An electron microscopic investigation of human familial bone dysplasia. Inhibition of osteocytic osteolysis and induction of osteocytic formation of elastic fibers following calcitonin treatment.

Familial bone dysplasia with hyperphosphatasemia is characterized by excessive bone resorption early in life with resulting severe skeletal deformity. The disease can be ameliorated by treatment with human calcitonin. We have the studied the ultrastructure of bone from diseased patients before treatment and at intervals during 1 year of treatment with calcitonin. Pretreatment osteoblasts, osteoclasts, and osteocytes exhibited mitochondria which contained vast amounts of dense microcrystal deposits. Osteocytes were also distinguished by minimal organellar development. Osteoclasts were rare. Calcitonin treatment included a progressive development of a more normal bone structure. Intramitochondrial crystal deposits were absent in mitochondria of osteocytes and osteoclasts but were still present in mitochondria of osteoblasts. Surprisingly, the developing bony matrix during calcitonin treatment exhibited large numbers of elastic fibers. These appeared to develop normally in alignment with the surface membrane of osteocytes. Calcitonin treatment caused a proliferation of osteocyte organellar development. It is concluded that familial bone dysplasia is primarily a disease of osteocytes and that osteocytic activity is influenced by calcitonin.