People with Sickle Cell Anaemia have Sickle haemoglobin (HbS – Hb = Haemoglobin), Which is different from the normal haemoglobin, (HbA). When Oxygen is given up by HbS to the tissues, it sticks together and long rod shapes are formed inside the red blood cells, making them disfigured and rigid. This is where the name “Sickle” comes from, sickle meaning “hooked” or “crescent-shaped”. This change in shape, makes it very hard for the red blood cells to be transported through small blood vessels. Normal red blood cells are flexible and doughnut shaped, an ideal shaped for being pushed through tight spaces. Here is a diagram to show the deformation of the normal red blood cell into the sickle red blood cell.
This inability to squeeze though small blood vessels can lead to major problems all around the body. First of all, as the sickle cells can’t travel through, the create a blockade of cells causing healthy oxygen carrying cells to become stuck, later leading to a starvation of oxygen from where it is needed the most. This can cause severe pain and damage to organs.
Sickle Cell Anaemia is an inherited disease, therefore it cannot be contracted from the people around you, through touch, inhalation etc. The haemoglobin gene is present in pairs in all humans. One copy from the Mother, and the second from the Father. A person that is said to have the Sickle Cell Trait, has one gene which carries instructions to make sickle haemoglobin (HbS), and the other gene with the instructions to make normal haemoglobin (HbA). This person is therefore a carrier of the sickle haemoglobin gene. A person with Sickle cell Trait, has enough normal haemoglobin in their blood to keep the red blood cells flexible and have no symptoms of the sickle cell disorder. One thing that a person with sickle cell trait must do is to be careful when doing activities where there are less than normal oxygen levels, for example scuba diving. As less normal haemoglobin is present to transport sufficient oxygen to where it is required.
If one parent had the sickle cell trait and the other had normal haemoglobin then the offspring would be:
If both parents have the sickle cell trait then the offspring would be:
On the other hand, if one parent had the sickle cell trait, and the other had the actual sickle cell disease, the offspring would be:
When both copies of the haemoglobin gene carry instructions to make the sickle haemoglobin, sickle cells will occur as a result. Sickle cell Anaemia (and normal cases of anaemia, on a lesser scale) can cause problems. Problems such as fatigue, light-headiness, in cases of sickle cell anaemia, damage to vital organs such as the liver, kidney, lungs, heart and spleen due to starvation of oxygen. It also reduces life expectancy to about 45. In severe cases death is a result.
One other problem is that sickle red blood cells live less longer. A normal red blood cell lives for approximately 120 days, whereas a sickle red blood cell lives about 15 days.
Sickle Cell Anaemia is created due to a genetic mutation. Genes are found on Chromosomes in the nuclei of cells. There are 23 pairs of chromosomes and it is on the 11th pair of chromosomes where this mutation occurs, because it is here where the gene responsible for red blood cell production is found. The responsible mutation is thought to originate from parts of the globe where the disease Malaria is common, i.e. Africa, since people with the Sickle Trait are somewhat protected from the malaria parasite. This is because the sickle blood cells are a bad host for the parasite that reproduces asexually inside healthy red blood cells full of nutrients.
Sickle cell Anaemia is most common in people of African descent and also Hispanics with Caribbean origins.
As you look at these two images you can see that the malaria risks are higher around the areas with high percentages of people with Sickle Cell Anaemia.
There are many treatments available for Sickle cell Anaemia, but they are limited:
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Penicillin - to prevent infections
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Pain medications - for sickle cell painful events
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Drinking plenty of fluids daily (8 to 10 glasses) to prevent and treat painful events
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Blood transfusions - for anaemia, and to prevent stroke; transfusions are also used to dilute the HbS with normal red blood cells to treat chronic pain, acute chest syndrome, splenic sequestration, and other emergencies.
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Folic acid (to help prevent severe anaemia)
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Hydroxyurea - a medication recently developed that may help reduce the frequency of pain crises and acute chest syndrome; it may also help decrease the need for frequent blood transfusions. The long-term effects of the medication are unknown.
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Bone marrow transplant has been effective in curing some children with sickle cell disease; the decision to undergo this procedure is based on the severity of the disease and a suitable bone marrow donor. These decisions need to be discussed with a paediatric blood specialist.
Sickle Cell Anaemia is a terrible hereditary disease that can’t be completely cured. But as socio-economic conditions improve and as our knowledge of the human genome broadens, we can only hope gene manpulation will prevent this disorder from causing pain around the world.
BIBLIOGRAPHY
Text Books
Indge, B, Rowland,M, & Baker,M. (2000), AS, A New Introduction to Biology, London, Hodder & Stoughton Educational.
Smart, T. (1998), , Philip’s Science & Technology Encyclopedia,
London, George Philip Limited
Websites
http://www.physics.ohio-state.edu/~wilkins/writing/Samples/shortmed/nelson/sickle.html
Images
1 = Image 1 courtesy of “AS, A New Introduction to Biology”
2= Philip’s Science & Technology Encyclopedia,
3= http://www.merck.com/pubs/mmanual_home/sec14/154.htm
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9= http://www.mara.org.za/images/picendem.gif
