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OPINION article

Front. Genet., 30 April 2013
Sec. Epigenomics and Epigenetics

Asthma—snapshot or motion picture?

  • 1Human Genetics Laboratory, University of Madeira, Funchal, Portugal
  • 2Medical Sciences Unit, Life Sciences Center, University of Madeira, Funchal, Portugal

Asthma is a complex disease physiologically characterized by shortness of breath, coughing, and wheezing (Holgate, 2011). In response to a variety of stimuli, the airways become more sensitive leading to bronchial hyperresponsiveness (Sterk and Bel, 1989; Scichilone et al., 2006; Kang et al., 2012). Consequently, in a process known as bronchoconstriction, airways become narrower, impeding the normal airflow into and out of the lungs (WHO, 2011), by contraction of the bronchial smooth muscle (EPR-3, 2007). In addition, increased production of mucus occurs, further contributing to airway obstruction (EPR-3, 2007). Asthma is a chronic inflammatory disease, which if untreated can lead to structural changes in the smooth muscle and may result in airway remodeling (EPR-3, 2007).

At the molecular level, asthma usually involves a T-helper 2-type cell response (Th2)-(Lloyd and Hessel, 2010; Wenzel, 2012). The antigen-presenting cells (APC), including dendritic cells, present the antigen to the T-cell precursor, through the major histocompatibility complex II (MHCII) molecule coupled to the T-cell receptor (Kim et al., 2010). This leads to the activation of Th2 pathway, with the production of IL4, IL5, and IL13 cytokines and the consequent activation of B-lymphocytes and production of plasma cells, these last responsible for IgE production (Wenzel, 2012). Subsequently, basophils, eosinophils, and mast cells are activated, amplifying the allergic inflammation (Lloyd and Hessel, 2010; Wenzel, 2012).

More than 100 genes have been implied in asthma susceptibility across populations (Bijanzadeh et al., 2011; Torgerson et al., 2012; Zhang et al., 2013) while the association of environmental factors ranges from excessive cleanliness, constituting the “hygiene hypothesis” (Graham-Rowe, 2011), to poor socioeconomic development (Neto et al., 2012) and smoke exposure (Burke et al., 2012) to “anything and asthma” (Buchanan et al., 2006). Furthermore, replication studies of asthma candidate genes are often inconsistent (Rogers et al., 2009). Among the main reasons pointed out for this lack of replication are the populations' heterogeneous genetic backgrounds and their interaction with environmental factors, the different study designs and the lack of statistical power of the studied sample sets (Cardon and Bell, 2001; Nicolae and Ober, 2009; Grant and Hakonarson, 2010). Additionally, it is believed that in complex diseases many factors with weak effect rather than few with strong predictive power are thought to contribute to the disease susceptibility (Buchanan et al., 2006; von Mutius, 2009).

However, and despite of our current understanding of the biology and the contribution of environmental and genetic factors (Vercelli, 2008; Mukherjee and Zhang, 2011; Antó, 2012; Kumari and Rana, 2012), asthma is still a puzzling concept. The identification of causal factors and their contribution to complex diseases remain mostly unanswered questions, given the lack of robustness, inadequacy and/or limitations of many of the present-day methodologies (Buchanan et al., 2006). In addition, the broadly used case-control and GWA approaches, designed to unveil genetic variants underlying multifactorial diseases, do not take into consideration the evolutionary history of each biological trait (Buchanan et al., 2009).

The increasing incidence of complex diseases in the human populations suggests a high frequency of deleterious genetic variants (Kryukov et al., 2007). One may speculate that these genetic variations could have been beneficial or neutral in the past but have become detrimental as a result of changes in the surrounding environment and lifestyle of contemporary societies (Kryukov et al., 2007). A classical example supporting this idea is the “thrifty genes hypothesis” (Neel, 1962), sustaining that genotypes that once were protective against food scarcity are currently predisposing to obesity and diabetes, due to the current abundance in food resources and sedentary lifestyle (McDermott, 2006; Kryukov et al., 2007; Vardi and Bloch, 2008). Given the interface between genes and environment underlying this premise, it has been proposed that not only genetic but also epigenetic factors might be involved in the heritability of type 2 diabetes (Goh and Sum, 2010; Pijl, 2011).

Epigenetics, the study of changes in DNA expression that do not imply changes in the DNA sequence (Miller and Ho, 2008) but can be transgenerationally transmitted (Anway et al., 2005), have been transforming the way complex diseases and their risk are perceived (Miller and Ho, 2008; Feinberg and Irizarry, 2010; Relton and Smith, 2010). There is increasing evidence that epigenetic patterns can be altered by environmental factors since as early as in utero life (Fraga et al., 2005; Relton and Smith, 2010; Thornburg et al., 2010; Durham et al., 2011). Ethnic differences in human DNA methylation have been observed between an African and an European population (Fraser et al., 2012) and methylation-associated SNPs (mSNPs) were also found to exist, in which one of the alleles was associated with higher levels of methylation (Fraser et al., 2012). Furthermore, given a particular environmental exposure, genetic variants affecting the susceptibility to DNA methylation (methQTL-methylation quantitative trait loci) can modify the response of modifiable genetic variants (modGV), influencing the expression of the disease phenotype. This finding may partially explain conflicting results among several genetic studies (Karmaus et al., 2013). Taken together, these findings prompt us to a combined action of environment and genetics to epigenetic signatures, therefore modulating the genetic basis of a trait or disease.

While many genes are potential targets for epigenetic modification we will mainly focus our remarks on IL4. IL4 is a key cytokine involved in inducing IgE production via Th2 pathway (Oh et al., 2010), central in allergic response (Minton, 2008). IL4 DNA methylation appears to be important in T-helper cell differentiation: while methylation of a highly conserved region at the 3′ end of IL4 gene drives Th1 differentiation, demethylation of sites within the first intron of IL4 results in enhanced IL4 production and Th2 differentiation (Miller and Ho, 2008) which is associated with an atopic asthmatic phenotype. Further, evidence of the importance of IL4 comes from observations of individuals with atopic asthma. Asthmatics who were sensitized to house dust mite extract (Dermatophagoides pteronyssinus/Dermatophagoides farinae) demonstrate a decreased level of methylation in the IL4 gene that was strongly correlated to their IL4 concentration (Kwon et al., 2008).

The IL4-c.590 C/T SNP variant (rs2243250) is located in the IL4 promoter region, with allele IL4-590*T being associated to a 3-fold increase in IL4 transcription and expression, given its extra NFAT transcription activator binding site (Rockman et al., 2003) and/or likely association of the SNP to methylation patterns, to our knowledge yet to be tested.

The frequency of IL4-590*T varies across populations, from 10.5% in Madeira Island population (Berenguer et al., 2012) to 11.3% in the South of England (Howell, 2004), and 15% in Spain (Leon et al., 2006). However, when considering Africans, the allele frequency increases dramatically, reaching 54.4% (Burchard et al., 1999), 59.2% in Cabo–Verde, and 76.5% in Guinea–Bissau (Berenguer et al., 2012). This frequency variation across present-day populations was likely shaped by positive selection, particularly influenced by pathogens (Fumagalli et al., 2009; Casto and Feldman, 2011). The IL4-590*T allele has been in fact associated with elevated anti-malarial IgG and IgE levels (Luoni et al., 2001; Farouk et al., 2005) and inversely correlated with parasitaemia in different African populations (Tangteerawatana et al., 2007). Because the Th2 response—in which IL4 plays a key role (Fumagalli et al., 2009)—is likely to be advantageous in tropical regions, where the likelihood of helminthic infection is higher (Le Souëf et al., 2006), differences in the allele frequencies across populations are likely to have occurred by natural selection (Le Souëf et al., 2006). The same allele has been linked to asthma susceptibility in a number of studies, mostly in Eurasian populations (Wang et al., 2004; Gervaziev et al., 2006; Kabesch et al., 2006; Chiang et al., 2007; Li et al., 2008; de Guia and Ramos, 2010; Berenguer et al., 2012) likely a side-effect of IL4 positive selection, acting not only over genetic and environmental factors, but also over epigenetic signatures shaped through time.

One of many questions concerning asthma that have been in discussion over the last 20 years is the apparent sudden increase of asthma prevalence in westernized societies (von Mutius, 1998; Bloomfield et al., 2006; Umetsu and DeKruyff, 2006; Graham-Rowe, 2011) and, in particular, the implications on the disease incidence in developing countries, where selection has favored the Th2–cell immune response (Le Souëf et al., 2006). On one hand, the “hygiene hypothesis” postulates that increased hygiene and reduced exposure to microbes could be responsible for the increase in asthma prevalence in developed countries (Romagnani, 2007; Brooks et al., 2013). On the other hand, exposure to outdoor pollution resulting from traffic and other sources has been also associated to asthma in a number of studies (Lee et al., 2006; McConnell et al., 2010; Patel et al., 2011; Tzivian, 2011). It has been recently shown that methylation levels in the promoter of Neuropeptide S Receptor 1 (NPSR1) gene were associated to asthma in both children and adults as a result of smoking exposure (Reinius et al., 2013). Another recent study suggests that promoter variants in NOS2 encoding for the inducible nitric oxide synthase (iNOS), when exposed to particulate matter with aerodynamic diameter ≤2.5 μm (PM2.5), were found to influence iNOS methylation pattern and thus affect the concentration of nitric oxide in exhaled breath (FeNO) levels, FeNO being considered a predictor for the future risk of asthma and wheeze (Salam et al., 2012). Interestingly, simultaneous exposure to inhaled diesel particles and allergen were found to induce hypomethylation within a CpG−408 site of the IL4 gene promoter in vivo correlating to IgE production putting forward a new model for the aetiology of asthma (Liu et al., 2008).

These observations provide evidence that the role of the environment on epigenetic “angels and devils over DNA” should be of central interest to research.

Although, asthma is a likely intricate network of factors and these observations regarding IL4 gene cannot be considered per se, they can still provide the opportunity for reflection about the current understanding of asthma targeting for new strategies, aimed to understand complex multifactorial diseases.

Rather than a present-day snapshot, asthma is more likely a motion picture across evolutionary time, in permanent interaction with the surrounding environment.

Acknowledgments

Anabela Berenguer is a recipient of a PhD scholarship from Fundação para a Ciência e Tecnologia (FCT) with the reference SFRH/BD/31273/2006.

References

Antó, J. M. (2012). Recent advances in the epidemiologic investigation of risk factors for asthma: a review of the 2011 literature. Curr. Allergy Asthma Rep. 12, 192–200.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Anway, M. D., Cupp, A. S., Uzumcu, M., and Skinner, M. K. (2005). Epigenetic transgenerational actions of endocrine disruptors and male fertility. Science 308, 1466–1469.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Berenguer, A. G., Câmara, R. A., Brehm, A. D., Oliveira, S., and Fernandes, A. T. (2012). Distribution of polymorphisms IL4-590 C/T and IL4 RP2 in the human populations of Madeira, Azores, Portugal, Cape Verde and Guinea-Bissau. Int. J. Mol. Epidemiol. Genet. 3, 179–183.

Pubmed Abstract | Pubmed Full Text

Bijanzadeh, M., Mahesh, P. A., and Ramachandra, N. B. (2011). An understanding of the genetic basis of asthma. Indian J. Med. Res. 134, 149–161.

Pubmed Abstract | Pubmed Full Text

Bloomfield, S. F., Stanwell-Smith, R., Crevel, R. W. R., and Pickup, J. (2006). Too clean, or not too clean: the hygiene hypothesis and home hygiene. Clin. Exp. Allergy 36, 402–425.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Brooks, C., Pearce, N., and Douwes, J. (2013). The hygiene hypothesis in allergy and asthma: an update. Curr. Opin. Allergy Clin. Immunol. 13, 70–77.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Buchanan, A. V., Sholtis, S., Richtsmeier, J., and Weiss, K. M. (2009). What are genes “for” or where are traits “from”? What is the question? Bioessays 31, 198–208.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Buchanan, A. V., Weiss, K. M., and Fullerton, S. M. (2006). Dissecting complex disease: the quest for the Philosopher's Stone? Int. J. Epidemiol. 35, 562–571.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Burchard, E. G., Silverman, E. K., Rosenwasser, L. J., Borish, L., Yandava, C., Pillari, A., et al. (1999). Association between a sequence variant in the IL-4 gene promoter and FEV(1) in asthma. Am. J. Respir. Crit. Care Med. 160, 919–922.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Burke, H., Leonardi-Bee, J., Hashim, A., Pine-Abata, H., Chen, Y., Cook, D. G., et al. (2012). Prenatal and passive smoke exposure and incidence of asthma and wheeze: systematic review and meta-analysis. Pediatrics 129, 735–744.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Cardon, L. R., and Bell, J. I. (2001). Association study designs for complex diseases. Nat. Rev. Genet. 2, 91–99.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Casto, A. M., and Feldman, M. W. (2011). Genome-wide association study SNPs in the human genome diversity project populations: does selection affect unlinked SNPs with shared trait associations? PLoS Genet. 7:e1001266. doi: 10.1371/journal.pgen.1001266

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Chiang, C. H., Tang, Y. C., Lin, M. W., and Chung, M. Y. (2007). Association between the IL-4 promoter polymorphisms and asthma or severity of hyperresponsiveness in Taiwanese. Respirology 12, 42–48.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

de Guia, R. M., and Ramos, J. D. (2010). The -590C/T IL4 single-nucleotide polymorphism as a genetic factor of atopic allergy. Int. J. Mol. Epidemiol. Genet. 1, 67–73.

Pubmed Abstract | Pubmed Full Text

Durham, A. L., Wiegman, C., and Adcock, I. M. (2011). Epigenetics of asthma. Biochim. Biophys. Acta 1810, 1103–1109.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Farouk, S. E., Dolo, A., Bereczky, S., Kouriba, B., Maiga, B., Färnert, A., et al. (2005). Different antibody- and cytokine-mediated responses to Plasmodium falciparum parasite in two sympatric ethnic tribes living in Mali. Microbes Infect. 7, 110–117.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Feinberg, A. P., and Irizarry, R. A. (2010). Stochastic epigenetic variation as a driving force of development, evolutionary adaptation and disease. Proc. Natl. Acad. Sci. U.S.A. 107(Suppl. 1), 1757–1764.

Fraga, M. F., Ballestar, E., Paz, M. F., Ropero, S., Setien, F., Ballestar, M. L., et al. (2005). Epigenetic differences arise during the lifetime of monozygotic twins. Proc. Natl. Acad. Sci. U.S.A. 102, 10604–10609.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Fraser, H. B., Lam, L. L., Neumann, S. M., and Kobor, M. S. (2012). Population-specificity of human DNA methylation. Genome Biol. 13:R8. doi: 10.1186/gb-2012-13-2-r8

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Fumagalli, M., Pozzoli, U., Cagliani, R., Comi, G. P., Riva, S., Clerici, M., et al. (2009). Parasites represent a major selective force for interleukin genes and shape the genetic predisposition to autoimmune conditions. J. Exp. Med. 206, 1395–1408.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Gervaziev, Y. V., Kaznacheev, V. A., and Gervazieva, V. B. (2006). Allelic polymorphisms in the interleukin-4 promoter regions and their association with bronchial asthma among the Russian population. Int. Arch. Allergy Immunol. 141, 257–264.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Goh, K. P., and Sum, C. F. (2010). Connecting the dots: molecular and epigenetic mechanisms in type 2 diabetes. Curr. Diabetes Rev. 6, 255–265.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Graham-Rowe, D. (2011). Lifestyle: when allergies go west. Nature 479, S2–S4.

Grant, S. F. A., and Hakonarson, H. (2010). “Functional genomics and proteomics in allergy,” in Allergy Frontiers: Future Perspectives, Vol. 6, eds R. Pawankar, S. T. Holgate, and L. J. Rosenwasser (Tokyo: Springer Japan), 1–18.

Holgate, S. T. (2011). Asthma: a simple concept but in reality a complex disease. Eur. J. Clin. Invest. 41, 1339–1352.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Howell, W. M. (2004). Cytokine polymorphism frequencies in a population from the South of England. Hum. Immunol. 65, 935.

Kabesch, M., Schedel, M., Carr, D., Woitsch, B., Fritzsch, C., Weiland, S. K., et al. (2006). IL-4/IL-13 pathway genetics strongly influence serum IgE levels and childhood asthma. J. Allergy Clin. Immunol. 117, 269–274.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Kang, S. H., Kim, H. Y., Seo, J. H., Kwon, J. W., Jung, Y. H., Song, Y. H., et al. (2012). Bronchial hyperresponsiveness to methacholine and AMP in children with atopic asthma. Allergy Asthma Immunol. Res. 4, 341–345.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Karmaus, W., Ziyab, A. H., Everson, T., and Holloway, J. W. (2013). Epigenetic mechanisms and models in the origins of asthma. Curr. Opin. Allergy Clin. Immunol. 13, 63–69.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Kim, H. Y., DeKruyff, R. H., and Umetsu, D. T. (2010). The many paths to asthma: phenotype shaped by innate and adaptive immunity. Nat. Immunol. 11, 577–584.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Kryukov, G. V., Pennacchio, L. A., and Sunyaev, S. R. (2007). Most rare missense alleles are deleterious in humans: implications for complex disease and association studies. Am. J. Hum. Genet. 80, 727–739.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Kumari, K., and Rana, A. C. (2012). A review on epidemology, pathopysiology and management of asthma. J. Appl. Pharm. Sci. 02, 55–64.

Kwon, N. H., Kim, J. S., Lee, J. Y., Oh, M. J., and Choi, D. C. (2008). DNA methylation and the expression of IL-4 and IFN-gamma promoter genes in patients with bronchial asthma. J. Clin. Immunol. 28, 139–146.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Lee, S. L., Wong, W. H. S., and Lau, Y. L. (2006). Association between air pollution and asthma admission among children in Hong Kong. Clin. Exp. Allergy 36, 1138–1146.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Leon, J., Leon, A. J., Cercen, M. L. H., and Garcia, J. L. (2006). Interleukin genes polymorphisms in the population of Castilla y Leon (Spain). Tissue Antigens 67:P-270. doi: 10.1111/j.1399-0039.2006.00611x

CrossRef Full Text

Le Souëf, P. N., Candelaria, P., and Goldblatt, J. (2006). Evolution and respiratory genetics. Eur. Respir. J. 28, 1258–1263.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Li, Y., Guo, B., Zhang, L., Han, J., Wu, B., and Xiong, H. (2008). Association between C-589T polymorphisms of interleukin-4 gene promoter and asthma: a meta-analysis. Respir. Med. 102, 984–992.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Liu, J., Ballaney, M., Al-alem, U., Quan, C., Jin, X., Perera, F., et al. (2008). Combined inhaled diesel exhaust particles and allergen exposure alter methylation of T helper genes and IgE production in vivo. Toxicol. Sci. 102, 76–81.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Lloyd, C. M., and Hessel, E. M. (2010). Functions of T cells in asthma: more than just TH2 cells. Nat. Rev. Immunol. 10, 838–848.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Luoni, G., Verra, F., Arcà, B., Sirima, B. S., Troye-Blomberg, M., Coluzzi, M., et al. (2001). Antimalarial antibody levels and IL4 polymorphism in the Fulani of West Africa. Genes Immun. 2, 411–414.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

McConnell, R., Islam, T., Shankardass, K., Jerrett, M., Lurmann, F., Gilliland, F., et al. (2010). Childhood incident asthma and traffic-related air pollution at home and school. Environ. Health Perspect. 118, 1021–1026.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

McDermott, R. (2006). “Thrifty gene hypothesis: challenges,” in eLS. Chichester: John Wiley and Sons Ltd. doi: 10.1002/9780470015902.a0005854. Available online at: http://www.els.net

CrossRef Full Text

Miller, R. L., and Ho, S. M. (2008). Environmental epigenetics and asthma: current concepts and call for studies. Am. J. Respir. Crit. Care Med. 177, 567–573.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Minton, K. (2008). Allergy and asthma: what “drives” IL-4 versus IL-13 signalling? Nat. Rev. Immunol. 8, 166–167.

Mukherjee, A. B., and Zhang, Z. (2011). Allergic asthma: influence of genetic and environmental factors. J. Biol. Chem. 286, 32883–32889.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

National Asthma Education and Prevention Program. (2007). Expert Panel Report 3 (EPR-3): guidelines for the diagnosis and management of asthma-summary report 2007. J. Allergy Clin. Immunol. 120, S94–S138.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Neel, J. V. (1962). Diabetes mellitus: a “thrifty” genotype rendered detrimental by “progress”? Am. J. Hum. Genet. 14, 353–362.

Pubmed Abstract | Pubmed Full Text

Neto, H. J. C., Rosário, N. A., and Solé, D. (2012). Asthma and rhinitis in South America: how different they are from other parts of the world. Allergy Asthma Immunol. Res. 4, 62–67.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Nicolae, D. L., and Ober, C. (2009). (Too) great expectations: the challenges in replicating asthma disease genes. Am. J. Respir. Crit. Care Med. 179, 1078–1079.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Oh, C. K., Geba, G. P., and Molfino, N. (2010). Investigational therapeutics targeting the IL-4/IL-13/STAT-6 pathway for the treatment of asthma. Eur. Respir. Rev. 19, 46–54.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Patel, M. M., Quinn, J. W., Jung, K. H., Hoepner, L., Diaz, D., Perzanowski, M., et al. (2011). Traffic density and stationary sources of air pollution associated with wheeze, asthma, and immunoglobulin E from birth to age 5 years among New York city children. Environ. Res. 111, 1222–1229.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Pijl, H. (2011). Obesity: evolution of a symptom of affluence. Neth. J. Med. 69, 159–166.

Pubmed Abstract | Pubmed Full Text

Reinius, L. E., Gref, A., Sääf, A., Acevedo, N., Joerink, M., Kupczyk, M., et al. (2013). DNA Methylation in the Neuropeptide S Receptor 1 (NPSR1) promoter in relation to asthma and environmental factors. PLoS ONE 8:e53877. doi: 10.1371/journal.pone.0053877

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Relton, C. L., and Smith, G. D. (2010). Epigenetic epidemiology of common complex disease: prospects for prediction, prevention and treatment. PLoS Med. 7:e1000356. doi: 10.1371/journal.pmed.1000356

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Rockman, M. V., Hahn, M. W., Soranzo, N., Goldstein, D. B., and Wray, G. A. (2003). Positive selection on a human-specific transcription factor binding site regulating IL4 expression. Curr. Biol. 13, 2118–2123.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Rogers, A. J., Raby, B. A., Lasky-Su, J. A., Murphy, A., Lazarus, R., Klanderman, B. J., et al. (2009). Assessing the reproducibility of asthma candidate gene associations, using genome-wide data. Am. J. Respir. Crit. Care Med. 179, 1084–1090.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Romagnani, S. (2007). Coming back to a missing immune deviation as the main explanatory mechanism for the hygiene hypothesis. J. Allergy Clin. Immunol. 119, 1511–1513.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Salam, M. T., Byun, H. M., Lurmann, F., Breton, C. V., Wang, X., Eckel, S. P., et al. (2012). Genetic and epigenetic variations in inducible nitric oxide synthase promoter, particulate pollution, and exhaled nitric oxide levels in children. J. Allergy Clin. Immunol. 129, 232–239.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Scichilone, N., Battaglia, S., Sala, A. L., and Bellia, V. (2006). Clinical implications of airway hyper-responsiveness in COPD. Int. J. Chron. Obstruct. Pulmon. Dis. 1, 49–60.

Pubmed Abstract | Pubmed Full Text

Sterk, P. J., and Bel, E. H. (1989). Bronchial hyperresponsiveness: the need for a distinction between hypersensitivity and excessive airway narrowing. Eur. Respir. J. 2, 267–274.

Pubmed Abstract | Pubmed Full Text

Tangteerawatana, P., Pichyangkul, S., Hayano, M., Kalambaheti, T., Looareesuwan, S., Troye-Blomberg, M., et al. (2007). Relative levels of IL4 and IFN-gamma in complicated malaria: association with IL4 polymorphism and peripheral parasitemia. Acta Trop. 101, 258–265.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Thornburg, K. L., Shannon, J., Thuillier, P., and Turker, M. S. (2010). In utero life and epigenetic predisposition for disease. Adv. Genet. 71, 57–78.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Torgerson, D. G., Gignoux, C. R., Galanter, J. M., Drake, K. A., Roth, L. A., Eng, C., et al. (2012). Case-control admixture mapping in Latino populations enriches for known asthma-associated genes. J. Allergy Clin. Immunol. 130, 76–82.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Tzivian, L. (2011). Outdoor air pollution and asthma in children. J. Asthma 48, 470–481.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Umetsu, D. T., and DeKruyff, R. H. (2006). The regulation of allergy and asthma. Immunol. Rev. 212, 238–255.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Vardi, P., and Bloch, K. (2008). “Thrifty genotype hypothesis and complex genetic disease,” in eLS. Chichester: John Wiley and Sons. doi: 10.1002/9780470015902.a0006077.pub2. Available online at: http://www.els.net

CrossRef Full Text

Vercelli, D. (2008). Discovering susceptibility genes for asthma and allergy. Nat. Rev. Immunol. 8, 169–182.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

von Mutius, E. (1998). The rising trends in asthma and allergic disease. Clin. Exp. Allergy 28, 45–49.

Pubmed Abstract | Pubmed Full Text

von Mutius, E. (2009). Gene-environment interactions in asthma. J. Allergy Clin. Immunol. 123, 3–11.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Wang, W., Halmurat, W., Yilihamu, S., Xiang, Y. B., and Ablikemu, A. (2004). A study on the relationship between interleukin-4 promoter polymorphism and asthma in a Xinjiang Uyger population. Zhonghua Jie He He Hu Xi Za Zhi 27, 460–464.

Pubmed Abstract | Pubmed Full Text

Wenzel, S. E. (2012). Asthma phenotypes: the evolution from clinical to molecular approaches. Nat. Med. 18, 716–725.

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

World Health Organization-WHO. (2011). Asthma Fact sheet N°307. Available online at: http://www.who.int/mediacentre/factsheets/fs307/en/index.html. (Accessed September 15, 2012).

Zhang, Y., Han, Y., Dong, L., Yu, H., Cheng, L., Zhao, X., et al. (2013). Genetic variation of ITGB3 is associated with asthma in Chinese Han Children. PLoS ONE 8:e56914. doi: 10.1371/journal.pone.0056914

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text

Citation: Berenguer AG, Rosa A and Brehm A (2013) Asthma—snapshot or motion picture? Front. Genet. 4:73. doi: 10.3389/fgene.2013.00073

Received: 05 April 2013; Accepted: 15 April 2013;
Published online: 30 April 2013.

Edited by:

Richard D. Emes, University of Nottingham, UK

Reviewed by:

William Carroll, Derbyshire Children's Hospital, UK

Copyright © 2013 Berenguer, Rosa and Brehm. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.

*Correspondence: brehm@uma.pt

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