1206 ACROMESOMELIC DYSPLASIA, A HISTOCHEMICAL STUDY OF THE ENDOCHONRAL GROWTH PLATE

Endochondral growth plate cartilage from a patient with the typical clinical and radiographic features of acromesomelic dysplasia was studied histochemically and immunohistochemically. The investigation revealed many previously undescribed abnormalities. The cartilage was hypercellular in general. There were numerous small areas of matrix degeneration scattered through the resting zone and a few large islands of hypertrophic cartilage in the growth plate region. Staining indicated excessive amounts of chondroitin sulfate and an absence of collagen fibers in both of these areas. In the remaining cartilage, collagen fibers tended to aggregate around the cells. The resting chondrocytes were irregular in size and distribution, and many exhibited protein containing cytoplasmic inclusions. The growth plate per se was poorly organized; hypertrophic chondrocytes were randomly oriented. The provisional calcification of cartilage matrix was absent, but the mineralization of subchondral bone appeared normal except along the outer margin where bone formation extended into the perichondrial space. These abnormalities appear to be distinct for acromesomelic dysplasia. Moreover, they provide several clues regarding the pathogenesis of the disorder.