B. Stiburkova 1,3, K. Pavelcova 1,2, J. Bohata 1,2, M. Pavlikova 4, Y. Toyoda 5, T. Takada 5, H. Suzuki 5, L. Petru 1,2, J. Zavada 1, K. Pavelka 1
1. Institute of Rheumatology, Prague, Czech Republic; 2. Department of Rheumatology, First Faculty of Medicine, Charles University, Prague, Czech Republic; 3. Department of Pediatrics and Adolescent Medicine, First Faculty of Medicine, Charles University and General University Hospital In Prague, Prague, Czech Republic; 4. Department of Probability And Mathematical Statistics, Faculty of Mathematics And Physics, Charles University, Prague, Czech Republic; 5. Department of Pharmacy, The University of Tokyo Hospital, Tokyo, Japan
Objective: The urate transporters are one of the main genetic determinants of serum uric acid concentrations. In this study we investigated the effects of non-synonymous allelic variants of 10 genes of urate transportosome in a cohort of patients with primary gout and/or asymptomatic hyperuricemia.
Methods: The cohort consisted of 207 gout patients; 114 hyperuricemic individuals; 274 normouricemic controls were used for comparison. Gouty arthritis was diagnosed according to the 1977 preliminary criteria of the American College of Rheumatology. Coding regions of ABCG2, SLC22A12, SLC2A9, SLC17A3, SLC17A1, SLC22A13, SLC22A11, ABCC4/MRP4, SLC22A6, and SLC22A8 genes were amplified and sequenced directly.
Results: We identified 39 non-synonymous allelic variants in the urate transportosome in the hyperuricemia/gout cohort. For 22 variants, a European MAF <0.0001 is documented. From the total of 39 identified non-synonymous allelic variants in the cohort of patients with hyperuricemia/gout, we selected 23 variants for functional characterization based on a) finding of a newly identified variant, b) MAF variant was significantly different in the group of patients with hyperuricemia/gout, c) with high probability, in silico predictions showed devastating influence of each variant on protein function (PolyPhen, Provean, Mutation Taster, SIFT, Human Splicing Finder, MutPred predictive software). From those 39 variants, 16 were in ABCG2 genes (two common, ten rare and three novel) and we published the function characterization on urate uptake in most of them previously [1,3]. In the context of urate transport the precise impact of identified variants in SLC17A1, SLC22A13, SLC22A11, SLC22A6 and SLC22A8 (totally 10 rare allelic variants included four novel) is unclear and we are performing further studies to include functional characterization of these selected dysfunctional variants. Of the identified non-synonymous allelic variants of the urate transportosome, rs2231142 (common dysfunction variant p.Q141K) in the ABCG2 gene proved to be the most clinically significant: its frequency in the European population is 0.094, in our cohort it occurred with a frequency of 0.239 (0.219 in hyperuricemic subcohort, 0.249 in gout subcohort). The median age of onset among patients with zero, one, or two variants p.Q141K were 42, 40, and 22 years, respectively (P < 0.0002, Kruskal-Wallis test).
Conclusions: Although further analyzes are needed to elucidate the contribution of urate transportosome to urate homeostasis, our results clearly show that ABCG2 transporter analysis has significant clinical potential in terms of frequency and functional effects of allelic variants. Genetic variants of ABCG2, regardless of frequency - common or rare, increased the risk of gout and had a significant effect on earlier onset of gout and the presence of a familial gout history.
References: 1. Toyoda Y, et al. Functional Characterization of Clinically-Relevant Rare Variants in ABCG2 Identified in a Gout and Hyperuricemia Cohort. Cells. 2019 Apr 18;8(4). 2. Stiburkova B, et al. Novel dysfunctional variant in ABCG2 as a cause of severe tophaceous gout: biochemical, molecular genetics and functional analysis. Rheumatology (Oxford). 2016 Jan;55(1):191-4. 3. Toyoda Y, Pavelcová K, Klein M, Suzuki H, Takada T, Stiburkova B. Familial early-onset hyperuricemia and gout associated with a newly identified dysfunctional variant in urate transporter ABCG2. Arthritis Res Ther. 201.