Investigating the genetic basis for ankylosing spondylitis. Linkage studies with the major histocompatibility complex region

The relationship between vitamin D receptor gene polymorphisms and ankylosing spondylitis: a systematic review, meta-analysis and trial sequential analysis

The relation between vitamin D receptor (VDR) gene polymorphisms and ankylosing spondylitis (AS) remains unclear. A systematic review and meta-analysis were conducted using six databases, including PubMed, Web of Science, EMBASE, CNKI, Wanfang and Cochrane Library. The selection of each study was based on inclusion and exclusion criteria. The Newcastle-Ottawa Scale was applied to assess the quality of the included studies, while the strength was evaluated by odds ratios and 95% confidence intervals. The following contrasts were used: allele contrast (H vs h), homozygous contrast (HH vs hh), heterozygous contrast (Hh vs hh), dominant contrast (HH + Hh vs hh) and recessive contrast (HH vs Hh + hh). For the BsmI-rs1544410 polymorphism, three studies were included of 782 cases and 863 controls. The data showed a significant relationship under allele contrast H vs h (OR = 1.66, 95% CI 1.20-2.30 (P = 0.002)). For the TaqI-rs731236 polymorphism, 675 cases and 697 controls were included in two studies. The data showed a significant relationship under allele contrast H vs h (OR = 1.57, 95% CI 1.11-2.21 (P < 0.05)), homozygous contrast Hh vs hh (OR = 1.65, 95% CI 1.12-2.43 (P < 0.05)), and recessive contrast HH + Hh vs hh (OR = 1.66, 95% CI 1.13-2.43 (P < 0.05)). There were significant relationships between VDR gene BsmI-rs1544410 and TaqI-rs731236 polymorphisms and AS, while no associations were found between FokI-rs2228570 and ApaI-rs7975232 polymorphisms and AS. In the future, additional studies with larger case numbers are need.

T cell-mediated autoimmunity in immune thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune disorder characterized by a low platelet count and an increased risk of bleeding. In addition to anti-platelet autoantibodies, CD8⁺ T cells have been implicated as a mechanism of platelet destruction. The current evidence for the existence of platelet-specific CD8⁺ T cells in ITP is inconclusive. The purpose of this review is to summarize the studies that investigated CD8⁺ T cells in ITP and to review the methods that have been used to detect autoreactive CD8⁺ T cells in other autoimmune diseases.

HLA associations in inflammatory arthritis: emerging mechanisms and clinical implications

Our understanding of the mechanisms underlying HLA associations with inflammatory arthritis continues to evolve. Disease associations have been refined, and interactions of HLA genotype with other genes and environmental risk factors in determining disease risk have been identified. This Review provides basic information on the genetics and molecular function of HLA molecules, as well as general features of HLA associations with disease. Evidence is discussed regarding the various peptide-dependent and peptide-independent mechanisms by which HLA alleles might contribute to the pathogenesis of three types of inflammatory arthritis: rheumatoid arthritis, spondyloarthritis and systemic juvenile idiopathic arthritis. Also discussed are HLA allelic associations that shed light on the genetic heterogeneity of inflammatory arthritides and on the relationships between adult and paediatric forms of arthritis. Clinical implications range from improved diagnosis and outcome prediction to the possibility of using HLA associations in developing personalized strategies for the treatment and prevention of these diseases.

Recent advances in ankylosing spondylitis: understanding the disease and management

The term spondyloarthritis refers to a group of immune-mediated diseases characterised by inflammation of the axial skeleton, peripheral joints, and entheses. Ankylosing spondylitis (AS) is the most common and characteristic of these entities and even though it was first described over two centuries ago, the understanding of the underlying disease mechanism remains incomplete. It is known that around 40% of patients with AS have subclinical bowel inflammation, suggesting that the origin of the disease could be in the gut. Also, more genes and new molecules have demonstrated a role in the pathogenesis of AS. In this review, we analyse the latest therapies for spondyloarthritis and the most relevant discoveries over the last three years, together with their implications for different aspects of the disease.

Genetic variants of TREML2 are associated with HLA-B27-positive ankylosing spondylitis

Although ankylosing spondylitis (AS) is a common, highly heritable arthropathy, the precise genetic mechanism underlying the disease remains elusive. Here, we investigate the disease-causing mutations in a large AS family with distinguished complexity, consisting of 23 patients covering four generations and exhibiting a mixed HLA-B27 (+) and (-) status. Linkage analysis with 32 members using three methods and whole-exome sequencing analysis with three HLA-B27 (+) patients, one HLA-B27 (-) patient, and one healthy individual did not identify a mutation common to all of the patients, strongly suggesting the existence of genetic heterogeneity in this large pedigree. However, if only B27-positive patients were analyzed, the linkage analysis located a 22-Mb region harboring the HLA gene cluster in chromosome 6 (LOD = 4.2), and the subsequent exome analysis identified two non-synonymous mutations in the TREML2 and IP6K3 genes. These genes were resequenced among 370 sporadic AS patients and 487 healthy individuals. A significantly higher mutation frequency of TREML2 was observed in AS patients (1.51% versus 0.21%). The results obtained for the AS pedigree and sporadic patients suggest that mutation of TREML2 is a major factor leading to AS for HLA-B27 (+) members in this large family and that TREML2 is also a susceptibility gene promoting the development of ankylosing spondylitis in HLA-B27 (+) individuals.

Genetic association between TNF-α -857 C/T polymorphism and ankylosing spondylitis susceptibility: evidence from a meta-analysis

Certain studies have suggested that the tumor necrosis factor-α (TNF-α) −857 C/T polymorphism is associated with risk of ankylosing spondylitis. However, the conclusions remain controversial. Therefore, we performed a meta-analysis to provide a more precise conclusion. Such databases as PubMed, Embase, CBM, CNKI, and Wanfang Data were searched to identify relevant studies up to August 26, 2015. Odds ratios (ORs) and 95% confidence intervals (CIs) were used to estimate the association between TNF-α −857 C/T polymorphism and ankylosing spondylitis susceptibility. A total of 10 studies were included in the meta-analysis. Overall, an elevated risk between TNF-α −857 C/T polymorphism and ankylosing spondylitis was observed in three genetic model (T vs. C: OR 1.86, 95% CI 1.19–2.92; CT vs. CC: OR 2.51, 95% CI 1.49–4.23; TT + CT vs. CC: OR 2.46, 95% CI 1.40–4.30), except in homozygote model (TT vs. CC: OR 2.41, 95% CI 0.96–6.06) and recessive model (TT vs. CT + CC: OR 1.54, 95% CI 0.71–3.35). Sensitivity analysis showed the overall results were robust. Subgroup analyses according to Hardy–Weinberg equilibrium and ethnicity showed that the increased risk of ankylosing spondylitis were predominant in Asian population. This meta-analysis indicated that TNF-α −857 C/T polymorphism might increase the susceptibility of ankylosing spondylitis, especially in Asians. Further studies were needed to verify the conclusion.

Dose reduction of recombinant human tumor necrosis factor inhibitors (etanercept) can be effective in ankylosing spondylitis patients with synovitis of the hip in a Chinese population

Ankylosing spondylitis (AS) is an immune-mediated inflammatory arthritis and enthesitis involving the spine and peripheral joints. In recent years, specific antagonist of tumor necrosis factor (anti-TNFα, etanercept) 50 mg weekly therapy has rapidly gained popularity for the treatment of AS. However, the dose of etanercept has not been determined in Asian, particularly Chinese populations. The purpose of the study was to evaluate the efficacy and safety of dose reduction of etanercept (50 mg/week in 4 weeks followed by 25 mg/week in 8 weeks) in the treatment of AS with synovitis of the hip, as against the conventional dose (50 mg/week in 12 weeks) in a Chinese population. Forty-three Chinese AS patients with synovitis of the hip were involved in this study. Seventeen of them were randomized to receive conventional dose of etanercept treatment and 26 were given a dose reduction regimen for 12 weeks. The primary efficacy endpoint was disease activity of response for AS at week 12, including Bath AS Disease Activity Index (BASDAI), the serum erythrocyte sediment rate (ESR), C-reactive protein (CRP), and assessment of synovitis of the hip by ultrasonography. At 12 weeks, all of the patients had responses to some extent and the efficacy variables improved significantly over time, but not between treatment groups. Nine patients experienced at least one adverse event (generally, infections and injection site reactions), most of them mild or moderate. In sum, the dose reduction of etanercept regimen in the 12-week AS treatment was confirmed as a safe and effective therapy as the conventional dose was given.

Beneficial effects of tripterygium glycosides tablet on biomarkers in patients with ankylosing spondylitis

The aim of the current study was to explore the effects and possible mechanisms of tripterygium glycosides tablet (TGT) in the treatment of active ankylosing spondylitis (AS). Thirty-six patients with active AS were given a 20 mg TGT treatment three times per day for 12 weeks, and 21 unrelated healthy controls were recruited as the control group. Efficacy measures included the Bath AS disease activity index (BASDAI), erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) prior and subsequent to TGT treatment. Serum dickkopf homolog 1 (DKK1) and interleukin-17 (IL-17) levels before and after TGT treatment were assessed using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and ELISA assay. The levels of several serum biomarkers were determined by ELISA, including receptor activator of nuclear factor κ-B ligand (RANKL), osteoprotegerin (OPG), bone alkaline phosphatase (BAP), bone morphogenetic protein-2 (BMP-2), matrix metalloproteinase-3 (MMP-3), cross-linked telopeptide of type II collagen (CTX-II), vascular endothelial growth factor (VEGF), and prostaglandin E2 (PGE2). After 12 weeks of TGT treatment, the BASDAI score of the patients was significantly reduced (P<0.05), their levels of ESR and CRP were significantly reduced to a normal level (P<0.05, P<0.05), RT-PCR and ELISA showed a significant increase in the level of DKK1 expression (P<0.05) and a significant decreased IL-17 expression (P<0.05), there was a significant increase in the expression of OPG, BAP and BMP-2 (P<0.01, P<0.01, P<0.01) and a significant reduction in the expression levels of RANKL, CTX-II. MMP-3, PGE2, and VEGF (P<0.01, P<0.01, P<0.01, P<0.05, P<0.01) compared with those of the controls. TGT is effective at improving the signs and symptoms of patients with AS through the regulation of serum biomarkers, and the mechanisms may be associated with the anti-inflammatory effect, inhibition of new bone formation and potential bone-protective effects.

The roles of genetic factors in uveitis and their clinical significance

BACKGROUND

Uveitis is a diverse group of intraocular inflammatory disease and is a significant cause of visual loss worldwide. Recent studies have identified various endogenous immune mechanisms and genetic factors that are involved in the pathogenesis of uveitis. This review provides an overview on the role of genetics in the development and clinical course of uveitis.

METHODS

PUBMED was used for literature search, and articles published from 1970 to 2012 that evaluated the genetic associations and mechanisms involved in the development and clinical features of uveitis were included.

RESULTS

Studies have demonstrated associations between various genetic factors and the development and clinical course of intraocular inflammatory conditions. Genes involved included genes expressing interleukins, chemokines, chemokine receptors, and tumor necrosis factor and genes involved in complement system, oxidation, and other intracellular molecular pathways.

CONCLUSION

Multiple genetic factors play important roles in the pathogenesis of uveitis and may influence the clinical course of uveitis. Further studies to investigate the genetic mechanisms of uveitis might identify additional genetic associations and might have the potential for identifying novel therapeutic targets in the treatment of intraocular inflammation.

Immunogenetic study in Chinese population with ankylosing spondylitis: are there specific genes recently disclosed?

Purpose. Ankylosing spondylitis (AS) is a systemic, autoimmune disease resulting in the destruction of the affected joints. Over the past 5 years, several new genes or genetic regions associated with AS have been identified in the Chinese population. This paper aims to discuss the major findings and related potential mechanisms of these studies in our population. Recent Findings. In recent years, due to the rapid advances in computational genetics and technology, there has been an increasing list of well-validated genes or genetic regions associated with AS susceptibility. So far, several genes or genetic regions have now been reported in the Han ethnic Chinese population, containing the major histocompatibility complex (MHC), ERAP1, IL-23R, 12q12, 2p15, 5q14.3, and so on. Different hypotheses for disease mechanisms have been investigated on the basis of the functional studies of these genes or genetic regions. Summary. This paper tries to summarize the association of several candidate genes with risk for AS in the Han ethnic Chinese population and aims to identify the novel inflammatory pathways and provide potential strategies for better therapies.

Genome-wide association study of African and European Americans implicates multiple shared and ethnic specific loci in sarcoidosis susceptibility

Sarcoidosis is a systemic inflammatory disease characterized by the formation of granulomas in affected organs. Genome-wide association studies (GWASs) of this disease have been conducted only in European population. We present the first sarcoidosis GWAS in African Americans (AAs, 818 cases and 1,088 related controls) followed by replication in independent sets of AAs (455 cases and 557 controls) and European Americans (EAs, 442 cases and 2,284 controls). We evaluated >6 million SNPs either genotyped using the Illumina Omni1-Quad array or imputed from the 1000 Genomes Project data. We identified a novel sarcoidosis-associated locus, NOTCH4, that reached genome-wide significance in the combined AA samples (rs715299, P(AA-meta) = 6.51 × 10(-10)) and demonstrated the independence of this locus from others in the MHC region in the same sample. We replicated previous European GWAS associations within HLA-DRA, HLA-DRB5, HLA-DRB1, BTNL2, and ANXA11 in both our AA and EA datasets. We also confirmed significant associations to the previously reported HLA-C and HLA-B regions in the EA but not AA samples. We further identified suggestive associations with several other genes previously reported in lung or inflammatory diseases.

Progress in the genetics of ankylosing spondylitis

Ankylosing spondylitis (AS) is a common, highly heritable, inflammatory arthropathy. In addition to being strongly associated with HLA-B27, a further 13 genes have been robustly associated with the disease. These genes highlight the involvement of the IL-23 pathway in disease pathogenesis, and indicate overlaps between the pathogenesis of AS, and of inflammatory bowel disease. Genetic associations in B27-positive and -negative disease are similar, with the main exception of association with ERAP1, which is restricted in association to B27-positive cases. This restriction, and the known function of ERAP1 in peptide trimming prior to HLA Class I presentation, indicates that HLA-B27 is likely to operate in AS by a mechanism involving aberrant peptide handling. These advances point to several potential novel therapeutic approaches in AS.

Characterization of tumor necrosis factor-α block haplotypes associated with susceptibility to chronic venous leg ulcers in Caucasian patients

Polymorphisms in the central major histocompatibility complex (MHC) are associated with several immunopathologic and inflammatory diseases, including chronic venous leg ulcers (CVLU). Because of strong linkage disequilibrium, identification of loci affecting disease susceptibility must be based on comparisons between haplotypes. Here we examine the association of conserved tumor necrosis factor (TNF) block haplotypes with CVLU susceptibility. A total of 171 Caucasian patients with CVLU were compared with 173 age-/gender-matched controls, excluding individuals with type 1 diabetes or rheumatoid arthritis. A total of 194 healthy subjects formed a separate population-based control group. Samples were typed for 38 tumor necrosis factor (TNF) block single nucleotide polymorphisms (SNP), human leukocyte antigen (HLA)-B and HLA-DRB1 alleles. TNF haplotypes were derived using the PHASE algorithm and assigned numbers (FVx) defined previously. The patients and matched controls shared 16 TNF block haplotypes. The patients had increased carriage of FV16 and alleles of the 8.1 and 60.3 MHC ancestral haplotypes (AH). CVLU risk is modulated by alleles within FV16 (e.g., TNF-308A and BAT1intron10 C insertion) or near FV16 in the 8.1AH. CVLU risk may also be mediated by unidentified alleles (not in FV22) marked by HLA-B40 and HLA-DR13. FV16 appears to be the best MHC and TNF block marker of susceptibility. After disease onset, an individual's TNF block haplotype does not modulate CVLU severity.

Genetics of ankylosing spondylitis

PURPOSE OF REVIEW

Over the past 3 years, several new genes and gene deserts have been identified that are associated with ankylosing spondylitis (AS). The purpose of this review is to discuss the major findings of these studies, and the answers they provide and questions they raise about the pathogenesis of this common condition.

RECENT FINDINGS

Five genes/genetic regions have now definitively been associated with AS [the major histocompatibility complex (MHC), IL23R, ERAP1, 2p15 and 21q22]. Strong evidence to support association with the disease has been demonstrated for the genes IL1R2, ANTXR2, TNFSF15, TNFR1 and a region on chromosome 16q including the gene TRADD. There is an overrepresentation of genes involved in Th17 lymphocyte differentiation/activation among genes associated with AS and the related diseases inflammatory bowel disease and psoriasis, pointing strongly to this pathway as playing a major causative role in the disease. Increasing information about differential association of HLA-B27 subtypes with disease suggests a hierarchy of strength of association of those alleles with AS, providing a useful test as to the validity of different potential mechanisms of association of HLA-B27 with AS. The mechanism underlying the association of the gene deserts, 2p15 and 21q22, suggests the involvement of noncoding RNA in AS etiopathogenesis.

SUMMARY

The increasing list of genes identified as being definitely involved in AS provides a useful platform for hypothesis-driven research in the field, providing a potential alternative route to determining the underlying mechanisms involved in the disease to research focusing on HLA-B27 alone.

Non-B27 MHC associations of ankylosing spondylitis

Ankylosing spondylitis (AS) has been associated with human leukocyte antigen (HLA)-B27 for over 30 years; however, the mechanism of action has remained elusive. Although many studies have reported associations between AS and other genes in the major histocompatibility complex (MHC) in AS, no conclusive results have emerged. To investigate the contribution of non-B27 MHC genes to AS, a large cohort of AS families and controls were B27 typed and genotyped across the region. Interrogation of the data identified a region of 270 kb, lying from 31 952 649 to 32 221 738 base pairs from the p-telomere of chromosome 6 and containing 23 genes, which is likely to include genes involved with susceptibility to AS.

HLA-C expression pattern is spatially different between psoriasis and eczema skin lesions

Interactions between genetic and environmental factors underlie the immune dysregulation and keratinocyte abnormalities that characterize psoriasis. Among known psoriasis susceptibility loci (PSORS), PSORS1 on chromosome 6 has the strongest association to disease. Altered expression of some PSORS1 candidate genes has been reported but little is known about HLA-C expression in psoriasis. This study compared expression of major histocompatibility complex class Ia and HLA-C in psoriasis, allergic contact eczema, and normal skin. Although HLA-C was abundant in protein extracts from both eczema and psoriasis, a consistent and intriguing difference in the expression pattern was observed; strong immunoreactivity in the basal cell layer, polarized towards the basement membrane in psoriasis, whereas in eczema lesions HLA-C immunostaining was present mostly in suprabasal cells. Inflammatory cells in the dermis were strongly stained in both diseases. Normal skin epithelium showed less intense but similar HLA-C staining as eczema lesions. HLA class Ia expression overall resembled that of HLA-C in all samples. The distinct HLA-C expression patterns in psoriasis and eczema suggest a functional role in the specific psoriasis immune response and not only a general feature of inflammation.

Experimental spondyloarthropathies: Animal models of ankylosing spondylitis

Spondyloarthropathies (SpAs), including ankylosing spondylitis, are chronic inflammatory diseases of the axial skeleton. Genomic scans of SpA families revealed the overwhelming complexity of the disease, which appears to be under the control of over 20 chromosome loci, including the major SpA gene HLA-B27 within class I of the major histocompatibility complex (MHC). Animal models confirmed the primary role of MHC in SpA susceptibility and supported the hypothesis that certain enterobacterial infections can trigger SpA. Immunization of mice with proteoglycan aggrecan also can provoke SpA, thus providing the opportunity to study genetic and clinical details of the disease initiation.

The genetic basis of ankylosing spondylitis

PURPOSE OF REVIEW

Genetic factors provide over 90% of the overall susceptibility to ankylosing spondylitis, with about half of the genetic contribution attributed to HLA-B27 and other major histocompatibility complex genes. Recent studies have focused on non-major histocompatibility complex genes. This review is aimed at summarizing the status of major histocompatibility complex and non-major histocompatibility complex genes in ankylosing spondylitis susceptibility, and suggests areas for future studies.

RECENT FINDINGS

A recent meta-analysis of published scans of ankylosing spondylitis susceptibility has confirmed sites on chromosomes 3q, 6p (the major histocompatibility complex), 10q, 16q and 19q in ankylosing spondylitis susceptibility. Non-major histocompatibility complex candidate gene analyses have confirmed a role for the IL-1 gene complex. The search for other non-major histocompatibility complex candidate genes, however, has been complicated by inadequate power in most previous studies. Innovations in genetic methodologies will allow thorough genome wide linkage disequilibrium mapping studies in large cohorts of patients that will result in the dissection of the genetic susceptibility to ankylosing spondylitis.

SUMMARY

Nearly half of the susceptibility to ankylosing spondylitis is provided by major histocompatibility complex genes. Non-major histocompatibility complex genes, most notably the IL-1 gene complex, have been identified and novel technologies promise that a more thorough examination of the rest of the genome will soon elucidate the genetic basis of this disease.

The history of pediatric rheumatology

The care and study of children with rheumatic diseases began slowly in the 19th century, with the most attention centered on rheumatic fever. Other rheumatic diseases of children received little attention until the 1940s. Rheumatic diseases taken together remain a significant cause of chronic illness in children throughout the world. A number of other conditions that masquerade as rheumatic diseases in children also demand recognition and management. Although ultimate causes and cures of childhood rheumatic diseases remain elusive, advances in therapy have improved the outlook for affected children, and advances in biomedical research are adding to our basic understanding of the disease process involved. Pediatric rheumatology has become a well-organized, although underpopulated, specialty that enhances recognition and care of affected children and contributes to basic research knowledge in infectious disease, immunology, and genetics. This review focuses most prominently on the early history of pediatric rheumatology and its development as a specialty. The recent burgeoning of new biomedical science and new means of treatment will be better told in the historical perspective of years to come.

Two Major Interacting Chromosome Loci Control Disease Susceptibility in Murine Model of Spondyloarthropathy

Autoimmune spondylitis was induced in BALB/c mice and their MHC-matched (BALB/c x DBA/2)F1 and F2 hybrids by systemic immunization with cartilage/intervertebral disk proteoglycan (PG). As in human ankylosing spondylitis, the MHC was the major permissive genetic locus in murine PG-induced spondylitis (PGIS). Two major non-MHC chromosome loci with highly significant linkage were found on chromosomes 2 (Pgis2) and 18 (Pgis1) accounting for 40% of the entire F2 trait variance. The dominant spondylitis-susceptibility allele for Pgis2 locus is derived from the BALB/c strain, whereas the Pgis1 recessive allele was present in the disease-resistant DBA/2 strain. The Pgis1 locus significantly affected the disease-controlling Pgis2 locus, inducing as high incidence of spondylitis in F2 hybrids as was found in the spondylitis-susceptible parent BALB/c strain. Additional disease-controlling loci with suggestive linkage were mapped to the chromosomes 12, 15, and 19. Severity of spondylitis in F2 mice positively correlated with serum levels of amyloid A, IL-6, and Pg-specific Abs, and showed negative correlation with Ag-induced T cell proliferation, IFN-gamma, IL-4, and TNF-alpha production. A major locus controlling serum IL-6 was found on chromosome 14 near osteoclast differentiation factor Tnfsf11. Locus on chromosome 11 near the Stat3 and Stat5 genes controlled serum level of the Ig IgG2a isotype. The two major genetic loci Pgis1 and Pgis2 of murine spondylitis were homologous to chromosome regions in human genome, which control ankylosing spondylitis in human patients. Thus, this animal model of experimentally induced spondylitis might facilitate the identification of spondylitis-susceptibility genes in humans.

Association study of LMP gene polymorphisms in Mexican patients with spondyloarthritis

To evaluate the role of LMP (low molecular weight protein) genes as susceptibility markers for spondyloarthritis (SpA), LMP gene polymorphisms were analyzed in 223 Mexican patients with SpA (81 undifferentiated SpA [U-SpA], 117 with ankylosing spondylitis [AS], 25 with reactive arthritis) and in 139 ethnically matched healthy individuals. LMP genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism. The LMP2 and LMP7 allele frequencies were similar in patients and healthy controls. Genotype analysis revealed an increased frequency of LMP2 R/R genotype in the whole group of SpA (pC = 0.003, OR = 2.06, 95%CI = 1.3-3.25) and in the clinical subgroups of AS (pC = 0.039, OR = 1.88, 95%CI = 1.1-3.22) and U-SpA (pC = 0.003, OR = 2.56, 95%CI = 1.37-4.8) compared with healthy controls. Analysis in the LMP7 did not reveal significant differences in patients and healthy controls. The HLA-B27-negative AS subgroup also showed an increased frequency of LMP2 R/R genotype (pC = 0.027, OR = 4.81, 95%CI = 1.21-22.13). The LMP2-R/R AS patients were younger than LMP2-H/R and H/H patients at onset of the disease (16.0 +/- 6.8 years for R/R, 22.0 +/- 11.2 years for H/R and 28.6 +/- 10.9 years for H/H) (p < 0.05). The data suggest that, besides HLA-B27, LMP2 genotypes are also involved in the genetic susceptibility to develop AS in Mexicans. Furthermore, the age at onset of this disease might also be influenced by genotypes of this gene.

Association of CYP17 with HLA-B27-negative seronegative spondyloarthropathy in Japanese males

Susceptibility genes for seronegative spondyloarthropathy (SNSA) other than HLA-B27 remain unclarified. Sex hormones are implicated in the pathogenesis of SNSA. Cytochrome P450c17a (CYP17) is a key regulator of androgen biosynthesis, and a single nucleotide polymorphism (SNP) in the 5'-untranslated region of the CYP17 gene (CYP17), -34C > T, is associated with variety of diseases. We have investigated the association between the CYP17 SNP and SNSA in Japanese males. Genomic DNA was extracted from 149 Japanese male SNSA patients and 380 controls. The CYP17 SNP was genotyped using polymerase chain reaction-restriction fragment length polymorphism analysis. Allelic and genotypic frequencies of the SNP were compared between SNSA patients and controls, and within SNSA patients. We also computed haplotype frequencies using an expectation-maximization algorithm, analyzed the difference between SNSA and control groups, and examined the potential association of other known SNPs in the CYP17 gene. The frequency of the -34T allele was significantly increased in HLA-B27-negative SNSA, but not in total or HLA-B27-positive SNSA when compared to controls. The T allele was more prevalent in HLA-B27-negative SNSA than in HLA-B27-positive SNSA, and the T/T genotype was over-represented in HLA-B27-negative SNSA. Haplotype analysis did not demonstrate more significant association. The CYP17 SNP is associated with SNSA in HLA-B27-negative Japanese males.

Expanding the armamentarium for the spondyloarthropathies

Ankylosing spondylitis (AS) is a member of the family of spondyloarthropathies, which are inflammatory arthritides largely involving the axial skeleton and commonly accompanied by peripheral arthritis. Genetic factors, particularly the presence of HLA-B27, are major contributors to the susceptibility for AS. Despite some therapeutic advances, the treatment options for patients with AS and related disorders have been limited. Several lines of evidence have led to the hypothesis that patients with AS might benefit from treatment with tumor necrosis factor (TNF). Specifically, TNF concentrations are known to be significantly elevated in the synovium of patients with rheumatoid arthritis (RA), in the inflamed gut of patients with inflammatory bowel disease, and in the inflamed sacroiliac joints of patients with AS. The anti-TNF agents have been shown to be of benefit in, and currently have indications for, RA (etanercept, infliximab, adalimumab), Crohn's disease (infliximab), and psoriatic arthritis (etanercept). Because the spondyloarthropathies share pathogenetic mechanisms with the above-specified disease states, studies have been conducted to evaluate the effectiveness of anti-TNF agents in several disorders, including AS. Data from clinical trials so far with infliximab and etanercept show that patients with AS and related disorders achieve significant improvement in clinical signs and symptoms based on validated outcomes measures. Computed tomography and magnetic resonance imaging (MRI) can facilitate the early diagnosis of AS. Studies with infliximab using MRI together with updated scoring methods demonstrated significant decreases in associated spinal inflammation. TNF antagonist therapy is well tolerated in patients with AS, with a side effect profile consistent with the prior experience of patients with RA.

Persistent diarrhea, arthritis, and other complications of enteric infections: a pilot survey based on California FoodNet surveillance, 1998-1999

Numerous complications of enteric infections have been described, including persistent diarrhea, reactive arthritis, and Guillain-Barre syndrome. We determined the frequency of self-reported complications of enteric infections in a pilot study in the California site of the Foodborne Diseases Active Surveillance Network. From 1 April 1998 through 31 March 1999, active surveillance identified 1454 infections in Alameda and San Francisco counties, of which 52% were Campylobacter infections, 22% were Salmonella infections, 15% were Shigella infections, 6% were Cryptosporidium infections, 2% were Escherichia coli O157:H7 infections, 2% were Yersinia infections, and 1% were Vibrio infections. We mailed surveys to 1331 eligible participants, and 571 (43%) were returned. A new health problem following infection was reported by 153 (27%) of the respondents: 12 (8%) reported new onset of joint pain and 53 (35%) reported new gastrointestinal symptoms, of whom 38 reported persistent diarrhea, including 2 who reported irritable bowel syndrome. Three respondents reported hair loss. The frequency, nature, and etiology of these complications merit further investigation.

Juvenile ankylosing spondylitis?is it the same disease as adult ankylosing spondylitis?

OBJECTIVES

Juvenile and adult forms of ankylosing spondylitis (AS) have been shown to have different clinical presentation and outcome in Caucasians. We did this retrospective analysis to see if similar differences exist in the Indian population.

PATIENTS AND METHODS

Case records of 210 Indian patients diagnosed with AS according to modified New York criteria were reviewed. Data were collected regarding age of onset, clinical features, drug treatment, and outcome at last follow-up. Patients with onset before 17 years of age were classified as having juvenile AS (JAS) and the rest with adult AS (AAS).

RESULTS

There were 150 patients with AAS and 60 with JAS. The latter had higher male preponderance, more frequent onset with peripheral arthritis, and greater involvement of hip and knee joints. Valvular dysfunction was seen only in patients with JAS.

CONCLUSION

In this group of subjects, juvenile AS had onset more often with oligoarthritis and enthesitis than with spinal disease. Hip and knee joint involvement was more common in JAS than AAS.

HLA-B27 modulates nuclear factor kappaB activation in human monocytic cells exposed to lipopolysaccharide

OBJECTIVE

To study whether HLA-B27 modifies some key factors controlling inflammatory responses on lipopolysaccharide (LPS) stimulation in human monocytic cells.

METHODS

U937 human monocytic cells were stably transfected with either HLA-B27 genomic DNA, HLA-B27 complementary DNA, HLA-A2 genomic DNA, or with the resistant vector pSV2neo (mock) alone. The cells were stimulated with LPS. Electrophoretic mobility shift assay was performed to determine nuclear factor kappaB (NF-kappaB) and heat-shock factor 1 activities, Western blotting was performed to detect the expressions of inhibitory kappaBalpha (IkappaBalpha) and heat-shock proteins (HSPs), and enzyme-linked immunosorbent assay was performed to measure tumor necrosis factor alpha (TNFalpha) secretion.

RESULTS

The expression of HLA-B27 modulated the response to LPS in U937 human monocytic cells. Stimulation with LPS led to faster degradation of IkappaBalpha regulatory proteins, accompanied by faster and prolonged activation of NF-kappaB in HLA-B27-expressing cells compared with HLA-A2 and mock transfectants. The secretion of TNFalpha upon LPS stimulation correlated well with the activation of NF-kappaB. No activation of the heat-shock response was observed.

CONCLUSION

Our data indicate that HLA-B27 has effects on host responses to LPS that are unrelated to antigen presentation. Two crucial events in the development of arthritis, the activation of NF-kappaB and the secretion of TNFalpha, were found to be enhanced in HLA-B27-expressing cells upon LPS stimulation. Because LPS is known to be present in the inflamed joints of patients with reactive arthritis (ReA), the enhanced inflammatory response of HLA-B27-positive cells upon LPS stimulation offers an attractive explanation for the role of HLA-B27 in the development of ReA.

The role of HLA genes in familial spondyloarthropathy: a comprehensive study of 70 multiplex families

OBJECTIVES

To investigate whether HLA alleles, other than HLA-B27, influence predisposition to spondyloarthropathy (SpA) in multiplex families.

METHODS

Seventy French families with at least two affected SpA members were recruited. Patients, and their first degree relatives were typed for HLA-A, B, C, and DR, and extended HLA haplotypes were determined. The distribution of HLA-A, C, and DR alleles carried on HLA-B27+ haplotypes in SpA families was compared with the distribution of these alleles among HLA-B27+ haplotypes in the French general population. Contribution to SpA susceptibility of HLA-A, B, C, and DR alleles, other than HLA-B27, was tested by transmission disequilibrium test. The contribution of HLA alleles to specific presentation features of SpA was examined.

RESULTS

Frequencies of HLA-A, C, and DR alleles carried on HLA-B27+ haplotypes from SpA families were comparable with those seen in the French population, except for DR13 which was overrepresented among patients (pcorr<0.001). Most interestingly, the HLA-DR4 allele was transmitted in excess to patients with SpA, independently of linkage to HLA-B27 (pcorr=0.05), and in a direction opposite to that for HLA-B27+ unaffected siblings (pcorr=0.01). Finally, the distribution of HLA alleles was not related to the presentation feature of SpA.

CONCLUSION

HLA predisposition to familial SpA appears not to be limited to HLA-B27, but some HLA-DR alleles also have a significant influence. In particular, HLA-DR4 contributes significantly to a genetic predisposition to SpA, which may have implications in our understanding of SpA pathogenesis.

Interactions of HLA-B27 with the peptide loading complex as revealed by heavy chain mutations

MHC class I heavy chains assemble in the endoplasmic reticulum with beta(2)-microglobulin and peptide to form heterotrimers. Although full assembly is required for stable class I molecules to be expressed on the cell surface, class I alleles can differ significantly in their rates of, and dependencies on, full assembly. Furthermore, these differences can account for class I allele-specific disparities in antigen presentation to T cells. Recent studies suggest that class I assembly is assisted by an elaborate complex of proteins in the endoplasmic reticulum, collectively referred to as the peptide loading complex. In this report we take a mutagenesis approach to define how HLA-B27 molecules interact with the peptide loading complex. Our results define subtle differences between how B27 mutants interact with tapasin (TPN) and calreticulin (CRT) in comparison to similar mutations in other mouse and human class I molecules. Furthermore, these disparate interactions seen among class I molecules allow us to propose a spatial model by which all class I molecules interact with TPN and CRT, two molecular chaperones implicated in facilitating the binding of high-affinity peptide ligands.

Is disease severity in ankylosing spondylitis genetically determined?

OBJECTIVE

To assess the role of genes and the environment in determining the severity of ankylosing spondylitis.

METHODS

One hundred seventy-three families with >1 case of ankylosing spondylitis were recruited (120 affected sibling pairs, 26 affected parent-child pairs, 20 families with both first- and second-degree relatives affected, and 7 families with only second-degree relatives affected), comprising a total of 384 affected individuals. Disease severity was assessed by the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and functional impairment was determined using the Bath Ankylosing Spondylitis Functional Index (BASFI). Disease duration and age at onset were also studied. Variance-components modeling was used to determine the genetic and environmental components contributing to familiality of the traits examined, and complex segregation analysis was performed to assess different disease models.

RESULTS

Both the disease activity and functional capacity as assessed by the BASDAI and the BASFI, respectively, were found to be highly familial (BASDAI familiality 0.51 [P = 10(-4)], BASFI familiality 0.68 [P = 3 x 10(-7)]). No significant shared environmental component was demonstrated to be associated with either the BASDAI or the BASFI. Including age at disease onset and duration of disease as covariates made no difference in the heritability assessments. A strong correlation was noted between the BASDAI and the BASFI (genetic correlation 0.9), suggesting the presence of shared determinants of these 2 measures. However, there was significant residual heritability for each measure independent of the other (BASFI residual heritability 0.48, BASDAI 0.36), perhaps indicating that not all genes influencing disease activity influence chronicity. No significant heritability of age at disease onset was found (heritability 0.18; P = 0.2). Segregation studies suggested the presence of a single major gene influencing the BASDAI and the BASFI.

CONCLUSION

This study demonstrates a major genetic contribution to disease severity in ankylosing spondylitis. As with susceptibility to ankylosing spondylitis, shared environmental factors play little role in determining the disease severity.

Whole-genome screening in ankylosing spondylitis: evidence of non-MHC genetic-susceptibility loci

Ankylosing spondylitis (AS) is a common inflammatory arthritis predominantly affecting the axial skeleton. Susceptibility to the disease is thought to be oligogenic. To identify the genes involved, we have performed a genomewide scan in 185 families containing 255 affected sibling pairs. Two-point and multipoint nonparametric linkage analysis was performed. Regions were identified showing "suggestive" or stronger linkage with the disease on chromosomes 1p, 2q, 6p, 9q, 10q, 16q, and 19q. The MHC locus was identified as encoding the greatest component of susceptibility, with an overall LOD score of 15.6. The strongest non-MHC linkage lies on chromosome 16q (overall LOD score 4.7). These results strongly support the presence of non-MHC genetic-susceptibility factors in AS and point to their likely locations.

Interleukin 1 gene cluster polymorphisms in multiplex families with spondylarthropathies

Interleukin 1alpha (IL-1alpha) has been implicated in the pathogenesis of infectious, auto-immune and inflammatory diseases. Polymorphisms in the genes encoding IL-1alpha, IL-1beta and the IL-1 receptor antagonist (ILRN) molecules have been associated with several inflammatory diseases. As the marker D2S160 has been characterized as a candidate locus for Ankylosing Spondylitis (AS) after a genome-wide scan, and since this locus is located approximately 0.3 cM telomeric to the IL-1 gene cluster, we hypothesized that these cytokines might be good candidates for Spondylarthropathies (SpA). Therefore we tested this hypothesis using the transmission disequilibrium test (TDT) in 37 families representing 217 subjects from three intragenic IL-1 gene cluster polymorphisms, the IL1B Taq I, the ILRN 2nd intron, and the IL1A Nco I, taking HLA B27 status into account or not. In conclusion, by means of intra-familial TDT analysis we found no linkage or intra-familial association between SpA and the three IL-1 gene-cluster polymorphisms in SpA multiplex family material.

Increased risk of developing ankylosing spondylitis among first-born children

OBJECTIVE

Studies in mice have demonstrated an increased risk of ankylosing enthesopathy in earlier litters compared with later-born offspring. In humans, birth order and maternal age as risk factors for ankylosing spondylitis (AS) have not been investigated previously. This study was undertaken to investigate whether first-born children have a higher risk of AS than later-born children and whether maternal age at delivery is another risk factor.

METHODS

The birth order of 162 AS patients was compared with that of their healthy siblings, both for the total group and with stratification for maternal age at first delivery. Maternal age at the time of delivery of AS patients who were first-born children was compared with the mean maternal age at first delivery in the Dutch population.

RESULTS

The number of first-born children with AS was significantly higher than would be expected in case of an equal risk between first-born and later-born children (26 versus 20 for families with 2 children [P = 0.029] and 63 versus 47.6 for all families [P = 0.004]). Also, the mean maternal age at first delivery was lower in mothers of AS patients (24.8 years) compared with mothers of healthy controls (26.1 years).

CONCLUSION

Low birth order is a risk factor for AS in humans.

Recurrence risk modelling of the genetic susceptibility to ankylosing spondylitis

OBJECTIVES

It has long been suspected that susceptibility to ankylosing spondylitis (AS) is influenced by genes lying distant to the major histocompatibility complex. This study compares genetic models of AS to assess the most likely mode of inheritance, using recurrence risk ratios in relatives of affected subjects.

METHODS

Recurrence risk ratios in different degrees of relatives were determined using published data from studies specifically designed to address the question. The methods of Risch were used to determine the expected recurrence risk ratios in different degrees of relatives, assuming equal first degree relative recurrence risk between models. Goodness of fit was determined by chi(2) comparison of the expected number of affected subjects with the observed number, given equal numbers of each type of relative studied.

RESULTS

The recurrence risks in different degrees of relatives were: monozygotic (MZ) twins 63% (17/27), first degree relatives 8.2% (441/5390), second degree relatives 1.0% (8/834), and third degree relatives 0. 7% (7/997). Parent-child recurrence risk (7.9%, 37/466) was not significantly different from the sibling recurrence risk (8.2%, 404/4924), excluding a significant dominance genetic component to susceptibility. Poor fitting models included single gene, genetic heterogeneity, additive, two locus multiplicative, and one locus and residual polygenes (chi(2) >32 (two degrees of freedom), p<10(-6) for all models). The best fitting model studied was a five locus model with multiplicative interaction between loci (chi(2)=1.4 (two degrees of freedom), p=0.5). Oligogenic multiplicative models were the best fitting over a range of population prevalences and first degree recurrence risk rates.

CONCLUSIONS

This study suggests that of the genetic models tested, the most likely model operating in AS is an oligogenic model with predominantly multiplicative interaction between loci.

Probing for genes in seronegative spondyloarthropathy

Seronegative spondyloarthropathies are a group of disorders characterized by inflammation of the spine, sacroiliac joints, and peripheral arthritis along with various characteristic extra-articular features. Their pathogenesis and immunogenetics have not yet been fully elucidated. Ankylosing Spondylitis (AS) is probably the best studied of these disease. It has now been 27 years since the association of human leukocyte antigen (HLA) B27 and AS has been demonstrated. Since then, a plethora of association studies and linkage studies unequivocally demonstrate that genetic determinants within or near the major histocompatible complex (MHC) are critical to the etiology of AS. Surprisingly though, the total MHC contribution to AS has been estimated at only 30%. In this review, we highlight the genetic basis of AS as the prototypical chronic axial arthritis, and discuss the rationale and approach in searching for non-HLA linked genes.

Misfolding of HLA-B27 as a Result of Its B Pocket Suggests a Novel Mechanism for Its Role in Susceptibility to Spondyloarthropathies

The MHC class I protein HLA-B27 is strongly associated with susceptibility to spondyloarthropathies and can cause arthritis when expressed in rats and mice, implying a direct role in disease pathogenesis. A prominent hypothesis to explain this role suggests that the unique peptide binding specificity of HLA-B27 confers an ability to present arthritogenic peptides. The B pocket, a region of the peptide binding groove that is an important determinant of allele-specific peptide binding, is thought to be critical for arthritogenicity. However, this hypothesis remains unproven. We show that in addition to its role in peptide selection, the B pocket causes a portion of the pool of assembling HLA-B27 heavy chains in the endoplasmic reticulum to misfold, resulting in their degradation in the cytosol. The misfolding phenotype is corrected by replacing the HLA-B27 B pocket with one from HLA-A2. Our results suggest an alternative to the arthritogenic peptide hypothesis. Misfolding and its consequences, rather than allele-specific peptide presentation, may underlie the strong link between the HLA-B27 B pocket and susceptibility to spondyloarthropathies.

Overlapping peptide-binding specificities of HLA-B27 and B39: evidence for a role of peptide supermotif in the pathogenesis of spondylarthropathies

OBJECTIVE

Previous studies indicated the increase of HLA-B39 among HLA-B27 negative patients with spondylarthropathies (SpA). This study was performed to examine whether the natural ligands of HLA-B27 are capable of binding to HLA-B39.

METHODS

Peptides were synthesized according to the sequences of known natural ligands of HLA-B27 or B39 and were tested for their binding to HLA-B*3901 and B*2705 by quantitative peptide binding assay, using a TAP-deficient RMA-S cell line transfected with human beta2-microglobulin and HLA class I heavy chain genes.

RESULTS

Four of the 10 HLA-B27 binding peptides significantly bound to HLA-B*3901. All 4 peptides had hydrophobic/aromatic amino acids (Leu or Phe) at the C-terminus. In contrast, peptides with basic residues (Lys, Arg) or Tyr at the C-terminus did not bind to B*3901. In parallel experiments, 1 of the 2 natural ligands of HLA-B*3901 was found to bind to B*2705.

CONCLUSION

A subset of natural HLA-B27 ligands was capable of binding to B*3901. In addition to Arg at position 2 (Arg2), hydrophobic/aromatic C-terminal residues, such as Leu or Phe, seemed to be crucial for the cross-specificity. These results suggested that HLA-B27 and B39 recognize overlapping peptide repertoires, supporting the hypothesis that the peptides presented by both of these class I antigens play a role in the pathogenesis of SpA.

The immunogenetics of the seronegative spondyloarthropathies

In none of the rheumatic diseases has the genetic contribution to pathogenesis been so well characterized as in the seronegative spondyloarthropathies. Most important has been the elucidation of the structure and effect on disease expression of HLA-B27, where 11 subtypes have been distinguished to date. These vary in frequency in different ethnic groups and seem to show differential disease associations. The high frequency of this gene in patients with the seronegative spondyloarthropathies, especially ankylosing spondylitis (AS) and Reiter's syndrome (RS)/reactive arthritis (ReA), has emerged as probably the best example of a disease association with a hereditary marker. Other HLA genes, in addition to HLA-B27, have been implicated in psoriasis and psoriatic arthritis. These include those from the HLA-C locus and from HLA-DR. In addition, recent family studies have implicated other genes outside the MHC that further enhance the susceptibility to AS.

Genes in the spondyloarthropathies

Ankylosing spondylitis is a highly genetic disease, with up to 98% of the population variance genetically determined. The major genetic effect arises from HLA-B27, but other HLA class I molecules, including HLA-B60, also play a role. HLA class II association may indicate either an independent effect for these genes or the existence of extended MHC haplotype containing other relevant genetic loci. The HLA-linked component of the genetic contribution to AS is substantially less than 50%, and preliminary analysis of affected sibling pairs by whole genome screening has revealed several potential regions of interest. The next 5 years should lead to the confirmation of some of these linkages, their refinement, and the testing of candidate genes within them. Ultimately, a better understanding of the genetic etiology of AS should yield insight into the pathogenic mechanisms and the development of novel strategies for treatment and prevention.

Clinical aspects of the spondyloarthropathies

The spondyloarthropathies are a group of inflammatory arthritic conditions characterized by the absence of rheumatoid factor, and the presence of spondylitis, sacroiliitis, and an asymmetric peripheral arthritis. Familial aggregation and the presence of enthesitis, skin and mucous membrane lesions, bowel complaints, eye involvement, and aortic root dilatation are also features of these conditions. An association with HLA-B27 has been documented in the diseases constituting the spondyloarthropathies, including ankylosing spondylitis, Reiter's disease/reactive arthritis, psoriatic arthritis, and the arthritis of inflammatory bowel disease. Although there are similarities among the entities included in this group, each of these conditions have specific characteristics that help distinguish them. Differences in response to medications and in prognosis are such that it is important to make the correct diagnosis in the individual patient.