Genetic polymorphisms and decreased protein expression of ABCG2 urate transporters are associated with susceptibility to gout, disease severity and renal-overload hyperuricemia.

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.

Pattern of SQSTM1 Gene Variants in a Hungarian Cohort of Paget's Disease of Bone.

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.

Clinically relevant mutations in the ABCG2 transporter uncovered by genetic analysis linked to erythrocyte membrane protein expression.

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.