Seasonality of Type 1 (insulin-dependent) diabetes mellitus: values of C-peptide, insulin antibodies and haemoglobin A1c show evidence of a more rapid loss of insulin secretion in epidemic patients

Abstract

According to month of diagnosis, 165 children who developed Type 1 (insulin-dependent) diabetes mellitus at the age of 0-16.2 years (mean±SD, 7.6±4.1 years) could be divided into 69 patients diagnosed during peak seasons (epidemic cases) and 96 patients diagnosed during months of low incidence (non-epidemic cases). Seasonality of onset of symptoms and of diagnosis was observed in both sexes in all age groups. The patients diagnosed during peak seasons had shorter duration of symptoms (13.2±8.1 days) as compared to 22.9±10.3 days; p<0.001 in the patients diagnosed during months of low incidence. At diagnosis, 88.4% (61/69) of the epidemic group had ketonuria as compared to 71.9% (69/96); p<0.06 in the non-epidemic patients. The values of C-peptide, insulin antibodies, haemoglobin A1c and HLA-DR phenotype frequencies in the 69 epidemic patients were compared with those of the 96 non-epidemic patients. In the epidemic patients, the C-peptide values of 0.11±0.05 mmol/l at diagnosis had increased to 0.12±0.05 mmol/l at one month and 0.13±0.06 mmol/l at 3 months. These values were significantly lower (p<0.001) than in the non-epidemic patients at the same time points: 0.17±0.08 nmol/l; p<0.001, 0.23±0.11 nmol/l; p<0.001, and 0.22±0.10 nmol/l. Values of insulin antibodies (U/l) of 0.06±0.03, 0.05±0.05 and 0.17±0.10 in the epidemic group compared to 0.014±0.015, 0.02±0.01, and 0.04±0.04 in the non-epidemic group at the same aforementioned time points also showed significant differences (p<0.001). Differences in these variables between the two groups continued until four years after diagnosis. Significant differences were also observed in the values of haemoglobin A1c and HLA-DR phenotype frequencies in the two groups. The results suggest that children with Type 1 diabetes can be divided into two sub-groups with different early clinical course which might depend on a different aetiology, related both to seasonal variation at diagnosis and to a genetic heterogeneity. © 1989 Springer-Verlag.