Genetic variants of ABCG2, common and rare, increased the risk of gout. Non-synonymous allelic variants of ABCG2 had a significant effect on earlier onset of gout and the presence of a familial gout history. ABCG2 should thus be considered a common and significant risk factor for gout.

The Roma represents a transnational ethnic group, with a current European population of 8-10 million. The evolutionary process that had the greatest impact on the gene pool of the Roma population is called the founder effect. Renal hypouricemia (RHUC) is a rare heterogenous inherited disorder characterized by impaired renal urate reabsorption. The affected individuals are predisposed to recurrent episodes of exercise-induced nonmyoglobinuric acute kidney injury and nephrolithiasis. To date, more than 150 patients with a loss-of-function mutation for the SLC22A12 (URAT1) gene have been found, most of whom are Asians. However, RHUC 1 patients have been described in a variety of ethnic groups (e.g., Arab Israelis, Iraqi Jews, Caucasians, and Roma) and in geographically noncontiguous countries. This study confirms our previous findings regarding the high frequency of SLC22A12 variants observed. Frequencies of the c.1245_1253del and c.1400C>T variants were found to be 1.92% and 5.56%, respectively, in a subgroup of the Roma population from five regions in three countries: Slovakia, Czech Republic, and Spain. Our findings suggested that the common dysfunction allelic variants of URAT1 exist in the general Roma population and thus renal hypouricemia should be kept in differential diagnostic algorithm on Roma patients with defect in renal tubular urate transport. This leads to confirm that the genetic drift in the Roma have increased the prevalence of hereditary disorders caused by very rare variants in major population.

Background and objectivesIn the present study, we describe the identification and functional analysis of allelic variants in the ABCG2 gene, a physiologically important urate transporter whose dysfunction plays a major role in pathogenesis of gout, in a cohort with primary hyperuricemia and gout.Materials and methodsThe cohort consisted of 128 individuals: 29/99 primary hyperuricemics/gout. The definition of hyperuricemia was as follows: >420/360 µmol/l at two repeated measurements at intervals of at least 4 weeks in men/women. Gouty arthritis was diagnosed according to the 1977 preliminary criteria of the American College of Rheumatology for acute arthritis of gout. Patients suffering from secondary gout were excluded. We analysed 15 exons of ABCG2 by PCR amplification and sequenced directly. The functional analysis of identified allelic variants is in process (Xenopus oocyte, HEK cells).ResultsIn the ABCG2 gene, 16 intronic sequence variants and seven exon variants were detected. In the case of c.689+1G >A, related to an individual with severe gouty phenotype, two abnormal splicing variants were identified: a) r.[532_689del]; b) r.[532_689del], r.[944_949del]. Identified deletions lead to frameshift and premature stop codon introduction.From the 7 exon variants detected, there were five non-synonymous: p.V12M (rs2231137), p.Q141K (rs2231142), p.T153M (rs753759474), p.F373C (rs752626614) and p.D620N (rs34783571). Heterozygous p.V12M variant was detected in seven individuals. Variant p.T153M, p.F373C and p.D620N was detected once in heterozygous state. Variants p.T153M and p.F373C were in silico predicted using Polyphen and Sift program as a probably damaging. The p.Q141K, previously functionally characterised allelic variant with an strong effect on uric acid secretion impairment, was in cohort of hyperuricemic/gout patients presented with higher frequency: 40 heterozygotes/5 homozygotes, allele frequency 0.195 than in population of European origin (MAF = 0.09) and world-wide population (MAF = 0.12).ConclusionsOur results show that genetic factor ABCG2 should be considered to be one of the common risks for hyperuricemia/gout. In clinical practice, ABCG2 dysfunction can be estimated easily by genotyping and these findings will help to recognise a trait of hyperuricemia at a very early stage. This study was supported by the grants from the Czech Republic Ministry of Health AZV 15–26693A and the IMI-funded project BeTheCure 115142–2f.

BackgroundThe urate transporter ABCG2 is one of the genetic determinants of serum uric acid concentrations1.ObjectivesIn the present study, we describe the identification and functional analysis of allelic variants in the ABCG2 gene, a physiologically important urate transporter whose dysfunction plays a major role in pathogenesis of gout, in a cohort with primary hyperuricemia and gout.MethodsThe cohort consisted of 150 individuals: 32/118 primary hyperuricemics/gout. The definition of hyperuricemia was as follows: >420/360 μmol/l at two repeated measurements at intervals of at least 4 weeks in men/women. Gouty arthritis was diagnosed according to the 1977 preliminary criteria of the American College of Rheumatology for acute arthritis of gout. Patients suffering from secondary gout were excluded. We analyzed 15 exons of ABCG2 gene by PCR amplification and sequenced directly. The functional analysis of identified allelic variants is in process (HEK cells).ResultsIn the ABCG2 gene, 16 intronic sequence variants were detected. In the case of c.689+1G>A, related to an individual with severe gouty phenotype, two abnormal splicing variants were identified: a) r.[532_689del]; b) r.[532_689del], r.[944_949del]. Identified deletions lead to frameshift and premature stop codon introduction2.From the nine exon variants detected, there were seven non-synonymous: p.V12M (rs2231137), p.Q141K (rs2231142), p.R147W (rs372192400), p.T153M (rs753759474), p.F373C (rs752626614), p.T434M (rs769734146) and p.D620N (rs34783571). Heterozygous p.V12M variant was detected in seven individuals. Heterozygous variant p.R147W, p.T153M, p.F373C and p.D620N was detected once, variant p.D620N was detected twice also in heterozygous state. Variants p.R147W, p.T153M, p.F373C and p.T434M were in silico predicted using Polyphen, Sift and Provean program as a probably damaging. The p.Q141K, previously functionally characterized allelic variant with a strong effect on uric acid secretion impairment, was in cohort of hyperuricemic/gout patients presented with significantly higher allele frequency MAF=0.19 (42 heterozygotes/5 homozygotes), than in population of European origin (MAF=0.09) and world-wide population (MAF=0.12).ConclusionsOur results show that genetic factor ABCG2 should be considered as one of the common risks for hyperuricemia/gout. In clinical practice, ABCG2 dysfunction can be estimated easily by genotyping and these findings will help to recognize a trait of hyperuricemia at a very early stage.ReferencesStibůrková B, Pavlíková M, Sokolová J, Kožich V. Metabolic syndrome, alcohol consumption and genetic factors are associated with serum uric acid concentration. PLoS One. 2014 May 14;9(5):e97646.Stiburkova B, Miyata H, Závada J, Tomčík M, Pavelka K, Storkanova G, Toyoda Y, Takada T, Suzuki H. 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.AcknowledgementThis study was supported by the grants from the Czech Repu...