The HLA-G gene is primarily expressed in placental cells that invade the maternal decidua during pregnancy. This gene encodes multiple isoforms that fulfill a variety of functions at the maternal-fetal interface throughout gestation. Recently, a null allele for the most abundant HLA-G isoform was associated with recurrent miscarriage in two independent studies, suggesting that reduced levels of the HLA-G1 protein may compromise successful pregnancy. We initiated the present study to determine whether other polymorphisms that could affect expression levels of HLA-G were associated with fetal loss in women participating in a 15-year prospective study of pregnancy outcome. We genotyped these subjects for 18 single-nucleotide polymorphisms in the 1,300 bp upstream of exon 1, 13 of which were identified as part of this study, as well as for an insertion/deletion (in/del) polymorphism in the 3′ untranslated region. The 18 SNPs defined eight unique haplotypes. One polymorphism, - 725C/G, was associated with fetal loss, with an increased risk for miscarriage in couples in which both partners carried the - 725G allele, compared with couples not carrying this allele (odds ratio 2.76, 95% confidence interval 1.08-7.09; P = .035). Further, the G at nucleotide - 725 creates a CpG dinucleotide, and we demonstrate that this CpG site is methylated on -725G alleles. Overall, this study identified extraordinary levels of variation in the 5′-upstream regulatory region of HLA-G and provides evidence for an association between a promoter-region SNP and fetal loss rates, further attesting to the novel features and critical role of this gene in pregnancy.
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We thank the Hutterites who participated in this study, for their continued cooperation; Soma Das, for helpful discussions and comments; Harvey Dytch, Robert Stanaker, April Chan, and Rebecca Brown, for assistance; and Warner-Lambert, for providing pregnancy test kits. This work was supported by National Institutes of Health grant HD21244.