Gene Expression

Please read: Follow up post.

Genetic Variation Increases HIV Risk In Africans:

A genetic variation which evolved to protect people of African descent against malaria has now been shown to increase their susceptibility to HIV infection by up to 40 per cent, according to new research. Conversely, the same variation also appears to prolong survival of those infected with HIV by approximately two years.

HIV affects 25 million people in sub-Saharan Africa today, an HIV burden greater than any other region of the world. Around 90 per cent of people in Africa carry the genetic variation, meaning that it may be responsible for an estimated 11 per cent of the HIV burden there. The authors observe that sexual behaviour and other social factors do not fully explain the large discrepancy in HIV prevalence in populations around the world, which is why genetic factors are a vital field of study.

The full paper is Duffy Antigen Receptor for Chemokines Mediates trans-Infection of HIV-1 from Red Blood Cells to Target Cells and Affects HIV-AIDS Susceptibility. This shouldn’t surprise; there are other genes which can explain HIV susceptibility. It seems plausible that many recessive diseases, such as cystic fibrosis, are evolutionary relics of selection pressures past. Disparate selection pressures and the constant reconfiguration of the adaptive landscape means there are going to be many variations across time and space which we’re going to have to keep track of. Remember the truism that 85% of genetic variation on any given locus is within populations and only 15% between? This is one of those loci where this isn’t true. Almost no Europeans have the nonfunctional variant of DARC, while the majority of Africans lack the functional variant. From Wikipedia:

The Duffy antigen/chemokine receptor gene (DARC) is composed of a single exon. Most Duffy negative blacks carry a silent Fy-b allele with a single T to C substitution at nucleotide -46, impairing the promoter activity in erythroid cells by disrupting a binding site for the GATA1 erythroid transcription factor. The gene is still transcribed in non erythroid cells in the presence of this mutation.

Differences in the racial distribution of the Duffy antigens were discovered in 1954 when it was found that the majority of blacks had the erythrocyte phenotype Fy(a-b-): 68% in African Americans and 88-100% in African blacks (including more than 90% of West African blacks). This phenotype is exceedingly rare in whites.

The silent allele has evolved at least twice in the black population of Africa and evidence for selection for this allele has been found. The selection pressure involved here appears to be more complex than many text books might suggest. An independent evolution of this phenotype occurred in Papua New Guinea has also been documented.


  1. #1 Ann
    July 18, 2008

    I had trouble parsing this:
    “Almost no Europeans have the nonfunctional variant of DARC, while the majority of Africans lack the functional variant.”

    Could you say “The majority of Europeans have the functional variant of DARC, while the majority of Africans do not”?

    Or am I misunderstanding this completely?

  2. #2 razib
    July 18, 2008

    Could you say “The majority of Europeans have the functional variant of DARC, while the majority of Africans do not”?

    anglais is my second language! and you have it right.

  3. #3 Neil B.
    July 18, 2008

    Interesting, and the article didn’t mention another reason for asymmetry in AIDS progression in Africa: Many of European descent possess genes originally developed in selective response to bubonic plague, which coincidentally also offer resistance to AIDS. Bubonic plague did not occur as much AFAIK in tropical Africa, hence fewer Africans have that sort of resistance.

  4. #4 yogi-one
    July 19, 2008

    Ouch. This does not bode well for Africans. We just hope that the world community will do the right thing, pursue this new finding, and get the medicines to the Africans without tying it up behind greedy patent-protecting legislation and price-fixing while people continue to die.

  5. #5 Francois
    July 19, 2008

    The findings state that HIV just happens to attach to the black host without any resistance; as if the disease was created just for blacks. This should now be the focal point how one race of people hit the HIV lottery. This needs to be further researched because I truly believe this disease is killing all of us because someone had a problem with one race. So if it is man made which probability agrees it is than we definitely have the capability to find the cure or release the cure or whatever it takes for US ALL to no longer be at RISK!

    Bottomline this disease would not be smart enough to only want to attach and thrive best through a black host; unless it was genetically engineered to do just that. By the way how is this not headline news, but 1200 people with food poisoning can outweigh the 40,000 new cases of African-American HIV victims that will die from this disease in this society. There is no way a world where promiscuity runs rapids in all societies should blacks who only make up 12% of the world’s population should attribute for more than 70% of new HIV cases.

    Once again I’m asking whoever is reading this article and understands the magnitude of this message please forward it along. This is not just OUR scientist fight, this is OUR fight. OUR family members and OUR friends are dying from this disease and they don’t care why they got it, they just want to know how to get rid of it. So, before another dollar gets spent on some research that is driven towards a global cure for mans most recent plague than do me a favor and save your findings because we are still burying OUR sons and daughters, OUR brothers and sisters, OUR mothers and fathers and worst of all OUR babies and elderly are dying from this lobotomy created disease. PLEASE MANKIND we don’t deserve to have a weapon of mass destruction pointed directly in to all off OUR bedrooms please let’s stand for something. If you would like to find out what I’m doing to continue this movement please e-mail me @ I am only one man but I have several thousand people who believe in the eradication of this disease just as strongly as you and I do.

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