This is the first prospective follow-up study to describe the effects of oral
alendronate medication on
neurofibromatosis 1 (NF1)-related
osteoporosis. NF1 is a neurocutaneous skeletal syndrome associated with increased fracture risk and high frequency of
osteopenia and
osteoporosis.
Alendronate is a
bisphosphonate drug which inhibits the function of bone-resorbing osteoclasts, ultimately leading to an increase in bone mineral density (BMD) and reduction in fracture risk. However, in vitro studies have shown that NF1 osteoclasts display insensitivity to apoptotic signals caused by
bisphosphonates. Our aim was to monitor the effects of
alendronate medication in patients with NF1. Five men and one woman, aged 28-76 years, with NF1-related
osteoporosis were enrolled to the study. Study participants did not have other conditions and were not taking any medication known to affect bone. The medication included a weekly dose of 70 mg
alendronate and a daily 20 μg
vitamin D supplementation. After 23 months of follow-up, BMD was increased in five out of six patients, but the increase was not statistically significant. Serum levels of the bone turnover markers CTX and PINP were reduced, suggesting slower bone remodeling, as expected. An unexpected result was that serum levels of the osteoclast activity marker TRAP5b did not change during the follow-up. One new
stress fracture of the tibia was documented during the
alendronate therapy. Even though the study group was small, the findings of the current study (one new fracture and one patient with decreased BMD) call for a larger study to assess the efficacy of
bisphosphonates in NF1-related
osteoporosis.