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. 2014 Mar;133(3):885–888. doi: 10.1016/j.jaci.2013.08.049

Novel childhood asthma genes interact with in utero and early-life tobacco smoke exposure

Salome Scholtens a,b, Dirkje S Postma b,c, Miriam F Moffatt d, Sviatlana Panasevich e, Raquel Granell f, A John Henderson f, Erik Melén e,g, Fredrik Nyberg e,h, Göran Pershagen e, Deborah Jarvis i, Adaikalavan Ramasamy i, Matthias Wjst j,k, Cecilie Svanes l, Emmanuelle Bouzigon m,n,o, Florence Demenais m,n,o, Francine Kauffmann p,q, Valérie Siroux r,s, Erika von Mutius t, Markus Johannes Ege t, Charlotte Braun-Fahrländer u,v, Jon Genuneit w; GABRIELA study group, Bert Brunekreef x,y, Henriette A Smit y,z, Alet H Wijga z, Marjan Kerkhof a,b, Ivan Curjuric u,v, Medea Imboden u,v, Gian A Thun u,v, Nicole Probst-Hensch u,v, Maxim B Freidin aa, Elena Iu Bragina aa, IA Deev bb, VP Puzyrev aa,bb, Denise Daley cc, Julie Park cc, Allan Becker dd, Moira Chan-Yeung ee, Anita L Kozyrskyj ff, Peter Pare cc, Ingo Marenholz gg,hh, Susanne Lau ii, Thomas Keil jj, Young-Ae Lee gg,hh, Michael Kabesch kk, Cisca Wijmenga ll, Lude Franke ll, Ilja M Nolte a, Judith Vonk a, Ashish Kumar u,v,mm, Martin Farrall mm, William OCM Cookson d, David P Strachan nn, Gerard H Koppelman b,oo, H Marike Boezen a,b
PMCID: PMC3969577  PMID: 24315450

To the Editor:

Complex diseases, including asthma, have genetic and environmental origins. Genome-wide association studies have identified multiple genes for the development of asthma, yet they only explain a limited proportion of asthma heritability. Interactions between genetic predisposition and exposure to passive smoking might explain in part the hidden heritability of childhood asthma. However, to date, this approach has not been reported for the discovery of interactions between genes and tobacco smoke exposure.

We performed a genome-wide interaction study (GWIS) on childhood asthma to identify genes that interact with 2 well-known environmental risk factors for childhood-onset asthma: in utero and childhood tobacco smoke exposure. We meta-analyzed interaction results from 9 studies participating in the GABRIEL consortium1 including more than 6,000 subjects of European descent. We replicated our findings in 4 independent studies including more than 13,000 subjects. Childhood-onset asthma was defined as asthma diagnosed by a doctor before the age of 16 years, which is consistent with the definition in the GABRIEL consortium.1 In utero tobacco smoke exposure was defined as “exposure to maternal tobacco smoking at any time during pregnancy.” Childhood tobacco smoke exposure was defined as “exposure to passive tobacco smoking at any time from birth until 16 years of age.” Details on the number of subjects, the design of the individual studies, and outcome and exposure definitions are provided in Tables E1 to E4 in this article's Online Repository at www.jacionline.org.

The effects of in utero tobacco smoke exposure and childhood tobacco smoke exposure were analyzed separately. All individual studies were analyzed by using a logistic regression model containing the genetic effect, the effect of tobacco smoke exposure, and an interaction term indicating the interaction between the genetic effect and tobacco smoke exposure. Further methodological considerations on GWISs and details on the statistical analyses are described in this article's Online Repository at www.jacionline.org.

For in utero tobacco smoke exposure, the discovery genome-wide meta-analysis consisted of 2,654 cases and 3,073 control subjects derived from 7 studies (see Table E1). Overall, in utero tobacco smoke exposure increased the risk of childhood-onset asthma (see Fig E1 in this article's Online Repository at www.jacionline.org). A total of 536,705 single nucleotide polymorphisms (SNPs) were included in the interaction meta-analysis. Fig E2 in this article's Online Repository at www.jacionline.org shows the Manhattan plot. We identified 27 SNPs in the discovery sample with a P value of less than 10−4 based on the fixed effect model (Table I and see Table E5 in this article's Online Repository at www.jacionline.org). Findings did not reach genome-wide significance but were consistent over all studies included, and no significant heterogeneity across studies was present (P value Q-statistic < .05). Four of these SNPs on chromosome 10 were in high linkage disequilibrium with each other in the discovery meta-analysis (r2 = 0.82-0.96). The most prominent marker was located on chromosome 18 near EPB41L3 (Forest plot, see Fig E3 in this article's Online Repository at www.jacionline.org). Table E6 in this article's Online Repository at www.jacionline.org shows the associations in exposed and nonexposed subjects. EPB41L3 belongs to the protein 4.1 family of membrane-associated proteins, is involved in cell-cell junctions,2 and might play a role in apoptosis.3 The literature shows that in utero tobacco smoke exposure affects the expression of genes involved in biological processes, such as cell proliferation and apoptosis, and influences lung development of the child in general.4 Our data suggest that this effect of in utero smoke exposure might potentially occur through mechanisms involving EPB41L3 (see the additional text in this article's Online Repository).

Table I.

Results of the GWIS of in utero tobacco smoke exposure and childhood-onset asthma

Ch SNP Closest gene Type Discovery
Replication
N ORint Pf N ORint Pf
1 rs1674877 Intergenic 2654 0.51 2.19 × 10−5 201 1.06 .89
2 rs4670230 FAM82A1 Intronic 2654 1.94 2.10 × 10−5 201 0.78 .51
2 rs12624082 GALNT13 Intronic 2654 1.78 3.22 × 10−5 697 1.00 .98
2 rs11684139 GALNT13 Intronic 2654 1.77 7.57 × 10−5 697 0.85 .35
2 rs729454 Intergenic 2654 1.67 9.52 × 10−5 697 1.13 .45
3 rs3856848 IL5RA Intronic 2654 1.96 5.32 × 10−6 201 0.59 .19
4 rs7682603 Intergenic 2247 0.54 1.19 × 10−5 562 1.20 .29
5 rs1990977 RNU6ATAC2P Intergenic 2654 2.12 7.79 × 10−5 697 0.88 .60
5 rs4700239 Intergenic 2654 2.15 6.39 × 10−5 562 0.78 .34
6 rs6456433 Intergenic 2654 1.99 7.99 × 10−5 562 0.71 .15
6 rs14398 WDR46 Nonsynonymous 2654 0.45 5.44 × 10−5 562 1.77 .01
8 rs360968 Intergenic 2654 0.54 5.05 × 10−5 697 0.93 .72
9 rs943856 Intergenic 2654 0.59 4.94 × 10−5 697 0.70 .04
10 rs11006296 Intergenic 2654 2.01 3.70 × 10−5 562 0.84 .47
10 rs1407696 PDCD4 Intronic 2654 0.57 2.36 × 10−5 66 0.58 .34
10 rs7079511 SHOC2 Intronic 2654 0.58 3.24 × 10−5 697 0.98 .91
10 rs521674 ADRA2A Upstream 2654 0.57 5.35 × 10−5 562 1.16 .45
10 rs602618 ADRA2A Downstream 2654 0.57 5.63 × 10−5 562 1.15 .45
11 rs1123991 OR51E2 Synonymous 2654 0.50 6.51 × 10−5 697 0.68 .11
11 rs3898589 CNTN5 Intronic 2654 1.83 6.11 × 10−5 562 1.17 .40
11 rs10892848 CNTN5 Intronic 2654 1.82 5.72 × 10−5 697 1.07 .71
12 rs706793 ACCN2 Intronic 2654 1.66 3.62 × 10−5 697 0.75 .07
13 rs7321384 C13orf35 Intronic 2654 0.58 9.82 × 10−5 697 0.92 .63
16 rs8051325 ANKS4B Intronic 2654 0.47 8.37 × 10−5 562 0.80 .37
18 rs8094633 EPB41L3 Intergenic 2654 2.13 4.29 × 10−5 201 2.87 .03
21 rs858003 KCNJ6 Intronic 2654 1.81 8.50 × 10−5 697 1.00 1.00
22 rs9613256 CTA-211A9.5 Within noncoding gene 2654 0.59 5.44 × 10−5 562 1.11 .60

Ch, Chromosome; ORint, odds ratio interaction; Pf, P value, fixed effect.

Closest gene within range of 500 kb of the position of the SNP.

Number of studies and cases included in meta-analysis.

Additive genetic model.

For childhood tobacco smoke exposure, the discovery genome-wide meta-analysis consisted of 3,048 cases and 3,509 control subjects derived from 9 studies (see Table E1). Overall, childhood tobacco smoke exposure increased the risk of childhood-onset asthma (see Fig E1). A total of 538,233 SNPs were included in the interaction meta-analysis. Fig E4 in this article's Online Repository at www.jacionline.org shows the Manhattan plot. We identified 35 SNPs in the discovery sample with a P value of less than 10−4 based on the fixed effect model. Four of these SNPs were excluded because they showed heterogeneity, and the P value of the random effect was greater than 10−4. Findings did not reach genome-wide significance. Table II and Table E7 (see this article's Online Repository at www.jacionline.org) the results for the top SNPs. Seven SNPs on chromosome 5 (except rs2312164) were in high linkage disequilibrium with each other in the discovery studies (r2 = 0.83-1.00).

Table II.

Results of the GWIS on childhood tobacco smoke exposure and childhood-onset asthma

Ch SNP Closest gene Type Discovery
Replication
N ORint Pf N ORint Pf
1 rs2026604 S100A7L2 Downstream 3048 1.44 7.49 × 10−5 1003 0.83 .17
2 rs10184453 Intergenic 3048 1.53 8.85 × 10−5 1003 1.18 .30
2 rs895565 Intergenic 3048 1.53 7.26 × 10−5 1003 1.18 .30
2 rs11126185 Intergenic 3048 0.67 6.81 × 10−6 868 1.22 .16
3 rs4234677 CTD-2230D16.1 Within noncoding gene 3048 0.65 6.57 × 10−5 261 1.58 .22
3 rs264096 MAGI1 Intronic 3048 0.62 6.93 × 10−6 396 0.89 .63
3 rs17239426 KCNAB1 Intronic 3048 0.58 7.28 × 10−5 1003 1.18 .39
4 rs1425551 IRF2 Intronic 3048 1.40 6.92 × 10−5 1003 0.98 .86
5 rs162036 MTRR Nonsynonymous 3048 0.60 8.26 × 10−5 1003 1.14 .45
5 rs7719963 Intergenic 3048 0.56 3.06 × 10−5 868 0.89 .59
5 rs7447231 Intergenic 3048 1.55 8.36 × 10−6 868 0.85 .31
5 rs10155635 Intergenic 3048 1.56 7.55 × 10−6 261 0.62 .11
5 rs10038850 Intergenic 3048 1.53 1.51 × 10−5 261 0.41 .04
5 rs10479335 Intergenic 3048 1.52 5.98 × 10−5 868 0.85 .29
5 rs2312164 Intergenic 3048 1.42 7.18 × 10−5 1003 0.82 .14
5 rs13357477 Intergenic 3048 1.58 3.59 × 10−6 868 0.83 .24
5 rs12719549 Intergenic 3048 1.57 4.61 × 10−6 868 0.82 .21
5 rs4607330 Intergenic 3048 1.59 2.70 × 10−6 868 0.85 .31
6 rs441463 LYRM4 Intronic 3048 1.41 4.91 × 10−5 1003 0.90 .42
6 rs1575472 PACRG Intronic 3048 1.78 1.37 × 10−5 1003 1.51 .06
7 rs17544971 GRB10 Intronic 3048 1.70 8.12 × 10−5 868 1.26 .28
9 rs4977750 MTAP Nonsense-mediated decay transcript 3048 0.61 1.91 × 10−5 1003 0.93 .66
13 rs4769148 Intergenic 2445 0.67 4.45 × 10−5 261 0.72 .21
13 rs12874184 Intergenic 3048 1.98 8.75 × 10−5 868 1.18 .50
13 rs16972472 Intergenic 3048 1.79 9.59 × 10−5 868 0.79 .32
14 rs10141836 OR11G2 Upstream 3048 0.70 8.89 × 10−5 1003 0.90 .41
15 rs2602923 C15orf41 Intronic 3048 1.61 4.52 × 10−5 1003 1.19 .33
16 rs13331814 ZP2 Intronic 3048 0.62 8.38 × 10−5 868 0.85 .34
19 rs11085080 PLIN5 Intronic 3048 0.51 6.30 × 10−5 1003 1.12 .63
20 rs6077755 PSMF1 Upstream 3048 1.52 6.65 × 10−6 1003 1.11 .47
X rs6641609 PRKX Intronic 1939 0.49 3.43 × 10−5 261 1.90 .15

Ch, Chromosome; ORint, odds ratio interaction; Pf, P value, fixed effect.

Closest gene within range of 500 kb of the position of the SNP.

Number of cases and control subjects included in the meta-analysis.

Additive genetic model.

The most prominent marker was located on chromosome 6 in PACRG (parkin coregulated gene; Forest plot, see Fig E5 in this article's Online Repository at www.jacionline.org). Table E8 in this article's Online Repository at www.jacionline.org shows the associations in exposed and nonexposed subjects. PACRG is located next to and has an overlapping promoter region with parkin 2 (PARK2).5 The gene has been associated with leprosy and parkinsonian diseases and has an important role in motile cilia function and cilia morphogenesis.2,6 PACRG is relatively highly expressed in the trachea and nasal mucosa. Ciliary dysfunction might impair mucus clearance from the airways and has been shown to affect asthma severity. Our data suggest that changes in ciliary function particularly affect the development of asthma in children exposed to passive tobacco smoke.

The genes that have been reported previously to interact with tobacco smoke exposure with respect to asthma development (ie, TNF,7 GSTP1,7 and ADAM338) were not among our most significant hits. This can be explained by the fact that the genetic variants in these candidate gene studies have a strong main effect on asthma development. Bouzigon et al9 showed a more pronounced effect of the 17q21 region on the development of early-onset asthma in children with early-life tobacco smoke exposure than in those without. The genetic effect of these markers in our GWIS showed a similar direction, but the interaction was not significant.

This study on childhood asthma is the first hypothesis-free GWIS specifically aiming to identify SNPs that interact with tobacco smoke exposure in disease development. We found suggestive evidence for an interaction between rs8094633 on chromosome 18 near EPB41L3 and in utero tobacco smoke exposure and an interaction between rs1575472 on chromosome 6 in PACRG and childhood tobacco smoke exposure. The SNPs found have not been identified previously in general genome-wide association studies on childhood asthma. Interestingly, the SNPs interacting with in utero and childhood tobacco smoke exposure were different and were not involved in the same pathway (see Fig E6 in this article's Online Repository at www.jacionline.org). Interactions between these SNPs and tobacco smoke exposure in utero and in childhood might explain part of the missing heritability of asthma. Future research needs to confirm these findings and further unravel the biological pathways.

Acknowledgments

For acknowledgments, see this article's Online Repository at www.jacionline.org.

Footnotes

This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-No Derivative Works License, which permits non-commercial use, distribution, and reproduction in any medium, provided the original author and source are credited.

The GABRIEL study (a multidisciplinary study to identify the genetic and environmental causes of asthma in the European Community) was supported by the European Commission, contract number 018996, under the Integrated Program LSH-2004-1.2.5-1 and the Wellcome Trust (WT084703MA). Funding of the individual studies is described in this article's Online Repository at www.jacionline.org.

Disclosure of potential conflict of interest: A. J. Henderson has been supported by grants from the Medical Research Council (UK) and from the Wellcome Trust. F. Nyberg is employed by AstraZeneca. G. Pershagen has been supported by one or more grants from the European Union and the Swedish Research Council. D. Jarvis has been supported by one or more grants from the European Union. M. Wjst has been supported by one or more grants from the European Union (FP6). F. Kauffmann has been supported by one or more grants from the ANR French National Agency of research, the French Agency for Environmental and Occupational Health Safety, Inserm, and Merck Sharp and Dohme. E. Von Mutius has been supported by one or more grants from the European Commission; is an Associate Editor of the Journal of Allergy and Clinical Immunology; and has consultancy arrangements with GlaxoSmithKline, Novartis, ALK-Abelló, and Astellas Pharma. M. J. Ege has been supported by grants from the European Commission and from Deutsche Forschungsgemeinschaft. P. Pare has been supported by one or more grants from Allergen NCE. S. Lau has been supported by one or more grants from the German Research Foundation, is a member of a Drug Monitoring Committee, has consultancy arrangements with Symbiopharm and Allergopharm, and has received one or more payments for lecturing from or is on the speakers' bureau for Symbiopharm, Dannone, GlaxoSmithKline, and Novartis. T. Keil has received one or more grants from or has one or more grants pending with EU-FP7. Y. Lee has received one or more grants from or has one or more grants pending with the European Union and the German Research Foundation. M. Kabesch has been supported by one or more grants from the European Union, the German Ministry of Education and Research, and the German Research Foundation and has received one or more payments for lecturing from or is on the speakers' bureau for the European Respiratory Society, the European Academy of Allergy and Clinical Immunology, the American Thoracic Society, Novartis, and GlaxoSmithKline. M. Farrall has been supported by one or more grants from and has received support for travel from EU FP7. G. H. Koppelman has been supported by one or more grants from the European Union and has received one or more grants from or has one or more grants pending with the Netherlands Asthma Foundation, Stichting Asthma Bestrijding. The rest of the authors declare that they have no relevant conflicts of interest.

Supplementary data

Online Repository Data
mmc1.doc (139KB, doc)
Tables E1-E8
mmc2.doc (358KB, doc)
Figures E1-E6 Legends and Figures
mmc3.doc (1.9MB, doc)

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Tables E1-E8
mmc2.doc (358KB, doc)
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mmc3.doc (1.9MB, doc)

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