Genomewide association study of HLA alloimmunization in previously pregnant blood donors

Abstract

Background: Alloimmunization through blood transfusion, transplantation, or circulating fetal cells during pregnancy is a significant concern. Some exposed individuals make alloantibodies while others do not, implying variation in genetic risk factors.

Study design and methods: We conducted a genomewide association study (GWAS) of 9,427,497 single-nucleotide polymorphisms (SNPs) to identify genetic variants for HLA alloimmunization in previously pregnant blood donors with (n = 752) and without (n = 753) HLA Class I or II alloantibodies.

Results: A SNP in the neurexophilin 2 (NXPH2) gene surpassed genome-wide significance (p = 2.06 × 10^-8 ), with multiple adjacent markers p < 10^-6 , for women with anti-Class I alloantibodies only. Little is currently known about the function of NXPH2, although gene family members have been shown to impact immunity. SNPs in the E2F7 gene, a transcription factor related to cell cycle control and cellular proliferation, also approached genomewide significance (p = 2.5 × 10^-7 ).

Conclusion: Further work to extend the GWAS approach and to characterize variants in NXPH2 and E2F7 in the context of alloantibody formation is warranted.

Figure 1

Manhattan plots showing negative log p-values of associations, plotted by chromosome and position. (A) HLA class I or II alloantibody positive; (B) HLA class I alloantibody positive only, (C) HLA class II alloantibody positive, and (D) both HLA class I and class II alloantibody positive. Controls in all cases are neither HLA class I nor II positive.

Figure 2

Expanded view of SNP associations with HLA class I alloimmunization. (A) Detailed view of SNP associations for the genome-wide significant hit on chromosome 2 for the analysis of HLA class I alloantibody formation. The dots represent the –log₁₀ of the p-values for each SNP. The colored dots show the linkage disequilibrium between the most significant SNP and other SNPs. The purple graph in the background shows the recombination rate and indicates two 2 recombination hot spots flanking the significant result group of SNPs that are in high LD with one another. (B) Detailed view of SNP associations for the second most significant hit near the E2F7 gene on chromosome 12.

Figure 2

Expanded view of SNP associations with HLA class I alloimmunization. (A) Detailed view of SNP associations for the genome-wide significant hit on chromosome 2 for the analysis of HLA class I alloantibody formation. The dots represent the –log₁₀ of the p-values for each SNP. The colored dots show the linkage disequilibrium between the most significant SNP and other SNPs. The purple graph in the background shows the recombination rate and indicates two 2 recombination hot spots flanking the significant result group of SNPs that are in high LD with one another. (B) Detailed view of SNP associations for the second most significant hit near the E2F7 gene on chromosome 12.

Figure 3

Distribution of HLA mismatches between mother and children for controls (mothers without detectable alloantibodies) and cases (those mothers with alloantibodies) for Class I [A] and Class II [B].