sickle cell anaemia

ndmmxiaomayi SG

Studies conducted on the African population have uncovered that a huge proportion of the population actually suffers from sickle cell anaemia. Could there be a reason for this somewhat unique situation to arise in Africa?

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I am thinking that it could be the high number of malaria cases over in Africa. Since people who have sickle cell anaemia don't get malaria, could this be the reason?

Are there other reasons?

ndmmxiaomayi SG

Forgot got one question.

Why is that people with sickle cell anaemia don't get malaria?

ndmmxiaomayi SG

I got one question as for now.

Read from one website that there are a few types of sickle cell diseases, depending on which gene you inherited.

What's the differences between them?

By the way, my school work. Can't find much info.

The website is http://www.yourgenesyourhealth.org/sickle/inherited.htm

ndmmxiaomayi SG

The explanation given by Wikipedia is too chim to understand. Crying or Very sad

http://en.wikipedia.org/wiki/Sickle_cell_anaemia

This one give complication but no explanation:

http://www.nlm.nih.gov/medlineplus/ency/article/000527.htm

charlemagne SG

Just have to wait Dr Renorenal’s answer then. By the way, I don’t see him around for queit some time already. Wonder what happened to him.

oxford mushroom SG

Not true that they don't get malaria but they tend to have a milder disease and less likely to die. They have some resistance against malaria.

The red blood cells in sickle cell anaemia and thalassaemia are abnormal and so do not support the growth of malarial parasites. As you know, these parasites have to replicate in the red blood cells. In patients with sickle cell anaemia, these parasites enter the red blood cells and die there instead of dividing and then infecting other cells. As a result, these patients tend to have a survival advantage in places where malaria is common and so the gene is passed on.

oxford mushroom SG

Haemoglobin consists of 2 alpha chain and 2 beta globin chains in the adult, a haeme molecule and a ferrous iron atom. The alpha chain is controlled by 4 alpha globin chain genes and the beta chain is controlled by 2 beta chain genes.

If there is a mutation in the globin chain gene, an abnormal globin chain results. Most mutations occur in the beta globin gene. Depending on the type of mutation, you can get different types of abnormal globin chains and hence, different types of abnormal haemoglobin.

For example, mutation of the beta globin gene may result in a substitution of amino acid, giving rise to different abnormal haemoglobin:
Glutamic acid (position 6) to valine results in HbS
Glutamic acid (position 6) to lysine results in HbC
Glutamic acid (position 26) to lysine results in HbE

HbS is the abnormal haemoglobin type you see in sickle cell anaemia. If one gene is mutated and the other is normal (heterozygous state) you get sickle cell trait. Because the half of the haemoglobin is normal, the patient is usually well althgough he/she can transmit the diseased gene to his/her children.

If both beta globin genes are mutated in this way (homozygous state), you get sickle cell anemia.

Apart from mutations that result in formation of abnormal haemoglobin, mutations or deletions of the globin chain gene can also result in the reduction or loss of production of the normal globin chains. This condition is called thalassaemia. The globin chain produced in this condition is normal qualitatively but greatly reduced in amount (a quantitative defect). If the alpha chains are affected, you get alpha thalassaemia. If the beta chains are affected, you get beta thalassaemia. If one gene is affected in this way, you have beta thalassaemia trait or thalassaemia minor. If both genes are affected, you have beta thalassaemia major.

The website you referred to mention something they call HbSbeta. What they mean is a composite disease, with one beta globin gene having a mutation that results in a glutamic acid to valine substitution, and the other beta globin chain gene having a mutation that results in loss of production of normal globin chains. In other words, you have a combination of sickle cell trait and beta thalassaemia minor.

There are various other possible combinations. One disease more commonly seen in Malays in Singapore is HbE-thal, where there is a combination of HbE disease with beta thalassaemia minor.

Hope that answers your question, little ant.

ndmmxiaomayi SG

Thanks a lot, oxford, it helps a lot. Wink

ndmmxiaomayi SG

He says he got research to do. alfagal is going to step into the working world soon, so won't be seeing them any time sooner.

ndmmxiaomayi SG

Is it for both the heterozygous and homozygous people or just homozygous sickle cell patients?

oxford mushroom SG

Both have resistance..

ndmmxiaomayi SG

Thanks. Wink

AugoeideS SG

Lols.

Because glutamic acid is hydrophilic, and valine is hydrophobic.

This causes the hemoglobin molecule to fold in a distorted conformation, reducing its ability to maintain optimal solubility. Hence the "stickiness" of hemoglobin, which the thousands of hemoglobin sticks together, forming a clump of red blood cell that looks like a sickle.

Why people with sickle cell trait are more resistant to malaria:
For symptoms of malaria to show, give or take 9 to 14 days for the parasite to burst out of its host red blood cell.

Sickled red blood cell remains less than 20days before it is broken down in the spleen. Parasites that infect cells that only have 8 or less days to go wouldn't have the time to fully perform its production cycle.

Malaria is fatal, only when the parasites are in substantial numbers in the body, infecting the red blood cells, till one dies due to the lack of red blood cells in the body to sustain life.