Methodologic quality and genotyping reproducibility in studies of tumor necrosis factor -308 G-->A single nucleotide polymorphism and bacterial sepsis: implications for studies of complex traits

Haplotypes composed of minor frequency single nucleotide polymorphisms of the TNF gene protect from progression into sepsis: A study using the new sepsis classification

OBJECTIVES

Several articles have provided conflicting results regarding the role of single nucleotide polymorphisms (SNPs) in the promoter region of the TNF gene in susceptibility to sepsis. Former articles have been based on previous definitions of sepsis. This study investigated the influence of TNF haplotypes on the development of sepsis using the new Sepsis-3 definitions.

METHODS

DNA was isolated from patients suffering from infection and systemic inflammatory response syndrome. Haplotyping was performed for six SNPs of TNF. The serum levels of tumour necrosis factor alpha (TNF-α) of these patients were measured using an enzyme immunosorbent assay. Patients were classified into infection and sepsis categories using the Sepsis-3 definitions. Associations between the TNF haplotypes and the clinical characteristics and serum TNF-α levels of the patients were examined.

RESULTS

The most common TNF haplotype h1 was composed of major alleles of the studied SNPs. Carriage of haplotypes composed of minor frequency alleles was associated with a lower risk of developing sepsis (odds ratio 0.41, 95% confidence interval 0.19-0.88, p=0.022), but this did not affect the 28-day outcome. Serum TNF-α levels were significantly higher among patients homozygous for h1 haplotypes who developed sepsis compared to infection (p=0.032); a similar result was not observed for patients carrying other haplotypes.

CONCLUSIONS

Haplotypes containing minor frequency SNP alleles of TNF protect against the development of sepsis without affecting the outcome.

Collagen type III alpha 1 polymorphism (rs1800255, COL3A1 2209 G>A) assessed with high-resolution melting analysis is not associated with pelvic organ prolapse in the Dutch population

INTRODUCTION AND HYPOTHESIS

The rs1800255, COL3A1 2209 G>A polymorphism in the alpha 1 chain of collagen type III has been associated with an increased risk of pelvic organ prolapse (POP). In one of our previous studies however, polymerase chain reaction-based restriction fragment length polymorphism (PCR-RFLP) misdiagnosed rs1800255, COL3A1 2209 G>A in 6 % of cases. The high-resolution melting (HRM) analysis on the contrary obtained a 100 % accordance for this specific polymorphism and was used in the present study to validate this risk factor for POP.

METHODS

In this case-control study, women with and without symptoms of POP were included and compared. DNA was extracted from blood samples. HRM analysis was used to assess for the presence of the homozygous rs1800255. Groups were compared using the Pearson chi-square, Mann-Whitney, and t tests. The discrepancy between HRM and PCR-RFLP results was investigated using PCR-RFLP results available from our previous study.

RESULTS

The study included 354 women: 272 patients with POP and 82 controls; 18 (7 %) cases versus 3 (4 %) controls had a homozygous rs1800255, COL3A1 2209 G>A polymorphism (odds ratio 1.9, 95 % confidence interval 0.5-6.9, compared to the wild type), and thus no association between POP and the homozygous polymorphism could be demonstrated. A discrepancy between HRM and PCR-RFLP results was found in 8 % of the samples.

CONCLUSIONS

The previously found statistically significant association between the rs1800255, COL3A1 2209 G>A polymorphism as measured with PCR-RFLP and POP could no longer be demonstrated. This raises concerns regarding the results of other association studies using PCR-RFLP.

Assessment of systematic effects of methodological characteristics on candidate genetic associations

Candidate genetic association studies have been found to have a low replication rate in the past. Here, we aimed to assess whether aspects of reported methodological characteristics in genetic association studies may be related to the magnitude of effects observed. An observational, literature-based investigation of 511 case-control studies of genetic association studies indexed in 2007, was undertaken. Meta-regression analyses were used to assess the relationship between 23 reported methodological characteristics and the magnitude of genetic associations. The 511 studies had been conducted in 52 countries and were published in 220 journals (median impact factor 5.1). The multivariate meta-regression model of methodological characteristics plus disease category accounted for 17.2 % of the between-study variance in the magnitude of the reported genetic associations. Our findings are consistent with the view that better conducted and better reported genetic association research may lead to less inflated results.

Prediction of sepsis-related outcomes in neonates through systematic genotyping of polymorphisms in genes for innate immunity and inflammation: a narrative review and critical perspective

CONTEXT AND OBJECTIVE

Neonatal sepsis is associated with premature birth and maternal infection. Large-scale studies seek to define markers that identify neonates at risk of developing sepsis. Here, we examine whether the scientific evidence supports systematic use of polymorphism genotyping in cytokine and innate immunity genes, to identify neonates at increased risk of sepsis.

DESIGN AND SETTING

Narrative literature review conducted at Fernandes Figueira Institute, Brazil.

METHODS

The literature was searched in PubMed, Embase (Excerpta Medica Database), Lilacs (Literatura Latino-Americana e do Caribe em Ciências da Saúde), SciELO (Scientific Electronic Library Online) and Cochrane Library. From > 400,000 references, 548 were retrieved based on inclusion/exclusion criteria; 22 were selected for detailed analysis after quality assessment.

RESULTS

The studies retrieved addressed the impact of gene polymorphisms relating to immune mechanisms (most often TNF-a, LT-a, IL-6, IL-1β, IL-1ra, L-selectin, CD14 and MBL) or inflammatory mechanisms (ACE and angiotensin II receptors; secretory PLA2; and hemostatic factors). Despite initial reports suggesting positive associations between specific polymorphisms and increased risk of sepsis, the accumulated evidence has not confirmed that any of them have predictive power to justify systematic genotyping.

CONCLUSIONS

Sepsis prediction through systematic genotyping needs to be reevaluated, based on studies that demonstrate the functional impact of gene polymorphisms and epidemiological differences among ethnically distinct populations.

STrengthening the REporting of Genetic Association Studies (STREGA)--an extension of the STROBE statement

Making sense of rapidly evolving evidence on genetic associations is crucial to making genuine advances in human genomics and the eventual integration of this information in the practice of medicine and public health. Assessment of the strengths and weaknesses of this evidence, and hence the ability to synthesize it, has been limited by inadequate reporting of results. The STrengthening the REporting of Genetic Association studies (STREGA) initiative builds on the STrengthening the Reporting of OBservational Studies in Epidemiology (STROBE) Statement and provides additions to 12 of the 22 items on the STROBE checklist. The additions concern population stratification, genotyping errors, modelling haplotype variation, Hardy-Weinberg equilibrium, replication, selection of participants, rationale for choice of genes and variants, treatment effects in studying quantitative traits, statistical methods, relatedness, reporting of descriptive and outcome data, and the volume of data issues that are important to consider in genetic association studies. The STREGA recommendations do not prescribe or dictate how a genetic association study should be designed but seek to enhance the transparency of its reporting, regardless of choices made during design, conduct, or analysis.

STrengthening the REporting of Genetic Association studies (STREGA)--an extension of the STROBE statement

Making sense of rapidly evolving evidence on genetic associations is crucial to making genuine advances in human genomics and the eventual integration of this information in the practice of medicine and public health. Assessment of the strengths and weaknesses of this evidence, and hence the ability to synthesize it, has been limited by inadequate reporting of results. The STrengthening the REporting of Genetic Association studies (STREGA) initiative builds on the STrengthening the Reporting of OBservational Studies in Epidemiology (STROBE) Statement and provides additions to 12 of the 22 items on the STROBE checklist. The additions concern population stratification, genotyping errors, modelling haplotype variation, Hardy-Weinberg equilibrium, replication, selection of participants, rationale for choice of genes and variants, treatment effects in studying quantitative traits, statistical methods, relatedness, reporting of descriptive and outcome data and the volume of data issues that are important to consider in genetic association studies. The STREGA recommendations do not prescribe or dictate how a genetic association study should be designed, but seek to enhance the transparency of its reporting, regardless of choices made during design, conduct or analysis.

STrengthening the REporting of Genetic Association Studies (STREGA): an extension of the STROBE statement

Making sense of rapidly evolving evidence on genetic associations is crucial to making genuine advances in human genomics and the eventual integration of this information in the practice of medicine and public health. Assessment of the strengths and weaknesses of this evidence, and hence the ability to synthesize it, has been limited by inadequate reporting of results. The STrengthening the REporting of Genetic Association studies (STREGA) initiative builds on the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Statement and provides additions to 12 of the 22 items on the STROBE checklist. The additions concern population stratification, genotyping errors, modelling haplotype variation, Hardy-Weinberg equilibrium, replication, selection of participants, rationale for choice of genes and variants, treatment effects in studying quantitative traits, statistical methods, relatedness, reporting of descriptive and outcome data, and the volume of data issues that are important to consider in genetic association studies. The STREGA recommendations do not prescribe or dictate how a genetic association study should be designed but seek to enhance the transparency of its reporting, regardless of choices made during design, conduct, or analysis.

Strengthening the reporting of genetic association studies (STREGA): an extension of the STROBE statement

Making sense of rapidly evolving evidence on genetic associations is crucial to making genuine advances in human genomics and the eventual integration of this information in the practice of medicine and public health. Assessment of the strengths and weaknesses of this evidence, and hence the ability to synthesize it, has been limited by inadequate reporting of results. The STrengthening the REporting of Genetic Association studies (STREGA) initiative builds on the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Statement and provides additions to 12 of the 22 items on the STROBE checklist. The additions concern population stratification, genotyping errors, modeling haplotype variation, Hardy–Weinberg equilibrium, replication, selection of participants, rationale for choice of genes and variants, treatment effects in studying quantitative traits, statistical methods, relatedness, reporting of descriptive and outcome data, and the volume of data issues that are important to consider in genetic association studies. The STREGA recommendations do not prescribe or dictate how a genetic association study should be designed but seek to enhance the transparency of its reporting, regardless of choices made during design, conduct, or analysis.

INS VNTR is not associated with childhood obesity in 1,023 families: a family-based study

Previous studies have described genetic associations of the insulin gene variable number tandem repeat (INS VNTR) variant with childhood obesity and associated phenotypes. We aimed to assess the contribution of INS VNTR genotypes to childhood obesity and variance of insulin resistance, insulin secretion, and birth weight using family-based design. Participants were either French or German whites. We used transmission disequilibrium tests (TDTs) for assessing binary traits and quantitative pedigree disequilibrium tests for assessing continuous traits. In contrast to previous findings, we did not observe any familial association with childhood obesity (T = 50%, P = 0.77) in the 1,023 families tested. In French obese children, INS VNTR did not associate with fasting insulin levels (P = 0.23) and class I allele showed only borderline association with increased insulin secretion index at 30 min (P = 0.03). INS VNTR did not associate with birth weight in obese children (P = 0.98) and TDT analyses in 350 French families with history of low birth weight (LBW) showed no association with this condition (P = 0.92). In summary, our study, the largest performed so far, does not support the previously reported associations between INS VNTR and childhood obesity, insulin resistance, or birth weight, and does not suggest any major role for this variant in modulating these traits.

Reporting of human genome epidemiology (HuGE) association studies: an empirical assessment

BACKGROUND

Several thousand human genome epidemiology association studies are published every year investigating the relationship between common genetic variants and diverse phenotypes. Transparent reporting of study methods and results allows readers to better assess the validity of study findings. Here, we document reporting practices of human genome epidemiology studies.

METHODS

Articles were randomly selected from a continuously updated database of human genome epidemiology association studies to be representative of genetic epidemiology literature. The main analysis evaluated 315 articles published in 2001-2003. For a comparative update, we evaluated 28 more recent articles published in 2006, focusing on issues that were poorly reported in 2001-2003.

RESULTS

During both time periods, most studies comprised relatively small study populations and examined one or more genetic variants within a single gene. Articles were inconsistent in reporting the data needed to assess selection bias and the methods used to minimize misclassification (of the genotype, outcome, and environmental exposure) or to identify population stratification. Statistical power, the use of unrelated study participants, and the use of replicate samples were reported more often in articles published during 2006 when compared with the earlier sample.

CONCLUSION

We conclude that many items needed to assess error and bias in human genome epidemiology association studies are not consistently reported. Although some improvements were seen over time, reporting guidelines and online supplemental material may help enhance the transparency of this literature.

Genetic approach to pediatric septic shock

Septic shock is a complex and heterogeneous clinical syndrome, triggered by infection, and having significant morbidity and mortality in children. Emerging data indicate that the genetic make-up of the pediatric host may have a strong influence on the development and outcome of septic shock in children. Herein, we review this broad topic by focusing on pediatric-specific data (both recent and historical), as well as the broad topics of SNPs, genome-wide association studies and epigenetics. The historical and emerging data strongly suggest that a genetics-based perspective will need to be considered in future investigations and strategies aimed at improving the outcome of children with septic shock.

The Genetics of Sepsis: The Promise, the Progress and the Pitfalls

Physicians are used to taking a family history of cardiovascular disease because of the known significant hereditary risk; yet the familial risk of dying from infection is even greater than that for atherosclerotic disease (Sorensen et al. 1988). There is certainly no doubt that genetic differences impact on the risk of developing or dying from infection. Obvious but rare examples include selective immunoglobulin deficiencies, complement deficiencies, and neutrophil function abnormalities. Genetic factors may also be protective, such as with sickle cell trait and malaria or mutations conferring resistance to human immunodeficiency virus infection.

Much more subtle differences in immune responses are now being described, usually as the result of one or more single nucleotide polymorphisms (SNP) in a gene. Rather than causing the failure of production of a protein or the production of a nonfunctional protein, SNPs are usually associated with changes in the rate of transcription, producing a much less severe phenotype than the classical examples of genetic defects mentioned above. It is now being appreciated that for many complex diseases, such as sepsis, the ultimate phenotype is the result of the interaction of genetic differences across many loci, not the dominant effect of a few key mutations.

As seen in Fig. 3.1, since the mid 1990s, an increasing body of literature has focused on the role that gene polymorphisms in key inflammatory genes play in sepsis. Indeed, with advances in knowledge of the human genome, greater understanding of the inflammatory response, and the development of high throughput genotyping technologies, so many genetic associations have been described that discussion of each one is well beyond the scope of this chapter. I will however summarize those findings that have been reported by multiple groups, as well as give an overview of the major groups of genes that have been implicated in genetic predisposition to sepsis and its adverse outcomes.

A systematic review of the quality of genetic association studies in human sepsis

OBJECTIVE

Epidemiological studies demonstrate that inherited factors play a major role in the development and prognosis of sepsis. However, genetic association studies in sepsis have produced contradictory evidence of an effect from individual polymorphisms. Major methodological flaws have been reported in a number of genetic association studies in non-septic populations, relating to problems with experimental design, statistical analysis, study size, power and replication. We hypothesised that genetic association studies investigating sepsis suffer from similar problems, and that this explains the lack of consistent evidence for an effect from polymorphisms.

DESIGN

A systematic review was conducted of published genetic association studies in sepsis from 1996-2005 using a newly devised scoring system for study quality and rigour. A Bayesian statistical analysis was also carried out to assess the false-positive report probability of identified studies.

MEASUREMENTS AND RESULTS

Study quality was assessed using a 10-point scoring system designed from published reporting guidelines. The majority of studies were of low to intermediate quality, with deficiencies in control group selection, genetic assay technique, study blinding, statistical interpretation, study replication, study size and power. Bayesian analysis indicated that many of the studies reporting a positive association between a genetic polymorphism and sepsis were likely to represent false-positive associations.

CONCLUSIONS

The quality and size of genetic association studies in septic patients needs to improve if advances in identifying genetic effects in sepsis are to occur. Investigators should, as a minimum, follow recommended guidelines when designing studies.

Biomarkers of sepsis

Sepsis is a highly heterogeneous clinical disorder currently characterized almost exclusively by the use of physiologic variables. A burgeoning interest in the potential descriptive role of biomarkers in sepsis holds the promise of transforming the diagnosis from a clinical one to a biologic one, and so permitting better evaluation and use of a spectrum of adjuvant therapies. Biomarkers provide information in one of three domains: diagnosis, prognosis, and monitoring of response to treatment. Their primary prognostic utility, however, is not in forecasting outcome, but in identifying patients who are more likely to benefit from (or be harmed by) a particular intervention. A proposed template for staging sepsis in a manner analogous to systems used in oncology provides a framework for evaluating sepsis biomarkers. The model stratifies patients on the basis of predisposition, insult, response, and organ dysfunction, generating the acronym PIRO. This brief review considers the methodologic basis for biomarker development and validation and situates some emerging sepsis biomarkers within the framework of the PIRO model.

What is new in cytokine research related to trauma/critical care

Cytokines are low molecular weight proteins whose production can be modified by various insults. They have the potential to modify cellular responses to these insults. Recent years have seen a plethora of research in cytokine biology in trauma and critical care.

APOE polymorphism is associated with risk of severe sepsis in surgical patients

OBJECTIVE

To test for an association between apolipoprotein E (APOE) genotypes and the occurrence of severe sepsis in an elective surgical cohort.

DESIGN

Prospective, observational, single cohort study.

SETTING

Sixteen-bed surgical intensive care unit (ICU) at a university hospital.

PATIENTS

Patients were 343 patients with planned admission to the ICU after major elective noncardiac surgery.

INTERVENTIONS

Blood samples, together with demographic data, baseline clinical data, and Acute Physiology and Chronic Health Evaluation II scores, were collected on admission to the ICU and on each subsequent ICU day. APOE genotyping was conducted using a polymerase chain reaction-based assay. The primary outcome was diagnosis of severe sepsis; secondary outcomes included time on mechanical ventilation, ICU length of stay, and ICU mortality.

MEASUREMENTS AND MAIN RESULTS

Severe sepsis was diagnosed in 34 of 343 patients (9.9%). Carriers of the APOepsilon3 allele (one or two copies) had a lower incidence of severe sepsis than patients with no APOepsilon3 allele (p = .014), with a relative risk of 0.284 (95% confidence interval 0.127-0.635). The protective effect of APOepsilon3 genotype on the incidence of severe sepsis remained significant (p < .01) after adjusting for age, gender, or race in a logistic regression model. Supporting our findings, presence of the APOepsilon3 allele was also associated with fewer days spent in the ICU (p = .007). In contrast, APOE genotypes were not associated with duration of mechanical ventilation or ICU mortality.

CONCLUSIONS

In an elective surgical cohort, presence of the APOepsilon3 allele is associated with decreased incidence of severe sepsis and a shorter ICU length of stay.

Defining the proinflammatory phenotype using high sensitive C-reactive protein levels as the biomarker

CONTEXT

Inflammation is pivotal in atherosclerosis. The prototypic marker of inflammation is C-reactive protein (CRP). Numerous studies have confirmed that high CRP levels in normal volunteers predict cardiovascular events.

OBJECTIVE

The objective of this study was to define proximal and associated abnormalities of the proinflammatory phenotype using CRP levels as the biomarker.

DESIGN AND SUBJECTS

Two groups of normal, healthy subjects, selected by stringent criteria from an initial cohort of 252, were studied over the period of 12 months. Group 1 included subjects with consistently low CRP (<0.004 microM or <0.5 mg/liter; low CRP group; n = 15). Group 2 included subjects with consistently high CRP (>2.0 or >0.016 microM to <10 mg/liter or <0.085 microM; high CRP group; n = 13).

MAIN OUTCOME MEASURES

Fasting blood (50 ml) was obtained, and the following parameters were assayed: high sensitivity CRP, fibrinogen, lipid profile, insulin, whole blood cytokines after stimulation with lipopolysaccharide (LPS; 100 ng/ml for 24 h), soluble cell adhesion molecules, plasminogen activator inhibitor-1, CD40, CD40 ligand, leptin, adiponectin, monocyte chemoattractant protein-1, IL-8, matrix metalloproteinase-3 (MMP-3), and MMP-9. Genomic DNA was obtained from peripheral blood leukocytes, and the TNF-alpha -308 genotype was determined.

RESULTS

The median CRP levels were 0.0018 microM (0.21 mg/liter) and 0.031 microM (3.7 mg/liter) for the low and high groups, respectively. High CRP subjects were older and had significantly higher body mass indexes, triglycerides, insulin, homeostasis model assessment, and leptin levels compared with low CRP subjects. The markers of inflammation, plasminogen activator inhibitor-1, MMP-9, fibrinogen, and vascular cell adhesion molecule-1 levels were significantly higher in the high compared with the low CRP group. LPS-stimulated levels of whole blood IL-1beta, IL-6, and TNF were significantly higher, and IL-4 levels were significantly lower in the high CRP group. After age- and body mass index-adjusted analysis of covariance, only plasma MMP-9 levels and LPS-stimulated whole blood IL-1beta and TNF levels were significantly higher in the high CRP group. The frequency of the rare A allele at TNF-alpha -308 was equivalent in high and low CRP groups.

CONCLUSIONS

A phenotype characterized by increased plasma inflammatory mediators as well as increased LPS-stimulated whole blood TNF-alpha and IL-1beta levels is associated with high plasma CRP levels. This systemic inflammatory phenotype may contribute to vascular inflammation or may reflect inflammation in vessels or at other sites.

Relationship between the Arg72Pro Polymorphism of p53 and outcome for patients with traumatic brain injury

OBJECTIVE

To determine the relationship between the Arg72Pro polymorphism of p53 and the outcome after traumatic brain injury (TBI) in humans.

DESIGN AND SETTING

A prospective study was carried out in a ten-bed surgical intensive care unit (SICU) of a university hospital.

PATIENTS

The study included 90 caucasian patients who had experienced a severe TBI within the previous 24 h. The exclusion criterion was a previous deficit in the central nervous system.

MEASUREMENTS AND RESULTS

The main recorded outcomes were values on the Glasgow Outcome Scale (GOS) at discharge from the SICU (GOS-0) and 6 months later (GOS-6). A blood sample was taken from each patient and all samples were analyzed by an allele-specific polymerase chain reaction for detection of Arg72Pro polymorphism of p53. These polymorphisms were tested for their association with values of GOS-0 and GOS-6. A two-tailed value of p<0.05 was considered statistically significant. The frequency of the argine/argine (Arg/Arg) genotype was greater among the patients who had a bad outcome at GOS-0 (69 vs 31% in the bad-outcome group; p=0.029). A multiple logistic regression analysis showed that patients with the Arg/Arg variation had a 2.9-fold greater risk of having a bad outcome at discharge from the SICU (95% confidence interval, 1.05-8.31; p=0.039 ). There was no similar relationship with respect to GOS-6.

CONCLUSION

The Arg/Arg genotype of the Arg72Pro polymorphism in p53 is associated with increased likelihood of a bad outcome at discharge from the SICU.

Assessing the quality of case-control association studies on the genetic basis of sepsis

OBJECTIVE

To define methodological standards that would improve the quality and reproducibility of case-control genetic association studies in sepsis.

DESIGN

Summary of the published standards.

RESULTS

Twelve main criteria and measures for evaluation of those criteria were developed from a variety of reviews and editorials on the subject.

CONCLUSIONS

Case-control candidate gene association studies represent an important tool for understanding the role that genes play in the pathogenesis of sepsis. It is important, however, to understand the limitations of these studies and the need for replication.

TNF and TNFR polymorphisms in severe sepsis and septic shock: a prospective multicentre study

Tumour necrosis factor (TNF) is an important pro-inflammatory cytokine produced in sepsis. Studies examining the association of individual TNF single nucleotide polymorphisms with sepsis have produced conflicting results. This study investigated whether common polymorphisms of the TNF locus and the two receptor genes, TNFRSF1A and TNFRSF1B, influence circulating levels of encoded proteins, and whether individual polymorphisms or extended haplotypes of these genes are associated with susceptibility, severity of illness or outcome in adult patients with severe sepsis or septic shock. A total of 213 Caucasian patients were recruited from eight intensive care units (ICU) in the UK and Australia. Plasma levels of TNF (P = 0.02), sTNFRSF1A (P = 0.005) and sTNFRSF1B (P = 0.01) were significantly higher in those who died on ICU compared to those who survived. There was a positive correlation between increasing soluble receptor levels and organ dysfunction (increasing SOFA score) (sTNFRSF1A R = 0.51, P < 0.001; sTNFRSF1B R = 0.53, P < 0.001), and in particular with the degree of renal dysfunction. In this study, there were no significant associations between the selected candidate TNF or TNF receptor polymorphisms, or their haplotypes, and susceptibility to sepsis, illness severity or outcome. The influence of polymorphisms of the TNF locus on susceptibility to, and outcome from sepsis remains uncertain.

Genetic determinants of the inflammatory response

PURPOSE OF REVIEW

Despite substantial advances in our understanding of the biology of sepsis and inflammation, improvements in clinical outcomes have been more sporadic and, with few notable exceptions, are related to improvements in supportive care rather than to specific therapies. As a result, morbidity, mortality, and cost remain high. Investigation into the genetic determinants of this response span a broad spectrum and include those aimed at deciphering the mechanisms and involved pathways on a molecular level, to those aiming to identify how genetic variation may be clinically important. While it is clear that gene sequencing and manipulation of experimental models have provided insight into the biology of the inflammatory response to infection, these technologies and their application to the study of naturally occurring human genetic variation have yet to provide the same insight or clinical benefit. The purpose of this review is to summarize what is known about the genetic determinants of the inflammatory response. We make particular reference to this broad scope of investigation introduced above but with a focus on the present status of studies examining the role of human genetic variation in the risk for and outcome from severe bacterial infection, or sepsis.

RECENT FINDINGS

Using the examples of two candidate genes tumor necrosis factor-alpha (TNF-alpha) and toll-like receptor 4 (TLR4), we illustrate the spectrum of studies concerning the genetic determinants of the inflammatory response. We highlight recent literature across this spectrum, focusing on genetic association studies examining the relationships between SNPs in these genes and sepsis risk and outcome. We then review the literature addressing discordant findings in basic experimental observations and studies of clinical association.

SUMMARY

Naturally occurring genetic variants in important inflammatory mediators such as TNF-alpha and TLR4 appear to alter inflammatory responses in numerous experimental and a few clinical models of inflammation. However, inconsistencies exist in the literature regarding the association between these genetic variants and disease (eg, sepsis) susceptibility and prognosis. The main limitations relate to the translation of experimental observations into reproducible genotype-phenotype associations. The reasons for these are multifactorial and include deficiencies in study design (insufficient sample size), and the complexities introduced by background genetic heterogeneity.