Objective: To investigate the relationships between recurrent pregnancy loss and single nucleotide polymorphisms (-634C-->G and -174G-->C genotypes) in the promoter region of the interleukin (IL)-6 gene in the Japanese population.
Design: A case-control study.
Setting: Obstetrics and gynecology department of a university hospital.
Patient(s): Cases were 76 women with recurrent pregnancy loss; controls were 93 fertile women.
Intervention(s): Determination of IL-6 promoter gene polymorphisms performed by polymerase chain reaction and gel electrophoresis.
Main outcome measure(s): Frequency and distribution of the promoter region of the IL-6 gene allele.
Results: There was a significant difference in the -634C-->G genotype frequency (CC vs. CG/GG) between women with recurrent pregnancy loss and controls. The risk of recurrent pregnancy loss was lower in the carriers of the G allele than in women with the wild type (CC) (odds ratio = 0.46; 95% confidence interval = 0.24-0.91). On the other hand, we did not detect any carrier of -174C among the 169 subjects.
Conclusion(s): The results suggest that, in the Japanese population, women carrying the -634G allele of the IL-6 gene might have a decreased risk of recurrent pregnancy loss.