Ethnic differences in interleukin 6 (IL-6) and IL6 receptor genes in spontaneous preterm birth and effects on amniotic fluid protein levels.

Preterm birth (PTB) is a significant neonatal health problem that is more common in African-Americans (AA) than in European-Americans (EA). Part of this disparity is likely to result from the differing genetic architectures of EA and AA. To begin assessing the role of these differences, patterns of genetic variation in two previously proposed candidate genes, encoding interleukin 6 (IL6) and its receptor (IL6R), were analyzed in mothers and fetuses from 496 EA birth-events (149 cases and 347 controls) and 397 birth-events in AA (76 cases and 321 controls). IL-6 levels in amniotic fluid (AF) samples were determined in a subset of these pregnancies. Case-control comparisons revealed a single SNP in IL6R associated with PTB (p=0.04 for allelic and p=0.05 for genotype association). In addition, all of the SNPs studied showed significant frequency differences between AA and EA in at least one comparison, significantly in excess of that expected from general population databases. Higher IL-6 concentrations were associated with the IL6 SNP -661 in EA preterm samples (p=0.0056), and this result seems to be driven by microbial invasion of the amniotic cavity, indicating a gene by infection interaction. These findings indicate that, as a function of IL6 genotype, EA and AA women respond differently to infection with respect to their expression of IL-6. Our data support differential genetic control of levels of IL-6 in amniotic fluid between EA and AA.