Osteoclast abnormalities in idiopathic osteopetrosis. Reference to the ultrastructural histochemistry study.

In order to investigate skeletal abnormalities in a case of idiopathic osteopetrosis, a bone biopsy was taken from the anterior iliac crest and prepared for ultrastructural and histochemical study. There was a drastic reduction in osteoclastic bone resorption. The ruffle border and sealing zone, which are the osteoclast cell surface markers of bone resorption, were absent. The cells were highly vacuolated, and the vacuoles contained large amounts of a residual organic material which reacted strongly with acid phosphatase. Acid phosphatase activity was never found outside the cell, and in particular, not at the bone-cell interface. This suggests that the defect in bone resorption is caused by cell membrane abnormalities and the lack of ruffle border formation, rather than the inability of the lysosomal enzymes to digest the bone matrix.