Bone density and fractures in Turner syndrome

Apparent demineralization of the skeleton has been noted in females with Turner syndrome (TS) since the first descriptions of the disorder. Studies, using quantitative methods to measure areal bone mineral density (BMD) in TS, have often been confounded by small skeletal size and variable exposure to estrogen. Recent studies taking bone size into account suggest that BMD at skeletal sites of predominantly trabecular bone, e.g., the lumbar spine and ultra distal radius, is normal in women that have used estrogen consistently. However, these women have significantly lower than normal BMD at skeletal sites with predominantly cortical bone, e.g., the radial shaft and femoral neck. It is unknown whether the reduction in cortical BMD is an intrinsic feature of TS perhaps related to haploinsufficiency for SHOX or another X-linked gene, or due to deficient estrogen exposure during childhood and adolescence, and whether this cortical bone deficit increases fracture risk. Current recommendations to begin low dose estrogen treatment in the early teens may clarify these issues. Wide use of bisphosphonates to treat low BMD in young women with TS is not warranted since these agents have little if any effect on cortical bone while trabecular bone has excellent response to estrogens.