Amazing Genetics – Are Some People Immune to HIV?

27 Mar

HIV, the virus that leads to AIDS, has led to the deaths of over 30 million people since its discovery. Something that many people may not be aware of is that scientists and doctors classify different species and subtypes of the virus. There are two ‘species’; HIV 1 and HIV 2, and these are further divided into subgroups, and then subtypes within the subgroups.

So, put very simply, there are many different ‘strains’ of the virus, with each having varying rates of transmission, transmission pathways, and resistance to treatment. Many of these forms of HIV bind to a certain protein on white blood cells in order to infect a person, and this protein is known as CCR5.

Amazingly, however, some people are naturally resistant to these forms of HIV, because they carry a mutation. So, what is this mutation, and how does it work?

Computer-generated image of CCR5 receptor in cell membrane. Credit to Thomas Splettstoesser

Computer-generated image of CCR5 receptor in cell membrane. Credit to Thomas Splettstoesser

Basically, these people carry a mutated version of the CCR5 gene, known as CCR5-delta-32. This mutation results in the ‘deletion’ of part of the CCR5 gene, which leads to the virus being unable to bind to the protein and enter the white blood cells like it normally would.

It is thought that this mutation arose in Europe, and around 10% of Europeans are thought to carry it, along with this resistance to certain forms of HIV. Furthermore, it has also been suggested that the mutation confers resistance to smallpox, and may have actually originated and spread via natural selection during the plague period in Europe’s history, which challenges the assumption that the plague period was caused by the spread of bubonic plague. Apparently, the normal frequency of the mutation’s occurrence is 1 in 20,000, but the plagues are thought to have increased the rate to 1 in 10 amongst Europeans. Of course, people from other regions can also carry the gene mutation, but it is a lot rarer for them.

Depiction of the horrors of the plague within medieval Europe - By Pieter Bruegel (1562)

Depiction of the horrors of the plague within medieval Europe – By Pieter Bruegel (1562)

Interestingly, a man suffering from leukaemia and AIDS was cured of both illnesses when given bone marrow transplants as part of his cancer treatment. It turns out that the donor of the bone marrow was a carrier of the ccr5-delta-32 mutation, and this has led scientists to believe that the mutation could be used as a potential cure for HIV infections.

For further reading on this matter, check out http://www.sciencedaily.com/releases/2005/03/050325234239.htm and http://online.wsj.com/article/SB122602394113507555.html

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