New susceptibility loci associated with kidney disease in type 1 diabetes.

Diabetic kidney disease, or diabetic nephropathy (DN), is a major complication of diabetes and the leading cause of end-stage renal disease (ESRD) that requires dialysis treatment or kidney transplantation. In addition to the decrease in the quality of life, DN accounts for a large proportion of the excess mortality associated with type 1 diabetes (T1D). Whereas the degree of glycemia plays a pivotal role in DN, a subset of individuals with poorly controlled T1D do not develop DN. Furthermore, strong familial aggregation supports genetic susceptibility to DN. However, the genes and the molecular mechanisms behind the disease remain poorly understood, and current therapeutic strategies rarely result in reversal of DN. In the GEnetics of Nephropathy: an International Effort (GENIE) consortium, we have undertaken a meta-analysis of genome-wide association studies (GWAS) of T1D DN comprising ~2.4 million single nucleotide polymorphisms (SNPs) imputed in 6,691 individuals. After additional genotyping of 41 top ranked SNPs representing 24 independent signals in 5,873 individuals, combined meta-analysis revealed association of two SNPs with ESRD: rs7583877 in the AFF3 gene (P = 1.2 × 10(-8)) and an intergenic SNP on chromosome 15q26 between the genes RGMA and MCTP2, rs12437854 (P = 2.0 × 10(-9)). Functional data suggest that AFF3 influences renal tubule fibrosis via the transforming growth factor-beta (TGF-ß1) pathway. The strongest association with DN as a primary phenotype was seen for an intronic SNP in the ERBB4 gene (rs7588550, P = 2.1 × 10(-7)), a gene with type 2 diabetes DN differential expression and in the same intron as a variant with cis-eQTL expression of ERBB4. All these detected associations represent new signals in the pathogenesis of DN.

Association testing of previously reported variants in a large case-control meta-analysis of diabetic nephropathy.

We formed the GEnetics of Nephropathy-an International Effort (GENIE) consortium to examine previously reported genetic associations with diabetic nephropathy (DN) in type 1 diabetes. GENIE consists of 6,366 similarly ascertained participants of European ancestry with type 1 diabetes, with and without DN, from the All Ireland-Warren 3-Genetics of Kidneys in Diabetes U.K. and Republic of Ireland (U.K.-R.O.I.) collection and the Finnish Diabetic Nephropathy Study (FinnDiane), combined with reanalyzed data from the Genetics of Kidneys in Diabetes U.S. Study (U.S. GoKinD). We found little evidence for the association of the EPO promoter polymorphism, rs161740, with the combined phenotype of proliferative retinopathy and end-stage renal disease in U.K.-R.O.I. (odds ratio [OR] 1.14, P = 0.19) or FinnDiane (OR 1.06, P = 0.60). However, a fixed-effects meta-analysis that included the previously reported cohorts retained a genome-wide significant association with that phenotype (OR 1.31, P = 2 × 10(-9)). An expanded investigation of the ELMO1 locus and genetic regions reported to be associated with DN in the U.S. GoKinD yielded only nominal statistical significance for these loci. Finally, top candidates identified in a recent meta-analysis failed to reach genome-wide significance. In conclusion, we were unable to replicate most of the previously reported genetic associations for DN, and significance for the EPO promoter association was attenuated.

Novel susceptibility locus at 22q11 for diabetic nephropathy in type 1 diabetes.

BACKGROUND: Diabetic nephropathy (DN) affects about 30% of patients with type 1 diabetes (T1D) and contributes to serious morbidity and mortality. So far only the 3q21-q25 region has repeatedly been indicated as a susceptibility region for DN. The aim of this study was to search for new DN susceptibility loci in Finnish, Danish and French T1D families. METHODS AND RESULTS: We performed a genome-wide linkage study using 384 microsatellite markers. A total of 175 T1D families were studied, of which 94 originated from Finland, 46 from Denmark and 35 from France. The whole sample set consisted of 556 individuals including 42 sib-pairs concordant and 84 sib-pairs discordant for DN. Two-point and multi-point non-parametric linkage analyses were performed using the Analyze package and the MERLIN software. A novel DN locus on 22q11 was identified in the joint analysis of the Finnish, Danish and French families by genome-wide multipoint non-parametric linkage analysis using the Kong and Cox linear model (NPL(pairs) LOD score 3.58). Nominal or suggestive evidence of linkage to this locus was also detected when the three populations were analyzed separately. Suggestive evidence of linkage was found to six additional loci in the Finnish and French sample sets. CONCLUSIONS: This study identified a novel DN locus at chromosome 22q11 with significant evidence of linkage to DN. Our results suggest that this locus may be of importance in European populations. In addition, this study supports previously indicated DN loci on 3q21-q25 and 19q13.

Effect of parental type 2 diabetes on offspring with type 1 diabetes.

OBJECTIVE: The purpose of this study was to study the association between a parental history of type 2 diabetes and the metabolic profile as well as the presence of the metabolic syndrome and diabetes complications in patients with type 1 diabetes. RESEARCH DESIGN AND METHODS: This was a cross-sectional study design in 1,860 patients with type 1 diabetes from the Finnish Diabetic Nephropathy (FinnDiane) Study (620 patients with and 1,240 age-matched patients without a parental history of type 2 diabetes). Information on parental history was received from the type 1 diabetic offspring by a standardized questionnaire. RESULTS: Patients with type 1 diabetes and a positive parental history of type 2 diabetes had a higher prevalence of the metabolic syndrome (44 vs. 38%; P = 0.013) and a metabolic profile related to insulin resistance (higher BMI, larger waist circumference, and higher triglycerides, A1C, and insulin dose per kilogram) and also had a later onset of type 1 diabetes (17.2 +/- 9.2 vs. 16.1 +/- 8.9 years; P = 0.008), which was also confirmed in the publicly available Diabetes Control and Complications Trial data set. In contrast, no association was observed with blood pressure, diabetes complications, or HLA genotype distribution. Parental history of type 2 diabetes was independently associated with age at onset of type 1 diabetes (odds ratio 1.02 [95% CI 1.01-1.03]), BMI (1.07 [1.02-1.12]), triglycerides (1.18 [1.03-1.35]), and insulin dose per kilogram (1.63 [1.04-2.54]). CONCLUSIONS: Parental history of type 2 diabetes is associated with a later onset of type 1 diabetes, the metabolic syndrome, and a metabolic profile related to insulin resistance.