AORTIC-ANEURYSM IN MARFANS-SYNDROME - CHANGES IN THE ULTRASTRUCTURE AND COMPOSITION OF COLLAGEN

  • 1 January 1979
    • journal article
    • research article
    • Vol. 129  (OCT) , 645-657
Abstract
A 36 yr old woman with Marfan''s syndrome had punch skin biopsies for the study of collagen solubility and collagen biosynthesis in fibroblast tissue culture. Later, surgical replacement of a thoracic aortic aneurysm became necessary. The aortic tissue and mitral valve obtained at operation were examined by light microscopy and EM. SDS [sodium dodecylsulfate] acrylamide gel electrophoresis of the collagen extracted from the aortic aneurysm and from the skin showed a split or doubled .alpha.2 chain. The CM cellulose elution pattern of radioactive collagen from skin fibroblast culture media showed a double peak in the .alpha.1 region, absent to minimal .alpha.2 chain and normal type III collagen. EM examination of aortic tissue and a mitral valve revealed a loose matrix, few elastic fibers which showed degenerative changes, and collagen fibers which appeared either normal or showed a helical twist in longitudinal section and a flower-like shape in cross section. Bundles of non-banded microfibrils were noted. The majority of the smooth muscle cells showed incresed metabolic activity as evidenced by the number of pinocytotic vesicles, well developed Golgi, many mitochondria, dilated RER [rough endoplosmic reticulum] and local loss of cytoplasmic membrane. The quantitative and qualitative change of the .alpha.2 chain suggests a defect in the biosynthesis of type I collagen resulting in decreaed tensile strength. Based on these observations a scheme for the pathogenesis of aortic aneurysm in Marfan''s syndrome is proposed. The collagen fibers are not able to withstand cyclic stresses and the wall of the aorta dilates. This leads to disintegration of elastic fibers and, in response to these changes, smooth muscle cells become metabolically active and produce collagen fibers which appear twisted.