Structural changes of collagen fibrils in skeletal dysplasias. Ultrastructural findings in the iliac crest.

The skeletal dysplasias are constitutional, generalized or localized disorders of the skeletal system involving a disturbance of growth and/or bone density; their genetic transmission varies. Pathomorphologically, a combined functional-structural disturbance of the cartilaginous and/or bone tissue is present. Clinically, the result is varying degrees of dwarfism. Within the framework of a systematic examination of skeletal dysplasias, a total of 84 iliac crest specimens/biopsies obtained from stillborn infants and patients varying in age from a few days to 40 years, were investigated in the electron microscope. The sections prepared extended from the perichondrium through the proximal resting zone to the primary mineralization zone. The structure of the collagen fibrils was studied in diastrophic dysplasia, pseudoachondroplasia, the WOLCOTT-RALLISON syndrome, osteogenesis imperfecta, and idiopathic juvenile osteoporosis. In diastrophic dysplasia, pseudoachondroplasia and idiopathic osteoporosis, the cartilaginous ground substance contains collagen fibrils that can vary considerably in length, structure and diameter. In one case of WOLCOTT-RALLISON syndrome, the lacunae of the chondrocytes are found to contain very wide amianthoid-like and inadequately aggregated collagen fibrils. In numerous cases, osteogenesis imperfecta reveals very fine and also irregularly structured collagen fibrils with scarcely discernible cross-striation in the region of the osteoid, which is of varying width. In some of the cases, catechin has a favourable effect on the formation of collagen fibrils, resulting in broader and more densely packed fibrils. In addition, the conditions are associated with considerable intracellular changes in the rough endoplasmic reticulum, the Golgi apparatus and the mitochondria. The varying collagen fibril findings in the cartilage and bone tissue also represent a morphological marker of the combined functional-structural disorder of chondrocytes and/or osteoblasts, and an expression of the differing aetiopathogenesis.