Residual β-Cell Function and Male/Female Ratio Are Higher in Incident Young Adults Than in Children

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Abstract
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 β-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.
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