A functional SNP in the promoter of the SERPINH1 gene increases risk of preterm premature rupture of membranes in African Americans

Abstract

Prematurity is more prevalent in African Americans than in European Americans. We investigated the contribution of a functional SNP in the promoter of the SERPINH1 gene, enriched among those of African ancestry, to preterm premature rupture of membranes (PPROM), the leading identifiable cause of preterm birth. SERPINH1 encodes heat-shock protein 47, a chaperone essential for collagen synthesis. The SERPINH1 -656 minor T allele had a greater frequency in African populations and African Americans than in European Americans (7.4% [corrected] vs. 4.1%). The -656 T allele displayed significantly reduced promoter activity compared to the major -656 C allele in amnion fibroblasts, which lay down the fibrillar collagen that gives tensile strength to the amnion. An initial case-control study demonstrated that the -656 T allele is significantly more frequent in African-American neonates (P < 0.0009) born from pregnancies complicated by PPROM compared with controls (odds ratio of 3.22, 95% confidence interval 1.50, 7.22). There was no significant difference in ancestry among cases and controls using a dihybrid model based on 29 ancestry-informative markers. Adjusting the results of the case-control study for admixture still yielded a statistically significant association between the -656 T allele and PPROM (P < 0.002). A follow-up case-control study gave similar results. The combined case-control findings showed a highly significant (P < 0.0000045) association between the -656 T allele and PPROM. The SERPINH1 -656 T allele is the first example of an ancestry-informative marker associated with preterm birth in African Americans.

Fig. 1.

Effect of the −656 SERPINH1 SNP on promoter activity. SERPINH1 promoter fragments representing the −656 C and T alleles were cloned into the pGL3 basic vector. The relative Photinus luciferase activities ± SE (n = 3 separate experiments performed with triplicate wells for each cell host) standardized to Renilla luciferase were compared by using the Tukey–Kramer test. Values with different letters are significantly different (P < 0.05) from each other within each cell host.

Fig. 2.

The −656 region specifically binds a nuclear protein. EMSA studies were performed with nuclear extracts prepared from amnion fibroblasts (FBs) (Left), dermal fibroblasts (Center), and uterine smooth muscle cells (SMCs) (Right) and ³²P-labeled double-strand oligonucleotides representing the −656 C and T alleles. Specific binding was established by addition of increasing amounts of unlabeled double-strand oligonucleotide representing the two SERPINH1 alleles or an irrelevant nucleotide sequence. Arrowheads indicate specific complexes and free probe.