Association of Endometrial HAND2 Expression with β₂-Glycoprotein I Antibodies in Recurrent Pregnancy Loss

Background: Recurrent pregnancy loss (RPL) is frequently linked to antiphospholipid antibodies, yet many affected women are seronegative for the classical (Sydney) criteria antibodies. In a previously characterized cohort, an extended antiphospholipid antibody panel was positive in 79% of women with RPL, with the strongest associations for antibodies against prothrombin, annexin V and β₂-glycoprotein I. Whether this association reflects molecular endometrial dysfunction was unclear. Objective: To examine endometrial expression of ten decidualization- and inflammation-related genes in women with RPL, stratified by APL status, focusing on the dominant antibody specificity: anti-β₂-glycoprotein I. Methods: Thirty-nine women with RPL (≥2 losses), a subsample of a published 100-patient cohort, underwent mid-luteal Pipelle endometrial biopsy followed by RT-PCR for C4BPA, CXCL1, HAND2, HPRT1, IFNG, IL15, IL8 (CXCL8), MMP10, TNC and VEGFB. Antibodies were measured by antiphospholipid 10 Dot line immunoblot (Generic Assays, Germany). The analysis used Mann-Whitney U, Fisher's exact test, Benjamini-Hochberg correction and ROC analysis. Results: Antibody prevalence in the subsample matched the parent cohort (Pearson r = 0.999). Of ten transcripts, only HAND2 showed a nominally significant reduction in APL+ women (median ΔCt -2.04 vs. -1.30; p = 0.037; rank-biserial r = -0.47); this signal did not survive Benjamini-Hochberg correction (q = 0.372). The signal was specific to anti-β₂GPI (p = 0.064; AUC 0.700), not to annexin V or prothrombin. A cut-off of HAND2 ΔCt ≤ -1.60 identified APL+ status with 73% sensitivity, 78% specificity and OR 9.62 (95% CI 1.64-56.4; p = 0.015). HAND2 clustered with IL15 (ρ = 0.65) and VEGFB (ρ = 0.70). Conclusions: Anti-β₂-glycoprotein I antibodies, the dominant APL specificity in RPL, are associated with reduced endometrial HAND2 expression. This exploratory data outline a candidate molecular pathway linking extended antiphospholipid serology to impaired endometrial receptivity.