Objective. To characterize the alterations, as well as their mechanisms, induced in the HLA-B27-bound peptidome expressed in live cells by the natural ERAP1 polymorphisms predisposing to ankylosing spondylitis (AS): R528K and N575D/Q725R.Methods. HLA-B*27:05-bound peptides were isolated from 3 human lymphoid cell lines expressing distinct ERAP1 variants differing at residues 528 and/or 575/725. The high-performance liquid chromatographyfractionated peptide pools were compared by mass spectrometry based on identity of molecular mass and chromatographic retention time. The relative amount of each shared peptide in any given cell line pair was estimated from the respective ion peak intensities. Peptide sequencing was also carried out by mass spectrometry.Results. HLA-B27-bound ligands predominant in the context of the ERAP1 variant with K528 collectively showed higher molecular mass, higher frequency of N-terminal residues resistant to ERAP1, and bulkier residues downstream of the N-terminus, relative to peptides predominant in the R528 context. None of these differences were observed with ERAP1 variants differing at positions 575/725, but not at residue 528. Neither R528K nor N575D/Q725R altered the mean length of B*27:05-bound ligands.Conclusion. The R528K, but not the N575D/ Q725R, polymorphism alters the expression levels of many HLA-B*27:05-bound peptides, depending on the susceptibility of their N-terminal residues to trimming and depending on the size of the amino acid side chains at multiple positions downstream of the N-terminus. The significant alterations in the B*27:05 peptidome and the structural features of the peptides that determine their differential expression in distinct ERAP1 contexts account for the association of the R528K polymorphism with AS.

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Aim: Tumor necrosis factor inhibitors (TNFi) are effective in controlling disease activity in spondyloarthritis (SpA). However, in a proportion of patients these treatments are ineffective or lead to adverse events. Recently, alternative therapies, such as interleukin (IL)-17 or IL-23 inhibitors, have emerged in the treatment of these pathologies. This study aimed to determine clinical and genetic predictors of non-response to TNFi treatment in 118 spondyloarthritis patients diagnosed according to Assessment in SpondyloArthritis International Society (ASAS) criteria.Method: From the literature, 41 single nucleotide polymorphisms (SNPs) were selected that had previously been associated with TNFi treatment response in spondyloarthropathies, rheumatoid arthritis and psoriasis. A clinical non-response was defined as a decrease of <50% of initial Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) in axial involvement, or a reduction of less than 1.2 of initial Disease Activity Score of 28 joints-C-reactive protein (DAS28-CRP) in patients with only peripheral involvement. Univariate and multivariate hazard ratios (HR) were determined using Cox proportional hazard models to analyze the potential prognostic factors affecting non-response to TNFi treatment. Results:The clinical factors that significantly increased the non-response rate were: global visual analog scale (VAS), CRP, BASDAI, Bath Ankylosing Spondylitis Functional Index (BASFI), and the number of TNFi used. Only rs11591741 SNP showed an association with non-response. In the multivariate analysis, females had a non-response rate 4.46 times higher than males; each one-point increase in the BASFI index increased the non-response rate by 75%, and being a genotype GG vs GC or CC carrier was associated with an almost 4 times greater non-response rate. Conclusion:We developed a clinical-genetic model to identify SpA patients with a long-term non-response to TNFi therapy. K E Y W O R D Santi-TNF treatment, genetics, single nucleotide polymorphisms, spondyloarthritis

There is limited information on the underlying physiological mechanisms promoting obesity in patients with Prader-Willi syndrome (PWS). The aim of this study was to investigate whether body fat regulation in children with PWS is similar to that in children with non-syndromal obesity and non-obese children. We studied three groups: 1) 72 non-obese children and adolescents; 2) 68 children with non-syndromal obesity; and 3) 11 patients with PWS. Height and weight were measured and body mass index (BMI) and BMI SDS were calculated. Fasting serum leptin concentrations were determined. Median leptin serum concentrations were similar in PWS patients and children with non-syndromal obesity. Median leptin serum concentrations were higher in these two groups than in the non-obese group. Log leptin serum concentrations and BMI SDS showed significant correlations in the three groups of patients; correlation coefficients were 0.525, 0.285 and 0.854, respectively. In conclusion, median leptin serum concentrations are similar in PWS patients and children with non-syndromal obesity. The relationship between log serum leptin concentrations and BMI SDS was different in the three groups of patients studied.

Biologic and targeted synthetic disease-modifying antirheumatic drugs (ts/bDMARDs) play a pivotal role in the treatment of rheumatoid arthritis (RA), psoriatic arthritis (PsA), and ankylosing spondylitis (AS). Persistence of therapy provides an index of a drug’s overall effectiveness. The objective of the study was to identify factors associated with discontinuation of ts/bDMARDs in a real-world dataset. The study population comprised patients diagnosed with RA, PsA, and AS included in the BIOBADASER registry for whom follow-up data were available until November 2019. Patient features and treatment data were included in the analysis. The Kaplan–Meier method was used to study survival of the different drugs according to the reason for discontinuation. Factors associated with discontinuation were studied using Cox regression models and bivariate and multivariate analyses. P values of less than 0.05 were regarded as statistically significant. The study population comprised 4,752 patients who received a total of 8,377 drugs, of which 4,411 (52.65%) were discontinued. The Kaplan–Meier curves showed that survival for first-line treatment was greater in all 3 groups (p < 0.001). Patients with RA had a greater risk of discontinuation if they were younger (HR, 0.99; 95% CI 0.99–1.00), if they were receiving anti-TNFα agents (HR, 0.61; 95% CI 0.54–0.70), and if they had more comorbid conditions (HR, 1.09; 95% CI 1.00–1.17). Patients with PsA had a higher risk if they were women (HR, 1.36; 95% CI 1.15–1.62) and if they were receiving other ts/bDMARDs (HR, 1.29; 95% CI 1.05–1.59). In patients with AS, risk increased with age (HR, 1.01; 95% CI 1.00–1.02), as did the number of comorbid conditions (HR, 1.27; 95% CI 1.12–1.45). The factors that most affected discontinuation of ts/bDMARDs were line of treatment, age, type of drug, sex, comorbidity and the year of initiation of treatment. The association with these factors differed with each disease, except for first-line treatment, which was associated with a lower risk of discontinuation in all 3 diseases.