Polymorphisms Of The Nephrin-G349A Gene And Diabetic Nephropathy In Type 2 Diabetic Patients

Objective and background:Diabetic nephropathy, which is characterized by proteinuria and relentless decline in renal function, is one of the major causes of end-stage renal disease (ESRD). There is evidence for a genetic involvement in the pathogenesis of the complication.Nephrin, which separating the protein from the urinary space, is a crucial structural component of the slit membrane. The nephrin gene, NPHS1, consists of 29 exons spanning 26kb in the chromosomal region 19q13.1. At least 60 mutations in the NPHS1 have been identified and most of these mutations are disease-causing, resulting in the lack of the nephrin protein with consequent congenital nephrosis syndrome (CNS). However, several sequence variants are also found in healthy control population. The single nucleotide polymorphism (SNP) G349A exists in exon three of the nephrin gene and is accompanied by the substitution of amino acid Lys for Glu. The functional implication of these polymorphisms is not known but they might influence the permeability of the slit diaphragm in kidney diseases such as diabetic nephropathy in which proteinuria is displayed. In this study, we determined the frequency of the genotypes and alleles of NPHS1-G349A single nucleotide polymorphisms in normal controls and type 2 diabetic patients in Zhejiang Hang population, and further investigated the possible association of the NPHS1-G349A single nucleotide polymorphism with the susceptibility of diabetic nephropathy.Methods:The NPHS1-G349A single nucleotide polymorphism was determined by polyraerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). A total of 84 normal controls (NC group, 49 male and 35 female, average age was 50. 4+11. 7) and 141 type 2 diabetic patients were involved. The diabetic patients were divided into two groups: the normal albumin excretion rate (AER) group(T2DM1 group, 27 male and 47 female, average age was 62.2 ± 10.7, duration of disease was 11.6 + 4.9 years) and proteinuria group (T2DM2 group, 38 male and 29 female, average age was 63.8 + 10.5, duration of disease was 11.7 + 3.8 years). The frequency of the genotypes and alleles of NPHS1-G349A were compared using the chi-square test. Clinical characteristics between different groups were tested with one-way ANOVA or nonparametric test. Multiple linear regression was used to analyse the relationship between different clinical index.Results:1. The genotype distribution of the control group and T2DM group was in the Hardy-Weinberg equilibrium (p>0.05).2. The polymorphism of NPHS1-G349A was screened in the normal control group and type 2 diabetes group. AA, GA and GG genotypes and A, G allele were found. The frequency of the genotype and allele in the control group was 40. 5% for AA, 44.0% for GA and 15. 5% for GG genotype, 62. 5% for A allele. There was no significant difference in the NC group between different sex for the respective frequency of the genotype ( *2 =0. 31, p=0. 86) and allele ( ** =0. 32, p=0. 57) . The frequency of the genotype for AA, GA, GG were 39.0%, 48. 2%, 12. 8% respectively and A allele was 63.1% in type 2 diabetes group. There was no significant difference between the NC and T2DM for the respective frequency of the genotype and allele.3. The frequency of genotype and allele among NC, T2DMland T2DM2 had no significant difference. No significant difference was found amongthese three groups between different sex, either.4. There was no significant difference between the two groups classified as different duration within the T2DM2 group (duration^10 years vs duration>10 years) for the respective frequency of the genotype and allele (jpO. 05).5. The frequency of genotype and allele among normoalbuminuria group, microalbuminuria group and macroalbuminuria group had no significant difference(jOO. 05).6. Within the T2DM group, patients carrying GG genotype of G349A tended to" present with lower renal function (CCr 68.9+39. 5ml/min ? 1.73m2 VS 93.4 ±33. 3ml/min ? 1.73m2 />=0.016).7. Multiple linear regression analysis indicated that age, sex, AER and the GG genotype of NPHS1-G349A were independent risk factors for the deteriorated renal function.Conclusion:1. There is a polymorphism of NPHS1-G349A in Zhejang Han population.2. NPHS1-G349A polymorphism is not a susceptibility gene of type 2 diabetes.3. NPHS1-G349A polymorphism is not associated with the AER in type 2 diabetes mellitus in Zhejiang Hang population.4. NPHS1-G349A polymorphism may be associated with the decline in renal function in patients with type 2 diabetes mellitus in Zhejiang Hang population, and G allele is probably one of the genes responsible for deteriorated renal function in T2DM.