Histomorphometric analysis of the tibial growth plate in a feline model ofmucopolysaccharidosis type VI

Mucopolysaccharidosis type VI (MPS VI) is a genetically inherited lysosomal storage disorder. Severely affected children exhibit a range of skeletal a bnormalities including short stature, facial dysmorphia, and dysostosis mul tiplex. Naturally occurring and transgenic animal models of MPS VI are also found which exhibit pathology similar to the human disorder. In this paper we have characterized the formation of trabecular bone from growth plate c artilage in a feline model of MPS VI. Tibial trabecular bone was shown to b e osteopenic in MPS VI animals with a bone mineral volume (BV/TV) of 4.51% compared with a BV/TV of 15.64% in normal animals. In addition to osteopeni a, a rearrangement of trabecular bone architecture was also observed in MPS VI tibiae, with fewer, thinner trabeculae noted; bone formation rate was a lso decreased. These observations support those previously made in the L5 v ertebrae of MPS VI animals. When the sequential formation of growth plate c artilage structural elements, their transition into primary bone spongiosa, and remodeling into secondary bone spongiosa was characterized, no differe nce between normal and MPS VI could be detected in the number of cartilage septae and their arrangement in the proliferative and hypertrophic regions of the growth plate or trabecular elements in the primary spongiosa. Howeve r, a deviation from normal was observed in the resting zone of the growth p late and in the secondary spongiosa of bone. Thus, the osteopenia observed in MPS VI bone appears to arise primarily from a defect in bone production within the metaphysis and diaphysis rather than the creation of an abnormal template in the preceding growth plate cartilage.