[Show abstract][Hide abstract] ABSTRACT: Insufficient insulin secretion and reduced pancreatic beta cell mass are hallmarks of type 2 diabetes (T2DM). Here, we confirm that a previously identified polymorphism (rs2295490/Q84R) in exon 2 of the pseudokinase-encoding 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 beta cell function. Overexpression of TRB3 84R in mouse beta cells, human islet cells, and the murine beta 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 beta cells displayed decreased beta 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.
Full-text · Article · Aug 2010 · The Journal of clinical investigation
[Show abstract][Hide abstract] ABSTRACT: 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.
We genotyped approximately 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.
A total of 13 SNPs located in four genomic loci were associated with diabetic nephropathy with P < 1 x 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 x 10(-7)). A strong association was also identified at the CARS (cysteinyl-tRNA synthetase) locus (OR = 1.36, P = 3.1 x 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.
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.
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: The T allele of the C677T polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene is associated with elevated plasma homocysteine levels, and it has been postulated to be a risk factor for the development of diabetic nephropathy. We examined this hypothesis in both a case-control and a follow-up study in individuals with type 1 diabetes.
In the case-control study, the control group included 310 subjects with normoalbuminuria and diabetes duration of 15 years or greater, and the case group included 88 prevalent cases with end-stage renal disease (ESRD). The follow-up study included 235 subjects with overt proteinuria followed up for 6 years (on average), during which time ESRD developed in 69 subjects. DNA from each individual was genotyped for the C677T MTHFR polymorphism.
The frequency of TT homozygotes did not vary significantly among the four groups: 10% in controls, 15% in prevalent cases of ESRD, 13% in cases with new-onset ESRD, and 11% in those who remained proteinuric during follow-up (P = 0.9, 6 df). Similarly, frequency of the T allele varied little among the same groups (range, 33% to 36%; P = 0.9, 3 df) During follow-up, 52 of 323 individuals with diabetic nephropathy died. Total mortality rates were 4.3/100 person-years in TT homozygotes, 2.4/100 person-years in CT heterozygotes, and 3.0/100 person-years in CC homozygotes (P = 0.55, 2 df).
Using both a large case-control and a follow-up study, we found no evidence that the C677T MTHFR polymorphism has a significant role in the development of diabetic nephropathy in type 1 diabetes.
Full-text · Article · Jul 2003 · American Journal of Kidney Diseases
[Show abstract][Hide abstract] ABSTRACT: Type 2 diabetes mellitus (T2DM) is a complex disease. Genetic and environmental factors cooperate together to form its clinical picture. Polymorphisms in genes involved in the metabolism of vitamin D may influence susceptibility to T2DM. One of them is the vitamin D 1alpha-hydroxylase (CYP1alpha) gene. In this study we searched for the association of two markers, one in its intron 6 and the another one located upstream from the 5' end of CYP1alpha gene, with T2DM in a Polish population.
Overall 522 individuals were included in this study: 291 T2DM patients and 231 controls. The sequences, which contain both examined variants, were amplified by polymerase chain reaction (PCR). The T-->C polymorphism in intron 6 was assessed by the dot-blotting method using P(32). Genotyping of the other variant in the 5' end of CYP1alpha gene was carried out by restriction fragment length polymorphism (RFLP) method. Since variants of both SNPs were in very strong linkage disequilibrium, haplotypes could be assigned to phase-unknown individuals. The distribution of alleles, genotypes, haplotypes and haplotype combinations was compared between the groups by chi(2) test.
The frequency of T/C alleles of the 5'end variant was 81.7%/18.3% in T2DM patients and 82.8%/17.2% in the controls (chi(2)=0.2, 1.d.f., p=0.65). For a T-->C polymorphism in intron 6 the frequency of alleles was 65.1%/34.9% and 67.5%/32.5% in T2DM patients and controls, respectively (chi(2)=0.413, 1.d.f., p=0.669). Distribution of genotypes, haplotypes and haplotype combinations were similar in both groups. In stratified analysis, we observed that the T-C/T-T heterozygous haplotype combination was more prevalent in the subgroup of obese T2DM patients (BMI >=30) than in the controls (41.5% vs 28.6%, p=0.01).
Vitamin D 1alpha-hydroxylase is not a major gene for T2DM in a Polish population. However, this gene may be associated with T2DM in subjects with obesity. Thus, to definitely determine the role of this gene in T2DM further studies are necessary in other populations using larger sample size.
No preview · Article · May 2003 · Diabetes & Metabolism