What Have We Learned From Family-Based Studies About Spondyloarthritis?

International audienceSpondyloarthritis (SpA) is a chronic inflammatory disorder with a high familial aggregation, emphasizing the existence of genetic susceptibility factors. In the last decades, family-based studies have contributed to better understand the genetic background of SpA, in particular by showing that the most likely model of transmission is oligogenic with multiplicative effects. Coexistence of different SpA subtypes within families also highlighted the complex interplay between all subtypes. Several whole-genome linkage analyses using sib-pairs or multiplex families were performed in the 1990s to try to identify genetic susceptibility factors besides HLA-B27. Unfortunately, no consistent results were obtained and family-based studies have been progressively set aside in favor of case-control designs. In particular, case-control genome-wide association studies allowed the identification of more than 40 susceptibility regions. However, all these loci explain only a small fraction of disease predisposition. Several hypotheses have been advanced to account for this unexplained heritability, including rare variants involvement, leading to a renewed interest in family-based designs, which are probably more powerful in the detection of such variants. In this review, our purpose is to summarize what has been learned to date regarding SpA genetics from family-based studies, with a special focus on recent identification of rare associated variants through next-generation sequencing studies

Abrupt and unexpected stressful life events are followed with increased disease activity in spondyloarthritis: A two years web-based cohort study

International audienceObjectiveThe contribution of environmental factors to spondyloarthritis (SpA) course remains poorly characterized. We previously reported a possible triggering of disease flares by stressful life events and vaccination. The objective of the present study was to specify the types of vaccine and life event that may influence disease activity.MethodsA prospective cohort of adult SpA was followed for two years. Patients logged on to a secured website every month to complete a standardized auto-questionnaire. They reported whether they had been exposed to stressful life events, vaccinations or other environmental factors. Patients were asked to rate the distress resulting from exposure to life events on a numerical rating scale (NRS: 0–10). Primary outcome variable was the variation of Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) measured on two consecutive connections. Months where an event occurred were compared to months without events. The cut-off value of 1 is defined as the minimal clinically important variation for the BASDAI.ResultsThe 272 enrolled SpA patients returned 3,388 questionnaires. Months where an abrupt and unexpected traumatic event occurred were associated with a significant increase of BASDAI of 0.57 [95%CI: 0.29; 0.85] (P < 0.001). The higher the rating of distress, the larger the impact on BASDAI, reaching a clinically meaningful increase of 0.99 [0.17; 1.82] for a VNS ≥ 9. The effect of stressful events on BASDAI persisted during a median of 3 months. No other environmental factor was significantly associated with BASDAI variations.ConclusionAmong stressful life events, abrupt and unexpected events were associated with transient worsening of disease activity in SpA, which reached a clinically meaningful increase for the highest rating of distress. Association between vaccines and disease flare was not confirmed

Faecal microbiota study reveals specific dysbiosis in spondyloarthritis

International audienceAltered microbiota composition or dysbiosis is suspected to be implicated in the pathogenesis of chronic inflammatory diseases, such as spondyloarthritis (SpA) and rheumatoid arthritis (RA). Methods 16S ribosomal RNA gene sequencing was performed on faecal DNA isolated from stool samples in two consecutive cross-sectional cohorts, each comprising three groups of adult volunteers: SpA, RA and healthy controls (HCs). In the second study, HCs comprised a majority of aged-matched siblings of patients with known HLA-B27 status. Alpha and beta diversities were assessed using QIIME, and comparisons were performed using linear discriminant analysis effect size to examine differences between groups. Results In both cohorts, dysbiosis was evidenced in SpA and RA, as compared with HCs, and was disease specific. A restriction of microbiota biodiversity was detected in both disease groups. The most striking change was a twofold to threefold increased abundance of Ruminococcus gnavus in SpA, as compared with both RA and HCs that was significant in both studies and positively correlated with disease activity in patients having a history of inflammatory bowel disease (IBD). Among HCs, significant difference in microbiota composition were also detected between HLA-B27+ and HLA-B27 negative siblings, suggesting that genetic background may influence gut microbiota composition. Conclusion Our results suggest that distinctive dysbiosis characterise both SpA and RA and evidence a reproducible increase in R. gnavus that appears specific for SpA and a marker of disease activity. This observation is consistent with the known proinflammatory role of this bacteria and its association with IBD. It may provide an explanation for the link that exists between SpA and IBD

La survenue brutale et inattendue d’événements stressants est suivie d’une augmentation d’activité de la spondyloarthrite : étude longitudinale en ligne sur deux ans

International audienceObjectifL’effet des facteurs environnementaux sur le cours de la spondyloarthrite (SpA) est encore mal caractérisé. Nous avons rapporté précédemment la possibilité que des poussées de la maladie soient déclenchées par des événements stressants et par la vaccination. L’objectif de la présente étude était de spécifier les types de vaccin et d’événements de la vie pouvant avoir une influence sur l’activité de la maladie.MéthodesUne cohorte prospective d’adultes atteints de SpA a été suivie pendant deux ans. Les patients se sont connectés chaque mois à un site Web sécurisé pour répondre à un autoquestionnaire normalisé. Ils ont indiqué s’ils avaient subi des événements stressants, été vaccinés ou avaient été exposés à d’autres facteurs environnementaux. Ils ont été invités à noter l’angoisse provoquée par ces événements sur une échelle numérique (EN : 0-10). La principale variable d’évaluation était l’indice d’activité de la maladie BASDAI (Bath Ankylosing Spondylitis Disease Activity) enregistré lors de deux connexions consécutives. Les mois où un événement s’était produit ont été comparés aux mois sans événement. Une valeur seuil de 1 a été définie comme la variation minimale cliniquement importante pour le score BASDAI.RésultatsLes 272 patients atteints de SpA recrutés ont rempli 3 388 questionnaires. Les mois durant lesquels un événement traumatisant brutal et inattendu s’était produit ont été associés à une augmentation significative du score BASDAI de 0,57 (IC 95 % 0,29–0,85) (p < 0,001). Plus la note d’angoisse était élevée, plus l’impact sur le score BASDAI était important, atteignant une hausse cliniquement pertinente de 0,99 (0,17-1,82) pour une ENV ≥ 9. L’effet des événements stressants sur le score BASDAI a persisté pendant une durée médiane de trois mois. Aucun autre facteur environnemental n’a été associé de manière significative à des variations du score BASDAI.ConclusionLa survenue brutale et inattendue d’événements stressants a été associée à une dégradation transitoire de l’activité de la SpA, dont l’augmentation était cliniquement pertinente lorsque l’angoisse générée était notée comme maximale. L’association entre vaccins et poussées n’a pas été confirmée

Faecal microbiota study reveals specific dysbiosis in spondyloarthritis

International audienceObjective Altered microbiota composition or dysbiosis is suspected to be implicated in the pathogenesis of chronic inflammatory diseases, such as spondyloarthritis (SpA) and rheumatoid arthritis (RA). Methods 165 ribosomal RNA gene sequencing was performed on faecal DNA isolated from stool samples in two consecutive cross-sectional cohorts, each comprising three groups of adult volunteers: SpA, RA and healthy controls (HCs). In the second study, HCs comprised a majority of aged-matched siblings of patients with known HLA-B27 status. Alpha and beta diversities were assessed using QIIME, and comparisons were performed using linear discriminant analysis effect size to examine differences between groups. Results In both cohorts, dysbiosis was evidenced in SpA and RA, as compared with HCs, and was disease specific. A restriction of microbiota biodiversity was detected in both disease groups. The most striking change was a twofold to threefold increased abundance of Ruminococcus gnavus in SpA, as compared with both RA and HCs that was significant in both studies and positively correlated with disease activity in patients having a history of inflammatory bowel disease (IBD). Among HCs, significant difference in microbiota composition were also detected between HLA-B27+ and HLA-B27 negative siblings, suggesting that genetic background may influence gut microbiota composition. Conclusion Our results suggest that distinctive dysbiosis characterise both SpA and RA and evidence a reproducible increase in R. gnavus that appears specific for SpA and a marker of disease activity. This observation is consistent with the known proinflammatory role of this bacteria and its association with IBD. It may provide an explanation for the link that exists between SpA and IBD

Rheumatoid arthritis, as a clinical disease, but not rheumatoid arthritis-associated autoimmunity, is linked to cardiovascular events

International audienceBackground: Rheumatoid arthritis (RA) is characterized by increased cardiovascular (CV) mortality. CV events are particularly high in patients with RA-specific autoimmunity, including rheumatoid factor (RF) and anti-citrullinated protein antibodies (ACPA), raising the question whether RA-specific autoimmunity itself is associated with CV events. Methods: New CV events (myocardial infarction, stroke or death by CV cause) were recorded in 20,625 subjects of the Electricité de France – Gaz de France (GAZEL) cohort. Self-reported RA cases in the GAZEL cohort were validated by phone interview on the basis of a specific questionnaire. In 1618 subjects, in whom plasma was available, RF and ACPA were measured. A piecewise exponential Poisson regression was used to analyze the association of CV events with presence of RA as well as RA-specific autoimmunity (without RA). Results: CV events in GAZEL were associated with age, male sex, smoking, hypertension, hyperlipidemia, and diabetes mellitus (HR from 1.06 to 1.87, p < 0.05). Forty-two confirmed RA cases were identified. Confirmed RA was significantly associated with CV risk increase (HR of 3.03; 95% CI: 1.13–8.11, p = 0.03) independently of conventional CV risk factors. One hundred seventy-eight subjects showed RF or ACPA positivity without presence of RA. CV events were not associated with ACPA positivity (HR: 1.52, 95% CI: 0.47–4.84, p = 0.48) or RF positivity (HR: 1.15, 95% CI: 0.55–2.40, p = 0.70) in the absence of RA. Conclusions: RA, as a clinical chronic inflammatory disease, but not mere positivity for RF or ACPA in the absence of clinical disease is associated with increased CV risk

Investigating the genetic association between ERAP1 and spondyloarthritis

Objective: A robust association between polymorphisms in the non-major histocompatibility complex gene ERAP1 and ankylosing spondylitis (AS) in several populations was recently identified. The aim of the current study was to determine the level of association of ERAP1 polymorphisms with spondyloarthritis (SpA) in French/Belgian populations with particular attention to genotype-phenotype correlations. Methods: We studied 734 independent SpA cases and 632 controls from two European cohorts. Five single-nucleotide polymorphisms (SNPs), rs27044, rs17482078, rs10050860, rs30187 and rs2287987 were genotyped, and case-control association analyses were carried using PLINK 1.07 software. Linkage disequilibrium and haplotypes were estimated with Haploview. Analysis was first carried out in SpA as a whole group, and then separately in AS and non-radiographic SpA (non-AS) patients. Results: Consistent with previous studies conducted in AS, rs30187 was the most significantly associated SNP with SpA (p = 0.008 in the French, and p = 6.46 x 10(-4) in the Belgian cohorts). In the combined cohorts, this SNP was associated with both AS and non-AS (P-combined = 3.9 x 10(-5) and P-combined = 0.005, respectively). A similar trend was observed with other SNPs. The rs17482078/rs10050860/rs30187-CCT haplotype was significantly associated with increased risk of SpA in both cohorts (P-combined = 9.08 x 10(-4)), including AS and non-AS (P-combined = 6.16 x 10(-4) and P-combined = 0.049, respectively), whereas the -TTC haplotype was associated with reduced risk of SpA, including AS and non-AS (P-combined = 2.36 x 10(-7), P-combined = 5.69 x 10(-6) and P-combined = 2.13 x 10(-4), respectively). Conclusions: This is the first study to show an association between several polymorphisms located in ERAP1 and SpA as a whole. Our findings demonstrate consistent association of the same SNPs and haplotypes with both AS and non-AS subtypes of SpA

Whole-genome single nucleotide polymorphism-based linkage analysis in spondyloarthritis multiplex families reveals a new susceptibility locus in 13q13

International audienceAbstractObjective Spondyloarthritis (SpA) is a chronic inflammatory disorder with high heritability but with complex genetics. Apart from HLA-B27, most of the underlying genetic components remain to be identified. We conducted a whole-genome high-density non-parametric linkage analysis to identify new genetic factors of susceptibility to SpA.Methods 914 subjects including 462 with SpA from 143 multiplex families were genotyped using Affymetrix 250K microarrays. After quality control, 189 368 single nucleotide polymorphisms (SNPs) were kept for further analyses. Both non-parametric and parametric linkage analyses were performed using Merlin software. Association was tested with Unphased.Results Non-parametric linkage analysis identified two regions significantly linked to SpA: the major histocompatibility complex (LODmax=24.77) and a new 13q13 locus (LODmax=5.03). Additionally, eight loci achieved suggestive LOD scores, including the previously identified SPA2 locus at 9q33 (LODmax=3.51). Parametric analysis supported a codominant model in 13q13 with a maximum heterogeneity LOD, ‘HLOD’ score of 3.084 (α=0.28). Identification of meiotic recombination events around the 13q13 linkage peak in affected subjects from the 43 best-linked families allowed us to map the disease interval between 38.753 and 40.040 Mb. Family-based association analysis of the SNPs inside this interval in the best-linked families identified a SNP near FREM2 (rs1945502) which reached a p value close to statistical significance (corrected p=0.08).Conclusion We report here for the first time a significant linkage between 13q13 and SpA. Identification of susceptibility factor inside this chromosomal region through targeted sequencing in linked families is underway

Targeted resequencing of the 13q13 spondyloarthritis-linked locus identifies a rare variant in FREM2 possibly associated with familial spondyloarthritis

International audienceObjectives: The strong heritability of spondyloarthritis remains poorly explained, despite several large-scale association studies. A recent linkage analysis identified a new region linked to SpA on 13q13. Here we searched for variants potentially explaining this linkage signal by deep-sequencing of the region. Methods: Re-sequencing of the 1.4 Mb target interval was performed in 92 subjects from the 43 best-linked multicases families (71 spondyloarthritis and 21 unaffected relatives), using hybridization capture-based protocol (Illumina Nextera®). Variants of interest were then genotyped by TaqMan and high resolution melting to check their co-segregation with disease in the same families and to test their association with spondyloarthritis in an independent cohort of 1,091 unrelated cases and 399 controls. Expression of FREM2 was assessed by immunostaining. Results: Of the 7,563 variants identified, 24 were non-synonymous coding single-nucleotide variants. Two of them were located in the FREM2 gene on a haplotype co-segregating with the disease, including one common variant (R1840 W, minor allele frequency = 0.11) and one rare variant (R727H, minor allele frequency = 0.0001). In the case-control analysis, there was no significant association between R1840 W and spondyloarthritis (P-value = 0.21), whereas R727H was not detected in any of the genotyped individuals. Immunostaining experiments revealed that FREM2 is expressed in synovial membrane, cartilage and colon. Conclusions: Targeted re-sequencing of a spondyloarthritis-linked region allowed us to identify a rare non-synonymous coding variant in FREM2, co-segregating with spondyloarthritis in a large family. This gene is expressed in several tissues relevant to spondyloarthritis pathogenesis, supporting its putative implication in spondyloarthritis

Systematic candidate gene investigations in the SPA2 locus (9q32) show an association between TNFSF8 and susceptibility to spondylarthritis

Objective. Our group previously identified a new susceptibility region linked to spondylarthritis (SpA) on chromosome 9q31-34. Fine mapping of this SPA2 locus allowed us to refine the peak of linkage to a 1.3-Mb interval. The objective of this study was to resequence most positional candidate genes lying in that region, to identify polymorphisms, and to examine their association with SpA. Methods. Variants screening was performed in 30 independent patients with SpA from families with a high linkage score to the SPA2 locus and 30 control subjects. The coding regions, intron-exon boundaries, and 5'- and 3'-flanking regions of ZNF618, A1L4R1_HUMAN (AF495724), AMBP, KIF12, ORM1, ORM2, C9ORF91, ENSESTG000000230601, and TNFSF8 were resequenced to identify polymorphisms. Selected variants were genotyped in an extended French cohort (442 patients and 268 control subjects overall). Replication was performed in a combined Belgian and Portuguese cohort (433 patients and 299 control subjects). Results. Variants screening allowed us to identify 98 polymorphisms, 5 of which were selected for further studies, based on statistical significance. The rare intronic single-nucleotide polymorphism (SNP) rs3181357, located in TNFSF8, was significantly associated with SpA in the French and the replication cohorts (odds ratio [OR] 2.03, P = 0.009 and OR 2.26, P = 0.0014, respectively) and in the pooled analysis (OR 2.14, P = 0.0001). Conclusion. Positional candidate gene screening in the SPA2 locus allowed us to identify and replicate an association between a rare SNP located in TNFSF8 and SpA. This new finding appears to be independent of an association with a haplotype near TNFSF15, which we recently reported