Possible mechanisms of osteopenia in Rett syndrome: bone histomorphometric studies.

The etiology of frequently occurring osteoporosis in Rett syndrome is unknown. Five girls, ages 9.75, 11, 12, 13.5, and 14 years, with typical Rett syndrome requiring scoliosis surgery presented an opportunity to study bone remodeling by quantitative bone histomorphometry. Anterior iliac crest bone biopsies taken 1 to 2 days after double labeling of the bone surfaces with tetracycline were submitted for histomorphometry. Bone volume was reduced, and the surface parameters of formation (osteoid surface) were normal, whereas the parameters of resorption (osteoclast surface and number) were decreased. In four girls, the rate of bone formation was reduced but could not be measured in one girl owing to poor labeling. It is possible that the slow rate of bone formation impedes the development and accumulation of peak bone mass and contributes to the decreased bone volume in Rett syndrome. Perhaps MECP2 mutations in Rett syndrome not only influence brain development but also affect bone formation.