Synalbumin antagonist was investigated in a group of forty-eight siblings of diabetic children. Nine parents of these patients, ten normal controls and eleven diabetic children were included in this study. In twenty-six of the forty-eight siblings synalbumin was detected. Glucose uptake by the rat hemidiaphragm was depressed from a mean of 13.36 to 0.99 mg. per cent of glucose per 10 mg. of tissue in ninety minutes incubation in the presence of 1,000 μU. of insulin. In five of nine parents tested, synalbumin was present. In only three of fourteen families in which two or more siblings were studied was synalbumin absent. These findings suggest a familial distribution of the antagonist. Fasting blood sugar, glucose tolerance test and plasma insulin were normal in synalbumin positive siblings. Negligible amounts of immunoreactive insulin were detected in the albumin extracted from nondiabetic relatives. The synalbumin did not interfere with the immunoassay of insulin. In extracts of insulin treated diabetics, various amounts of insulin were found. Five of eleven diabetics showed antagonism, three were border line, and three did not show antagonism. The results obtained suggest that synalbumin may be used as a genetic marker and encourage further investigation to assess the role of this inhibitor in the development of diabetes and as an indicator of prediabetes.

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