Sickle cell anemia
Table of Contents
Anaemia is generally described as a decrease in red blood cell count, packed cell volume, and haemoglobin concentration. It could be caused by factors such as bleeding, premature destruction of red cells, or a deficiency of some components needed to produce red cells in the body.
Sickle cell anaemia is a genetic disorder that results from more of the red blood cells being sickled rather than biconcave or disc-like in shape. It is more rampant in sub-Saharan Africa with Nigeria having a record of over 150,000 babies born every year with sickle cell disease.
Overview of sickle cell anaemia
Normal red blood cells are biconcave or disc-like in shape; this shape enables them to squeeze through capillaries of various sizes and transport nutrients to every part of the body.
Nevertheless, just like every other feature of the body, the shape of red blood cells is determined by the structure the haemoglobin takes.
The word “Haemoglobin” is a combination of two words: haem and globin.
Haem is formed when iron in the form of Fe2+ combines with porphyrin. Porphyrins are synthesized by various steps and have very distinct features which follow to give haem its characteristic feature.
On the other hand, globin is a protein with a three-dimensional structure that is responsible for binding haem and transporting oxygen. Adult haemoglobin consists of two alpha and two beta polypeptide chains wrapped about each other in a perfect structure held by non-covalent bonds.
Each of these chains is formed as a result of a well-patterned arrangement of amino acids. The alpha chain contains 141 amino acids, while the beta chains each have 146 amino acids.
The shape, structure and nature of the red blood cells enable them to perform their function in the body, and any change to this structure can lead to an impairment of these functions.
Haemoglobin in Sickle red cells
In the red blood cell of patients with sickle cell anemia, the heme part remains intact, but there is a little fluctuation in the globin content.
There is a substitution of glutamic acid for valine in position six (6) of the beta chain of sickled red cells; this singular substitution leads to a change in the shape of red cells.
The arrangement of the first to the eighth amino acids in the beta chains of both haemoglobin A and haemoglobin S is shown below
Valine – Histidine – Leucine – Threonine – Proline – Glutamic acid – Glutamic acid – Lysine
For haemoglobin S
Valine – Histidine – Leucine – Threonine – Proline – Valine – Glutamic acid – Lysine
Notice that in the beta chain of haemoglobin S, every other amino acid remains the same except where valine replaces glutamic acid. This is described as a mutation.
Why is this mutation dangerous?
Glutamic acid interacts better with other amino acids to give a good structure and enhance the solubility of the beta chains; valine, however, interacts very poorly hence reduced the solubility of the beta chains in haemoglobin S.
In normal red blood cells, nutrients and oxygen are transported as red blood cells circulate around the body; in sickled cells, however, the ability to squeeze through these capillaries is lost, and as a result, these cells are broken down (lysed) as they try forcing their ways through small capillaries.
When does sickle cell anaemia manifest?
Sickle cell anaemia is seen in persons who have the SS genotype; implying that they have two of the mutated haemoglobin present in their blood.
In individuals with genotype AS, there is only one mutated beta chain, and the non-mutated haemoglobin can make up for it. As a matter of fact, in persons with genotype AS, only about one per cent (1%) of their red blood cells is sickle-shaped, hence they are able to lead a normal life.
Signs and manifestations of sickle cell anaemia
In many rural areas where individuals are unaware of the importance of knowing one’s genotype before getting married, they attribute some of these signs to spiritual powers and forces. These signs however are a result of the mechanisms going on in the body usually described generally as the sickle cell crisis; some of them include
- Poor wound healing
Due to the insufficiency of red blood cells, injuries sustained by sickle cell patients usually take a very long time to heal and in most cases lead to further infections.
- Pale appearance
This is one of the signs of anemia. The redness of blood is responsible for the bright way our skin looks.
- Continuous pain
As sickled cells continue to block capillaries of several organs because of their inability to squeeze through them, they cause periodic episodes of pain
- Swelling of hands and feet (oedema) due to a continuous breakdown of red blood cells and accumulation of fluid in the body.
- Frequent infections due to a compromised immune system.
- In children, prolonged jaundice is a very common symptom
In complicated cases, shock and death may even result; it is, therefore, advisable that intending couples continue to check for compatibility of their genotypes before getting into marriage and having children.