Bone histomorphometry in three females with Rett syndrome.

The frequent occurrence of osteoporosis in Rett syndrome raises questions about the etiology of this finding. It is unknown whether there is any relationship between low bone mass and the underlying genetic disorder. We recently had an opportunity to study the status of bone remodeling by quantitative bone histomorphometry in three girls ages 9.75, 13.5, and 14 years, with typical Rett syndrome who required scoliosis surgery.Anterior iliac crest bone biopsies were performed 1-2 days after double labeling of the bone surfaces with tetracycline. Samples were processed for plastic embedding, sectioned, stained, and histomorphometry performed in the cancellous bone. The same observer performed all measurements. Bone volume was reduced, surface parameters of formation (osteoid surface) were normal while parameters of resorption (osteoclast surface and number) were decreased. The rate of bone formation was reduced in the first two girls but could not be measured in the third girl due to lack of double labeling. It may be that the slow rate of bone formation seen in each age group impedes the development and accumulation of peak bone mass and contributes to the decreased bone volume associated with Rett syndrome, although the data is limited. This is the first report to document decreased bone volume determined by quantitative bone histomorphometry in patients with Rett syndrome. With the recent identification of MECP2 mutations in Rett syndrome it is quite likely that genetic factors not only play a major role in brain development but may also influence other organ growth including bone formation.