Case Control Study
Copyright ©The Author(s) 2015. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Jul 7, 2015; 21(25): 7786-7794
Published online Jul 7, 2015. doi: 10.3748/wjg.v21.i25.7786
NOD2/CARD15 gene mutations in North Algerian patients with inflammatory bowel disease
Aziza Boukercha, Hamida Mesbah-Amroun, Amira Bouzidi, Houria Saoula, Mhamed Nakkemouche, Maryline Roy, Jean-Pierre Hugot, Chafia Touil-Boukoffa
Aziza Boukercha, Hamida Mesbah-Amroun, Amira Bouzidi, Chafia Touil-Boukoffa, Team Cytokines and NO Synthases, Laboratory of Cellular and Molecular Biology, Faculty of Biological Sciences, University of Sciences and Technology Houari Boumediene, Algiers 16111, Algeria
Houria Saoula, Mhamed Nakkemouche, Department of Gastroenterology, Maillot University Hospital, Algiers 16111, Algeria
Maryline Roy, Jean-Pierre Hugot, Team Intestinal Inflammation, INSERM UMR1149, Xavier Bichat Faculty, Paris Diderot University, 75018 Paris, France
Jean-Pierre Hugot, Department of Gastroenterology, Robert Debré University Hospital, 75013 Paris, France
Author contributions: Boukercha A and Mesbah-Amroun H contributed equally to this work; Boukercha A, Mesbah-Amroun H, Nakkemouche M, Hugot JP and Touil-Boukoffa C designed the research; Boukercha A performed the research; Bouzidi A and Roy M contributed new reagents/analytic tools; Saoula H and Nakkemouche M treated patients and collected material and clinical data from patients; Boukercha A, Mesbah-Amroun H, Bouzidi A, Saoula H, Roy M and Hugot JP analyzed the data; Boukercha A and Mesbah-Amroun H wrote the paper; Hugot JP revised the article critically; Mesbah-Amroun H, Nakkemouche M, Hugot JP and Touil-Boukoffa C approved the final version to be published.
Supported by the Agence Thématique de la Recherche Scientifique en Santé, (ATRSS, ex ANDRS) (PNR N°37-ANDRS-2011).
Ethics approval: The study was reviewed and approved by the Ethics Committee of the Agence Thématique de la Recherche Scientifique en Santé (ATRSS, ex ANDRS).
Informed consent statement: All study participants, or their legal guardian, provided informed written consent prior to study enrollment.
Conflict-of-interest statement: Mesbah-Amroun Hamida has received research funding from the Agence Thématique de la Recherche Scientifique en Santé (ATRSS, ex ANDRS).
Data sharing statement: Technical appendix, statistical code, and dataset are available from the corresponding author, Mesbah-Amroun H, at amrounhamida@yahoo.com or hamroun@usthb.dz. Consent was not obtained by participants for data sharing but the presented data are anonymized and risk of identification is low.
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Correspondence to: Hamida Mesbah-Amroun, PhD, Laboratory of Cellular and Molecular Biology, Faculty of Biological Sciences, University of Sciences and Technology Houari Boumediene, BP32, Bab-Ezzouar, Algiers 16111, Algeria. amrounhamida@yahoo.com
Telephone: +213-7-79387611 Fax: +213-21-247217
Received: March 12, 2015
Peer-review started: March 13, 2015
First decision: March 26, 2015
Revised: April 23, 2015
Accepted: May 7, 2015
Article in press: May 7, 2015
Published online: July 7, 2015

Abstract

AIM: To analyse allelic frequency of NOD2 gene variants and to assess their correlation with inflammatory bowel disease (IBD) in Algeria.

METHODS: We studied 132 unrelated patients diagnosed with IBD, 86 with Crohn’s disease (CD) and 46 with ulcerative colitis (UC). Data was prospectively collected between January 2011 and December 2013. The demographic and clinical characteristics were recorded for all the patients. A group of 114 healthy unrelated individuals were selected as controls. All groups studied originated from different regions of North Algeria and confirmed the Algerian origin of their parents and grandparents. Informed and written consent was obtained from each of the participants. All individuals were genotyped for the three CD-associated NOD2 variants (p.Arg702Trp, p.Gly908Arg and p.Leu1007fsinsC mutations) using the polymerase chain reaction-restriction fragment length polymorphism method. Allele and genotype frequencies in patients and control subjects were compared by χ2 test and Fisher’s exact test where appropriate. Odds ratios (OR) and 95% confidence intervals (95%CI) were also estimated. Association analyses were performed to study the influence of these variants on IBD and on clinical phenotypes.

RESULTS: The p.Arg702Trp mutation showed the highest frequency in CD patients (8%) compared to UC patients (2%) (P = 0.09, OR = 3.67, 95%CI: 0.48-4.87) and controls (5%) (P = 0.4, OR = 1.47, 95%CI: 0.65-3.31). In CD patients allelic frequencies of p.Gly908Arg and p.Leu1007fsinsC variants compared to HC were 3% vs 2% (P = 0.5, OR = 1.67, 95%CI: 0.44-6.34); 2% vs 1% (P = 0.4 OR = 2.69 95%CI: 0.48-14.87 respectively). In UC patients, allelic frequencies of p.Gly908Arg and p.Leu1007fsinsC variants compared to HC were 1% vs 2% (P = 1, OR = 1.62, 95%CI: 0.17-4.74) and 2% vs 1% (P = 0.32, OR = 0.39, 95%CI: 0.05-2.87). The total frequency of the mutated NOD2 chromosomes was higher in CD (13%), than in HC (8%) and UC (5%). In addition, NOD2 variants were linked to a particular clinical sub-phenotype in CD in this Algerian cohort. As expected, the three NOD2 variants showed a significant association with CD but did not reach statistical significance, despite the fact that the allele frequency of NOD2 variants was in the range found in most of the European populations. This might be due to the non-exposure of the NOD2 carriers to environmental factors, required for the expression of the disease.

CONCLUSION: Further analyses are necessary to study genetic and environmental factors in IBD in the Algerian population, using larger patient groups.

Key Words: Algeria, Crohn’s disease, Ulcerative colitis, Inflammatory bowel disease, NOD2 mutations, Polymerase chain reaction-restriction fragment length polymorphism method

Core tip: We evaluated allelic frequency of NOD2 variants among 132 inflammatory bowel disease (IBD) patients and 114 unrelated healthy subjects from Algeria. Despite the fact that the frequency of NOD2 mutant alleles is in the range found in most of the European populations, we failed to demonstrate the association of these NOD2 variants with IBD susceptibility. This might be due to the non exposure of the NOD2 carriers to environmental factors, required for the expression of the disease. We can expect in the coming years to see an increased incidence of IBD associated with the spread of Western lifestyle in this region.



INTRODUCTION

The nucleotide-binding oligomerization domain containing 2 gene (NOD2) is 3.1 kb in size and is located on chromosome 16q12.1[1-3]. Consisting of 12 exons and 11 introns, NOD2 encodes a protein expressed mainly in monocytes, dendritic cells, enterocytes and Paneth cells. NOD2 has an important role in immune system function[4]. In response to bacterial infection, NOD2 acts as an intracellular bacterial receptor in monocytes and activates nuclear factor kappa B (NF-κB) specifically after recognition of the bacterial cell wall component, muramyl dipeptide (MDP)[5] and leads to activation of the inflammatory response[6,7]. NOD2 mutations are associated with Crohn’s disease (CD) as well as other disorders, including Blau syndrome[8,9] and bipolar disorder[10]. NOD2 mutations have also been associated with a higher incidence of specific types of cancer in affected patients[11].

More than 40 non-conservative mutations were identified on the NOD2 gene[12]. The most common are two missense mutations, p.Arg702Trp (SNP8, C/T) in exon 4, leading to substitution of arginine in position 702 by tryptophan, p.Gly908Arg (SNP12,G/C) in exon 8, leading to substitution of glycine in position 908 by arginine and an insertion mutation of a C in exon 11, a frame shift resulting in a truncated NOD2 protein at position 1007, p-Leu1007fsinsC (SNP13, insC). Independent groups have reported the association of these three mutations with increased susceptibility to CD[12-14]. These mutations affect the structure of either the carboxy-terminal leucine-rich repeat (LRR) domain of the protein or the adjacent region. The activating functions of NF-κB are regulated by the LRR domain, which has an inhibitory role and acts as an intracellular receptor for components of microbial pathogens[12]. In particular, these NOD2 mutations are associated with the phenotypes of CD that involve the ileum, and with fibrostenosing disease[15]. In Caucasian populations, the contribution of the NOD2 gene mutations to CD has been studied. The risk of CD has been evaluated to be 1.5-3-fold for heterozygous carriers and 10-44-fold for homozygous/compound heterozygous carriers[15-19]. However, the background prevalence of NOD2 mutations depends on ethnicity. In Asian populations such as Chinese, Korean and Japanese, the three previously described major variants of the NOD2 gene were not found in CD patients and controls[20,21], indicating that although ethnically divergent populations may present identical phenotypes, they do not necessarily share the same set of predisposing genes. In African populations, very few studies have been performed to investigate the influence of genetic factors in the development of CD. Gasche et al[22], screened the three NOD2 SNPs in a collection of 1064 DNA samples from 52 worldwide populations, including seven sub-Saharan populations and one North African population composed of 30 Algerian Mozabites. They likewise found no NOD2 mutations in African populations except for a single positive case of p.Arg702Trp mutation in the Algerian Mozabite population. They concluded that the three CD-associated single nucleotide polymorphisms (SNPs) were almost exclusively found in Europe and are absent in native populations from Africa. In North African populations, two previous genotyping analyses in Morocco and Tunisia[23,24] revealed that the NOD2 allele’s frequencies are very low when compared to the frequencies seen in Caucasians of European origin. More recently, the contribution of NOD2 polymorphisms to CD has been studied for the first time in an Algerian population[25] and a strong association between CD and NOD2 variants was reported. However, p.Leu1007fsinsC variant was not investigated in this study even it showed the strongest association with CD in previous studies[15,17]. The objectives of the present study were thus to determine allelic frequency of the three major NOD2 gene variants and to investigate whether they determined specific phenotypes of IBD among North Caucasian Algerians.

MATERIALS AND METHODS

The study was performed in accordance with the Declaration of Helsinki of the World Medical Association and was approved by the ethics committee of the Agence Thématique de la Recherche Scientifique en Santé, (ATRSS, ex ANDRS). All patients signed an informed consent form for this investigation.

Patients with IBD

A total of 132 unrelated patients diagnosed with IBD (86 Crohn’s disease (CD), 46 ulcerative colitis (UC)) reported in this study were recruited from Maillot Hospital, Algiers, Algeria, between January 2011 and December 2013 and represented an independent cohort not studied before in any IBD genetic studies. Diagnosis of IBD was based on standard clinical, radiological, endoscopic and histological criteria. The following demographic and clinical characteristics were recorded for all the patients: geographical origin, gender, age, age at diagnosis, disease location, presence of extra intestinal manifestations, surgery and familial or sporadic disease (familial disease was considered if one first or second degree relative had IBD). In addition, we carried out an evaluation of the incidence of IBD in our monocentric study, since no published epidemiological data on IBD in Algeria are available. Data were obtained from the registry of IBD of the Department of Gastroenterology at the Maillot University Hospital of Algiers. We have considered all patients permanent residents of Algiers, consulted for the first time between January 1988 and December 2008, for symptoms consistent with a diagnosis of IBD.

Healthy control subjects

One hundred and fourteen healthy unrelated individuals (mainly students, blood donors and hospital employees) with a mean age of 25.21 ± 8.66 were selected as controls on the basis of a lack of personal or family history of IBD or any other autoimmune or immune diseases.

Stastical analysis

A comparison of genotype frequencies between different groups was evaluated using the χ2 test or Fisher’s exact test. Odds ratios (OR) were noted with a 95%CI. Expected and observed heterozygosity and Hardy-Weinberg equilibrium (HWE) were calculated. Variables were considered to indicate a statistically significant difference for a P value less or equal to 0.05. We used GraphPad prism version 6.01 (GraphPad Software, San Diego, California, United States).

DNA extraction

DNA was extracted from blood samples by the phenol-chloroform method according to standard protocols[26].

We screened samples for the presence of p.Arg702Trp, p.Gly908Arg and p.Leu1007fsinsC mutations of the NOD2 gene by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Primers and PCR reactions were previously described[27]. Primers used were synthesized by Invitrogen (Invitrogen, Life Technologies, Carlsbad, California, United States) and PCR reactions were carried out using a T100 thermal cycler (BIO-RAD, Richmond CA, United States). PCR products were analysed on 1% agarose gels and stained with 1 mg/mL ethidium bromide. The digestion reaction and restriction enzyme digestion conditions were taken from the manuals included with the restriction enzymes MspI, HhaI purchased from Promega (Promega, Madison, wisconsin, United States) and NlaIV purchased from New England Biolabs (New England Biolabs, Massachusetts, United States). Digestion products were loaded on polyacrylamide gel electrophoresed under 120 volts for 60 min, coloured with 1 mg/mL ethidium bromide. Images were captured with a Gel Doc EZ imager analyser (BIO-RAD, Richmond CA, United States).

RESULTS

In our study, we have analysed two series of data. We have obtained data retrospectively from the Department of Gastroenterology’s register. A group of 770 IBD patients resident in Algiers, were consulted between January 1988 and December 2008. Based on these data, we evaluated the incidence rate for IBD. It ranges from 0.5 to 2 cases/105 per year, with an average rate of 1.2. The second series of data was obtained prospectively between January 2011 and December 2013. Our cohort was composed of 132 IBD patients (86 CD and 46 UC). The mean age of the patients at diagnosis was 25.28 ± 14.85 and 36.86 ± 12.30 years for CD and UC, respectively. The clinical characteristics and phenotype data are reported in Tables 1 and 2. Family history in a first- or second-degree relative was found in 27% and 24% of the CD and UC patients studied, respectively, which is higher than reported before in CD patients in the same population[25]. There was a slight female gender predominance in IBD patients (57%). PCR-RFLP was employed to detect p.Arg702Trp, p.Gly908Arg and p.Leu1007fsinsC mutations of the NOD2 gene in 132 IBD patients and 114 healthy control subjects. Allele frequencies of mutant alleles of each NOD2 variant are shown in Table 3. The p.Arg702Trp mutation showed the highest frequency in CD patients (8%) compared to UC patients (2%) (P = 0.09, OR = 3.67, 95%CI: 0.48-4.87) but its frequency was also high in controls (5%) (P = 0.4, OR = 1.47, 95%CI: 0.65-3.31). Likewise, p.Gly908Arg and p.Leu1007fsinsC mutations showed similar frequency in CD patients and in controls (3% vs 2%, P = 0.5, OR = 1.67, 95%CI: 0.44-6.34; 2% vs1%, P = 0.4, OR = 2.69, 95%CI: 0.48-14.87, respectively). In UC patients, allelic frequencies of p.Gly908Arg and p.Leu1007fsinsC variants compared to HC were 1%vs 2%, (P = 1, OR = 1.62, 95%CI: 0.17-4.74) and 2% vs 1% (P = 0.32, OR = 0.39, 95%CI: 0.05-2.87)). As expected, the total frequency of the mutated NOD2 chromosomes was higher in CD (13%), than in HC (8%) and UC (5%). However, this difference was not statistically significant (CD vs HC, P = 0.12, OR = 1.71, 95%CI: 0.88-3.3; UC vs HC, P = 0.63, OR = 0.67, 95%CI: 0.24-1.86). In addition, the comparison of the total allelic frequencies between CD and UC patients did not show any statistical difference (P = 0.08, OR = 0.39, 95%CI: 0.14-1.07).

Table 1 Demographic, clinical data and genotype-phenotype correlations in Crohn's disease patients n (%).
VariablesAll subjectsNon carriersCarriersP value
HC114102 (89.47)12 (10.52)0.120
CD patients8670 (81.39)16 (18.6)0.103
Sex (F/M)46/4040/306/100.155
Age at diagnosis25.28± 14.8525.70 ± 15.5522.12 ± 10.66
A128 (32.5)2260.809
A243 (50)358
A315 (17.5)132
Location
L1: Ileum25 (29)2320.020
L2: Ileo-colon49 (57)3514
L3: Colon12 (14)120
Resective Surgery37 (43)3160.620
EIM24 (28)1860.343
Positive family history for CD23 (27)1760.281
Table 2 Demographic, clinical data and genotype-phenotype correlations in ulcerative colitis patients n (%).
VariablesAll subjectsNon carriersCarriersP value
HC114102 (89.47)12 (10.52)0.120
UC patients4642(91.3)4(8.7)0.726
Sex (F/M)30/1627/153/10.667
Age at diagnosis36.86 ± 12.3036.92 ± 11.3436.25 ± 22.60
A11 (2.1)100.916
A231 (67.4)283
A314 (30.5)131
Location
E1: proctitis9 (20)900.115
E2: distal colitis19 (41.5)163
E3: extensive colitis18 (39)171
Resection Surgery4 (9)310.225
EIM11 (24)1100.240
Positive family history for UC11 (24)1010.957
Table 3 NOD2 Allele frequencies in Crohn's disease, ulcerative colitis and healthy control groups.
PolymorphismsAllele frequency (%)
CDUCHCIBDP value1ORP value2ORP value3ORP value4OR
(n = 86)(n = 46)(n = 114)(n = 132)(95%CI)(95%CI)(95%CI)(95%CI)
p.Arg702Trp (C/T)C929895940.093.670.401.471.000.920.362.5
T82560.48-4.870.65-3.310.42-2.010.54-11.4
p.Gly908Arg (G/C)G979998980.662.720.501.670.750.761.001.62
C31220.31-23.690.44-6.340.21-2.750.17-14.74
p.Leu1007fsinsC (WT/insC)WT989899981.001.070.402.690.290.380.320.39
insC22120.19-5.90.48-14.870.07-1.90.05-2.87
Total frequency (%)1358100.080.390.121.710.431.320.630.67
0.14-1.070.88-3.30.71- 2.480.24-1.86

When considering the carriers of at least one copy of mutant alleles in any variant and the carriers of two copies (Table 4), a similar result was observed. 18.6% of CD patients and 8.7% of UC patients carried at least one mutant allele in any of the three considered variants, vs 10.52% of controls (P = 0.103, P = 0.726, respectively). Two copies of mutant alleles were carried by 7% of the CD subjects (either homozygous for one variant or compound heterozygous), vs 5.26% in the control group (P = 0.613). Only a single subject was compound heterozygous for p.Arg702Trp and p.Leu1007fsinsC variant in the UC group (2.17%) (P = 0.397). No subjects were homozygous for p.Gly908Arg or p.Leu1007fsinsC variants in the whole sample of CD. This reveals the risk conferred by the possession of more than one of these mutations.

Table 4 Number of different genotypes observed in Crohn's disease/ulcerative colitis/healthy controls groups.
Variantp.Arg702Trpp.Gly908Argp.Leu1007fsinsCWT
p.Arg702Trp2/0/41/0/12/1/16/1/2
p.Gly908Arg0/0/01/0/03/1/3
p.Leu1007fsinsC0/0/01/1/1
WT70/42/102

When analysing the genotype data, the HWE test P value was not significant for any of the SNPs except for p.Arg702Trp (Table 5). The observed excess of p.Arg702Trp homozygous genotypes in the HC sample was significant and could be due to consanguinity.

Table 5 Hardy-Weinberg equilibrium and the P value.
NOD2 polymorphisms
p.Arg702Trp
p.Gly908Arg
p.Leu1007fsinsC
GroupsGenotypesCCCTTTP valueGGGCCCP valueWT/WTinsC/WTinsC/insCP value
Frequencies
HCObserved92.983.513.51096.493.5100.848898.251.7500.9247
Expected89.759.970.2896.523.450.03NS98.251.740NS
CDObserved87.2110.462.330.011794.195.8100.781395.354.6500.8252
Expected86.9212.620.4694.275.640.08NS95.414.540.05NS
IBDObserved90.158.331.520.010695.454.5500.789395.454.5500.7893
Expected88.9610.720.3295.514.440.05NS95.514.440.05NS

No significant associations were found with NOD2 mutations for family history, presence of extra intestinal manifestations or surgery, even when p.Arg702Trp/p.Gly908Arg/p.Leu1007fsinsC polymorphisms were considered together or separately or when only p.Gly908Arg/p.Leu1007fsinsC were considered.

The stratification of CD according to age at diagnosis showed that CD patients carrying one or two copies of any rare variant had a mean age at diagnosis lower than non-carrier CD patients. However, this association was not significant (P = 0.809).

One positive association was shown between NOD2 mutations and location of disease. In the CD group, 59% of patients had combined small bowel and colonic involvement, 30% had isolated small bowel involvement and 11% had an isolated colonic disease. NOD2 carriers with any risk allele showed ileal or ileocolonic CD and none of them had an isolated colonic CD. There were significant differences between allele frequencies and location of disease (P = 0.020). In our study, NOD2 alleles were associated with a particular CD sub-phenotype. This result is in agreement with previous studies in which ileal disease was found associated with NOD2 variants[15].

In the UC group, no significant associations were found among the NOD2 mutations and age at diagnosis, presence of extra intestinal manifestations, surgery or family history. When considering extent of disease, 9 (20%) patients had proctitis, 19 (41.5%) distal colitis and 18 (39%) extensive colitis. Interestingly, none of the UC patients with NOD2 risk alleles had E1 disease location, suggesting a potential association between NOD2 mutations carrier status and disease severity. However, the frequency of NOD2 mutations did not achieve statistical significance (P = 0.115), probably because of the small number of patients in this sub-group (only 4).

DISCUSSION

Allele frequency of the three major NOD2 gene variants was assessed in this analysis. As expected, the total allele frequency was higher in CD patients than in UC patients and HC. The frequencies of the three NOD2 variants range from 4% to 5%, 1% to 2% and 2% to 3% for p.Arg702Trp, p.Gly908Arg and p.Leu1007fsinsC, respectively, in healthy Caucasian populations[28]. The corresponding frequencies among Caucasian CD patients range from 9% to 13%, 3% to 6% and 7% to 16%, respectively[29]. In UC patients, the frequencies of these three variants are lower, ranging from 4% to 6%, 2% and 2.5% to 3.3%[30-32]. In our cohort of IBD and controls, the observed frequency of NOD2 mutant alleles is in agreement with a high Caucasian component of the targeted population and is in the range found in most European populations, except for p.Leu1007fsinsC frequency which was lower. Much lower frequency was also found for the frameshift mutation in neighbouring populations from Morocco and Tunisia, with similar sample size (Table 6). Interestingly, another study in a North Tunisian population has shown that p.Leu1007fsinsC mutation was strongly associated with susceptibility to CD with an allelic frequency value of 15%[33], indicating that significant differences might be obtained for the same population.

Table 6 Comparative study of NOD2 allele frequencies in North African populations.
PopulationNumber
Allele frequency (%)
p.Arg702Trp
p.Gly908Arg
p.Leu1007fsinsC
Total allele
CDHCCDHCCDHCCDHCCDHC
North Algeria (this study)86114853221138
Algeria[25]20420150.5030.5NDNDNDND
Morocco[23]1011070.490.466.432.80.9083.2
Tunisia[24]1309020.60531083.6

The p.Arg702Trp allelic frequency obtained on 114 North Algerian healthy controls is likewise significantly different from that recently determined on 201 controls (P = 0.0002, OR = 11.11)[25]. This divergence indicates that the control samples used in the two studies are significantly different. Previous studies described the population of North Africa as extremely heterogeneous, composed of a mosaic of sub-populations with significantly different genetic structures and with high endogamy rates[33,34]. This is confirmed by the Hardy-Weinberg analyses performed in our study. Thus, recruitment from different geographic origins in Algeria may lead to different NOD2 frequencies. Taken together, all these data from the Algerian population suggested that genetic variations of NOD2 gene are not homogeneously distributed.

The correlation of NOD2 genotypes with phenotypic expression of IBD was assessed in this analysis. IBD is a heterogeneous disorder characterized by the presence of different clinical sub-phenotypes. In our study, we have established different sub-groups, after the stratification of IBD patients according to demographic and phenotypic data. In CD patients, no significant association was found between NOD2 variants and phenotypic data (Tables 1 and 2). However, this association was significant with disease location, as described previously. In the UC group, our data suggests that NOD2 mutations appear to be associated with a more aggressive course of UC. Similar findings have been recently reported on UC in the Portuguese population[35]. To our knowledge, this study is the first one performed to investigate the influence of genetic factors in the development of UC in the Algerian population. The small number of UC patients with NOD2 risk alleles is the limitation in our study and a larger sample is certainly needed to clarify the role of NOD2 gene variants in phenotype severity of UC in Algeria.

Finally, our results clearly show an influence of NOD2 gene variants on specific CD clinical sub-groups. Since only 18.6% of CD patients and 8.69% of UC patients carry at least one mutation in the NOD2 gene, it is possible that other polymorphisms in the NOD2 gene or in other genes, in combination with environmental factors, are involved in IBD susceptibility. Indeed, despite the fact that the observed frequency of NOD2 mutant alleles is in the range found in most European populations, the association of these polymorphisms on IBD susceptibility in our studied population could not be demonstrated. This might be due not only to the statistical test power failure but also to an environmental effect. NOD2 carriers do not express the disease, because they are not exposed to environmental factors required for the expression of the disease and are probably protected because they lead a lifestyle that is not at risk. In these conditions, the OR values attributed to the NOD2 mutations are proportional to the population exposure. Our study showed that the incidence rate for IBD increased from 0.5 to 2 cases/105 per year, between 1988 and 2008. This incidence rate is lower than that of other population groups and is certainly underestimated because it is evaluated only in a monocentric study. However, it is interesting to note that over these two decades the population in Algeria became predominantly urban. Thus, the increased incidence of IBD observed in the targeted population might be associated with the change in lifestyle. This is in agreement with a previous study demonstrating that urbanization of society is an important risk factor for the development of IBD. Soon et al[36], demonstrated that living in an urban society was positively associated with the development of IBD. Since change in lifestyle is relatively recent in Algeria, an increased incidence in IBD associated with the spread of Western lifestyle in this region can be expected in the coming years.

In conclusion, the data we obtained are relevant to estimate the NOD2 gene variants in the Algerian population. Our study confirmed that the NOD2 gene is significantly associated with a specific clinical sub-phenotype in CD. The results obtained up to now in Algeria have shown that the NOD2 gene is involved in IBD susceptibility and have suggested a heterogeneous distribution of NOD2 mutations across Algerian populations. Further analyses are necessary to study genetic and environmental factors in IBD in the Algerian population, using larger patient groups.

COMMENTS
Background

Very few studies have been performed to investigate the influence of genetic factors in the development of Crohn’s disease (CD) in Algeria.

Research frontiers

The authors have explored NOD2/CARD15 gene mutations in North Algerian patients with inflammatory bowel disease (IBD).

Innovations and breakthroughs

This is a novel study in which we determine, for the first time, the allelic frequency of the three major NOD2 gene variants among the North Caucasian Algerians and investigate whether they determine specific phenotypes of IBD. The authors clearly showed an influence of NOD2 gene variants on specific CD clinical sub-groups. The authors also proposed that an increased incidence of IBD observed in the targeted population might be associated with the change in lifestyle.

Applications

Investigating other genetic determinants, but also environmental factors, in IBD patients could help us to understand the pathogenic pathway of disease both in CD and ulcerative colitis (UC).

Peer-review

This is an original work in which a genetic study has revealed the importance of the environment on the expression of IBD. The format of the manuscript was slightly revised.

Footnotes

P- Reviewer: Capasso R, Perse M S- Editor: Ma YJ L- Editor: O’Neill M E- Editor: Liu XM

References
1.  Hugot JP, Laurent-Puig P, Gower-Rousseau C, Olson JM, Lee JC, Beaugerie L, Naom I, Dupas JL, Van Gossum A, Orholm M. Mapping of a susceptibility locus for Crohn’s disease on chromosome 16. Nature. 1996;379:821-823.  [PubMed]  [DOI]
2.  Brant SR, Fu Y, Fields CT, Baltazar R, Ravenhill G, Pickles MR, Rohal PM, Mann J, Kirschner BS, Jabs EW. American families with Crohn’s disease have strong evidence for linkage to chromosome 16 but not chromosome 12. Gastroenterology. 1998;115:1056-1061.  [PubMed]  [DOI]
3.  Annese V, Latiano A, Bovio P, Forabosco P, Piepoli A, Lombardi G, Andreoli A, Astegiano M, Gionchetti P, Riegler G. Genetic analysis in Italian families with inflammatory bowel disease supports linkage to the IBD1 locus--a GISC study. Eur J Hum Genet. 1999;7:567-573.  [PubMed]  [DOI]
4.  Sabbah A, Chang TH, Harnack R, Frohlich V, Tominaga K, Dube PH, Xiang Y, Bose S. Activation of innate immune antiviral responses by Nod2. Nat Immunol. 2009;10:1073-1080.  [PubMed]  [DOI]
5.  Inohara N, Ogura Y, Fontalba A, Gutierrez O, Pons F, Crespo J, Fukase K, Inamura S, Kusumoto S, Hashimoto M. Host recognition of bacterial muramyl dipeptide mediated through NOD2. Implications for Crohn’s disease. J Biol Chem. 2003;278:5509-5512.  [PubMed]  [DOI]
6.  Ogura Y, Inohara N, Benito A, Chen FF, Yamaoka S, Nunez G. Nod2, a Nod1/Apaf-1 family member that is restricted to monocytes and activates NF-kappaB. J Biol Chem. 2001;276:4812-4818.  [PubMed]  [DOI]
7.  Gutierrez O, Pipaon C, Inohara N, Fontalba A, Ogura Y, Prosper F, Nunez G, Fernandez-Luna JL. Induction of Nod2 in myelomonocytic and intestinal epithelial cells via nuclear factor-kappa B activation. J Biol Chem. 2002;277:41701-41705.  [PubMed]  [DOI]
8.  Miceli-Richard C, Lesage S, Rybojad M, Prieur AM, Manouvrier-Hanu S, Häfner R, Chamaillard M, Zouali H, Thomas G, Hugot JP. CARD15 mutations in Blau syndrome. Nat Genet. 2001;29:19-20.  [PubMed]  [DOI]
9.  Okafuji I, Nishikomori R, Kanazawa N, Kambe N, Fujisawa A, Yamazaki S, Saito M, Yoshioka T, Kawai T, Sakai H. Role of the NOD2 genotype in the clinical phenotype of Blau syndrome and early-onset sarcoidosis. Arthritis Rheum. 2009;60:242-250.  [PubMed]  [DOI]
10.  Oliveira J, Hamdani N, Etain B, Bennabi M, Boukouaci W, Amokrane K, Fortier C, Marzais F, Bengoufa D, Bellivier F. Genetic association between a ‘standing’ variant of NOD2 and bipolar disorder. Immunobiology. 2014;219:766-771.  [PubMed]  [DOI]
11.  Liu J, He C, Xu Q, Xing C, Yuan Y. NOD2 polymorphisms associated with cancer risk: a meta-analysis. PLoS One. 2014;9:e89340.  [PubMed]  [DOI]
12.  Hugot JP, Chamaillard M, Zouali H, Lesage S, Cézard JP, Belaiche J, Almer S, Tysk C, O’Morain CA, Gassull M. Association of NOD2 leucine-rich repeat variants with susceptibility to Crohn’s disease. Nature. 2001;411:599-603.  [PubMed]  [DOI]
13.  Cavanaugh J. International collaboration provides convincing linkage replication in complex disease through analysis of a large pooled data set: Crohn disease and chromosome 16. Am J Hum Genet. 2001;68:1165-1171.  [PubMed]  [DOI]
14.  Ogura Y, Bonen DK, Inohara N, Nicolae DL, Chen FF, Ramos R, Britton H, Moran T, Karaliuskas R, Duerr RH. A frameshift mutation in NOD2 associated with susceptibility to Crohn’s disease. Nature. 2001;411:603-606.  [PubMed]  [DOI]
15.  Lesage S, Zouali H, Cézard JP, Colombel JF, Belaiche J, Almer S, Tysk C, O’Morain C, Gassull M, Binder V. CARD15/NOD2 mutational analysis and genotype-phenotype correlation in 612 patients with inflammatory bowel disease. Am J Hum Genet. 2002;70:845-857.  [PubMed]  [DOI]
16.  Hampe J, Cuthbert A, Croucher PJ, Mirza MM, Mascheretti S, Fisher S, Frenzel H, King K, Hasselmeyer A, MacPherson AJ. Association between insertion mutation in NOD2 gene and Crohn’s disease in German and British populations. Lancet. 2001;357:1925-1928.  [PubMed]  [DOI]
17.  Ahmad T, Armuzzi A, Bunce M, Mulcahy-Hawes K, Marshall SE, Orchard TR, Crawshaw J, Large O, de Silva A, Cook JT. The molecular classification of the clinical manifestations of Crohn’s disease. Gastroenterology. 2002;122:854-866.  [PubMed]  [DOI]
18.  Cuthbert AP, Fisher SA, Mirza MM, King K, Hampe J, Croucher PJ, Mascheretti S, Sanderson J, Forbes A, Mansfield J. The contribution of NOD2 gene mutations to the risk and site of disease in inflammatory bowel disease. Gastroenterology. 2002;122:867-874.  [PubMed]  [DOI]
19.  Bonen DK, Ogura Y, Nicolae DL, Inohara N, Saab L, Tanabe T, Chen FF, Foster SJ, Duerr RH, Brant SR. Crohn’s disease-associated NOD2 variants share a signaling defect in response to lipopolysaccharide and peptidoglycan. Gastroenterology. 2003;124:140-146.  [PubMed]  [DOI]
20.  Yamazaki K, Takazoe M, Tanaka T, Kazumori T, Nakamura Y. Absence of mutation in the NOD2/CARD15 gene among 483 Japanese patients with Crohn’s disease. J Hum Genet. 2002;47:469-472.  [PubMed]  [DOI]
21.  Leong RW, Armuzzi A, Ahmad T, Wong ML, Tse P, Jewell DP, Sung JJ. NOD2/CARD15 gene polymorphisms and Crohn’s disease in the Chinese population. Aliment Pharmacol Ther. 2003;17:1465-1470.  [PubMed]  [DOI]
22.  Gasche C, Nemeth M, Grundtner P, Willheim-Polli C, Ferenci P, Schwarzenbacher R. Evolution of Crohn’s disease-associated Nod2 mutations. Immunogenetics. 2008;60:115-120.  [PubMed]  [DOI]
23.  Hama I, Ratbi I, Reggoug S, Elkerch F, Kharrasse G, Errabih I, Ouazzani H, Sefiani A. Non-association of Crohn’s disease with NOD2 gene variants in Moroccan patients. Gene. 2012;499:121-123.  [PubMed]  [DOI]
24.  Zouiten-Mekki L, Zaouali H, Boubaker J, Karoui S, Fekih M, Matri S, Hamzaoui S, Filali A, Chaabouni H, Hugot JP. CARD15/NOD2 in a Tunisian population with Crohn’s disease. Dig Dis Sci. 2005;50:130-135.  [PubMed]  [DOI]
25.  Meddour Y, Chaib S, Bousseloub A, Kaddache N, Kecili L, Gamar L, Nakkemouche M, Djidjik R, Abbadi MC, Charron D. NOD2/CARD15 and IL23R genetic variability in 204 Algerian Crohn’s disease. Clin Res Hepatol Gastroenterol. 2014;38:499-504.  [PubMed]  [DOI]
26.  Sambrook J, Fritsch EF, Maniatis F.  Molecular Cloning: A Laboratory Manual. New York: Cold Spring Harbor Laboratory Press, Cold Spring Harbor 1989; .  [PubMed]  [DOI]
27.  Rigoli L, Romano C, Caruso RA, Lo Presti MA, Di Bella C, Procopio V, Lo Giudice G, Amorini M, Costantino G, Sergi MD. Clinical significance of NOD2/CARD15 and Toll-like receptor 4 gene single nucleotide polymorphisms in inflammatory bowel disease. World J Gastroenterol. 2008;14:4454-4461.  [PubMed]  [DOI]
28.  Hugot JP, Zaccaria I, Cavanaugh J, Yang H, Vermeire S, Lappalainen M, Schreiber S, Annese V, Jewell DP, Fowler EV. Prevalence of CARD15/NOD2 mutations in Caucasian healthy people. Am J Gastroenterol. 2007;102:1259-1267.  [PubMed]  [DOI]
29.  Cavanaugh J. NOD2: ethnic and geographic differences. World J Gastroenterol. 2006;12:3673-3677.  [PubMed]  [DOI]
30.  Brant SR, Wang MH, Rawsthorne P, Sargent M, Datta LW, Nouvet F, Shugart YY, Bernstein CN. A population-based case-control study of CARD15 and other risk factors in Crohn’s disease and ulcerative colitis. Am J Gastroenterol. 2007;102:313-323.  [PubMed]  [DOI]
31.  Andriulli A, Annese V, Latiano A, Palmieri O, Fortina P, Ardizzone S, Cottone M, D’Inca R, Riegler G. The frame-shift mutation of the NOD2/CARD15 gene is significantly increased in ulcerative colitis: an *IG-IBD study. Gastroenterology. 2004;126:625-627.  [PubMed]  [DOI]
32.  McGovern DP, Van Heel DA, Negoro K, Ahmad T, Jewell DP. Further evidence of IBD5/CARD15 (NOD2) epistasis in the susceptibility to ulcerative colitis. Am J Hum Genet. 2003;73:1465-1466.  [PubMed]  [DOI]
33.  Marrakchi R, Bougatef K, Moussa A, Ouerhani S, Khodjet-el-Khil H, Messai Y, Mestiri O, Najar T, Benammar-Elgaaeid A. 3020insC insertion in NOD2/CARD15 gene, a prevalent variant associated with anti-Saccharomyces cerevisiae antibodies and ileal location of Crohn’s disease in Tunisian population. Inflamm Res. 2009;58:218-223.  [PubMed]  [DOI]
34.  Labie D, Benabadji M, Elion J. Genetic disorders in North African populations of the Maghreb. Genetic Disorders Among Arab Populations. New York: Oxford University Press 1997; 290-321.  [PubMed]  [DOI]
35.  Freire P, Cardoso R, Figueiredo P, Donato MM, Ferreira M, Mendes S, Ferreira AM, Vasconcelos H, Portela F, Sofia C. NOD2 gene mutations in ulcerative colitis: useless or misunderstood? Int J Colorectal Dis. 2014;29:653-661.  [PubMed]  [DOI]
36.  Soon IS, Molodecky NA, Rabi DM, Ghali WA, Barkema HW, Kaplan GG. The relationship between urban environment and the inflammatory bowel diseases: a systematic review and meta-analysis. BMC Gastroenterol. 2012;12:51.  [PubMed]  [DOI]