Genetic analysis of ANXA5 haplotype and its effect on recurrent pregnancy loss

Recurrent pregnancy loss (RPL) is often associated with dysregulated Annexin A5 (ANXA5) expression. Moreover, the variants of Anxa5, a protein that is enriched in the placenta to prevent coagulation, have been reported to affect RPL risks. The haplotypes M1 [including single nucleotide polymorphisms (SNPs) 1A/C and 27T/C] and M2 (including SNPs 19G/A, 1A/C, 27T/C and 76G/A) of ANXA5 were also reported to affect RPL risks. The present study aimed to investigate the association between the haplotype located in the promoter region of ANXA5 and the risk of RPL. Patients with RPL (n=235) or intrauterine fetus death (IUFD; n=154), as well as healthy control subjects (n=375) were enrolled in the current research. Their haplotypes of ANXA5 were determined using genotyping, and the association between ANXA5 haplotypes and the risk of RPL was accordingly analyzed. A luciferase assay was conducted to investigate the haplotype responsible for ANXA5 activity. Reverse transcription‑quantitative PCR, western blot analysis, immunohistochemistry and ELISA were performed to assess the expression level and activity of ANXA5 in patients with RPL. Consequently, the majority (n=214) of patients with RPL had a history of early RPL, whereas 31 patients with RPL had a history of both early and late RPL episodes. A significant difference was found between cases and controls in terms of gravidity and parity, whereas no significant differences were found in terms of age. The percentage of patients with RPL carrying the M2 haplotype of ANXA5 was significantly higher compared with that in control subjects, indicating that the M2 haplotype of ANXA5 was an independent risk of RPL as it influenced the transcription efficiency of ANXA5 promoter. In patients with RPL, ANXA5 activity was suppressed and the mRNA and protein expression levels of Anxa5 were decreased. Thus, the ANXA5 M2 haplotype may be an independent risk factor of RPL by affecting Anxa5 activity.