Intracellular collagen fibrils in prolapsed ("floppy") human atrioventricular valves.

Ultrastructural study of prolapsed atrioventricular valves from five patients, one of whom also had the Marfan syndrome, disclosed granular cells that were characterized by numerous membrane-bound, electron-dense inclusions resembling those in the Hurler syndrome. Collagen fibrils were present within some of these inclusions. The intracellular collagen deposits may form as a consequence of abnormal interactions between newly secreted collagen and acid mucopolysaccharides.