Genome-wide and species-wide dissection of the genetics of arthritis severity in heterogeneous stock mice.

OBJECTIVE: Susceptibility to inflammatory arthritis is determined by a complex set of environmental and genetic factors, but only a portion of the genetic effect can be explained. Conventional genome-wide screens of arthritis models using crosses between inbred mice have been hampered by the low resolution of results and by the restricted range of natural genetic variation sampled. The aim of this study was to address these limitations by performing a genome-wide screen for determinants of arthritis severity using a genetically heterogeneous cohort of mice. METHODS: Heterogeneous stock (HS) mice derive from 8 founder inbred strains by serial intercrossing (n>60), resulting in fine-grained genetic variation. With a cohort of 570 HS mice, we performed a genome-wide screen for determinants of arthritis severity in the K/BxN serum-transfer model. RESULTS: We mapped regions on chromosomes 1, 2, 4, 6, 7, and 15 that contain quantitative trait loci influencing arthritis severity at a resolution of a few megabases. In several instances, these regions proved to contain 2 quantitative trait loci: the region on chromosome 2 included the C5 fraction of complement known to be required for K/BxN serum-transfer arthritis but also contained a second adjacent quantitative trait locus, for which an intriguing candidate is Ptgs1 (Cox1). Interesting candidates on chromosome 4 included the Padi family, encoding the peptidyl arginine deiminases responsible for citrulline protein modification; suggestively, Padi2 and Padi4 RNA expression was correlated with arthritis severity in HS mice. CONCLUSION: These results provide a broad overview of the genetic variation that controls the severity of K/BxN serum-transfer arthritis and suggest intriguing candidate genes for further study.

A broad analysis of IL1 polymorphism and rheumatoid arthritis.

OBJECTIVE: It has been suggested that polymorphisms in IL1 are correlated with severe and/or erosive rheumatoid arthritis (RA), but the implicated alleles have differed among studies. The aim of this study was to perform a broad and well-powered search for association between allelic polymorphism in IL1A and IL1B and the susceptibility to or severity of RA. METHODS: Key coding and regulatory regions in IL1A and IL1B were sequenced in 24 patients with RA, revealing 4 novel single-nucleotide polymorphisms (SNPs) in IL1B. These and a comprehensive set of 24 SNPs tagging most of the underlying genetic diversity were genotyped in 3 independent RA case-control sample sets and 1 longitudinal RA cohort, totaling 3,561 patients and 3,062 control subjects. RESULTS: No fully significant associations were observed. Analysis of the discovery case-control sample sets indicated a potential association of IL1B promoter region SNPs with susceptibility to RA (for RA3/A, odds ratio [OR] 1.27, P = 0.0021) or with the incidence of radiographic erosions (for RA4/C, OR 1.56, P = 0.036), but these findings were not replicated in independent case-control samples. No association with rheumatoid factor, anti-cyclic citrullinated peptide, or the Disease Activity Score in 28 joints was found. None of the associations previously observed in other studies were replicated here. CONCLUSION: In spite of a broad and highly powered study, we observed no robust, reproducible association between IL1A/B variants and the susceptibility to or severity of RA in white individuals of European descent. Our results provide evidence that, in the majority of cases, polymorphism in IL1A and IL1B is not a major contributor to genetic susceptibility to RA.

Comparison of 2 doses of etanercept (50 vs 100 mg) in active rheumatoid arthritis: a randomized double blind study.

OBJECTIVE: To assess the safety and efficacy of etanercept 50 mg administered twice weekly versus 25 mg administered twice weekly as monotherapy in patients with tumor necrosis factor-alpha (TNF-alpha) blocker-naäve active rheumatoid arthritis (RA). METHODS: Seventy-seven patients with RA were randomized in an unequal allocation (2:1) in a blinded fashion to receive either 50 mg (51 patients) or 25 mg (26 patients) of etanercept twice a week for 24 weeks. RESULTS: The primary outcome measure, the ACR-N AUC at 24 weeks, showed no difference between the 2 dose groups. In addition, there was no difference in ACR 20, 50, and 70 responses or in EULAR response criteria by Week 24. There were no statistically significant differences between the 2 groups in the proportion of patients with any non-infectious adverse event. The proportion of patients with upper respiratory tract infections was significantly higher in patients receiving 50 mg etanercept compared with those receiving 25 mg (26% vs 4%, p = 0.027). CONCLUSION: Etanercept as a monotherapy at 50 mg twice weekly does not provide increased efficacy when compared to the standard dose of 25 mg twice weekly in TNF-alpha blocker-naäve patients.