MUltiplex Measurement of Cytokine/Receptor Gene Polymorphisms and interaction Between Interleukin-10 (-1082) Genotype and Chorioamnionitis in Extreme Preterm Delivery

Association of IL-4 and IL-10 Polymorphisms With Preterm Birth Susceptibility: A Systematic Review and Meta-Analysis

Objective

Preterm birth (PTB) is a typical inflammatory disease with unclear pathogenesis. The studies investigating the relationship between anti-inflammatory factors IL-4 and IL-10 gene polymorphisms and PTB produced conflicting results. This systematic review and meta-analysis aimed to summarize the effects of IL-4 and IL-10 gene polymorphisms and clarify their possible association with PTB.

Methods

A systematic literature review was conducted using PubMed, Web of Science, and Cochrane library (up to 02 April 2022). The MeSH terms, related entry terms, and other names in “Gene” database were used to find relevant articles. A fixed- or random-effects model was used to calculate the significance of IL-4 and IL-10 gene polymorphisms, depending on study heterogeneity. The odds ratios (OR) and 95% confidence intervals (CIs) were calculated in the allele, recessive, dominant, co-dominant, and over-dominant models. The Eggers publication bias plot was used to graphically represent the publication bias.

Results

Polymorphisms in two interleukins (IL-4-590C/T (rs2243250) = 5 and IL-10-592A/C (rs1800872), -819T/C (rs1800871) and -1082A/G (rs1800896) = 16) were found in 21 articles. Overall, only the over-dominant gene model AA + GG vs. AG revealed significant association between IL-10-1082A/G (rs1800896) and PTB (OR [95% CI] = 0.87 [0.76, 0.99], p = 0.04). However, in the allele model, recessive model, dominant model, co-dominant model, and over-dominant model, the polymorphisms for IL-4-590C/T (rs2243250), IL-10-592A/C (rs1800872), and IL-10-819T/C (rs1800871) were not found to be associated with the risk of PTB. In gene models, no statistically significant association was found between IL-4-590C/T (rs2243250), IL-10-592A/C (rs1800872), IL-10-819T/C (rs1800871), and IL-10-1082A/G (rs1800896) polymorphisms and PTB in subgroup analyses by racial or control group Hardy-Weinberg Equilibrium (HWE) p-value. Eggers’s publication bias plot and heterogeneity test (I2<50%, p = 0.05) of IL-10-1082A/G (rs1800896) suggested that the funnel asymmetry could be due to publication bias rather than heterogeneity.

Conclusion

The current study suggests that the over-dominant gene model AA + GG vs. AG of IL-10-1082A/G (rs1800896) polymorphism may be associated with genetic susceptibility to PTB and may have a protective function against PTB risk. There was unclear association found between IL-4-590C/T (rs2243250), IL-10-592A/C (rs1800872) and IL-10-819T/C (rs1800871) polymorphisms and PTB. Due to the limitations of included studies and the risk of publication bias, additional research is required to confirm our findings.

Systematic Review Registration

https://inplasy.com/inplasy-2022-4-0044, identifier INPLASY202240044.

Cytokines and pregnancy: Potential regulation by histone deacetylases

Cytokines are important regulators of pregnancy and parturition. Aberrant expression of proinflammatory cytokines during pregnancy contributes towards preterm labor, pre-eclampsia, and gestational diabetes mellitus. The regulation of cytokine expression in human cells is highly complex, involving interactions between environment, transcription factors, and feedback mechanisms. Recent developments in epigenetic research have made tremendous advancements in exploring histone modifications as a key epigenetic regulator of cytokine expression and the effect of their signaling molecules on various organ systems in the human body. Histone acetylation and subsequent deacetylation by histone deacetylases (HDACs) are major epigenetic regulators of protein expression in the human body. The expression of various proinflammatory cytokines, their role in normal and abnormal pregnancy, and their epigenetic regulation via HDACs will be discussed in this review.

Association of a placental Interleukin-6 genetic variant (rs1800796) with DNA methylation, gene expression and risk of acute chorioamnionitis

BACKGROUND

Acute chorioamnionitis (aCA), inflammation of the placenta and fetal membranes, is a frequently reported lesion in preterm deliveries. Genetic variants in innate immune system genes such as Interleukin-6 (IL6) may contribute to the placenta's inflammatory response, thus predisposing some pregnancies to aCA. These genetic variants may modulate molecular processes such as DNA methylation and gene expression, and in turn might affect susceptibility to aCA. Currently, there is remarkably little research on the role of fetal (placental) genetic variation in aCA. We aimed to explore the associations between genetic variants in candidate immune-system genes and susceptibility towards inflammatory responses in the placenta, which is linked to a strong inflammatory response in the newborn.

METHODS

DNA samples from 269 placentas (72 aCA cases, 197 non-aCA cases) were collected for this study. Samples were genotyped at 55 ancestry informative markers (AIMs) and 16 additional single nucleotide polymorphisms (SNPs) in 12 candidate innate immune system genes using the Sequenom iPLEX Gold Assay. Publicly available datasets were used to obtain DNA methylation (GSE100197, GSE74738, GSE115508, GSE44667, GSE98224) and gene expression data (GSE44711, GSE98224).

RESULTS

Differences in IL6 placental allele frequencies were associated with aCA (rs1800796, p = 0.04) with the CC genotype specifically implicated (OR = 3.1; p = 0.02). In a subset of the placental samples (n = 67; chorionic villi), we showed that the IL6 SNP (rs1800796) was associated with differential DNA methylation in five IL6-related CpG sites (cg01770232, cg02335517, cg07998387, cg13104385, and cg0526589), where individuals with a CC genotype showed higher DNA methylation levels than individuals carrying the GG genotype. Using two publicly available datasets, we observed that the DNA methylation levels at cg01770232 negatively correlated with IL6 gene expression in the placenta (r = - 0.67, p < 0.004; r = - 0.56, p < 2.937e-05).

CONCLUSIONS

We demonstrated that the minor C allele at the IL6 SNP (rs1800796), which is largely limited to East Asian populations, is associated with the presence of aCA. This SNP was associated with increased DNA methylation at a nearby MEPC2 binding site, which was also associated with decreased expression of IL6 in the placenta. Decreased expression of IL6 may increase vulnerability to microbial infection. Additional studies are required to confirm this association in Asian populations with larger sample sizes.

DNA methylation profiling of acute chorioamnionitis-associated placentas and fetal membranes: insights into epigenetic variation in spontaneous preterm births

BACKGROUND

Placental inflammation, often presenting as acute chorioamnionitis (aCA), is commonly associated with preterm birth. Preterm birth can have both immediate and long-term adverse effects on the health of the baby. Developing biomarkers of inflammation in the placenta can help to understand its effects and potentially lead to new approaches for rapid prenatal diagnosis of aCA. We aimed to characterize epigenetic variation associated with aCA in placenta (chorionic villi) and fetal membranes (chorion and amnion) to better understand how aCA may impact processes that lead to preterm birth. This study lays the groundwork for development of novel biomarkers for aCA.

METHODS

Samples from 44 preterm placentas (chorionic villi) as well as matched chorion and amnion for 16 of these cases were collected for this study. These samples were profiled using the Illumina Infinium HumanMethylation850 BeadChip to measure DNA methylation (DNAm) at 866,895 CpGs across the genome. An additional 78 placental samples were utilized to independently validate the array findings by pyrosequencing.

RESULTS

Using a false discovery rate of < 0.15 and average group difference in DNAm of > 0.05, 66 differentially methylated (DM) CpG sites were identified between aCA cases and non-aCA cases in chorionic villi. For the majority of these 66 DM CpGs, the DNAm profile of the aCA cases as compared to the non-aCA cases trended in the direction of the blood cell DNAm. Interestingly, neutrophil-specific DNAm signatures, but not those associated with other immune cell types, were capable of separating aCA cases from the non-aCA cases.

CONCLUSIONS

Our results suggest that aCA-associated placentas showed altered DNAm signatures that were not observed in the absence of aCA. This DNAm profile is consistent with the activation of the innate immune response in the placenta and/or reflect increase in neutrophils as a response to inflammation.

Ancestry informative markers and selected single nucleotide polymorphisms in immunoregulatory genes on preterm labor and preterm premature rupture of membranes: a case control study

Background

A genetic predisposition to Preterm Labor (PTL) and Preterm Premature Rupture of Membranes (PPROM) has been suggested; however the relevance of polymorphisms and ancestry to susceptibility to PTL and PPROM in different populations remains unclear. The aim of this study was to evaluate the contribution of maternal and fetal SNPs in the IL1B, IL6, IL6R, TNFA, TNFR, IL10, TLR2, TLR4, MMP9, TIMP1 and TIMP2 genes and the influence of ancestry background in the susceptibility to PTL or PPROM in Brazilian women.

Methods

Case–control study conducted at a tertiary hospital in São Paulo State, Brazil. We included women with PTL or PPROM and their babies (PTL: 136 women and 88 babies; PPROM: 65 women and 44 babies). Control group included 402 mother-babies pairs of term deliveries. Oral swabs were collected for identification of AIMs by fragment analysis and SNPs by Taqman® SNP Genotyping Assays and PCR. Linkage Disequilibrium and Hardy-Weinberg proportions were evaluated using Genepop 3.4. Haplotypes were inferred using the PHASE algorithm. Allele, genotype and haplotype frequencies were compared by Fisher’s exact test or χ² and Odds Ratio. Logistic regression was performed. Clinical and sociodemographic data were analyzed by Fisher’s exact test and Mann–Whitney.

Results

PTL was associated with European ancestry and smoking while African ancestry was protective. The fetal alleles IL10-592C (rs800872) and IL10-819C (rs1800871) were also associated with PTL and the maternal haplotype TNFA-308G-238A was protective. Maternal presence of IL10-1082G (rs1800896) and TLR2A (rs4696480) alleles increased the risk for PPROM while TNFA-238A (rs361525) was protective. Family history of PTL/PPROM was higher in cases, and time to delivery was influenced by IL1B-31T (rs1143627) and TLR4-299G (rs4986790).

Conclusion

There is an association between European ancestry and smoking and PTL in our Brazilian population sample. The presence of maternal or fetal alleles that modify the inflammatory response increase the susceptibility to PTL and PPROM. The family history of PTL/PPROM reinforces a role for genetic polymorphisms in susceptibility to these outcomes.

Postnatal Infections and Immunology Affecting Chronic Lung Disease of Prematurity

Premature infants suffer significant respiratory morbidity during infancy with long-term negative consequences on health, quality of life, and health care costs. Enhanced susceptibility to a variety of infections and inflammation play a large role in early and prolonged lung disease following premature birth, although the mechanisms of susceptibility and immune dysregulation are active areas of research. This article reviews aspects of host-pathogen interactions and immune responses that are altered by preterm birth and that impact chronic respiratory morbidity in these children.

California Very Preterm Birth Study: design and characteristics of the population- and biospecimen bank-based nested case-control study

Very preterm birth (VPTB) is a leading cause of infant mortality, morbidity and racial disparity in the US. The underlying causes of VPTB are multiple and poorly understood. The California Very Preterm Birth Study was conducted to discover maternal and infant genetic and environmental factors associated with VPTB. This paper describes the study design, population, data and specimen collection, laboratory methods and characteristics of the study population. Using a large, population-based cohort created through record linkage of livebirths delivered from 2000 to 2007 in five counties of southern California, and existing data and banked specimens from statewide prenatal and newborn screening, 1100 VPTB cases and 796 control mother-infant pairs were selected for study (385/200 White, 385/253 Hispanic and 330/343 Black cases/controls, respectively). Medical record abstraction of cases was conducted at over 50 hospitals to identify spontaneous VPTB, improve accuracy of gestational age, obtain relevant clinical data and exclude cases that did not meet eligibility criteria. VPTB was defined as birth at <32 weeks in Whites and Hispanics and <34 weeks in Blacks. Approximately 55% of all VPTBs were spontaneous and 45% had medical indications or other exclusions. Of the spontaneous VPTBs, approximately 41% were reported to have chorioamnionitis. While the current focus of the California Very Preterm Birth Study is to assess the role of candidate genetic markers on spontaneous VPTB, its design enables the pursuit of other research opportunities to identify social, clinical and biological determinants of different types of VPTB with the ultimate aim of reducing infant mortality, morbidity and racial disparities in these health outcomes in the US and elsewhere.

Perinatal inflammation and lung injury

Bronchopulmonary dysplasia (BPD) remains the major morbidity of extreme preterm birth. The incidence of BPD has remained stable despite recent efforts to reduce postnatal exposures to volutrauma and hyperoxia. This review will focus on recent clinical and experimental insights that provide support for the concept that the 'new BPD' is the result of inflammation-mediated injury and altered lung development during a window of vulnerability in genetically susceptible infants that is modified by maternal and postnatal exposures.

Evolutionary-developmental perspectives on immune system interactions among the pregnant woman, placenta, and fetus, and responses to sexually transmitted infectious agents

A balance has evolved over deep time between the various immune systems of the "triad" that is linked together for a short period: the pregnant woman, the fetus, and the placenta. This balance is affected by, and helps to determine, the immune responses to maternal infectious agents that may be transmitted to the fetus/infant transplacentally, intrapartum, or via breast milk. This review identifies newer evolutionary concepts and processes related particularly to the human placenta, innate and adaptive immune systems involved in tolerance, and in responses to sexually transmitted infectious (STI) agents that may be pathogenic to the fetus/infant at different gestational periods and in the first year of life. An evolutionary-developmental (EVO-DEVO) perspective has been applied to the complexities within, and among, the different actors and their beneficial or deleterious outcomes. Such a phylogenetic and ontogenic approach has helped to stimulate several basic questions and suggested possible explanations and novel practical interventions.

Association of IL-10-1082 G/G genotype with lower mortality of acute respiratory distress syndrome in a Chinese population

We aimed to investigate whether interleukin-10 (IL-10) -1082 G/G genotype is associated with lower mortality of acute respiratory distress syndrome (ARDS) in a Chinese population. A hospital-based case-control study was conducted in 314 cases of ARDS and 210 controls who were admitted to an intensive care unit with sepsis, trauma, aspiration or massive transfusions. Cases were followed for 30-day mortality. The -1082G/G genotype was associated with lower development of ARDS (OR=0.51; 95% CI 0.34-0.76; P=0.001). Among patients with ARDS, the -1082G/G genotype was associated with lower 30-day mortality (OR=0.44; 95% CI 0.25-0.76; P=0.003). In conclusion, IL-10-1082 G/G genotype is associated with lower development and mortality of ARDS in a Chinese population.

Identification of fetal and maternal single nucleotide polymorphisms in candidate genes that predispose to spontaneous preterm labor with intact membranes

OBJECTIVE

The purpose of this study was to determine whether maternal/fetal single nucleotide polymorphisms (SNPs) in candidate genes are associated with spontaneous preterm labor/delivery.

STUDY DESIGN

A genetic association study was conducted in 223 mothers and 179 fetuses (preterm labor with intact membranes who delivered <37 weeks of gestation [preterm birth (PTB)]), and 599 mothers and 628 fetuses (normal pregnancy); 190 candidate genes and 775 SNPs were studied. Single locus/haplotype association analyses were performed; the false discovery rate was used to correct for multiple testing.

RESULTS

The strongest single locus associations with PTB were interleukin-6 receptor 1 (fetus; P=.000148) and tissue inhibitor of metalloproteinase 2 (mother; P=.000197), which remained significant after correction for multiple comparisons. Global haplotype analysis indicated an association between a fetal DNA variant in insulin-like growth factor F2 and maternal alpha 3 type IV collagen isoform 1 (global, P=.004 and .007, respectively).

CONCLUSION

An SNP involved in controlling fetal inflammation (interleukin-6 receptor 1) and DNA variants in maternal genes encoding for proteins involved in extracellular matrix metabolism approximately doubled the risk of PTB.

TLR9 activation coupled to IL-10 deficiency induces adverse pregnancy outcomes

Pregnancy outcome is severely compromised by intrauterine infections and inflammation. Although the pregnant uterine microenvironment is replete with innate immune cells and TLR expression, the mechanisms that facilitate adverse effects of their activation are largely unknown. In this study, we mimic the activation of TLR9 with its pathogenic ligand hypomethylated CpG and demonstrate that IL-10 proficiency protects against CpG-induced pregnancy complications. We show that fetal resorption and preterm birth are rapidly induced in IL-10(-/-) mice by low doses of CpG (approximately 25 microg/mouse) when injected i.p. on gestational day 6 or gestational day 14, respectively. In contrast, wild-type mice failed to experience such effects at comparable doses, but pups born at term displayed craniofacial/limb defects in response to higher doses (approximately 400 microg/mouse). Pregnancy complications in IL-10(-/-) mice were associated with unexpected and robust TLR9-triggered activation and amplification of uterine neutrophil and macrophage subpopulations followed by their migration to the placental zone. Furthermore, a dramatic increase in serum levels of mouse KC and TNF-alpha production by uterine F4/80(+) cells, but not uterine NK or Gr-1(+)CD11b(+) cells, was observed. Depletion of F4/80(+) macrophages or neutralization of TNF-alpha rescued pregnancy to term. Our results have important implications for IL-10-mediated "uterine tolerance" against CpG-driven innate immune activation.

Immaturity, perinatal inflammation, and retinopathy of prematurity: a multi-hit hypothesis

OBJECTIVE

To explore the relationship among markers of infection/inflammation in their association with retinopathy of prematurity (ROP).

METHODS

We studied clinical characteristics and 4 single nucleotide polymorphisms in infection/inflammation-associated genes in a group of 73 children with a gestational age<32 weeks. Forty-four children (60%) had ROP, of whom 13 (30% of those with ROP) progressed to stage 3 ROP. No child had grade 4 or 5 ROP. We employed both descriptive and analytic statistical methods.

RESULTS

Clinical variables of infection/inflammation were consistently associated with an increased risk of ROP. Among infants with ROP, they were also associated with progression to ROP grade 3. Genetic markers were not associated with ROP occurrence, but with progression to high grade disease. In tri-variable analyses exploring the effects of gestational age <29 weeks, clinical chorioamnionitis (CAM) and neonatal systemic inflammatory response syndrome (SIRS) on ROP occurrence, low gestational age was the most important antecedent, while additional individual or joint exposure to SIRS and CAM add appreciably to this risk of progression to high grade disease.

CONCLUSION

Both antenatal and neonatal exposure to inflammation appear to contribute to the increased ROP risk in preterm infants.

Antioxidant therapy and neuroprotection in the newborn

Injury to the perinatal brain is a leading cause of childhood mortality and lifelong disability. Despite recent improvements in neonatal care, no effective treatment for perinatal brain lesions is available. The newborn, especially if preterm, is highly prone to oxidative stress (OS) and to the toxic effect of free radicals (FRs). At birth, the newborn is exposed to a relatively hyperoxic environment caused by an increased oxygen bioavailability with greatly enhanced generation of FRs. Additional sources (e.g., inflammation, hypoxia, ischemia, glutamate and free iron release) occur, magnifying OS. In the preterm baby, the perinatal transition is accompanied by the immaturity of the antioxidant systems and the reduced ability to induce efficient homeostatic mechanisms designed to control overproduction of cell-damaging FRs. Improved understanding of the pathophysiological mechanism involved in perinatal brain lesions helps to identify potential targets for neuroprotective interventions, and the knowledge of these mechanisms has enabled scientists to develop new therapeutic strategies that have confirmed their neuroprotective effects in animal studies. Considering the growing role of OS in preterm newborn morbidity in respect to the higher risk of FR damage in these babies, erythropoietin, allopurinol, melatonin and hypothermia demonstrate great promise as potential neuroprotectans. This article provides an overview of the pathogenesis of FR-mediated diseases of the newborn and the antioxidant strategies now tested in order to reduce OS and its damaging effects.

Genetic regulation of cervical antiinflammatory cytokine concentrations during pregnancy

OBJECTIVE

The purpose of this study was to evaluate the contribution of maternal genotype to the concentration of interleukin (IL)-4, -10, and -13 in the cervix during the first trimester in the context of bacterial vaginosis and cigarette smoking.

STUDY DESIGN

In this prospective cohort of 116 pregnant women, we examined 72 single nucleotide polymorphisms (SNPs) in 6 genes: IL-4, IL-4 receptor, IL-10, IL-10 receptor alpha, IL-10 receptor beta, and IL-13.

RESULTS

Among black women, an IL-10 receptor beta SNP (rs6517158) demonstrated significant association with IL-10 concentration (P = .04), adjusted for bacterial vaginosis. Among white women, there were 4 SNPs in IL-10 receptor alpha with a highly significant association with IL-10 concentration, adjusted for bacterial vaginosis and smoking.

CONCLUSION

Our data demonstrate a significant relation between cervical concentrations of IL-10 and SNPs in the IL-10 receptor alpha and beta genes. The contribution of genotype to IL-10 concentration is significant, even in the consideration of bacterial vaginosis and smoking.

The anti-inflammatory limb of the immune response in preterm labor, intra-amniotic infection/inflammation, and spontaneous parturition at term: a role for interleukin-10

OBJECTIVE

The anti-inflammatory limb of the immune response is crucial for dampening inflammation. Spontaneous parturition at term and preterm labor (PTL) are mediated by inflammation in the cervix, membranes, and myometrium. This study focuses on the changes in the amniotic fluid concentrations of the anti-inflammatory cytokine interleukin (IL)- 10. The objectives of this study were to determine whether there is a relationship between amniotic fluid concentrations of IL-10 and gestational age, parturition (at term and preterm), and intra-amniotic infection/inflammation (IAI).

STUDY DESIGN

A cross-sectional study was conducted including 301 pregnant women in the following groups: (1) mid-trimester of pregnancy who delivered at term (n = 112); (2) mid-trimester who delivered preterm neonates (n = 30); (3) term not in labor without IAI (n = 40); (4) term in labor without IAI (n = 24); (5) term in labor with IAI (n = 20); (6) PTL without IAI who delivered at term (n = 31); (7) PTL without IAI who delivered preterm (n = 30); (8) PTL with IAI who delivered preterm (n = 14). IL-10 concentrations in amniotic fluid were determined by a specific and sensitive immunoassay. Non-parametric statistics were used for analysis.

RESULTS

(1) IL-10 was detectable in amniotic fluid and its median concentration did not change with gestational age from mid-trimester to term. (2) Patients in labor at term had a significantly higher median amniotic fluid IL-10 concentration than that of patients at term not in labor (p = 0.04). (3) Women at term in labor with IAI had a significantly higher median amniotic fluid IL-10 concentration than that of patients at term in labor without IAI (p = 0.02). (4) Women with PTL and IAI who delivered preterm had a significantly higher median amniotic fluid concentration of IL-10 than those without IAI who delivered preterm and than those who delivered at term (p = 0.009 and p < 0.001, respectively). (5) Among patients with preterm labor without IAI, those who delivered preterm had a significantly higher median amniotic fluid IL-10 concentration than those who delivered at term (p = 0.03).

CONCLUSIONS

The anti-inflammatory cytokine IL-10 is detectable in the amniotic fluid of normal pregnant women. Spontaneous parturition at term and in preterm gestation is associated with increased amniotic fluid concentrations of IL-10. IAI (preterm and at term) is also associated with increased amniotic fluid concentrations of IL-10. We propose that IL-10 has a role in the regulation of the immune response in vivo by initiating actions that dampen inflammation.

Therapeutics for neonatal brain injury

Neonatal brain injury is an important cause of death and neurodevelopmental delay. Multiple pathways of oxidant stress, inflammation, and excitotoxicity lead to both early and late phases of cell damage and death. Therapies targeting these different pathways have shown potential in protecting the brain from ongoing injury. More recent therapies, such as growth factors, have demonstrated an ability to increase cell proliferation and repair over longer periods of time. Even though hypothermia, which decreases cerebral metabolism and possibly affects other mechanisms, may show some benefit in particular cases, no widely effective therapeutic interventions for human neonates exist. In this review, we summarize recent findings in neuroprotection and neurogenesis for the immature brain, including combination therapy to optimize repair.

Oxidative stress-related gene interactions with preterm delivery in Korean women

OBJECTIVE

We hypothesized that the cytochrome P450IA1 (CYP1A1), glutathione S-transferases mu 1 (GSTM1), and theta 1 (GSTT1) polymorphisms are associated with the risk for preterm delivery. This study was undertaken to identify gene-gene interactions and haplotypes that increase the risk of preterm delivery.

STUDY DESIGN

This case-control study was performed in Korea on 145 women with preterm birth and 120 normal controls. Logistic regression and multifactor dimensionality reduction analysis were used to explore single genes and gene-gene interactions, which have an impact on the risk of preterm delivery, respectively.

RESULTS

The GSTM1 null genotype and the interaction between the CYP1A1-I462V and GSTM1 null type conferred a risk of preterm birth. The association between preterm delivery and the CYP1A1-T6235C/I462V haplotype plus GSTM1 null type was verified.

CONCLUSION

The interaction between the CYP1A1-I462V and GSTM1 null genotype were found to increase the risk for preterm birth in Korean women. This finding provides evidence of a gene-gene interaction, which has an impact on preterm delivery.