November 03, 2010

Sickle cell and malaria (Piel et al. 2010)

The authors ascribe the lack of correlation between malaria endemicity and HbS in Asia primarily to either the presence of other protective polymorphisms or the fact that Plasmodium vivax rather than Plasmodium falciparum is the causative agent there.

Nature Communications 1 , Article number: 104 doi:10.1038/ncomms1104

Global distribution of the sickle cell gene and geographical confirmation of the malaria hypothesis

Frédéric B. Piel et al.

It has been 100 years since the first report of sickle haemoglobin (HbS). More than 50 years ago, it was suggested that the gene responsible for this disorder could reach high frequencies because of resistance conferred against malaria by the heterozygous carrier state. This traditional example of balancing selection is known as the 'malaria hypothesis'. However, the geographical relationship between the transmission intensity of malaria and associated HbS burden has never been formally investigated on a global scale. Here, we use a comprehensive data assembly of HbS allele frequencies to generate the first evidence-based map of the worldwide distribution of the gene in a Bayesian geostatistical framework. We compare this map with the pre-intervention distribution of malaria endemicity, using a novel geostatistical area-mean comparison. We find geographical support for the malaria hypothesis globally; the relationship is relatively strong in Africa but cannot be resolved in the Americas or in Asia.


1 comment:

German Dziebel said...

Interesting study. If it weren't for the association with malaria endemicity apparently attested in Africa and Europe, the pure gene evolution would point to a migration out of America (ancestral state) through East Asia to Europe and Africa (derived state). India is a bridge between the east and the West and a "swing" continent. Africa still preserves the original state in some pockets such as Madagascar, Horn of Africa and northwest Africa but overall it has shifted away from the original condition.

But even with the malaria association in Africa and Europe this scenario would work.

The map of Hbs distribution reminds me of Y-DNA YAP+ distribution, with Africa being heavy on YAP+ but with pockets of YAP-, Europe intermediary and Asia showing a strange small pocket of YAP+. India has Hbs, Tibetans and Andaman islanders have high frequencies of YAP+. America is devoid of YAP+ completely. There's a parallelism here, I think.