Ian A. Yang

Genetics of allergic disease

Allergic diseases are complex genetic diseases resulting from the effect of multiple genetic and interacting environmental factors on their pathophysiology. Recent years have seen considerable progress in unraveling the contribution of these factors to an individual subjects susceptibility to, subsequent development of, and severity of disease. This has resulted in increasing insight into novel areas of allergic disease pathophysiology, for example the significant role played by locally acting tissue susceptibility factors like epithelial/epidermal barrier function and remodeling, such as filaggrin, ADAM33, and GSDML/ORMDL3, in patients with atopic dermatitis and asthma. Furthermore, studies of gene-environment interactions and Mendelian randomization approaches have led to increased insight into the importance of environmental triggers for allergic disease. Studies of the timing of action of genetic variants in determining disease susceptibility have highlighted the importance of in utero development and early life in determining susceptibility to allergic disease. In the future, genetic discoveries in allergic disease will potentially lead to better endophenotyping, prognostication, prediction of treatment response, and insights into molecular pathways to develop more targeted therapy for these conditions.

TOLL-LIKE RECEPTOR 4 POLYMORPHISM AND SEVERITY OF ATOPY IN ASTHMATICS

Endotoxin exposure may have a protective effect against asthma and atopy. An Asp299Gly polymorphism in the Toll-like receptor 4 (TLR4) gene reduces responsiveness to endotoxin. This study determined the effect of TLR4 polymorphism on the risk and severity of asthma and atopy. In all, 336 UK Caucasian families with ≥2 affected sibs (physicians diagnosis of asthma and current medication use) and 179 Caucasians without asthma or a family history of asthma were genotyped using ARMS-PCR. No association of the TLR4 polymorphism was found with the risk of developing asthma, either in parent-affected sibling trios, or in case–control analyses (P>0.05). In the first affected asthmatic siblings, the atopy severity score (based on size and number of positive skin-prick tests and specific IgE) was higher in those with the Asp/Gly or Gly/Gly genotypes (mean 1.8, s.d. 1.1, n=39) compared to those with the Asp/Asp genotype (mean 1.2, s.d. 1.0, n=279) (P=0.003, t-test). No associations were found with total IgE, FEV1 % predicted, slope of FEV1 response to methacholine or asthma severity score (P>0.05). This study confirms the previously observed lack of association of TLR4 polymorphisms with asthma. In contrast, the findings suggest that genetically determined hyporesponsiveness to endotoxin may increase atopy severity.

Genetic susceptibility to the respiratory effects of air pollution

There is large variation between individuals in their response to air pollutants. This review summarises the existing evidence that genetic factors influence the mechanisms of lung injury caused by air pollutants. Genetic association studies have compared the adverse effects of air pollutants between subjects with specific genotypes in biologically relevant genes. In human studies of ozone exposure, polymorphisms in oxidative stress genes (NQO1, GSTM1, GSTP1) modify respiratory symptoms, lung function, biomarkers and risk of asthma. Inflammatory gene polymorphisms (TNF) influence the lung function response to ozone, and the effect of different levels of ozone on the development of asthma. Polymorphisms in oxidative stress genes (GSTM1, GSTP1) alter the response to combined exposure to ragweed pollen and diesel exhaust particles. Importantly, polymorphisms in an oxidative stress gene (GSTM1) have predicted patients with asthma who benefit from antioxidant supplementation in Mexico City, which has chronically high ozone exposure. Genetic linkage studies of families have not been feasible for studying the effects of air pollution in humans, but some progress has been made with pedigrees of specially bred mice, in identifying chromosomal regions linked to effects of ozone or particles. A high priority now, in addition to avoiding exposure in the most susceptible people, is to clearly identify the most effective and safe chemopreventive agents for individuals who are genetically susceptible to the adverse effects of air pollution (eg, antioxidants to be taken during high ozone levels).There is large variation between individuals in their response to air pollutants. This review summarises the existing evidence that genetic factors influence the mechanisms of lung injury caused by air pollutants. Genetic association studies have compared the adverse effects of air pollutants between subjects with specific genotypes in biologically relevant genes. In human studies of ozone exposure, polymorphisms in oxidative stress genes (NQO1, GSTM1, GSTP1) modify respiratory symptoms, lung function, biomarkers and risk of asthma. Inflammatory gene polymorphisms (TNF) influence the lung function response to ozone, and the effect of different levels of ozone on the development of asthma. Polymorphisms in oxidative stress genes (GSTM1, GSTP1) alter the response to combined exposure to ragweed pollen and diesel exhaust particles. Importantly, polymorphisms in an oxidative stress gene (GSTM1) have predicted patients with asthma who benefit from antioxidant supplementation in Mexico City, which has chronically high ozone exposure. Genetic linkage studies of families have not been feasible for studying the effects of air pollution in humans, but some progress has been made with pedigrees of specially bred mice, in identifying chromosomal regions linked to effects of ozone or particles. A high priority now, in addition to avoiding exposure in the most susceptible people, is to clearly identify the most effective and safe chemopreventive agents for individuals who are genetically susceptible to the adverse effects of air pollution (eg, antioxidants to be taken during high ozone levels).

MicroRNA-218 is deleted and downregulated in lung squamous cell carcinoma.

MicroRNAs (miRNAs) are a family of small, non-coding RNA species functioning as negative regulators of multiple target genes including tumour suppressor genes and oncogenes. Many miRNA gene loci are located within cancer-associated genomic regions. To identify potential new amplified oncogenic and/or deleted tumour suppressing miRNAs in lung cancer, we inferred miRNA gene dosage from high dimensional arrayCGH data. From miRBase v9.0 (http://microrna.sanger.ac.uk), 474 human miRNA genes were physically mapped to regions of chromosomal loss or gain identified from a high-resolution genome-wide arrayCGH study of 132 primary non-small cell lung cancers (NSCLCs) (a training set of 60 squamous cell carcinomas and 72 adenocarcinomas). MiRNAs were selected as candidates if their immediately flanking probes or host gene were deleted or amplified in at least 25% of primary tumours using both Analysis of Copy Errors algorithm and fold change (≥±1.2) analyses. Using these criteria, 97 miRNAs mapped to regions of aberrant copy number. Analysis of three independent published lung cancer arrayCGH datasets confirmed that 22 of these miRNA loci showed directionally concordant copy number variation. MiR-218, encoded on 4p15.31 and 5q35.1 within two host genes (SLIT2 and SLIT3), in a region of copy number loss, was selected as a priority candidate for follow-up as it is reported as underexpressed in lung cancer. We confirmed decreased expression of mature miR-218 and its host genes by qRT-PCR in 39 NSCLCs relative to normal lung tissue. This downregulation of miR-218 was found to be associated with a history of cigarette smoking, but not human papilloma virus. Thus, we show for the first time that putative lung cancer-associated miRNAs can be identified from genome-wide arrayCGH datasets using a bioinformatics mapping approach, and report that miR-218 is a strong candidate tumour suppressing miRNA potentially involved in lung cancer.

TLR4 Asp299Gly polymorphism is not associated with coronary artery stenosis

UNLABELLED Inflammation and innate immunity may play a role in the pathogenesis of atherosclerosis. The Asp299Gly polymorphism in the toll-like receptor 4 (TLR4) gene reduces responsiveness to lipopolysaccharide and has been associated with reduced incidence and slower progression of carotid atherosclerosis. We analyzed this polymorphism in relation to susceptibility to and severity of coronary artery disease. METHODS 1400 participants (mean age: 63 years, 31% female) in the Southampton Atherosclerosis Study were genotyped for the TLR4 Asp299Gly polymorphism using the tetra-primer PCR method. RESULTS There was no significant difference between the frequencies of the Asp/Gly or Gly/Gly genotypes combined, compared to the Asp/Asp genotype, in patients with 0, 1, 2 or 3 coronary arteries with >50% stenosis (chi2(3 d.f.)2=0.4, P=0.94). No associations were observed between genotype groups and cardiac risk factors (P>0.05). CONCLUSION The findings of this study do not support the hypothesis that the TLR4 Asp299Gly polymorphism influences predisposition to and progression of coronary artery disease.

Polymorphisms in Toll-like receptor 4 and the systemic inflammatory response syndrome

The systemic inflammatory response syndrome (SIRS) is a major cause of morbidity and mortality, and is thought to be due to an over-amplification of an inflammatory response. The Toll-like receptor 4 ( TLR4 ) Asp-299-->Gly polymorphism has been shown to reduce lipopolysaccharide responsiveness. We examined whether this TLR4 polymorphism is associated with severity of SIRS. A trend was found between the minor allele and mortality in SIRS (odds ratio of 4.3; P =0.076), suggesting a role for TLR4 signalling in the severity of SIRS.

Systematic review of multidisciplinary teams in the management of lung cancer.

BACKGROUND In several countries, clinical practice guidelines for lung cancer recommend that multidisciplinary (MD) teams should be used to plan the management of all lung cancer patients. We conducted a systematic review to evaluate and critically appraise the effectiveness of multidisciplinary teams for lung cancer. MATERIALS AND METHODS Medline searches were carried out for the period 1984 to July 2007. We included any study that mentioned team working among specialists with diagnostic and curative therapeutic intent, where members of the team met at a specified time, either in person or by video or teleconferencing, to discuss the diagnosis and management of patients with suspected lung cancer. All study designs were included. We were particularly interested in whether multidisciplinary working improved survival but also considered other outcomes such as practice patterns and waiting times. RESULTS Sixteen studies met the criteria for inclusion. Statistical pooling was not possible due to clinical heterogeneity. Only two of the primary studies reported an improvement in survival. Both were before-and-after designs, providing weak evidence of a causal association. Evidence of the effect of MD teams was stronger for changing patient management than for affecting survival. Six of the studies reported an increase in the percentage of patients undergoing surgical resection or an increase in the percentage of patients undergoing chemotherapy or radiotherapy with curative intent. CONCLUSION This systematic review shows limited evidence linking MD teams with improved lung cancer survival. This does not mean that MD teams do not improve survival, merely that currently available evidence of this is limited. It seems intuitively obvious that MD teams should improve outcomes for lung cancer patients, but there are difficulties in conducting randomised trials to show this. The best way forward would be prospective evaluation of the effectiveness of MD teams as they are implemented, paying particular attention to collecting data on potential confounders.

Arg389Gly-[beta]1-adrenergic receptors determine improvement in left ventricular systolic function in nonischemic cardiomyopathy patients with heart failure after chronic treatment with carvedilol

Objective Administration of the &bgr;-adrenergic receptor blocker carvedilol to patients with chronic heart failure leads to clinically significant benefits, including improvement in left ventricular systolic function in some, but not all, patients. We sought to determine the basis of the variable effect obtained with carvedilol in patients with heart failure. Carvedilol blocks both &bgr;1-adrenergic and &bgr;2-adrenergic receptors, and both receptors exist as polymorphisms. We aimed to determine whether these polymorphisms contribute to variability in response to carvedilol in patients with chronic heart failure. Methods We retrospectively and prospectively investigated 135 patients with nonischemic cardiomyopathy and chronic stable heart failure (New York Heart Association class II, III) treated with carvedilol. Baseline echocardiography was obtained before introduction of carvedilol and repeated after stabilization of a maximally tolerated dose of carvedilol (50–100 mg/day) for at least 1 year. Polymerase chain reaction and restriction fragment length polymorphism analysis were used to genotype &bgr;1-adrenergic and &bgr;2-adrenergic receptor polymorphisms. Results When grouped according to receptor polymorphisms patients were well matched for severity of heart failure, comorbidity and treatment. No significant difference was observed in baseline left ventricular ejection fraction (LVEF) between groups (P>0.05). After 1.5 years of treatment with carvedilol patients with Arg389Arg-&bgr;1-adrenergic receptors had a significantly greater improvement in LVEF compared with Gly389 carriers (Arg389Arg 18.8%; Arg389Gly 9.4%; Gly389Gly 6.0%; P<0.001) whereas there were no differences attributable to other &bgr;1-adrenergic and &bgr;2-adrenergic receptor polymorphisms (P>0.05). Conclusion In patients with nonischemic dilated cardiomyopathy, carvedilol leads to a significantly greater improvement in LVEF in patients with the Arg389Arg-&bgr;1 adrenergic receptor phenotype.

The role of toll-like receptors and related receptors of the innate immune system in asthma

Purpose of reviewThe biology of the innate immunity receptors is of central importance in the host response to the environment. Identifying genetic variants that alter the innate immune response is highly relevant to understanding asthma pathogenesis. This review summarizes recent studies of the role of innate immunity receptors, including Toll-like receptors and CD14, in the pathogenesis of asthma. Recent findingsThe majority of studies published since 2004 have been genetic association studies in various clinical settings, which have found positive associations of single nucleotide polymorphisms in TLR2, TLR4, TLR6 and TLR10 with asthma or atopy, although the number of studies is small and the results not yet replicated. The designs for CD14 genetic studies have been more sophisticated and have included gene–environment interaction. The results of CD14 gene associations with asthma and atopy are suggestive but have not been fully replicated. Potential reasons for non-replication of TLR and CD14 association studies include insufficient power, type I error, population heterogeneity and different phenotypes studied. In addition, there may be differences in CD14 genetic effects between childhood and adulthood, and between levels of endotoxin exposure. SummaryThe evidence is still being accumulated for the role of Toll-like receptor polymorphisms in the pathogenesis of asthma. There is emerging evidence for the role of CD14 polymorphisms in the development of asthma and atopy. Further studies of innate immunity in asthma and allergy are required, using rigorous study design, measurement of environmental exposure and intermediate phenotypes to demonstrate single nucleotide polymorphism functionality.

Variation in the toll-like receptor 4 gene and susceptibility to myocardial infarction

Variation in the gene encoding toll-like receptor 4 (TLR4), a transmembrane receptor that mediates inflammatory responses to bacterial endotoxin, has been associated with susceptibility to atherosclerosis and its complications, such as myocardial infarction (MI), the pathogenesis of which involves inflammation. A recent study has also indicated that TLR4 gene variation influences the effect of statin treatment on reducing atherosclerosis complications. We studied the TLR4 gene Asp299Gly polymorphism in relation to susceptibility to myocardial infarction in a cohort of patients with angiographically documented coronary artery disease, and performed a meta-analysis using data sets from three independent studies. The meta-analysis showed that overall, odds ratio (OR) for MI was 0.73 [95% confidence interval (CI) 0.55–0.96, P=0.024] in 299Gly carriers compared to non-carriers, and there was no evidence of heterogeneity among the sample sets (P=0.679). In our patient cohort, a significant association of 299Gly bearing genotypes with lower susceptibility to myocardial infarction was observed only in patients receiving statin treatment, with 299Gly carriers having an OR of 0.49 (95% CI 0.27–0.78, P=0.015) for MI compared to non-carriers. These results are consistent with the notion that variation in the TLR4 gene contributes to inter-individual variability in susceptibility to coronary ischaemic events, and that TLR4 genotype and statin treatment may have a synergistic effect.