OBJECTIVE Despite extensive evidence for genetic susceptibility to diabetic nephropathy, the identification of susceptibility genes and their variants has had limited success. To search for genes that contribute to diabetic nephropathy, a genome-wide association scan was implemented on the Genetics of Kidneys in Diabetes collection. RESEARCH DESIGN AND METHODS We genotyped ∼360,000 single nucleotide polymorphisms (SNPs) in 820 case subjects (284 with proteinuria and 536 with end-stage renal disease) and 885 control subjects with type 1 diabetes. Confirmation of implicated SNPs was sought in 1,304 participants of the Diabetes Control and Complications Trial (DCCT)/Epidemiology of Diabetes Interventions and Complications (EDIC) study, a long-term, prospective investigation of the development of diabetes-associated complications. RESULTS A total of 13 SNPs located in four genomic loci were associated with diabetic nephropathy with P < 1 × 10 −5 . The strongest association was at the FRMD3 (4.1 protein ezrin, radixin, moesin [FERM] domain containing 3) locus (odds ratio [OR] = 1.45, P = 5.0 × 10 −7 ). A strong association was also identified at the CARS (cysteinyl-tRNA synthetase) locus (OR = 1.36, P = 3.1 × 10 −6 ). Associations between both loci and time to onset of diabetic nephropathy were supported in the DCCT/EDIC study (hazard ratio [HR] = 1.33, P = 0.02, and HR = 1.32, P = 0.01, respectively). We demonstratedexpression of both FRMD3 and CARS in human kidney. CONCLUSIONS We identified genetic associations for susceptibility to diabetic nephropathy at two novel candidate loci near the FRMD3 and CARS genes. Their identification implicates previously unsuspected pathways in the pathogenesis of this important late complication of type 1 diabetes.

Insufficient insulin secretion and reduced pancreatic β cell mass are hallmarks of type 2 diabetes (T2DM).Here, we confirm that a previously identified polymorphism (rs2295490/Q84R) in exon 2 of the pseudokinaseencoding gene tribbles 3 (TRB3) is associated with an increased risk for T2DM in 2 populations of people of mixed European descent. Carriers of the 84R allele had substantially reduced plasma levels of C-peptide, the product of proinsulin processing to insulin, suggesting a role for TRB3 in β cell function. Overexpression of TRB3 84R in mouse β cells, human islet cells, and the murine β cell line MIN6 revealed reduced insulin exocytosis, associated with a marked reduction in docked insulin granules visualized by electron microscopy. Conversely, knockdown of TRB3 in MIN6 cells restored insulin secretion and expression of exocytosis genes.Further analysis in MIN6 cells demonstrated that TRB3 interacted with the transcription factor ATF4 and that this complex acted as a competitive inhibitor of cAMP response element-binding (CREB) transcription factor in the regulation of key exocytosis genes. In addition, the 84R TRB3 variant exhibited greater protein stability than wild-type TRB3 and increased binding affinity to Akt. Mice overexpressing TRB3 84R in β cells displayed decreased β cell mass, associated with reduced proliferation and enhanced apoptosis rates. These data link a missense polymorphism in human TRB3 to impaired insulin exocytosis and thus increased risk for T2DM.

The K121Q polymorphism in ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) is associated with type 2 diabetes and obesity. The possibility of other ENPP1 polymorphisms influencing these phenotypes has received little attention. Our aim was to examine the associations of tagging single nucleotide polymorphisms (SNPs) and haplotypes of the linkage disequilibrium (LD) block containing K121Q polymorphism with type 2 diabetes in a Polish population, controlling for any effect of obesity. We genotyped 426 type 2 diabetic case and 370 control subjects for seven SNPs in ENPP1. In the total group, neither type 2 diabetes nor obesity was significantly associated with any SNP. However, in obese subjects, two SNPs were significantly associated with type 2 diabetes: the Q allele of K121Q (odds ratio 1.6 [95% CI 1.003-2.6]) and T allele of rs997509 (4.7 [1.6 -13.9]). In the LD block, four SNPs plus the K121Q polymorphism distinguished six haplotypes, three of which carried the Q allele. Interestingly, the T allele of rs997509 sufficed to distinguish a 121Q-carrying haplotype that was significantly more associated with type 2 diabetes than the other two (4.2 [1.3-13.5]). These other two 121Q-carrying haplotypes were not associated with type 2 diabetes. In conclusion, we found a new SNP, rs997509, in intron 1 that is strongly associated with risk of type 2 diabetes in obese individuals. The molecular mechanisms underlying this association are unknown. Diabetes 55: 2626 -2630, 2006 T he ectonucleotide pyrophosphatase/phosphodiesterase 1 gene (ENPP1 or PC-1) is located on the long arm of chromosome 6 (6q23.2) and encodes for a protein that inhibits insulin signaling (1). A polymorphism in exon 4 (K121Q) of the gene has been examined for association with features of insulin resistance, type 2 diabetes, and obesity with inconsistent results. The 121Q allele was associated with insulin resistance in nondiabetic subjects in many (2-8) but not in all (2,3,9,10) populations. Similarly, it was associated with type 2 diabetes in South Asians living in India and in the U.S., as well as in Caucasians living in the U.S. (2,3) and Finland (6) but not Caucasians in Sweden (4) or Denmark (10). Although a recent study (11) found no association of obesity with the 121Q allele, Meyre et al. (12) recently reported that a particular haplotype, defined by 121Q and alleles at two other single nucleotide polymorphisms (SNPs) (a T deletion at IVS20 delT-11 and G allele at A3 Gϩ1044TGA/rs7754561), was associated with obesity as well as increased risk of type 2 diabetes. However, the role of obesity is unclear from this study. Does the 121Q allele increase the risk of type 2 diabetes directly or through its effect on obesity?Several factors may explain the discrepant effects of the 121Q allele on metabolic traits in different populations. Its effect may be modified by environmental factors or functional polymorphisms in other genes (13), either of which may vary across populations. Unknown polymorphisms within ENPP1 that influence these meta...

Chemokines and their receptors have been implicated in the development of diabetic nephropathy. To determine whether the risk of diabetic nephropathy is influenced by two functional polymorphisms in the regulated upon activation normal T-cell expressed and secreted (RANTES) receptor gene (CCR5), we recruited patients with type 1 diabetes, including 496 case subjects with overt proteinuria or end-stage renal disease and 298 control subjects with normoalbuminuria. Male carriers of the 59029G allele, which is associated with diminished expression of CCR5 on the surface of immunocompetent cells, had significantly higher risk of developing diabetic nephropathy than noncarriers (OR [95% CI] 1.9 [1.2-3.0]). Similarly, male carriers of the 32-bp deletion, which causes truncation of the protein, had significantly higher risk of diabetic nephropathy than noncarriers (2.3 [1.3-4.2]). Combining both polymorphisms, three haplotypes were distinguished: one nonrisk haplotype carrying the 59029A allele and the 32-bp insertion and two risk haplotypes carrying the 59029A allele with the 32-bp deletion and carrying the 59029G allele with the 32-bp insertion. The distribution of these haplotypes differed significantly (P < 0.00001) in men with and without diabetic nephropathy but was not associated with diabetic nephropathy in women. In conclusion, two functional polymorphisms in CCR5 that decrease expression of the RANTES receptor on immunocompetent cells are associated with increased risk of diabetic nephropathy in type 1 diabetes, but only in men. Diabetes 54:3331-3335, 2005 I n diabetic nephropathy, the infiltration of the glomeruli and interstitium by immunocompetent cells is a common finding both in rodent models of diabetes and in biopsy specimens collected from diabetic patients (1,2). Moreover, the increased synthesis of chemokines and other inflammatory mediators by glomerular and tubular cells has been reported in hyperglycemic conditions (2,3). This includes such chemokines as regulated upon activation normal T-cell expressed and secreted (RANTES) and macrophage inflammatory protein-1␣ and macrophage inflammatory protein-1␤ (4 -5). These molecules are able to recruit to kidney monocytes by binding to chemokine receptors such as CCR1, CCR3, and CCR5 (6).Recent studies have reported that polymorphisms in the RANTES receptor gene (CCR5) were associated with the increased risk of nephropathy in type 2 diabetes in a Japanese population (7) and with a higher risk of kidney rejection among nondiabetic individuals with kidney transplants (8). The present study aims to examine the association of two functional polymorphisms in CCR5 with the risk of diabetic nephropathy in Caucasians with type 1 diabetes.CCR5 has been mapped to the short arm of chromosome 3 within the chemokine receptor gene cluster (9). Recent studies established that this gene comprises three exons spanning a region of about 6 kb. The clinical and functional relevance of many polymorphisms and haplotypes in CCR5 has been reported (10 -13). The most consistent d...