Finland has the world's highest incidence of type 1 diabetes, and it is steadily increasing. We determined concordance rates and estimated heritability for type 1 diabetes in the Finnish Twin Cohort, a population-based twin cohort of 22,650 twin pairs. In addition, we studied age of onset in the first affected twin and discordance time between concordant twin pairs. Finnish twins born between 1958 and 1986 were followed for type 1 diabetes until 1998. We identified 228 twin pairs with type 1 diabetes: 44 monozygotic (MZ), 183 dizygotic (DZ), and 1 pair with unknown zygosity. The pairwise concordance for type 1 diabetes was 27.3% (95% CI 22.8 -31.8) in MZ and 3.8% (2.7-4.9) in DZ twins. The probandwise concordance was 42.9% (26.7-59.2) and 7.4% (2.2-12.6), respectively. The longest discordance times were 6.9 years among concordant MZ twins and 23.6 years among DZ twins. The risk for type 1 diabetes was highest in cotwins of the index twins diagnosed at a very young age. The model with additive genetic and individual environmental effects was the best-fitting liability model, with 88% of phenotypic variance due to genetic factors and the remaining variance due to unshared environmental factors. In conclusion, these nationwide twin data demonstrated high genetic liability for type 1 diabetes. Early-onset diabetes increases the risk in cotwins. However, the majority of affected MZ twin pairs remain discordant for type 1 diabetes. Diabetes 52: 1052-1055, 2003A recent study showed that Finland's record type 1 diabetes incidence increased predominantly in younger age-groups (1,2). The exact mechanism underlying the process leading to type 1 diabetes remains elusive, despite years of research. It is known that genes in the HLA region substantially influence the risk of type 1 diabetes and familial clustering (3,4). Several environmental factors have been proposed to contribute to its pathogenesis, but their causative role has not been established (5-7).Twins provide a powerful tool to investigate relative importance of genetic and environmental factors on traits by comparing of concordance in monozygotic (MZ) and dizygotic (DZ) twins. Finland is one of the few countries with a population-based twin cohort (8) offering uniquely large, representative, and therefore unbiased data on type 1 diabetes among twins. The objective of this study was to determine concordance rates and to estimate heritability for type 1 diabetes in the Finnish population-based cohort. Furthermore, we examined risk for progression to diabetes in cotwins in relation to age at onset of the first affected twin (index twin) and the discordance time among concordant twin pairs.Of 303 diabetic twins identified from different sources, 247 cases (in 228 pairs) had type 1 diabetes (116 females, 131 males), 28 had type 2 diabetes, 15 had secondary diabetes, and 13 had gestational diabetes. Of the type 1 diabetic twin pairs, 44 belonged to MZ pairs, 90 to opposite-sex DZ pairs, 93 to same-sex DZ pairs, and 1 to a same-sex pair of unknown zygosity, totaling 22...

Objective-This study compares mortality from type 1 diabetes in Japan and Finland and examines the effects of sex, age at diagnosis, and calendar time period of diagnosis on mortality.Research Design and Methods-Patients with type 1 diabetes from Japan (n = 1,408) and Finland (n = 5,126), diagnosed from 1965 through 1979, at age <18 years, were followed until 1994. Mortality was estimated with and without adjustment for that of the general population to assess absolute and relative mortality using Cox proportional hazard models.Results-Overall mortality rates in Japan and Finland were 607 (95% CI 510-718) and 352 (315-393), respectively, per 100,000 person-years; standardized mortality ratios were 12.9 (10.8-15.3) and 3.7 (3.3-4.1), respectively. Absolute mortality was higher for men than for women in Finland, but relative mortality was higher for women than for men in both cohorts. Absolute mortality was higher in both cohorts among those whose diabetes was diagnosed during puberty, but relative mortality did not show any significant difference by age at diagnosis in either cohort. In Japan, both absolute and relative mortality were higher among those whose diagnosis was in the 1960s rather than the 1970s.Conclusions-Mortality from type 1 diabetes was higher in Japan compared with Finland. The increased risk of death from type 1 diabetes seems to vary by sex, age at diagnosis, and calendar time period of diagnosis. Further investigation, especially on cause-specific mortality, is warranted in the two countries.Mortality from childhood-onset type 1 diabetes differs greatly from country to country (1)(2)(3)(4) 1979 had higher mortality rates than patients in three other countries: Israel, Finland, and the U.S. (5,6). The greater risk of diabetic renal disease in Japan is one reason for the higher mortality rate (7).We conducted a follow-up study through 1994 of the Japanese and Finnish cohorts of the original DERI study (5,6) to observe how mortality patterns from type 1 diabetes might have changed with the age of the subjects and longer duration of diabetes. Because some of the subjects had reached their forties, the increasing risk of death unrelated to diabetes could not be ignored. Likewise, with follow-up lasting 25 years, mortality in each country's general population might have changed significantly and have affected the mortality from type 1 diabetes. Therefore, we needed to examine both the absolute and relative mortality of type 1 diabetes. The aims of this extended comparative study were, thus, to compare the mortality of patients with type 1 diabetes in Japan and Finland and to examine the effects of sex, age at diagnosis, and calendar time period of diagnosis on mortality. Research Design and Methods SubjectsInclusion criteria are described in detail elsewhere (5,6). In short, patients were eligible if they 1) had received a diagnosis of diabetes before the age of 18 years, 2) had started insulin treatment within 1 month after diagnosis, and 3) had received a diagnosis of diabetes from 1965 t...

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