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"Ground truth" for selection on CCR5-Delta32.
Philip W Hedrick1, Brian C Verrelli
1School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501, USA. philip.hedrick@asu.edu
Trends in Genetics : TIG
|May 9, 2006
Summary
The CCR5-Delta32 genetic variant, offering AIDS resistance, is at least 3,000 years old, not recent. Its ancient origins challenge theories of rapid human genome adaptation to historical epidemics.
Area of Science:
- Human evolutionary genetics
- Population genetics
- Immunogenetics
Background:
- The CCR5-Delta32 deletion is a well-known human genomic variant.
- This variant confers resistance to HIV/AIDS.
- It was previously hypothesized to be a recent adaptation to diseases like plague or smallpox.
Purpose of the Study:
- To determine the ancient origins of the CCR5-Delta32 allele.
- To investigate the evolutionary history of CCR5 in human populations.
- To re-evaluate claims of recent positive selection in the human genome.
Main Methods:
- Analysis of ancient DNA from Bronze Age skeletal remains.
- Genomic sequencing and population genetic analyses.
- Comparison of CCR5-Delta32 allele frequencies across different time periods and populations.
Main Results:
- CCR5-Delta32 allele frequencies in Bronze Age samples are comparable to modern populations.
- The allele's age is estimated to be at least 3,000 to 5,000 years old.
- Genetic diversity metrics (heterozygosity, differentiation, linkage disequilibrium) in the CCR5 region resemble other genomic regions.
Conclusions:
- The CCR5-Delta32 variant is significantly older than previously assumed.
- The genetic data challenges the hypothesis of recent, rapid positive selection for CCR5-Delta32.
- Human adaptation patterns may involve longer evolutionary timescales than suggested by some models.