The ABCG2 membrane protein is a key xeno- and endobiotic transporter, modulating the absorption and metabolism of pharmacological agents and causing multidrug resistance in cancer. ABCG2 is also involved in uric acid elimination and its impaired function is causative in gout. Analysis of ABCG2 expression in the erythrocyte membranes of healthy volunteers and gout patients showed an enrichment of lower expression levels in the patients. By genetic screening based on protein expression, we found a relatively frequent, novel ABCG2 mutation (ABCG2-M71V), which, according to cellular expression studies, causes reduced protein expression, although with preserved transporter capability. Molecular dynamics simulations indicated a stumbled dynamics of the mutant protein, while ABCG2-M71V expression in vitro could be corrected by therapeutically relevant small molecules. These results suggest that personalized medicine should consider this newly discovered ABCG2 mutation, and genetic analysis linked to protein expression provides a new tool to uncover clinically important mutations in membrane proteins.

Gout is a common crystal induced disease of high personal and social burden, characterised by severe arthritis and comorbidity if untreated. Impaired function of ABCG2 transporter is causative in gout and may be responsible for renal-overload type hyperuricemia. Despite its importance, there is limited information on how clinical parameters correlate with protein expression and that with genetic changes. Urate and clinical parameters of 78 gouty patients and healthy controls were measured among standardised circumstances from a Hungarian population. ABCG2 membrane expression of red blood cells was determined by flow cytometry-based method and SNPs of this protein were analysed by TaqMan-based qPCR. The prevalence of ABCG2 functional polymorphisms in gouty and control patients were 32.1 and 13.7%, respectively. Most common SNP was Q141K while one sample with R236X, R383C and the lately described M71V were found in the gouty population. These polymorphisms showed strong linkage with decreased protein expression while the latter was also associated with higher fractional urate excretion (FUE) and urinary urate excretion (UUE). This study firstly evaluated ABCG2 protein expression in a clinically defined gouty population while also proving its associations between ABCG2 genetic changes and renal-overload hyperuricemia. The paper also highlighted relations between ABCG2 SNPs, gout susceptibility and disease severity characterised by an early onset disease with frequent flares and tophi formation.

Paget’s disease of bone (PDB) is characterized by focal or multifocal increase in bone turnover. One of the most well-established candidate genes for susceptibility to PDB is Sequestosome 1 (SQSTM1). Mutations in SQSTM1 have been documented among Western-European, British and American patients with PDB. However, there is no information on SQSTM1 mutation status in PDB patients from the Central- and Eastern-European regions. In this study, we conducted a mutation screening for SQSTM1 gene variants in 82 PDB patients and 100 control participants in Hungary. Mutations of SQSTM1 were detected in 18 PDB patients (21.95%); associations between genotype and clinical characteristics were also analyzed. Altogether, six different exonic alterations, including two types of UTR variants in the SQSTM1 gene, were observed in our PDB patients. Similarly, to previous genetic studies on Paget’s disease, our most commonly detected variant was the c.1175C > T (p.Pro392Leu) in nine cases (four in monostotic and five in polyostotic form). We have surveyed the germline SQSTM1 variant distribution among Hungarian patients with PDB. We also highlighted that the pattern of the analyzed disease-associated pathophysiological parameters could partially discriminate PDB patients with normal or mutant SQSTM1 genotype. However, our findings also underline and strengthen that not solely SQSTM1 stands in the background of the complex PDB etiology.

Background and objectives Several recent studies highlighted the importance of special gene loci related to gout and hyperuricaemia. However, it is remarkable that only a minor fraction of hyperuricemic population produces the symptoms of gout. Discussing the pathomechnism of gouty inflammation a potential autoinflammatory explanation has emerged recently. Induced by MSU crystals, the pathologic activity of a multi-protein complex (NLRP3 inflammasome) might be responsible for the increased activation of interleukin 1-beta (IL-1β), a cytokine playing a central role in inflamation. Toll-like receptors (TLR2–4) have also been studied for the stepped-up production of pre- IL-1β, the pre form of the active metabolit. Human erythrocytes express numerous membrane proteins, several of them already identified as homologue proteins to those with specific function in other tissue, such as urate transporters. Our objective was to verify genetical variations, single nucleotid polymorphisms (SNP) leading to hyperuricemia and gout. We also analysed these gene loci coded proteins linked to elevated urate level, using a unique technique (EryTest) based on the presence of special membrane proteins on human erythrocytes. Materials and methods We studied the results of three groups. Patients with gout, control patients with hyperuricemia but with no arthritic event and patients with normal serum uric acid level. Specific monoclonal antibodies and IgG control were used for quantitative flow cytometry to determine proteins. Polymorphism specific and control primers were used for polymerase chain reaction (PCR) detecting SNPs. Results Increased level of CARD8 polymorphism was found in the gout group compared to the two control groups. Decreased ABCG2 protein expression was detected in heterozygous individuals in gouty and hyperuricemic groups compared to normouricemic controls. Conclusions We presume that depending on complex genetic and environmental factors, patients with CARD8 polymorphisms may have increased inflammatory response and those with decreased ABCG2 protein expression may have higher serum urate levels. From the clinical introduction of EryTest, a simple and rapid clinical method in the evaluation of hyperuricemia is expected. To confirm recent results of genetic variability and the clinical use of EryTest, further investigation is planned.