Heterogeneity of axial spondyloarthritis: genetics, sex and structural damage matter

Rethinking spondyloarthritis: beyond lumping and splitting

PURPOSE OF REVIEW

The classification of spondyloarthritis (SpA) has long been debated, with ongoing discussions about whether to "lump" various subtypes together or "split" them into smaller distinct disease categories. This review explores the evolution of the SpA concept and discusses novel approaches that move beyond traditional models of SpA classification.

RECENT FINDINGS

Since its introduction in the 1970s, the SpA concept has undergone substantial modifications, incorporating advances in genetics, imaging, and clinical research. The recognition of axial and peripheral SpA as distinct yet overlapping entities has reshaped classification and drug approval processes. Data-driven methodologies have provided new insights into disease heterogeneity. Recent research highlights the limitations of traditional classification systems, emphasizing the need for unbiased approaches that integrate clinical and molecular features.

SUMMARY

Current historically derived classification paradigms for SpA are largely based on clinical phenotype and fail to capture the full spectrum of disease heterogeneity. Defining SpA subsets by incorporating genetic and immunological characteristics may improve diagnostic precision and improve outcomes. Future research should focus on refining classification frameworks across the entire clinical spectrum of SpA to improve patient stratification, guide treatment decisions, and address existing gaps in SpA care.

Performance of classification criteria for spondyloarthritis: where do we stand in many Latin American countries? A systematic literature review and meta-analysis

INTRODUCTION

Spondyloarthritis (SpA) encompasses a group of chronic inflammatory diseases affecting the spine and peripheral joints. Although classification criteria for SpA have been tested globally, their validity and performance in Latin American (LA) populations remain debated.

METHODS

A systematic literature review was conducted following PRISMA guidelines, with the protocol registered in PROSPERO (CRD42023464861). Searches were performed in Medline, Cochrane library, Embase and Virtual Health Library databases based on the PIRO framework. Studies assessing SpA classification criteria in LA patients were included, focusing on performance characteristics. Pooled sensitivity and specificity were estimated using a proportional meta-analysis with random-effect model, followed by sensitivity analysis.

RESULTS

Six studies met the inclusion criteria. Of the multinational studies, fewer than 10% included LA patients. Most of the studies evaluated the ASAS, the most recent criteria, and clinical diagnosis by a physician as the gold standard. The Amor criteria reported a pooled sensitivity of 71% and specificity of 46%. The ESSG criteria had a pooled sensitivity of 83% and specificity of 35%. The ASAS criteria had a pooled sensitivity of 75% and specificity of 43%.

CONCLUSIONS

These systematic literature review and meta-analysis, including SpA patients from six LA countries, suggest that the ASAS classification criteria offer the best balance for sensitivity and specificity. However, these findings highlight the need for high-quality, homogeneous studies to validate SpA classification criteria in LA populations as patient assessment continues to evolve.

Associations of sociodemographic, clinical factors and HLA-B alleles with enthesitis and peripheral arthritis in patients with ankylosing spondylitis

OBJECTIVES

Factors associated with peripheral arthritis and enthesitis, especially Achilles tendonitis and plantar fasciitis, were examined in a longitudinal cohort of 1075 patients with ankylosing spondylitis (AS) (also known as radiographic axial spondyloarthritis).

METHODS

Patients were derived from the Prospective Study of Outcomes in Ankylosing Spondylitis cohort. Disease activity and functional indices, as well as physical examination and medications used, were measured at every study visit. Univariable and multivariable analyses of the association of peripheral arthritis and enthesitis with clinical, sociodemographic factors were performed. Human leucocyte antigen (HLA)-B alleles were analysed by single-stranded conformational polymorphism analysis.

RESULTS

Those with peripheral arthritis on examination were more likely to have psoriasis (p=0.001, OR=1.68; CI, 1.11, 2.54), greater functional impairment (p<0.001 OR=1.72; CI, 1.31, 2.27), higher erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels (p<0.001), greater tumour necrosis factor (TNF) inhibitor (p<0.001, OR=1.50; CI, 1.14, 1.97) and use methotrexate/sulfasalazine (p<0.001, OR=2.25, CI [1.57, 3.23]). Patients with enthesitis were less likely to be male (p<0.001, OR=0.57; CI, 0.43, 0.75) and have peripheral arthritis (p<0.001, OR=2.35; CI, 1.47, 3.75), greater functional impairment (p<0.001, OR=1.91; CI, 1.43, 2.55) and higher ESR/CRP levels (p<0.001). Patients with plantar fasciitis and/or Achilles' tendonitis on examination were less likely to male (p<0.001 OR=0.57; CI, 0.43, 0.75), to have significant functional impairment (p<0.001), to be using TNF inhibitors (p<0.001, OR=1.48; CI 1.13, 1.93) and to be using either sulfasalazine or methotrexate (p<0.001, OR=1.86, CI, 1.30, 2.67). HLA-B*15 (p=0.03, OR=1.84; CI, 1.05, 3.21) and HLA-B*37 (p=0.04, OR=3.00; CI, 1.03, 8.74) were marginally increased in frequency in those with peripheral arthritis on examination compared with those without.

CONCLUSION

There was a higher prevalence of peripheral musculoskeletal manifestations in women with AS, with significant impact on physical function and greater use of methotrexate or sulfasalazine and TNF inhibitors and enrichment for certain non-HLA-B27 HLA-B alleles.

Sex differences in biomarkers and biologic mechanisms in psoriatic diseases and spondyloarthritis

Psoriasis and spondyloarthritis (SpA), including psoriatic arthritis (PsA), are immune-mediated inflammatory conditions that affect the skin and musculoskeletal system. Males and female patients with psoriatic disease and SpA exhibit differences in clinical presentation, disease progression, and treatment response. The underlying biological mechanisms driving these sex differences remain poorly understood. This review explores the current evidence on sex-related differences in biomarkers and biological pathways in psoriasis, PsA, and SpA. While no conclusive sex-specific biomarkers have been validated, this review highlights several sex-related differences in biomarkers and biological pathways, including differences in bone turnover markers, IL-23/IL-17 pathway activity, pro-inflammatory cytokines, and cardio-metabolic profiles that may partially contribute to the clinical differences observed between male and female patients. Sex hormones may contribute to the altered bone metabolism and immune regulation in females. To effectively identify and validate sex-specific biomarkers, there is a need to prioritize sex as a biological variable in future research. Adopting such an approach should enhance more personalized therapeutic strategies and improve management for male and female patients with psoriatic disease and SpA.

Fast, Present and Future of the Concept of Spondyloarthritis

PURPOSE OF REVIEW

Axial spondyloarthritis (axSpA) is a rather prevalent chronic inflammatory rheumatic disease that affects already relatively young patients. It has been known better since the end of the nineteenth century but quite a lot has been learned since the early 60ies when the first classification (diagnostic) criteria for ankylosing spondylitis (AS) were agreed on. I have been part of many developments in the last 30 years, and I'm happy to have been able to contribute to the scientific progress in terms of diagnosis, imaging, pathophysiology and therapy. When I was asked to write a manuscript about the SpA concept I felt honored. Thus, the purpose of this extensive review was, on the one hand, to describe the history of AS and axSpA, and on the other hand, to reason about the concept and the gestalt of axSpA, and finally to deliver some ideas what future researchers could possibly do to further study the disease.

RECENT FINDINGS

The last 3 decades were full of innovations for both, classification and treatment of axSpA which also helped us to learn about the pathophysiology. Thus, TNFa, IL-17, IL-23 and Janus kinase are established targets to reduce inflammation. IL-17 and IL-23 are very special in that regard because they both work for psoriasis but only anti-IL-17 agents which don't work in IBD are approved for axSpA, while IL 23 inhibitors are approved for both, psoriasis and IBD, but they don't work in axSpA. New imaging techniques such as low dose CT and synthetic MRI are likely to improve the detection of both active and structural lesions of axSpA. This manuscript tries to describe the most important findings about axSpA. The main aim of research remains to discover the pathophysiology and to further improve treatment options in order to reduce and abolish inflammation and prevent new bone formation to increase the quality of life of our patients. The differences between male and female disease and the role of the immune system in axSpA are now the main challenges, and the role of special T-cell receptors seem to deserve special interest.

Utility of polygenic risk scores to aid in the diagnosis of rheumatic diseases

Rheumatic diseases (RDs) are characterized by autoimmunity and autoinflammation and are recognized as complex due to the interplay of multiple genetic, environmental, and lifestyle factors in their pathogenesis. The rapid advancement of genome-wide association studies (GWASs) has enabled the identification of numerous single nucleotide polymorphisms (SNPs) associated with RD susceptibility. Based on these SNPs, polygenic risk scores (PRSs) have emerged as promising tools for quantifying genetic risk in this disease group. This chapter reviews the current status of PRSs in assessing the risk of RDs and discusses their potential to improve the accuracy of the diagnosis of these complex diseases through their ability to discriminate among different RDs. PRSs demonstrate a high discriminatory capacity for various RDs and show potential clinical utility. As GWASs continue to evolve, PRSs are expected to enable more precise risk stratification by integrating genetic, environmental, and lifestyle factors, thereby refining individual risk predictions and advancing disease management strategies.

[Sex-specific aspects in rheumatology]

Women and men differ in terms of the development and manifestation of inflammatory rheumatic diseases and outcomes as well as with respect to disease perception, health behavior and response to antirheumatic treatment. Sex-specific aspects are increasingly being researched in nearly all medical disciplines to optimize treatment strategies with the aim to improve individual treatment success. This article describes sex differences that can even now be taken into account in rheumatological care.

Differences between radiographic and non-radiographic axial spondyloarthritis patients in a Mexican cohort

To compare the demographic, clinical, and laboratory characteristics, disease onset, and clinical features of radiographic axial Spondyloarthritis (r-axSpA) and non-radiographic axial Spondyloarthritis (nr-axSpA) patients. All patients who attended outpatient spondylarthritis (SpA) clinics at Hospital General de Mexico and the Instituto Nacional de la Nutrición from 1998 to 2005 and met the rheumatologist diagnostic criteria for SpA were selected. Then the SpA patients were classified by European Spondyloarthropathy Study Group criteria (ESSG). We selected SpA patients with axial presentation as axial SpA (axSpA), and they were classified as r-axSpA if they met modified New York (mNY) criteria for sacroiliitis and as nr-axSpA if they did not meet mNY criteria; to compared clinical, demographic, and laboratory test between the subgroups. It included 148 SpA patients; 55 (37.2%) patients had r-axSpA, and 70 (47.3%) had nr-axSpA. The nr-axSpA patients had a lower proportion of males (58.6% vs 78.2%, P < 0.05), lower HLA-B27 frequency (54.3%. vs. 92.7%, P < 0.05), were older at disease onset (21 vs 16 years; P < 0.01) and had a higher frequency of infections at disease onset (9.1% vs 32.9, P < 0.05) than r-axSpA. BASFI (2.9 vs 4.8; P < 0.0001), Dougados functional index (7 vs. 14; P < 0.05), and BASDAI (4.1 vs. 5.2; P < 0.001) were lower in patients with nr-axSpA than r-axSpA, respectively. The factors that most influenced the presentation of r-axSpA were history of uveitis (OR 14, 95% CI 2.3-85), HLA-B27 (OR 7.97, 95% CI, 2.96-122), male sex (OR 6.16, 95% CI, 1.47-25.7), axial enthesopathy count (OR 1.17 95% CI, 1.03-1.33). This study provides insight into the differences between nr-axSpA and r-axSpA in Mexico. Patients with r-axSpA were mainly male, with a younger presentation age, a higher prevalence of HLA-B27, more history of uveitis, fewer episodes of dactylitis, more axial enthesopathy, and higher disease activity than nr-axSpA.

To be or not to B27 positive: implications for the phenotypes of axial spondyloarthritis outcomes. Data from a large multiracial cohort from the Brazilian Registry of Spondyloarthritis

BACKGROUND

There is a remarkable variability in the frequency of HLA-B27 positivity in patients with spondyloarthritis (SpA), which may be associated with different clinical presentations worldwide. However, there is a lack of data considering ethnicity and sex on the evaluation of the main clinical and prognostic outcomes in mixed-race populations. The aim of this study was to evaluate the frequency of HLA-B27 and its correlation with disease parameters in a large population of patients from the Brazilian Registry of Spondyloarthritis (RBE).

METHODS

The RBE is a multicenter, observational, prospective cohort that enrolled patients with SpA from 46 centers representing all five geographic regions of Brazil. The inclusion criteria were as follow: (1) diagnosis of axSpA by an expert rheumatologist; (2) age ≥18 years; (3) classification according to ASAS axial. The following data were collected via a standardized protocol: demographic data, disease parameters and treatment historical.

RESULTS

A total of 1096 patients were included, with 73.4% HLA-B27 positivity and a mean age of 44.4 (±13.2) years. Positive HLA-B27 was significantly associated with male sex, earlier age at disease onset and diagnosis, uveitis, and family history of SpA. Conversely, negative HLA-B27 was associated with psoriasis, higher peripheral involvement and disease activity, worse quality of life and mobility.

CONCLUSIONS

Our data showed that HLA-B27 positivity was associated with a classic axSpA pattern quite similar to that of Caucasian axSpA patients around the world. Furthermore, its absence was associated with peripheral manifestations and worse outcomes, suggesting a relevant phenotypic difference in a highly miscegenated population.

[Diagnosis and classification of axial spondyloarthritis (axSpA) - the current status]

Axial spondyloarthritis (axSpA) is an inflammatory rheumatic disease typically characterized by inflammatory back pain (IBP). The term axSpA has largely replaced the long-used term ankylosing spondylitis (AS). IBP is caused by inflammation in the axial skeleton, with the sacroiliac joints (SIJ) being particularly frequently affected initially. The spine is usually added in later stages, which is then increasingly characterized structurally by the formation of new bone. The overall concept of spondyloarthritis includes other disease manifestations such as uveitis, psoriasis and colitis and comorbidities such as cardiovascular disease and osteoporosis.The ASAS classification criteria for axSpA, in place since 2009, have replaced the 1984 modified New York criteria. In the former, in addition to conventional X-rays, changes in the SIJ detected by magnetic resonance imaging (MRI) and also the detection of HLA B27 have, for the first time, played a role. It is important to note that these are not diagnostic criteria, as they do not exist. This paper outlines 10 points that should be considered when making a diagnosis.

Polygenic risk scores

Polygenic risk scores (PRS) estimate an individual's genetic risk for a disease or trait compared to a matched population. For many rheumatic diseases PRS have been developed that have discriminatory capacity better than some widely used biomarkers, and in some cases are the most discriminatory tests available. These PRS assessments do not rely on the disease being present or its activity level, making them highly valuable for predicting disease development or enabling early diagnosis. However, most PRS to date have been developed in research settings, and in populations of European-ancestry. Further studies are required to assess their utility in clinical settings, in relation to existing tests, and in non-European populations. Such studies are underway, and it is likely in the near future these tests will become widely available, with significant benefits for the practice of medicine.

Dry and wet experiments reveal diagnostic clustering and immune landscapes of cuproptosis patterns in patients with ankylosing spondylitis

Cuproptosis is a new manner of mitochondrial cell death induced by copper. There is evidence that serum copper has a crucial impact on ankylosing spondylitis (AS) by copper-induced inflammatory response. However, the molecular mechanisms of cuproptosis modulators in AS remain unknown. We aimed to use a bioinformatics-based method to comprehensively investigate cuproptosis-related subtype identification and immune microenvironment infiltration of AS. Additionally, we further verified the results by in vitro experiments, in which peripheral blood and fibroblast cells from AS patients were used to evaluate the functions of significant cuproptosis modulators on AS. Finally, eight significant cuproptosis modulators were identified by analysis of differences between controls and AS cases from GSE73754 dataset. Eight prognostic cuproptosis modulators (LIPT1, DLD, PDHA1, PDHB, SLC31A1, ATP7A, MTF1, CDKN2A) were identified using a random forest model for prediction of AS risk. A nomogram model of the 8 prognostic cuproptosis modulators was then constructed; the model could be beneficial in clinical settings, as indicated by decision curve analysis. Consensus clustering analysis was used to divide AS patients into two cuproptosis subtypes (clusterA & B) according to significant cuproptosis modulators. The cuproptosis score of each sample was calculated by principal component analysis to quantify cuproptosis subtypes. The cuproptosis scores were higher in clusterB than in clusterA. Additionally, cases in clusterA were closely associated with the immunity of activated B cells, Activated CD4 T cell, Type17 T helper cell and Type2 T helper cell, while cases in clusterB were linked to Mast cell, Neutrophil, Plasmacytoid dendritic cell immunity, indicating that clusterB may be more correlated with AS. Notably, key cuproptosis genes including ATP7A, MTF1, SLC31A1 detected by RT-qPCR with peripheral blood exhibited significantly higher expression levels in AS cases than controls; LIPT1 showed the opposite results; High MTF1 expression is correlated with increased osteogenic capacity. In general, this study of cuproptosis patterns may provide promising biomarkers and immunotherapeutic strategies for future AS treatment.

Identification of patient endotypes and adalimumab treatment responders in axial spondyloarthritis using blood-derived extracellular matrix biomarkers

OBJECTIVE

To explore the potential of a panel of ECM remodelling markers as endotyping tools for axial spondyloarthritis (axSpA) by separating patients into subtypes and investigate how they differ among each other in disease activity scores and response to treatment with adalimumab.

METHODS

In three axSpA studies, a panel of 14 blood-based ECM biomarkers related to formation of collagen (PRO-C2, PRO-C3, PRO-C6), degradation of collagen by metalloproteinases (C1M, C2M, T2CM, C3M, C4M, C6M, C10C), matrix metalloproteinase (MMP)-degraded prolargin (PROM), MMP-degraded and citrullinated vimentin (VICM), basement membrane turnover (PRO-C4) and neutrophil activity (CPa9-HNE) were assessed to enable patient clustering (endotyping). MASH (n=41) was a cross-sectional study, while Adalimumab in Axial Spondyloarthritis study (ASIM,n=45) and Danish Multicenter Study of Adalimumab in Spondyloarthritis (DANISH, n=49) were randomised, double-blind placebo-controlled trials of adalimumab versus placebo every other week for 6 or 12 weeks, respectively, followed by active treatment. Biomarker data were log-transformed, standardised by mean centering and scaled by the SD prior to principal component analysis and K-means clustering.

RESULTS

Based on all three studies, we identified two orthogonal dimensions reflecting: (1) inflammation and neutrophil activity (driven by C1M and CPa9-HNE) and (2) collagen turnover (driven by PRO-C2). Three endotypes were identified: high inflammation endotype (Endotype1), low inflammation endotype (Endotype 2) and high collagen turnover endotype (Endotype3). Endotype1 showed higher disease activity (Ankylosing Spondylitis Disease Activity Score (ASDAS)) at baseline compared with Endotype2 and Endotype3 and higher percentage of patients responding to adalimumab based on ASDAS clinical improvement at week 24. Endotype3 showed higher percentage of patients with 50% improvement in Bath Ankylosing Spondylitis Disease Activity Index response at week 24 compared with Endotype2.

CONCLUSION

These endotypes differ in their tissue remodelling profile and may in the future have utility for patient stratification and treatment tailoring.

HLA-B*27 and Ankylosing Spondylitis: 50 Years of Insights and Discoveries

PURPOSE OF REVIEW

To commemorate the 50th anniversary of the groundbreaking discovery of a remarkably strong association between HLA-B*27 and ankylosing spondylitis (AS).

RECENT FINDINGS

In addition to HLA-B*27, more than 116 other recognized genetic risk variants have been identified, while epigenetic factors largely remain unexplored in this context. Among patients with AS who carry the HLA-B*27 gene, clonally expanded CD8 + T cells can be found in their bloodstream and within inflamed tissues. Moreover, the α and β chain motifs of these T-cell receptors demonstrate a distinct affinity for certain self- and microbial-derived peptides, leading to an autoimmune response that ultimately results in the onset of the disease. These distinctive peptide-binding and presentation characteristics are a hallmark of the disease-associated HLA-B*27:05 subtype but are absent in HLA-B*27:09, a subtype not associated with the disease, differing by only a single amino acid. This discovery represents a significant advancement in unraveling the 50-year-old puzzle of how HLA-B*27 contributes to the development of AS. These findings will significantly accelerate the process of identifying peptides, both self- and microbial-derived, that instigate autoimmunity. This, in return, will pave the way for the development of more accurate and effective targeted treatments. Moreover, the discovery of improved biomarkers, in conjunction with the emerging technology of electric field molecular fingerprinting, has the potential to greatly bolster early diagnosis capabilities. A very recently published groundbreak paper underscores the remarkable effectiveness of targeting and eliminating disease-causing T cells in a HLA-B*27 patients with AS. This pivotal advancement not only signifies a paradigm shift but also bolsters the potential for preventing the disease in individuals carrying high-risk genetic variants.

Causal relationship between endometriosis with infertility and ankylosing spondylitis

Retrospective studies have identified an increased risk of ankylosing spondylitis (AS) in endometriosis patients. The purpose of this study was to investigate the causal relationship between clinical phenotypes of endometriosis and AS using mendelian randomized analysis (MR). MR was performed using data from genome-wide association studies (GWASs). Heterogeneity, pleiotropy and sensitivity analyses were performed to evaluate the robustness of the results by MR Egger and inverse variance weighted (IVW), leave-one-out analysis. IVW, IVW-MRE (inverse variance weighted multiplicative random effects), weighted median and MR Egger were used to explore the relationship between endometriosis and AS. The IVW analysis showed a causal relationship between infertile endometriosis and AS (OR = 0.8334, P = 0.02191), and the same result was observed with IVW-MRE (OR = 0.8334, P = 0.0007933). However, further stratified analysis showed that no matter which statistical method was used, ovarian endometriosis (IVW: OR = 0.1662, P = 0.4986; IVW-MRE: OR = 0.1662, P = 0.4986; MR Egger: OR = - 0.9577, P = 0.2798; Weighted median: OR = 0.2628, P = 0.3452), pelvic peritoneum endometriosis (IVW: OR = 0.4363, P = 0.225; IVW-MRE: OR = 0.4363, P = 0.225, MR Egger: OR = 4.159, P = 0.1705; Weighted median: OR = 0.4112, P = 0.2714), rectovaginal endometriosis (IVW: OR = 0.1365, P = 0.805; IVW-MRE: OR = 0.1365, P = 0.805) there was no causal relationship between endometriosis and AS. This study suggested that patients with infertility endometriosis are at increased risk for AS. This study supports clinicians to pay more attention to the occurrence of AS in endometriosis patients with infertility.

Impact of sex on spinal radiographic progression in axial spondyloarthritis: a longitudinal Swiss cohort analysis over a period of 10 years

OBJECTIVE

To investigate sex differences in spinal radiographic progression in axial spondyloarthritis (axSpA).

METHODS

AxSpA patients in the Swiss Clinical Quality Management cohort with available spinal radiographs every 2 years were included. Paired radiographs were scored by two readers according to the modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS). Progression was defined as an increase of ≥2 mSASSS units in 2 years. The relationship between sex and progression was investigated with binomial generalised estimating equation models, considering baseline spinal damage as an intermediate covariate. Additional analyses included adjustments for explanatory variables and multiple imputations for missingness.

RESULTS

In a total of 505 axSpA patients (317 men and 188 women), mean±SD radiographic progression over 2 years was 1.0±2.8 years in men and 0.3±1.1 years in women (p<0.001). Male sex was associated with enhanced progression in a small model not including baseline damage (OR 3.41, 95% CI 1.87 to 6.21). Both a direct effect of male sex on spinal progression, and an indirect effect, via enhancement of baseline spinal damage were significant (OR 2.06, 95% CI 1.15 to 3.67 and OR 1.04, 95% CI 1.01 to 1.07, respectively). A significant impact of male sex on spinal radiographic progression was still demonstrated after multiple adjustments for covariates known to potentially affect spinal radiographic progression (OR 1.97, 95% CI 1.04 to 3.71).

CONCLUSIONS

Spinal radiographic progression in axSpA is more severe in men than in women, with three times higher odds of progression in male patients and an effect that is mediated in part through an increase in baseline radiographic damage.

HLA-B27 positivity in a large miscegenated population of 5,389,143 healthy blood marrow donors in Brazil

BACKGROUND

The prevalence of HLA-B27 gene positivity in healthy Caucasian communities varies between 8 and 14%. However, there is a lack of information in countries with a high rate of miscegenation, such as Brazil.

AIM

To estimate the frequency of HLA-B27 in the Brazilian general population using a large national registry database.

METHODS

This is a cross-sectional ecological study using the Brazilian Registry of Volunteer Bone Marrow Donors (REDOME) database on HLA-B27 allelic frequency and proportion of positives of healthy donors (18-60 years old). Data were analyzed according to sex, age, race (by self-reported skin color recommended by the Brazilian Institute of Geography and Statistics - IBGE), and geographic region of residence.

RESULTS

From 1994 to 2022, a total of 5,389,143 healthy bone marrow donors were included. The overall positivity for HLA-B27 was 4.35% (CI 95% 4.32-4.37%), regardless of sex and age (57.2% were women, mean age was 41.7yo). However, there was a difference between races: 4.85% in Whites; 2.92% in Blacks; 3.76% in Pardos (Browns i.e. mixed races); 3.95% in Amarelos (Yellows i.e. Asian Brazilians); and 3.18% in Indigenous. There was also a difference regarding geographic region of residence (North: 3.62%; Northeast: 3.63%; Southeast: 4.29%; Midwest: 4.5% and 5.25% in South). The homozygosity rate for the HLA-B27 was 1.32% of all the positives and only 0.06% in the general population.

CONCLUSIONS

Our findings provide the first Brazilian national prevalence for HLA-B27 in 4.35%. There is a gradient gene positivity from North to South, suggesting that the genetic background related to the miscegenation due to colonization, slavery, and some later waves of immigration together with internal migratory flows, could explain our findings.