ORIGINAL ARTICLE Polymorphisms of the MDR1 and MIF genes in children with nephrotic syndrome Hyun Jin Choi & Hee Yeon Cho & Han Ro & So Hee Lee & Kyung Hee Han & HyunKyung Lee & Hee Gyung Kang & Il Soo Ha & Yong Choi & Hae Il Cheong Received: 17 January 2011 /Revised: 13 April 2011 /Accepted: 14 April 2011 /Published online: 8 May 2011 # IPNA 2011 Abstract Oral steroid treatment is the first line of therapy for childhood nephrotic syndrome (NS). Nonetheless, some patients are resistant to this treatment. Many efforts have been made to explain the differences in the response to steroid treatment in patients with NS based on the genetic background. We have investigated single nucleotide poly- morphisms of the MDR1 [C1236T (rs1128503), G2677T/A (rs2032582), and C3435T (rs1045642)] and MIF (G-173C, rs755622) genes in 170 children with NS. Of these children, 69 (40.6%) were initial steroid non-responders, and 23 (13.5% of total) developed chronic kidney disease. Renal biopsy findings, which were available for 101 patients, showed that 35 patients had minimal change lesion and 66 had focal segmental glomerulosclerosis. The frequencies of the MDR1 1236 CC (18.8 vs 7.2%) or TC (53.5 vs 43.5%) genotype and C allele (45.5 vs 29.0%) were significantly higher in the initial steroid responders than in the non-responders. Analysis of MDR1 three-marker haplotypes revealed that the frequency of the TGC haplotype was significantly lower in the initial steroid responders than in the non-responders (15.8 vs 29.0%). There was no association between the MIF G-173C polymorphism and clinical parameters, renal histological findings, and steroid responsiveness. These data suggest that the initial steroid response in children with NS may be influenced by genetic variations in the MDR1 gene. Keywords Childhood nephrotic syndrome . Macrophage migration inhibitory factor gene . Multiple drug resistance 1 gene . Single nucleotide polymorphism Introduction Idiopathic nephrotic syndrome (NS) is one of the most common primary glomerular diseases in children. It can be clinically classified as steroid sensitive (SSNS) and steroid resistant (SRNS) according to the responsiveness to oral steroid treatment, which is the first line of therapy in childhood idiopathic NS. Responsiveness to the initial oral steroid treatment is one of the major prognostic factors of this disease. However, the detailed therapeutic mechanism of steroids on idiopathic NS is currently unknown, as is the pathogenesis. Strenuous efforts have been made to explain the differ- ences in the response to steroid treatment in patients with NS with various genetic backgrounds. These efforts have focused on the analysis of polymorphisms in a number of H. J. Choi : H. Y. Cho : S. H. Lee : K. H. Han : H. Lee : H. G. Kang : I. S. Ha : H. I. Cheong (*) Department of Pediatrics, Seoul National University Children’s Hospital, 101 Daehang-no, Jongno-Gu, Seoul 110–744, Korea e-mail: cheonghi@snu.ac.kr H. Ro Transplantation Research Institute, Seoul National University, Seoul, Korea H. G. Kang : H. I. Cheong Research Center for Rare Diseases, Seoul National University Hospital, Seoul, Korea I. S. Ha : H. I. Cheong Kidney Research Institute, Medical Research Center, Seoul National University College of Medicine, Seoul, Korea Y. Choi Department of Pediatrics, Inje University Haeundae Paik Hospital, Seoul, Korea Pediatr Nephrol (2011) 26:1981–1988 DOI 10.1007/s00467-011-1903-0