ObjectiveA genome-wide association study (GWAS) of gout and its subtypes was performed to identify novel gout loci, including those that are subtype-specific.MethodsPutative causal association signals from a GWAS of 945 clinically defined gout cases and 1213 controls from Japanese males were replicated with 1396 cases and 1268 controls using a custom chip of 1961 single nucleotide polymorphisms (SNPs). We also first conducted GWASs of gout subtypes. Replication with Caucasian and New Zealand Polynesian samples was done to further validate the loci identified in this study.ResultsIn addition to the five loci we reported previously, further susceptibility loci were identified at a genome-wide significance level (p<5.0×10−8): urate transporter genes (SLC22A12 and SLC17A1) and HIST1H2BF-HIST1H4E for all gout cases, and NIPAL1 and FAM35A for the renal underexcretion gout subtype. While NIPAL1 encodes a magnesium transporter, functional analysis did not detect urate transport via NIPAL1, suggesting an indirect association with urate handling. Localisation analysis in the human kidney revealed expression of NIPAL1 and FAM35A mainly in the distal tubules, which suggests the involvement of the distal nephron in urate handling in humans. Clinically ascertained male patients with gout and controls of Caucasian and Polynesian ancestries were also genotyped, and FAM35A was associated with gout in all cases. A meta-analysis of the three populations revealed FAM35A to be associated with gout at a genome-wide level of significance (pmeta=3.58×10−8).ConclusionsOur findings including novel gout risk loci provide further understanding of the molecular pathogenesis of gout and lead to a novel concept for the therapeutic target of gout/hyperuricaemia.

ObjectiveGout is characterised by severe interleukin (IL)-1-mediated joint inflammation induced by monosodium urate crystals. Since IL-37 is a pivotal anti-inflammatory cytokine suppressing the activity of IL-1, we conducted genetic and functional studies aimed at elucidating the role of IL-37 in the pathogenesis and treatment of gout.MethodsVariant identification was performed by DNA sequencing of all coding bases of IL37 using molecular inversion probe-based resequencing (discovery cohort: gout n=675, controls n=520) and TaqMan genotyping (validation cohort: gout n=2202, controls n=2295). Predictive modelling of the effects of rare variants on protein structure was followed by in vitro experiments evaluating the impact on protein function. Treatment with recombinant IL-37 was evaluated in vitro and in vivo in a mouse model of gout.ResultsWe identified four rare variants in IL37 in six of the discovery gout patients; p.(A144P), p.(G174Dfs*16), p.(C181*) and p.(N182S), whereas none emerged in healthy controls (Fisher’s exact p-value=0.043). All variants clustered in the functional domain of IL-37 in exon 5 (p-value=5.71×10−5). Predictive modelling and functional studies confirmed loss of anti-inflammatory functions and we substantiated the therapeutic potential of recombinant IL-37 in the treatment of gouty inflammation. Furthermore, the carrier status of p.(N182S)(rs752113534) was associated with increased risk (OR=1.81, p-value=0.031) of developing gout in hyperuricaemic individuals of Polynesian ancestry.ConclusionHere, we provide genetic as well as mechanistic evidence for the role of IL-37 in the pathogenesis of gout, and highlight the therapeutic potential of recombinant IL-37 for the treatment of gouty arthritis.

Objective The Māori and Pacific (Polynesian) population of Aotearoa New Zealand (NZ) has a high prevalence of gout. Our aim was to identify potentially functional missense genetic variants in candidate inflammatory genes amplified in frequency that may underlie the increased prevalence of gout in Polynesian populations. Methods A list of 712 inflammatory disease-related genes was generated. An in silico targeted exome set was extracted from whole genome sequencing data in people with gout of various ancestral groups (Polynesian, European, East Asian; n = 55, 780, 135, respectively) to identify Polynesian-amplified common missense variants (AF > 0.05). Candidate functional variants were tested for association with gout by multivariable-adjusted regression analysis in 2,528 individuals of Polynesian ancestry. Results We identified 26 variants common in the Polynesian population and uncommon in the European and East Asian populations. Three of the 26 population-specific variants were nominally associated with the risk of gout (rs1635712, KIAA0319, ORmeta = 1.28, Pmeta = 0.028; rs16869924, CLNK, ORmeta = 1.37, Pmeta = 0.0017; rs2070025, FGA, ORmeta = 1.34, Pmeta = 0.017). The CLNK variant, within the established SLC2A9 gout locus, was genetically-independent of the association signal at SLC2A9. Conclusion We provide nominal evidence for the existence of population-amplified genetic variants conferring risk of gout in Polynesian populations. Polymorphisms in CLNK have previously been associated with gout in other populations, supporting our evidence for association of this gene with gout.

BackgroundMitochondria execute critical roles in diverse cellular pathways. As a danger signal mitochondria induce inflammation in response to stress through NLRP3 inflammasome activation, central to gout development. We recently reported association of reduced mtDNA copy number (CN) with prevalent gout in New Zealand Māori and Pacific (Polynesian) populations1. However the cause-effect relationship is unknown. This could be evaluated by testing for association with gout using nuclear genetic variants that associate with mtDNA CN.Objectives1) Genome wide association study (GWAS) for mtDNA CN to identify nuclear and mitochondrial loci controlling mtDNA copy number 2) test any such loci for association with gout.MethodsThe mtDNA CN GWAS comprised 1340 Eastern Polynesian (EP), 816 Western Polynesian (WP) and 4579 European samples (New Zealand, Germany, The Netherlands, Scotland) genotyped on the Illumina CoreExome v24 array. 343 mitochondrial single nucleotide polymorphisms (SNPs) were evaluated. As previously described2 the median of the absolute difference in X and Y probe intensities was used as a measure of mtDNA CN, and additional 10 000 randomly selected autosomal SNPs were used to calculate the principal components (PCs). A mtDNA CN GWAS was run on chromosomes 1–22 and the mitochondrial genome using Plink 1.9 .v2, adjusting for the first 10 PCs, age and sex followed by association analysis with gout adjusting by age, sex and the first 10 PCs generated from a separate set of 3000 autosomal SNPs.ResultsThe association of reduced mtDNA CN with gout in the EP and WP groups was reproduced but there was no evidence of association of mtDNA CN with gout in Europeans. Two genome-wide significant (p<1x10–7) variants MUC17 rs78010183 (T-allele) and SLC16A8 rs75640043 (T-allele) were associated with increased mitochondrial CN in EP and WP, respectively, and mitochondrial variant rs3928306 was associated with mtDNA CN (p=4.49x10–12) in Europeans. MUC17 rs78010183 also associated with increased mtDNA CN in Europeans, with the T allele also increasing CN (β=0.06, p=1.07x10–4). The T-allele of rs78010183 was associated with gout in Europeans (OR=9.32, p=5.53x10–3) and the SLC16A8 rs75640043 T-allele was associated with gout in the WP group (OR=6.85, p=5.50x10–3). The mitochondrial variant rs3928306 A-allele (very rare in Polynesian) was not associated with gout in Europeans (OR=1.09, p=0.36).ConclusionsThat genetic variants associated with mitochondrial copy number also associate with gout provides evidence for a potential causal role of mitochondrial copy number in gout. However, the nuclear genetic variants support a causal relation of increased mtDNA CN with gout, conflicting with our previous observational report of association of reduced mtDNA CN with gout1.References[1] Gosling A, et al. Mitochondrial genetic variation and gout in Māori and Pacific people living in Aotearoa New Zealand. Ann Rheum Dis2017Dec 15. [Epub ahead of print].[2] Asher FN, et al. Association of mitochondrial DNA levels with frailty and all-cause ...