Incidence of type 1 and type 2 diabetes in adults aged 30-49 years: the population-based registry in the province of Turin, Italy.

OBJECTIVE: Incidence of type 1 diabetes is considered to be low in adults, but no study has been performed in Mediterranean countries. RESEARCH DESIGN AND METHODS: We extended the study base of the registry of the province of Turin, Italy, to subjects aged 30-49 years in the period 1999-2001 to estimate the incidences of type 1 and type 2 diabetes. Diagnosis of type 1 diabetes was based on permanent insulin treatment or a fasting C-peptide level < or =0.20 nmol/l or islet cell (ICA) or GAD (GADA) antibody positivities. RESULTS: We identified 1,135 case subjects with high completeness of ascertainment (99%), giving an incidence rate of 58.0 per 100,000 person-years (95% CI 54.7-61.5). The incidence of type 1 diabetes was 7.3 per 100,000 person-years (6.2-8.6), comparable with the rates in subjects aged 0-14 and 15-29 years (10.3 [9.5-11.2] and 6.8 [6.3-7.4]). Male subjects had a higher risk than female subjects for both type 1 (rate ratio [RR] 1.70 [95% CI 1.21-2.38]) and type 2 (2.10 [1.84-2.40]) diabetes. ICA and/or GADA positivities were found in 16% of the cohort. In logistic regression, variables independently associated with autoimmune diabetes were age 30-39 years (odds ratio [OR] 2.39 [95% CI 1.40-4.07]), fasting C-peptide <0.60 nmol/l (3.09 [1.74-5.5]), and BMI <26 kg/m2 (2.17 [1.22-3.85]). CONCLUSIONS: Risk of type 1 diabetes between age 30 and 49 years is similar to that found in the same area between age 15 and 29 years. Further studies are required to allow geographical comparisons of risks of both childhood and adulthood autoimmune diabetes, the latter being probably higher than previously believed.

Residual beta-cell function and male/female ratio are higher in incident young adults than in children: the registry of type 1 diabetes of the province of Turin, Italy, 1984-2000.

OBJECTIVE: The hypothesis of age-dependent variations in epidemiologic and clinical features at onset of type 1 diabetes has been assessed in the registry of the province of Turin, Italy. RESEARCH DESIGN AND METHODS: The study base is the population 0-29 years of age of the province of Turin, in the period from 1984 to 2000. Islet cell antibody (ICA), GAD antibody (GADA), antibodies to protein tyrosine phosphatase (IA2), and C-peptide were measured in subgroups of the cohort. RESULTS: One thousand fifty-six incident cases have been identified (completeness of ascertainment 98.1%). Rates per 100,000 person-years were similar in males and females in the age-group 0-14 years (10.7, 95% CI 9.5-12.0 vs. 9.8, 8.6-11.1). In the age-group 15-29 years, males had higher risk than females (7.7, 6.9-8.6 vs. 5.3, 4.6-6.1; rate ratio, 1.46, 95% CI 1.23-1.74; P = 0.00002). Fasting plasma C-peptide values (n = 575) were twofold lower in the age-group 0-14 years than in the age-group 15-29 years (0.10 vs. 0.23 nmol/l; P < 0.0001). Frequencies of ICA and IA2 positivities (n = 183) decreased with increasing age, whereas frequency of GADA positivity increased. Idiopathic cases were 12.6% and had higher mean values of fasting (0.28 vs. 0.14 nmol/l; P = 0.043) and stimulated C-peptide (0.59 vs. 0.34 nmol/l; P = 0.05). In logistic regression analyses, subjects with fasting C-peptide values in the upper quartile had higher likelihood of being older (odds ratio 1.20 for year, 95% CI 1.11-1.28), ICA negative (0.26, 0.10-0.70), and female (1.29, 0.48-3.42). CONCLUSIONS: This study shows 1) sex differences in incidence rates in young adults; 2) better preserved beta-cell function in young adults, in idiopathic cases (12%), and in ICA-negative cases; and 3) lower frequencies of ICA and IA2 positivities and higher frequency of GADA positivity in young adults than in children.