Clinical features among adult-onset type 1 diabetes, distribution of subtypes, and differences in probable and definite slowly progressive insulin-dependent diabetes mellitus: A single hospital-based study over a 13-year period.

Aims: In Japan, type 1 diabetes (T1D) is classified into three subtypes based on its onset patterns; however, the proportion of each subtype remains unexplored. To elucidate the heterogeneity in adult-onset type 1 diabetes, we compared the frequencies of subtypes and clinical features by age at onset.

Materials And Methods: This cross-sectional, observational, single-institution study included 482 individuals (161 male) with T1D. The clinical and laboratory data, including glutamic acid decarboxylase autoantibodies, were extracted from the medical records.

Results: The number of adults who developed T1D decreased with age. Among all patients, 62% (n = 299) had acute-onset T1D, 27% (n = 131) had slowly progressive T1D (SPIDDM), and 11% (n = 52) had fulminant T1D. The proportion of patients with fulminant T1D was approximately equivalent in all age groups; however, the percentage of patients with acute-onset T1D decreased from 78% in the 20-29 age group to 27% in the 70-79 age group. The proportion of patients with SPIDDM significantly increased with age, ranging from 16% in the 20-29 age group to 60% in the 70-79 age group. Among patients with SPIDDM, the prevalence of definite SPIDDM was 89%, and this prevalence did not differ based on the age at onset. Body mass index and C-peptide levels among patients with probable SPIDDM were significantly higher than those among patients with definite SPIDDM.

Conclusions: The proportion of adult-onset T1D subtypes differed according to the age at onset. In adult-onset T1D, some etiological differences may be based on age at onset.