Natural Selection: Uncovering Evolutionary Correlations between Sickle Cell Anemia (HBB gene & HbS allele), Malaria, and ENT proteins By: Kali Nason, Kelly Colthorpe, and Greg Kinstler

Evolutionary Questions about Malaria and sickle cell anemia? What do you think?

Questions?? What is it sickle-cell anemia? When did it arise? How did it evolve? Why did it evolve? Where is it most prevalent? Correlation between endemicity and HbS trait What are the areas where malaria is most prevalent? Are there other correlations with this mutation other than malaria resistance with equal positive effect? Is this why the mutation has such a high rate in endemic areas?

Sickle-cell Anemia Autosomal recessive Normal HbA/HbA Heterozygote/Carrier of trait HbS/HbA Homozygous recessive/Sickled HbS/HbS

J. B. S. Haldane (1949) Observed many tropical regions where malaria was endemic and red blood cell disorders such as sickle-cell anemia and various thalassemias (**also autosomal recessive either partial or no synthesis of one of the globin chains in hemoglobin due to deletion or mutation) The “Malaria Hypothesis”: Disorders had become common in these certain areas because natural selection increased the prevalence of these traits to protect individuals from malaria

Geographical Distribution of Malaria (2005)

A. C. Allison (1954) Confirmed “Malaria Hypothesis” The geographical distribution of sickle-cell mutation in the beta hemoglobin gene (HBB) was limited to Africa and correlated with malaria endemicity (**So there was clearly some sort of selective advantage for having the sickle cell trait, otherwise this deleterious allele would have been selected against) Individuals with the HbS trait were resistant to malaria (**autosomal recessive full blown sickle-cell anemia, one allele of HbS and one regular…almost no symptoms at all but resistance still there)

***Point mutation at position 6 and on the short arm of the chromosome at position 11p15.5

Convergent Evolution and Malaria Four identified different sickle-cell variants (of HbS allele) among different African populations Suggesting same mutation arose independently among the different populations several different times ***Beyond HbS, there’s other mutations in the HBB gene have generated HbC and HbE alleles, which arose and spread in Africa and in Southeast Asia

Interesting Correlations Haldane was on the right track! Different RBC diseases (a-thalassemia, G6PD deficiency, and ovalocytosis) ALL correlate to malaria endemicity and are linked to malaria resistance Mutation in Duffy antigen gene (FY) (**Plasmodium vivax uses this protein to enter RBCs and mutation in this protein disrupts its pathway of entry = PROTECTION! Occurs at 100% prevalence in thru most of sub-Saharan Africa..non existent outside Africa) (**Again)Convergent evolution in Southeast Asia (**independent mutation has arisen of the FY gene) ENT proteins possible target for new malaria drug (**get to that in a bit)

Malaria and the World Health Organization According to WHO “In 2008, there were 247 million cases of malaria and nearly one million deaths – mostly among children living in Africa. In Africa a child dies every 45 seconds of Malaria, the disease accounts for 20% of all childhood deaths.”

Evolution What does this have to do with Evolution? EVERYTHING! Malaria is one of the most understood examples of an infectious disease and its evolutionary drive in humans

EVOLUTIONARY ARMS RACE! Malaria is currently treated with a cocktail of drugs The initial drug is usually an artemisinin (this wipes out malaria symptoms) Partial treatment…some parasites still present, continue life cycle! ACT used in combination = DEATH! **problem with about partial treatment…without the second drug many of the patients are not taking it so the life cycle continues and the parasites become more and more resistant to the currently known drugs Example: Chloroquine and Sulfacoxine-pyrimethamine (SP) **in the past malaria became resistant to these two drugs. Dire effects on populations if there are no new drugs in the making…populations could be wiped out.

P. falciparum is resistant to most drugs available and is the deadliest form of any Plasmodium species (P. vivax, P. knowlesi, P. ovale) Fever Table (**this is why p.falciparum is so deadly…longer period of time with fever)

Novel Treatments Available?? No… Unfortunately there are no current new drugs in development Possible ideas! ENT proteins (Equilibrative Nucleoside Transporter proteins) **we need to get a one up of the parasite to create a new drug before it becomes resistant to the current ones available

ENT proteins?? New target Needed by Plasmodium falciparum Needs purines (adenosine) for DNA replication Steals purines from host RBCs ENT proteins are the pathway which P. falciparum enters a RBC

ENT’s P. falciparum uses the already existing ENT proteins to channel the needed purines into the RBC where the parasite is Idea behind this is to target these ENT proteins and inhibit them ENTs are highly conserved! Almost no evolution of this protein through different organisms

Other ENT proteins When P. falciparum’s sequence was entered into the database the first couple of hits are different species Important why? Evolution?

Future Pathway inhibited = new drugs = Malaria wiped out! Would sickle cell anemia trait still be prevalent? Or would evolution select against it? Duffy antigen mutation? Lots of evolutionary questions!

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