Thickening of basal lamina'(BL) which occurs with advancing age (1) and various diseases (4, 7, 10) is most common and severe in patients with diabetes mellitus(2, 8, 6, 12, 14). The reasons, for. and the mechanism of this thickening have thus far escaped satisfactory explanation. In this communication, we wish to provide new evidence which elucidates the development of thick BL and which directs attention to the underlying defect.

In a detailed study of capillaries in skeletal muscle from 40 overt diabetics (15), 26 chemical diabetics, and 41 nondiabetics (14), several findings suggested the possibility that the BL thickening is the result of repeated episodes of cell death and cell regeneration. These are:(a) The BL is not homogeneously thickened but is composed of concentrically arranged lamellae (6, 12, 14, 16), each measuring between 800 and 2000 A (Fig. 1). The thickness of individual lamellae increases with the distance from endothelium, while their electron opacity decreases. The innermost lamella is usually well defined, intimately applied to the endothelium, and encompasses the pericytes. The outermost lamella may be partly missing or it may be arranged in redundant folds.