This treatment strategy provides an efficacious alternative to more aggressive forms of therapy and should therefore be considered for the treatment of patients with severe EOP.

Zinc (Zn 2؉ ) has long been known to play important roles in mineralization and ossification of skeletal tissues, but the mechanisms of Zn 2؉ action are not well understood. In this study we investigated the effects of Zn 2؉ on mineralization in a cell culture system in which terminal differentiation and mineralization of hypertrophic growth plate chondrocytes was induced by retinoic acid (RA) treatment. Addition of Zn 2؉ to RA-treated cultures decreased mineralization in a dose-dependent manner without affecting alkaline phosphatase (APase) activity. Characterization of matrix vesicles (MVs), particles that initiate the mineralization process, revealed that vesicles isolated from RA-treated and RA/Zn 2؉ -treated cultures showed similar APase activity, but vesicles from RA/Zn 2؉ -treated cultures contained significantly less Ca 2؉ and P i . MVs isolated from RA-treated cultures were able to take up Ca 2؉ and mineralize in vitro, whereas vesicles isolated from RA/Zn 2؉ -treated cultures were not able to do so. Detergent treatment, which ruptures the MV membrane and exposes preformed intravesicular Ca 2؉ -P i -phospholipid complexes, did not restore the Ca 2؉