Association of the PTPN22*R620W polymorphism with autoimmune myasthenia gravis

PTPN22 R620W polymorphism in the ANCA-associated vasculitides

OBJECTIVES

PTPN22 is involved in T-cell activation and its R620W single-nucleotide polymorphism (SNP) has been shown to predispose to different autoimmune diseases. The aims of this study were to investigate the role of the PTPN22 R620W SNP in conferring susceptibility to the ANCA-associated vasculitides (AAVs), and to explore potential associations between the PTPN22 genotype and the disease manifestations.

METHODS

PTPN22 R620W SNP was genotyped in a cohort of 344 AAV patients [143 with granulomatosis with polyangiitis (Wegener's) (GPA), 102 with microscopic polyangiitis (MPA) and 99 with Churg-Strauss syndrome (CSS)] and in 945 healthy controls.

RESULTS

The frequency of the minor allele (620W) was significantly higher in GPA patients than in controls [P = 0.005, χ(2 )= 7.858, odds ratio (OR) = 1.91], while no statistically significant association was found with MPA or CSS. Among GPA patients, the 620W allele was particularly enriched in ANCA-positive patients as compared with controls (P = 0.00012, χ(2 )= 14.73, OR = 2.31); a particularly marked association was also found with ENT involvement (P = 0.0071, χ(2 )= 7.258, OR = 1.98), lung involvement (P = 0.0060, χ(2 )= 7.541, OR = 2.07) and skin manifestations of all kinds (P = 0.000047, χ(2 )= 16.567, OR = 3.73).

CONCLUSION

The PTPN22 620W allele confers susceptibility to the development of GPA (but not of MPA or CSS), and particularly of its ANCA-positive subset.

Towards systemic sclerosis and away from primary biliary cirrhosis: the case of PTPN22

Primary biliary cirrhosis (PBC) is a chronic cholestatic liver disease characterized by immune-mediated destruction of the small and medium size intrahepatic bile ducts. PBC patients often have concomitant autoimmune diseases, which are most often autoimmune thyroid disease, as well as Sicca syndrome. Occasionally, some PBC patients will also have systemic sclerosis of the limited cutaneous type (lcSSc). Conversely, up to one-fourth of SSc patients are positive for antimitochondrial antibody, the serologic hallmark of PBC. It is also common for SSc patients to have concomitant autoimmune disease, which may include PBC in rare cases. This has led to speculation of shared environmental and/or genetic factors, which lead to the development of PBC in SSc patients and vice versa. Recent genetic studies have revealed associations with several genes in both SSc and PBC. PTPN22 is one gene that has been associated with SSc, but not with PBC. It may be argued that some SSc patients with a particular genotype, which shares genes found in both conditions may develop PBC. Likewise, particular genes such as PTPN22 may infer susceptibility to SSc alone. The presence of PTPN22 may also contribute to the development of SSc in PBC patients. The lack of a large number of overlapping genes may, in part, explain the relative rarity of PBC with SSc and vice versa. This review will examine the literature surrounding the genetic associations of PBC and SSc, and the role of PTPN22 in particular.

Association of PTPN22 1858T/T genotype with type 1 diabetes, Graves' disease but not with rheumatoid arthritis in Russian population

The protein tyrosine phosphatase nonreceptor 22 gene (PTPN22) is an important negative regulator of signal transduction through the T-cell receptors (TCR). Recently a single-nucleotide polymorphism (SNP) 1858 C/T within this gene was shown to be a risk factor for several autoimmune diseases, such as rheumatoid arthritis (RA), Graves' Disease (GD), systemic lupus erythematosus (SLE), Wegener's granulomatosis (WG) and type 1 diabetes mellitus (T1D). The aim of this study was to analyze a possible association between 1858 C/T SNP and a number of autoimmune diseases, including RA, GD and T1D in Russian population. Patients with T1D, GD, RA and healthy controls were genotyped for the 1858 C/T SNP in PTPN22 gene. We found a significant association between PTPN22 1858 C/T SNP and T1D and GD. 1858T/T genotype was observed more frequently in T1D and GD patients compared to control subjects. No such association was observed for RA. In concordance with a previous data establishing PTPN22 1858 C/T SNP association with several autoimmune diseases, our findings provide further evidence that the PTPN22 gene may play an important role in the susceptibility to some autoimmune diseases.

Utilizing twins concordance rates to infer the predisposition to myasthenia gravis

Myasthenia gravis (MG) is an autoimmune disorder in which patients experience muscular fatigability due to the presence of anti-acetylcholine receptor (AChR) antibodies which inhibit signal transduction across the neuro-muscular junction. Like all complex disorders, disease is caused by an interaction between genetic and environmental factors. Although several genes have been identified which appear to be associated with MG, both classic twin studies and current multi-gene models are insufficient to explain either disease pathogenesis or inheritance. We examined the literature on MG to determine both mono- and dizygotic twin concordance rates, and used this data to (1) estimate the proportion of the population with underlying genetic predisposition to MG and the frequency of the environmental component and (2) derive the number of inherited genetic regions that are required to confer predisposition to MG. Using a MZ twin concordance rate of 35.5%, and a dizygotic rate of approximately 4-5% (based on family data), the probability of encountering environmental components necessary to develop MG in an individual with genetic predisposition is approximately 52.4%, making the frequency of predisposition (1:5240) roughly twice the rate of incidence. Furthermore, the number of genetic regions co-inherited between affected individuals is between two and four, which may be large haplotypes with interacting activity. Determining these haplotypes, by fully sequencing associated regions in cases and controls to identify mutations present, may therefore be a practically step toward the understanding of complex disease.

A CD40 and an NCOA5 gene polymorphism confer susceptibility to psoriasis in a Southern European population: a case-control study

Recent genome-wide association studies of many complex diseases have successfully identified novel susceptibility loci, with many of them shared by multiple disease-associated pathways. The genes CD40 and nuclear receptor coactivator 5 (NCOA5), located in a 400-kb region surrounding CD40, have been reported to be associated with increased risk for rheumatoid arthritis and other autoimmune diseases. We hypothesized that those genes may also have a role in psoriasis (PS), an autoimmune, chronic inflammatory skin disease. In a case-control study, 198 patients with PS and 400 controls were genotyped for 2 single nucleotide polymorphisms (SNPs) of the CD40 and NCOA5 genes located on chromosome 20q.12-q13.12. Here, we demonstrate for the first time the association of both SNPs with susceptibility to PS, thus suggesting a putative key role of both genes in multiple autoimmune diseases. Alleles G and C of the CD40 rs4810485 and NCOA5 rs2903908 SNPs, respectively, were more common in individuals with PS than in controls (p = 0.03, odds ratio [OR] = 1.42, 95% confidence interval [95% CI] 1.05-1.95 and p = 0.000 003, OR = 1.93, 95% CI 1.47-2.55, respectively). The identification of shared genetic susceptibility loci may provide insight into our understanding of the pathophysiology of autoimmune diseases.

Why is PTPN22 a good candidate susceptibility gene for autoimmune disease?

The PTPN22 locus is one of the strongest risk factors outside of the major histocompatability complex that associates with autoimmune diseases. PTPN22 encodes lymphoid protein tyrosine phosphatase (Lyp) which is expressed exclusively in immune cells. A single base change in the coding region of this gene resulting in an arginine to tryptophan amino acid substitution within a polyproline binding motif associates with type 1 diabetes, rheumatoid arthritis, systemic lupus erythematosis, Hashimotos thyroiditis, Graves disease, Addison's disease, Myasthenia Gravis, vitiligo, systemic sclerosis juvenile idiopathic arthritis and psoriatic arthritis. Here, we review the current understanding of the PTPN22 locus from a genetic, geographical, biochemical and functional perspective.

Association of the PTPN22 R620W polymorphism with increased risk for SLE in the genetically homogeneous population of Crete

Autoimmune diseases affect approximately 5% of the population, but much work remains to define the genetic risk factors and pathogenic mechanisms underlying these conditions. There is accumulating evidence that common genetic factors might predispose to multiple autoimmune disorders. Systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) are complex autoimmune disorders with multiple susceptibility genes. The functional R620W (C1858T) polymorphism of the protein tyrosine phosphatase non-receptor type 22 (PTPN22) gene, a member of the PTPs that negatively regulate T-cell activation, has been recently associated with susceptibility to various autoimmune diseases. The aim of this study was to assess whether the C1858T polymorphism of PTPN22 also confers increased risk for SLE and RA in the genetically homogeneous population of Crete. It was found that the minor T allele of the PTPN22 C1858T SNP was more common in SLE patients than in control individuals (odds ratio [OR] = 1.91, 95% confidence interval [CI] = 1.11 to 3.9, p = 0.017). No significant difference was observed in the frequency of this allele when RA patients were compared with controls (OR = 1.14, 95% CI = 0.65 to 1.9, p = 0.64). Although the PTPN22 1858 T allele is found at decreased frequency in Southern Europe, including Crete, an association was found between this allele and SLE in the population studied.

The CD45 77C/G allele is not associated with myasthenia gravis - a reassessment of the potential role of CD45 in autoimmunity

Background

The G allele of the CD45 77C/G SNP (rs17612648), which has previously been suggested to be associated with autoimmune disorders, was genotyped in 446 Swedish myasthenia gravis (MG) patients and 2303 matched controls.

Results

There was no association between the polymorphism and patient group as a whole (p = 0.199), nor with clinical subgroups. Our results add to a growing number of studies unable to find association between the 77C/G polymorphism and autoimmune disorders. One control sample, from an adult blood donor, was homozygous for the G allele, yet negative for a panel of auto-antibodies, representing the first homozygous individual studied in this respect.

Conclusions

The 77C/G mutation does not predispose to MG, and its role in autoimmunity may have to be re-evaluated.

Dysregulation of thymic clonal deletion and the escape of autoreactive T cells

Events ongoing in the thymus are critical for deleting developing thymocytes specific for tissue antigens, and establishing self-tolerance within the T cell compartment. Aberrant thymic negative selection, however, is believed to generate a repertoire with increased self-reactivity, which in turn can contribute to the development of T cell-mediated autoimmunity. In this review, mechanisms that regulate the efficacy of negative selection and influence the deletion of autoreactive thymocytes will be discussed.

Thymoma and paraneoplastic myasthenia gravis

Paraneoplastic autoimmune diseases associate occasionally with small cell lung cancers and gynecologic tumors. However, myasthenia gravis (MG) occurs in at least 30% of all patients with thymomas (usually present at MG diagnosis). These epithelial neoplasms almost always have numerous admixed maturing polyclonal T cells (thymocytes). This thymopoiesis-and export of mature CD4(+)T cells-particularly associates with MG, though there are rare/puzzling exceptions in apparently pure epithelial WHO type A thymomas. Other features potentially leading to inefficient self-tolerance induction include defective epithelial expression of the autoimmune regulator (AIRE) gene and/or of major histocompatibility complex class II molecules in thymomas, absence of myoid cells, failure to generate FOXP3(+) regulatory T cells, and genetic polymorphisms affecting T-cell signaling. However, the strong focus on MG/neuromuscular targets remains unexplained and suggests some biased autoantigen expression, T-cell selection, or autoimmunization within thymomas. There must be further clues in the intriguing serological and cellular parallels in some patients with late-onset MG but without thymomas-and in others with AIRE mutations-and in the contrasts with early-onset MG, as discussed here.

Target-specific control of lymphoid-specific protein tyrosine phosphatase (Lyp) activity

Lymphoid-specific protein tyrosine phosphatase (Lyp), a member of the protein tyrosine phosphatase (PTP) superfamily of enzymes, is an important mediator of human-leukocyte signaling. Lyp has also emerged as a potential anti-autoimmune therapeutic target, owing to the association of a Lyp-activating mutation with an array of autoimmune disorders. Toward the goal of generating a selective inhibitor of Lyp activity that could be used for investigating Lyp's roles in cell signaling and autoimmune-disease progression, here we report that Lyp's PTP domain can be readily sensitized to target-specific inhibition by a cell-permeable small molecule. Insertion of a tetracysteine-motif-containing peptide at a conserved position in Lyp's catalytic domain generated a mutant enzyme (Lyp-CCPGCC) that retains activity comparable to that of wild-type Lyp in the absence of added ligand. Upon addition of a tetracysteine-targeting biarsenical compound (FlAsH), however, the activity of the Lyp-CCPGCC drops dramatically, as assayed with either small-molecule or phosphorylated-peptide PTP substrates. We show that FlAsH-induced Lyp-CCPGCC inhibition is potent, specific, rapid, and independent of the nature of the PTP substrate used in the inhibition assay. Moreover, we show that FlAsH can be used to specifically target overexpressed Lyp-CCPGCC in a complex proteomic mixture. Since the mammalian-cell permeability of FlAsH is well established, it is likely that FlAsH-mediated inhibition of Lyp-CCPGCC will be useful for specifically targeting Lyp activity in engineered leukocytes and autoimmune-disease models.

The protein tyrosine phosphatase, non-receptor type 22 R620W polymorphism does not confer susceptibility to psoriasis in the genetic homogeneous population of Crete

Recent whole-genome and candidate-gene association studies in patients with psoriasis (PS) have identified a number of single-nucleotide polymorphisms (SNPs) that predispose to disease with moderate risk. Predisposition to PS is known to be affected by genetic variation in human leukocyte antigen-C as well as other non-human leukocyte antigen genes. We recently reported for the first time as a PS-associated SNP the signal transducer and activator of transcription-4 (STAT4) rs7574865 polymorphism, which is also associated with several autoimmune diseases. The aim of this study was to assess whether the functional R620W polymorphism of protein tyrosine phosphatase, non-receptor type 22 (PTPN22) gene encoding the lymphoid-specific tyrosine phosphatase, which is known to be associated with various autoimmune diseases, also confers increased risk for PS in the genetic homogeneous population of Crete. A case-control study was performed with 173 PS patients consecutively recruited and 348 healthy controls, all of them from the island of Crete. We found that the mutated T allele of the PTPN22 1858T SNP was more common in control individuals than in patients with PS (odds ratio = 0.39, 95% confidence interval = 0.11-1.04, p = 0.09). No considerable difference was observed in terms of sex, age of onset, or clinical presentation of psoriatic arthritis. Our results provide evidence that the PTPN22 1858T allele is not a susceptibility factor for PS in the Cretan population.

Update on the genetic risk factors for rheumatoid arthritis

Rheumatoid arthritis (RA) is a complex disease, meaning that multiple genetic variants, environmental factors and random events interact to trigger pathological pathways. Although many of these etiological factors have not yet been identified, recent groundbreaking advances have expanded our knowledge about the genetic factors that contribute to RA. Here, we review the most recent findings on the genetic risk factors for RA. First, we give an overview of the genetics of RA and briefly describe the susceptibility loci discovered prior to the availability of genome-wide association studies (GWAS). Second, we focus on the newly discovered RA loci that have arisen from GWAS in populations of European ancestry. Through these studies, the number of established RA susceptibility loci has now grown to 13. Third, we discuss several important issues emerging from GWAS, such as ethnic heterogeneity and shared autoimmunity risk loci. Finally, we discuss what still needs to be accomplished before a more complete picture of the genetic risk to RA can be attained.

Lymphoid tyrosine phosphatase and autoimmunity: human genetics rediscovers tyrosine phosphatases

A relatively large number of protein tyrosine phosphatases (PTPs) are known to regulate signaling through the T cell receptor (TCR). Recent human genetics studies have shown that several of these PTPs are encoded by major autoimmunity genes. Here, we will focus on the lymphoid tyrosine phosphatase (LYP), a critical negative modulator of TCR signaling encoded by the PTPN22 gene. The functional analysis of autoimmune-associated PTPN22 genetic variants suggests that genetic variability of TCR signal transduction contributes to the pathogenesis of autoimmunity in humans.

Lymphoid tyrosine phosphatase R620W variant and inflammatory bowel disease in Tunisia

AIM: To assess the possible association between PTPN22 (R620W) gene polymorphism and inflammatory bowel disease (IBD).

METHODS: One hundred and sixty-four patients with IBD [105 Crohn’s disease (CD) and 59 ulcerative colitis (UC)] and 100 healthy controls were recruited. Genotyping of the PTPN22 gene 1858C→T polymorphism was performed by restriction fragment length polymorphism-polymerase chain reaction with RsaI digestion.

RESULTS: The genotypic and allelic frequencies of (R620W) PTPN22 gene polymorphism reveal a significant association of the PTPN22 620-W allele with IBD, compared to the healthy control group (OR: 17.81, 95% CI: 4.18-21.86, P = 0.00001). Nevertheless, no difference in this polymorphism was found between CD and UC patients. No significant association was found between the frequencies of genotypes of the PTPN22 gene with either the clinical features such as sex, age, age at disease onset, and extent of colitis, or the production of serological markers (anti-Saccharomyces cerevisiae antibody in CD and perinuclear anti-neutrophil cytoplasmic antibody in UC).

CONCLUSION: These observations confirm the association of IBD susceptibility with the PTPN22 1858T (620-W) allele in Tunisian patients.

The PTPN22gain-of-function+1858T(+) genotypes correlate with low IL-2 expression in thymomas and predispose to myasthenia gravis

Protein tyrosine phosphatase, non-receptor type 22 (PTPN22) inhibits T-cell activation and interleukin-2 (IL-2) production. The PTPN22(gain-of-function)+1858T(+) genotypes predispose to multiple autoimmune diseases, including early-onset (non-thymomatous) myasthenia gravis (MG). The disease association and the requirement of IL-2/IL-2 receptor signaling for intrathymic, negative T-cell selection have suggested that these genotypes may weaken T-cell receptor (TCR) signaling and impair the deletion of autoreactive T cells. Evidence for this hypothesis is missing. Thymoma-associated MG, which depends on intratumorous generation and export of mature autoreactive CD4(+) T cells, is a model of autoimmunity because of central tolerance failure. Here, we analyzed the PTPN22 +1858C/T single nucleotide polymorphism in 426 German Caucasian individuals, including 125 thymoma patients (79 with MG), and investigated intratumorous IL-2 expression levels. Unlike two previous studies on French and Swedish patients, we found strong association of PTPN22 +1858T(+) genotypes not only with early-onset MG (P=0.00034) but also with thymoma-associated MG (P=0.0028). IL-2 expression in thymomas with PTPN22 +1858T(+) genotypes (P=0.028) was lower, implying weaker TCR signaling. We conclude that the PTPN22(gain-of-function) variant biases towards MG in a subgroup of thymoma patients possibly by impeding central tolerance induction.

The autoimmunity-related polymorphism PTPN22 1858C/T is associated with anti-titin antibody-positive myasthenia gravis

Genetic variation in the intracellular tyrosine phosphatase PTPN22 has been recently associated with susceptibility to various autoimmune diseases. Myasthenia gravis (MG) is a complex genetic disease with a distinct clinical and pathological heterogeneity. We conducted a case-control association study for the PTPN22 1858C/T polymorphism in Hungarian and German MG patients (n = 282) and regional controls (n = 379). We detected an association of the PTPN22 1858T allele with MG in the subgroup of nonthymoma patients with anti-titin antibodies present (n = 50; T allele frequency 21% vs 11% in controls; p = 0.005, odds ratio 2.1, 95% confidence interval 1.23-3.58). This overrepresentation was reported independently in both Hungarian and German MG patients compared with regional controls. We conclude that the common autoimmune polymorphism PTPN22 1858C/T may account for disease susceptibility in a subset of nonthymoma MG patients with anti-titin antibodies present.

Genes and Sjögren's syndrome

The evidence for a strong genetic component conferring susceptibility to primary Sjögren's syndrome (SS) is mounting. Several associations with SS have been reported and provide evidence that the HLA region harbors important susceptibility loci and that multiple genes outside the HLA region play a role. Genetic discovery lags behind success observed in related autoimmune diseases. Identifying genetic factors that cause SS will allow more precise definition of pathogenic mechanisms leading to the overall SS phenotype and clinically heterogeneous subsets of patients. Critical opportunities are certain to follow for translation into improved diagnosis and therapies for SS and its spectrum diseases.

Recent advances in the genetics of autoimmune disease

Extraordinary technical advances in the field of human genetics over the past few years have catalyzed an explosion of new information about the genetics of human autoimmunity. In particular, the ability to scan the entire genome for common polymorphisms that associate with disease has led to the identification of numerous new risk genes involved in autoimmune phenotypes. Several themes are emerging. Autoimmune disorders have a complex genetic basis; multiple genes contribute to disease risk, each with generally modest effects independently. In addition, it is now clear that common genes underlie multiple autoimmune disorders. There is also heterogeneity among subphenotypes within a disease and across major racial groups. The current crop of genetic associations are only the start of a complete catalog of genetic factors for autoimmunity, and it remains unclear to what extent common variation versus multiple rare variants contribute to disease susceptibility. The current review focuses on recent discoveries within functionally related groups of genes that provide clues to novel pathways of pathogenesis for human autoimmunity.

Rheumatoid arthritis: a view of the current genetic landscape

The field of genetics and autoimmune diseases is undergoing a rapid and unprecedented expansion with new genetic findings being reported at an astounding pace. It is now clear that multiple genes contribute to each of the major autoimmune disorders, with significant genetic overlaps among them. Rheumatoid arthritis (RA) is no exception to this, and emerging data are beginning to reveal the outlines of new diagnostic subgroups, complex overlapping relationships with other autoimmune disorders and potential new targets for therapy. This review describes the evolving genetic landscape of RA, with the full knowledge that our current view is far from complete. However, with the first round of genome-wide association scans now completed, it is reasonable to begin to take stock of the direction in which the major common genetic risk factors are leading us.

Genetic factors in autoimmune myasthenia gravis

Autoimmune myasthenia gravis (MG) is a multifactorial disease, markedly influenced by genetic factors, even though it shows limited heritability. The clinically typical form of autoimmune MG with thymus hyperplasia shows the most reproducible genetic associations, especially with the A1-B8-DR3 (8.1) haplotype of the major histocompatibility complex (MHC). However, because of strong linkage disequilibrium, the causative polymorphism in this region is not known yet. Increasing the density of genetic markers has nevertheless recently revealed the complex, but highly significant contribution of this essential genetic region in controlling the disease phenotype and the quantitative expression of serum autoantibodies. The advances of the human genome program, the development of genotyping and sequencing tools with increasing throughput, and the availability of powerful statistical methods now make feasible the dissection of a complex genetic region, such as the MHC and beyond, the systematic search throughout the genome for variants influencing disease predisposition. The identification of such functional variants should provide new clues to the pathogenesis of MG, as recently illustrated by the study of a promoter polymorphism of the CHRNA1 locus, influencing its thymic expression and central tolerance, or of a coding variant of the PTPN22 intracellular phosphatase.

Protein tyrosine phosphatases in autoimmunity

Protein tyrosine phosphatases (PTPs) are important regulators of many cellular functions and a growing number of PTPs have been implicated in human disease conditions, such as developmental defects, neoplastic disorders, and immunodeficiency. Here, we review the involvement of PTPs in human autoimmunity. The leading examples include the allelic variant of the lymphoid tyrosine phosphatase (PTPN22), which is associated with multiple autoimmune diseases, and mutations that affect the exon-intron splicing of CD45 (PTPRC). We also find it likely that additional PTPs are involved in susceptibility to autoimmune and inflammatory diseases. Finally, we discuss the possibility that PTPs regulating the immune system may serve as therapeutic targets.

PTPN22 R620W promotes production of anti-AChR autoantibodies and IL-2 in myasthenia gravis

In order to investigate the potential involvement of PTPN22 R620W in the pathogenesis of myasthenia gravis (MG), we performed a case-control study including 409 Swedish MG patients and 1557 normal controls. The W620 variant was significantly overrepresented in patients (odds ratio, 1.52; 95% confidence interval, 1.21-1.90; p=0.00027). Incubation of patient (n=100) derived PBMC cells with the autoantigen, the acetylcholine receptor, resulted in a significantly higher number of cells producing anti-AChR antibodies and IL-2 in W620 carriers, suggesting that PTPN22 W620 may be a loss-of-function variant in MG.

Reduced CD4+T cell activation in children with type 1 diabetes carrying the PTPN22/Lyp 620Trp variant

The 620Trp variant of the LYP protein, encoded by the lymphoid tyrosine phosphatase 22 gene (PTPN22), is associated with autoimmunity. In this study we aimed at characterising the role of this variant on lymphocyte activation. We analysed cytokine secretion and proliferation of peripheral blood mononuclear cells (PBMCs) and CD4(+)T cells in a cohort of clinically non-diabetic, multiple autoantibody-positive children, healthy controls and in children with type 1 diabetes (T1D). We found a decreased proliferation and IL-2 production of CD4(+)T cells after anti-CD3/anti-CD28 stimulation (p=0.04 for IL-2) among T1D patients. In addition, a profoundly decreased intracellular calcium flux in CD4(+)T cells after PHA stimulus was detected among 620Trp carriers. In contrast, no effect of this polymorphism on tuberculin and tetanus toxoid induced PBMC proliferation and cytokine secretion was observed in autoantibody positive children, healthy controls and children with newly-diagnosed T1D. In conclusion, the LYP 620Trp variant is associated with reduced activation, proliferation and IL-2 production in CD4(+)T cells among T1D patients. In accordance with our previous findings on the key role of this variant on disease progression, this mechanism is likely to contribute to the development of beta-cell specific autoimmunity.

PTPN22 gene polymorphism in Behçet's disease

A functional single nucleotide polymorphism (SNP) of PTPN22 gene encoding the protein tyrosine phosphatase has been reported to be associated with autoimmune disorders such as rheumatoid arthritis, systemic lupus erythematosus and type I diabetes. PTPN22 R620W polymorphism has a wide variation of allelic frequencies among different populations. This polymorphism is investigated in Turkish patients with Behçet's disease (BD), a systemic vasculitis with immune activation. DNA samples from 134 patients with BD and 177 healthy controls are genotyped by polymerase chain reaction (PCR)-restriction fragment length polymorphism method for the SNP (rs2476601, A/G) of PTPN22 gene. Polymorphic region was amplified by PCR and digested with XcmI enzyme. The frequency of heterozygous genotype (AG) was 5.1% (9/177) in control group, whereas polymorphic allele was not present in the whole BD group (P = 0.012, OR 0.65, 95% confidence interval 0.0-1.1). Both the lower prevalence in the general population and the absence in BD show the limited role of PTPN22 polymorphism in the pathogenesis of autoimmunity in Turkey.

STAT4 and the risk of rheumatoid arthritis and systemic lupus erythematosus

BACKGROUND

Rheumatoid arthritis is a chronic inflammatory disease with a substantial genetic component. Susceptibility to disease has been linked with a region on chromosome 2q.

METHODS

We tested single-nucleotide polymorphisms (SNPs) in and around 13 candidate genes within the previously linked chromosome 2q region for association with rheumatoid arthritis. We then performed fine mapping of the STAT1-STAT4 region in a total of 1620 case patients with established rheumatoid arthritis and 2635 controls, all from North America. Implicated SNPs were further tested in an independent case-control series of 1529 patients with early rheumatoid arthritis and 881 controls, all from Sweden, and in a total of 1039 case patients and 1248 controls from three series of patients with systemic lupus erythematosus.

RESULTS

A SNP haplotype in the third intron of STAT4 was associated with susceptibility to both rheumatoid arthritis and systemic lupus erythematosus. The minor alleles of the haplotype-defining SNPs were present in 27% of chromosomes of patients with established rheumatoid arthritis, as compared with 22% of those of controls (for the SNP rs7574865, P=2.81x10(-7); odds ratio for having the risk allele in chromosomes of patients vs. those of controls, 1.32). The association was replicated in Swedish patients with recent-onset rheumatoid arthritis (P=0.02) and matched controls. The haplotype marked by rs7574865 was strongly associated with lupus, being present on 31% of chromosomes of case patients and 22% of those of controls (P=1.87x10(-9); odds ratio for having the risk allele in chromosomes of patients vs. those of controls, 1.55). Homozygosity of the risk allele, as compared with absence of the allele, was associated with a more than doubled risk for lupus and a 60% increased risk for rheumatoid arthritis.

CONCLUSIONS

A haplotype of STAT4 is associated with increased risk for both rheumatoid arthritis and systemic lupus erythematosus, suggesting a shared pathway for these illnesses.

Susceptibility to type 1 diabetes conferred by the PTPN22 C1858T polymorphism in the Spanish population

Background

The protein tyrosine phosphatase N22 gene (PTPN22) encodes a lymphoid-specific phosphatase (LYP) which is an important downregulator of T cell activation. A PTPN22 polymorphism, C1858T, was found associated with type 1 diabetes (T1D) in different Caucasian populations. In this study, we aimed at confirming the role of this variant in T1D predisposition in the Spanish population.

Methods

A case-control was performed with 316 Spanish white T1D patients consecutively recruited and 554 healthy controls, all of them from the Madrid area. The PTPN22 C1858T SNP was genotyped in both patients and controls using a TaqMan Assay in a 7900 HT Fast Real-Time PCR System.

Results

We replicated for the first time in a Spanish population the association of the 1858T allele with an increased risk for developing T1D [carriers of allele T vs. CC: OR (95%) = 1.73 (1.17–2.54); p = 0.004]. Furthermore, this allele showed a significant association in female patients with diabetes onset before age 16 years [carriers of allele T vs. CC: OR (95%) = 2.95 (1.45–6.01), female patients vs female controls p = 0.0009]. No other association in specific subgroups stratified for gender, HLA susceptibility or age at onset were observed.

Conclusion

Our results provide evidence that the PTPN22 1858T allele is a T1D susceptibility factor also in the Spanish population and it might play a different role in susceptibility to T1D according to gender in early-onset T1D patients.

Association of the PTPN22 R620W polymorphism with anti-topoisomerase I- and anticentromere antibody-positive systemic sclerosis

OBJECTIVE

To determine any associations of the PTPN22 R620W single-nucleotide polymorphism (SNP) with systemic sclerosis (SSc) or with anticentromere antibody (ACA)-positive or anti-topoisomerase I (anti-topo I) antibody-positive SSc, in a case-control study of US white, black, Hispanic, and Choctaw Indian individuals.

METHODS

A total of 850 white, 130 black, 120 Hispanic, and 20 Choctaw Indian patients with SSc were compared with 430 white, 164 black, 146 Hispanic, and 76 Choctaw Indian control subjects, respectively. All subjects were living in the US. PTPN22 SNP (rs2476601) genotyping was performed by TaqMan 5' allelic discrimination assay and pyrosequencing.

RESULTS

The PTPN22 CT/TT genotype showed significant association with anti-topo I antibody-positive SSc in white patients (odds ratio [OR] 2.21, 95% confidence interval [95% CI] 1.3-3.7) and with ACA-positive white patients with SSc (OR 1.70, 95% CI 1.1-2.7). Frequency of the PTPN22*T allele also showed significant association with anti-topo I antibody-positive SSc in white patients (OR 2.03, 95% CI 1.3-3.2). When data for patients in the 3 ethnic groups (black, white, and Hispanic) were combined, a significant association with both genotype and allele frequencies was observed, suggesting a trend toward association in ACA-positive and anti-topo I antibody-positive SSc. Stepwise logistic regression analysis (controlled for the confounding effects of sex and race) showed that the PTPN22 CT/TT genotype was associated with a significantly higher risk of SSc compared with the CC genotype (for patients with SSc, OR 1.64, 95% CI 1.2-2.2; for ACA-positive patients with SSc, OR 1.63, 95% CI 1.0-2.6; for anti-topo I antibody-positive SSc, OR 2.33, 95% CI 1.5-3.7).

CONCLUSION

Our results indicate that the PTPN22 R620W polymorphism is associated with ACA-positive and anti-topo I antibody-positive subsets of SSc and represents a risk factor in both white patients and black patients. The association of subsets of SSc with the PTPN22 R620W polymorphism further strengthens the classification of SSc within the spectrum of autoimmune diseases and strongly suggests the involvement of common susceptibility genes and similarly disordered immunoregulatory pathways.

Genetics of autoimmune diseases--disorders of immune homeostasis

In the past few years, our extensive knowledge of the mammalian immune system and our increasing ability to understand the genetic causes of complex human disease have opened a window onto the pathways that lead to autoimmune disorders. In addition to the well-established role of genetic variation that affects the major histocompatibility complex, a number of rare and common variants that affect a range of immunological pathways are now known to have important influences on the phenotypic diversity that is seen among autoimmune diseases. Recent studies have also highlighted a previously unanticipated interplay between the innate and adaptive immune system, providing a new direction for research in this field.

PTPN22: setting thresholds for autoimmunity

The 620W allelic variant of the intracellular tyrosine phosphatase, PTPN22, is associated with a number of different autoimmune disorders, and this provides direct evidence for common mechanisms underlying many of these diseases. The associated allele appears to influence thresholds for T cell receptor signaling, and a variety of disease models involving both central and peripheral tolerance can be proposed. However, given the fact that PTPN22 is expressed in a variety of immunologically relevant cell types, the precise mechanisms for these associations remain unclear. In general, the PTPN22 620W allele appears to play a role in autoimmune disorders that have a prominent humoral component, suggesting that further investigation of PTPN22 activity in B cells will be useful. From a genetic perspective, the data highlights the genetic heterogeneity underlying autoimmunity in different ethnic groups.