If Pygmies are known for one trait, it is their short stature: Pygmy men stand just 4'11" on average. A study of the Western African Pygmies in Cameroon, led by geneticists from the University of Pennsylvania, has identified genes that may be responsible for the Pygmies' relatively small size.
The work, published in PLoS Genetics, also provides evidence based on genetic signatures of natural selection to suggest why these groups evolved to be small, with signs pointing to hormonal pathways and immune system regulation as possible drivers.
In order to seek genes responsible for the Pygmies' short stature, the researchers conducted a genome-wide association study and found several promising candidates appeared in a region of chromosome 3.
Taking a closer look, the genes DOCK3 and CISH stood out. Both have been linked to size variation. CISH has also been implicated in susceptibility to infectious disease, a potentially meaningful finding since Pygmies, living in a tropical climate, shoulder heavy burdens of parasites and other disease-causing agents.
Finally, the researchers identified genetic mutations in the Pygmies that appeared to be subject to natural selection. In many cases, they found that the mutations were associated with biological pathways that govern reproductive hormone activation, such as immune system function and growth hormone regulation.
"Genes in those pathways are important in reproduction and metabolism and that was intriguing in light of the hypothesis that the reason Pygmies are short is so that they can reach reproductive maturity early," said Sarah Tishkoff, senior author on the study and a Penn Integrates Knowledge Professor.
"Early reproduction could be a significant advantage in Pygmies, whose life spans average between 15 and 24 years," she added.
Offering clues to the factors that drove Pygmies' adaptation to their local environment, the researchers' multi-faceted approach also provides a method that might be replicated in studying other complex genetic traits, from physical characteristics to disease susceptibility.
This work was funded by NSF grants BCS-0196183 and BCS-0827436 and by NIH grants DP1-OD-006445-01, R01-GM076637, and R01-GM083606 to SAT. JPJ is supported by an NIH, NRSA fellowship (1F32HG005290-01). BF is supported by a Rubicon grant of The Netherlands Organization for Scientific Research. LO and JM are funded by the Department of Genetic Medicine (Weill Cornell Medical College), NIH grant 1P50MH079513-02, and NSF grants DEB-0922432 and IOS-1026555. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
The authors have declared that no competing interests exist.
Jarvis JP, Scheinfeldt LB, Soi S, Lambert C, Omberg L, et al. (2012) Patterns of Ancestry, Signatures of Natural Selection, and Genetic Association with Stature in Western African Pygmies. PLoS Genet 8(4): e1002641. doi:10.1371/journal.pgen.1002641
Katherine Unger Baillie
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