Detecting genetic predisposition for complicated clinical outcomes after burn injury

Sepsis, septic shock and organ failure are common among patients with moderate to severe burns. The inability of demographic and clinical factors to identify patients at high risk for such complications suggests that genetic variation may influence clinical outcome. Moreover, the genetic predisposition to death from infection has been estimated to be greater than for cardiovascular disease or cancer . While it is widely accepted that genetic factors influence many complex disease processes, controversy has emerged regarding the most appropriate methods for detection and even the validity of many published allelic associations . This article will review the few studies of genetic predisposition that have been conducted in the setting of burn injury, then discuss some of the obstacles and potential approaches for the discovery of additional allelic associations.

TLR4 and TNF-alpha polymorphisms are associated with an increased risk for severe sepsis following burn injury

CONTEXT

Sepsis, organ failure, and shock remain common among patients with moderate to severe burn injuries. The inability of clinical factors to identify at-risk patients suggests that genetic variation may influence the risk for serious infection and the outcome from severe injury.

OBJECTIVE

Resolution of genetic variants associated with severe sepsis following burn injury.

PATIENTS

A total of 159 patients with burns > or =20% of their total body surface area or any smoke inhalation injury without significant non-burn related trauma (injury severity score (ISS)> or =16), traumatic or anoxic brain injury, or spinal cord injury and who survived more than 48 h post-admission.

METHODS

Candidate single nucleotide polymorphisms (SNPs) within bacterial recognition (TLR4 +896, CD14 -159) and inflammatory response (TNF-alpha -308, IL-1beta -31, IL-6 -174) loci were evaluated for association with increased risk for severe sepsis (sepsis plus organ dysfunction or septic shock) and mortality.

RESULTS

After adjustment for age, full-thickness burn size, ethnicity, and gender, carriage of the TLR4 +896 G-allele imparted at least a 1.8-fold increased risk of developing severe sepsis following a burn injury, relative to AA homozygotes (adjusted odds ratio (aOR) 6.4; 95% confidence interval (CI) 1.8 to 23.2). Carriage of the TNF-alpha -308 A-allele imparted a similarly increased risk, relative to GG homozygotes (aOR = 4.5; 95% CI 1.7 to 12.0). None of the SNPs examined were significantly associated with mortality.

CONCLUSIONS

The TLR4 +896 and TNF-alpha -308 polymorphisms were significantly associated with an increased risk for severe sepsis following burn trauma.

Hierarchical modeling of gene-environment interactions: estimating NAT2 genotype-specific dietary effects on adenomatous polyps

Data sparseness currently limits gene-environment interaction estimation. To improve effect estimates of gene-environment interactions, we give an overview of one approach, hierarchical modeling, and propose a two-stage hierarchical model. The first stage is a logistic model for the joint effects of the genetic and environmental factors. The second stage regresses the joint effects on genotype-specific enzymatic activity of the environmentally derived substrate. The model is illustrated using a case-control study of adenomas of the large bowel, for which NAT2 genotype and dietary data were collected. The first-stage interactions of dietary components and genotype were regressed on initial conversion rates of dietary heterocyclic amines to aryl nitrenium ions. We fit the hierarchical model by penalized likelihood. Compared to effect estimates from maximum-likelihood logistic regression, hierarchical results are more reasonable and precise. These results lend further support to previous observations that hierarchical regression is preferable to ordinary logistic regression when multiple factors and their interactions are being studied. We propose that hierarchical modeling can act as a bridge between molecular epidemiology studies and laboratory data, combining both efficiently.

A linkage analysis of D17S74 (CMM86) in thirty-five families with premenopausal bilateral breast cancer

We report here results of a linkage analysis of a marker in 35 families in which the proband had premenopausal bilateral breast cancer. This group is of particular interest given their high family risk and the question of etiological heterogeneity. Probands were ascertained from cancer registries in Los Angeles County and Connecticut and major hospitals in Montréal and Québec. Assuming no residual heterogeneity and summing lod scores over all families, we obtained strong evidence against tight linkage (e.g., lod score at theta = 0.000001 is -3.39). To address the issue of heterogeneity, we performed admixture and predivided sample analyses. Using an admixture model we were able to reject the hypothesis of no linkage versus that of linkage with homogeneity (P = 0.045). However, we were unable to reject the hypothesis of no linkage versus linkage with heterogeneity (P = 0.119) or to distinguish between linkage with homogeneity and linkage with heterogeneity (P = 0.500). Predivided sample analyses based upon age of onset, pathological characteristics, time between diagnoses of the breast cancers in each bilateral proband, and the span of ages at diagnoses within a family did not discriminate between apparently linked and unlinked families.

Oral contraceptives and premenopausal bilateral breast cancer: a case-control study

We estimated the effect of oral contraceptive (OC) use on premenopausal bilateral breast cancer in a matched case-control study. One hundred forty-four cases were identified from population-based registries of Los Angeles County, California, and of Connecticut and from the major hospitals in Montreal and Quebec City. Matched controls were the unaffected sisters of the cases. When age was included in the model, ever-use of OCs for 1 year or more was associated with an odds ratio 1.7 (95% confidence interval = 1.0-2.9). The odds ratios associated with 1-2, 3-6, and 7 years of use were 1.2 (0.61-2.4), 2.5 (1.2-5.3), and 2.0 (0.93-4.2), respectively. Too few women had used OCs before their first full-term pregnancy or before age 25 for these estimates to be informative. Restricting the analyses to women who had ever given birth yielded an odds ratio for ever-use of OCs of 2.1 (1.0-4.4). The results indicate an increased risk of premenopausal bilateral breast cancer associated with OC use.