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People with type 2 diabetes frequently use low-calorie sweeteners to manage glycemia and reduce caloric intake. Use of erythritol, a low-calorie sweetener, has increased recently. Higher circulating concentration associates with major cardiac events and metabolic disease in observational data, prompting some concern. As observational data may be prone to confounding and reverse causality, we undertook bidirectional Mendelian randomization (MR) to investigate potential causal associations between erythritol and coronary artery disease (CAD), BMI, waist-hip-ratio (WHR), and glycemic and renal traits in cohorts of European ancestry. Analyses were undertaken using instruments comprising genome-wide significant variants from three cohorts with erythritol measurement. Across instruments, we did not find supportive evidence that increased erythritol increases CAD (b = −0.033 ± 0.02, P = 0.14; b = 0.46 ± 0.37, P = 0.23). MR indicates erythritol may decrease BMI (b = −0.04 ± 0.018, P = 0.03; b = −0.04 ± 0.0085, P = 1.23 × 10−5; b = −0.083 ± 0.092, P = 0.036), with potential evidence from one instrument of increased BMI adjusted for WHR (b = 0.046 ± 0.022, P = 0.035). No evidence of causal association was found with other traits. In conclusion, we did not find supportive evidence from MR that erythritol increases cardiometabolic disease. These findings await confirmation in well-designed prospective studies. Article Highlights: Circulating concentration of erythritol is associated with increased risk of type 2 diabetes and cardiovascular disease. Bidirectional Mendelian randomization was undertaken to assess potential causal associations between circulating erythritol and cardiometabolic disease. Mendelian randomization analyses did not find supportive evidence for a causal association between circulating erythritol and cardiometabolic disease. [ABSTRACT FROM AUTHOR]

Obesity is postulated to independently increase chronic kidney disease (CKD), even after adjusting for type 2 diabetes (T2D) and hypertension. Dysglycemia below T2D thresholds, frequently seen with obesity, also increases CKD risk. Whether obesity increases CKD independent of dysglycemia and hypertension is unknown and likely influences the optimal weight loss (WL) needed to reduce CKD. T2D remission rates plateau with 20–25% WL after bariatric surgery (BS), but further WL increases normoglycemia and normotension. We undertook bidirectional inverse variance weighted Mendelian randomization (IVWMR) to investigate potential independent causal associations between increased BMI and estimated glomerular filtration rate (eGFR) in CKD (CKDeGFR) (<60 mL/min/1.73 m2) and microalbuminuria (MA). In 5,337 BS patients, we assessed whether WL influences >50% decline in eGFR (primary outcome) or CKD hospitalization (secondary outcome), using <20% WL as a comparator. IVWMR results suggest that increased BMI increases CKDeGFR (b = 0.13, P = 1.64 × 10−4; odds ratio [OR] 1.14 [95% CI 1.07, 1.23]) and MA (b = 0.25; P = 2.14 × 10−4; OR 1.29 [1.13, 1.48]). After adjusting for hypertension and fasting glucose, increased BMI did not significantly increase CKDeGFR (b = −0.02; P = 0.72; OR 0.98 [0.87, 1.1]) or MA (b = 0.19; P = 0.08; OR 1.21 [0.98, 1.51]). Post-BS WL significantly reduced the primary outcome with 30 to <40% WL (hazard ratio [HR] 0.53 [95% CI 0.32, 0.87]) but not 20 to <30% WL (HR 0.72 [0.44, 1.2]) and ≥40% WL (HR 0.73 [0.41, 1.30]). For CKD hospitalization, progressive reduction was seen with increased WL, which was significant for 30 to <40% WL (HR 0.37 [0.17, 0.82]) and ≥40% WL (HR 0.24 [0.07, 0.89]) but not 20 to <30% WL (HR 0.60 [0.29, 1.23]). The data suggest that obesity is likely not an independent cause of CKD. WL thresholds previously associated with normotension and normoglycemia, likely causal mediators, may reduce CKD after BS. ARTICLE HIGHLIGHTS: Obesity is likely not an independent contributor to chronic kidney disease (CKD). Obesity likely contributes to CKD via effects on glycemia and blood pressure. Weight loss at thresholds associated with normoglycemia and normotension may reduce CKD. [ABSTRACT FROM AUTHOR]

Mendelian randomization (MR) suggests that postprandial hyperinsulinemia (unadjusted for plasma glucose) increases BMI, but its impact on cardiometabolic disease, a leading cause for mortality and morbidity in people with obesity, is not established. Fat distribution i.e., increased centripetal and/or reduced femoro-gluteal adiposity, is causally associated with and better predicts cardiometabolic disease than BMI. We therefore undertook bidirectional MR to assess the effect of corrected insulin response (CIR) (insulin 30 min after a glucose challenge adjusted for plasma glucose) on BMI, waist-to-hip ratio (WHR), leg fat, type 2 diabetes (T2D), triglyceride (TG), HDL, liver fat, hypertension (HTN), and coronary artery disease (CAD) in people of European descent. Inverse variance-weighted MR suggests a potential causal association between increased CIR and increased BMI (b = 0.048 ± 0.02, P = 0.03), increased leg fat (b = 0.029 ± 0.012, P = 0.01), reduced T2D (b = -0.73 ± 0.15, P = 6 × 10-7, odds ratio [OR] 0.48 [95% CI 0.36-0.64]), reduced TG (b = -0.07 ± 0.02, P = 0.003), and increased HDL (b = 0.04 ± 0.01, P = 0.006) with some evidence of horizontal pleiotropy. CIR had neutral effects on WHR (b = 0.009 ± 0.02, P = 0.69), liver fat (b = -0.08 ± 0.04, P = 0.06), HTN (b = -0.001 ± 0.004, P = 0.7, OR 1.00 [95% CI 0.99-1.01]), and CAD (b = -0.002 ± 0.002, P = 0.48, OR 0.99 [95% CI 0.81-1.21]). T2D decreased CIR (b -0.22 ± 0.04, P = 1.3 × 10-7), with no evidence that BMI, TG, HDL, liver fat, HTN, and CAD modulate CIR. In conclusion, we did not find evidence that increased CIR increases cardiometabolic disease. It might increase BMI with favorable fat distribution, reduce T2D, and improve lipids. [ABSTRACT FROM AUTHOR]

Objective: The role of genetic factors in the risk of cardiovascular disease (CVD) for patients with type 1 diabetes (T1D) remains unknown. We therefore examined whether previously identified genetic factors for coronary artery disease (CAD) are associated with the risk of CVD above and beyond established demographic and clinical factors in the Diabetes Control and Complications Trial (DCCT)/Epidemiology of Diabetes Interventions and Complications (EDIC) study.Research Design and Methods: Polygenic risk scores (PRS) and individual genetic variants identified in previous studies were obtained from genome-wide genotyping performed in 1,371 DCCT/EDIC participants. Two composite CVD outcomes were considered: major adverse cardiovascular events (MACE) (CVD death or nonfatal myocardial infarction [MI] or stroke) and any CVD (MACE plus confirmed angina, silent MI, revascularization, or congestive heart failure). Cox proportional hazards models assessed the association between the genetic factors and the risk of CVD with adjustment for other factors (including age, lipids, blood pressure, and glycemia).Results: CAD PRS was strongly associated with the subsequent risk of any CVD (42% and 38% higher risk per 1-SD increase in unadjusted and fully adjusted models, respectively; P < 0.0001) and with the risk of MACE (50% and 40% higher risk per 1-SD increase in unadjusted and fully adjusted models, respectively; P < 0.0001). Several individual single nucleotide polymorphisms were also nominally associated with the risk of any CVD and MACE.Conclusions: Genetic factors are associated with the risk of subsequent CVD in individuals with T1D above and beyond the effect of established risk factors such as age, lipids, blood pressure, and glycemia. [ABSTRACT FROM AUTHOR]

Objective: Individuals with diabetes have higher resting heart rate compared with those without, which may be predictive of long-term cardiovascular disease (CVD) risk. Using data from the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications (DCCT/EDIC) study, we evaluated whether the beneficial effect of intensive versus conventional diabetes therapy on heart rate persisted, the factors mediating the differences in heart rate between treatment groups, and the effects of heart rate on future CVD risk.Research Design and Methods: Longitudinal changes in heart rate, from annual electrocardiograms over 22 years of EDIC follow-up, were evaluated in 1,402 participants with type 1 diabetes. Linear mixed models were used to assess the effect of DCCT treatment group on mean heart rate over time, and Cox proportional hazards models were used to estimate the effect of heart rate on CVD risk during DCCT/EDIC.Results: At DCCT closeout, 52% of participants were male and mean ± SD age was 33 ± 7 years, diabetes duration 12 ± 5 years, and HbA1c 7.4 ± 1.2% (intensive) and 9.1 ± 1.6% (conventional). Through EDIC, participants in the intensive group had significantly lower heart rate in comparison with the conventional group. While significant group differences in heart rate were fully attenuated by DCCT/EDIC mean HbA1c, higher heart rate predicted CVD and major adverse cardiovascular events independent of other risk factors.Conclusions: After 22 years of follow-up, former intensive versus conventional therapy remained significantly associated with lower heart rate, consistent with the long-term beneficial effects of intensive therapy on CVD. DCCT treatment group effects on heart rate were explained by differences in DCCT/EDIC mean HbA1c. [ABSTRACT FROM AUTHOR]

Most replicated genetic determinants for type 1 diabetes are common (minor allele frequency [MAF] >5%). We aimed to identify novel rare or low-frequency (MAF <5%) single nucleotide polymorphisms with large effects on risk of type 1 diabetes. We undertook deep imputation of genotyped data followed by genome-wide association testing and meta-analysis of 9,358 type 1 diabetes case and 15,705 control subjects from 12 European cohorts. Candidate variants were replicated in a separate cohort of 4,329 case and 9,543 control subjects. Our meta-analysis identified 27 independent variants outside the MHC, among which 3 were novel and had MAF <5%. Three of these variants replicated with Preplication < 0.05 and Pcombined < Pdiscovery In silico analysis prioritized a rare variant at 2q24.3 (rs60587303 [C], MAF 0.5%) within the first intron of STK39, with an effect size comparable with those of common variants in the INS and PTPN22 loci (combined [from the discovery and replication cohorts] estimate of odds ratio [ORcombined] 1.97, 95% CI 1.58-2.47, Pcombined = 2.9 × 10-9). Pharmacological inhibition of Stk39 activity in primary murine T cells augmented effector responses through enhancement of interleukin 2 signaling. These findings provide insight into the genetic architecture of type 1 diabetes and have identified rare variants having a large effect on disease risk. [ABSTRACT FROM AUTHOR]

Objective: In type 1 diabetes (T1D), the course of microalbuminuria is unpredictable and timing of glomerular filtration rate (GFR) loss is uncertain. Thus, there is a need to identify the risk factors associated with the development of more advanced stages of kidney disease through large, long-term systematic analysis.Research Design and Methods: Multivariable Cox proportional hazards models assessed the association of baseline and time-dependent glycemic and nonglycemic risk factors for incident macroalbuminuria and reduced estimated GFR (eGFR; defined as <60 mL/min/1.73 m2) over a mean of 27 years in the Diabetes Control and Complications Trial (DCCT) cohort.Results: Higher mean HbA1c (hazard ratio [HR] 1.969 per 1% higher level [95% CI 1.671-2.319]) and male sex (HR 2.767 [95% CI 1.951-3.923]) were the most significant factors independently associated with incident macroalbuminuria, whereas higher mean triglycerides, higher pulse, higher systolic blood pressure (BP), longer diabetes duration, higher current HbA1c, and lower mean weight had lower magnitude associations. For incident reduced eGFR, higher mean HbA1c (HR 1.952 per 1% higher level [95% CI 1.714-2.223]) followed by higher mean triglycerides, older age, and higher systolic BP were the most significant factors.Conclusions: Although several risk factors associated with macroalbuminuria and reduced eGFR were identified, higher mean glycemic exposure was the strongest determinant of kidney disease among the modifiable risk factors. These findings may inform targeted clinical strategies for the frequency of screening, prevention, and treatment of kidney disease in T1D. [ABSTRACT FROM AUTHOR]

Glycated hemoglobin (HbA1c) is an important measure of glycemia in diabetes. HbA1c is influenced by environmental and genetic factors both in people with and in people without diabetes. We performed a genome-wide association study (GWAS) for HbA1c in a Finnish type 1 diabetes (T1D) cohort, FinnDiane. Top results were examined for replication in T1D cohorts DCCT/EDIC, WESDR, CACTI, EDC, and RASS, and a meta-analysis was performed. Three SNPs in high linkage disequilibrium on chromosome 13 near relaxin family peptide receptor 2 (RXFP2) were associated with HbA1c in FinnDiane at genome-wide significance (P < 5 × 10-8). The minor alleles of rs2085277 and rs1360072 were associated with higher HbA1c also in the meta-analysis with RASS (P < 5 × 10-8), where these variants had minor allele frequencies ≥1%. Furthermore, these SNPs were associated with HbA1c in an East Asian population without diabetes (P ≤ 0.013). A weighted genetic risk score created from 55 HbA1c-associated variants from the literature was associated with HbA1c in FinnDiane but explained only a small amount of variation. Understanding the genetic basis of glycemic control and HbA1c may lead to better prevention of diabetes complications. [ABSTRACT FROM AUTHOR]

Skin fluorescence (SF) noninvasively measures advanced glycation end products (AGEs) in the skin and is a risk indicator for diabetes complications. N-acetyltransferase 2 (NAT2) is the only known locus influencing SF. We aimed to identify additional genetic loci influencing SF in type 1 diabetes (T1D) through a meta-analysis of genome-wide association studies (N = 1,359) including Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications (DCCT/EDIC) and Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR). A locus on chromosome 1, rs7533564 (P = 1.9 × 10(-9)), was associated with skin intrinsic fluorescence measured by SCOUT DS (excitation 375 nm, emission 435-655 nm), which remained significant after adjustment for time-weighted HbA1c (P = 1.7 × 10(-8)). rs7533564 was associated with mean HbA1c in meta-analysis (P = 0.0225), mean glycated albumin (P = 0.0029), and glyoxal hydroimidazolones (P = 0.049), an AGE measured in skin biopsy collagen, in DCCT. rs7533564 was not associated with diabetes complications in DCCT/EDIC or with SF in subjects without diabetes (nondiabetic [ND]) (N = 8,721). In conclusion, we identified a new locus associated with SF in T1D subjects that did not show similar effect in ND subjects, suggesting a diabetes-specific effect. This association needs to be investigated in type 2 diabetes. [ABSTRACT FROM AUTHOR]

The risk of long-term diabetes complications is not fully explained by diabetes duration or long-term glycemic exposure, suggesting the involvement of genetic factors. Because thiamine regulates intracellular glucose metabolism and corrects for multiple damaging effects of high glucose, we hypothesized that variants in specific thiamine transporters are associated with risk of severe retinopathy and/or severe nephropathy because they modify an individual's ability to achieve sufficiently high intracellular thiamine levels. We tested 134 single nucleotide polymorphisms (SNPs) in two thiamine transporters (SLC19A2/3) and their transcription factors (SP1/2) for an association with severe retinopathy or nephropathy or their combination in the FinnDiane cohort. Subsequently, the results were examined for replication in the DCCT/EDIC and Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR) cohorts. We found two SNPs in strong linkage disequilibrium in the SLC19A3 locus associated with a reduced rate of severe retinopathy and the combined phenotype of severe retinopathy and end-stage renal disease. The association for the combined phenotype reached genome-wide significance in a meta-analysis that included the WESDR cohort. These findings suggest that genetic variations in SLC19A3 play an important role in the pathogenesis of severe diabetic retinopathy and nephropathy and may explain why some individuals with type 1 diabetes are less prone than others to develop microvascular complications. [ABSTRACT FROM AUTHOR]

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 P1105. The strongest association was at the FRMD3 (4.1 protein ezrin, radixin, moesin [FERM] domain containing 3) locus (odds ratio [OR]1.45, P5.0107). A strong association was also identified at the CARS (cysteinyl-tRNA synthetase) locus (OR 1.36, P3.1106). Associations between both loci and time to onset of diabetic nephropathy were supported in the DCCT/EDIC study (hazard ratio [HR]1.33, P0.02, and HR1.32, P 0.01, respectively). We demonstrated expression 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.

Few genes for diabetic nephropathy have been identified. After testing 1450 SNPs in 212 genes, we identified association of rs17880135 in SOD1 with time to severe nephropathy (SN: AER>300mg/24hrs or end-stage renal failure) in 1,362 white T1DM probands from the DCCT/EDIC study (p=5.6 x 10-5, Hazard Ratio (HR)=2.62, 95% CI=1.64-4.18). We followed this up by genotyping a total of 10 SNPs from the region, selected to tag common variations. Similarly to rs17880135, rs17881180 was also associated with SN, while both rs202446 and rs204732 (HR=1.59, 95% CI 1.28-2.00, p=5 x 10;5) were associated with time to persistent microalbuminuria (PM; 2 consecutive AER>30 mg/24hrs). In backward selection of multiple markers, only rs17881180 was associated with SN, while either rs202446 or rs204732 were associated with PM. Multi-state and -marker models confirmed that rs 17881180 is associated only with the progression from PM to SN, but not with the development of PM. Family-based association results were non-significant for rs17881180 and SN (p=0.57), likely due to low power, however, rs202446 was significant with PM (p=0.048). Association of rs17880135 with renal function was supported by borderline association with serum cystatin C in non-diabetic relatives (p=0.056). Because association of rs17880135 with SN was detected as the most significant after testing 1450 SNPs, the reported HR may be optimistic, and the effect size in independent samples more modest. Bootstrap estimates suggested that the upward bias in logHR may be 50% or more. We attempted to replicate the association in GoKinD, a cross-sectional case-control study of nephropathy, but the results for rs17880135 and rs202446 were non-significant in both case-control and family-based association analyses. To help understand the discrepancies between DCCT/EDIC and GoKinD, we performed a cross-sectional analysis of DCCT/EDIC data. This produced results that were much attenuated compared to the primary analysis model of time to event, which included baseline covariates and repeated measures of glycemic control: rs17880135 and SN, p=0.0039 cf 5.6 x 10-5; rs202446 and PM, p=0.14 cf 4.3 x 10-5), suggesting that the use of longitudinal designs and modelling of appropriate risk factors over time can increase power to detect gene effects for complex traits like nephropathy. [ABSTRACT FROM AUTHOR]

The Diabetes Control and Complications Trial (DCCT) established the salutary effects of intensive insulin treatment on the development and progression of retinopathy, neuropathy and nephropathy in type 1 diabetes. The DCCT cohort continues to be followed in the Epidemiology of Diabetes Interventions and Complications (EDIC) a long term observational study. We describe the association of single nucleotide polymorphic (SNP) variants in VEGF gene in 1,365 white DCCT/EDIC subjects with incident mild and severe retinopathy (time from DCCT baseline to > 3 step [mild], and to 53/<53 [severe] on Early Treatment Diabetic Retinopathy Study scale), macular edema (ME) (time to clinically significant ME or focal laser treatment); and persistent microalbuminuria (2 consecutive albumin excretion > 30 mg/24 h), and severe nephropathy (albumin excretion > 300 mg/24 h, dialysis or kidney transplant). We studied 18 variants in VEGF to capture all linkage disequilibrium bins containing variants (pairwise r² ≥ .64). Multi-SNP global tests of the five clinical phenotypes indicated that SNPs in VEGF were significantly associated only with time to severe retinopathy (SR) (P= 6.8 x 10[sup -5]). Controlling for all measured risk factors for retinopathy, 7 SNPs were significantly (P<0.05) associated with this phenotype. The most significant single-marker association was for rs3025021 (Hazard Ratio, 1.43, 95% confidence interval [1.16-1.76], P= 8.6 x 10[sup -4]). Significant excess transmission of the rs3025021 (T) allele to probands with SR was also observed in family-based analysis (P=0.013). Backward selection of 15 markers, and allowing for pairwise interactions, selected six SNPs that are independently significant in the model (P < 0.05), suggesting that multiple variants in VEGF are associated with SR. These data demonstrate the genetic involvement of VEGF in predisposition to the development of SR type 1 diabetes. [ABSTRACT FROM AUTHOR]

To identify genetic variants associated with diabetic retinopathy (DR), we performed a large multiethnic genome-wide association study. Discovery included eight European cohorts ( n = 3,246) and seven African American cohorts ( n = 2,611). We meta-analyzed across cohorts using inverse-variance weighting, with and without liability threshold modeling of glycemic control and duration of diabetes. Variants with a P value <1 × 10 -5 were investigated in replication cohorts that included 18,545 European, 16,453 Asian, and 2,710 Hispanic subjects. After correction for multiple testing, the C allele of rs142293996 in an intron of nuclear VCP-like ( NVL ) was associated with DR in European discovery cohorts ( P = 2.1 × 10 -9 ), but did not reach genome-wide significance after meta-analysis with replication cohorts. We applied the Disease Association Protein-Protein Link Evaluator (DAPPLE) to our discovery results to test for evidence of risk being spread across underlying molecular pathways. One protein-protein interaction network built from genes in regions associated with proliferative DR was found to have significant connectivity ( P = 0.0009) and corroborated with gene set enrichment analyses. These findings suggest that genetic variation in NVL, as well as variation within a protein-protein interaction network that includes genes implicated in inflammation, may influence risk for DR., (© 2018 by the American Diabetes Association.)

Identification of sequence variants robustly associated with predisposition to diabetic kidney disease (DKD) has the potential to provide insights into the pathophysiological mechanisms responsible. We conducted a genome-wide association study (GWAS) of DKD in type 2 diabetes (T2D) using eight complementary dichotomous and quantitative DKD phenotypes: the principal dichotomous analysis involved 5,717 T2D subjects, 3,345 with DKD. Promising association signals were evaluated in up to 26,827 subjects with T2D (12,710 with DKD). A combined T1D+T2D GWAS was performed using complementary data available for subjects with T1D, which, with replication samples, involved up to 40,340 subjects with diabetes (18,582 with DKD). Analysis of specific DKD phenotypes identified a novel signal near GABRR1 (rs9942471, P = 4.5 × 10 -8 ) associated with microalbuminuria in European T2D case subjects. However, no replication of this signal was observed in Asian subjects with T2D or in the equivalent T1D analysis. There was only limited support, in this substantially enlarged analysis, for association at previously reported DKD signals, except for those at UMOD and PRKAG2 , both associated with estimated glomerular filtration rate. We conclude that, despite challenges in addressing phenotypic heterogeneity, access to increased sample sizes will continue to provide more robust inference regarding risk variant discovery for DKD., (© 2018 by the American Diabetes Association.)

Elevated concentrations of albumin in the urine, albuminuria, are a hallmark of diabetic kidney disease and are associated with an increased risk for end-stage renal disease and cardiovascular events. To gain insight into the pathophysiological mechanisms underlying albuminuria, we conducted meta-analyses of genome-wide association studies and independent replication in up to 5,825 individuals of European ancestry with diabetes and up to 46,061 without diabetes, followed by functional studies. Known associations of variants in CUBN, encoding cubilin, with the urinary albumin-to-creatinine ratio (UACR) were confirmed in the overall sample (P = 2.4 × 10(-10)). Gene-by-diabetes interactions were detected and confirmed for variants in HS6ST1 and near RAB38/CTSC. Single nucleotide polymorphisms at these loci demonstrated a genetic effect on UACR in individuals with but not without diabetes. The change in the average UACR per minor allele was 21% for HS6ST1 (P = 6.3 × 10(-7)) and 13% for RAB38/CTSC (P = 5.8 × 10(-7)). Experiments using streptozotocin-induced diabetic Rab38 knockout and control rats showed higher urinary albumin concentrations and reduced amounts of megalin and cubilin at the proximal tubule cell surface in Rab38 knockout versus control rats. Relative expression of RAB38 was higher in tubuli of patients with diabetic kidney disease compared with control subjects. The loci identified here confirm known pathways and highlight novel pathways influencing albuminuria., (© 2016 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered.)

Background: Despite familial clustering of nephropathy and retinopathy severity in type 1 diabetes, few gene variants have been consistently associated with these outcomes., Research Design and Methods: We performed an individual-based genetic association study with time to renal and retinal outcomes in 1,362 white probands with type 1 diabetes from the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications (DCCT/EDIC) study. Specifically, we genotyped 1,411 SNPs that capture common variations in 212 candidate genes for long-term complications and analyzed them for association with the time from DCCT baseline to event for renal and retinal outcomes using multivariate Cox proportion hazards models. To address multiple testing and assist interpretation of the results, false discovery rate q values were calculated separately for each outcome., Results: We observed association between rs17880135 in the 3' region of superoxide dismutase 1 (SOD1) and the incidence of both severe nephropathy (hazard ratio [HR] 2.62 [95% CI 1.64-4.18], P = 5.6 x 10(-5), q = 0.06) and persistent microalbuminuria (1.82 [1.29-2.57], P = 6.4 x 10(-4), q = 0.46). Sequencing and fine-mapping identified additional SOD1 variants, including rs202446, rs9974610, and rs204732, which were also associated (P < 10(-3)) with persistent microalbuminuria, whereas rs17880135 and rs17881180 were similarly associated with the development of severe nephropathy. Attempts to replicate the findings in three cross-sectional case-control studies produced equivocal results. We observed no striking differences between risk genotypes in serum SOD activity, serum SOD1 mass, or SOD1 mRNA expression in lymphoblastoid cell lines., Conclusions: Multiple variations in SOD1 are significantly associated with persistent microalbuminuria and severe nephropathy in the DCCT/EDIC study.