Comprehensive analysis of HLA-G: implications for recurrent spontaneous abortion

Miscarriage is one of the most common pregnancy complications. Recurrent spontaneous abortion is defined as 2 or more pregnancy losses and may be associated with genetic variation. Human leukocyte antigen-G (HLA-G) is a ligand for natural killer (NK) cell receptors and has the ability to block NK cell activity, which if not blocked can potentially harm a fetus. Consequently a deletion or mutation of the HLA-G gene could lead to miscarriage. Our cases (n = 238) include Caucasian women experiencing 2 or more spontaneous abortions, and controls (n = 233) include women with at least 1 live birth and no history of SA. We sequenced approximately 1400 base pairs (bp) of the HLA-G promoter region, genotyped the 14 bp exon 8 insertion/deletion and single nucleotide polymorphism (SNP) in the coding region of HLA-G. Promoter haplotypes were constructed from sequence information. Twenty-three SNPs were observed in the promoter region with minor allele frequency >0.02. Twelve SNPs differed significantly in frequency between cases and controls. Two haplotypes incorporating these 12 SNPs accounted for 90% of haplotypes and differed significantly in frequency between the 2 populations. Cases were more likely to carry haplotype 2 (P = .0078) and controls to have haplotype 6 (P = .0004). Cases also had a higher frequency of individuals homozygous for the 14 bp insertion. Among the 12 alleles carried on haplotype 2, 5 are predicted to disrupt transcription factor binding sites. The HLA-G promoter is highly associated with the risk of spontaneous abortion, but high linkage disequilibrium in the promoter prevents assignment of the causal variant.