Mourad Ben Ayed

Immunogenetics of pemphigus: An update

Pemphigus are rare but informative models of organ-specific autoimmune diseases, resulting from the interplay of environmental, genetic and stochastic factors. There are many arguments to consider that pemphigus have a genetic basis involving, as many other autoimmune diseases, several different genes with additive or synergistic effects. So far, the unique strategy used to identify the contributive loci has been direct analysis of candidate genes through conventional case-control association studies. The major histocompatibility complex in particular the class II locus was demonstrated to be associated with pemphigus with a high rate of replicability. The progresses in the understanding of pemphigus physiopathology and the development of new molecular tools offer new perspectives to unveiled the genetic basis of this group of autoimmune blistering diseases, as shown by recent studies of candidate genes expressed at different levels of the autoimmune process.

The CREM gene is involved in genetic predisposition to inflammatory bowel disease in the Tunisian population

The identification of susceptibility genes for inflammatory bowel disease (IBD) is key to understanding pathogenic mechanisms. Recently, the results of genetic association studies have highlighted many loci that are shared among several autoimmune diseases. We aimed to study the genetic epidemiology of polymorphisms in specific genes previously associated with other autoimmune diseases, namely the CREM, STAT4, STAT5a, Stat5b, and IRF5 genes. Twelve polymorphisms in the CREM, STAT4, STAT5a, Stat5b, and IRF5 genes were genotyped in a cohort of 107 IBD patients (39 Crohns disease [CD] and 68 ulcerative colitis [UC]) and 162 controls from southern Tunisia. One CREM single nucleotide polymorphism (SNP) displayed evidence for genetic association with IBD (p=8.7×10(-4), odds ratio [OR]=2.84 [1.58; 5.09]). One STAT4 SNP (p=0.026; OR=1.65 [1.06; 2.58]) exhibited a marginal association with UC but not with CD. No significant association was observed with the SNPs in STAT5a, IRF5, and STAT5b. These results suggest that common variants of the CREM gene are involved in the genetic component conferring general susceptibility to IBD, whereas STAT4 appears to be more specifically associated with UC. This work provides motivation for studies aiming to replicate these findings in larger populations.

Non-HLA autoimmunity genetic factors contributing to Autoimmune Polyglandular Syndrome type II in Tunisian patients

Autoimmune Polyglandular Syndrome Type II (APSII) is characterized by the co-occurrence of clinical insufficiency of at least two endocrine glands. Although, HLA determinants of APSII predisposition have been identified, little attention has been paid to non-HLA genes. Here, we used SNP genotyping in a Sequenom platform and genetic association tests to study a cohort of 60 APSII Tunisian patients presenting highly frequent co-occurrence of Autoimmune Thyroid Disease (AITD) and Type 1 Diabetes (T1D) and lower frequency of Addisons disease (AD). We tested the high a priori possibility that well-established non-HLA autoimmunity loci were involved in APSII and confirmed five association signals to APSII, namely: (1) two T1D-associated SNPs, in CTLA4 and IL2RA, suggest their involvement in T1D pathogenesis in this cohort; (2) two SNPs in STAT4 and IL15 not previously associated to endocrinopathies, are possibly involved in co-occurrence of organ autoimmunity in APSII, and; (3) one SNP in TNF alpha showed association to APSII irrespective of AD. While this work was performed in a relatively small cohort, these results support the notion that the non-HLA genetic component of APSII include genetic factors specific of particular autoimmune manifestations as well as genetic factors that promote the co-occurrence of multiple autoimmune endocrinopathies.

Catalase and Lipid Peroxidation Values in Serum of Tunisian Patients with Pemphigus Vulgaris and Foliaceus

Pemphigus is an autoimmune disorder resulting from the interaction between autoantibodies and desmoglein. Oxidative stress seems to be responsible for the onset/aggravation of many human diseases. Actually, it is considered as one of the several factors for the etiopathogenesis of pemphigus. The present study aims to evaluate the oxidative state in the sera of pemphigus vulgaris and pemphigus foliaceus patients by assessing lipid peroxidation, proteins oxidation, and antioxidant enzyme activity. This study included 36 pemphigus vulgaris and 42 pemphigus foliaceus patients as well as a group of controls consisting of 78 healthy volunteers. Malondialdehyde levels (p < 0.001) and catalase activity (p < 0.001) are higher in both groups of patients than in the control group. The two groups of patients showed a nonsignificant decrease in the thiol groups compared with the healthy one. A nonsignificant difference was shown between pemphigus vulgaris and pemphigus foliaceus patients, except for the catalase which shows an increase in the pemphigus vulgaris group. We have also found significant correlations between serum oxidative stress marker levels and serum anti-desmoglein antibody levels in the two pemphigus groups. These findings underline the implication of oxidative stress in the physiopathology of pemphigus by the increase in the autoantibodies’ reactivity.

Association of ZAP70 and PTPN6, but Not BANK1 or CLEC2D, with inflammatory bowel disease in the Tunisian population.

Inflammatory bowel diseases (IBDs), consisting of ulcerative colitis (UC) and Crohns disease (CD), are complex disorders with multiple genes contributing to disease pathogenesis. We aimed to identify the associations of genetic variations in the ZAP70, PTPN6, BANK1, and CLEC2D genes encoding for intracellular signaling molecules with IBDs. One hundred seven patients (39 CD and 68 UC) with IBD and 162 healthy control subjects from the Southern Tunisia were recruited. We genotyped 4 single-nucleotide polymorphisms (SNPs) in ZAP70 (rs1020396, rs11686881, rs13420683, and rs17695937), 2 SNPs in PTPN6 (rs7310161 and rs759052), 3 SNPs in BANK1 (rs10516487, rs17266594, and rs3733197), and 1 SNP in CLEC2D (rs3764021). ZAP70 displayed a strong genetic association with CD for rs13420683 [allele C, p=0.003, P(corr)=0.006, odds ratio (OR)=2.25 (1.32; 3.85); genotype CC, p=0.016, P(corr)=0.048, OR=2.57 (1.22; 5.41)]. However, in UC, a weak association with PTPN6 was observed [TT (p=0.01; P(corr)=0.03; OR=2.11 (1.18; 3.76)]. No significant association in the BANK1 and CLEC2D genes was observed. These results suggest the involvement of the ZAP70 and PTPN6 genes in the genetic component conferring a general susceptibility to CD and UC, respectively. This work provides motivation for studies aiming to replicate these findings in larger populations.

Association of BANK1 and cytokine gene polymorphisms with type 1 diabetes in Tunisia.

Type 1 diabetes (T1D) is an autoimmune disease (AID) with both genetic and environmental components. We aimed to investigate the genetic association of polymorphisms in genes previously linked with other AIDs, namely BANK1, IL15 and IL2/IL21 region. A total of 76 T1D patients and 162 controls from Southern Tunisia were recruited for a case-control association study investigating the relationship between sixteen SNPs of the BANK1, IL15 and IL2/IL21 gene region and T1D. In the BANK1 gene, G allele and GG genotype of rs3733197 were significantly increased in the group of T1D patients compared to controls. In addition, in the IL15 gene, the minor allele A of rs10519613 polymorphism was significantly higher in patients than in controls. No significant association was found for SNPS in IL2/IL21 gene region. The analysis of the haplotype structure revealed the G-C-A-C-T haplotype of the IL15 gene as associated with a reduction in the risk of developing T1D, while A-T-A-C-T haplotype increased the risk of developing the disease. Furthermore, in the IL2/IL21 region, only one haplotype consisting of eight SNPs was markedly associated with T1D susceptibility. Moreover, G-C combination of the BANK1/IL15 was significantly increased in T1D patients, compared to controls. Our results establish BANK1 and IL15 as new T1D genetic susceptibility factors and replicate the association of the 4q27 region with T1D. Our data agree with the effect previously observed for other autoimmune conditions and delineate a shared underlying mechanism.

Genetic Factors Contributing to Systemic Lupus Erythematosus in Tunisian Patients

Systematic lupus erythematosus (SLE) is a multi system autoimmune disease characterized by autoantibodies production, multi-organ damage and complex genetic inheritance. Multiple genetic and environemental factors contribute to the pathogenesis of this disease. Recent genome-wide studies, have added substantially to the number of genes associated with SLE. We performed a case control study using 138 SNPs in 93 Tunisian patients affected with lupus and 162 healthy controls. All SNPs were genotyped in a Sequenom platform. To confirm some associations, associated SNPs were analyzed using logistic regression which allows the test of association with a given SNP by adjusting for the effect of confounding variables. Association was especially reported with rs3733197 (P=0.0026, OR=2.04), rs17266594 (P=0.046, OR=1.56) in BANK1 gene, rs2070197 (P=0.0016, OR=2.31), rs2004640 (P=0.024, OR=1.54), rs10954213 (P=0.035, OR=1.53) in IRF5 gene and rs7574865 (P=0.017, OR=1.77) in STAT4 gene: previously confirmed SLE susceptibility genes. rs1800629 (P=0.00036, OR=2.26), rs4147359 (P=0.026, OR=1.55) and rs11575812 (P=0.037, OR=1.57) of TNF-α, IR2RA and IL2 genes respectively were also associated with SLE. Haplotypic analysis reported 2 susceptibility haplotypes: TGG (P=0.00421, OR=1.87) in BANK1 and TCA (P=0.00177, OR=2.34) in IRF5 genes. Our results show that numerous genes, some with known immune related function predispose to lupus.