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Tumor Necrosis Factor Gene Polymorphisms and their Association with Susceptibility to Rheumatoid Arthritis, Disease Activity and Severity

Rabab A. Mohamed et. al.

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Tumor Necrosis Factor Gene Polymorphisms and their Association with Susceptibility to Rheumatoid Arthritis, Disease Activity and Severity

Research Article

 

Heba M. Zagloul1, Sanaa A. Elshafy1, Rabab A. Mohamed1, Enas A. Abdelaleem2, Rania E. Sheir3, Heba H. El-Demellawy3

1 Clinical  and Chemical Pathology Department, Faculty of Medicine, BENI-SUEF UNIVERSITY Hospital , Beni-Suef, Egypt

2 Rheumatology and Rehabilitation Department, Faculty of Medicine, BENI SUEF UNIVERSITY Hospital ,Beni-Suef, Egypt

3 Department of Internal Medicine, Faculty of Medicine, BENI SUEF UNIVERSITY Hospital ,Beni-Suef, Egypt

*Correspondence: : Dr Rabab A.Mohamed, Immunology unit, Clinical pathology Department, Beni- Suef Faculty of Medicine, BENI-SUEF UNIVERSITY, Beni-Suef 62511, Egypt . phone:+201001533425 E-mail: Rabab.eltememy@gmail.com

 

Key words: Rheumatoid arthritis (RA), genetic susceptibility, TNF polymorphisms, Polymerase chain reaction, Restriction fragment length polymorphism (PCR-RFLP).

 

 

Received: 1 June 2018

Accepted: 10 June  2018; electronically published: 10 June  2018

 

Summary

Rheumatoid arthritis (RA) is a chronic autoimmune disease that shows multifactorial inheritance resulting from a complex interplay between an individualÕs environmental and genetic background. Tumor necrosis factor (TNF), a pro-inflammatory cytokine that has been shown to play a central role in the pathogenesis of numerous autoimmune diseases including RA. Aim: The present case control study was conducted to assess the association of LTA252A>G, TNFα-308G>A and TNFα-1031T>C gene polymorphisms with RA and their involvement in disease activity and severity. Methods: PCR-RFLP was used to detect the association of LTA252A>G, TNFα-308G>A and TNFα-1031T>C gene polymorphisms with RA. Results: TNF-α 308 G allele  and TNF –α 308 GG  genotype were significantly higher in RA patients compared to healthy control subjects (P=0.04; P=0.001, respectively). TNF-α 308 G allele and GG genotype were significantly higher in the RA non-remission group (P=0.008; P<0.001, respectively) compared to the remission group .On analysis of disease severity ,the TNF-α 308 AG genotype was more frequently represented among RA patients compared to GG and AA genotypes (P=0.007). There was no significant association between LTA252A>G and TNFα-1031T>C gene polymorphisms and RA. Conclusion: Our results suggest that TNF-α 308 G/A gene polymorphism is genetically associated with Rheumatoid Arthritis and involved in disease activity and severity in the Egyptian population.

 

 


I. Introduction

Rheumatoid arthritis (RA) is a chronic autoimmune disease that affects 1% of the population worldwide (World Health Organization, 2012) It is a systemic disease which involves the joints, organs and other areas of body such as the skin, eyes, heart,  lungs, kidney and the spleen (Goldsby et al; 2006 and Atif   et al;2016).

 

RA exhibits multifactorial inheritance resulting from a complex interplay between an individualÕs environmental and genetic background ( Chen  et al; 2007).

It has a complex etiology, including a wide spectrum of clinical manifestations, variability in disease, progression, severity, and response to therapies  

( Firestein ;  2003).

Increased expression of pro- and anti- inflammatory cytokines detected in the affected tissues and serum of RA patients clearly indicates the  role of cytokines in the etiopathology of RA (Gambhir et al; 2010).Tumor necrosis factor (TNF), a proinflammatory cytokine has been shown to play a major role in the pathogenesis of numerous autoimmune diseases including RA (Gambhir et al; 2010 , Brennanet al; 1992 and Feldmann et al; 2001).

TNF-α and TNF-β are closely related cytokines that share 30% amino acid residues and have the same cell surface receptor ( Beutler et al;1989). Nedwin et al (1985) reported that the TNF-α and TNF-β genes are located in tandem on chromosome 6 between the Class I and Class II cluster of the major histocompatibility complex (chromosome 6p21.1–6p21.3). The proinflammatory cytokine TNFα is one of the major factors involved in RA inflammatory state (Brennan et al; 1992). TNFα pleiotropic biological activities are mediated binding to TNF receptors (TNFR) Type I and II (Hohmann et al; 1989).

 TNFα plays a pivotal role in inflammation by inducing the expression of other proinflammatory molecules, chemotactic cytokines and adhesion factors ( Bradley ,2008 , Hehlgans and Pfeffer ; 2005 and Lee et al; 2015).In vivo and in vitro studies have demonstrated that high levels of TNFα lead to aggravation of the inflammatory response. This, together with its strong immunomodulatory activities, has been suggested to be important to the pathogenesis of multiple diseases such as asthma, systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) (Thomson etal; 2001, Aringer and Smolen, 2003 and Brennan et al; 1992).

 Amongst the five polymorphisms (at position +691,-238, -308, -851, and -857) of TNFα-308gene detected by  PCR-single strand conformation polymorphism (PCR-SSCP) analysis, TNFα-308 polymorphism has been reported to be associated with autoimmune diseases including RA (Khanna  et al; 2006 and Chen et al; 2007).The genetic variation on position −308 resulted in two allelic forms in which the existence of guanine (G) defines the common variant and the existence of adenine (A) determines the less common one. Tumor necrosis factor β (TNF-β) which is linked closely to TNF-α, has also been shown to contribute to the susceptibility of multiple autoimmune diseases(Panoulas  et al; 2008 and Boraska  et al; 2009 ).A polymorphism has been detected at position +252 within the first intron of the TNF-β gene, consisting of a Guanine (TNF-β +252G) on one allele and an Adenine (TNF-β +252Α) on the alternate allele.[28] The presence of G at this position detemined the mutant allele known as TNF-β 1 (allele-1) which is less the  frequent allele in white subjects and is associated with increased TNF-α and TNF−β production ( Messer et al; 1991 and Abraham et al; 1993).

Recently, a study on  a Japanese population has indicated that TNFβ (+252) polymorphism together with HLADRB1* 0405 may have an influence on  the susceptibility to RA (Takeuchi  et al; 2005).To the best of our knowledge there are only two cohorts elucidating the role of TNF 308 G/A polymorphism in RA patients in Egypt. On the other hand, there are no reports investigating the roles of TNFα-1031T>C and LTA252A>G gene polymorphisms in RA patients among Egyptian population. Given the known importance of TNF gene in inflammatory and/or immune functions and the variation in susceptibility to immune disorders in different ethnic groups, we investigated the possible association between LTA252A>G, TNFα-308G>A and TNFα-1031T>C polymorphisms and susceptibility to RA in Egyptian patients. In addition, we investigated the association of these polymorphisms with disease activity and severity.

.

 

 

II.  Materials and Methods

 

A. Patients

 

A total of 70 subjects of Egyptian origin, including 35 cases and 35 control subjects, were included in the study. The RA patients were 34 females and one male. The RA patients were recruited from outpatient's clinic of the Rheumatology Department of Beni Suef University Hospital, Egypt, between March 2014 and January 2015.Cases with RA were diagnosed by a rheumatologist and fulfilled the 2010 ACR/EULAR (formerly, the American Rheumatism Association) classification criteria (Aletaha et al; 2010).The healthy control subjects were unrelated Egyptian age- and sex matched individuals who had no family history of autoimmune diseases. The control group lives in the same geographical area and has the same ethnic origin as the patients.  All cases and control subjects were informed of the purpose of the study, and their consent was obtained. The local ethics committee approved the study.

 

B. Clinical and laboratory assessment

 

Blood samples were obtained from all patients for determination of erythrocyte sedimentation rate (ESR; Westergreen), C-reactive protein (CRP), Rheumatoid factor (RF) by semi quantitative latex (AVITEX¨ CRP and AVITEX¨ RF, Omega Diagnostics). CRP was considered positive> 6mg/Litre while RF is considered positive³8 IU/ml. Anti-cyclic cetrulinated peptide(Anti-CCP) was determined using Enzyme linked immunosorbent technique (ELISA) using(QUANTA Lite¨ CCP3IgG ELISA, INOVA Diagnostics). According to the manufacturer's protocol serum was considered positive when the reading  was ³20 units.

The modified disease activity score DAS 28 was calculated from hospital medical records for all patients (Villaverde et al; 2000). DAS 28 score of higher than5-1 is indicative of high disease activity, whereas a DAS 28 below3.2 indicates low disease activity. A patient is considered in remission if the DAS 28 score is lower than 2.6.

 In all patients plain radiographs of both hand and feet in the postroanterior projection were obtained. Van Der Heijde-modified Sharp Score (vdHSS) was used to assess radiological changes (Van der Heijde  ,1999).

 

C.Genotyping

 

Genomic DNA was extracted from EDTA anti-coagulated whole blood using QIAamp DNA Mini Kit(Cat.no.51104,QIAGEN) according to the manufacturer's  protocol. The three sequences flanking TNFα-1031T>C, TNFα-308G>A and LTA252A>G single nucleotide polymorphisms were amplified by polymerase chain reaction (PCR). Genotyping of these polymorphisms was determined by a restriction fragment length-polymorphism (RFLP) assay (Avise , 1994).

The270-bp region of the TNF-α1031gene, encompassing the1031T/C polymorphism site, was amplified via polymerase chain reaction (PCR) using the sense (5'-GGGGAGAACAAAAGGATAAG) and antisense (5'-CCCCATACTCGACTTTCATA) primer pair (Karray, 2011).The total reaction volume was 25 µl.: 5µl. DNA, 12.5µl. Dream Taq green PCR master mix (Fermentas), 1µl. of each primer and 5.5µl.nuclease –free water. Initially, the PCR reaction was subjected to denaturation for 5 min at 95¡C, followed by 30 cycles of amplification (30 s at 95¡C, 30 s at 55¡C and 30 s at 72¡C). A final elongation step (5 min at 72¡C) was applied at the end of the 30 cycles ( Bonyadi et al; 2009).The PCR is followed by digestion with the restriction enzyme BbsI (Thermo Scientific Cat. No.: FDo574) according to the manufacturer's protocol (C allele, 159 and 111 bp; T allele, 270 bp).  (Fig. 1) (Bonyadi et al;  2009). Digested PCR fragments were separated by 4% agarose gel electrophoresis stained with ethidium bromide followed by ultra violet visualization.

The Primers (5Õ-AGGCAATAGGTTTTGAGGGCCAT-3Õ) and

(5ÕTCCTCCCTGCTCCGATTCC G-3Õ) were used to amplify the107-bp DNA fragment of the TNFα-308G>A polymorphism (Karray, 2011).The total  PCR reaction mixture was 25µl.: 5µl. DNA, 12.5µl. Dream Taq green PCR master mix(Fermentas), 1µl. of each primer and 5.5µl.nuclease –free water .The PCR Cycling conditions for TNFα-308G>A were performed according to the protocol described by Bonyadi et al.: 5 min for  initial denaturation at 95¡C; 35cycles at 95¡C for 1 min for denaturation, 30 s at 65¡C for annealing and 30 s at 72¡C for extension, followed by5 min at 72¡C for final extension ( Bonyadi et al; 2009). After amplification, PCR products were digested (at 37¡C) by NcoI (Themo Scientific Cat. No.: FD0574) according to the manufacturer's protocol (G allele, 87 and 20 bp; A allele, 107 bp) (Fig.2) (Bonyadi et al; 2009). Digested PCR products were electrophoresed in 4% agarose gel stained with ethedium bromide and followed by ultraviolet visualization. Primers (5Õ-CCGTGCTTCGTGCTTTGGACTA-3Õ) and (5ÕAGAGCTGGTGGGGACATGT CT G-3Õ) were used to amplify the740-bp DNA fragment to genotype the LTA252A>G polymorphism  The total PCR reaction mixture was 25µl.: 5µl. DNA, 12.5µl. Dream Taq green PCR master mix(Fermentas), 1µl. of each primer and 5.5µl.nuclease –free water .The PCR cycling conditions were performed according to the protocol  described by Cabrara et al; (1995) with a slight modification: initial denaturation at 95 ¡C for 5 minutes  Followed by 35 cycles of amplification: 94¡ C for 45 sec., 62.5 ¡ C for 45 sec. and a final extension at 72 ¡C for 1.5 min. PCR products were digested (at 37¡C) by NcoI (Thermo Scientific Cat. No.: FD0574) according to the manufacturer's protocol .Digested PCR products were electrophoresed in 4% agarose gel stained with ethidium bromide and followed by ultraviolet visualization. The digested products generated 185 bp and 555 bp bands for the G allele and a 107 bp band for the A allele (Fig. 3) (Cabrara  et al; 1995).

D.Statistical Analysis

The collected data was reviewed, coding and statistical analysis was done by using SPSS program (statistical package of social science; SPSS Inc., Chicago, IL, USA) version 16 for Microsoft Windows. Mean, median, range and standard deviation, were calculated to measure central tendency and dispersion of quantitative data while frequency of occurrence was calculated to measure qualitative data. Student t test was used to determine the significance in difference between two means. Chi-square-test (c2) was done for comparison of qualitative data and fisherÕs exact test was used instead when the count of cell was less than 5. Odds ratios  (ORs) with 95% confidence intervals (CI) were calculated whenever applicable, to test association between genotype and RA.Analysis of varience(ANVA) test used to determine the difference betweenmore than 2 means. The significance of the OR was calculated by a 2 by 2 contingency table. Genotype distributions were compared with those expected for samples from populations in Hardy-Weinberg equilibrium using a χ2 test (1df).The level of significance was taken at p-value of <0.05.


 

 

 

Description: C:\Users\user\Documents\photo 1.jpg

Fig (1): PCR-RFLP analysis of TNF 1031 gene polymorphism using BbsI restriction enzyme:

M: DNA molecular weight marker: (50 , 75 ,100 ,150, 200, 300 bp)

Lanes 1, 4, 7, 9: Wild type (TT): 1 bands 270 bp

Lane 6: Homozygous mutant type (CC): 2bands at 111 and 15 9 bp

Lanes 2, 3, 5, 8: Heterozygous mutant type (TC): 3 band 111, 159 & 270 bp

 

 

Fig (2): PCR-RFLP analysis of TNF 308 gene polymorphism using NcoI restriction enzyme:

M: DNA molecular weight marker: (50 ,75 ,100 ,150, 200, 300 bp)

Lanes 1, 2, 3, 4,6,7,8,9,: Wild type (GG): 2 bands 87 & 20 bp

Lanes 5: Homozygous mutant type (AA): 1 band 107 bp

 

 

Description: C:\Users\user\Documents\photo 3.jpg

Fig (3): PCR-RFLP analysis of LTA 252 gene polymorphism using NcoI restriction enzyme:

M: DNA molecular weight marker: (50 ,100 ,150 ,200,ÉÉ500 bp)

Lanes 1, 2, 3, 7, 9, 11, 13, 16 : Wild type (AA): 1 bands 750 bp

Lanes 5, 6, 8, 10, 12, 14, 15, 17 : Heterozygous mutant type (AG): 3 band 185, 555 & 750 bp

Lane 4: Homozygous mutant type (GG): 2 bands 185& 555

 

 

 

 


 

III. Results

In the current study, we investigated the possible association between RA disease and the TNFα gene promoter polymorphisms α-308A>G, α-1031 T>C and the TNFβ polymorphism+252A>G (LTA252A>G) in the Egyptian population in Beni- Suef Governorate. We further compared the association of these polymorphisms with disease severity according to Sharp Score and disease activity according to DAS 28 scoring system.

 Concerning LTA252A>G gene polymorphism, the genotype frequencies of RA patients and healthy controls conformed to the Hardy-Weinberg equilibrium (P= 0.2531; P=0.224, respectively). Similarly, for the TNFα-1031T>C gene polymorphism, the genotype frequencies of RA patients and healthy controls conformed to the Hardy-Weinberg equilibrium (P=0.97; P=013, respectively). As regards, TNFα-308A>G gene polymorphism the genotype frequencies for cases showed deviation from HWE (P=0.0019), while the genotype frequencies of controls conformed to HWE (P=0.08).

The demographic, clinical and laboratory data of RA patients and control group are demonstrated in Table 1.

 

Analysis of the distribution of TNFα-308 G/A alleles in RA patients and controls revealed that the G allele was higher than the A allele in the patients' group compared to the control group and the difference was statistically significant (OR =2.67, CI: 0.940-7.791; P=0.040). Regarding the distribution of TNFα-308 genotypes, the GG genotype was significantly higher in patients than controls (OR= 8.42; CI: 1.9-42.3, P<0.001 (Table 2).

         Further on, analysis of the distribution of TNFα-1031T/C and the TNFβ polymorphism+252A/G, revealed non-significant differences in both allelic and genotypic distributions among patient and control groups( Table 2).

For the next analysis, the patients were divided into 2 groups according to the degree of disease activity. The first group represented the patients in remission (DAS 28<2.6). The second group represented the non-remission patients which included: low activity patients (DAS 28³ 2.6-<3.2), moderate activity patients (DAS 28³ 3.2-² 5.2) and high activity group (DAS 28 >5.1) (Bonyadi et al; 2009).

Analysis of the distribution of TNF-α 308 G/A revealed, that the frequency of the G allele was higher than the A allele in the non- remission group. On the other hand, only two patients carrying the A allele were in remission and there were no patients in remission carrying the A allele. The difference between the two groups was statistically significant (P=0.008). On comparing the distribution TNF-α 308 genotypes in both remission and non- remission group patients, the GG genotype was more frequently represented than the AG genotype and the AA genotypes, respectively and the difference was highly statistically significant (P<0.001 Table 3). Analysis of the frequency of distribution of alleles and genotypes in TNF-α1031 T/C and TNFβ +252A/G polymorphism was statistically non- significant (Table 3).

In the current study, we assessed the degree of disease severity in all patients, according to Van der Heijde-modified Sharp Score (vdHSS). Next, disease severity was compared to TNF-α and TNF-β gene polymorphisms. On comparing the frequency of distribution of TNF-α308 genotypes with disease severity, we detected that the heterozygous mutant type( AG )was more frequently represented  than the wild type( GG )genotype and the homozygous mutant (AA) genotype, respectively, and the difference was statistically significant(P=0.007) (Table 4). On the other hand, Analysis of the frequency of distribution of genotypes in TNF-α1031 and TNFβ+252 polymorphism according to disease severity was statistically non- significant (P=0.105 and P=0.691, respectively) (Table 4).

 We did not detect any association between the distribution of TNF-α 308,TNF-α 1031 and LTA252 genotypes , and age/sex of patients  disease duration, CRP, RF and Anti CCP positivity (data not shown).

 

 

 

 

 

 

 

 


Table 1. Demographic, clinical and laboratory of RA patients and control group

 

Demographic and clinical data

Cases(35)

Controls(35)

Significance Test

P value

Age

Mean ±SD

Range

 

45.63±13.93

20-70

 

40.51±12.63

22-65

 

 

 

Student t test

t= 1.60

 

0.112

Sex:

Female

Male

 

34       97.1%

 1          2.9%       

 

33         94.3%

2             5.7%

 

c2=0.348

 

0.555

Disease Duration (years)  

Mean ±SD

median

Range

 

8.49±6.95

6

1-30

 

Sharp Score

Mean ±SD

Median

Range

 

 

37.31±26.40

30

10-90

 

DAS 28

Mean ±SD

Range

 

4.77±1.44

2.30-7.75

 

 

ESR

Mean ±SD

Range

 

CRP Positive cases

 

 

RF  Positive cases

 

 

Anti CCP Positive cases

 

56.40±22.74

10-100

 

17/35   (48.6%)

 

 

25/35 (71.4%)

 

 

29/35 (82.9%)

 

 

 

*Significant Difference (Pvalue<0.05)

Table 2. Comparison of TNF- α and TNF+β polymorphisms between Egyptian RA patients and healthy controls.

 

Cases

(n=35)

    %

Controls

(n=35)

     %

Odds Ratio and 95% Confidence interval

Significance Test

P value

TNFα 308:

GG

AG

AA

 

 

A

G

 

30   85.7%

 3     8.6%

 2     5.7%

 

 

63    90%

 7     10%

 

  19    54.3%

  16     45.7%

  0        0.0%

 

 

  54      77.14%                                       

   16     22.86%

 

Reference

8.42 (1.9- 42.3)

0-0(0.0-7.18)       

 

 

Reference

2.67(0.94-7.791)    

     

 

 

      c2=11.32

c2=1.24       

 

 

c2= 4.21 

 

 

 

 

                <0.001

  0.266                                                         

 

 

0.040*

 

TNFα 1031:

TT

TC

CC

 

 

T

C

 

24      68.5%

10      28.6%

1        2.9%

 

 

58       82.86%

12       17.14%

 

 

   21      60.0%

  14       40.0%

   0          0.0%

 

 

   56        80%

   14        20%

 

Reference

0.63(0.20-1.90)

     NAa

 

 

Reference

1.21(0.47-3.084)

 

 

         c2=0.85  c2=0.86

 

 

c2= 0.189

 

 

 

 

0.355

0.354

 

 

 0.664

 

LTA 252:

AA

AG

GG

 

 

A

G

 

15        42.9%%

18        51.4%

 2          5.7%

 

 

48          68.57%

22          31.43%

 

  18         51.4%

  16         45.7%

   1          2.9%

 

 

  52         74.29%

  18         25.71%

 

Reference

1.35(0.46-3.95)

2.40(0.15-74.6)

 

 

Reference

0.76(0.33-1.67)

 

 

c2=0.38

c2=0.50

 

 

c2=0.56

 

 

 

0.540

0,481

 

 

P=0.454

*Significant difference (p value <0.05)

 –Allele frequency was calculated according to Hardy-Weinberg Equation(HWE)

- NAa  : non-applicable

 

Table3. Comparison of TNF- α and TNF+β polymorphisms distribution according to DAS 28 scoring system:

DAS28

Remission**

  N=1

Non- Remission***

   N=34

 

Significance Test

P value

TNFα 308:

GG

AG

AA

 

A

G

 

0              0.0%

0               0.0%

1             100%

 

2              100%

0               0.0%

 

30        88.2%

3          8.9%

1          2.9%

 

5        7.4%

63       92.6%

 

 

 

 

 

 

 

c2=16.98

 

 

 

c2= 18.53

 

 

<0.001

 

 

 

0.008*

TNFα 1031:

             CC

             TC

             TT

 

             C

             T

 

 0               0.0%

0                0.0%

1                100.0%

 

0             0.0%

2             100%

 

1          2.9%

10        29.4%

23         67.7%

 

12         17.6%

56          82.4%

 

 

 

 

 

 

 

 

 

c2=0.47

 

 

 c2= 0.43

 

 

0.790

 

 

0.513

LTA 252:

           GG

           AG

           AA

 

            G

            A

 

0                 0.0%

1              100.0%

0                  0.0%

 

1            50.0%

1            50.0%

 

 2            5.9%

17           50.0%

15           44.1%

 

21           30.9%

47          79.1%

 

 

 

 

 

 

 

   c2=0.97

 

 

 

c2=0.33

 

 

0.615

 

 

 

P=0.532

*Significant Difference (p value <0.05)

**Remission group (DAS 28<2.6)

*** Non- remission group includes: (low activity patients (DAS 28³ 2.6-<3.2), moderate activity patients (DAS 28³ 3.2-² 5.2) and high activity group(DAS 28 >5.1)

-Allele frequency was calculated according to HWE

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 4.Comparison between disease severity (represented by Sharp Score) with gene polymorphisms in RA patients

 

Genotypes           Sharp Score          ANOVA Test            P value

                              (mean± SD)     

TNF-α308

    GG                     34.13±24.24                      

    AG                     80.00±10.00            F=5.79                   0.007*

    AA                     21.00±12.72

TNF-α1031

   CC                      90.00±

   CT                      31.50±24.86            F=2.42                0.105           

   TT                      37.54±

LTA 252

   GG                   37.50±24.74

   GA                   41.00±28.67             F=0.37                   0.691

   AA                   32.87±24.75

    

 

 

*Significant difference(P<0.05)   -The total number of cases analyzed  for each gene is 35 cases


-

 

IV. Discussion

   Rheumatoid arthritis (RA) is a complex, multifactorial, inflammatory disease of unknown etiology with significant variability. Both environmental and genetic factors can contribute to susceptibility to disease initiation as well as progression of disease course (Reveille, 1998). Fifty percent of risk of developing rheumatoid arthritis is attributable to genetic factors (van der Woude etal; 2009). Much progress has been made in detection of genetic regions characterized by structural variation (single nucleotide polymorphisms); more than 30 genetic regions are associated with susceptibility to rheumatoid arthritis (Orozco et al; 2010).  

    SNPs are highly abundant, substantial, and spread throughout the genome. These variations are associated with diversity in the population, individuality, susceptibility to diseases, and differential response to medical treatment (Hussein et al; 2013).

Multiple polymorphisms within the promoter region of TNF-α and the intron 1 polymorphism of TNF-β, in particular, have been linked with altered levels of circulating TNF-α (Sharma et al; 2008).

In the present study, on investigating the genetic association of TNFα 308 A/G and RA, the G allele was more frequently represented among RA patients than the A allele compared to the healthy control group (p = 0.040).  Similarly, The wild type (GG) genotype was more frequently represented among RA patients (85.7%)  in comparison to mutant (AA) genotype (P<0.001).

 In accordance with our results Mosaad et al., ( 2011) reported that the G allele was more frequently represented than the A allele among RA patients compared to the healthy control group (OR=6.7, P< 0.001). In addition, the distribution of TNFα- 308 genotype, the GG homozygous genotype was higher in patients with rheumatoid arthritis than in healthy control group (P< 0.001).  Several studies conducted in other parts of the world were in agreement with our results (Balog et al; 2004 and Al-Rayes et al; 2011).

          However, in contrast to the results of the current study, Hussein et al., (2013) reported that TNF 308 AA genotype was more frequently prevalent among the patients and associated with RA susceptibility. Similarly, in contrast to our findings, numerous studies showed significantly higher frequency of allele A or genotype AA in RA patients compared to control group suggesting that TNF-α –308A allele is a predis­posing factor of RA (Khanna et al; 2006, Nemec et al; 2008, Ursum et al;2010 and Stojanovic' et al;2011).

         On the other hand, non-significant association between TNF-α –308 polymorphism and RA susceptibil­ity was observed in other case control studies

(Lee et al; 2007 and Reneses et al; 2009).

         Our results regarding TNF-α308 G/A polymorphism could be explained by the fact that these differences in findings may be attributed to the eth­nicity-related genetic  constitution in different pop­ulations, which is evident from the highly sig­nificant variations in genotype data of TNF-α –308 polymorphism among the healthy sub­jects of various ethnicities (Reneses et al; 2009 and Al-Rayes etal; 2011). Hence, the gene-environment synergy might be responsible for the significant differences in the results of polymorphism association studies on RA pa­tients from heterogeneous ethnicities/geographical lo­cations (Reneses et al; 2009). The difference in results between patients groups in different Egyptian governorates might be attributed to differences in study design, mean duration of RA and sample size.

In the current study, there was no statistical significant difference detected on analyzing allelic and genotypic frequency distribution, of TNFα 1031 T/C polymorphism in RA patients compared to healthy control group (OR: 0.89, P=0.784 and OR=0.68, P=0.393, respectively).In agreement with our results Karry et al; (2011) found no significant difference between RA patients and healthy controls (P=0.79).

Although there is a plethora of literature regarding the role of TNF-α polymorphism in the pathogenesis of a variety of autoimmune diseases as RA, only few studies have been reported on the role of TNF-b in the pathogenesis of RA.

TNF-b belonging to the surrounding of TNF-α locus has indeed been shown to play major role in the pathogenesis of numerous autoimmune diseases including RA.  Immunological studies on TNF-b showed its close similarity to TNF-α in terms of their pro-inflammatory and apoptotic activity (Panoulas et al; 2008).

A polymorphism has been detected at position +252 residing within the first intron of the TNF-b gene, consisting of nucleotides Guanine (TNF-b +252G) on one allele and Adenine (TNF-b +252A) on the alternate allele ( Al-Rayes et al;2011).

    In the current study, LTA 252 A>G allele and genotype frequency distribution was similar between patients and healthy controls (OR=1.32,P=0.454and OR=1.41, P=0.696,respectively).    In accordance with the results of the current study, Al Rayes et al., (2011) reported that the frequency of the mutated G allele in cases and controls was (47.64 % vs. 51.19%). The frequency of the wild A allele in both cases and controls respectively, was (52.45% vs. 48.80%) and the difference between alleles was statistically insignificant (P= 0.457).

    In contrast, Takeuchi et al., (2005) and Santos et al.,(2011) reported an association between A allele with RA. These studies showed that TNF-β +252 polymorphism together with with HLA-DRB1*0405 has an influence on the susceptibility to RA.

  In accordance with the results of the current study, Zake et al. (2002) reported that LTA 252 A>G genotype distribution was similar between patients and controls.

     On the contrary, Karray et al.,(2011) reported that the LTA252A>G polymorphism is more frequent in RA patients than in controls group. The frequency of subjects with the G allele was significantly higher in RA patients than in controls group (p =0.01).They also, reported that the homozygous mutant GG genotype was more frequently represented among RA patients in comparison to controls (p = 0.017).  Similarly, Al-Rayes et al (2011) reported that GG genotype of TNF-β (+252) polymorphism occurs more frequently in RA patients as compared to general population

    In the current study, we assessed the influence of TNF- α 308, TNF α- 1031 and LTA 252 allele and genotype distribution on disease activity. Analysis of the distribution of TNF-α 308 G/A revealed, that the frequency of the G allele was higher than the A allele in the non- remission group compared to the remission group and the difference between the two groups was statistically significant (P=0.008). There was a highly statistically significant association between wild type (GG) genotype and disease activity represented by DAS28 (P<0.001).  This could be explained be explained by the fact that the activity of RA might be modified by the severity of the inflammatory processes which are influenced by SNPs in genes that code for the TNFα and iNOS ( Zake et al;2002)

    In accordance with our results Petra et al., (2009) and Hussein et al ;(2013) indicated a positive association between GG genotype and disease activity. On the other hand, Nemec et al.,(2008) and Mosaad et al., (2011) found no significant differences in genotype distribution and allelic frequencies of the TNF- α 308 G/A promoter  polymorphism between RA patients according to the disease activity score DAS28.

Regarding disease severity represented by sharp score, the heterozygous mutant (AG) genotype was more frequently represented among RA patients compared to the wild type (GG) and the homozygous mutant type (AA) that were less frequently represented among RA patients. The difference between the three groups was statistically significant (P= 0.007). The effect of TNF-α 308 G/A polymorphism on disease severity could be explained by differences in the rate of TNF-α synthesis. The production of TNF-α may be associated with TNF-α promoter polymorphism. In fact, role of linkage disequilibrium is intense in this area, and it may be difficult to study the role of SNPs separately (Nemec et al; 2008).  Moreover, circulating TNF-α levels might be under a complex regulatory process. Circulating TNF-α level is regulated at different stages: gene transcription, post transcription control of mRNA stability, cleavage of the membrane form to release the soluble form, and the expression of receptors (Hajeer and Hutchinson, 2001).

     Our results regarding radiological joint damage were in accordance with Rezaieyazdi et al, (2007) which documented the association between heterozygous mutant (AG) genotype with a worse course of the disease.

    However, in contrast, Nemec et al., (2008) reported an association between severe course of RA and TNF-α 308 GG genotype .This was also reported by Barton et al., (2004) who reported that the G allele showed a tendency towards worse radiological outcome at five years, as measured by the presence or absence of erosions, in patients with inflammatory arthritis. On the other hand, Mosaad et al., (2011) and Wilson et al., (1995) reported that RA patients with A allele tend to have an increased number of erosions.

 

In the current study, no statistically significant association was found between TNF-α 1031T/C polymorphism and RA disease activity and severity.

    Contrary to our findings, Karray et al., (2011) pointed out that the C allele was significantly higher in patients in  remission of RA activity than those in the non-remission group (P= 0.028).In addition, TNF-α 1031 CC genotype frequency was higher among the patients in the remission group compared with patients in the non- remission group (P= 0.0035).

          In agreement with the results of the current study, Barton et al., (2004) reported the absence of a significant association between TNF-α 1031 and disease severity in RA patients.

          There was no statistically significant association detected as regards disease activity and severity and their association with LTA 252 polymorphism. In agreement with our findings, Karray et al. (2011) and Al Rayes et al (2011) found also no association with RA activity and severity.

In conclusion, these results suggest that the TNF-α 308 G/A polymorphism of the TNF gene can be genetically associated with the susceptibility to Rheumatoid Arthritis in our study group and might bet involved in both disease activity and severity. Therefore, the TNF molecule might have a major genetic and/or functional involvement in the pathogenesis of RA and might also be implicated in disease activity and severity in the Egyptian population.

Acknowledgements

The authors wish to thank Dr Dina Nabil for her kind support throughout the completion of the work. This work was financially supported by Dr. Heba M. zagloul . The authors declare no conflict of interest.

 

 

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