We have studied skeletal muscle capillary basement membrane width (CBMW) and intensity of skeletal muscle extracellular basement membrane staining for albumin and IgG in eight families with maturity-onset diabetes in the young (MODY).

Ninety-two MODY patients were identified. Sixtythree of these patients, 33 relatives with nondiagnostic oral glucose tolerance studies, and 61 normoglycemic relatives were studied for glucose and insulin. Twentysix of these MODY patients, 20 normoglycemic relatives, and 16 unrelated normal controls had skeletal muscle capillary morphologic studies.

The muscle capillary basement membrane was significantly increased in MODY patients younger than 40 yr when compared with unrelated normal subjects and relatives of the same age (P < 0.001). However, in these families, the CBMW of MODY patients showed no significant thickening with age (slope = 0.45, P < 0.14), as expected and seen in the normal subjects and in the normoglycemic relatives of the patients (slope = 1.21, P < 0.001). The slope derived from the linear regression of age and CBMW in MODY patients (0.45 ± 0.29) was significantly less (P < 0.05) than that of the nondiabetic subjects (1.21 ± 0.19). The mean intensity of skeletal muscle extracellular basement membrane staining for albumin was higher in MODY patients (1.1 ± 0.15) than in unrelated normal subjects (0.7 ± 0.1, P < 0.025) and normal MODY family members (0.6 ± 0.08, P < 0.01).

The unexpected absence of basement membrane thickening with age in the MODY patients may explain the paucity of vascular complications that have been reported by some. However, these findings may also reflect genetic heterogeneity, mild hyperglycemia, shorter duration of disease, or any combination of these factors. The immunohistochemical studies indicate that the increased localization of plasma proteins in extracellular membranes in diabetes, also seen in insulin-dependent diabetes, is a marker of hyperglycemia and is not specific for different types of diabetes.

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