Association study using combination analysis of SNP and STRP markers: CD14 promoter polymorphism and IgE level in Taiwanese asthma children

Racial differences in the association of CD14 polymorphisms with serum total IgE levels and allergen skin test reactivity

Background

The CD14 C-159T single nucleotide polymorphism (SNP) has been investigated widely as a candidate genetic locus in patients with allergic disease. There are conflicting results for the association of the CD14 C-159T SNP with total serum immunoglobulin E (IgE) levels and atopy. There are limited data regarding the association of the CD14 C-159T SNP in subjects of African ancestry. The aim of the study was to determine whether the C-159T SNP and other CD14 SNPs (C1188G, C1341T) were associated with total serum IgE levels and with allergy skin test results in nonatopic and atopic subjects; as well as in Caucasian and African American subjects.

Methods

A total of 291 participants, 18–40 years old, were screened to determine whether they were atopic and/or asthmatic. Analyses were performed to determine the association between CD14 C-159T, C1188G, or C1341T genotypes with serum IgE levels and with the number of positive skin tests among Caucasian or African American subjects.

Results

We found no significant association of serum total IgE level with CD14 C-159T, C1188G, or C1341T genotypes within nonatopic or atopic subjects. Subjects with CD14-159 T alleles had significantly more positive allergen skin tests than subjects without CD14-159 T alleles (P = 0.0388). There was a significant association between the CD14 1188 G allele, but not the CD14 1341 T allele, with the number of positive skin-test results in Caucasians, but not in African Americans.

Conclusion

These results support a possible association between CD14 polymorphisms and atopy. CD14-159 T or CD14 1188 G alleles were associated with atopic disease. For subjects with CD14 1188 G alleles, the association with atopic disease was stronger in Caucasians compared to African Americans.

The burden of allergic asthma in children: a landscape comparison based on data from Lithuanian, Latvian, and Taiwanese populations

Asthma is one of the most common chronic respiratory diseases with an increasing prevalence and financial burden worldwide. This disease affects individuals in all countries and all ethnic groups; however, prevalence rates of asthma have been reported to vary significantly between different regions. To understand the origin of asthma and to manage it effectively, it is necessary to analyze the genetic and environmental factors that cause these geographic differences. Therefore, we aimed to review published data from the investigations of asthma patients in Eastern Europe, represented by Latvia and Lithuania, and of patients from Eastern Asia represented by Taiwan. We hope that some of the common factors can be identified and different variants can be compared among these three countries for development of a new strategy to prevent childhood asthma.

Genetic factors in the treatment of bronchial asthma

Owing to the recent vast progress in analytical tools and procedures to elucidate the relationship between genes and diseases, many candidate genes leading to the development of bronchial asthma have been reported. However, the quantitative phenotypes of asthma, such as decrease in forced expiratory volume in the first second, serum hyper-IgE, bronchial hyperresponsiveness and blood hyper-eosinophilia, do not represent this disease completely. On the other hand, eosinophilic inflammation of the bronchial mucosa represents accurately the feature of bronchial asthma, although accurate quantification of its status is difficult. While the production of interleukin (IL)-5 in peripheral CD4(+) T cells probably correlates with eosinophilic inflammation of the airway, the effectiveness of anti-IL-5 antibody for the treatment of bronchial asthma is controversial. Since intervention with asthma-causing gene products may not be sufficient for the treatment of this disease, identification of therapy-responsive genes should become more important in the near future.

The role of lipopolysaccharide in the development of atopy in humans

Atopy is a highly prevalent condition and remains the single biggest risk factor for asthma. Although atopy has a heritable component, the time frame of the increase in the prevalence indicates that it is not due to genetic factors alone. The relationship between allergen exposure and sensitization is complex. Lipopolysaccharide (LPS) and its bioactive moiety endotoxin are common to all gram-negative bacteria, and have been used as a surrogate of microbial load. Endotoxin can be readily measured in dust collected from homes. Some studies have demonstrated a clear inverse dose-response relationship between exposure to endotoxin and the risk of atopy but this finding has not been reproduced in all studies. Our innate immune system recognizes LPS readily via the LPS signal transduction pathway, which has the trimolecular complex of CD14/TLR4/MD2 at the core. A common single-nucleotide polymorphism in the promoter region of CD14 rs2569190 C to T (CD14/-260 or CD14/-159) has been associated with elevated sCD14. Although early studies suggested that this variant was associated with more severe atopy, this finding was not uniformly replicated. It has now been demonstrated in four independent populations that high exposure to endotoxin in the domestic environment is protective against the development of atopy, but only among carriers of the C allele, that is, the environmental exposure is only relevant when taken in the context of the genotype. Furthermore, this interaction is biologically plausible. We propose that neither the environmental exposure nor the genotype in isolation is sufficient to cause complex diseases like asthma and atopy, but disease results from the one acting in the context of the other, of which CD14 and endotoxin is one example contributing to the risk for atopy.

Polymorphisms in interleukin-1 receptor-associated kinase 4 are associated with total serum IgE

BACKGROUND

Serum immunoglobulin E (IgE) level is recognized to be under strong genetic control, but the causal and susceptibility genes remain to be identified. We sought to investigate the association between single nucleotide polymorphisms (SNPs) in the Toll-like receptor (TLR) signaling pathway and total serum IgE level.

METHODS

A population of 206 patients with severe chronic rhinosinusitis (CRS) was used. Precise phenotyping of patients was accomplished by means of a questionnaire and clinical examination. Blood was drawn for measurement of total serum IgE, as well as DNA extraction. A maximally informative set of SNPs in the TLR1, 2, 3, 4, 6, 9, 10, CD14, MD2, MyD88, IRAK4, and TRAF6 genes were selected and genotyped. Significant findings were replicated in a second independent population of 956 subjects from 227 families with asthma.

RESULTS

A total of 97 out of 104 SNPs were successfully genotyped. Three SNPs in IRAK4--rs1461567, rs4251513, and rs4251559--were associated with total serum IgE levels (P < 0.004). In the replication sample, the same SNPs as well as the same orientation of the risk allele were associated with IgE levels (P < 0.031).

CONCLUSIONS

These results demonstrate a clear association between polymorphisms in the IRAK4 gene and serum IgE levels in patients with CRS and asthma. IRAK4 may be important in the regulation of IgE levels in patients with inflammatory diseases of the airways.

Does the relationship between IgE and the CD14 gene depend on ethnicity?

This review considers the data from studies analysing associations between the CD14C-159T single nucleotide polymorphism (SNP) and asthmatic phenotypes and discusses the variability of the conclusions. By searching PubMed and EMBASE for articles on CD14C-159T -related population or family-based association studies, 47 were identified up till September 2007. Collectively, the studies reviewed herein consistently showed population differences in frequencies of the alleles of the SNP, with African descent having the highest C allele frequencies, followed by Caucasians and Asians. The T allele of the SNP was associated with increased sCD14 in some studies but not in others. Inconsistently, the C allele, or even occasionally the T allele, was associated with atopic phenotypes in a population subgroup. There are several explanations for these inconsistencies, including lack of power, linkage disequilibrium, gene-gene interactions, population admixture and gene-environment interactions. If the SNP was associated with functional changes to the coded protein and thus modulating susceptibility to allergic disease, its effect may be modest and dependent on other co-existent, ethnicity-specific, genetic or environmental risk factors.

An association study of 13 SNPs from seven candidate genes with pediatric asthma and a preliminary study for genetic testing by multiple variants in Taiwanese population

INTRODUCTION

Asthma is one of the most common chronic diseases in children. It is caused by complex interactions between various genetic factors and exposures to environmental allergens and irritants. Because of the heterogeneity of the disease and the genetic and cultural differences among different populations, a proper association study and genetic testing for asthma and susceptibility genes is difficult to perform.

MATERIALS AND METHODS

We assessed 13 single-nucleotide polymorphisms (SNPs) in seven well-known asthma susceptibility genes and looked for association with pediatric asthma using 449 asthmatic subjects and 512 non-asthma subjects in Taiwanese population.

RESULTS

CD14-159 C/T and MS4A2 Glu237Gly were identified to have difference in genotype/allele frequencies between the control group and asthma patients. Moreover, the genotype synergistic analysis showed that the co-contribution of two functional SNPs was riskier or more protective from asthma attack. Our study provided a genotype synergistic method for studying gene-gene interaction on polymorphism basis and genetic testing using multiple polymorphisms.

Toll-like receptors and CD14 genes polymorphisms and susceptibility to asthma in Tunisian children

Many studies have shown the implication of CD14 and toll-like receptors (TLRs) 2, 4 and 9 in the pathogenesis of asthma or atopy. To evaluate the association of CD14 and TLRs gene polymorphisms with asthma or atopy, 210 asthmatic children, 224 controls and 80 families were enrolled in this study. Six single nucleotide polymorphisms TLR2 (+2408 G-->A), TLR4 (+1196 C-->T), TLR4 (+896 A-->G), TLR9 (-1237 T-->C), TLR9 (-1486 T-->C) and CD14 (-159 C-->T) were genotyped using polymerase chain reaction followed by restriction fragment length polymorphism in the case-control and family study. The -1237C allele in TLR9 gene polymorphisms was associated with increased risk of asthma [odds ratio 1.53, 95% confidence interval (1.03-2.27)], although no statistically significant differences in allele or genotype frequencies of four other TLRs polymorphisms were evident between the asthmatic and control groups. The CD14 -159 C allele was found to be significantly higher in the asthmatic group when compared with controls (P=0.0006<0.05). Transmission disequilibrium test of 80 asthmatic families showed significant transmission of the -159 C allele in the CD14 gene to asthma-affected offspring. It was concluded that TLR9 and CD14 gene polymorphisms may contribute to an inherited predisposition to asthma in Tunisian children.

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

PURPOSE OF REVIEW

The 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 FINDINGS

The 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.

SUMMARY

The 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.

Family studies and positional cloning of genes for asthma and related phenotypes

Although it is not yet known how many genes may contribute to the susceptibility or the severity of asthma and related phenotypes, genome-wide screens and positional cloning techniques have been successful in identifying contributing genes in multiple populations. The results of these studies provide additional insight into the molecular mechanisms responsible for the development of a variety of phenotypes. Replication with additional populations--particularly in large-scale studies--has been used to distinguish between false positive results or population-specific effects or to further quantify the conferred risk. Even when individual markers do not replicate in multiple population, association of the same region or gene has been useful in directing future studies. As further understanding of linkage disequilibrium patterns within the genome has allowed greater efficiency for genetic studies, advances in high-throughput genotyping technology, genetic analysis methodologies, and a more in-depth understanding of clinical phenotypes has made genome-wide studies more accessible and cost-effective. In the future, identification of function variants with clinical relevance may be used to influence the diagnosis and treatment of asthma.

Gene by Environment Interaction: The -159C/T Polymorphism in the Promoter Region of the CD14 Gene Modifies the Effect of Alcohol Consumption on Serum IgE Levels

BACKGROUND

Serum IgE is increased in heavy drinkers. Endotoxin mediates most of the immunological alterations associated with heavy drinking. The -159C/T polymorphism in the promoter region of the gene encoding CD14 (an endotoxin receptor) is associated with serum IgE levels in different populations.

AIM

To investigate the possible interaction between alcohol intake and the -159C/T polymorphism in the promoter region of the CD14 gene for serum IgE levels.

METHODS

A total of 415 individuals (51.6% males, median age 50 years, range 18-92 years) were studied. A total of 140 individuals were alcohol abstainers, 112 were moderate drinkers (1-280 g/week), and 163 were heavy drinkers (>280 g/week). Main determinations included the CD14/-159C/T genotype, a panel of skin prick tests, total serum IgE, and specific serum IgE against common aeroallergens (Phadiatop test).

RESULTS

Heavy drinking was associated with increased total serum IgE values and with positive specific serum IgE to common aeroallergens, but the association was stronger in carriers of the CD14/-159C allele (either CC homozygotes or CT heterozygotes) than in CD14/-159TT homozygotes. Both additive and multiplicative interactions between heavy drinking and the CD14/-159C allele for total and specific serum IgE values was still present after adjusting for potential confounders. Neither alcohol consumption nor the CD14/-159 genotype was associated with skin prick test positivity.

CONCLUSIONS

The CD14/-159C/T polymorphism modifies the effect of alcohol consumption on serum IgE levels.

Association of CD14 promoter polymorphisms and soluble CD14 levels in mite allergen sensitization of children in Taiwan

CD14 is responsible for environmental lipopolysaccharide recognition and is a positional candidate gene for allergy. We hypothesized that genetic polymorphisms in the promoter region of the CD14 gene may be associated with Dermatophagoides pteronysinnus (Der p) allergen sensitization in children. Three single nucleotide polymorphisms (SNPs) of the CD14 promoter region, C(-159)T, A(-1,145)G, and G(-1,359)T were genotyped, and analyzed in 240 randomized case-control school-age children in Taiwan. Serum concentrations of IgE and soluble CD14 (sCD14) were also assayed. We found a significant inverse correlation of sCD14 and total serum IgE levels in our study population. Moreover, sCD14 binds Der p allergen in vitro in a dose-dependent manner. The distribution of three SNPs genotypes was similar in asthmatic children and the control group. However, there was a significant difference in the distribution of genotype CD14 G(-1,359)T, but not C(-159)T, between mite-sensitive and non-sensitive children. Haplotype analysis showed strong linkage disequilibrium among these three SNPs in the CD14 promoter region. Carriers of the CD14-159C/-1,145A/-1,359T haplotype had the highest IgE and lowest sCD14 levels as compared to other haplotypes. Our results support the hypothesis that CD14 gene variants may play an important role in influencing allergen sensitization of children in Taiwan.