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We investigated residual beta cell function in participants from the DCCT/EDIC study with an average of 35 (range 27, 48) years duration of T1D. Between 2015-2017 after 22-24 years of follow-up in EDIC, a 4-hour mixed meal tolerance test was administered to 944 participants and 7 timed plasma specimens were collected and assayed for C-peptide using a chemiluminescent immunoassay (Roche). We defined a significant post-stimulus response as a peak C-peptide concentration >0.03 nmol/L, based on an earlier DCCT study which demonstrated that the risk of microvascular disease progression was markedly higher among participants who entered the trial with values below this concentration. Overall, 71 (7.5%) participants were classified as “responders” with a median peak C-peptide of 0.10 nmol/L (IQR 0.06, 0.15). Among the 873 participants classified as “non-responders”, 46 had detectable peak C-peptide between 0.003 (limit of detection) and 0.029 nmol/L. Responders were slightly older than non-responders (58.5 ± 6.2 vs. 56.5 ± 6.8 y; p=0.02), yet had similar age of onset of diabetes (22.5 ± 7.0 vs. 21.4 ± 7.8 y) and duration of diabetes (35.9 ± 5.1 vs. 35.0 ± 4.9 y). Compared to non-responders, responders had lower HbA1c values (8.6 ± 1.7 vs. 8.9 ± 1.5%; p=0.01) and higher stimulated C-peptide (0.22 ± 0.14 vs. 0.11 ± 0.11 nmol/L; p In conclusion, beta cell function persists in some very long duration T1D patients and is associated with clinically meaningful reductions in the frequency of severe hypoglycemia. Disclosure R. Gubitosi-Klug: None. B. Braffett: None. S.M. Hitt: None. V. Arends: None. M. Steffes: None. A.K. Saenger: Advisory Panel; Self; Alere Inc. J. Lachin: Board Member; Self; AbbVie Inc., Celgene Corporation. J.P. Palmer: None.

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 × 10−5, q = 0.06) and persistent microalbuminuria (1.82 [1.29–2.57], P = 6.4 × 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.

Despite familial clustering of nephropathy and retinopathy severity in type 1 diabetes, few gene variants have been consistently associated with these outcomes.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.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 (P10(-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.Multiple variations in SOD1 are significantly associated with persistent microalbuminuria and severe nephropathy in the DCCT/EDIC study.