NF1 tumor suppressor protein and mRNA in skeletal tissues of developing and adult normal mouse and NF1-deficient embryos

Vitamin D deficiency associated with number of neurofibromas in neurofibromatosis 1

Neurofibromatosis 1 (NF1) is a tumour suppressor gene syndrome characterized by multiple cutaneous and plexiform neurofibromas. Focal osseous abnormalities, short stature, and decreased bone mineral density are also frequent in people with NF1. We measured serum 25-hydroxyvitamin D concentrations in 55 patients with NF1 and 58 healthy controls, and correlated the findings in the patients with NF1 with their estimated number of dermal neurofibromas. Geometric mean (SD) serum 25-hydroxyvitamin D concentration was 14.0 (1.6) ng/mL among the patients with NF1 compared with 31.4 (1.7) ng/mL among healthy controls (p<<0.0001). The serum vitamin D concentration and number of dermal neurofibromas reported by patients with NF1 were inversely correlated (Spearman's rho = -0.572, p<0.00001). The occurrence of low serum vitamin D concentrations in people with NF1, especially those with many dermal neurofibromas, may provide new pathogenic insights and have important therapeutic implications.

NF1 gene expression in mouse fracture healing and in experimental rat pseudarthrosis

Neurofibromatosis type 1 (NF1) is an inherited disease with an incidence of about 1:3000 worldwide. Approximately half of all patients with NF1 present osseous manifestations, which can vary from mild to severely debilitating changes such as congenital pseudarthrosis. In the present study, fracture healing of mouse tibia was followed and specimens were collected 5, 9, 14, and 22 days postoperatively. Experimental pseudarthrosis of rat was followed up to 15 weeks postoperatively. In situ hybridization and immunohistochemistry were used to demonstrate expression of NF1 tumor suppressor and phosphorylated p44/42 mitogen-activated protein kinase (MAPK), an indicator of the Ras-MAPK pathway. The results showed that ossified callus was formed in mouse fracture 22 days after the operation. The final outcome of rat pseudarthrosis was detected 9 weeks after the operation, presenting abundant cartilaginous callus at the pseudarthrosis. NF1 gene expression was noted in the maturing and in the hypertrophic cartilages during normal mouse fracture healing, and in rat pseudarthrosis. Phosphorylated p44/42 MAPK was detected in a subpopulation of the hypertrophic chondrocytes in both models. Furthermore, positive labeling for NF1 mRNA and protein was detected in endothelium in both the pseudarthrosis and in the fracture. In conclusion, NF1 gene expression and function are needed for normal fracture healing, possibly restraining excessive Ras-MAPK pathway activation.

Decreased bone mineral density in patients with neurofibromatosis 1

Neurofibromatosis 1 (NF1) is one of the most common autosomal dominant diseases. Although there is a considerable variability in clinical expression, NF1 is almost fully penetrant in adult patients and may be associated with a variety of skeletal anomalies. Spinal deformities are the most common skeletal manifestation, with an incidence estimated from 10-25% in various studies. Some NF1 patients have a dystrophic form of scoliosis, which is characterized by early age at onset and rapid progression. Complications have been reported during spinal instrumentation of dystrophic curves due to soft, non-resistant vertebral bony tissue, suggesting that an alteration of bone quality may occur in NF1 patients. Recent studies have suggested that decreased bone mineral density (BMD) may occur among patients with NF1. We performed a cross-sectional study on 104 adults with NF1, using quantitative ultrasonometry (QUS) to investigate whether decreased BMD is a general phenomenon in NF1 patients. The data reveal that BMD, as measured by age- and gender- adjusted Z-scores, is significantly lower in NF1 patients than in the normal reference population. The decrease in BMD appears to be even more marked among NF1 patients with scoliosis that requires surgical treatment. The findings indicate that NF1 produces a generalized alteration of bone in addition to the focal osseous dysplasias of the vertebrae, tibia, and sphenoid wing that characterize this condition. The pathological mechanism underlying these bony changes remains to be elucidated.

Decreased bone mineral density and content in neurofibromatosis type 1: lowest local values are located in the load-carrying parts of the body

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.

Unilateral limb enlargement in a dog with a malignant peripheral nerve sheath tumor

A 3- to 4-month-old female Golden Retriever dog presented with right hind limb enlargement. Physical examination of the limb and radiographic findings initially included soft tissue swelling with elongation, bowing, and cortical irregularity of the femur and tibia. During a period of approximately 7 months, pathology in the limb progressed to include tarsal laxity, muscle atrophy, avulsion of the gastrocnemius muscle, and luxation of the patella. During surgical intervention to shorten the limb and repair the patellar luxation, a large soft tissue cyst was identified along the caudal aspect of the femur and stifle. The limb was later amputated, and a final diagnosis of malignant peripheral nerve sheath (PNS) tumor of the sciatic nerve and surrounding soft tissues was made. The unilateral limb enlargement in this dog appears to have been because of the development and progression of a malignant PNS tumor. The presentation and associated pathologic changes in the limb are unusual for canine PNS tumor but have similarities with neurofibromatosis in the limbs of humans.