Population genetic studies of HLA-G: allele frequencies and linkage disequilibrium with HLA-A1.

HLA-G is a class I gene that is expressed in the extravillous cytotrophoblast. Although the function of this gene is still unknown, its expression at the maternal-fetal interface suggests that HLA-G may play a key role in the induction of tolerance during pregnancy. Preliminary to our studies of the effects of HLA-G polymorphisms on pregnancy outcome, we have defined HLA-G alleles in the Hutterites. We report here the presence of nine HLA-G alleles that differ with respect to nucleotide sequences, including four groups of alleles that differ with respect to amino acid sequences, and striking linkage disequilibrium between HLA-G and HLA-A alleles. The levels and sites of polymorphism in HLA-G suggest that this gene had a unique evolutionary history and may perform nonclassical functions at the maternal-fetal interface.