Neurofibromatosis type 1 (NF1) is a dominantly inherited disease. Skeletal ailments such as short stature, kyphoscoliosis, tibial bowing and pseudarthrosis are common osseous manifestations of NF1. Previously, a correlation with scoliosis and decreased bone mineral density (BMD) of the lumbar spine has been reported in 12 NF1 patients. A total of 35 NF1 patients and 26 healthy controls were included in the present study. Of the participants over 20 years of age (26 NF1 patients and all controls) 14 were male and 12 were female, seven of whom were premenopausal. The controls were matched for age, sex and body mass index (BMI). Physical activity and medical history of NF1 patients were evaluated to screen the fractures and osseous manifestations of the disease and to rule out the factors that effect BMD. BMD and bone mineral content (BMC) were measured with DXA, using a total body program. The present study detected a lowered bone mineral density (p =0.028) and content (p <0.001) in NF1 patients of both sexes. The results of the present study also show that NF1 patients have an increased risk for osteoporosis. Among NF1 patients seven cases of osteoporosis and 13 cases of osteopenia were detected. In controls, one case of osteoporosis and 13 cases of osteopenia were detected. The location of the lowest local BMD was clustered to the load-carrying parts of the body in NF1 patients. Physical activity and the medical history of the NF1 patients did not explain the decreased BMD and BMC. The findings of the present and previous studies suggest that the pathogenesis of the osseous manifestations in NF1 may involve impaired development of the skeletal system and impaired maintenance of bone structure.

NF1 is a heritable disease with multiple osseous lesions. The expression of the NF1 gene was studied in embryonic and adult rodent skeleton and in NF1-deficient embryos. The NF1 gene was expressed intensely in the cartilage and the periosteum. Impaired NF1 expression may lead to inappropriate development and dynamics of bones and ultimately to the osseous manifestations of the disease.Introduction: Neurofibromatosis type 1 is caused by mutations in the NF1 gene encoding the Ras GTPase activating protein (Ras-GAP) neurofibromin. Skeletal ailments such as short stature, kyphoscoliosis, and tibial bowing and pseudarthrosis are common osseous manifestations of NF1. These symptoms are congenital, implying a role for neurofibromin in proper bone growth. However, little is known about its expression in skeletal tissues during their development. Materials and Methods:The expression of the NF1 gene was studied in normal and NF1 ϩ/Ϫ mouse fetuses at embryonic days 12.5-15.5 and in skeletal tissues of adult mice and rats. In situ hybridization, immunohistochemistry, and Western blot analysis were used to identify the NF1 gene expression profile. Results: NF1 mRNA and protein were elevated in resting, maturation, and hypertrophic chondrocytes at the growth plate. Parallel studies on NF1 ϩ/Ϫ embryos showed expression patterns identical to wildtype. The periosteum, including osteoblasts and osteoclasts, and osteocytes of the cortical bone of adult mice were also intensely labeled for NF1 protein and mRNA. Western transfer analysis detected NF1 protein in the respective rat tissues. Phosphorylation of p42 and p44 MAP kinases, the downstream consequence of Ras activation, was elevated in hypertrophic chondrocytes of NF1 ϩ/Ϫ embryos. Conclusions:The results suggest that neurofibromin may act as a Ras-GAP in skeletal cells to attenuate Ras transduced growth signals and thus play a role during ossification and dynamics of bone. Loss of NF1 function may therefore lead to dysplastic bone growth, thereby causing the debilitating osseous symptoms of NF1.

No abstract

Neurofibromatosis 1 (NF1, von Recklinghausen's disease) is an autosomal dominant neurocutaneous-skeletal syndrome in which low bone mineral density (BMD) and osteoporosis are common. Low BMD is, however, not the sole component of fracture risk. In the current study, 460 Finnish patients with NF1 were identified from the hospital medical records and their fracture risk was evaluated. The control population included 3988 appendectomy patients whose age and gender distribution was similar to that of the NF1 patients. Medical records of NF1 and control cohorts were screened for fractures according to the International Statistical Classification of Diseases and Related Health Problems, 10th Revision (ICD-10) between January 2000 and October 2011. The results show that patients with NF1 had increased age-dependent fracture risk compared to controls. Specifically, patients with NF1 aged 41 years and older had a risk ratio of Â5.2 for fractures compared to controls, and children with NF1 had a Â3.4 risk ratio for fractures compared to children without NF1. In contrast, the fracture risk was not increased in NF1 patients aged 17 to 40 years. When fractures not traditionally related to osteoporosis such as fractures of fingers, toes, and skull were excluded, the results were essentially the same. No gender related differences were observed. In conclusion, patients with NF1 have increased fracture risk depending on age. We recommend considering prophylactic measures, such as lifestyle advice, to prevent fractures from occurring. ß

No abstract