Islet-cell (ICA) and organ-specific autoantibodies (OSA) were determined by the indirect immunofluorescence technique in 920 diabetics, 1,159 nondiabetic patients, and 100 young and 100 adult healthy controls with normal glucose tolerance. In control subjects ICA were not detected, and only 20 miscellaneous patients with normal glucose tolerance showed ICA (1.7 per cent). ICA were present in 45.4 per cent of patients with juvenile insulin-dependent diabetes (IDD) during the first six months of disease and in 29.1 per cent of patients between 6 and 12 months of disease onset; ICA presence decreased to 19.2 per cent and 20.6 per cent after one and five years of duration of diabetes.

In patients with maturity-onset IDD, ICA incidence was 19.4 per cent in the first year, 20 per cent between one and five years, and 12.2 per cent after five years of disease. In this group, 64 per cent of ICA-positive patients showed clinical and/or serologie evidence of thyroid, gastric, or adrenal autoimmune disorders.

In sera from young patients with non-insulin-dependent diabetes (J-NIDD), ICA were not detected. In adult patients with the same type of diabetes (M-NIDD) ICA incidence was 9.8, 7, and 8.9 per cent and was not related to the duration of diabetes. Patients with chemical diabetes were divided into two groups (younger and older than 35 years), and ICA incidence was 18.9 and 12.9 per cent, respectively. In two nondiabetic patients, glucagon cell autoantibodies were detected. ICA titers were variable in juvenile IDD of recent onset. Persistent ICA titers, frequently associated with OSA, were observed in the other types of diabetes, with the exception of J-NIDD. ICA may be considered markers of severe beta-cell alteration, with consequent reduction of insulin secretion, even though insulin dependency is sometimes delayed in a few patients.

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