A TIR domain receptor-associated protein (TIRAP) variant SNP (rs8177374) confers protection against premature birth

Emerging role of toll-like receptors signaling and its regulators in preterm birth: a narrative review

INTRODUCTION

Despite intensive research, preterm birth (PTB) rates have not decreased significantly in recent years due to a lack of understanding of the underlying causes and insufficient treatment options for PTB. We are committed to finding promising biomarkers for the treatment of PTB.

METHODS

An extensive search of the literature was conducted with MEDLINE/PubMed, and in total, 151 studies were included and summarized in the present review.

RESULTS

Substantial evidence supports that the infection and/or inflammatory cascade associated with infection is an early event in PTB. Toll-like receptor (TLR) is a prominent pattern recognition receptor (PRR) found on both immune and non-immune cells, including fetal membrane cells. The activation of TLR downstream molecules, followed by TLR binding to its ligand, is critical for infection and inflammation, leading to the involvement of the TLR signaling pathway in PTB. TLR ligands are derived from microbial components and molecules released by damaged and dead cells. Particularly, TLR4 is an essential TLR because of its ability to recognize lipopolysaccharide (LPS). In this comprehensive overview, we discuss the role of TLR signaling in PTB, focus on numerous host-derived genetic and epigenetic regulators of the TLR signaling pathway, and cover ongoing research and prospective therapeutic options for treating PTB by inhibiting TLR signaling.

CONCLUSION

This is a critical topic because TLR-related molecules and mechanisms may enable obstetricians to better understand the physiological changes in PTB and develop new treatment and prevention strategies.

Evidence of a gene-environment interaction of NODAL variants and inflammation in preterm birth

OBJECTIVE

NODAL has been implicated in timing of parturition and immune regulation. We investigated the relationship between NODAL polymorphisms, infection/inflammation, and preterm birth.

STUDY DESIGN

For this secondary analysis, 613 women (189 preterm and 424 term) from the Montreal Prematurity Study were genotyped for NODAL polymorphisms and assessed for bacterial vaginosis and placental inflammation.

RESULT

NODAL polymorphisms were not associated with preterm birth. However, the rs2231947(C>T) variant allele was associated with increased risk for preterm birth among women with bacterial vaginosis (odds ratio: 2.76, 95% confidence interval: 1.12-6.85). Among women without placental inflammation, the rs1904589(A>G) variant allele was associated with increased risk of preterm birth (odds ratio: 1.31, 95% confidence interval: 1.02-1.70). Among women with placental inflammation, the rs10999338(C>T) variant allele was associated with reduced risk of preterm birth (odds ratio: 0.50, 95% confidence interval: 0.29-0.87).

CONCLUSION

The effect of NODAL polymorphisms on preterm birth depends on maternal infection/inflammation status.

The Burden of Genetic and Epigenetic Traits in Prematurity

Despite decades of investigations and accumulated scientific knowledge, preterm birth (PTB) remains a significant burden worldwide. Several mechanisms have been proposed to explain this condition, and a number of risk factors from infectious to behavioral and genetic/epigenetic factors influence this outcome. The heritability of PTB is estimated to be 17% to 36%, which demonstrates that genetic predisposition plays a key role in PTB. Structural DNA modifications without changes in the DNA sequence and post-transcriptional regulation also have an impact on gene expression and thus influence pregnancy outcomes. There is a complex interplay between environmental factors and the individual's genetics and epigenetics that may culminate in PTB, but the complete regulatory pathways and networks involved in this context are still unclear. Here, we outline what is known so far about the genetic and epigenetic factors involved in preterm delivery, including polymorphisms, DNA methylation, and microRNAs, and suggest fields for research.

Spontaneous preterm birth and single nucleotide gene polymorphisms: a recent update

Background

Preterm birth (PTB), birth at <37 weeks of gestation, is a significant global public health problem. World-wide, about 15 million babies are born preterm each year resulting in more than a million deaths of children. Preterm neonates are more prone to problems and need intensive care hospitalization. Health issues may persist through early adulthood and even be carried on to the next generation. Majority (70 %) of PTBs are spontaneous with about a half without any apparent cause and the other half associated with a number of risk factors. Genetic factors are one of the significant risks for PTB. The focus of this review is on single nucleotide gene polymorphisms (SNPs) that are reported to be associated with PTB.

Results

A comprehensive evaluation of studies on SNPs known to confer potential risk of PTB was done by performing a targeted PubMed search for the years 2007–2015 and systematically reviewing all relevant studies. Evaluation of 92 studies identified 119 candidate genes with SNPs that had potential association with PTB. The genes were associated with functions of a wide spectrum of tissue and cell types such as endocrine, tissue remodeling, vascular, metabolic, and immune and inflammatory systems.

Conclusions

A number of potential functional candidate gene variants have been reported that predispose women for PTB. Understanding the complex genomic landscape of PTB needs high-throughput genome sequencing methods such as whole-exome sequencing and whole-genome sequencing approaches that will significantly enhance the understanding of PTB. Identification of high risk women, avoidance of possible risk factors, and provision of personalized health care are important to manage PTB.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3089-0) contains supplementary material, which is available to authorized users.

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.

A toll-like receptor 9 (rs352140) variant is associated with placental inflammation in newborn infants

OBJECTIVE

Chorioamnionitis contributes to premature birth and associated postnatal morbidity. The genetic basis of altered immune responses underlying placental inflammation (PI) remains understudied. The aim of this study was to evaluate the relationship among TLR signaling pathway polymorphisms and different patterns of PI.

METHODS

Prospective cohort study in infants involving cord blood collection and placental examination for PI. One hundred and fifty-nine infants enrolled in study out of which 28 were term (eight with PI) and 131 preterm (47 with PI). DNA from blood was genotyped for SNPs in TLR2, 4, 5, 9, NFKBI, NFKBIA, TIRAP, and IRAK1 genes using multiplexed single base extension assay.

RESULTS

While there were no differences in BW, GA, gender, race, and SPL among infants with or without PI, there was a higher incidence of PPROM, maternal smoking, drug use, and clinical chorioamnionitis among infants with PI. Out of nine TLR variants, only CT and/or TT genotypes of the TLR9 variant (rs352140) were significantly associated (p = 0.004) with any PI and maternal pattern of inflammation (p = 0.012) both by univariate analysis and logistic regression.

CONCLUSIONS

The presence of a variant T allele in a common SNP (rs352140) in the TLR9 gene whose product recognizes bacterial DNA is associated with increased PI.

Genetics and preterm birth

Although the etiology of preterm birth is incompletely understood, phenotype classifications combined with recent technologies such as genome-wide association studies and next-generation sequencing could lead to discovering genotypes associated with preterm birth. Identifying genetic contributions will allow for genetic screening tests to predict or detect pregnancies with potential for preterm birth. In this article we discuss current knowledge regarding phenotype classifications, genotypes, and their associations with preterm birth.