Background and objectives In 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 methods The 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).
Results In 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).
Conclusions Our 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.