Background: The putative genetic regulation of multidrug resistance gene-1 (MDR-1) gene expression and P-glycoprotein function has not yet been clearly delineated in patients with nephrotic syndrome (NS). We undertook this study to examine the distribution of three most frequent MDR-1 exonic polymorphisms G3435C, G2677T/A and C1236T in patients with NS and control children to investigate their usefulness as markers of responsiveness of the disease to steroids.
Methods: Two hundred and sixteen children with NS and 216 healthy controls were genotyped for three exonic MDR-1 polymorphisms (G3435C, G2677T/A and C1236T) by using the polymerase chain reaction-restriction fragment length polymorphism technique. The frequency distribution of genotypes/alleles was compared between patients with NS and controls and also between steroid-sensitive NS (SSNS) and steroid-resistant NS (SRNS) patients.
Results: Of the total 216 cases of NS (median age of onset 5 years, 165 males), 137 had SSNS, and 79 had SRNS. Homozygous mutants of C3435T (TT versus CC, P = 0.034) and G2677T/A (TT + AA versus GG), P = 0.030) were significantly higher in patients with NS compared to controls. The frequency distribution of homozygous mutant TT + AA compared to wild genotype GG was significantly higher in SRNS than SSNS patients (P = 0.011) for G2677T/A, while the mutant genotypes for C3435T and C1236T were not different between SRNS and SSNS patients. The combination-bearing mutant genotype either of C3435T or G2677T/A exhibited a significantly higher frequency of mutant genotypes distribution in SRNS patients. MDR-1 haplotypes did not differ significantly between SSNS and SRNS patients.
Conclusions: Patients with NS carrying homozygous mutants of single nucleotide polymorphism (SNP) G2677T/A are prone to develop SRNS. The synergistic effect of mutant genotypes of SNPs G2677T/A and C3435T in different combinations increase the risk of developing steroid resistance in patients with NS.