A NOVEL DIABETES SYNDROME IN AMERICAN BLACKS (TYPE 1.5 DIABETES): INSULIN SECRETORY AND BINDING STUDIES

Abstract

We have recently described an early onset (<30y/o) diabetes syndrome (1.5 diabetes) in Blacks characterized by 1) Absence of HLA DR3 and DR4 (unusual in whites (3%) vs Blacks with diabetes (26%) ) and islet cell autoantibodies, 2) insulin dependence at onset, 3) frequent noninsulin dependent course thereafter and 4) frequent autosomal dominant family history of diabetes. We studied 14 such pts (1.5 DM) for their plasma C-peptide (CP) responses to oral sustacal (4 cal/kg) and their monocyte insulin binding characteristics. Six controls (C) and 5 pts with classical IDD were also studied for CP responses. Peak stimulated CP levels for the 1.5 DM pts (0.31±0.8 pmol/ml) were less than C (0.78±0.05; p=0.004), but greater than IDD (0.05±0.02) despite their having diabetes of greater duration (4±3 years for IDD vs 11±10 years for 1.5 DM). Maximal insulin binding in the 1.5 DM pts was no different from 18 controls (8.9±3.1% vs 7.4±1.6%; p=0.10), and all 1.5 DM pts had normal insulin affinities. Insulin receptor sites were increased in pts with 1.5 DM (29.7K±24 sites/peripheral monocyte) over C (13.2K±5K; p<0.01). 1.5 DM is reminiscent of Jamacian (J) type diabetes. In summary, 1.5 DM patients had CP responses intermediate between IDD and C. In general, there were no defects in insulin binding or affinity; however there appears to be upregulation of the number of insulin receptors secondary to insulinopenia.

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