A two-stage study on multiple sclerosis susceptibility and chromosome 2q33

Genetics of primary progressive multiple sclerosis

Multiple sclerosis (MS) patients are classified as either having relapsing onset or progressive onset disease, also known as primary progressive MS (PPMS). Relative to relapsing onset patients, PPMS patients are older at disease onset, are equally likely to be men or women, and have more rapid accumulation of disability that does not respond well to treatments used in relapsing onset MS. Although estimates vary, 5-15% of all MS patients have a PPMS disease course. Genetic variance is a proposed determinant of MS disease course. If distinct genes associated with PPMS were identified study of these genes might lead to an understanding of the biology underlying disease progression and neural degeneration that are the hallmarks of PPMS. These genes and their biological pathways might also represent therapeutic targets. This chapter systematically reviews the PPMS genetic literature. Despite the intuitively appealing notion that differences between PPMS and relapsing onset MS are due to genetics, definite differences associated with these phenotypes at the major histocompatibility complex or elsewhere in the genome have not been found. Recent large-scale genome wide screens identified multiple genes associated with MS susceptibility outside the MHC. The genetic variants identified thus far make only weak individual contributions to MS susceptibility. If the genetic effects that contribute to the differences between PPMS and relapsing MS are similar in magnitude to those that distinguish MS from healthy controls then, given the relative scarcity of the PPMS phenotype, very large datasets will be needed to identify PPMS associated genes. International collaborative efforts could provide the means to identify such genes. Alternately, it is possible that factors other than genetics underlie the differences between these clinical phenotypes.

CTLA4 exon 1 and promoter polymorphisms in patients with multiple sclerosis

OBJECTIVE

The polymorphisms of exon 1 (+49 A/G) and promoter regions (-1722 T/C, -1661 A/G and -318 C/T)of cytotoxic T lymphocyte antigen 4 (CTLA4) and also haplotypes constructed from mentioned loci were investigated amongst 153 Iranian patients with definite multiple sclerosis (MS) and 190 healthy controls.

METHODS

The polymorphisms were genotyped by PCR-restriction fragment length polymorphisms and PCR-amplification refractory mutation system. The 4-locus haplotypes were estimated by Arlequin software (University of Berne, Berne, Switzerland).

RESULTS

Preliminary results showed significant increase of +49 G allele and -1661 AG genotype, as well as TGCA haplotype among patients than controls (P < 0.036, P = 0.009 and P < 0.010, respectively). The distribution of -1722 T/C, -1661 A/G, -318 C/T and +49 A/G (TACA) haplotype, from the contrary, was observed to be significantly increased among controls (P < 0.001).

CONCLUSIONS

After Bonferroni correction, the results provide preliminary evidence that CTLA4 genetic variation at -1661 locus may render Iranian individuals to be more susceptible to MS, whereas harboring TACA haplotype might be protective.

The role of costimulation in antibody deficiencies: ICOS and common variable immunodeficiency

SUMMARY

The identification of mutations in the inducible costimulator (ICOS) gene in nine patients with common variable immunodeficiency (CVID) was a major breakthrough. CVID is a complex, highly heterogeneous primary immunodeficiency disease, and the discovery of these mutations revealed a molecular basis. ICOS belongs to the CD28 family of costimulatory molecules and is expressed exclusively on activated T cells. It has at least three critical functions: germinal center formation, isotype class switching, and the development of memory B cells. The discovery of human ICOS deficiency showed that a monogenic disorder could account for the full spectrum of manifestations seen in childhood and adulthood-onset CVID, including autoimmune, inflammatory, and malignant disease complications, as well as recurrent infections. Moreover, this discovery showed that a disorder which had previously been perceived as a B-cell disease might in fact have its genetic origin in human T cells. In this article, we review the role of ICOS in the mammalian immune system and human disease, as well as the discovery and characteristics of patients with ICOS deficiency. Finally, we also discuss how these 'human knockouts' have contributed to our understanding of ICOS functions and have suggested potential avenues for using therapeutic ICOS manipulation to treat other diseases.

Cytotoxic T lymphocyte antigen-4 promoter -658CT gene polymorphism is associated with ulcerative colitis in Chinese patients

BACKGROUND AND AIM

Cytotoxic T lymphocyte antigen-4 (CTLA-4) plays a role in the downregulation of T cell activation. The present study aimed to examine an association between the CTLA-4 gene polymorphisms and ulcerative colitis (UC) in the Han Chinese in central China.

MATERIALS AND METHODS

One hundred seventeen patients with UC and 246 healthy controls were genotyped for CTLA-4 gene -658CT in the promoter and CT61 at the 3' untranslated region using a method of polymerase chain reaction-based restriction fragment length polymorphism and single-strand conformation polymorphism, respectively. The distributions of the genotypes and the allele frequencies of the CTLA-4 gene in UC patients and healthy controls were compared by chi-square test.

RESULTS

The frequency of the T/T+C/T genotype at the CTLA-4 gene -658CT in the promoter was significantly higher in UC patients than in healthy controls (26.5% vs 15.4%, chi (2) = 6.287, P = 0.015, OR = 1.973, 95%CI = 1.153-3.375). The frequency of the T allele at the CTLA-4 -658CT was also significantly higher in UC patients than in the controls (13.2% vs 8.1%, chi (2) = 4.707, P = 0.033, OR = 1.726, 95%CI = 1.049-2.838). The frequency of the T/T genotype at the -658 locus was highly associated with extensive colitis in UC patients (P = 0.037, OR = 3.955, 95%CI = 1.068-14.647). The frequency of the T allele at the -658 locus was highly associated with extensive colitis in UC patients (P = 0.0067, OR = 3.05, 95%CI = 1.320-7.048).

CONCLUSION

The T allele of CTLA-4 -658 polymorphism in the promoter of CTLA-4 gene was highly associated with UC in the Han Chinese in central China.

Multiple sclerosis and the CTLA4 autoimmunity polymorphism CT60: no association in patients from Germany, Hungary and Poland

Polymorphisms in the CTLA4 gene region have been associated with susceptibility to autoimmune diseases. The recently described single nucleotide polymorphism CT60, located in the 3' untranslated region of CTLA4 is associated with Graves' disease, thyroiditis, autoimmune diabetes and other autoimmune diseases. A case-control association study was conducted in German, Hungarian and Polish multiple sclerosis (MS) patients and regional control individuals for the CTLA4 CT60 and + 49A/G polymorphisms. No significant association of these polymorphisms or respective haplotypes with MS was found. No association of CT60 genotypes with T cell expression of ICOS and CTLA-4 after in vitro stimulation was detected. Multiple Sclerosis 2008; 14: 153—158. http://msj.sagepub.com

CTLA4 gene polymorphisms and multiple sclerosis in Northern Ireland

Four CTLA4 polymorphisms were investigated in a Northern Irish collection of relapsing-remitting (RR) and primary-progressive (PP) multiple sclerosis (MS) patients. The CTLA4 promoter (-318 C/T), exon 1 (+49 A/G) and intergenic CT60 SNPs, as well as a microsatellite found in the 3' UTR (AT(n)) were analysed in 246 RRMS, 84 PPMS and 158 healthy controls. The A allele of the exon 1 +49 A/G SNP (OR=1.36; 95% CI=1.11-1.81; P=0.038), and more so the AA genotype (OR=1.70; 95% CI=1.11-2.60; P=0.015) were associated with RR, but not PPMS. In the PPMS population, overall allele distribution of the AT(n) microsatellite was significantly different from that in the healthy controls. We did not find any association with the promoter (-318 C/T) or intergenic CT60 SNPs in either of the disease cohorts. In concordance with several recent studies, we detected a trend toward higher carriage rates of the +49 G allele in PP vs RR MS patients (66.7% vs 58.9%), though this was not significant. Our data highlight the CTLA4 +49 A/G and 3'UTR polymorphisms as potential modifiers of disease course in MS.

T-cell costimulation blockade in immunologic diseases: role of CD28 family members

The destruction of many immune-mediated diseases is a result of T-cell responses against usually harmless antigens. Extensive research has been conducted to discover new mechanisms to specifically modulate harmful effector T cells while leaving normal immune responses intact. Since proteins of the CD28 family members are expressed on T cells, blockade of these proteins has become a possible target for potential therapies. The CD28 family contains proteins that have the ability to both enhance and diminish T-cell responses. Therefore, blockade of targets that enhance T-cell signaling may reduce destructive autoimmune responses, while blockade of targets that diminish T-cell signaling may enhance antitumor responses. In this article, the function of these proteins will be reviewed and a sample of clinical trials highlighting the potential efficacy and drawbacks of their use in humans will be described briefly. Finally, inducible costimulator and programmed death-1, two future targets of T-cell therapies, will be highlighted.

Genetic variation in ICOS regulates mRNA levels of ICOS and splicing isoforms of CTLA4

Genetic and functional studies suggest that polymorphism in cytotoxic T lymphocyte-associated antigen-4 (CTLA4) and inducible costimulator (ICOS) genes, both reported to harbour autoimmune susceptibility loci, could regulate the immune activation through affecting their expression and splicing of CTLA4. To address this, we studied expression of CTLA4 and ICOS and the role of polymorphisms in the gene region by measuring the relative amounts of transcripts, including the soluble CTLA4 (sCTLA4) splicing isoform in healthy volunteers. We combined a physiologically relevant in vitro activation for human CD4(+) T lymphocytes and a quantitative RT-PCR. The susceptibility allele CT60G in CTLA4 gene was confirmed to be associated with a decreased amount of sCTLA4, but only in resting cells. During the T cell activation two genetic variants in ICOS gene, IVS1+173T/C and c.1624C/T, affected expression of CTLA4 isoforms and ICOS, respectively. We could not confirm that the level of sCTLA4 is down-regulated following T lymphocyte activation, instead the levels of CTLA4 splicing isoforms correlated to each others. Our results indicate that genetic variation in this gene region regulates the expression of both CTLA4 and ICOS and not only the splicing of sCTLA4 as suggested earlier.

Polymorphism of the promoter region and exon 1 of the CTLA4 gene in endemic pemphigus foliaceus (fogo selvagem)

Endemic pemphigus foliaceus (EPF) is an autoimmune bullous skin disease characterized by acantholysis and antibodies against a desmosomal protein, desmoglein 1. Genetic and environmental factors contribute to development of this multifactorial disease. HLA class II and some cytokine gene polymorphisms are the only genetic markers thus far known to be associated with susceptibility to or protection from EPF. The cytotoxic T-lymphocyte antigen-4 gene (CTLA4) encodes a key immunoreceptor molecule that regulates and inhibits T-cell proliferation. It participates in the regulatory process controlling autoreactivity and therefore has been considered a strong candidate gene in autoimmune diseases. In the search for genes that might influence EPF pathogenesis, we analyzed variants of the CTLA4 gene in a sample of 118 patients and 291 controls from a Brazilian population. This is the first study investigating the possible role of polymorphisms of the 2q33 chromosomal region in differential susceptibility to pemphigus foliaceus. Promoter region and exon 1 single nucleotide polymorphisms -318 (C,T) and 49 (A,G) were genotyped using sequence-specific oligonucleotide probes after amplification by the polymerase chain reaction. The allelic and genotypic frequencies did not differ significantly between the patient and the control groups (-318T: 9.8 and 10.9%, 49G: 33.0 and 35.2% were the allelic frequencies in patients and controls, respectively). In addition, no significant difference was found when the patient and control population samples were stratified by the presence of HLA-DRB1 alleles. We conclude that the CTLA4 -318 (C,T) and 49 (A,G) polymorphisms do not play a major role in EPF development.

Regulation of T:B cell interactions by the inducible costimulator molecule: does ICOS "induce" disease?

The Inducible Costimulator molecule (ICOS), a member of the CD28 family of costimulatory molecules, was identified in 1999 as a molecule expressed primarily on activated human T cells. Induced upon activation, ICOS appears to be an ideal target for modifying T-cell-mediated immune responses. ICOS was also found to be highly expressed on germinal center T cells, suggesting that ICOS was involved in T:B cell interactions. While ICOS has subsequently been shown to be important for both Th1 and Th2 cell activation and effector function, a central role for ICOS in the generation and maintenance of humoral immunity is emerging. In this review, we summarize the evidence that the level of ICOS expression regulates T-cell-dependent B cell responses and propose a model for the role of ICOS in diseases characterized by dysregulated humoral immunity.

Multiple sclerosis in G: Genes and geography

Multiple sclerosis (MS) shows uneven geographic distribution globally as well as within countries. In epidemiological studies we have previously demonstrated that there is a high-risk focus for MS in the southern Ostrobothnian region of western Finland. In genetic studies we recently identified haplotypes that associate with MS specifically in patients originating from southern Ostrobothnia suggesting a founder effect. Such haplotypes can be used as molecular tools for tracing common ancestry between patients in different geographic locations. In addition to providing clues to the historical origin, such a genetic archeological approach should help narrow the size of the shared haplotype, thus facilitating the identification of etiological variants and possibly define a superfamily of MS patients with common pathogenetic mechanisms.

Gene expression profiles in Finnish twins with multiple sclerosis

Background

Since genetic alterations influencing susceptibility to multiple sclerosis (MS), the most common autoimmune demyelinating disease of the central nervous system (CNS), are as yet poorly understood, the purpose of this study was to identify genes responsible for MS by studying monozygotic (MZ) twin pairs discordant for MS.

Methods

In order to identify genes involved in MS development, the gene expression profiles in blood mononuclear cells obtained from eight MZ twin pairs discordant for MS were analyzed by cDNA microarray technology detecting the expression of 8 300 genes. The twins were collected from the Finnish Twin Cohort Study and both affected subjects and their healthy siblings underwent neurological evaluation and cerebral and spinal magnetic resonance imaging. Gene expressions were confirmed by relative quantitative reverse transcription PCR.

Results

It appeared that 25 genes were at least two-fold up-regulated and 15 genes down-regulated in 25% (2/8) of twins with MS when compared to their healthy siblings. Moreover, 6/25 genes were up-regulated in 40% of MS twins and one gene, interferon alpha-inducible protein (clone IFI-6-16) (G1P3), in 50% of them. The six most constantly expressed genes are (1) G1P3, (2) POU domain, class 3, transcription factor 1, (3) myxovirus resistance 2, (4) lysosomal-associated multispanning membrane protein-5, (5) hemoglobin alpha 2 and (6) hemoglobin beta.

Conclusion

Over two-fold up-regulation of these six genes in almost half of MZ twins with MS suggests their role in MS pathogenesis. Studies using MZ MS twins obtained from genetically homogeneous population offer a unique opportunity to explore the genetic nature of MS.

The CTLA4 +49 A/G*G-CT60*G haplotype is associated with susceptibility to multiple sclerosis in Flanders

Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system white matter characterized by inflammation, demyelination and axonal damage. The cytotoxic T lymphocyte antigen-4 (CTLA-4) protein plays a key role in the down-regulation of T cell activation. We analysed the CTLA4 +49A/G and CT60 polymorphisms in a cohort of 120 MS trio families recruited from the Flanders region in Belgium. Both polymorphisms were genotyped by polymerase chain reaction-restriction fragment length polymorphism (RFLP). The +49 G-allele was significantly more transmitted to affected probands (P = 0.005). No transmission distortion was observed for the CT60 polymorphism. Haplotype analysis revealed significant overtransmission of the +49 A/G*G-CT60*G haplotype (P = 0.0025), and undertransmission of the +49 A/G*A-CT60*G haplotype (P = 0.015). The CTLA4 gene has been the focus of intense investigation in MS. Of 15 recently published papers, only six reported significant associations of various CTLA4 polymorphisms with MS, with the remainder being negative. Ours is the first report investigating the CT60 polymorphism in MS. Our data highlight a need for further scrutiny of the CTLA4 gene in MS.