**6. Genetic variants in** *interleukin 7 receptor α chain (IL-7Ra)* **gene**

IL7 is a type 1 short-chain cytokine of the haematopoietin family involved in the modulation of T- and B-cell development and T-cell homeostasis. To perform the immune system func‐ tions, IL7 binds to the transmembrane receptor that is formed by heterodimerisingthe common cytokine gamma chain and IL7 receptor alpha chain (IL7Ra or CD127). IL7Ra is a membrane glycoprotein folded to bind and mediate the action of IL7 and other alpha helical cytokines. IL7Ra consists of an extracellular domain, transmembrane region and cytoplasmic tail, which uses kinases for signal transduction [49]. The localization of the *IL7Ra* gene is chromosome 5p13.3. An increased expression of IL7Ra in peripheral blood mononuclear cells was found in MS patients when compared to controls [50, 51]. The IL7Ra and IL7 mRNA increased expres‐ sion was found also in the cerebrospinal fluid of MS patients, possibly suggesting an altered balance between the isoforms of IL7Ra and a higher signal-inducing immune cell proliferation and survival [52]. According to the alternative splicing of exon 6 in *IL7Ra* gene, membranebound or soluble isoforms of IL-7Ra are produced [53]. A significantly increased ratio of the membrane-bound to soluble isoforms of IL7Ra in MS patients can facilitate the aberrant activation of potentially auto-reactive T cells [54].

Single-nucleotide polymorphisms in *IL7Ra* gene are involved in the dysregulation of immune homeostasis and thus can be associated with susceptibility to MS [55]. A genome-wide study in a large group of subjects from the UK and USA identified the strong association between SNP rs6897932 in *IL7Ra* gene and the risk of MS [2]. The non-conservative aminoacid change on position 244 (Ile→Thr) ofIL7Ra is a result of the SNP rs6897932 (ATC → ACC) in exon 6 of *IL7Ra* gene [56]. This aminoacid change has a functional effect on the product of expression of alternative spliced *IL7Ra* gene, which is manifested by changes in the proportion of the soluble versus membrane-bound isoforms of IL7Ra. The change of this ratio can be followed by a different regulation of the IL7 signal transduction pathway and directly associates the SNP rs6897932 with MS [57].

It has been found that allele C of SNP rs6897932 in *IL7Ra* gene contributes to the increased genetic risk of MS in groups of MS patients from the USA [57, 58], South Spain [59], Nordic countries—Denmark, Finland, Norway and Sweden [52], France [60], Netherlands [61] and Japan [62]. The homozygosity for C allele was identified as a risk genotype for MS susceptibility in Netherlands [61] and Spain [59]. A genotype association was also confirmed by the finding of increased counts of CC genotype of rs6897932 in MS patients compared to controls in the cohorts from the USA [58] and Japan [62]. Corresponding with the contribution of allele C to the risk of MS, the protective effect of allele T for MS risk in a Nordic case-control group has been reported by Lundmark et al. [52]. The protective effect of allele T has been reported also in Spain by Alcina et al. [59]. On the contrary, no association between SNP rs6897932 and MS was found in cohorts of MS patients from Northern Ireland [58], Germany [44] and Western Balkan countries—Serbia, Croatia and Slovenia [63].

Only a few studies addressed the question whether the rs6897932 in *IL7Ra* gene contributes only to the genetic risk of MS, or whether it can also affect the disease course and disability progression [44, 57, 61, 64]. Groups of patients with different forms of MS were compared in several studies. In Northern European primary-progressive MS cases (PP MS), the underex‐ pression of *IL7Ra* gene as well as different allele frequencies of IL7Ra promoter SNP was confirmed. Moreover, *IL7Ra* gene expression was found to be up-regulated in secondaryprogressive MS (SP MS) patients [64]. In a study by Akkad et al. [44] in German MS patients, it was found that the soluble IL7Ra reduced the expression and allelic and genotypic associa‐ tion between rs6897932 and SP or PP MS but not with RR MS. In their study, a significantly higher frequency of allele C and genotype CC of rs6897932 in SP and PP MS patients was found, but not in RR MS patients compared to controls. The assessment of the severity of MS by MSSS did not show any association between rs6897932 genotype and disease severity in the USA [57]. Differences in allele frequencies in SP MS patients compared to healthy controls were reported in Dutch MS patients by Sombekke et al. [61]. In spite of that, no association between rs6897932 genotype and disease severity (MSSS, EDSS, other clinical tests) and disease activity (relapse rate and MRI markers) was found.

**6. Genetic variants in** *interleukin 7 receptor α chain (IL-7Ra)* **gene**

activation of potentially auto-reactive T cells [54].

Balkan countries—Serbia, Croatia and Slovenia [63].

rs6897932 with MS [57].

8 Trending Topics in Multiple Sclerosis

IL7 is a type 1 short-chain cytokine of the haematopoietin family involved in the modulation of T- and B-cell development and T-cell homeostasis. To perform the immune system func‐ tions, IL7 binds to the transmembrane receptor that is formed by heterodimerisingthe common cytokine gamma chain and IL7 receptor alpha chain (IL7Ra or CD127). IL7Ra is a membrane glycoprotein folded to bind and mediate the action of IL7 and other alpha helical cytokines. IL7Ra consists of an extracellular domain, transmembrane region and cytoplasmic tail, which uses kinases for signal transduction [49]. The localization of the *IL7Ra* gene is chromosome 5p13.3. An increased expression of IL7Ra in peripheral blood mononuclear cells was found in MS patients when compared to controls [50, 51]. The IL7Ra and IL7 mRNA increased expres‐ sion was found also in the cerebrospinal fluid of MS patients, possibly suggesting an altered balance between the isoforms of IL7Ra and a higher signal-inducing immune cell proliferation and survival [52]. According to the alternative splicing of exon 6 in *IL7Ra* gene, membranebound or soluble isoforms of IL-7Ra are produced [53]. A significantly increased ratio of the membrane-bound to soluble isoforms of IL7Ra in MS patients can facilitate the aberrant

Single-nucleotide polymorphisms in *IL7Ra* gene are involved in the dysregulation of immune homeostasis and thus can be associated with susceptibility to MS [55]. A genome-wide study in a large group of subjects from the UK and USA identified the strong association between SNP rs6897932 in *IL7Ra* gene and the risk of MS [2]. The non-conservative aminoacid change on position 244 (Ile→Thr) ofIL7Ra is a result of the SNP rs6897932 (ATC → ACC) in exon 6 of *IL7Ra* gene [56]. This aminoacid change has a functional effect on the product of expression of alternative spliced *IL7Ra* gene, which is manifested by changes in the proportion of the soluble versus membrane-bound isoforms of IL7Ra. The change of this ratio can be followed by a different regulation of the IL7 signal transduction pathway and directly associates the SNP

It has been found that allele C of SNP rs6897932 in *IL7Ra* gene contributes to the increased genetic risk of MS in groups of MS patients from the USA [57, 58], South Spain [59], Nordic countries—Denmark, Finland, Norway and Sweden [52], France [60], Netherlands [61] and Japan [62]. The homozygosity for C allele was identified as a risk genotype for MS susceptibility in Netherlands [61] and Spain [59]. A genotype association was also confirmed by the finding of increased counts of CC genotype of rs6897932 in MS patients compared to controls in the cohorts from the USA [58] and Japan [62]. Corresponding with the contribution of allele C to the risk of MS, the protective effect of allele T for MS risk in a Nordic case-control group has been reported by Lundmark et al. [52]. The protective effect of allele T has been reported also in Spain by Alcina et al. [59]. On the contrary, no association between SNP rs6897932 and MS was found in cohorts of MS patients from Northern Ireland [58], Germany [44] and Western

Only a few studies addressed the question whether the rs6897932 in *IL7Ra* gene contributes only to the genetic risk of MS, or whether it can also affect the disease course and disability progression [44, 57, 61, 64]. Groups of patients with different forms of MS were compared in Results of our own work suggest the relevance of rs6897932 allele and gene variants in MS pathogenesis in Slovaks [10]. Our results have revealed that allele C is present in a higher frequency in MS patients (77.4%) as compared to the control group (72.3%), which indicates an increased risk of MS development (OR=1.314, 95% CI=1.004–1.720, *p*=0.047). Interestingly, allele T was manifested in MS patients in a significantly lower frequency representing only 22.6% as compared to 27.7% in controls. This suggeststhat allele T seems to be protective against MS development (OR = 0.761, 95% CI= 0.582–0.996, *p* = 0.047). The additive model fitted the best to assess association between genotypes and MS risk. Logistic regression analysis adjusted for sex and age revealed that there is a significant associationbetween IL7Ra rs6897932 genotype and MS risk (OR = 0.764, 95% CI = 0.586–0.995, *p*log = 0.045). The genotype analysis showed that MS patients manifested a lower frequency of genotype CT when compared to controls (34.8% vs. 36.3) and genotype TT (5.2% vs. 9.9%) and a higher frequency of genotype CC (60.0% vs. 54.1%). When we used the additive genetic model, we found a significantly decreased risk of MS development in carriers of allele T with genotype CT (OR = 0.865, 95% CI = 0.609–1.228, *p* = 0.05) as well as with genotype TT (OR = 0.565, 95% CI = 0.282–1.132, *p* = 0.05).

After stratification of MS patients according to the disease disability progression rate, we found a significantly lower frequency of allele T in the subgroup of rapidly progressing MS patients (18.1%) as compared to 27.7% in controls. These results suggest that allele T is associated with protection against rapid disability progression of MS (OR = 0.576, 95% CI = 0.348–0.955, *p* = 0.031). An additive genetic model adjusted for sex and age fitted the best to assess the associ‐ ation between genotypes and the rate of disease disability progression. Linear logistic regres‐ sion with disease disability rate as the dependent variable—MSSS (1, 2, 3 and 0 for controls) revealed that there is a significant association between IL7Ra rs6897932 genotype and disability progression of MS (*p*log = 0.034). Genotype analysis showed that the frequency of genotype TT is higher in controls (9.6%) and lower in MS patients with rapid disability progression (3.5%). Frequency of genotype CC was higher in rapidly progressing MS patients (67.2%) and lower in controls (54.1%). The data suggest that individuals carrying genotype TT are protected against rapid disease disability progression of MS.

We have shown for the first time in a Central European Slovak population that allele C of rs6897932 is associated with the risk of MS, and allele T has a protective additive effect against MS susceptibility. Moreover,we revealed that minor allele T and genotype TT of rs6897932 in the *IL7Ra* gene are protective against rapid disease disability progression in MS [65].
