to the body through the blood is not guaranteed. In our article Anemia – these are the signs of anemia!
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