Subgroup analysis of individual NOD2 polymorphisms was next performed. On random-effects analysis, the R702W variant was not associated with surgical recurrence (OR: 1.65, 95% CI: 0.96–2.83, P = 0.071) (Fig. 4A) with a pooled sensitivity of 0.204 (95% CI: 0.140–0.282) and a specificity of 0.860 (95% CI: 0.814–0.898). The G908R variant was not associated with surgical recurrence (OR: 1.01, 95% CI: 0.53–1.91, P = 0.974) (Fig. 4B) with a pooled sensitivity of 0.117 (95% CI: 0.068–0.183) and a specificity of 0.885 (95% CI: 0.842–0.919). The L1007finsC variant was not associated with surgical recurrence (OR: 1.00, 95% CI: 0.44–2.76, P = 0.831) (Fig. 4C) with a pooled sensitivity of 0.153 (95% CI: 0.097–0.225) and a specificity of 0.832 (95% CI: 0.784–0.874).
Epidemiologic data indicate that the heterogeneity of CD may in part relate to genetic factors.30–34 Thus, considerable research has focused on the identification of genetic determinants of disease progression. Most of the discrepancies in the literature on predictors of postoperative recurrence are because of variable definitions of CD recurrence (endoscopic, histological, clinical, surgical, etc.) as well as length and type of follow-up. Although NOD2 polymorphisms are associated with increased risk of disease development14,15,35 (in particular, fibrostenosing disease21), controversy persists in relation to association with postoperative recurrence.22,23,29 The current study has shown that carriers of one or more NOD2 polymorphisms had a 58% increased risk of developing surgical recurrence compared with noncarriers; however, this did not reach statistical significance and was associated with significant across study heterogeneity.
This meta-analysis is based on all currently available published data comparing NOD2 polymorphism expression and surgical recurrence, thereby providing a strong appraisal of its predictive value. However, there are a number of important limitations. The past decade has seen a dramatic increase in gene association studies and a contemporaneous increase in experimental design variation.36 The STrengthening the REporting of Genetic Association studies (STREGA) initiative37 expanded the STrengthening the Reporting of Observational Studies in Epidemiology (STROBE) checklist to improve the interrogation of evidence from genetic studies and thereby standardize reporting of results. As the studies contained in this meta-analysis did not conform to STREGA guidelines this limits extrapolations from data contained. In addition, the studies contained small to moderate numbers of patients in mainly single centers. Taken together, these factors have contributed to a considerable level of heterogeneity. The only available data for inclusion were from European centers. Therefore, the results presented herein may apply only to a European population and cannot be extrapolated to other populations. The analysis is also limited by the absence of data to allow for evaluation of confounding factors such as smoking status, fistulating disease, ileal involvement, or did it clearly define what was considered surgical recurrence (stricturoplasty versus re-resection, etc).
The fact the fixed-effects analysis was significant and the random-effects analysis was not is not surprising. A fixed analysis assumes that there is no heterogeneity between individual trials and all trials are sampling the same population of patients,38,39 this is not the case in the current study. Furthermore, despite obvious graphical publication bias, the Begg-Mazumdar and Egger tests did not reach statistical significance. As the power of these methods is low when small numbers of studies are included40 this is to be expected. Likewise, tests for funnel plot asymmetry when there are fewer than 10 studies in the meta-analysis may not be able to distinguish chance from real asymmetry.41.
Of the 3 common NOD2 polymorphisms associated with the development of CD, homozygosity for the L1007finsC variant is characterized by earlier onset and more aggressive disease compared with other variants.42,43 Three of the 6 studies defined surgical recurrence in relation to the 3 polymorphisms and so a subset analysis was performed comparing the expression of each polymorphism with re-operation rates. None of the 3 genetic variants were associated with surgical recurrence with odds ratios ranging from 1.00 to 1.65. A subset analysis of homozygosity versus heterozygosity of gene expression was not possible to perform as these data could not be extracted from the literature.
This study reviewed the currently available literature to determine if it supports the relationship between the expression of NOD2 polymorphisms and recurrence of CD requiring operative intervention. Although currently available data do not support NOD2 genetic polymorphisms as biomarkers of surgical recurrence in patients with CD, this is possibly because of the small numbers of patients genotyped across the studies and the heterogeneous nature of the populations studied. Therefore, it may be suggested the data support the conduction of a large multicenter homogenous study designed to ensure sufficient patient accrual as well as consistency in data reporting. It is noteworthy that the 58% cumulative increased risk of surgical recurrence is identical to the risk of index resection induced by being a NOD2 carrier.43 The current findings indicate that there are insufficient data to support a role for NOD2 in predicting surgical recurrence, but do not exclude a role for it. It is more likely that the reason no association with surgical recurrence was found is because of the small numbers of patients genotyped across the studies and the heterogeneous nature of the populations studied rather than a genuine lack of association.
The authors would like to thank Dr Jean-Paul Achkar and Prof Claudio Fiocchi (Dept. of Gastroenterology, Digestive Disease Institute, Cleveland Clinic Foundation, Cleveland, OH) for their critical review and comments on this manuscript.
1. Sachar DB. Recurrence rates in Crohn's disease: predicting the future and predicting the past. Gut. 2006;55:1069–1070.
2. Bernell O, Lapidus A, Hellers G. Risk factors for surgery and postoperative recurrence in Crohn's disease. Ann Surg. 2000;231:38–45.
3. Olaison G, Smedh K, Sjodahl R. Natural course of Crohn's disease after ileocolic resection: endoscopically visualised ileal ulcers preceding symptoms. Gut. 1992;33:331–335.
4. Rutgeerts P, Geboes K, Vantrappen G, et al.. Natural history of recurrent Crohn's disease at the ileocolonic anastomosis after curative surgery. Gut. 1984;25:665–672.
5. Lock MR, Farmer RG, Fazio VW, et al.. Recurrence and reoperation for Crohn's disease: the role of disease location in prognosis. N Engl J Med. 1981;304:1586–1588.
6. Hampe J, Grebe J, Nikolaus S, et al.. Association of NOD2 (CARD 15) genotype with clinical course of Crohn's disease: a cohort study. Lancet. 2002;359:1661–1665.
7. Cunningham MF, Docherty NG, Coffey JC, et al.. Postsurgical recurrence of ileal Crohn's disease: an update on risk factors and intervention points to a central role for impaired host-microflora homeostasis. World J Surg. 2010;34:1615–1626.
8. Ahmed T, Rieder F, Fiocchi C, et al.. Pathogenesis of postoperative recurrence in Crohn's disease. Gut. 2011;60:553–562.
9. D'Haens GR, Vermeire S, Van Assche G, et al.. Therapy of metronidazole with azathioprine to prevent postoperative recurrence of Crohn's disease: a controlled randomized trial. Gastroenterology. 2008;135:1123–1129.
10. Regueiro M, Schraut W, Baidoo L, et al.. Infliximab prevents Crohn's disease recurrence after ileal resection. Gastroenterology. 2009;136:441–450; e441;quiz 716.
11. Present DH, Meltzer SJ, Krumholz MP, et al.. 6-Mercaptopurine in the management of inflammatory bowel disease: short- and long-term toxicity. Ann Intern Med. 1989;111:641–649.
12. Prefontaine E, Macdonald JK, Sutherland LR. Azathioprine or 6-mercaptopurine for induction of remission in Crohn's disease. Cochrane Database Syst Rev. 2009:CD000545.
13. Siegel CA, Hur C, Korzenik JR, et al.. Risks and benefits of infliximab for the treatment of Crohn's disease. Clin Gastroenterol Hepatol. 2006;4:1017–1024; quiz 1976.
14. Hugot JP, Chamaillard M, Zouali H, et al.. Association of NOD2 leucine-rich repeat variants with susceptibility to Crohn's disease. Nature. 2001;411:599–603.
15. Ogura Y, Bonen DK, Inohara N, et al.. A frameshift mutation in NOD2 associated with susceptibility to Crohn's disease. Nature. 2001;411:603–606.
16. Inohara N, Ogura Y, Fontalba A, et al.. Host recognition of bacterial muramyl dipeptide mediated through NOD2. Implications for Crohn's disease. J Biol Chem. 2003;278:5509–5512.
17. Economou M, Trikalinos TA, Loizou KT, et al.. Differential effects of NOD2 variants on Crohn's disease risk and phenotype in diverse populations: a metaanalysis. Am J Gastroenterol. 2004;99:2393–2404.
18. Lesage S, Zouali H, Cezard JP, et al.. CARD15/NOD2 mutational analysis and genotype-phenotype correlation in 612 patients with inflammatory bowel disease. Am J Hum Genet. 2002;70:845–857.
19. Cuthbert AP, Fisher SA, Mirza MM, et al.. The contribution of NOD2 gene mutations to the risk and site of disease in inflammatory bowel disease. Gastroenterology. 2002;122:867–874.
20. Ahmad T, Armuzzi A, Bunce M, et al.. The molecular classification of the clinical manifestations of Crohn's disease. Gastroenterology. 2002;122:854–866.
21. Abreu MT, Taylor KD, Lin YC, et al.. Mutations in NOD2 are associated with fibrostenosing disease in patients with Crohn's disease. Gastroenterology. 2002;123:679–688.
22. Maconi G, Colombo E, Sampietro GM, et al.. CARD15 gene variants and risk of reoperation in Crohn's disease patients. Am J Gastroenterol. 2009;104:2483–2491.
23. Alvarez-Lobos M, Arostegui JI, Sans M, et al.. Crohn's disease patients carrying Nod2/CARD15 gene variants have an increased and early need for first surgery due to stricturing disease and higher rate of surgical recurrence. Ann Surg. 2005;242:693–700.
24. Buning C, Genschel J, Buhner S, et al.. Mutations in the NOD2/CARD15 gene in Crohn's disease are associated with ileocecal resection and are a risk factor for reoperation. Aliment Pharmacol Ther. 2004;19:1073–1078.
25. DerSimonian R, Laird N. Meta-analysis in clinical trials. Control Clin Trials. 1986;7:177–188.
26. Dunne C, Burke JP, Morrow M, et al.. Effect of margin status on local recurrence after breast conservation and radiation therapy for ductal carcinoma in situ. J Clin Oncol. 2009;27:1615–1620.
27. Lau J, Ioannidis JP, Schmid CH. Quantitative synthesis in systematic reviews. Ann Intern Med. 1997;127:820–826.
28. Onnie CM, Fisher SA, Prescott NJ, et al.. Diverse effects of the CARD15 and IBD5 loci on clinical phenotype in 630 patients with Crohn's disease. Eur J Gastroenterol Hepatol. 2008;20:37–45.
29. Renda MC, Orlando A, Civitavecchia G, et al.. The role of CARD15 mutations and smoking in the course of Crohn's disease in a Mediterranean area. Am J Gastroenterol. 2008;103:649–655.
30. Polito JM 2nd, Childs B, Mellits ED, et al.. Crohn's disease: influence of age at diagnosis on site and clinical type of disease. Gastroenterology. 1996;111:580–586.
31. Satsangi J, Grootscholten C, Holt H, et al.. Clinical patterns of familial inflammatory bowel disease. Gut. 1996;38:738–741.
32. Bayless TM, Tokayer AZ, Polito JM 2nd, et al.. Crohn's disease: concordance for site and clinical type in affected family members—potential hereditary influences. Gastroenterology. 1996;111:573–579.
33. Colombel JF, Grandbastien B, Gower-Rousseau C, et al.. Clinical characteristics of Crohn's disease in 72 families. Gastroenterology. 1996;111:604–607.
34. Achkar JP, Duerr R. The expanding universe of inflammatory bowel disease genetics. Curr Opin Gastroenterol. 2008;24:429–434.
35. Hampe J, Cuthbert A, Croucher PJ, et al.. Association between insertion mutation in NOD2 gene and Crohn's disease in German and British populations. Lancet. 2001;357:1925–1928.
36. Ioannidis JP, Gwinn M, Little J, et al.. A road map for efficient and reliable human genome epidemiology. Nat Genet. 2006;38:3–5.
37. Little J, Higgins JP, Ioannidis JP, et al.. Strengthening the Reporting of Genetic Association Studies (STREGA): an extension of the STROBE statement. PLoS Med. 2009;6:e22.
38. Mantel N, Haenszel W. Statistical aspects of the analysis of data from retrospective studies of disease. J Natl Cancer Inst. 1959;22:719–748.
39. Mahid SS, Hornung CA, Minor KS, et al.. Systematic reviews and meta-analysis for the surgeon scientist. Br J Surg. 2006;93:1315–1324.
40. Egger M, Davey Smith G, Schneider M, et al.. Bias in meta-analysis detected by a simple, graphical test. BMJ. 1997;315:629–634.
41. Higgins JP, Altman DG, Gotzsche PC, et al.. The Cochrane Collaboration's tool for assessing risk of bias in randomised trials. BMJ. 2011;343:d5928.
42. Seiderer J, Schnitzler F, Brand S, et al.. Homozygosity for the CARD15 frameshift mutation 1007fs is predictive of early onset of Crohn's disease with ileal stenosis, entero-enteral fistulas, and frequent need for surgical intervention with high risk of re-stenosis. Scand J Gastroenterol. 2006;41:1421–1432.
43. Adler J, Rangwalla SC, Dwamena BA, et al.. The prognostic power of the NOD2 genotype for complicated Crohn's disease: a meta-analysis. Am J Gastroenterol. 2011;106:699–712.