[Ultrastructural abnormalities of the chondrocytes in pycnodysostosis. Their relation to a disorder of lipid metabolism].

The ultrastructural study of the growth cartilage of pycnodysostosis reveals the presence of abnormal inclusions in the majority of the chondrocytes. The inclusions are single membrane bound and contain granular material and lamellar irregularly interwoven structures which at very high magnification appear to be made up of dense parallel bands. These vacuoles displace adjacent structures and some of them appear to be closely related to the Golgi apparatus. In addition, appearances are sometimes seen which suggest the expulsion of the vacuoles into the cell capsules. The abnormal chondrocyte inclusions are visible by optic microscopy and stained with Nile blue on frozen section. Thus, histochemical and ultrastructural characteristics suggest a lipid (probably phospholipid) content. Many authors have already stressed the role of lipids in the process of calcification. The abnormalities described might bear some relation to the densification of the skeleton seen in pycnodysostosis.