Atopic asthma and TNF-308 alleles: linkage disequilibrium and association analyses

[Association between HLA-class II genes and asthma susceptibility in a selected Constantine population]

Introduction

l’asthme est une maladie complexe causé par l’interaction de plusieurs gènes dont certains ont un effet protecteur et d’autres contribuent à l’apparition de la maladie. Cet article s’intéresse à une partie du bras court du chromosome 6 où siègent les gènes codant pour le complexe majeur d’histocompatibilité dénommé HLA qui joue un rôle important dans la pathogénèse de l’asthme.

Méthodes

notre étude inclut 61 personnes dont 30 personnes non asthmatiques non allergiques et 31 patients atteints d’asthme allergique depuis plus de 2 ans. Le statut atopique de l’asthme a été confirmé par les tests cutanés et le typage HLA classe II a été réalisé suivant le principe de la technique sérologique de séparation par Fluorobeads B.

Résultats

l’analyse statistique révèle que les gènes HLA-DR11 et DQ2 sont significativement plus fréquents chez les asthmatiques par rapport aux témoins, les résultats sont comme suit: le HLA-DR11 avec une p=0,05 et le HLA-DQ2 avec une p=0.002, cela nous a conduit à dire qu’il s’agit peut-être de marqueurs HLA en association avec l’asthme. En revanche le marqueur HLA-DQ6 était nettement plus important chez la population témoin que chez les sujets asthmatiques avec p=0.003.

Conclusion

cela nous a conduit à dire que les marqueurs HLA-DR11 et DQ2 pourraient être des gènes potentiels de susceptibilité à l’asthme, alors que HLA-DQ6 pourrait avoir un effet protecteur.

TNF-alpha-308G>A polymorphism and the risk of familial CAD in a Pakistani population

A case-control and trio-families study was performed to establish a potential association between TNF-alpha gene promoter SNPs at -308 and -238, and occurrence of CAD in a Pakistani population. In the first phase, 150 patients and 150 controls were enrolled in the case-control association study. In the second phase, heritability of susceptible alleles was investigated from 88 trio-families with CAD affected offspring. Biochemical analysis of lipids and hs-CRP was carried out spectrophotometrically, while serum TNF-alpha concentrations were determined by enzyme-linked immunosorbent assay. Genotyping of the TNF-alpha SNPs were determined by PCR-RFLP method. Elevated serum TNF-alpha and hs-CRP were observed from CAD vs. controls (P<0.0001; for both). The evaluation of TNF-alpha-308G>A polymorphism in case-control study revealed that the said SNP was significantly associated with the increased risk of CAD. The findings demonstrated a significant link between the TNF-alpha variant allele A at -308 and CAD (P=0.0035), whereas the -238 SNP was not associated with the disease. Haplotype A-G of the TNF-alpha gene at -308G>A and -238G>A showed higher frequency in the patient group compared with controls (P<0.05). Moreover, data showed preferential transmission of the disease susceptible allele A at TNF-alpha-308 from parent to affected offspring in a trio-family study (P<0.0001). The current research leads to conclusion that the TNF-alpha-308G>A polymorphism is associated with CAD in the study population. Furthermore, for the first time, we showed that the TNF-alpha-308A allele was significantly associated with the familial CAD in our high risk population.

Impact of single nucleotide polymorphism in tumor necrosis factor-α gene 308G/A in Egyptian asthmatic children and wheezing infants

Bronchial asthma is a common disease with multiple determinants that include genetic variation. Although tumor necrosis factor alpha (TNF-α) is a major pro-inflammatory cytokine, the functions of genetic polymorphisms in this cytokine has not been thoroughly examined in the context of asthma pathology. Therefore, we aimed to investigate whether single nucleotide polymorphism (SNP) in TNF-α is associated with asthma and wheezing and whether the association is related to the severity of the disease and other epidemiological factors. Frequencies of TNF-α-308G/A polymorphism were compared in 100 asthmatic children, 100 wheezy infants and 100 age and gender matched controls. Genotype frequencies for TNF-α-308G/A were significantly higher in asthmatic children (60%) and wheezy infants (68%) than the control group (30%). Higher serum levels of TNF-α were observed in genotypes G/A and G/G of asthmatic children and wheezy infants than in controls. No association was found between the G/A polymorphism and the severity of the disease, the total eosinophil count and IgE levels in both groups. We can conclude that genetic variation in TNF-α-308G/A may contribute to childhood asthma and wheezing. These findings could be helpful for future early intervention studies which may have a potential impact on family counseling and management.

Tumour necrosis factor gene polymorphism and disease prevalence

Tumour necrosis factor (TNF), an important proinflammatory cytokine, plays a role in the regulation of cell differentiation, proliferation and death, as well as in inflammation, innate and adaptive immune responses, and also implicated in a wide variety of human diseases. The presence of DNA sequence variations in regulatory region might interfere with transcription of TNF gene, influencing the circulating level of TNF and thus increases the susceptibility to human diseases (infectious, cancer, autoimmune, neurodegenerative and other diseases). In this review, we have comprehensively analysed various published case-control studies of different types of human diseases, in which TNF gene polymorphism played a role, and computationally predicted several single nucleotide polymorphisms (SNPs) lie in transcription factor-binding sites (TFBS) of transcription factors (TFs). It has been observed that TNF enhancer polymorphism is implicated in several diseases, and TNF rs1800629 and rs361525 SNPs are the most important in human disease susceptibility as these might influence the transcription of TNF gene. Thirty-two SNPs lies in TFBS of 20 TFs have been detected in the TNF upstream region. It has been found that TNF enhancer polymorphism influences the serum level of TNF in different human diseases and thus affects the susceptibility to diseases. The presence of DNA sequence variation in TNF gene causes the modification of transcriptional regulation and thus responsible for association of susceptibility/resistance with human diseases.

HLA-DR polymorphism modulates response to house dust mites in a transgenic mouse model of airway inflammation

We and others have reported that HLA-DRB1*03 is associated with childhood asthma. To extend this observation and to prove this association, we sensitized and challenged either HLA-DR2 (HLA-DRB1*1502) or HLA-DR3 (HLA-DRB1*0301) transgenic mice with house-dust mite extract. Inflammatory cell counts and cytokine levels in the bronchoalveolar lavage (BAL) fluid between HLA-DR3 and DR2 mice were compared. HLA-DR3 transgenic mice had significantly elevated eosinophil counts, Interleukin-4 and Interleukin-13 levels in the BAL fluid but not interferron gamma-γ. Thus, our study suggests that HLA-DRB1*0301 plays an important role in mounting a Th2-predominant immune response to house dust mite and Th2-type inflammation in the lung.

Tumor necrosis factor-alpha in severe corticosteroid-refractory asthma

Tumor necrosis factor (TNF)-alpha is a proinflammatory cytokine. Blocking TNF-alpha has been demonstrated to be effective in various diseases, including both rheumatoid and psoriatic arthritis. There is evidence to show that levels of TNF-alpha are elevated in patients with severe asthma. TNF-alpha is involved in the initiation and perpetuation of the inflammatory process, epithelial damage and remodeling, and mucin hypersecretion. Furthermore, TNF-alpha polymorphism has also been reported in the asthmatic population. Based on the necessity for alternative treatments for asthmatics with severe disease and those who are particularly resistant to conventional asthma therapy, it has been shown that molecules targeted at blocking the effects of TNF-alpha probably constitute a considerable advance in the management of these difficult patients. This review focuses on the evidence of TNF-alpha axis upregulation in severe corticosteroid-refractory asthma, as well as the role of TNF-alpha inhibition and the adverse effects of treatment.

Association of the tumor necrosis factor-alpha -308 G/A polymorphism with nasal polyposis

Nasal polyposis (NP) is a chronic inflammatory disease in which several molecular and cellular interactions play important roles. Tumor necrosis factor-alpha (TNF-alpha) is a major pro-inflammatory cytokine with a key role in immune inflammatory responses in NP. Altered levels of TNF-alpha, which may occur due to polymorphisms in the TNF-alpha promoter region, may also be associated with NP susceptibility. Given these facts, we investigated the possible association of the TNF-alpha -308 G/A single nucleotide polymorphism (SNP) with NP. In this study, 97 consecutive adult patients with NP and 95 age- and gender-matched controls were recruited. For identification of SNP, restriction fragment length polymorphism analysis after polymerase chain reaction was carried out. The NP group had a significantly higher rate of polymorphism compared to controls (p = 0.015). Logistic regression analysis revealed that the presence of the TNF-alpha -308 G/A SNP is an independent risk factor for NP development (OR, 3.68; CI, 1.27-10.7; p = 0.016). The presence of a mutation failed to influence disease severity on the basis of resistance to medical and/or surgical treatment. This study suggests a possible linkage of a SNP in the TNF-alpha promoter with NP. These results need to be confirmed with multicentre studies for more precise interpretation and corroborative studies for investigating the influence of polymorphism on transcriptional activity.

Tumor necrosis factor-alpha is a common genetic risk factor for asthma, juvenile rheumatoid arthritis, and systemic lupus erythematosus in a Mexican pediatric population

There is a great deal of evidence that points to the association of the tumor necrosis factor-alpha (TNF-alpha) gene as a common genetic factor in the pathogenesis of diseases that are caused by inflammatory and/or autoimmune etiologies. Two single nucleotide polymorphisms (SNPs) identified in the TNF-alpha promoter region have been associated with disease susceptibility and severity. We investigated whether -308G/A and -238G/A TNF-alpha polymorphisms were associated with asthma, systemic lupus erythematosus (SLE), and juvenile rheumatoid arthritis (JRA) in a pediatric Mexican population. In a case-control study of 725 patients (asthma: 226, JRA: 171, and SLE: 328) and 400 control subjects, the participants were analyzed using the allelic discrimination technique. The genotype distribution of both TNF-alpha polymorphisms was in Hardy-Weinberg equilibrium in each group. However, there were significant differences in the allele frequency of TNF-alpha-308A between the patients and the healthy controls. This allele was detected in 2.9% of the controls, 6.0% of asthmatic and JRA patients (p = 0.002 and p = 0.0086), and 6.7% of SLE patients (p = 0.00049); statistical significance was maintained after ancestry stratification (asthma: p = 0.0143, JRA: p = 0.0083, and SLE: p = 0.0026). Stratification by gender showed that the risk for the -308A allele in asthma and JRA was greater in females (OR = 4.16, p = 0.0008 and OR = 4.4, p = 0.0002, respectively). The TNF-alpha -238A allele showed an association only with JRA in males (OR = 2.89, p = 0.004). These results support the concept that the TNF-alpha gene is a genetic risk factor for asthma, SLE, and JRA in the pediatric Mexican population.

Deciphering gene-environment interactions through mouse models of allergic asthma

Identifying the genetic origins of human complex traits is a time-consuming and labor-intensive process that has as yet only yielded a relatively small number of confirmed susceptibility genes and an even smaller number of confirmed susceptibility alleles. One potential explanation for these difficulties might be the presence of unrecognized environmental factors that moderate the contribution of genetic loci to disease and vary between populations. These factors need not necessarily be limited to environmental parameters of intuitive importance (eg, cigarette smoke or allergen exposure) but also can include more cryptic sources of variation associated with the specific study environment (eg, study apparatus or ambient temperature). Analysis of these interactions in human subjects, although a gold standard, is time-consuming and constrained by ethical and technical issues. Investigations in mouse models, on the other hand, represent a simple and flexible system in which to explore gene-environment interaction effects. In this review we discuss the utility of mouse models in the detection of gene-environment interaction effects and consider the limitations on their application.

Genetics of asthma: potential implications for reducing asthma disparities

Although genetic factors may partly explain the differences in asthma prevalence, morbidity, and mortality among ethnic groups in the United States, few studies of the genetics of asthma have included members of ethnic minority groups. Only one genome-wide linkage analysis of asthma and/or asthma-related phenotypes (conducted by the Collaborative Study on the Genetics of Asthma) has included any members of ethnic minority populations. The interpretation of the findings of genetic association studies of asthma in ethnic minority groups is complicated by reduced statistical power due to small sample sizes; the failure to correct for multiple comparisons; a lack of homogeneity of the populations studied with regard to area of residence, ancestral background, and/or country of origin; a lack of measurement of relevant environmental exposures; and (for case-control studies of genetic association) a lack of detection and control of potential population stratification. Genetic studies may improve our understanding of asthma and lead to new methods to prevent, diagnose, and treat this disease. Limited study of asthma genetics in ethnic minority populations is unacceptable, as it may prevent these groups from benefiting from future developments in asthma management and thus widen existing disparities in asthma care. Future genetic association studies of asthma among ethnic minorities in the United States should include large samples of populations that have been adequately defined with regard to area of residence, self-designated ancestry, and country of origin. These studies should also include an adequate assessment of potentially relevant environmental exposures and (for case-control association studies) population stratification.

HLA Dr-Dq haplotypes and the TNFA-308 polymorphism: associations with asthma and allergy

BACKGROUND

The HLA (human leukocyte antigen) class II genes DQB1 and DRB1 and the Tumor Necrosis Factor alpha gene (TNFA) within the HLA complex (chromosome 6p21) have been associated with asthma and allergy. Due to the strong linkage disequilibrium characterizing this complex and the multiple asthma/allergy expressions, we aimed to determine which of these genes were primarily involved in specific asthma/allergy traits.

METHODS

The DRB1-DQB1 alleles and TNFA-308 polymorphism were genotyped in 959 children from the Environment and Childhood Asthma study and analyzed for possible associations with allergic and non-allergic asthma (with/without at least one positive skin prick test for allergens) and specific allergic sensitization, as well as bronchial hyperresponsiveness and total IgE, using both allele and extended haplotype analyses.

RESULTS

Different genes within the HLA complex were associated with separate asthma and allergy traits. Nonallergic asthma was associated with both the TNFA-308A allele [Odds ratio (OR) 1.7 (1.3-2.3)] and DRB1 03 allele [OR 1.6(1-2.6)], but extended DRB1 03-TNFA-308 haplotype analysis suggested that the DRB1-DQB1 association was secondary to linkage disequilibrium with the TNFA-308 polymorphism. Allergies were associated with HLA class II alleles only; birch sensitization with DQB1 0603-DRB1 13 [OR 2.3 (1.4-4.0)] and mugwort sensitization with DQB1 0609-DRB1 13 [OR 7.1 (1.9-27.0)] and DQB1 0501-DRB1 01 [OR 2.0 (1.0-4.0)].

CONCLUSIONS

Our data suggests that asthma is not associated with DRB1 or DQB1 but rather TNFA or a gene(s) in linkage disequilibrium, while sensitization to specific allergens is associated with particular alleles at the DQ and/or DR loci. A novel association between DQB1 0603-DRB1 13 and birch allergy is identified.

Severity of childhood asthma and human leukocyte antigens type

We sought to learn if Class II HLA genes are associated with the severity of asthma in children. We examined a previously recruited cohort of 340 healthy children who had Class II HLA allele data available. We conducted a comprehensive review of their medical records to determine asthma status and, when present, its severity. We found that Class II HLA alleles, which were previously reported to have an association with asthma incidence, appear to have an association as well with asthma severity. These data support our hypothesis that both the incidence and severity of asthma are heritable and that HLA may play an important role in both development and severity of asthma. Because of limited statistical power, our study findings are subject to further investigation.

Parental smoking modifies the relation between genetic variation in tumor necrosis factor-alpha (TNF) and childhood asthma

BACKGROUND

Polymorphisms in the proinflammatory cytokine genes tumor necrosis factor-alpha (TNF) and lymphotoxin-alpha (LTA, also called TNF-beta) have been associated with asthma and atopy in some studies. Parental smoking is a consistent risk factor for childhood asthma. Secondhand smoke and ozone both stimulate TNF production.

OBJECTIVES

Our goal was to investigate whether genetic variation in TNF and LTA is associated with asthma and atopy and whether the association is modified by parental smoking in a Mexican population with high ozone exposure.

METHODS

We genotyped six tagging single nucleotide polymorphisms (SNPs) in TNF and LTA, including functional variants, in 596 nuclear families consisting of asthmatics 4-17 years of age and their parents in Mexico City. Atopy was determined by skin prick tests.

RESULTS

The A allele of the TNF-308 SNP was associated with increased risk of asthma [relative risk (RR) = 1.54; 95% confidence interval (CI), 1.04-2.28], especially among children of non-smoking parents (RR = 2.06; 95% CI, 1.19-3.55; p for interaction = 0.09). Similarly, the A allele of the TNF-238 SNP was associated with increased asthma risk among children of nonsmoking parents (RR = 2.21; 95% CI, 1.14-4.30; p for interaction = 0.01). LTA SNPs were not associated with asthma. Haplotype analyses reflected the single SNP findings in magnitude and direction. TNF and LTA SNPs were not associated with the degree of atopy.

CONCLUSIONS

Our results suggest that genetic variation in TNF may contribute to childhood asthma and that associations may be modified by parental smoking.

Childhood asthma and human leukocyte antigen type

Little is known about the relationship between human leukocyte antigen (HLA) class II genes and family history of asthma or atopy in relation to the incidence of childhood asthma. The objective of the study was to determine whether specific HLA class II genes (e.g., DRB1*03) are associated with asthma and whether such association explains the influences of family history of asthma or atopy on asthma incidence. A stratified random sample of 340 children who had HLA data available from the Rochester Family Measles Study cohort (n= 876) and a convenience sample of healthy children aged 5-12 years were the participants. We conducted comprehensive medical record reviews to determine asthma status of these children. The associations between the presence of specific HLA alleles and development of asthma and the role of family history of asthma or atopy in the association were evaluated by fitting Cox models. The cumulative incidence of asthma by 12 years of age among children who carry HLA DRB1*03 was 33%, compared to 24.2% among those who did not carry this allele. Adjusting for family history of asthma or atopy, gender, low birth weight, season of birth, HLA DRB1*04, and HLA DQB1*0302, the hazards ratio for HLA DRB1*03 carriers was 1.8 (95% confidence interval: 1.1-2.9, P= 0.020). We concluded that the HLA DRB1*03 allele is associated with asthma. However, the HLA class II gene does not explain the influences of family history of asthma or atopy on development of asthma. The mechanism underlying the association between asthma and HLA genes needs to be elucidated.

TNF-alpha (-308 G/A) and CD14 (-159T/C) polymorphisms in the bronchial responsiveness of Korean children with asthma

BACKGROUND

TNF-alpha is a pivotal proinflammatory cytokine increased in asthmatic airways. The TNF-alpha gene family might be linked to asthma or bronchial hyperresponsiveness (BHR), and TNF-alpha production might be modulated by CD14(+) cells.

OBJECTIVE

We investigated the association between asthma susceptibility or asthma-related phenotypes and TNF-alpha (-308G/A) polymorphism and examined the combined effect with CD14 (-159T/C) polymorphism in Korean children.

METHODS

Asthmatic (n = 788) and control (n = 153) children were evaluated for asthma phenotypes. Genotypes were determined by using the single-base extension method and PCR-restriction fragment length polymorphism.

RESULTS

There was no difference between asthmatic children and control subjects in terms of the allele frequencies of TNF-alpha (-308G/A) and CD14 (-159T/C). Significantly lower PC(20) values were seen in asthmatic (P = .016) children with the TNF-alpha risk allele (-308A). Higher frequencies of 1 or 2 copies of the risk allele were found in asthmatic children with moderate-to-severe BHR to methacholine and exercise compared with control children (adjusted odds ratio of 2.57 [95% CI, 1.30-5.08] and adjusted odds ratio of 2.04 [95% CI 0.99-4.20], respectively). In addition, asthmatic children with risk alleles at both loci had significantly greater BHR than those homozygous for the common alleles (P = .018).

CONCLUSION

The TNF-alpha promoter polymorphism (-308G/A) might be associated with severe BHR in Korean children with asthma. In addition, these children show a synergistic effect between the TNF-alpha promoter (-308A) and CD14 promoter (-159C) polymorphisms in terms of BHR.

CLINICAL IMPLICATIONS

The TNF-alpha polymorphism might be a disease-modifying gene in asthma and modulated by the CD14 gene.

Childhood asthma and measles vaccine response

BACKGROUND

Asthmatic patients have a TH2-predominant milieu that is associated with humoral immunity. However, little is known about whether humoral immune responses to viral antigens differ between asthmatic and nonasthmatic children.

OBJECTIVE

To determine whether humoral immune response differs in asthmatic patients vs nonasthmatic patients.

METHODS

Measles virus specific IgG antibody levels were determined for the Rochester Family Measles Study cohort (n = 876), a convenience sample of healthy children 5 to 12 years of age in Rochester, MN. We conducted comprehensive medical record reviews of 838 children who were eligible for this study. We determined the child's asthma status at the time of determination of antibody levels by applying predetermined criteria for asthma. Comparisons were made using the 2-sample t test or chi2 test.

RESULTS

Of the 838 children, 156 (18.6%) had asthma at the time of the determination of antibody levels and were not taking systemic steroids within 14 days of specimen collection. Among those with a nonequivocal antibody reading, the seropositive response rates were similar in asthmatic patients and nonasthmatic patients (89.7% vs 90.3%, respectively; P = .83). However, the equivocal response rates were slightly higher among asthmatic patients than nonasthmatic patients (6.4% vs 4.7%, respectively).

CONCLUSION

Asthmatic children seem to have similar humoral immune responses to measles vaccine as those without asthma. Although the findings reassure health care practitioners, whether this finding is generalizable to other vaccines and whether asthmatic patients with low antibody levels have normal cell-mediated immunity need to be elucidated in future studies.

An association between asthma and TNF-308G/A polymorphism: meta-analysis

Tumor necrosis factor (TNF) is a potent inflammatory cytokine that contributes to airway inflammation in asthma. Previous studies have reported that a G-to-A transition at position -308 (-308G/A, also referred to as TNF-alpha-308*1 and 308*2 respectively), is associated with asthma, but other studies have shown conflicting results. To investigate a possible association between the TNF-308G/A polymorphism and asthma, we performed transmission disequilibrium tests and a case-control study (family samples: 495 members in 165 Japanese trio families with one asthmatic child and both parents; case-control samples: 461 Japanese asthmatic children and 465 healthy controls). To increase the sample size and power, we performed a meta-analysis of all available relevant studies, including 2,477 asthmatics and 3,217 controls. We did not find a significant association between the TNF-308G/A polymorphism and childhood atopic asthma in two independent Japanese populations (P>0.05); however, meta-analysis revealed that the TNF-308G/A polymorphism was statistically significantly associated with asthma. The combined odds ratio with a fixed effects model and with a random effects for TNF-308A was 1.46 (95% confidence interval [CI], 1.27-1.68, P=0.0000001) and 1.46 (95% CI, 1.20-1.77, P=0.00014) respectively. Our data further support the importance of the TNF region in the development of asthma.

Tumor Necrosis Factor Alpha and Pulmonary Function in Saskatchewan Grain Handlers

OBJECTIVE

The objective of this study was to estimate the contribution of lifestyle (cigarettes) and tumor necrosis factor (TNF) alpha polymorphisms at position 308 of the tumor necrosis factor alpha gene promotor (TNF-308*1/*2) to pulmonary function among grain handlers.

METHODS

Employed male grain handlers (157) provided occupational and respiratory symptom information, pulmonary function measurements, and DNA for genotyping.

RESULTS

The genotypes of 101 were TNF-308*1/*1, 47 were *1/*2, and nine were *2/*2. Current smokers whose genotype was *2/*2 or *1/*2 had lower values compared with other combinations of genotype and smoking status. Among *1/*1 homozygotes, current smokers had better percent of predicted forced expiratory volume in 1 second (P = 0.04) mean values than nonsmokers and better percent of predicted forced vital capacity than exsmokers (P = 0.017) or nonsmokers (P = 0.008).

CONCLUSIONS

These results indicate the complexity of determining which workers will develop acute and chronic adverse pulmonary conditions in response to exposure to grain dust and the toxins in cigarette smoke interacting with their genotype.

Association between polymorphism of tumour necrosis factor alpha-308 gene promoter and asthma: a meta-analysis

BACKGROUND

Asthma is a complex polygenic disease in which gene-environment interactions are important. The gene encoding tumour necrosis factor alpha (TNFalpha) is one of several candidate loci for asthma pathogenesis and is highly polymorphic. A number of studies have investigated the polymorphism of TNFalpha-308 gene promoter (substitution G-->A, designated as TNF1 and TNF2) in relation to asthma susceptibility in different populations. However, the results of individual studies have been inconsistent.

METHODS

To address the inconsistent findings in studies of the association of the polymorphism of TNFalpha-308 gene promoter with susceptibility to asthma, a systematic review was undertaken of the published data and a meta-analysis was performed. The MEDLINE database was searched for case-control studies published in English language journals from 1966 to October 2005. Data were extracted using standardised forms and pooled odds ratios (ORs) with 95% confidence intervals (CIs) were calculated.

RESULTS

Fifteen eligible studies, comprising 2409 patients with asthma and 3266 controls, were included in the meta-analysis. Using the random effects model, the pooled result showed that the TNF2 allele is associated with overall susceptibility to asthma (OR 1.37, 95% CI 1.02 to 1.84, p=0.04). The ORs for asthma susceptibility in TNF2 homozygote individuals were significantly increased at 2.01 (95% CI 1.26 to 3.20, p=0.009) and 1.51 (95% CI 1.02 to 2.22, p=0.041) compared with TNF1 homozygotes and TNF2/1 heterozygotes, respectively. In addition, the pooled OR for asthma risk in TNF2/1 heterozygotes was also significantly higher than that in TNF1/1 homozygotes (OR 1.47, 95% CI 1.01 to 2.13, p=0.045).

CONCLUSIONS

The TNF2 allele confers a significant risk for developing asthma. A large scale case-control study is needed to clarify the functional effect of the polymorphism of the TNFalpha gene in the pathogenesis of asthma.

Associations of tumor necrosis factor G-308A with childhood asthma and wheezing

RATIONALE

Tumor necrosis factor (TNF) mediates a spectrum of airway inflammatory responses, including those to air pollutants, and is an asthma candidate gene. One TNF promoter variant (G-308A) affects expression of TNF and has been associated with inflammatory diseases; however, studies of asthma have been inconsistent. Because ozone produces oxidative stress, increased airway TNF, and inflammation, the associations of the -308 TNF polymorphism with asthma may vary by ozone exposure and variants of oxidant defense genes glutathione-S-transferase (GST) M1 and GSTP1.

OBJECTIVES

To investigate the association of TNF G-308A with asthma and wheezing and to determine whether these associations vary with ozone exposure and GSTM1 and GSTP1 genotype.

METHODS

We studied associations of TNF-308 genotype with lifetime and current wheezing and asthma among 3,699 children in the Children's Health Study. We examined differences in associations with community ozone and by GSTM1 null and GSTP1 105 Ile/Val (A105G) genotype.

RESULTS

Children with TNF-308 GG had decreased risk of asthma (odds ratio, 0.8; 95% confidence interval, 0.7-0.9) and lifetime wheezing (odds ratio, 0.8; 95% confidence interval, 0.7-0.9). The protective effects of GG genotype on wheezing outcomes were of greater magnitude in lower compared with higher ozone communities. These findings were replicated in the two cohorts of fourth-grade children recruited in 1993 and 1996. The reduction of the protective effect from the -308 GG genotype with higher ozone exposure was most marked in the GSTM1 null and GSTP1 Ile/Ile groups.

CONCLUSIONS

The TNF-308 GG genotype may have a protective role in asthma pathogenesis, depending on airway oxidative stress levels.

Extended haplotype in the tumor necrosis factor gene cluster is associated with asthma and asthma-related phenotypes

RATIONALE

Tumor necrosis factor is a proinflammatory cytokine found in increased concentrations in asthmatic airways. The TNF-alpha (TNF) and lymphotoxin-alpha (LTA) genes belong to the TNF gene superfamily located within the human major histocompatibility complex on chromosome 6p in a region repeatedly linked to asthma. The TNF position -308 and LTA NcoI polymorphisms are believed to influence TNF transcription and secretion, respectively.

OBJECTIVES

This study sought to determine whether polymorphisms in TNF or LTA, or in TNF-LTA haplotypes, are associated with asthma and asthma phenotypes.

METHODS

We genotyped the TNF -308 and LTA NcoI polymorphisms, and two other haplotype-tagging polymorphisms in the TNF and LTA genes, in 708 children with mild to moderate asthma enrolled in the Childhood Asthma Management Program and in their parents. Using an extension of the family-based association tests in the PBAT program, each polymorphism was tested for association with asthma, age at onset of asthma, and time series data on baseline FEV(1) % predicted, postbronchodilator FEV(1) % predicted, body mass index, and log of PC(20).

MEASUREMENTS AND MAIN RESULTS

Although no associations were found for the individual single-nucleotide polymorphisms, the haplotype analysis found the LTA NcoI_G/LTA 4371T/TNF -308G/TNF 1078G haplotype to be associated with asthma and with all five phenotype groups.

CONCLUSIONS

We conclude that it is unlikely that the TNF -308 or LTA NcoI polymorphisms influence asthma susceptibility individually, but that this haplotype of variants may be functional or may be in linkage disequilibrium with other functional single-nucleotide polymorphisms.

TNF-308 modifies the effect of second-hand smoke on respiratory illness-related school absences

RATIONALE

Exposure to second-hand smoke (SHS) has been associated with increased risk of respiratory illness in children including respiratory illness-related school absences. The role of genetic susceptibility in risk for adverse effects from SHS has not been extensively investigated in children.

OBJECTIVE

To determine whether the tumor necrosis factor (TNF) G-308A genotype influences the risk for respiratory illness-related school absences associated with SHS exposure.

METHODS

Incident school absences were collected, using an active surveillance system, between January and June 1996, as part of the Air Pollution and Absence Study, a prospective cohort study nested in the Children's Health Study. Buccal cells and absence reports were collected on 1,351 students from 27 elementary schools in California.

MEASUREMENTS AND MAIN RESULTS

Illness-related school absences were classified as nonrespiratory and respiratory illness-related, which were further categorized into upper or lower respiratory illness-related absences based on symptoms. The effect of SHS exposure on respiratory illness-related absences differed by TNF genotype (p interaction, 0.02). In children possessing at least one copy of the TNF-308 A variant, exposure to two or more household smokers was associated with a twofold risk of a school absence due to respiratory illness (relative risk, 2.13; 95% confidence interval, 1.34, 3.40) and a fourfold risk of lower respiratory illness-related school absence (relative risk, 4.15; 95% confidence interval, 2.57, 6.71) compared with unexposed children homozygous for the common TNF-308 G allele.

CONCLUSIONS

These results indicate that a subgroup of genetically susceptible children are at substantially greater risk of respiratory illness if exposed to SHS.

Cytokine and anti-cytokine therapy for the treatment of asthma and allergic disease

Until recently, the only controller treatment for chronic asthma has been corticosteroids. However, identification of specific effector molecules in asthma has led to targeting of specific pathways by using cytokines and cytokine inhibitors. Administration of a monoclonal blocking antibody against IgE has been shown to be highly efficacious in severe allergic asthma, but blockade of eosinophils using anti-IL-5 monoclonal antibodies has no clinical benefit. In more severe asthma, blockade of TNF-alpha using the decoy etanercept has revealed efficacy in a small open study suggesting that Th-1 in addition to Th-2 pathways are important as the disease adopts a more severe phenotype. It is likely that asthma is not a single disease but a group of disorders which differ in the relative contribution of specific pathophysiological pathways.

Gene-environment interactions in asthma and other respiratory diseases

It is generally agreed that many lung diseases such as asthma and chronic obstructive pulmonary disease (COPD) have polygenic inheritance, and that the association of a specific genotype or genotypes with the disease is likely to vary between populations. Furthermore, it is recognized that the etiology of many lung diseases involves a complex interplay between genetic background and exposure to multiple environmental stimuli, and understanding the mechanisms through which genes and environment interact represents a major challenge for pulmonary researchers. We discuss experimental approaches and challenges that must be overcome to identify disease genes for asthma, COPD and chronic bronchitis, and occupational lung diseases. In particular, common polymorphisms in CD14, glutathione S-transferase, and tumor necrosis factor alpha have been found to be important in gene-environment interaction and asthma pathogenesis. An understanding of gene-environment interactions in complex lung diseases is essential to the development of new strategies for lung disease prevention and treatment.

The role of genetics in the development of asthma and atopy

PURPOSE OF REVIEW

The mapping of complex traits such as asthma and atopy is one of the most important and central areas of human genetics. This article will present an overview of the current status of genetic studies of asthma and atopy using genome screens and association studies that have occurred in the literature since January 2003.

RECENT FINDINGS

Many regions of the genome have been found to have linkage with the phenotypes of asthma and atopy. Over 70 variants in candidate genes have been reported to be associated with these phenotypes. The main regions these variants have been found are on chromosomes 2q, 5q, 6p, 11q, 12q, 16q and 17q. Five potential asthma susceptibility genes or complexes have been identified using a positional approach. These are ADAM33, DPP10, PHF11 and SETDB2, GPRA and SPINK5. It is evident that environmental factors will influence the expression of genes and the ultimate clinical phenotype of asthma and atopy.

SUMMARY

The development of asthma and atopy involves many genes and environmental factors. An understanding of their genetic basis has great implications for their management.

Recent development in genomic and proteomic research for asthma

PURPOSE OF REVIEW

Asthma is a complex genetic disorder with a heterogeneous phenotype attributed to the interactions among many genes and the environment. This review highlights recent developments in asthma genomic and proteomic research.

RECENT FINDINGS

Numerous loci and candidate genes have been reported to show linkage and association of asthma and the asthma-associated phenotypes, atopy, elevated immunoglobulin E (IgE) levels, and bronchial hyperresponsiveness to alleles of microsatellite markers and single nucleotide polymorphisms within specific cytokine/chemokine, and IgE regulating genes. Although many studies reporting these observations are compelling, only a few genes conferring significant risk have been mapped. Although significant progress has been made in the field of asthma genetics in the past decade, the clinical implications of the genetic variations within the numerous candidate asthma genes, which have been found to associate with the expression of the asthmatic phenotype, remain largely undetermined. However, in the past year the scientific community has benefited from postgenomic discoveries, with the recent cloning of two asthma genes, ADAM 33 and PHF11, and this has generated new information that is benefiting others.

SUMMARY

The asthma genetics field has advanced considerably in recent years, with new information being generated that has led to improved understanding of the pathobiology underlying this complex disorder. This has also generated interest in the study of gene-gene interaction and how linkage disequilibrium blocks and haplotypes can be used as functional units to pinpoint mutations and capture relative risk of mutated genes in complex disorders.

Association studies for asthma and atopic diseases: a comprehensive review of the literature

Hundreds of genetic association studies on asthma-related phenotypes have been conducted in different populations. To date, variants in 64 genes have been reported to be associated with asthma or related traits in at least one study. Of these, 33 associations were replicated in a second study, 9 associations were not replicated either in a second study or a second sample in the same study, and 22 associations were reported in just a single published study. These results suggest the potential for a great amount of heterogeneity underlying asthma. However, many of these studies are methodologically limited and their interpretation hampered by small sample sizes.