Polymorphisms in the nephrin gene and diabetic nephropathy in type 1 diabetic patients

Background. Several mutations in the nephrin gene are responsible for the lack of slit membrane of the glomeruli leading to massive proteinuria present already in utero. Variations in the nephrin gene may also affect the degree of proteinuria in acquired kidney diseases. We tested the hypothesis of whether any of the polymorphisms identified in the coding region of the nephrin gene were associated with diabetic nephropathy. Methods. In a case-control, cross-sectional study, 996 Finnish type 1 diabetic patients from the FinnDiane Study were genotyped by standard polymerase chain reaction protocol. Results. The frequencies of the rare alleles in the E117K, R408Q, and N1077S polymorphisms in the entire cohort were 34%, 8%, and 12%, respectively. When comparing patients with a mutant allele with the wild genotype there was no difference between the patients with end-stage renal disease, proteinuria, microalbuminuria, and those with a normal albumin excretion rate (df =3, chi(2) =1.62, 1.31 and 0.77). Neither were the polymorphisms associated with the progression of kidney disease, nor with creatinine clearance and albumin excretion rate. Conclusion. This study does not support an involvement of the coding region of the nephrin gene in the pathogenesis of diabetic nephropathy in type 1 diabetic patients.