ADAM33 polymorphism: association with bronchial hyper-responsiveness in Korean asthmatics

Association of ADAM33 gene polymorphisms with adult allergic asthma and rhinitis in a Chinese Han population

Background

Rhinitis and asthma are very common diseases involving genetic and environmental factors. Most patients with asthma also have rhinitis, which suggests the concept of 'one airway, one disease.' A disintegrin and metalloproteinase 33 (ADAM33) is the first asthma-susceptible gene to be discovered by positional cloning. To evaluate the potential influence of ADAM33 gene polymorphisms on allergic rhinitis (AR) and allergic asthma (AS), a case-control study was conducted on the Han population of northeast China.

Methods

Six polymorphic sites (V4, T+1, T2, T1, S1, and Q-1) were genotyped in 128 patients with AR, 181 patients with AS, and 151 healthy controls (CTR). Genotypes were determined by the polymerase chain restriction fragment length polymorphism (PCR-RFLP) method. Data were analyzed using the chi-square test with Haploview software.

Results

The single nucleotide polymorphisms (SNPs), V4 G/C, T+1 A/G, and T1 G/A, of the ADAM33 gene may be the causal variants in AR, whereas ADAM33 V4 G/C, T2 A/G, T1 G/A, and Q-1A/G may participate in the susceptibility of AS.

Conclusion

These results suggest that polymorphisms of the ADAM33 gene may modify individual susceptibility to AR and AS in a Chinese Han population.

Association of ADAM33 gene polymorphisms with adult concomitant allergic rhinitis and asthma in Chinese Han population

Allergic Rhinitis (AR) and allergic asthma (AS) are very common diseases involving genetic and environmental factors. Most patients with asthma also have rhinitis, which suggests the concept of 'one airway, one disease'. A disintegrin and metalloproteinase 33 (ADAM33) was discovered as the first asthma-susceptible gene by positional cloning. To evaluate the potential influences of ADAM33 gene polymorphisms on concomitant allergic rhinitis and asthma (ARA), a case-control study was conducted in Han population of Northeast China. Six polymorphic sites (V4, T + 1, T2, T1, S1 and Q - 1) were genotyped in 135 ARA patients and 151 controls (CTR). Genotypes were determined by the polymerase chain restriction fragment length polymorphism (PCR-RFLP) method. Data was analyzed using the Chisquaretest and Haploview software. The SNPs (V4 G/C, T2 A/G, T1 G/A, and Q - 1A/G) of the ADAM33 gene may be the causal variants in ARA disease.

Race, ethnicity and social class and the complex etiologies of asthma

Asthma is a common but complex respiratory disease caused by the interaction of genetic and environmental factors. Significant racial and ethnic disparities in prevalence, mortality and drug response have been described. These disparities may be explained by racial and ethnic-specific variation in genetic, environmental, social and psychological risk factors. In addition, race, ethnicity and social class are important proxies for unmeasured factors that influence health outcomes. Herein, we review salient differences in the etiologies of asthma by race, ethnicity and social class, and argue for their continued use as variables in asthma research.

Modeling the impact of genetic screening technologies on healthcare: theoretical model for asthma in children

BACKGROUND AND OBJECTIVE

This study focuses on the potential impact of genetic screening technologies on healthcare. Genetic screening for asthma in children was chosen as a case study to explore the cost effectiveness of applying early genetic screening to infants, and preventive treatment to the population at risk. Early intervention could prevent progression and facilitate clinical management of the disease. From the elite group of genetic markers that have been associated with asthma-related phenotypes, ADAM33 was the first published candidate gene detected by a positional cloning approach, marking the entry of asthma research into the genomic era. The model was, therefore, initially set for an ex ante analysis of the cost effectiveness of applying the preventive program to an infant population at risk, i.e. infants presenting wheezing episodes during the first year of life, and the ADAM33 ST+7 genetic marker, with the idea of expanding to further markers and their combinations lat a later date.

METHODS

In accordance with the US National Heart, Lung, and Blood Institute, four categories of asthma were considered. A Markov model was constructed, consisting of six mutually exclusive disease states (including healthy and dead states) with a simulation horizon of 100 years and a cycle length of 1 year. We define a scenario where early genetic screening was applied to infants presenting wheezing episodes during the first year of life and a preventive treatment to those children within this group who tested positive for selected ADAM33 polymorphism (ST+7). The cost-effectiveness analysis was performed from the third-party payer and patient perspective after year 6. We applied our model to a hypothetical cohort of 100 European infants.

RESULTS

The number of quality-adjusted life-years (QALYs) gained during the 6 years was 1.483, and the incremental cost-effectiveness ratio per QALY gained was euro 10,100/QALY. A sensitivity analysis was carried out that varied the discount rate and cost of genetic testing, and considered two different transition matrices for the preventive program. Three main conclusions were drawn from the sensitivity analysis. Firstly, if the discount rate for both cost and health outcomes is increased by 2%, the cost effectiveness of the preventive program does not vary significantly. Discounting costs and benefits at 5%, the preventive program appears cost effective (euro 11,100/QALY). Secondly, if the cost of genetic testing is increased to euro 100, the cost effectiveness of the preventive program remains within the limits of cost effectiveness. Thirdly, the cost of genetic screening, together with transition probabilities between health states, will determine the cost effectiveness of applying a preventive program based on genetic information.

CONCLUSIONS

Preventive treatment based on an early genetic screening of those children who present wheezing episodes during the first year of life, with treatment applied to those who test positive for the asthma-associated genetic marker ADAM33 ST+7, is theoretically cost effective. The model is a valuable tool for the ex ante assessment of the cost effectiveness of preventive schemes based on genetic screening. The value of modeling prior to clinical trials lies in informing study design and setting priorities for future research.

Gene mapping in asthma-related traits

In asthma, as in many other common multifactorial diseases, the identification of the susceptibility genes has been challenging because consistent results at the genome-wide significance level have been scarce. So far, genome-wide scans have been reported in 17 study populations. By means of genome-wide linkage and hierarchical association analysis, six positional candidate genes (ADAM33, PHF11, DPP10, GPR154, HLA-G, and CYFIP2) for asthma-related traits have been cloned. The interactions of the proteins encoded by these genes and the biological relevance of these signaling pathways in the development of asthma are still poorly understood. Also, the disease mechanisms resulting from the genetic variance in the genes identified remain largely unknown. Although this information is gradually accumulating, we can examine the statistical robustness of each genetic finding in combination with the limited data available on the functional properties of the corresponding proteins to estimate the strengths and weaknesses in the chains of evidence.

Comprehensive testing of positionally cloned asthma genes in two populations

RATIONALE

Replication of gene-disease associations has become a requirement in complex trait genetics.

OBJECTIVES

In studies of childhood asthma from two different ethnic groups, we attempted to replicate associations with five potential asthma susceptibility genes previously identified by positional cloning.

METHODS

We analyzed two family-based samples ascertained through an asthmatic proband: 497 European-American children from the Childhood Asthma Management Program and 439 Hispanic children from the Central Valley of Costa Rica. We genotyped 98 linkage disequilibrium-tagging single-nucleotide polymorphisms (SNPs) in five genes: ADAM33, DPP10, GPR154 (HUGO name: NPSR1), HLA-G, and the PHF11 locus (includes genes SETDB2 and RCBTB1). SNPs were tested for association with asthma and two intermediate phenotypes: airway hyperresponsiveness and total serum immunoglobulin E levels.

MEASUREMENTS AND MAIN RESULTS

Despite differing ancestries, linkage disequilibrium patterns were similar in both cohorts. Of the five evaluated genes, SNP-level replication was found only for GPR154 (NPSR1). In this gene, three SNPs were associated with asthma in both cohorts, although the opposite alleles were associated in either study. Weak evidence for locus-level replication with asthma was found in the PHF11 locus, although there was no overlap in the associated SNP across the two cohorts. No consistent associations were observed for the three other genes.

CONCLUSIONS

These results provide some further support for the role of genetic variation in GPR154 (NPSR1) and PHF11 in asthma susceptibility and also highlight the challenges of replicating genetic associations in complex traits such as asthma, even for genes identified by linkage analysis.

[Asthma genetic factors]

Asthma is a chronic inflammatory airways disease, with a rising prevalence, particularly in childhood, and is considered an important public health problem. Its familial transmission is recognised, while the description and identification of the genes implicated in this disease are a challenge. In this revision paper the authors give a comprehensive explanation of the associated genes as well as the laboratorial methods that allow their identification.

Mechanistic role of a disease-associated genetic variant within the ADAM33 asthma susceptibility gene

BACKGROUND

ADAM33 has been identified as an asthma-associated gene in an out-bred population. Genetic studies suggested that the functional role of this metalloprotease was in airway remodeling. However, the mechanistic roles of the disease-associated SNPs have yet to be elucidated especially in the context of the pathophysiology of asthma. One disease-associated SNP, BC+1, which resides in intron BC toward the 5' end of ADAM33, is highly associated with the disease.

METHODS

The region surrounding this genetic variant was cloned into a model system to determine if there is a regulatory element within this intron that influences transcription.

RESULTS

The BC+1 protective allele did not impose any affect on the transcription of the reporter gene. However, the at-risk allele enforced such a repressive affect on the promoter that no protein product from the reporter gene was detected. These results indicated that there exists within intron BC a regulatory element that acts as a repressor for gene expression. Moreover, since SNP BC+1 is a common genetic variant, this region may interact with other undefined regulatory elements within ADAM33 to provide a rheostat effect, which modulates pre-mRNA processing. Thus, SNP BC+1 may have an important role in the modulation of ADAM33 gene expression.

CONCLUSION

These data provide for the first time a functional role for a disease-associated SNP in ADAM33 and begin to shed light on the deregulation of this gene in the pathophysiology of asthma.

DNA sequence variations of metalloproteinases: their role in asthma and COPD

Asthma and chronic obstructive pulmonary disease (COPD) are complex genetic diseases that cause considerable morbidity and mortality worldwide. Genetic variability interacting with environmental and ethnic factors is presumed to cause tobacco smoke susceptibility and to influence asthma severity. A disintegrin and metalloproteinase 33 (ADAM33) and matrix metalloproteinase-9 (MMP9) appear to have important roles in asthma and COPD pathogenesis. ADAM33 and MMP9 genetic alterations could possibly contribute to the establishment and progression of these multifactorial diseases, although their association with the clinical phenotypes has not yet been elucidated. However, the occurrence of these alterations does not always result in clear disease, implying that either they are an epiphenomenon or they are in proximity to the true causative alteration. This review summarises the most recent literature dealing with the genetic variations of metalloproteinases and outlines their potential pathogenetic outcome.

Increased expression of ADAM33 and ADAM8 with disease progression in asthma

BACKGROUND

ADAM33, a disintegrin and metalloproteinase 33 gene, has been identified as a risk factor for asthma and bronchial hyperresponsiveness and has been postulated as a gene for airway remodeling. ADAM8 is strongly induced by allergens and T(H)2 cytokines in the lung in experimental asthma.

OBJECTIVES

To assess the importance of these genes in asthma pathogenesis and to investigate whether expression relates to disease severity or deterioration in lung function, we measured the mRNA and protein expression of both genes in bronchial biopsies of subjects with asthma and control subjects.

METHODS

RNA was extracted from frozen endobronchial biopsies of mild, moderate, and severe adults with asthma and controls. Subjects with moderate and severe asthma were taking corticosteroids. The mRNA transcript of both genes was measured by real time RT-PCR using specific primers. Protein expression was examined by immunohistochemistry on paraffin sections.

RESULTS

ADAM33 mRNA expression was significantly higher in both moderate and severe asthma compared with mild asthma (P < .05) and controls. Immunostaining for ADAM33 was increased in the epithelium, submucosal cells, and smooth muscle in severe asthma compared with mild disease and controls. ADAM8 mRNA expression was significantly increased in all asthma groups compared with controls. Increased inflammatory cells stained positive for ADAM8 in both moderate (P < .05) and severe asthma (P < .005) compared with mild disease.

CONCLUSIONS

These results demonstrate increased expression of both ADAM genes as asthma severity increases.

CLINICAL IMPLICATIONS

These genes may contribute to the remodeling process that occurs with asthma progression and may have implications for future treatment in severe disease.

Association between ADAM33 polymorphisms and adult asthma in the Japanese population

BACKGROUND

ADAM33, a member of the ADAM (a disintegrin and metalloprotease) family, is a putative asthma susceptibility gene recently identified by positional cloning. It is important to know whether the association exists in ethnically diverse populations.

OBJECTIVE

To assess whether genetic functional variants of ADAM33 relate to the susceptibility or some phenotypes in adult patients with bronchial asthma in a Japanese population.

METHODS

We searched for single nucleotide polymorphisms (SNPs) in ADAM33 by PCR-directed sequencing and identified 48 SNPs. Fourteen SNPs were selected with regard to the LD pattern, and genotyped by Taq-Man and PCR-RFLP methods. We conducted an association study of ADAM33 with 504 adult asthmatic patients and 651 controls, and haplotype analyses of related variants were performed.

RESULTS

Significant associations with asthma were found for the SNPs T1 (Met764Thr), T2 (Pro774Ser), S2 and V-3 (with the lowest P-value for T1, P = 0.0015; OR 0.63). We analysed the haplotype using these four polymorphisms, and found a positive association with haplotype CCTG (P = 0.0024).

CONCLUSION

Our results replicate associations reported recently in other ethnic populations, and suggest that the ADAM33 gene is involved in the development of asthma through genetic polymorphisms.

Mouse genetic model for antigen-induced airway manifestations of asthma

Allergic asthma is a genetically complex disease characterized by allergen-specific immunoglobulin (Ig)E, eosinophilic inflammation of the lungs and airway hyper-responsiveness to bronchospasmogenic stimuli. In this study, we compared 13 recombinant congenic (RC) mouse strains in an ovalbumin model of allergic asthma. Different intensities and types of responses are observed throughout the RC strains. Intensities range from resistance to asthma in CcS05, to a very severe bronchoconstrictive reaction upon methacholine challenge for the parental STS strain. All strains show a 'modified' Th2 response except CcS14, which shows a 'true' Th2 response. When data from all strains are pooled, airway reactivity shows significant correlations with the serum Ig levels and the levels of interleukin (IL)-4, IL-5 and IL-13 in the broncho-alveolar lavage (BAL), at low dosage of methacholine (below 25 mg/ml), whereas at high dosage airway reactivity only correlates with BAL neutrophil levels. This indicates that at least two different mechanisms are involved in the airway reactivity to methacholine. None of these correlations can be found in every individual strain, which demonstrates that the asthma traits in this mouse model are genetically dissociated and that the loci can be genetically mapped.

ADAM33 polymorphisms are associated with asthma susceptibility in a Japanese population

BACKGROUND

Asthma is the most common chronic disorder in childhood, and asthma exacerbation is an important cause of childhood morbidity and hospitalization. Asthma is believed to be a complex disorder involving genetic and environmental factors, and several asthma susceptibility loci have been identified through genome-wide screening. A disintegrin and metalloprotease 33 (ADAM33) was the first asthma susceptibility gene to be discovered by positional cloning in 2002.

OBJECTIVE

The aim of the present study was to investigate whether single-nucleotide polymorphisms (SNPs) in ADAM33 are associated with childhood asthma in the Japanese population.

METHODS

Twenty-three ADAM33 SNPs were genotyped by fluorescence correlation spectroscopy with the use of DNA from 155 families (538 members) identified through children with atopic asthma. The transmission disequilibrium test (TDT) was performed for family-based association study.

RESULTS

TDT revealed that minor alleles of S+1, ST+4, and T2 SNPs were over-transmitted to asthma-affected offspring (P<0.05). According to the haplotype TDT, no haplotype of ADAM33 was transmitted preferentially to asthmatic offspring.

CONCLUSION

Our results confirm the involvement of ADAM33 in the development of childhood asthma among the Japanese.

ADAM33 polymorphisms are associated with aspirin-intolerant asthma in the Japanese population

Multiple single nucleotide polymorphisms (SNPs) within ADAM33 have been reported to be associated with asthma and bronchial hyper-responsiveness in Caucasian populations. We examined whether these SNPs contribute to a predisposition to asthma, especially aspirin-intolerant asthma (AIA), in the Japanese population. Ten polymorphic sites (ST+4, ST+7, T1, T2, T+1, V-3, V-2, V-1, V4, V5) were genotyped in 102 AIA patients, 282 aspirin-tolerant asthma (ATA) patients and 120 control (CTR) subjects by direct sequencing. Haplotype frequencies were estimated by the expectation-maximization method. Differences in allele and haplotype frequencies among phenotypes were analyzed by the chi-square and permutation tests. ST+7, V-1 and V5 sites in the AIA group were significantly different from those in the ATA group (P=0.034-0.004) and from those in the CTR group (P=0.019-0.002). Haplotypes at three sites (ST+7, V-1, and V5) were significantly different in frequency between the AIA and ATA (P=0.008) or CTR (P=0.001) groups. Sequence variations in ADAM33 are likely to correlate with susceptibility to AIA in the Japanese population.

ADAM33 is not essential for growth and development and does not modulate allergic asthma in mice

A disintegrin and metalloprotease 33 (ADAM33) is a transmembrane protease and integrin ligand that has been identified as an asthma susceptibility gene product. To determine whether ADAM33 plays important roles in mammalian development and the modulation of allergic airway dysfunction, we generated ADAM33-null mice by gene targeting. ADAM33-null mice were born at expected Mendelian ratios, and both male and females developed normally and were fertile. No anatomical or histological abnormalities were detected in any tissues. In an animal model of allergic asthma, ADAM33-null mice showed normal allergen-induced airway hyperreactivity, immunoglobulin E production, mucus metaplasia, and airway inflammation. Our results demonstrate that ADAM33 is not essential for growth or reproduction in the mouse and does not modulate baseline or allergen-induced airway responsiveness.

The role of novel genes in modifying airway responses in asthma

Major progress has been made during the past few years in developing a better understanding of the genetic basis of asthma, which has led to the identification of several chromosomal regions and loci showing linkage to and association with asthma and asthma-related phenotypes. Recent positional cloning approaches have also been informative in identifying several strong candidate genes for asthma. As another approach, association studies between candidate gene polymorphisms and asthma-related phenotypes have been conducted in many areas and replicated in different ethnic groups. These approaches need to be followed by validation processes to confirm their functional relevance in the pathophysiology of asthma. In this review, we describe several novel genes, including ADAM33, ADRB2, and eotaxin, that modify airway responsiveness in asthmatic patients.

Lack of association between ADAM33 gene and asthma in a Chinese population

Asthma is a complex polygenic disease with gene-environment interactions being important. It has been previously suggested that ADAM33, which is a member of a gene family that encodes membrane-anchored proteins with a disintegrin and a metalloprotease domain, is primarily expressed in lung fibroblasts and bronchial smooth muscle cells and has been associated with airway remodelling and bronchial hyperresponsiveness. A significant association has previously been demonstrated between single nucleotide polymorphisms (SNPs) and haplotypes of the ADAM33 and asthma in ethnically diverse populations. To assess whether SNPs or haplotypes of ADAM33 are related to asthma in a Chinese Han population, we genotyped three SNPs of ADAM33 (7575G/A in intron 6, 11188A/T in intron 19, and 12433T/C in exon 20) in a case-control study involving 296 patients with asthma and 270 healthy controls. No significant association was detected between these three SNPs and asthma susceptibility in the Chinese population.

ADAM33 haplotypes are associated with asthma in a large Australian population

The ADAM33 gene has recently been identified as being a potentially important asthma candidate gene, and polymorphisms in this gene have been shown to be associated with asthma and bronchial hyperresponsiveness in Caucasian individuals from several populations. We performed chip-based matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) mass spectrometry using the MassARRAY system and multiplexed genotyping assays to investigate the association between 10 single nucleotide polymorphisms (SNPs) in the ADAM33 gene (F_+1, Q_-1, S_1, ST_+4, ST_+7, V_-2, V_-1, V_2, V_4, V_5) and asthma and asthma severity in a large Australian Caucasian population of nonasthmatic controls (n = 473), and patients with mild (n = 292), moderate (n = 238) and severe (n = 82) asthma. No significant association was found between any one of the 10 SNPs and asthma or asthma severity, however, there was a significant global haplotypic association with asthma (P = 0.0002) and disease severity (P = 0.0001), driven by the combination of two key SNPs, V_-1 and ST_+7. A meta-analysis of all the genetic studies conducted to date found significant between-study heterogeneity, likely to reflect population stratification. Our analysis of ADAM33 haplotypes further suggests a likely role for ADAM33 in the asthma phenotype, although it does not exclude an association with another locus in linkage disequilibrium with ADAM33.

The current status of asthma in Korea

A systematic review of English and Korean articles published between 1990 and 2004 and a search of database and various online resources was conducted to determine the prevalences, mortality rates, socioeconomic burden, quality of life, and treatment pattern of asthma in Korean adults and children. Asthma morbidity and mortality in Korea are steadily increasing. The prevalence of asthma in Korea is estimated to be 3.9% and its severity is often underestimated by both physicians and patients. Mortality resulting from chronic lower respiratory diseases including asthma increased from 12.9 to 22.6 deaths per 100,000 of the population between 1992 and 2002. Disease severity, level of control, and symptom state were all found to negatively impact the quality of life of asthmatics. Although international and Korean asthma management guidelines are available, familiarity with and implementation of these guidelines by primary care physicians remain poor.

ADAM33: a newly identified gene in the pathogenesis of asthma

There is much to find out about this fascinating and complex molecule in relation to the development and progression of asthma. Added to it are three further new asthma/allergy genes identified by positional cloning: PDH Finger Protein II (PHF11) on chromosome 13q14, which encodes NY-REN-34 a protein first described in patients with renal cell carcinoma [67]; Dipeptidyl diptidase 10 (DDP10) on chromosome 2q14 [68]; and G protein-coupled receptor for asthma susceptibility (GPRA) on chromosome 7p [69]. For each of these genes, as is the case for ADAM33, determining their normal function(s) and how these become disordered in asthma is the future challenge.

Mapping and identifying genes for asthma and psoriasis

Susceptibility genes for complex diseases are characterized by reduced penetrance, caused by the influence of other genes, the environment or stochastic events. Recently, positional cloning efforts have yielded several candidate susceptibility genes in different complex disorders such as Crohn's disease and asthma. Within a genetic locus, however, the identification of the effector gene may pose further challenges and require functional studies. I review two examples of such challenges: the cloning of GPR154 (GPRA) and AAA1 on chromosome 7p14 at a susceptibility locus for atopy and asthma, and the study of HLA-Cw6, CCHCR1 (HCR) and CDSN on chromosome 6p21 at PSORS1, the major susceptibility locus for psoriasis. The susceptibility locus for atopy and asthma contains two genes and only one of them is protein coding. We studied its isoform-specific expression in bronchial biopsies and in a mouse model of ovalbumin-induced inflammation of bronchial epithelia. In the PSORS1 locus, strong linkage disequilibrium between genes has made it difficult to distinguish the effects of the three nearby genes. We engineered transgenic mice with either a HCR non-risk allele or the HCR*WWCC risk allele controlled by the cytokeratin-14 promoter. The results suggested that the overexpression of HCR in mouse skin was insufficient to induce a psoriasiform phenotype, but it appeared to induce allele-specific gene expression changes that were similar to those observed in psoriatic skin.

A disintegrin and metalloproteinase 33 protein in patients with asthma: Relevance to airflow limitation

BACKGROUND

ADAM33 has been identified as a novel asthma susceptibility gene in genomewide screening and association studies. High-level expression in smooth muscles and fibroblasts suggests that ADAM33 plays a role in airway remodeling in patients with asthma.

METHODS

The ADAM33 protein was identified in the bronchoalveolar lavage (BAL) fluids of patients with asthma and normal control subjects using Western blotting antibody against the catalytic domain. ADAM33 expression was analyzed using immunohistochemical staining of mucosal biopsy specimens. The levels of ADAM33 protein in the BAL fluids were measured by dot blotting, and were correlated with the FEV1 values of the patients with asthma.

RESULTS

Western blot analysis revealed the presence of the ADAM33 protein, with a molecular mass of approximately 55 kD in the BAL fluids. ADAM33 was expressed in the smooth muscles and basement membranes of almost all the patients with asthma, but was absent in the normal control subjects. The ADAM33 levels were increased significantly in patients with moderate to severe asthma and in patients with mild asthma, as compared with normal control subjects (p = 0.001 and p = 0.016, respectively). The ADAM33 protein levels correlated inversely with the FEV(1)% predicted in the patients with asthma (r = -0.486, p = 0.018).

CONCLUSIONS

ADAM33 is associated with asthma development, and the levels of ADAM protein are related to asthma severity.

ADAM33: a newly identified protease involved in airway remodelling

Asthma is a complex disorder in which major genetic and environmental factors interact to both initiate the disease and modify its progression. While asthma is recognised as a disorder of the conducting airways characterised by Th2-directed inflammation, it is being increasingly apparent that alteration of the structural cells of the airways (airway remodelling) is also fundamental to disease chronicity and severity. The gene ADAM33, encoding a novel member of a identified as an asthma susceptibility gene as the result of a positional cloning effort in a cohort of families recruited form the UK and USA. Subsequent genetic studies have now provided evidence that ADAM33 may be involved in determining lung function throughout life, associated with early life lung function as well as increased decline therapeutic intervention in asthma and future work will focus on the mechanisms by which it alters lung function and bronchial hyperresponsiveness.

A disintegrin and metalloprotease 33 polymorphisms and lung function decline in the general population

RATIONALE

A disintegrin and metalloprotease 33 (ADAM33) has been identified as a susceptibility gene for asthma and single nucleotide polymorphisms (SNPs) in this gene have been associated with excessive decline of lung function in individuals with asthma.

OBJECTIVES

To assess whether SNPs in ADAM33 are associated with accelerated lung function loss in the general population and with chronic obstructive pulmonary disease (COPD).

METHODS

DNA was collected from subjects of the Vlagtwedde-Vlaardingen cohort participating in the last survey in 1989-1990 after a follow-up of 25 years. Information was collected every 3 years, including lung function measurements. We defined COPD as GOLD stage 2 or higher at the last survey. A total of 1,390 subjects from the cohort was genotyped for the following SNPs in ADAM33: F+1, Q-1, S_1, S_2, T_1, T_2, V_4, and ST+5. Differences in prevalence of SNPs were analyzed with chi(2) tests. Linear mixed effects models were used to analyze FEV(1) decline according to genotype.

MEASUREMENTS AND MAIN RESULTS

In the whole population, mean adjusted decline was 18.7 and 12.7 ml/year in females and males, respectively. Individuals homozygous for minor alleles of SNPs S_2 and Q-1 and heterozygous for SNP S_1 had a significantly accelerated decline in FEV(1) of, respectively, 4.9, 9.6, and 3.6 ml/year compared with wild type. We found a significantly higher prevalence of SNPs F+1, S_1, S_2, and T_2 in subjects with COPD.

CONCLUSIONS

We demonstrated that SNPs in ADAM33 are associated with accelerated lung function decline in the general population. These SNPs are also risk factors for COPD.

Contribution of ADAM33 polymorphisms to the population risk of asthma

BACKGROUND

ADAM 33 is the first gene identified as a candidate for asthma by positional cloning techniques, with association studies reaching impressive statistical significance. It has a postulated role in myogenesis, airway modelling, and signalling via protein shedding. Concerns over the methodology of the initial study have led to several attempts at replication, with inconsistent results.

METHOD

To clarify the role of ADAM33 in determining the risk of asthma in the general population, new transmission disequilibrium and case-control studies were undertaken followed by a meta-analysis of all existing data.

RESULTS

Studies in Icelandic and UK populations revealed no association when taken in isolation. The meta-analysis, however, showed that the F+1 and ST+7 variants were significantly associated with asthma in both types of study.

CONCLUSIONS

The additional risk imparted by this variation would account for 50,000 excess asthma cases in the UK alone. This study also demonstrates the size of study required to investigate such hypotheses adequately.

Polymorphisms in a disintegrin and metalloprotease 33 (ADAM33) predict impaired early-life lung function

RATIONALE

Asthma commonly originates in early life in association with impaired lung function, which tracks to adulthood.

OBJECTIVES

Within the context of a prospective birth cohort study, we investigated the association between single nucleotide polymorphisms (SNPs) in a disintegrin and metalloprotease 33 (ADAM33) gene and early-life lung function.

METHODS

Children were genotyped for 17 SNPs in ADAM33. Lung function at age 3 (n = 285) and 5 years (n = 470) was assessed using plethysmographic measurement of specific airway resistance (sRaw). At age 5, we also measured FEV(1). SNPs were analyzed individually using logistic regression, followed by linkage disequilibrium mapping to identify the causal locus.

MAIN RESULTS

Carriers of the rare allele of F+1 SNP had reduced lung function at age 3 years (p = 0.003). When the recessive model was considered, four SNPs (F+1, S1, ST+5, V4) showed association with sRaw at age 5 years (p < 0.04). Using linkage disequilibrium mapping, we found evidence of a significant causal location between BC+1 and F1 SNPs, at the 5' end of the gene. Four SNPs were associated with lower FEV(1) (F+1, M+1, T1, and T2; p < or = 0.04). The risk of transient early wheezing more than doubled among children homozygous for the A allele of F+1 (odds ratio, 2.39; 95% confidence intervals, 1.18-4.86; p = 0.02), but there was no association between any SNP and allergic sensitization or physician-diagnosed asthma.

CONCLUSIONS

Polymorphisms in ADAM33 predict impaired early-life lung function. The functionally relevant polymorphism is likely to be at the 5' end of the gene.

Positionally cloned susceptibility genes in allergy and asthma

After several years of research to find asthma-susceptibility genes using genome-wide linkage scans and refined genetic mapping methods, four highly interesting candidate genes have recently been reported. Each of these genes represents a different functional class, and might point to a new pathway in the pathogenesis of asthma. Current research is focusing on confirming the genetic associations in diverse populations and understanding the biochemical functions of the proteins. These second-generation candidate genes for asthma susceptibility will stimulate much research, and might also enable the testing of multigenic models with sufficiently large sample sets.

ADAM33 expression in asthmatic airways and human embryonic lungs

RATIONALE

Polymorphic variation in ADAM33 (A Disintegrin And Metalloprotease) is strongly associated with asthma and bronchial hyperresponsiveness in different populations.

OBJECTIVE AND METHODS

To study the role of ADAM33 in asthma, we investigated its expression in normal, asthmatic, and embryonic airways using reverse transcriptase-quantitative polymerase chain reaction and immunochemistry.

RESULTS

Several ADAM33 mRNA splice variants were detected in bronchial biopsies and embryonic lung; however, the beta-isoform and variants encoding the metalloprotease domain were rare transcripts. Western blotting of bronchial biopsies confirmed the presence of multiple isoforms of ADAM33, which had molecular weights of 22, 37, 55, and 65 kD. Immunohistochemistry and laser confocal microscopy of adult bronchial biopsies showed that alpha-smooth muscle actin and ADAM33 immunoreactivity were mostly colocalized to smooth muscle and isolated cells in the submucosa. There was no significant difference in ADAM33 mRNA amplicons or protein in subjects with asthma compared with control subjects. In developing lung, ADAM33 was found around bronchial tubes; however, immunoreactivity was more widely distributed than alpha-smooth muscle actin within undifferentiated mesenchyme; on Western blots, an additional 25-kD ADAM33 variant was detected.

CONCLUSIONS

Several ADAM33 protein isoforms occur in adult bronchial smooth muscle and in human embryonic bronchi and surrounding mesenchyme, strongly suggesting its importance in smooth muscle development and/or function, which could explain its genetic association with bronchial hyperresponsiveness. The occurrence of ADAM33 in embryonic mesenchymal cells suggests that it may be involved in airway wall "modeling" that contributes to the early life origins of asthma.

Zinc metabolism in airway epithelium and airway inflammation: basic mechanisms and clinical targets. A review

In addition to basic housekeeping roles in metalloenzymes and transcription factors, dietary zinc (Zn) is an important immunoregulatory agent, growth cofactor, and cytoprotectant with anti-oxidant, anti-apoptotic, and anti-inflammatory roles. These properties of Zn are of particular importance in maintaining homeostasis of epithelial tissues which are at the front line of defense. This review is about the role of Zn in airway epithelium (AE). The first part focuses on the cellular biology of Zn, and what is known about its distribution and function in AE. The second part of the review considers evidence for altered Zn metabolism in asthma and other chronic diseases of airway inflammation. Important issues arise from a potential therapeutic perspective as to the optimal ways to monitor circulating and epithelial Zn levels in patients and the most effective means of supplementing these levels.