Variable number of tandem repeats polymorphism of MUC20 is associated with the progression of IgA nephropathy

Abstract

The MUC20 gene is a novel up-regulated gene that was identified in renal tissues of patients with IgA nephropathy (IgAN) by restriction endonucleolytic analysis of differentially expressed sequences. The variable number of tandem repeats (VNTR) polymorphism of MUC20 was detected in different cell lines. In this study we determined the distribution of MUC20 VNTR polymorphism in the healthy population, and the association between the MUC20 VNTR polymorphism and the pathogenesis or progression of IgAN. 282 healthy and 503 proved IgAN patients by biopsy were involved in this investigation. 113 patients had been followed-up for 3.5 +/- 1.5 years. Genomic DNAs were extracted from peripheral blood leucocytes. MUC20 VNTR polymorphism was detected by PCR amplification and several representational PCR products were confirmed by sequencing. The MUC20 genes were divided into small alleles (repeat times <or= 3) and large alleles (repeat times > 3) according to the repeat times of MUC20 VNTR. These patients were classified into group SS, SL and LL. MUC20 allele frequencies and genotypes of IgAN patients were analyzed and compared with healthy population. In addition, the associations of MUC20 polymorphism with the clinical and pathological parameters at the time of renal biopsy were analyzed. The data followed up in different groups were compared. There was MUC20 VNTR polymorphism in healthy population with 2 - 6 repeats. The repeat fragment was 57bp. The most frequent alleles included 3(R(3)) and 4(R(4)) repeats; otherwise the least ones included 6(R(6)) repeats. The most frequent genotype was R(3)R(4), then R(3)R(3) and R(4)R(4); the least ones were R(2)R(2), R(3)R(6) and R(5)R(5). The frequencies of MUC20 alleles and genotypes in the IgAN patients were similar to healthy population. Initial ages, blood pressure, proteinuria, and renal function did not differ significantly among the three groups. There was no difference of the urinary osmotic pressure, urinary NAG (N-acetyl-B-D-glucosaminidase) and alpha1 microglobulin (alpha1-MG), and the semiquantitative scores of renal interstitial fibrosis and tubular atrophy in the three groups. IgAN patients with SL/LL genotype had higher odds ratio for progression of renal function (OR = 7.29, 95% CI: 1.68 - 31.60, P = 0.008) than the SS genotype. There were MUC20 VNTR polymorphisms in the healthy population. The polymorphism did not associate with the pathogenesis and the clinico-pathological parameters at the time of renal biopsy. The SL/LL genotype was likely to be a risk factor for rapid progression of renal function in the patients with IgAN.