HLA polymorphism in the Havasupai: evidence for balancing selection

Area of Science:

• Population genetics
• Human evolution
• Immunogenetics

Background:

• The Human Leukocyte Antigen (HLA) loci are highly polymorphic, crucial for immune response and understanding human population genetics.
• Evolutionary forces shaping human populations can be elucidated through the analysis of genetic variation at HLA loci.

Purpose of the Study:

• To characterize genetic variation at the HLA-A and HLA-B loci in an isolated Native American population (Havasupai).
• To investigate evolutionary mechanisms maintaining genetic diversity at these critical immune system genes.

Main Methods:

• Serotyping of HLA-A and HLA-B loci.
• Statistical analysis of allele and haplotype frequencies.
• Assessment of linkage disequilibrium and Hardy-Weinberg equilibrium.

Main Results:

• Identified four alleles at HLA-A and eight alleles at HLA-B.
• Observed 20 of 32 potential two-locus haplotypes, with significant linkage disequilibrium in common haplotypes.
• Detected significant heterozygosity excess (homozygote deficiency) at both loci, deviating from Hardy-Weinberg proportions.
• Allele distribution was more even than predicted by neutrality theory.

Conclusions:

• The observed genetic patterns suggest that balancing selection plays a major role in maintaining genetic variation at the HLA-A and HLA-B loci.
• Non-selective factors do not explain the deviation from Hardy-Weinberg proportions.
• Findings provide insight into the evolutionary history and genetic diversity of the Havasupai population.