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Genetic variant in the promoter of connective tissue growth factor gene confers susceptibility to nephropathy in type 1 diabetes
  1. Bing Wang1,
  2. Rickey E Carter1,
  3. Miran A Jaffa1,2,
  4. Sashidhar Nakerakanti1,
  5. Daniel Lackland1,
  6. Maria Lopes-Virella1,
  7. Maria Trojanowska1,
  8. Louis M Luttrell1,
  9. Ayad A Jaffa1,3,
  10. The DCCT/EDIC Study Group4
  1. 1Department of Medicine, Medical University of South Carolina, Charleston, South Carolina, USA
  2. 2Epidemiology and Population Health Department, Faculty of Health Sciences, American University of Beirut, Beirut, Lebanon
  3. 3Department of Biochemistry, Faculty of Medicine, American University of Beirut, Beirut, Lebanon
  4. 4NDIC/EDIC Bethesda, Maryland, USA
  1. Correspondence to Dr Ayad A Jaffa, Department of Medicine, Endocrinology-Diabetes-Medical Genetics, Medical University of South Carolina, 114 Doughty Street, P.O. Box 250776 Charleston, SC 29425, USA; jaffaa{at}musc.edu

Abstract

Background The evidence for genetic susceptibility in the pathogenesis of diabetic nephropathy is well recognised, but the genes involved remain to be identified. It is hypothesised that mutations within the gene encoding connective tissue growth factor (CTGF/CCN2) will increase the propensity of diabetic subjects to develop nephropathy.

Methods and results Genomic screening was performed for single nucleotide polymorphisms (SNPs) within the CTGF gene in 862 subjects from the DCCT/EDIC cohort of type 1 diabetes. A novel SNP was identified in the promoter region that changes a C-G at the position −20. The frequency of GG genotype in microalbuminuric patients (albumin excretion rate (AER) >40 mg/24 h) is significantly greater than diabetics with AER <40 mg/24 h, p<0.0001. The relative risk (RR) to develop microalbuminuria in diabetic subjects with the polymorphism is 3X higher than diabetic subjects without the polymorphism (RR 3.142, 95% CI 1.9238 to 5.1249; p<0.05). Kaplan–Meier survival curves demonstrated that the GG genotype group developed microalbuminuria and macroalbuminuria at a more rapid rate than the GC or CC genotypes. Functional studies demonstrated that the basal activity of the substituted allele/promoter (−20 GG allele) was significantly greater than that of the wild type promoter (−20 CC genotype). This higher level of basal activity of substituted allele CTGF/CCN2 promoter was abrogated upon suppression of Smad1 levels, indicating that SNP region in the CTGF/CCN2 promoter plays a vital role in the gene expression.

Conclusions These findings provide the first evidence that variants within the promoter region of the CTGF/CCN2 gene predisposes diabetic subjects to develop albuminuria and demonstrate that Samd1 controls the expression of CTGF/CCN2 promoter through this region.

  • Diabetes
  • renal medicine
  • genetic epidemiology

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Footnotes

  • Competing interests None.

  • Patient consent Obtained.

  • Ethics approval The Institutional Review Boards of MUSC and all participating DCCT/EDIC clinics approved the study, and written informed consent was obtained from each participant.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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