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Objective: Mortality is increased in patients with hereditary hemochromatosis, in individuals from the general population with increased transferrin saturation (TS), and also in patients with type 1 diabetes and increased TS from a highly specialized diabetes clinic. Thus, we have recommended targeted screening for TS in specialized diabetes clinics. Whether mortality is also increased in individuals from the general population with diabetes and increased TS is unknown., Research Design and Methods: In two Danish population studies (N = 84,865), we examined mortality according to baseline levels of TS and hemochromatosis genotype (HFE) G → A substitution at nucleotide 845 in codon 282 (C282Y/C282Y) in individuals with diabetes (type 1, N = 118; type 2, N = 3,228; total, N = 3,346)., Results: The cumulative survival rate was reduced in individuals with diabetes with TS ≥50% vs. <50% (log-rank; P < 0.0001), with median survival ages of 66 and 79 years, respectively. The hazard ratio (HR) for TS ≥50% vs. <50% was 2.0 (95% CI 1.3-2.8; P = 0.0004) for total mortality overall (and similar for men and women separately); 2.6 (1.3-5.4; P = 0.008) for neoplasms; and 3.4 (2.0-6.0; P = 0.00002) for endocrinological causes. A stepwise increased risk of total mortality was observed for stepwise increasing TS (log-rank test, P = 0.0001), with an HR for TS ≥70% vs. TS <20% of 4.8 (2.0-12; P = 0.0006). The HR for total mortality in individuals with diabetes for C282Y/C282Y versus wild type/wild type was 3.3 (1.04-10; P = 0.04), and for C282Y/C282Y and TS ≥50% versus wild type/wild type and TS <50% was 6.0 (1.5-24; P = 0.01). Six percent of these premature deaths can possibly be avoided by early screening for TS or HFE genotype., Conclusions: Individuals with diabetes, ascertained in the general population, with increased TS or HFE genotype have a twofold to sixfold increased risk of premature death.

Objective: It is not known to what extent iron overload predicts prognosis in patients with diabetes after diagnosis or whether iron overload is a risk factor independent of the HFE genotype. We investigated total and cause-specific mortality according to increased transferrin saturation (≥ 50 vs. <50%), whether mortality is driven by the HFE genotype, and whether early measurement of transferrin saturation helps to predict mortality outcome., Research Design and Methods: Cohort 1 included patients with late-onset type 1 diabetes (n = 716) with a cross-sectional measurement of transferrin saturation and HFE genotype. Cohort 2 included consecutively recruited patients with any diabetes (n = 6,120), transferrin saturation measurement at referral, and HFE genotype if transferrin saturation was above 50%., Results: In cohort 1, the hazard ratio for total mortality was 2.3 (95% CI 1.3-3.9; P = 0.002) and for cause-specific mortality by neoplasms was 5.8 (2.4-14; P = 0.00007) in patients with transferrin saturation ≥ 50 vs. <50%. Excluding genotypes C282Y/C282Y and C282Y/H63D gave similar results. The hazard ratio for total mortality was 4.0 (1.2-13; P = 0.01) and for cause-specific mortality by neoplasms was 13 (3.6-49; P = 0.0001) in patients with C282Y/C282Y versus wild type. In cohort 2, total mortality was not different in patients with transferrin saturation ≥ 50 vs. <50%. In patients with late-onset type 1 diabetes and transferrin saturation ≥ 50%, the hazard ratio for total mortality was 0.4 (0.2-0.9; P = 0.03) in cohort 2 versus cohort 1., Conclusions: Increased transferrin saturation and HFE genotype C282Y/C282Y predict total mortality in patients with late-onset type 1 diabetes, and increased transferrin saturation after diagnosis is an independent risk factor. Early measurement of transferrin saturation in these patients leading to early intervention improves life expectancy.

Objective: We tested the hypothesis that elevated transferrin saturation is associated with an increased risk of any form of diabetes, as well as type 1 or type 2 diabetes separately., Research Design and Methods: We used two general population studies, The Copenhagen City Heart Study (CCHS, N = 9,121) and The Copenhagen General Population Study (CGPS, N = 24,195), as well as a 1:1 age- and sex-matched population-based case-control study with 6,129 patients with diabetes from the Steno Diabetes Centre and 6,129 control subjects, totaling 8,535 patients with diabetes and 37,039 control subjects., Results: In the combined studies, odds ratios in those with transferrin saturation ≥50% vs. <50% were 2.1 (95% CI 1.3-3.4; P = 0.003) for any form of diabetes; 2.6 (1.2-5.6; P = 0.01) for type 1 diabetes; and 1.7 (1.4-2.1; P = 0.001) for type 2 diabetes., Conclusions: Elevated transferrin saturation confers a two- to threefold increased risk of developing any form of diabetes, as well as type 1 and type 2 diabetes separately.