Although hereditary factors clearly modulate susceptibility to develop diabetes, their role as determinants of vascular complications associated with diabetes remains unclear. These studies were undertaken to further assess the extent to which capillary basement membrane thickening (CBMT) is governed by metabolic derangements associated with relative or absolute insulin deficiency versus genetic determinants of vascular disease closely linked to but independent of those modulating susceptibility to develop relative or absolute insulin deficiency. Quadriceps muscle capillary basement membranes obtained by needle biopsy were examined in eight pairs of identical twins discordant for insulin-dependent diabetes (IOD) for 11–29 yr. Biopsy material from one of the diabetic twins was technically unsuitable for study.

The average CBM width of the IDD twins was found to be significantly thicker than that of their nondiabetic (ND) twin mates (t = 2.50, P < 0.025). Three IDD, but none of the ND twins, had basement membrane width values in excess of 95% upper tolerance intervals for age- and sex-matched controls with no family history of diabetes.

The absence of CBMT in all of the ND twins and in four of the IDD twins with diabetes of 15–24 yr duration argues against the existence, in this group of subjects, of hereditary determinants of diabetic vascular disease linked to those governing susceptibility to develop diabetes. In addition, the absence of CBMT in four subjects with IDD of 15–24 yr duration is consistent with evidence from other studies indicating that diabetic microangiopathy is not an inevitable consequence of the diabetic milieu. The finding that muscle CBMT and retinopathy were restricted to IDD twins attests to the importance of the diabetic milieu as a predisposing or permissive factor in the initiation and progression of diabetic vascular disease.

This content is only available via PDF.