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Background Rare variants in gene coding regions likely have a greater impact on disease-related phenotypes than common variants through disruption of their encoded protein. We searched for rare variants associated with onset of end stage kidney disease (ESKD) in individuals with type 1 diabetes at advanced kidney disease stage. Methods Gene-based exome array analysis of 15,449 genes in 5 large incidence cohorts of individuals with type 1 diabetes and proteinuria were analyzed for survival time-to-ESKD, testing the top gene in a 6th cohort (N=2,372/1,115 events all cohorts) and replicating in two retrospective case-control studies (N=1,072 cases, 752 controls). Deep resequencing of the top associated gene in 5 cohorts confirmed the findings. We performed immunohistochemistry and gene expression experiments in human control and diseased cells, and in mouse ischemia reperfusion and aristolochic acid nephropathy models. Results Protein coding variants in the hydroxysteroid 17-beta dehydrogenase 14 gene (HSD17B14), predicted to affect protein structure, had a net protective effect against development of ESKD at exome-wide significance (N=4,196; p-value=3.3x10-7). The HSD17B14 gene and encoded enzyme were robustly expressed in healthy human kidney, maximally in proximal tubular cells. Paradoxically, gene and protein expression were attenuated in human diabetic proximal tubules and in mouse kidney injury models. Expressed HSD17B14 gene and protein levels remained low without recovery after 21 days in a murine ischemic reperfusion injury model. Decreased gene expression was found in other chronic kidney disease-associated renal pathologies. Conclusions HSD17B14 gene is mechanistically involved in diabetic kidney disease. The encoded sex steroid enzyme is a druggable target, potentially opening a new avenue for therapeutic development.

Rare variants in gene coding regions likely have a greater impact on disease-related phenotypes than common variants through disruption of their encoded protein. We searched for rare variants associated with onset of ESKD in individuals with type 1 diabetes at advanced kidney disease stage.Gene-based exome array analyses of 15,449 genes in five large incidence cohorts of individuals with type 1 diabetes and proteinuria were analyzed for survival time to ESKD, testing the top gene in a sixth cohort (Protein coding variants in the hydroxysteroid 17

Progressively decreasing glomerular filtration rate (GFR), or renal decline, is seen in patients with type 1 diabetes (T1D) and normoalbuminuria or microalbuminuria. Here we examined the associations of kidney injury molecule-1 (KIM-1) in plasma and urine with the risk of renal decline and determine whether those associations are independent of markers of glomerular damage. The study group comprised patients with T1D from the 2nd Joslin Kidney Study of which 259 had normoalbuminuria and 203 had microalbuminuria. Serial measurements over 4 to 10 years of follow-up (median 8 years) of serum creatinine and cystatin C were used jointly to estimate eGFRcr-cys slopes and time of onset of CKD stage 3 or higher. Baseline urinary excretion of IgG2 and albumin were used as markers of glomerular damage, and urinary excretion of KIM-1 and its plasma concentration were used as markers of proximal tubular damage. All patients had normal renal function at baseline. During follow-up, renal decline (eGFRcr-cys loss 3.3% or more per year) developed in 96 patients and 62 progressed to CKD stage 3. For both outcomes, the risk rose with increasing baseline levels of plasma KIM-1. In multivariable models, elevated baseline plasma KIM-1 was strongly associated with risk of early progressive renal decline, regardless of baseline clinical characteristics, serum TNFR1 or markers of glomerular damage. Thus, damage to proximal tubules may play an independent role in the development of early progressive renal decline in non-proteinuric patients with T1D.

A new model of diabetic nephropathy in type 1 diabetes emerged from our studies of Joslin Clinic patients. The dominant feature is progressive renal decline, not albuminuria. This decline is a unidirectional process commencing while patients have normal renal function and, in the majority, progressing steadily (linearly) to end-stage renal disease (ESRD). While an individual's rate of renal decline is constant, the estimated glomerular filtration rate (eGFR) slope varies widely among individuals from –72 to –3.0 ml/min/year. Kidney Disease: Improving Global Outcomes guidelines define rapid progression as rate of eGFR declines > 5 ml/min/year, a value exceeded by 80% of patients in Joslin's type 1 diabetes ESRD cohort. The extraordinary range of slopes within the rapid progression category prompted us to partition it into "very fast," "fast" and "moderate" decline. We showed, for the first time, that very fast and fast decline from normal eGFR to ESRD within 2 to 10 years constitutes 50% of the Joslin cohort. In this review we present data about frequency of fast decliners in both diabetes types, survey some mechanisms underlying fast renal decline, discuss methods of identifying patients at risk and comment on the need for effective therapeutic interventions. Whether the initiating mechanism of fast renal decline affects glomerulus, tubule, interstitium or vasculature is unknown. Since no animal model mimics progressive renal decline, studies in humans are needed. Prospective studies searching for markers predictive of the rate of renal decline yield findings that may make detection of fast decliners feasible. Identifying such patients will be the foundation for developing effective individualized methods to prevent or delay onset of ESRD in diabetes.

Design of Phase III trials for diabetic nephropathy currently requires patients at a high risk of progression defined as within three years of a hard end point (end-stage renal disease, 40% loss of estimated glomerular filtration rate, or death). To improve the design of these trials, we used natural history data from the Joslin Kidney Studies of chronic kidney disease in patients with diabetes to develop an improved criterion to identify such patients. This included a training cohort of 279 patients with type 1 diabetes and 134 end points within three years, and a validation cohort of 221 patients with type 2 diabetes and 88 end points. Previous trials selected patients using clinical criteria for baseline urinary albumin-to-creatinine ratio and estimated glomerular filtration rate. Application of these criteria to our cohort data yielded sensitivities (detection of patients at risk) of 70-80% and prognostic values of only 52-63%. We applied classification and regression trees analysis to select from among all clinical characteristics and markers the optimal prognostic criterion that divided patients with type 1 diabetes according to risk. The optimal criterion was a serum tumor necrosis factor receptor 1 level over 4.3 ng/ml alone or 2.9-4.3 ng/ml with an albumin-to-creatinine ratio over 1900 mg/g. Remarkably, this criterion produced similar results in both type 1 and type 2 diabetic patients. Overall, sensitivity and prognostic value were high (72% and 81%, respectively). Thus, application of this criterion to enrollment in future clinical trials could reduce the sample size required to achieve adequate statistical power for detection of treatment benefits.

OBJECTIVE We studied the serum concentration of tumor necrosis factor receptor 2 (TNFR2) and the rate of renal decline, a measure of the intensity of the disease process leading to end-stage renal disease (ESRD). RESEARCH DESIGN AND METHODS A cohort of 349 type 1 diabetic patients with proteinuria was followed for 5–18 years. Serum TNFR2, glycated hemoglobin A1c (HbA1c), and other characteristics were measured at enrollment. We used a novel analytic approach, a joint longitudinal-survival model, fitted to serial estimates of glomerular filtration rate (eGFR) based on serum creatinine (median seven per patient) and time to onset of ESRD (112 patients) to estimate the rate of renal decline (eGFR loss). RESULTS At enrollment, all patients had chronic kidney disease stage 1–3. The mean (±SD) rate of eGFR loss during 5–18 years of follow-up was −5.2 (±4.9) mL/min/1.73 m2/year. Serum TNFR2 was the strongest determinant of renal decline and ESRD risk (C-index 0.79). The rate of eGFR loss became steeper with rising concentration of TNFR2, and elevated HbA1c augmented the strength of this association (P = 0.030 for interaction). In patients with HbA1c ≥10.1% (87 mmol/mol), the difference in the rate of eGFR loss between the first and fourth quartiles of TNFR2 was 5.4 mL/min/1.73 m2/year, whereas it was only 1.9 in those with HbA1c CONCLUSIONS Circulating TNFR2 is a major determinant of renal decline in patients with type 1 diabetes and proteinuria. Elevated HbA1c magnifies its effect. Although the mechanisms of this synergism are unknown, our findings allow us to stratify patients according to risk of ESRD.

The ability of microalbuminuria to predict early progressive renal function decline in type-1 diabetic patients has been questioned. To resolve this, we determined the plasma proteome differences between microalbuminuric patients with type-1 diabetes and stable renal function (controls) and patients at risk for early progressive renal function decline (cases) and asked whether these differences have value as surrogate biomarkers. Mass spectrometry was used to analyze small (less than 3 kDa) plasma peptides isolated from well-matched case and control plasma obtained at the beginning of an 8-12 year follow-up period. Spearman analysis of plasma peptide abundance and the rate of renal function decline during follow-up identified seven masses with a significant negative correlation with early progressive renal function decline. Tandem mass spectrometry identified three fragments of high molecular weight kininogen. Increased plasma high molecular weight kininogen in the cases was confirmed by immunoblot. One peptide, des-Arg9-BK(1-8), induced Erk1/2 phosphorylation when added apically to two proximal tubular cell lines grown on permeable inserts. Thus, we have identified plasma protein fragments, some of which have biological activity with moderate to strong correlation, with early progressive renal function decline in microalbuminuric patients with type-1 diabetes. Other peptides are candidates for validation as candidate biomarkers of diabetes-associated renal dysfunction.

OBJECTIVE The patterns of estimated glomerular filtration rate (eGFR) decline to end-stage renal disease (ESRD) in patients with type 1 diabetes has not been conclusively described. Decline could be linearly progressive to ESRD but with a variable rate. Conversely, decline may be linear but interrupted by periods of plateaus or improvements. RESEARCH DESIGN AND METHODS This observational study included 364 patients with type 1 diabetes attending the Joslin Clinic who developed ESRD between 1991 and 2013. We retrieved serum creatinine measurements from clinic visits or research examinations up to 24 years (median 6.7 years) preceding the onset of ESRD. Using serial measurements of serum creatinine to estimate renal function (eGFR), we used regression-based spline methods and a data smoothing approach to characterize individual trajectories of eGFR over time for the 257 patients with five or more data points. RESULTS The rate of eGFR decline per year ranged widely, from −72 to −2 mL/min/1.73 m2 (median −8.5). The trajectories, as characterized with linear regression-based spline models, were linear or nearly so for 87% of patients, accelerating for 6%, and decelerating for 7%. Smoothed trajectories evaluated by a Bayesian approach did not significantly depart from a linear fit in 76%. CONCLUSIONS The decline of eGFR in type 1 diabetes is predominantly linear. Deviations from linearity are small, with little effect on the expected time of ESRD. A single disease process most likely underlies renal decline from its initiation and continues with the same intensity to ESRD. Linearity of renal decline suggests using slope reduction as the measure of effectiveness of interventions to postpone ESRD.

OBJECTIVE Patients with diabetes have a high risk of end-stage renal disease (ESRD). We examined whether prediction of this outcome, according to chronic kidney disease (CKD) staging by creatinine-based estimates of the glomerular filtration rate (eGFRcreat), is improved by further staging with serum cystatin C–based estimates (eGFRcyst). RESEARCH DESIGN AND METHODS Patients with diabetes in CKD stages 1–3 were selected from three cohorts: two from Joslin Diabetes Center, one with type 1 diabetes (N = 364) and one with type 2 diabetes (N = 402), and the third from the Finnish Diabetic Nephropathy (FinnDiane) Study of type 1 (N = 399). Baseline serum concentrations of creatinine and cystatin C were measured in all patients. Follow-up averaged 8–10 years and onsets of ESRD (n = 246) and death unrelated to ESRD (n = 159) were ascertained. RESULTS Although CKD staging by eGFRcyst was concordant with that by eGFRcreat for 62% of Joslin patients and 73% of FinnDiane patients, those given a higher stage by eGFRcyst than eGFRcreat had a significantly higher risk of ESRD than those with concordant staging in all three cohorts (hazard ratio 2.3 [95% CI 1.8–3.1]). Similarly, patients at a lower stage by eGFRcyst than by eGFRcreat had a lower risk than those with concordant staging (0.30 [0.13–0.68]). Deaths unrelated to ESRD followed the same pattern, but differences were not as large. CONCLUSIONS In patients with diabetes, CKD staging based on eGFRcyst significantly improves ESRD risk stratification based on eGFRcreat. This conclusion can be generalized to patients with type 1 and type 2 diabetes and to diabetic patients in the U.S. and Finland.

Elevated plasma concentrations of TNF receptors 1 and 2 (TNFR1 and TNFR2) predict development of ESRD in patients with type 2 diabetes without proteinuria, suggesting these markers may contribute to the pathogenesis of renal decline. We investigated whether circulating markers of the TNF pathway determine GFR loss among patients with type 1 diabetes. We followed two cohorts comprising 628 patients with type 1 diabetes, normal renal function, and no proteinuria. Over 12 years, 69 patients developed estimated GFR less than 60 mL/min per 1.73 m 2 (16 per 1000 person-years). Concentrations of TNFR1 and TNFR2 were strongly associated with risk for early renal decline. Renal decline was associated only modestly with total TNFa concentration and appeared unrelated to free TNFa. The cumulative incidence of estimated GFR less than 60 mL/min per 1.73 m 2 for patients in the highest TNFR2 quartile was 60% after 12 years compared with 5%–19% in the remaining quartiles. In Cox proportional hazards analysis, patients with TNFR2 values in the highest quartile were threefold more likely to experience renal decline than patients in the other quartiles (hazard ratio, 3.0; 95% confidence interval, 1.7–5.5). The risk associated with high TNFR1 values was slightly less than that associated with high TNFR2 values. TNFR levels were unrelated to baseline free TNFa level and remained stable over long periods within an individual. In conclusion, early GFR loss in patients with type 1 diabetes without proteinuria is strongly associated with circulating TNF receptor levels but not TNFa levels (free or total).

Levels of proinflammatory cytokines associate with risk for developing type 2 diabetes but whether chronic inflammation contributes to the development of diabetic complications, such as ESRD, is unknown. In the 1990s, we recruited 410 patients with type 2 diabetes for studies of diabetic nephropathy and recorded their characteristics at enrollment. During 12 years of follow-up, 59 patients developed ESRD (17 per 1000 patient-years) and 84 patients died without ESRD (24 per 1000 patient-years). Plasma markers of systemic inflammation, endothelial dysfunction, and the TNF pathway were measured in the study entry samples. Of the examined markers, only TNF receptors 1 and 2 (TNFR1 and TNFR2) associated with risk for ESRD. These two markers were highly correlated, but ESRD associated more strongly with TNFR1. The cumulative incidence of ESRD for patients in the highest TNFR1 quartile was 54% after 12 years but only 3% for the other quartiles (P

A genome-wide association (GWA) scan of the Genetics of Kidneys in Diabetes (GoKinD) collections identified four novel susceptibility loci, located on chromosomes 7p14.3, 9q21.32, 11p15.4, and 13q33.3 that were associated with nephropathy in type 1 diabetes. The recent examination of these loci in Japanese patients with type 2 diabetes further supported associations at the chromosome 13q33.3 locus. To follow up these findings, we focused on these same four loci and examined whether single nucleotide polymorphisms (SNPs) at these susceptibility loci were associated with diabetic nephropathy in the Joslin Study of Genetics of Nephropathy in Type 2 Diabetes collection. A total of six SNPs across these loci were genotyped in 646 normoalbuminuric controls and 743 nephropathy cases of European ancestry. A significant association was identified at the 13q33.3 locus (rs9521445: OR=1.25, P=4.4×10−3). At this same locus, rs1411766 was also associated with type 2 diabetic nephropathy in this collection (OR=1.19, P=0.03). A meta-analysis combining this data with that from the Japanese and GoKinD collections significantly improved the strength of this association (OR=1.29 P=9.7×10−9). Additionally, we also observed an association at the 11p15.4 locus (rs451041: OR=1.21, P=0.02). Our analysis increases support that associations identified in the GoKinD collections on chromosomes 11p15.4 (near the CARS gene) and 13q33.3 (within an intergenic region between MYO16 and IRS2) are true diabetic nephropathy susceptibility loci common to both type 1 and type 2 diabetes.

Genetic data support the notion that polymorphisms in members of the matrix metalloproteinase (MMP) family of genes play an important role in extracellular matrix remodeling and contribute to the pathogenesis of vascular disease. To identify novel genetic markers for diabetic nephropathy (DN), we examined the relationship between MMP gene polymorphisms and DN in the Genetics of Kidneys in Diabetes (GoKinD) population. Genotypic data from the Genetic Association Information Network (GAIN) type 1 DN project were analyzed for associations across 21 MMP genes in 1,705 individual with type 1 diabetes, including 885 normoalbuminuric control subjects and 820 advanced DN case subjects. In total, we investigated the role of 1,283 SNPs (198 genotyped SNPs and 1,085 imputed SNPs) mapping to the MMP genes. We identified associations at several correlated SNPs across a 29.2 kb interval on chromosome 11q at the MMP-3/MMP-12 locus. The strongest associations occurred at 2 highly-correlated SNPs, rs610950 (OR = 0.50, P = 1.6×10−5) and rs1277718 (OR = 0.50, P = 2.1×10−5). Further examination of this locus identified 17 SNPs (2 genotyped SNPs and 15 imputed SNPs) in complete linkage disequilibrium associated with DN (P-values < 2.5×10−4), including a non-synonymous SNP (rs652438, Asn357Ser) located in exon 8 of MMP-12 that significantly reduced the risk of DN among carriers of the serine substitution relative to homozygous carriers of asparagine (OR = 0.51; 95% CI = 0.37–0.71, P = 6.2×10−5). Taken together, our study suggests that genetic variations within the MMP-3/MMP-12 locus influence susceptibility of DN in type 1 diabetes.

Elevated urinary albumin excretion in patients with type 1 diabetes reverts to normoalbuminuria in a majority of patients but advances toward proteinuria in some. In order to gain valuable insights into the early pathophysiology of diabetic nephropathy we evaluated the association of kidney tubular injury biomarkers with changes in albuminuria in patients with type 1 diabetes mellitus. Urine levels of kidney injury molecule-1 (KIM-1), N-acetyl-β-D-glucosaminidase (NAG), and some inflammatory markers were determined in 38 healthy individuals and 659 patients with type 1 diabetes mellitus having varying degrees of albuminuria. Urinary interleukin-6, CXCL10/IP-10, NAG, and KIM-1 levels were very low in healthy individuals, increased in type 1 patients with normoalbuminuria, and were highest in diabetic patients that had microalbuminuria. Low baseline concentrations of urinary KIM-1 and NAG both individually and collectively were significantly associated with the regression of microalbuminuria over the subsequent 2 years; an effect independent of clinical characteristics. Progression and regression of microalbuminuria were unrelated to urinary levels of interleukins 6 and 8, CXCL10/IP-10, and monocyte chemoattractant protein-1. Thus our results show that lower urinary KIM-1 and NAG levels were associated with the regression of microalbuminuria in type 1 diabetes mellitus. Hence, tubular dysfunction is a critical component of the early course of diabetic nephropathy.

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.

OBJECTIVE We previously described a cross-sectional association between serum uric acid and reduced glomerular filtration rate (GFR) in nonproteinuric patients with type 1 diabetes. Here, we prospectively investigated whether baseline uric acid impacts the risk of early progressive renal function loss (early GFR loss) in these patients. RESEARCH DESIGN AND METHODS Patients with elevated urinary albumin excretion (n = 355) were followed for 4–6 years for changes in urinary albumin excretion and GFR. The changes were estimated by multiple determinations of albumin-to-creatinine ratios (ACRs) and serum cystatin C (GFRcystatin). RESULTS At baseline, the medians (25th–75th percentiles) for uric acid, ACR, and GFRcystatin values were 4.6 mg/dl (3.8–5.4), 26.2 mg/g (15.1–56.0), and 129 ml/min per 1.73 m2 (111–145), respectively. During the 6-year follow-up, significant association (P < 0.0002) was observed between serum uric acid and development of early GFR loss, defined as GFRcystatin decline exceeding 3.3% per year. In baseline uric acid concentration categories (in mg/dl: CONCLUSIONS We found a clear dose-response relation between serum uric acid and risk of early GFR loss in patients with type 1 diabetes. Clinical trials are warranted to determine whether uric acid–lowering drugs can halt renal function decline before it becomes clinically significant.

We sought to study new-onset microalbuminuria, its progression, and the decline of renal function in patients with type 1 diabetes. Using a cohort of 109 patients who developed new-onset microalbuminuria in the first 4 years following enrollment in the 1st Joslin Kidney Study, we simultaneously tracked the change in their renal function and urinary albumin excretion. Of these, 79 patients were followed for an average of 12 years after microalbuminuria onset, wherein their glomerular filtration rate was estimated by the Modification of Diet in Renal Disease Study formula and compared with their microalbuminuria and proteinuria. The concordance between these outcomes was weak. Only 12 of the 23 patients who progressed to advanced (stage 3–5) chronic kidney disease developed proteinuria, which, in general, did not precede but accompanied the progression to advanced chronic kidney disease. The remaining 11 patients who developed advanced disease had persistent microalbuminuria or returned to normal albuminuria. Thus, we found that one-third of patients with type 1 diabetes developed advanced chronic kidney disease relatively soon after the onset of microalbuminuria and this was not conditional on the presence of proteinuria. Contrary to the existing concept of early nephropathy in type 1 diabetes, less emphasis should be placed on the mechanisms of progression to proteinuria and more placed on mechanisms initiating and promoting the early decline of renal function that eventually progresses to advanced chronic kidney disease.

OBJECTIVE To examine the association between single nucleotide polymorphisms (SNPs) in the engulfment and cell motility 1 (ELMO1) gene, a locus previously shown to be associated with diabetic nephropathy in two ethnically distinct type 2 diabetic populations, and the risk of nephropathy in type 1 diabetes. RESEARCH DESIGN AND METHODS Genotypic data from a genome-wide association scan (GWAS) of the Genetics of Kidneys in Diabetes (GoKinD) study collection were analyzed for associations across the ELMO1 locus. In total, genetic associations were assessed using 118 SNPs and 1,705 individuals of European ancestry with type 1 diabetes (885 normoalbuminuric control subjects and 820 advanced diabetic nephropathy case subjects). RESULTS The strongest associations in ELMO1 occurred at rs11769038 (odds ratio [OR] 1.24; P = 1.7 × 10−3) and rs1882080 (OR 1.23; P = 3.2 × 10−3) located in intron 16. Two additional SNPs, located in introns 18 and 20, respectively, were also associated with diabetic nephropathy. No evidence of association for variants previously reported in type 2 diabetes was observed in our collection. CONCLUSIONS Using GWAS data from the GoKinD collection, we comprehensively examined evidence of association across the ELMO1 locus. Our investigation marks the third report of associations in ELMO1 with diabetic nephropathy, further establishing its role in the susceptibility of this disease. There is evidence of allelic heterogeneity, contributed by the diverse genetic backgrounds of the different ethnic groups examined. Further investigation of SNPs at this locus is necessary to fully understand the commonality of these associations and the mechanism(s) underlying their role in diabetic nephropathy.

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.

Background and objectives: The aim of our study was to examine serum markers of the TNF and Fas pathways for association with cystatin-C based estimated glomerular filtration rate (cC-GFR) in subjects with type 1 diabetes (T1DM) and no proteinuria. Design, setting, participants, & measurements: The study group (the 2nd Joslin Kidney Study) comprised patients with T1DM and normoalbuminuria (NA) (n = 363) or microalbuminuria (MA) (n = 304). Impaired renal function (cC-GFR

Renal functional changes in diabetic nephropathy conventionally have been linked to progression of urinary albumin excretion. This paradigm was based on historic evidence noting that hyperfiltration occurred in the setting of normoalbuminuria and microalbuminuria and that loss of renal function began in the context of proteinuria. More contemporaneous research findings, using serum cystatin-C-based estimates of glomerular filtration rate (cC-GFR), have challenged this paradigm. Rather, the process of renal function loss appears to begin prior to the onset of proteinuria. In the 2nd Joslin Kidney Study on the Natural History of Microalbuminuria, over one-third of type 1 diabetes (T1DM) patients with microalbuminuria at the time of enrollment already had evidence of mild (cC-GFR

OBJECTIVES— Recently, an association was found between diabetic nephropathy and the D18S880 microsatellite, located in the carnosinase gene (CNDP1) on chromosome 18q. Alleles of this microsatellite encode for a variable number of leucine residues (from four to seven) in the leader peptide of the carnosinase precursor. The frequency of subjects homozygous for the five leucines was higher in control subjects than in case subjects in studies focusing on type 2 diabetic patients. To test whether this finding can be extended to type 1 diabetic patients, we carried out a comprehensive study on association between diabetic nephropathy and the D18S880 microsatellite and 21 additional SNPs that tagged the genomic region containing CNDP1 and CNDP2. RESEARCH DESIGN AND METHODS— Overall, 1,269 Caucasian patients with type 1 diabetes were included in the study, including 613 patients with normoalbuminuria and a long duration of diabetes, 445 patients with persistent proteinuria, and 211 patients with end-stage renal disease (ESRD). All patients were genotyped for selected polymorphisms, the associations with diabetic nephropathy were tested by a χ2 test, and odds ratios were calculated. RESULTS— We did not find any significant association between diabetic nephropathy and any examined genetic markers. The negative findings of the case-control study were supported further by negative findings obtained from the 6-year follow-up study of 445 patients with persistent proteinuria, during which 135 patients developed ESRD. CONCLUSIONS— Our large, comprehensive study did not find an association between the D18S880 microsatellite or any other polymorphisms in the CNDP2–CNDP1 genomic region and susceptibility for diabetic nephropathy in type 1 diabetes.

Progressive renal function decline begins in one third of patients with microalbuminuria and type 1 diabetes. This study examined whether this decline is associated with elevated excretion of inflammatory markers in urine. Five inflammatory markers (IL-6, IL-8, monocyte chemoattractant protein-1, interferon-gamma-inducible protein (IP-10), and macrophage inflammatory protein-1delta) were measured in urine samples from the First Joslin Study of the Natural History of Microalbuminuria in Type 1 Diabetes, a cohort recruited in 1991. Samples were obtained from 43 participants with microalbuminuria and stable renal function (nondecliners), from 28 with microalbuminuria and early progressive renal function decline (decliners), and from 74 with normoalbuminuria and stable renal function (reference). Urinary concentrations of all five inflammatory markers were significantly higher in decliners than in nondecliners, who were similar to the reference group. Multivariate analysis revealed that those with more than two markers elevated were more than five times as likely to have early progressive decline of renal function. In contrast, serum concentrations of C-reactive protein, IL-8, and macrophage inflammatory protein-1delta did not differ between decliners and nondecliners. These results support the hypothesis that inflammatory processes in the kidney contribute to the progression of nephropathy in patients with type 1 diabetes.

OBJECTIVE—The purpose of this study was to examine whether known genetic risk factors for type 1 diabetes (HLA-DRB1, -DQA1, and -DQB1 and insulin locus) play a role in the etiology of diabetic nephropathy. RESEARCH DESIGN AND METHODS—Genetic analysis of HLA-DRB1, -DQA1, -DQB1 and the insulin gene (INS) was performed in the Genetics of Kidneys in Diabetes (GoKinD) collection of DNA (European ancestry subset), which includes case patients with type 1 diabetes and nephropathy (n = 829) and control patients with type 1 diabetes but not nephropathy (n = 904). The availability of phenotypic and genotypic data on GoKinD participants allowed a detailed analysis of the association of these genes with diabetic nephropathy. RESULTS—Diabetic probands who were homozygous for HLA-DRB1*04 were 50% less likely to have nephropathy than probands without any DRB1*04 alleles. In heterozygous carriers, a protective effect of this allele was not as clearly evident; the mode of inheritance therefore remains unclear. This association was seen in probands with both short ( CONCLUSIONS—These data suggest that carriers of DRB1*04 are protected from some of the injurious hyperglycemic effects related to nephropathy. Interestingly, DRB1*04 appears to be both a risk allele for type 1 diabetes and a protective allele for nephropathy.

OBJECTIVE— Epidemiological and family studies have demonstrated that susceptibility genes play an important role in the etiology of diabetic nephropathy, defined as persistent proteinuria or end-stage renal disease (ESRD) in type 1 diabetes. RESEARCH DESIGN AND METHODS— To efficiently search for genomic regions harboring diabetic nephropathy genes, we conducted a scan using 5,382 informative single nucleotide polymorphisms on 100 sibpairs concordant for type 1 diabetes but discordant for diabetic nephropathy. In addition to being powerful for detecting linkage to diabetic nephropathy, this design allows linkage analysis on type 1 diabetes via traditional affected sibpair (ASP) analysis. In weighing the evidence for linkage, we considered maximum logarithm of odds score (maximum likelihood score [MLS]) values and corresponding allelic sharing patterns, calculated and viewed graphically using the software package SPLAT. RESULTS— Our primary finding for diabetic nephropathy, broadly defined, is on chromosome 19q (MLS = 3.1), and a secondary peak exists on chromosome 2q (MLS = 2.1). Stratification of discordant sibpairs based on whether disease had progressed to ESRD suggested four tertiary peaks on chromosome 1q (ESRD only), chromosome 20p (proteinuria only), and chromosome 3q (two loci 58 cm apart, one for ESRD only and another for proteinuria only). Additionally, analysis of 130 ASPs for type 1 diabetes confirmed the linkage to the HLA region on chromosome 6p (MLS = 9.2) and IDDM15 on chromosome 6q (MLS = 3.1). CONCLUSIONS— This study identified several novel loci as candidates for diabetic nephropathy, none of which appear to be the sole genetic determinant of diabetic nephropathy in type 1 diabetes. In addition, this study confirms two previously reported type 1 diabetes loci.

Aims Recently, an association of Type 2 diabetes (T2DM) with polymorphisms in PTPN1 located on chromosome 20q was reported. We attempted to replicate this finding in an ethnically homogeneous Polish population. Methods The study groups comprised 474 cases with T2DM and 411 control subjects with normal fasting glucose. All individuals were genotyped for the five previously reported PTPN1 polymorphisms using a fluorescence polarization method. HAPLO.STAT software was used to infer and compare haplotype distributions. Results The distributions of alleles and genotypes for the five genotyped PTPN1 polymorphisms did not differ between the T2DM cases and control subjects (lowest P = 0.6). Similarly, the frequency of the common haplotype reported to be associated with T2DM did not differ in cases and control subjects. We also failed to find such an association in Whites by performing a meta-analysis of all the available data on the association of those five SNPs with T2DM. Conclusion This case-control study in a Polish population did not confirm the reported association between polymorphisms in PTPN1 and T2DM.

The aims of this study were to assess the frequency and determinants of ( 1 ) treatment with angiotensin-converting enzyme inhibitors (ACE-I) and ( 2 ) progression to proteinuria in the presence of ACE-I treatment in patients with type 1 diabetes and microalbuminuria. A clinic-based cohort study of patients with type 1 diabetes was begun in 1991. The patients who were included in this study ( n = 373) are the cohort members who received a diagnosis of microalbuminuria during a 2-yr baseline observation and were followed for 10 yr with frequent assessments of urinary albumin excretion and biennial examinations. Progression to proteinuria occurred when the median urinary albumin excretion during a 2-yr interval exceeded 299 μg/min. During the decade-long study, the proportion of patients who had a history of microalbuminuria and were treated with ACE-I rose from 17 to 67%. Patients who started this treatment had (on average) higher BP, higher urinary albumin excretion, and longer diabetes duration than those who did not. Microalbuminuria often progressed to proteinuria (6.3/100 person-years) in those who were treated. Poor glycemic control and elevated serum cholesterol were the major determinants/predictors of this progression. Although treatment with ACE-I increased during the past decade, it was not completely effective, because microalbuminuria progressed to proteinuria in many treated patients. Poor glycemic control and elevated serum cholesterol were the major determinants/predictors for progression while on ACE-I treatment. The mechanisms that are responsible for the frequent failure of ACE-I to prevent progression of microalbuminuria to proteinuria in a clinical setting are not clear.

This study aimed to establish the time of initiation and the determinants of renal function decline in type 1 diabetes. Until now, such decline has been assumed to be a late-occurring event associated with proteinuria. A total of 267 patients with normoalbuminuria and 301 patients with microalbuminuria were followed for 8 to 12 yr. Linear trends (slopes) in GFR were estimated by serial measurement of serum cystatin C. Cases of early renal function decline were defined by loss in cystatin C GFR that exceeded -3.3%/yr, a threshold that corresponds to the 2.5th percentile of the distribution of GFR slopes in an independent nondiabetic normotensive population. Cases of early renal function decline occurred in 9% (mean slope -4.4; range -5.9 to -3.3%/yr) of the normoalbuminuria group and 31% (mean slope -7.1; range -23.8 to -3.3%/yr) of the microalbuminuria group (P < 0.001). Risk for early renal function decline depended on whether microalbuminuria regressed, remained stable, or progressed, rising from 16 to 32 and 68%, respectively (P < 0.001). In multivariate analysis, risk for decline was higher after age 35 yr or when glycosylated hemoglobin exceeded 9% but did not vary with diabetes duration, smoking, BP, or angiotensin-converting enzyme inhibitor treatment. Contrary to the existing paradigm of diabetic nephropathy, progressive renal function decline in type 1 diabetes is an early event that occurs in a large proportion of patients with microalbuminuria. Together with testing for microalbuminuria, clinical protocols using cystatin C to diagnose early renal function decline and track response to therapeutic interventions should be developed.

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.

Previous investigations of the ACE gene as a susceptibility factor for diabetic nephropathy have primarily focused on its insertion/deletion (Ins/Del) polymorphism. In a departure from these earlier studies, we used three tagging markers (A-5466C, T-3892C, and Ins/Del) at the ACE locus to test for disease haplotype associations. A case-control study design was used where case subjects were type 2 diabetic patients with advanced diabetic nephropathy, as indicated by the presence of proteinuria or chronic renal failure/end-stage renal disease, while control subjects were normoalbuminuric, despite >6 years of diabetes. None of the individual markers showed significant disease association when considered on their own. However, haplotype analyses revealed a near doubling in the prevalence of the A.T.D risk haplotype in case subjects (0.136) compared with control subjects (0.075) (P = 0.009), thus providing first evidence for a disease haplotype for advanced diabetic nephropathy at the ACE locus.

The Genetics of Kidneys in Diabetes (GoKinD) study is an initiative that aims to identify genes that are involved in diabetic nephropathy. A large number of individuals with type 1 diabetes were screened to identify two subsets, one with clear-cut kidney disease and another with normal renal status despite long-term diabetes. Those who met additional entry criteria and consented to participate were enrolled. When possible, both parents also were enrolled to form family trios. As of November 2005, GoKinD included 3075 participants who comprise 671 case singletons, 623 control singletons, 272 case trios, and 323 control trios. Interested investigators may request the DNA collection and corresponding clinical data for GoKinD participants using the instructions and application form that are available at http://www.gokind.org/access. Participating scientists will have access to three data sets, each with distinct advantages. The set of 1294 singletons has adequate power to detect a wide range of genetic effects, even those of modest size. The set of case trios, which has adequate power to detect effects of moderate size, is not susceptible to false-positive results because of population substructure. The set of control trios is critical for excluding certain false-positive results that can occur in case trios and may be particularly useful for testing gene-environment interactions. Integration of the evidence from these three components into a single, unified analysis presents a challenge. This overview of the GoKinD study examines in detail the power of each study component and discusses analytic challenges that investigators will face in using this resource.

The main hallmark of diabetic nephropathy is elevation in urinary albumin excretion. We performed a genome-wide linkage scan in 63 extended families with multiple members with type II diabetes. Urinary albumin excretion, measured as the albumin-to-creatinine ratio (ACR), was determined in 426 diabetic and 431 nondiabetic relatives who were genotyped for 383 markers. The data were analyzed using variance components linkage analysis. Heritability (h2) of ACR was significant in diabetic (h2=0.23, P=0.0007), and nondiabetic (h2=0.39, P=0.0001) relatives. There was no significant difference in genetic variance of ACR between diabetic and nondiabetic relatives (P=0.16), and the genetic correlation (rG=0.64) for ACR between these two groups was not different from 1 (P=0.12). These results suggested that similar genes contribute to variation in ACR in diabetic and nondiabetic relatives. This hypothesis was supported further by the linkage results. Support for linkage to ACR was suggestive in diabetic relatives and became significant in all relatives for chromosome 22q (logarithm of odds, LOD=3.7) and chromosome 7q (LOD=3.1). When analyses were restricted to 59 Caucasian families, support for linkage in all relatives increased and became significant for 5q (LOD=3.4). In conclusion, genes on chromosomes 22q, 5q and 7q may contribute to variation in urinary albumin excretion in diabetic and nondiabetic individuals.

Objective: We sought to determine the role of the acute insulin secretory response to glucose (AIRg) in predicting weight gain in normoglycemic persons with no family history of diabetes, who are at low risk for development of disease. Research Methods and Procedures: One hundred five individuals (64 men and 41 women) who underwent measures of weight and AIRg and insulin sensitivity index (SI) by intravenous glucose tolerance test between 1963 and 1983 were surveyed again for weight between 1994 and 1999, with a mean follow-up of 26 ± 4 years. Results: Mean change in weight was 8 ± 10 kg. Annualized weight change was calculated as change in kilograms divided by change in year and averaged 0.27 ± 0.04 kg/yr. Dividing the cohort by either median AIRg or median SI demonstrated no association of either AIRg or SI with total or annualized weight gain. Subgroup analysis by ideal body weight or gender did not alter the association. Furthermore, no association between AIRg and weight gain rate was seen within insulin-sensitive or -resistant subgroups, although younger age at entry was associated with greater rates of weight gain. Discussion: Our data suggest that neither AIRg nor SI plays a role in predicting weight gain in normoglycemic individuals with no family history of diabetes.

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.

Research on early renal function decline in diabetes is hampered by lack of simple tools for detecting trends (particularly systematic decreases) in renal function over time when GFR is normal or elevated. This study sought to assess how well serum cystatin C meets that need. Thirty participants with type 2 diabetes in the Diabetic Renal Disease Study met these three eligibility criteria: GFR >20 ml/min per 1.73 m2 at baseline (based on cold iothalamate clearance), 4 yr of follow-up, and yearly measurements of iothalamate clearance and serum cystatin C. With the use of linear regression, each individual’s trend in renal function over time, expressed as annual percentage change in iothalamate clearance, was determined. Serum cystatin C in mg/L was transformed to its reciprocal (100/cystatin C), and linear regression was used to determine each individual’s trend over time, expressed as annual percentage change. In paired comparisons of 100/cystatin C with iothalamate clearance at each examination, the two measures were numerically similar. More important, the trends in 100/cystatin C and iothalamate clearance were strongly correlated (Spearman r = 0.77). All 20 participants with negative trends in iothalamate clearance (declining renal function) also had negative trends for 100/cystatin C. Results were discordant for only three participants. In contrast, the trends for three commonly used creatinine-based estimates of GFR compared poorly with trends in iothalamate clearance (Spearman r < 0.35). Serial measures of serum cystatin C accurately detect trends in renal function in patients with normal or elevated GFR and provide means for studying early renal function decline in diabetes.

Epidemic of end-stage renal disease in people with diabetes in the United States population: Do we know the cause? Background The number of individuals initiating renal replacement therapy in the United States population grew exponentially over the past two decades. Cases of end-stage renal diseae (ESRD) attributed to diabetes accounted for most of this increase. In this report we examined factors that may account for the increase to determine whether it truly represents an epidemic of ESRD due to diabetes. Methods We reviewed time trends in data of the United States Renal Data system, the Diabetes Surveillance Program of the Centers for Disease Control and Prevention, and diabetes literature. Results Recent growth of the number of individuals with diabetes accounted for less than 10% of the increase in the number of diabetes-related ESRD. Instead, most of it was due to a threefold increase in risk of ESRD in people with diabetes and, therefore, qualifies as an epidemic. Curiously, this epidemic occurred despite widening implementation of effective renoprotective therapies. Individuals with type 2 diabetes, regardless of gender, age, or race, experienced the greatest increase in risk. There is no evidence that diabetic patients have been surviving longer, so the increased risk was not attributable to the high risk associated with long duration diabetes. Conclusion We hypothesize that an epidemic of ESRD has occurred in people with diabetes in the United States population over the last two decades. The nature of the factor responsible for the epidemic and the reasons it affects patients with type 2 diabetes particularly are unknown. Research efforts to identify the putative factor deserve high priority, as does a commitment of resources to provide care for the burgeoning number of patients with ESRD and type 2 diabetes.

Proteinuria and impaired kidney function are 2 major traits of diabetic nephropathy that aggregate (are heritable) in families of diabetic individuals. Although both traits are heritable, they are not genetically correlated. These findings not only support the hypothesis that the development of diabetic nephropathy consists of 2 distinct disease processes (ie, increasing proteinuria and declining kidney function) but also strongly justify searches for the putative genes that separately determine variation in these processes. These searches have used both genome-wide scans and candidate-gene approaches. By use of genome-scan approaches, several research groups have identified genetic regions on chromosomes 7q, 18q, and 22q that harbor genes that determine either variation in urinary albumin excretion or susceptibility to proteinuria in families who have type 2 diabetes. The evidence for linkage in these 3 genetic regions was suggestive or strong, but, except for 7q, the regions did not overlap across studies. Two genome scans performed in families who have type 2 diabetes identified genetic regions on chromosome 3q, 6q, 7p, and 18q that harbor susceptibility genes that determine variation in glomerular filtration rate or susceptibility to the development of end-stage renal disease (ESRD). The region on 7p overlapped in both studies. Optimism is growing that a positional cloning approach applied to these putative genetic regions will lead to the isolation of the susceptibility genes for proteinuria and ESRD. Meanwhile, significant efforts that make use of the candidate-gene approach have been directed to the search for susceptibility genes for diabetic nephropathy. Unfortunately, positive findings have not been consistent.

Maturity-onset diabetes of the young (MODY) is a subtype of diabetes defined by an autosomal dominant inheritance and a young onset. Six MODY genes have been discovered to date. To identify additional MODY loci, we conducted a genome scan in 21 extended U.S. families (15 white and 6 from minorities, for a total of 237 individuals) in which MODY was not caused by known MODY genes. Seven chromosomal regions (1q42, 2q24, 2q37, 4p13, 8p23, 11p15, and 19q12) had a parametric heterogeneity logarithm of odds (HLOD) ≥1.00 or a nonparametric logarithm of odds (LOD) ≥0.59 (P ≤ 0.05) in the initial screen. After typing additional markers at these loci to reduce the spacing to 2–3 cM, significant linkage was detected on 8p23 (HLOD = 3.37 at D8S1130 and nonparametric LOD = 3.66; P = 2 × 10−5 at D8S265), where a 4.7-Mb inversion polymorphism is located. Thirty percent of the families (6 of 21) were linked with this region. Another linkage peak on chromosome 2q37 with an HLOD of 1.96 at D2S345/D2S2968 accounted for diabetes in an additional 25% of families (5 of 21). All 6 minority families were among the 11 families linked to these loci. None of the other loci followed up had an HLOD exceeding 1.50. In summary, we have identified a MODY locus on 8p23 that accounts for diabetes in a substantial proportion of MODY cases unlinked to known MODY genes. Another novel MODY locus may be present on 2q37. Cloning these new MODY genes may offer insights to disease pathways that are relevant to the cause of common type 2 diabetes.

Abnormal activation of protein kinase C-beta isoforms in the diabetic state has been implicated in the development of diabetic nephropathy. It is thus plausible that DNA sequence differences in the protein kinase C-beta1 gene (PRKCB1), which encodes both betaI and betaII isoforms, may influence susceptibility to nephropathy. Nine single-nucleotide polymorphisms (SNP) in PRKCB1 were tested for association with diabetic nephropathy in type I diabetes mellitus, by using both case-control and family-study designs. Allele and genotype distributions of two SNP in the promoter (--1504C/T and --546C/G) differed significantly between case patients and control patients (P0.05). These associations were particularly strong with diabetes mellitus duration of24 yr (P = 0.002). The risk of diabetic nephropathy was higher among carriers of the T allele of the --1504C/T SNP, compared with noncarriers (odds ratio, 2.54; 95% confidence interval, 1.39 to 4.62), and among carriers of the G allele of the --546C/G SNP (odds ratio, 2.45; 95% confidence interval, 1.37 to 4.38). Among individuals with diabetes mellitus duration of/==" BORDER="0"24 yr, these two SNP were not associated with diabetic nephropathy. These positive findings were confirmed by using the family-based transmission disequilibrium test. The T-G haplotype, with both risk alleles, was transmitted more frequently than expected from heterozygous parents to offspring who developed diabetic nephropathy during the first 24 yr of diabetes mellitus. It is concluded that DNA sequence differences in the promoter of PRKCB1 contribute to diabetic nephropathy susceptibility in type I diabetes mellitus.

Mutations in hepatocyte nuclear factor (HNF)-1α (MODY3) account for the largest proportion of maturity-onset diabetes of the young (MODY) cases in the U.S. This form of diabetes is characterized by impaired insulin secretion in response to glucose, but wide variability exists in the severity of hyperglycemia and in the age at which it becomes clinically manifest. We have previously shown that the age at onset of diabetes in MODY3 families is influenced by familial factors (including modifying genes) and exposure to diabetes in utero. To identify genes influencing the onset of MODY3, we conducted a genome scan in 13 extended MODY families in which diabetes segregates with an HNF-1α mutation. Linkage with age at onset of diabetes was assessed by genetic variance component analysis using SOLAR. The locus with the strongest evidence of linkage was on chromosome 14q24 (D14S588; logarithm of odds [LOD] = 2.58, P = 0.0004). This location overlaps with IDDM11 and includes SEL1L, a negative regulator of the Notch pathway that may control islet development. Linkage evidence also supported loci on 5p15 (D5S817; LOD = 2.44, P = 0.0004) and 9q22 (D9S910; LOD = 2.02, P = 0.0018). The latter matches a region linked to 2-h insulin levels in Pima Indians. Less strong linkage evidence was observed at three other regions: chromosomes 3p24 (LOD = 1.44), 7q21 (1.20), and 16q23 (1.51). Our data are consistent with the existence of multiple loci that contribute to the expression of the MODY3 phenotype. Identification of these genes will offer new insights into the pathophysiology of MODY that may, in turn, increase our understanding of the cellular events underlying more common forms of diabetes.

In normoglycemic offspring of two type 2 diabetic parents, low insulin sensitivity (S I ) and low insulin-independent glucose effectiveness (S G ) predict the development of diabetes one to two decades later. To determine whether low S I , low S G, or low acute insulin response to glucose are predictive of diabetes in a population at low genetic risk for disease, 181 normoglycemic individuals with no family history of diabetes (FH−) and 150 normoglycemic offspring of two type 2 diabetic parents (FH+) underwent i.v. glucose tolerance testing (IVGTT) between the years 1964–82. During 25 ± 6 years follow-up, comprising 2,758 person years, the FH− cohort (54 ± 9 years) had an age-adjusted incidence rate of type 2 diabetes of 1.8 per 1,000 person years, similar to that in other population-based studies, but significantly lower than 16.7 for the FH+ cohort. Even when the two study populations were subdivided by initial values of S I and S G derived from IVGTT's performed at study entry, there was a 10- to 20-fold difference in age-adjusted incidence rates for diabetes in the FH− vs. FH+ individuals with low S I and low S G . The acute insulin response to glucose was not predictive of the development of diabetes when considered independently or when assessed as a function of S I , i.e., the glucose disposition index. These data demonstrate that low glucose disposal rates are robustly associated with the development of diabetes in the FH+ individuals, but insulin resistance per se is not sufficient for the development of diabetes in individuals without family history of disease and strongly suggest a familial factor, not detectable in our current measures of the dynamic responses of glucose or insulin to an IVGTT is an important risk factor for type 2 diabetes. Low S I and low S G , both measures of glucose disposal, interact with this putative familial factor to result in a high risk of type 2 diabetes in the FH+ individuals, but not in the FH− individuals.

Background: Transforming growth factor-β1 (TGF-β1) is a profibrotic cytokine suspected to be a crucial factor underlying glomerulosclerosis in advanced diabetic nephropathy. However, its potential role as a susceptibility gene for the development of this microvascular complication is unresolved. Methods: We examined whether DNA sequence variants in the TGF-β1 gene are associated with advanced diabetic nephropathy among Caucasians with type 1 diabetes mellitus. These variants included three coding (Leu10Pro, Arg25Pro, and Thr263Ile) and two noncoding single-nucleotide polymorphisms (−800 and −509), as well as an insertion/deletion of a cytosine residue in intron 4. A large case-control study design was used in which cases were patients with type 1 diabetes with advanced diabetic nephropathy (presence of persistent proteinuria or end-stage renal disease [ESRD]; n=298) and controls were patients who remained normoalbuminuric despite greater than 15 years of type 1 diabetes (n = 263). Results: Genotype frequencies for all polymorphisms were in Hardy-Weinberg equilibrium. Genotype distributions of all six DNA sequence variants were very similar between cases and controls ( P = not significant). There was no significant difference in genotype distributions among cases regardless of whether these individuals with diabetes were proteinuric at the time of examination or had already developed ESRD secondary to diabetic nephropathy. Stratified analyses according to diabetes duration and glycemic control likewise did not detect an association between DNA sequence variants and advanced diabetic nephropathy. Conclusion: Genetic variation at the TGF-β1 locus is unlikely to confer significant susceptibility to advanced diabetic nephropathy in patients with type 1 diabetes mellitus. Am J Kidney Dis 41:22-28. © 2003 by the National Kidney Foundation, Inc.

OBJECTIVE—To determine the distribution of the age at onset of diabetes (maturity-onset diabetes of the young-3 [MODY3]) and to identify determinants of the onset of diabetes in carriers of HNF-1α mutations. RESEARCH DESIGN AND METHODS—Extended families (n = 104) with type 2 diabetes inherited in a dominant pattern were recruited and screened for diabetes-causing mutations in HNF-1α. RESULTS—HNF-1α mutations cosegregated with diabetes in only 13 families, all with a mean age at onset CONCLUSIONS—Mutations in HNF-1α accounts for diabetes in a small proportion of families with a dominant pattern of inheritance. Age at onset of diabetes in MODY3 families varied widely and was influenced by familial factors (including modifying genes) and parent of origin (whether a mutation carrier was exposed to diabetes in utero).

Elevation of intracellular glucose in mesangial cells as mediated by GLUT1 may be important in initiating cellular mechanisms that cause diabetic nephropathy. To determine whether DNA sequence differences in GLUT1 confer susceptibility to this complication, single-nucleotide polymorphisms (SNPs) in this gene were examined using a large case-control study. SNPs examined included the known XbaI (intron 2) and HaeIII SNPs (exon 2). Four novel SNPs located in three putative enhancers were also investigated. Homozygosity for the XbaI(-) allele was associated with diabetic nephropathy (odds ratio 1.83 [95% CI 1.01–3.33]). Furthermore, homozygosity for the A allele for a novel SNP (enhancer-2 SNP 1) located in a putative insulin-responsive enhancer-2 was associated with diabetic nephropathy (2.38 [1.16–4.90]). Patients who were homozygous for risk alleles at both XbaI SNP and enhancer-2 SNP 1 [i.e., homozygosity for XbaI(-)/A haplotype] also had an increased risk of diabetic nephropathy (2.40 [1.13–5.07]). Because enhancer-2 SNP 1 may directly control GLUT1 expression, the strong linkage disequilibrium between the two SNPs likely accounts for XbaI SNP being associated with diabetic nephropathy. In conclusion, our study confirms that SNPs at the GLUT1 locus are associated with susceptibility to diabetic nephropathy in type 1 diabetes. Although these SNPs confer a considerable personal risk for diabetic nephropathy, they account for a limited proportion of cases among type 1 diabetic patients.

Genes play a role in many processes underlying late diabetic complications, but efforts to identify genetic variants have produced disappointing and contradictory results. Here, we evaluate whether the study designs and analytic methods commonly being used are optimal for finding susceptibility genes for diabetic complications. We do so by generating plausible genetic models and assessing the performance of case-control and family-based trio study designs. What emerges as a key determinant of success is duration of diabetes. This perspective focuses on duration of diabetes before complication onset and its influence on the ability to detect major and minor gene effects. It does not delve into the distinct effect of duration after complication onset, which can enrich case subjects with genotypes conferring survival advantage. We use clinically diagnosed nephropathy in type 1 diabetes to show how ignoring duration can result in considerable power loss in both case-control and family-based trio designs. We further show how, under certain circumstances, disregard for duration information can paradoxically lead to implicating nonrisk alleles as causative. Our results indicate that problems can be minimized by selecting case subjects with short diabetes duration and, to a lesser extent, control subjects with long duration or, perhaps, by adjusting for duration during analysis.

Recent evidence indicates that IB kinase (Ikk) may be a mediator of acquired forms of insulin-resistance. In this study, we examined whether genetic variability at the Ikk locus (IKBKB) contributes to the development of genetic forms of early-onset type 2 diabetes transmitted with an autosomal dominant mode of inheritance. Linkage with four markers flanking the IKBKB gene was evaluated in 32 multigenerational families. Included in the study were 233 diabetic (mean age at Dx 37 18) and 152 nondiabetic subjects. The overall LOD scores were negative (54.9 and 46.2 on the centromeric and telomeric sides, respectively) indicating that variability in IKBKB was not a major determinant of diabetes in these families. Positive values, however, were observed for selected pedigrees. All 17 families for which linkage with the IKBKB locus could not be excluded were screened for sequence differences in the 22 exons and 1.6 kb of the 5 flanking region by dideoxyfingerprinting or direct sequencing. Polymorphisms were identified in the 5 flanking region (1775del/insC and 1547T > A), exon 11 (c.1083A > G, L361L) and in intron 12 (IVS1214t > a). However, no mutations segregating with diabetes could be found in these families. Furthermore, all four polymorphisms had similar allele frequencies in the 32 family probands, 171 individuals with common, later-onset type 2 diabetes, and 182 nondiabetic controls. We conclude that sequence differences in the IKBKB gene do not play a major role in either early-onset, autosomal dominant type 2 diabetes, or common forms with a later-onset. (J Clin Endocrinol Metab 87: 1894 –1897, 2002)

Cardiac autonomic neuropathy predicts future adverse renal outcomes in the general population. This study sought to determine its relationship with early progressive renal decline in type 1 diabetes.A subset of participants with normoalbuminuria (n=204) or microalbuminuria (n=166) from the First Joslin Kidney Study underwent assessment for cardiac autonomic neuropathy using heart rate variability during baseline visits performed from January 1991 to April 1992. Cardiac autonomic neuropathy was defined as an R-R variation (mean circular resultant)20. Participants also had baseline and follow-up measurement of eGFR. Early progressive renal decline was evaluated according to two definitions: early GFR loss (slope of eGFR estimated by cystatin C-3.3%/year) and incident advanced CKD (stage ≥3, defined by eGFR [calculated by Modification of Diet in Renal Disease method]60 ml/min per 1.73 m(2)). Association with baseline cardiac autonomic neuropathy was assessed by adjusted logistic regression and Cox proportional hazards.Among the 370 participants, 47 (13%) had baseline cardiac autonomic neuropathy, 51 (14%) had early GFR loss, and 68 (18%) had incident advanced CKD over a median 14-year follow-up. Early GFR loss occurred in 15 (32%) of the 47 patients with baseline autonomic neuropathy and in 32 (10%) of the 323 without baseline autonomic neuropathy (P0.001). Baseline autonomic neuropathy was strongly associated with odds of early GFR loss (adjusted odds ratio, 4.09; 95% confidence interval, 1.65 to 10.12; P=0.002). Incident advanced CKD was observed in 22 (47%) of those with baseline autonomic neuropathy and 46 (14%) of those without baseline autonomic neuropathy (P0.001). Autonomic neuropathy was independently associated with incident advanced CKD (adjusted hazard ratio, 2.76; 95% confidence interval, 1.44 to 5.30; P=0.002).Cardiac autonomic neuropathy was a strong independent predictor of the long-term risk of early progressive renal decline in type 1 diabetes. Future research should explore the mechanisms by which autonomic neuropathy may be associated with renal function loss.

OBJECTIVE Progressive decrease in the glomerular filtration rate (GFR), or renal decline, in type 1 diabetes (T1D) is observed in patients with macroalbuminuria. However, it is unknown whether this decline begins during microalbuminuria (MA) or normoalbuminuria (NA). RESEARCH DESIGN AND METHODS The study group (second Joslin Kidney Study) comprises patients with T1D and NA (n = 286) or MA (n = 248) who were followed for 4–10 years (median 8 years). Serial measurements (median 6, range 3–16) of serum creatinine and cystatin C were used jointly to estimate GFR (eGFRcr-cys) and assess its trajectories during follow-up. RESULTS Renal decline (progressive eGFRcr-cys loss of at least 3.3% per year) occurred in 10% of the NA and 35% of the MA (P < 0.001). In both groups, the strongest determinants of renal decline were baseline serum concentrations of uric acid (P < 0.001) and tumor necrosis factor receptor 1 or 2 (TNFR-1 or -2, P < 0.001). Other significant risk factors included baseline HbA1c, age/diabetes duration, and systolic blood pressure. Relative impacts of these determinants were similar in NA and MA. Renal decline was not associated with sex or baseline serum concentration of TNF-α, IL-6, IL-8, IP-10, MCP-1, VCAM, ICAM, Fas, or FasL. CONCLUSIONS Renal decline in T1D begins during NA and it is determined by multiple factors, similar to MA. Thus, this early decline is the primary disease process leading to impaired renal function in T1D. Changes in albumin excretion rate, such as the onset of MA or its progression to macroalbuminuria, are either caused by or develop in parallel to the early renal decline.