Interleukin-13 genetic polymorphisms in Singapore Chinese children correlate with long-term outcome of minimal-change disease

Background. Minimal-change nephrotic syndrome (MCNS) has been associated with atopy. As interleukin-13 (IL-13) has been implicated in the pathogenesis of MCNS, we postulated that IL-13 genetic polymorphisms could influence either susceptibility or clinical course of the disease. Methods. Seventy-two Singapore Chinese children with MCNS and 78 normal controls were screened for single nucleotide polymorphisms (SNPs) in the IL-13 gene by direct sequencing. Allele and genotype frequencies of these SNPs were determined and their relationship with different clinical courses was analysed. Results. Six SNPs were identified in the 5' promoter, exon 4 and 3' untranslated region (3'UTR). The three SNPs in the 3'UTR - 4738 (G/A), 4793 (C/A) and 4926 (C/T) - were in tight linkage disequilibrium (Delta >= 0.99). There was no difference in allele or genotype frequencies between MCNS children and normal controls. However, there was a significantly lower frequency of allele 4738G in those MCNS children who were still relapsing after 5 years of follow-up (G = 0.52), compared with those in complete remission (G = 0.72; P < 0.05) and normal controls (G=0.69; P < 0.05). Haplotype analysis showed a significantly higher frequency of the GCC haplotype in controls and MCNS patients in complete remission (x(2) = 6.35; P < 0.02), while the frequency of AAT haplotype was higher in those MCNS 2 children still relapsing after 5 years of follow-up (x(2) = 5.38; P < 0.02). Moreover, peripheral blood mononuclear cell IL-13 mRNA expression in patients with haplotype AAT was significantly higher than in those with haplotype GCC. Conclusions. These results suggest that genetic polymorphisms in the 3'UTR of the IL-13 gene correlate with long-term outcome of MCNS, rather than disease susceptibility, in Singapore Chinese children.