Maternal and Fetal HLA Heterozygosity in Preeclampsia: Insights From a Large Multi-Ancestry Pregnancy Cohort

Preeclampsia (PE) is a leading cause of maternal and neonatal morbidity, with immune dysregulation at the maternal-fetal interface central to its pathogenesis. The highly polymorphic HLA region mediates maternal immune tolerance of the semi-allogeneic fetus, yet the contribution of HLA diversity to PE risk remains poorly defined. Whether the HLA heterozygote advantage observed in other immune disorders is relevant to PE has not been systematically evaluated. Using data from the multi-ancestry TOPMed Boston-Colombia Collaborative for Adverse Pregnancy Outcomes (n = 12,790; 4770 PE, 8020 controls; 10,808 maternal, 1982 fetal, including 1848 pairs), we evaluated associations between heterozygosity across eight classical HLA loci and PE and four sub-phenotypes, adjusting for genetic ancestry. HLA heterozygosity was common across most loci (> 80%). No individual maternal HLA locus was associated with overall PE; however, heterozygosity across Class I loci showed a protective effect in preterm PE (OR = 0.81, 95% CI: 0.68-0.97), with a similar pattern for HLA-A heterozygosity (OR = 0.78, 95% CI: 0.64-0.97). In contrast, fetal heterozygosity at HLA-DQB1 was nominally associated with increased risk of PE (OR = 1.36, 95% CI: 1.03-1.80) and preterm PE (OR = 1.73, 95% CI: 1.13-2.74). No individual maternal or fetal HLA alleles were associated with PE. Maternal-fetal mismatch analysis demonstrated locus-specific associations with preterm PE, including increased risk with HLA-DQA1 mismatch and reduced risk with HLA-C mismatch. These findings highlight distinct maternal and fetal immunogenetic contributions to PE risk and underscore the importance of considering HLA diversity-rather than individual alleles alone-in studies of PE aetiology.