Decreased bone mineral density in patients with neurofibromatosis 1

Unraveling neuronal and metabolic alterations in neurofibromatosis type 1

Neurofibromatosis type 1 (OMIM 162200) affects ~ 1 in 3,000 individuals worldwide and is one of the most common monogenetic neurogenetic disorders that impacts brain function. The disorder affects various organ systems, including the central nervous system, resulting in a spectrum of clinical manifestations. Significant progress has been made in understanding the disorder's pathophysiology, yet gaps persist in understanding how the complex signaling and systemic interactions affect the disorder. Two features of the disorder are alterations in neuronal function and metabolism, and emerging evidence suggests a potential relationship between them. This review summarizes neurofibromatosis type 1 features and recent research findings on disease mechanisms, with an emphasis on neuronal and metabolic features.

Diagnosis and management of neurofibromatosis type 1 in Arabian Gulf Cooperation Council Region: challenges and recommendations

Neurofibromatosis type 1 (NF1) is a complex multisystem genetic disorder that requires long-term, age-specific monitoring and multidisciplinary care. NF1 symptom burden can significantly affect the quality of life and impose a substantial economic burden on patients and their families. The approval and widespread availability of mitogen-activated protein kinase (MEK) inhibitors such as selumetinib for NF1-related plexiform neurofibromas have revolutionized the standard of care for patients with NF1, however their effective utilization hinges on early recognition of NF1. We present a consensus manuscript describing the challenges observed in the Arabian Gulf Cooperation Council (GCC) for diagnosing and managing NF1. Experts from the GCC also present recommendations for the early recognition and management of NF1 and its complications. A referral pathway that can play a crucial role in helping primary healthcare providers refer their patients to experts is also proposed. Increasing the availability and accessibility of genetic testing at an affordable cost and optimizing personalized NF1 care are essential for NF1 management. Developing regional guidelines for NF1 management and establishing NF1 centers of excellence may facilitate better care and outcomes for patients with NF1 in the GCC region.

Surgical Treatment Outcomes of Anterior-Only Correction and Reconstruction for Severe Cervical Kyphotic Deformity with Neurofibromatosis-1: A Retrospective Study with a 5-Year Follow-Up

OBJECTIVES

Currently, anterior-only (AO), posterior-only, and combined anterior-posterior spinal fusions are common strategies for treating cervical kyphosis in patients with neurofibromatosis-1 NF-1. Nevertheless, the choice of surgical strategy remains a topic of controversy. The aim of our study is to evaluate the safety and effectiveness of anterior decompression and spinal reconstruction for the treatment of cervical kyphosis in patients with NF-1.

METHODS

Twelve patients with NF-1-associated cervical kyphotic deformity were reviewed retrospectively between January 2010 and April 2020. All patients underwent AO correction and reconstruction. The X-ray was followed up in all these patients to assess the preoperative and postoperative local kyphosis angle (LKA), the global kyphosis angle (GKA), the sagittal vertical axis, and the T1 slope. The visual analog scale score, Japanese Orthopedic Association (JOA) score, and neck disability index (NDI) score were used to evaluate the improvement inclinical symptoms. The results of the difference in improvement from preoperatively to the final follow-up assessment were assessed using a paired t-test or Mann-Whitney U-test.

RESULTS

The LKA and GKA decreased from the preoperative average of 64.42 (range, 38-86) and 35.50 (range, 10-81) to an average of 16.83 (range, -2 to 46) and 4.25 (range, -22 to 39) postoperatively, respectively. The average correction rates of the LKA and GKA were 76.11% and 111.97%, respectively. All patients had achieved satisfactory relief of neurological symptoms (p < 0.01). JOA scores were improved from 10.42 (range, 8-16) preoperatively to 15.25 (range, 11-18) at final follow-up (p < 0.01). NDI scores were decreased from an average of 23.25 (range, 16-34) preoperatively to an average of 7.08 (range, 3-15) at the final follow-up (p < 0.01).

CONCLUSION

Anterior-only correction and reconstruction is a safe and effective method for correcting cervical kyphosis in NF-1 patients. In fixed cervical kyphosis cases, preoperative skull traction should also be considered.

Potential endpoints for assessment of bone health in persons with neurofibromatosis type 1

Neurofibromatosis type 1 is a genetic syndrome characterized by a wide variety of tumor and non-tumor manifestations. Bone-related issues, such as scoliosis, tibial dysplasia, and low bone mineral density, are a significant source of morbidity for this population with limited treatment options. Some of the challenges to developing such treatments include the lack of consensus regarding the optimal methods to assess bone health in neurofibromatosis type 1 and limited data regarding the natural history of these manifestations. In this review, the Functional Committee of the Response Evaluation in Neurofibromatosis and Schwannomatosis International Collaboration: (1) presents the available techniques for measuring overall bone health and metabolism in persons with neurofibromatosis type 1, (2) reviews data for use of each of these measures in the neurofibromatosis type 1 population, and (3) describes the strengths and limitations for each method as they might be used in clinical trials targeting neurofibromatosis type 1 bone manifestations. The Response Evaluation in Neurofibromatosis and Schwannomatosis International Collaboration supports the development of a prospective, longitudinal natural history study focusing on the bone-related manifestations and relevant biomarkers of neurofibromatosis type 1. In addition, we suggest that the neurofibromatosis type 1 research community consider adding the less burdensome measurements of bone health as exploratory endpoints in ongoing or planned clinical trials for other neurofibromatosis type 1 manifestations to expand knowledge in the field.

Skeletal defects and bone metabolism in Noonan, Costello and cardio-facio-cutaneous syndromes

Noonan, Costello and Cardio-facio-cutaneous syndromes belong to a group of disorders named RASopathies due to their common pathogenetic origin that lies on the Ras/MAPK signaling pathway. Genetics has eased, at least in part, the distinction of these entities as they are presented with overlapping clinical features which, sometimes, become more pronounced with age. Distinctive face, cardiac and skeletal defects are among the primary abnormalities seen in these patients. Skeletal dysmorphisms range from mild to severe and may include anterior chest wall anomalies, scoliosis, kyphosis, short stature, hand anomalies, muscle weakness, osteopenia or/and osteoporosis. Patients usually have increased serum concentrations of bone resorption markers, while markers of bone formation are within normal range. The causative molecular defects encompass the members of the Ras/MAPK/ERK pathway and the adjacent cascades, important for the maintenance of normal bone homeostasis. It has been suggested that modulation of the expression of specific molecules involved in the processes of bone remodeling may affect the osteogenic fate decision, potentially, bringing out new pharmaceutical targets. Currently, the laboratory imprint of bone metabolism on the clinical picture of the affected individuals is not clear, maybe due to the rarity of these syndromes, the small number of the recruited patients and the methods used for the description of their clinical and biochemical profiles.

Bone health in RASopathies

The RASopathies are a group of disorders due to pathogenic variants in genes involved in the Ras/MAPK pathway, many of which have overlapping clinical features (e.g., neurofibromatosis type 1, Costello syndrome, cardiofaciocutaneous syndrome and Noonan syndrome) including musculoskeletal manifestations. Osteopenia and osteoporosis are reported in many of the RASopathies suggesting a shared pathogenesis. Even though osteopenia and osteoporosis are often detected and fractures have been reported, the clinical impact of bone mineralization defects on the skeleton of the various syndromes is poorly understood. Further knowledge of the role of the Ras/MAPK pathway on the bone cellular function, and more detailed musculoskeletal phenotyping will be critical in helping to develop therapies to improve bone health in the RASopathies.

Sectional Correction Technique in Dystrophic Scoliosis Secondary to Neurofibromatosis Type 1: A Comparison with Traditional 2-Rod Correction Technique

OBJECTIVE

The purpose of this study was to compare the traditional 2-rod correction technique with the sectional correction technique in terms of radiographic results and clinical outcomes for patients with dystrophic scoliosis caused by neurofibromatosis type 1 (NF1).

METHODS

From May 2015 to April 2018, 53 patients with dystrophic scoliosis caused by NF1 underwent 1-stage posterior corrective surgery. Patients were separated into 2 groups based on technique: the sectional correction technique (SC group) and the traditional 2-rod technique (TT group). Before surgery and at the final follow-up, the demographic information, radiographic parameters, and clinical outcomes were compared between the groups using independent-sample t tests.

RESULTS

The SC group consisted of 24 patients, while the TT group consisted of 29 patients. Patients in the SC group showed a higher coronal balance distance after the operation (8.3 ± 8.2 mm vs. 16.2 ± 8.8 mm, P = 0.002) and at the final follow-up (9.5 ± 9.3 mm vs. 19.3 ± 10.1 mm, P < 0.0001). At the last follow-up, the loss of correction in the SC group was 2.2 ± 0.9 and 2.1 ± 0.7 in the coronal and sagittal planes, respectively, and these values were significantly lower than those in the TT group (5.3 ± 1.6 in the coronal plane and 4.5 ± 1.9 in the sagittal plane, both P < 0.05). The SC group had better improvement based on appearance and satisfaction score at the final follow-up.

CONCLUSIONS

The sectional correction technique using a concave domino connector can restore coronal imbalance and reduce the risk of implant failure.

Bone metabolism in patients with type 1 neurofibromatosis: key role of sun exposure and physical activity

Bone metabolism has been rarely investigated in children affected by Neurofibromatosis type 1 (NF1). Aim of the present study was to assess bone mineral metabolism in children and adults NF1 patients, to determine the relevant factors potentially involved in the development of reduced bone mineral density (BMD), and provide possible therapeutic intervention in NF1 patients. 114 NF1 patients and sex and age matched controls were enrolled into the study. Clinical and biochemical factors reflecting bone metabolism were evaluated. Factors potentially affecting BMD were also investigated including: physical activity, sun exposure, vitamin D intake. Whenever the presence of vitamin D deficiency was recorded, cholecalciferol supplementation was started and z-score data obtained at Dual-Energy X-ray Absorptiometry (DXA) during supplementation were compared with previous ones. NF1 patients showed lower Z-scores at Dual-Energy X-ray Absorptiometry DXA than controls. Physical activity was significantly reduced in NF1 patients than in controls. Sun exposure was significantly lower in NF1 compared to control subjects. At linear regression analysis vitamin D was the most predictive factor of reduced z-score at DXA (p = 0.0001). Cholecalciferol supplementation significantly increased BMD z-score (p < 0.001). We speculated that a combination of different factors, including reduced sun exposure, possibly associated with reduced serum vitamin D levels, and poor physical activity, concur to the impaired bone status in NF1 patients. We also demonstrated that treatment with vitamin D can be effective in improving z-score value in NF1 patients, including children. In conclusion, the findings of the current study are expected to have important implications for the follow-up and prevention of osteopenia/osteoporosis in this common genetic disease.

Current Aspects on the Pathophysiology of Bone Metabolic Defects during Progression of Scoliosis in Neurofibromatosis Type 1

Neurofibromatosis type 1 (NF1), which is the most common phacomatoses, is an autosomal dominant disorder characterized by clinical presentations in various tissues and organs, such as the skin, eyes and nervous and skeletal systems. The musculoskeletal implications of NF1 include a variety of deformities, including scoliosis, kyphoscoliosis, spondylolistheses, congenital bony bowing, pseudarthrosis and bone dysplasia. Scoliosis is the most common skeletal problem, affecting 10-30% of NF1 patients. Although the pathophysiology of spinal deformities has not been elucidated yet, defects in bone metabolism have been implicated in the progression of scoliotic curves. Measurements of Bone Mineral Density (BMD) in the lumbar spine by using dual energy absorptiometry (DXA) and quantitative computer tomography (QCT) have demonstrated a marked reduction in Z-score and osteoporosis. Additionally, serum bone metabolic markers, such as vitamin D, calcium, phosphorus, osteocalcin and alkaline phosphatase, have been found to be abnormal. Intraoperative and histological vertebral analysis confirmed that alterations of the trabecular microarchitecture are associated with inadequate bone turnover, indicating generalized bone metabolic defects. At the molecular level, loss of function of neurofibromin dysregulates Ras and Transforming Growth factor-β1 (TGF-β1) signaling and leads to altered osteoclastic proliferation, osteoblastic activity and collagen production. Correlation between clinical characteristics and molecular pathways may provide targets for novel therapeutic approaches in NF1.

Low bone mass in Noonan syndrome children correlates with decreased muscle mass and low IGF-1 levels

Although musculoskeletal abnormalities have long been described in patients with Noonan syndrome (NS), only a few studies have investigated the bone status of these patients. The aim of this retrospective observational study was to describe the bone health of children with NS. Thirty-five patients with a genetically confirmed diagnosis of NS were enrolled. We analyzed the axial skeleton (lumbar spine) using dual energy X-ray absorptiometry and the appendicular skeleton (hand) with the BoneXpert system. Bone metabolism markers, including mineral homeostasis parameters, serum 25-hydroxy vitamin D (25-OHD) levels and markers of bone formation and resorption were also reported. Compared to the general population, axial and appendicular bone mass was significantly decreased in children with NS (p < 0.0001). Serum 25-OHD levels were low in about half of the patients and were negatively correlated with age (r = -0.52; p < 0.0001). Patients with NS exhibited reduced bone formation marker levels and increased bone resorption marker levels (p < 0.0001). No gender difference or genotype-phenotype correlations were found for the different bone parameters. Muscle mass and, to a lesser extent, serum insulin-like growth factor 1 (IGF-1) levels were independent predictors of whole-body bone mineral content (p < 0.0001 for both parameters; adjusted R² = 0.97). In conclusion, bone mass is reduced in children with NS and correlates with decreased muscle mass and low serum IGF-1 levels. These data justify addressing all potential threats to bone health including sufficient calcium and vitamin D intake, regular physical exercise, and hormone replacement therapy.

Halo traction combined with posterior-only approach correction for cervical kyphosis with Neurofibromatosis-1: minimum 2 years follow-up

Background

Surgical management of cervical kyphosis in patients with NF-1 is a challenging task. Presently, anterior-only (AO), posterior-only (PO) and combined anterior-posterior (AP) spinal fusion are common surgical strategies. However, the choice of surgical strategy and application of Halo traction remain controversial. Few studies have shown and recommended posterior-only approach for cervical kyphosis correction in patients with NF-1. The aim of this study is to evaluate the safety and the effectiveness of halo Traction combined with posterior-only approach correction for treatment of cervical kyphosis with NF-1.

Methods

Twenty-six patients with severe cervical kyphosis due to NF-1 were reviewed retrospectively between January 2010 and April 2018. All the cases underwent halo traction combined with posterior instrumentation and fusion surgery. Correction result, neurologic status and complications were analyzed.

Results

In this study, cervical kyphosis Cobb angle decreased from initial 61.3 ± 19.7 degrees to postoperative 10.6 ± 3.7 degrees (P<0.01), with total correction rate of 82.7%, which consist of 45.8% from halo traction and 36.9% from surgical correction. JOA scores were improved from preoperative 13.3 ± 1.6 to postoperative 16.2 ± 0.7 (P<0.01). Neurological status was also improved. There was no correction loss and the neurological status was stable in mean 43 months follow-up. Three patients experienced minor complications and one patient underwent a second surgery.

Conclusion

Halo traction combined with PO approach surgery is safe and effective method for cervical kyphosis correction in patients with NF-1. A satisfied correction result, and successful bone fusion can be achieved via this procedure, even improvement of neurological deficits can also be obtained. Our study suggested that halo traction combined with PO approach surgery is another consideration for cervical kyphosis correction in patients with NF-1.

Genetic Determinants of Inherited Endocrine Tumors: Do They Have a Direct Role in Bone Metabolism Regulation and Osteoporosis?

Endocrine tumors are neoplasms originating from specialized hormone-secreting cells. They can develop as sporadic tumors, caused by somatic mutations, or in the context of familial Mendelian inherited diseases. Congenital forms, manifesting as syndromic or non-syndromic diseases, are caused by germinal heterozygote autosomal dominant mutations in oncogenes or tumor suppressor genes. The genetic defect leads to a loss of cell growth control in target endocrine tissues and to tumor development. In addition to the classical cancer manifestations, some affected patients can manifest alterations of bone and mineral metabolism, presenting both as pathognomonic and/or non-specific skeletal clinical features, which can be either secondary complications of endocrine functioning primary tumors and/or a direct consequence of the gene mutation. Here, we specifically review the current knowledge on possible direct roles of the genes that cause inherited endocrine tumors in the regulation of bone modeling and remodeling by exploring functional in vitro and in vivo studies highlighting how some of these genes participate in the regulation of molecular pathways involved in bone and mineral metabolism homeostasis, and by describing the potential direct effects of gene mutations on the development of skeletal and mineral metabolism clinical features in patients.

Multiple versus solitary giant cell lesions of the jaw: Similar or distinct entities?

The majority of giant cell lesions of the jaw present as a solitary focus of disease in bones of the maxillofacial skeleton. Less frequently they occur as multifocal lesions. This raises the clinical dilemma if these should be considered distinct entities and therefore each need a specific therapeutic approach. Solitary giant cell lesions of the jaw present with a great diversity of symptoms. Recent molecular analysis revealed that these are associated with somatic gain-of-function mutations in KRAS, FGFR1 or TRPV4 in a large component of the mononuclear stromal cells which all act on the RAS/MAPK pathway. For multifocal lesions, a small group of neoplastic multifocal giant cell lesions of the jaw remain after ruling out hyperparathyroidism. Strikingly, most of these patients are diagnosed with jaw lesions before the age of 20 years, thus before the completion of dental and jaw development. These multifocal lesions are often accompanied by a diagnosis or strong clinical suspicion of a syndrome. Many of the frequently reported syndromes belong to the so-called RASopathies, with germline or mosaic mutations leading to downstream upregulation of the RAS/MAPK pathway. The other frequently reported syndrome is cherubism, with gain-of-function mutations in the SH3BP2 gene leading through assumed and unknown signaling to an autoinflammatory bone disorder with hyperactive osteoclasts and defective osteoblastogenesis. Based on this extensive literature review, a RAS/MAPK pathway activation is hypothesized in all giant cell lesions of the jaw. The different interaction between and contribution of deregulated signaling in individual cell lineages and crosstalk with other pathways among the different germline- and non-germline-based alterations causing giant cell lesions of the jaw can be explanatory for the characteristic clinical features. As such, this might also aid in the understanding of the age-dependent symptomatology of syndrome associated giant cell lesions of the jaw; hopefully guiding ideal timing when installing treatment strategies in the future.

Modulation of spine fusion with BMP-2, MEK inhibitor (PD0325901), and zoledronic acid in a murine model of NF1 double inactivation

BACKGROUND

Spine fusion is a common procedure for the treatment of severe scoliosis, a frequent and challenging deformity associated with Neurofibromatosis type 1 (NF1). Moreover, deficiencies in NF1-Ras-MEK signaling affect bone formation and resorption that in turn impacts on spine fusion outcomes.

METHODS

In this study we describe a new model for AdCre virus induction of Nf1 deficiency in the spines of Nf1^flox/flox mice. The virus is delivered locally to the mouse spine in a fusion procedure induced using BMP-2. Systemic adjunctive treatment with the MEK inhibitor (MEKi) PD0325901 and the bisphosphonate zoledronic acid (ZA) were next trialed in this model.

RESULTS

AdCre delivery resulted in abundant fibrous tissue (Nf1^null +393%, P < 0.001) and decreased marrow space (Nf1^null -67%, P < 0.001) compared to controls. While this did not significantly impact on the bone volume of the fusion mass (Nf1^null -14%, P = 0.999 n.s.), the presence of fibrous tissue was anticipated to impact on the quality of spine fusion. Multinucleated TRAP + cells were observed in the fibrous tissues seen in Nf1^null spines. In Nf1^null spines, MEKi increased bone volume (+194%, P < 0.001) whereas ZA increased bone density (+10%, P < 0.002) versus BMP-2 alone. Both MEKi and ZA decreased TRAP + cells in the fibrous tissue (MEKi -62%, P < 0.01; ZA -43%, P = 0.054). No adverse effects were seen with either MEKi or ZA treatment including weight loss or signs of illness or distress that led to premature euthanasia.

CONCLUSIONS

These data not only support the utility of an AdCre-virus induced knockout spine model, but also support further investigation of MEKi and ZA as adjunctive therapies for improving BMP-2 induced spine fusion in the context of NF1.

Bone Status According to Neurofibromatosis Type 1 Phenotype: A Descriptive Study of 60 Women in France

There is an increased risk of osteoporosis and an abnormal bone turn over in neurofibromatosis 1 (NF1). Our objective is to evaluate bone status in NF1 and to look for associations with cutaneous phenotype. We conducted a descriptive, monocentric study. We included 60 NF1 women, 18-51 years old, non-menopausal, divided in 2 groups: «at risk phenotype» (ARP) composed by 30 patients with at least 2 subcutaneous neurofibromas (SC-NF) and «classical phenotype» (CP) composed by 30 patients with none or 1 SC-NF. We evaluated low bone mineral density (BMD) risk factors and measured BMD, calcium and phosphorus homeostasis and bone turnover markers. Before 50 years old, Z-score has to be used to assess BMD. Z-score < - 2 is below expected range and represents 2.5% of the population. There was no difference between the two groups. Overall, Z-scores were low and 5 patients had a Z-score < - 2 (8.3%), which is 3 times general population low BMD frequency. 10 fragility fractures occurred in 8 patients, among which 2 were vertebral fractures. 85% had low calcium intake. 12 patients had hypophosphoremia, 25 elevated PTH. Vitamin D levels were low for 86.4%. 41 patients (69.5%) had at least one abnormal bone turnover markers. Low BMD is 3.3 times more frequent in NF1 than in general population, with high fracture risk, regardless of the skin phenotype, classical or at risk, because of high bone turn over and secondary hyperparathyroidism due to vitamin D deficiency and poor calcium intake.

Combined Anterior-Posterior Versus Posterior-only Spinal Fusion in Treating Dystrophic Neurofibromatosis Scoliosis With Modern Instrumentation: A Systematic Review and Meta-analysis

STUDY DESIGN

This is a systematic review and meta-analysis study.

OBJECTIVES

To compare the efficacy, long-term stability, and safety of combined anterior-posterior spinal fusion (APSF) with posterior-only spinal fusion (PSF) in treating dystrophic neurofibromatosis scoliosis with the use of modern instrumentation.

SUMMARY OF BACKGROUND DATA

When the Harrington or Luque technique was used, APSF had relatively reliable results and had been recommended by many authors. But with the development of instrumentation and techniques, many surgeons performed PSF with satisfactory results. No systematic review and meta-analysis have been conducted to compare the outcomes of the 2 approaches.

MATERIALS AND METHODS

Relevant studies on anterior-posterior or posterior fusion of dystrophic neurofibromatosis scoliosis were retrieved from the PubMed, Embase, Cochrane, Springer Link, and Google Scholar databases. Then studies were manually selected for inclusion based on predefined criteria. Data extraction and quality assessment were conducted, and a systematic review and meta-analysis were performed.

RESULTS

Sixteen eligible studies were included. The angles of scoliosis curves and kyphosis curves were significantly and similarly corrected after surgery in both APSF and PSF group, respectively. At the last follow-up, the loss of correction was significant in the coronal plane but not in the sagittal plane with a similar progression of scoliosis in 2 groups. The overall complication rate was slightly higher in the APSF group, but the difference was not statistically significant. Meanwhile, there was no visible difference in the incidence of pseudarthrosis and instrumentation failures between the 2 groups.

CONCLUSIONS

APSF and PSF by means of the third-generation spinal instrumentation system have similar efficacy, long-term stability, and safety for treating dystrophic scoliosis secondary to type-1 neurofibromatosis.

LEVEL OF EVIDENCE

Level III-systematic review and meta-analysis study.

Understanding the Biological Activities of Vitamin D in Type 1 Neurofibromatosis: New Insights into Disease Pathogenesis and Therapeutic Design

Vitamin D is a fat-soluble steroid hormone playing a pivotal role in calcium and phosphate homeostasis as well as in bone health. Vitamin D levels are not exclusively dependent on food intake. Indeed, the endogenous production-occurring in the skin and dependent on sun exposure-contributes to the majority amount of vitamin D present in the body. Since vitamin D receptors (VDRs) are ubiquitous and drive the expression of hundreds of genes, the interest in vitamin D has tremendously grown and its role in different diseases has been extensively studied. Several investigations indicated that vitamin D action extends far beyond bone health and calcium metabolism, showing broad effects on a variety of critical illnesses, including cancer, infections, cardiovascular and autoimmune diseases. Epidemiological studies indicated that low circulating vitamin D levels inversely correlate with cutaneous manifestations and bone abnormalities, clinical hallmarks of neurofibromatosis type 1 (NF1). NF1 is an autosomal dominant tumour predisposition syndrome causing significant pain and morbidity, for which limited treatment options are available. In this context, vitamin D or its analogues have been used to treat both skin and bone lesions in NF1 patients, alone or combined with other therapeutic agents. Here we provide an overview of vitamin D, its characteristic nutritional properties relevant for health benefits and its role in NF1 disorder. We focus on preclinical and clinical studies that demonstrated the clinical correlation between vitamin D status and NF1 disease, thus providing important insights into disease pathogenesis and new opportunities for targeted therapy.

AN ADJUNCTIVE USE OF ASFOTASE ALFA AND ZOLEDRONIC ACID AFTER SPINAL SURGERY IN NEUROFIBROMATOSIS TYPE 1 RELATED DYSTROPHIC SCOLIOSIS

Objective

Dystrophic scoliosis is a serious skeletal manifestation of neurofibromatosis 1 (NF1). The condition requires surgical intervention that is frequently associated with poor outcome due to the high rate of impaired bone healing, pseudoarthrosis, and loosening of the spinal instrumentation. New therapeutic approaches are needed to improve surgical outcomes.

Methods

Clinical, laboratory, and radiographic data are presented.

Results

A 54-year-old woman with severe NF1 related dystrophic scoliosis and 3 prior surgical interventions underwent revision of lumbar fusion with intraoperative recombinant human bone morphogenetic protein (rhBMP-2) for loosening and a fracture of the left vertical rod at the L4 pedicle screw connection. Two days after surgery, a computed tomography (CT) scan revealed a left posterior iliac periscrew fracture. Given a high risk of mechanical failure, zoledronic acid and asfotase alfa were also administered at 3 and 7 months after surgery. At 14 months after surgery, back pain improved, and a CT scan showed stable spinal fusion and a healed left posterior iliac screw fracture.

Conclusion

Combination therapy including asfotase alfa with rhBMP-2 and bisphosphonate resulted in solid arthrodesis after spinal surgery in NF1-related dystrophic scoliosis.

Reduced bone mineral content and density in neurofibromatosis type 1 and its association with nutrient intake

BACKGROUND Neurofibromatosis type 1 (NF1) is an autosomal dominant genetic disease characterized by multisystem involvement including low bone mineral density (BMD). OBJECTIVE To assess the bone phenotype of individuals with NF1 and verify its association with nutrient intake. METHODS Twenty-six adults with NF1 underwent bone phenotype assessments using dual-energy X-ray absorptiometry (DXA) and food intake evaluations. They were compared to 26 unaffected matched control patients. Weight, height, and waist circumference (WC) were measured. DXA provided total body, spine, and hip BMDs and bone mineral content (BMC) for all patients. Food intake was evaluated for energy, macro- and micro-nutrients. RESULTS Height (1.68 ± 0.1; 1.61 ± 0.1 cm; P = 0.003) and BMC (2.3 ± 0.4; 2.0 ± 0.5 kg; P = 0.046) were lower in the NF1 group. Individuals with NF1 also presented lower total body and spine BMDs (g/cm2) (1.1 ± 0.1, 1.0 ± 0.1, P = 0.036; 1.0 ± 0.1, 0.9 ± 0.1; P = 0.015, respectively). The frequency of total body bone mass below the expected level for patients' ages was higher in the NF1 group (7.7%; 34.6%, P = 0.016). There were no differences in energy consumption. No correlations between BMC and BMD with nutrient intake were observed in the NF1 group. CONCLUSIONS The NF1 group presented lower BMCs and BMDs. Although a lower consumption of calcium, iron, and vitamin A, and a higher intake of sodium and omega-6 were observed, there was no relationship between bone phenotype and nutrient intake.

Neurofibromatosis 1 French national guidelines based on an extensive literature review since 1966

Neurofibromatosis type 1 is a relatively common genetic disease, with a prevalence ranging between 1/3000 and 1/6000 people worldwide. The disease affects multiple systems with cutaneous, neurologic, and orthopedic as major manifestations which lead to significant morbidity or mortality. Indeed, NF1 patients are at an increased risk of malignancy and have a life expectancy about 10-15 years shorter than the general population. The mainstay of management of NF1 is a patient-centered longitudinal care with age-specific monitoring of clinical manifestations, aiming at the early recognition and symptomatic treatment of complications as they occur. Protocole national de diagnostic et de soins (PNDS) are mandatory French clinical practice guidelines for rare diseases required by the French national plan for rare diseases. Their purpose is to provide health care professionals with guidance regarding the optimal diagnostic and therapeutic management of patients affected with a rare disease; and thus, harmonizing their management nationwide. PNDS are usually developed through a critical literature review and a multidisciplinary expert consensus. The purpose of this article is to present the French guidelines on NF1, making them even more available to the international medical community. We further dwelled on the emerging new evidence that might have therapeutic potential or a strong impact on NF1 management in the coming feature. Given the complexity of the disease, the management of children and adults with NF1 entails the full complement healthcare providers and communication among the various specialties.

Determination of Vitamin D Levels in Patients With Neurofibromatosis Type 1 in the Pediatric Age Group

Introduction:

Neurofibromatosis type 1 (NF1) is one of the most common autosomal dominant genetic disorders. Some clinical manifestations are present at birth, while some develop during childhood, and others can occur at any age. Given the early age at which patients develop clinical features, diagnosis is often made during childhood. The most prevalent features of NF1 are café au lait spots, dermal and plexiform neurofibromas, and learning disability. A variety of skeletal problems may be seen in NF1, including scoliosis, short stature, and pseudoarthrosis. Reduced skeletal bone mass has been documented to be a common phenomenon in children and adults with NF1. Decreased serum 25-hydroxyvitamin D (vitamin D) levels have been noted in adults and children with NF1 and have been reported to be inversely correlated with the number of dermal neurofibromas in adults. However, the actual correlation of vitamin D level to bone density and dermal neurofibroma number in children with NF1 remains unclear.

Objectives:

The primary objective of this study was to evaluate vitamin D levels among children and adolescents with NF1. The secondary objective was to describe the levels of vitamin D among children and adolescents with NF1, to verify in which age group there is a higher frequency of vitamin D alterations, and to explore vitamin D level correlations between age, gender, sun exposure, number of neurofibromas, and number of plexiform neurofibromas.

Methods:

This was an observational, cross-sectional, hospital-based study. We obtained a convenience sample of individuals with confirmed diagnosis of NF1 from patients attending the Medical Genetics Service of the IPPMG-UFRJ and Santa Casa de Misericórdia of Rio de Janeiro over a 24-month period. We evaluated vitamin D levels in blood samples of patients with NF1 by a chemiluminescent immunoassay method, and we correlated the results with gender, age, number of neurofibromas, number of plexiform neurofibromas, and satisfactory sun exposure.

Results:

Of the 55 patients, 28 (50.9%) were female and 27 (49.1%) were male. Patient ages ranged from a minimum of 1.2 to a maximum of 19.6 years (mean age 10.95 years) and the median was 11.11 years. Median and mean body mass index (BMI; z score) were -0.09 (minimum value -1.63 and maximum of 4.62) and 0.16, respectively. The mean value of vitamin D was 30.82 ng/mL (±12.31) and the median was 29 ng/mL (minimum value of 10.40 ng/mL and maximum of 79.19 ng/mL).

Conclusions:

The levels of vitamin D did not differ according to gender, age group, or the presence or number of cutaneous neurofibromas. Among patients with adequate sun exposure, there was a higher incidence of sufficient serum vitamin D levels. Patients with cutaneous neurofibromas in the 0 to 11 age group had a greater tendency to vitamin D sufficiency in relation to patients aged 11 to 19 years.

When Low Bone Mineral Density and Fractures Is Not Osteoporosis

PURPOSE OF REVIEW

To review the differential diagnosis of low bone mineral density (BMD).

RECENT FINDINGS

Osteoporosis is the most common cause of low BMD in adults; however, non-osteoporotic causes of low BMD should be considered in the differential diagnosis of patients with low BMD. Mild osteogenesis imperfecta, osteomalacia, and mineral and bone disorder of chronic kidney disease as well as several other rare diseases can be characterized by low BMD. This review summarizes the differential diagnosis of low BMD. It is important to differentiate osteoporosis from other causes of low BMD since treatment regimens can vary tremendously between these different disease processes. In fact, some treatments for osteoporosis could worsen or exacerbate the mineral abnormalities in other causes of low BMD.

A case report of revision occipital-cervical fusion after atlanto-axial instrumentation failure for neurofibromatosis type I

BACKGROUND

Neurofibromatosis type 1 is an autosomal dominant genetic disease with characteristic café-au-lait spots, neurofibroma, and dystrophic changes in the bones. However, complications involving atlanto-axial dislocation are rare.

CASE PRESENTATION

We report a case of neurofibromatosis with atlanto-axial dislocation. The chief complaints were numbness of the upper limb and gait disturbance. We performed short fusion using the Brooks method. However, recurrence of the dislocation was found after 5 months recovery, and the patient underwent posterior fusion from the occipital bone to C4. Thereafter, she had a good postoperative course.

CONCLUSIONS

Neurofibromatosis patients often exhibit a low bone mineral density because of dystrophic changes, and are prone to fragile bones. In the present case, the use of long fusion at the first surgery may have helped to form a strong fusion of fragile bone.

Early and Midterm Outcomes of Surgical Correction for Severe Dystrophic Cervical Kyphosis in Patients with Neurofibromatosis Type 1: A Retrospective Multicenter Study

OBJECTIVE

To evaluate the early and midterm outcomes of surgical correction for severe dystrophic cervical kyphosis in patients with neurofibromatosis type 1 (NF-1) and analyze the pathomechanics and the influence on surgical efficacy of related systemic skeletal dystrophy.

METHODS

Ten patients who underwent surgical correction for NF-1-related severe dystrophic cervical kyphosis were reviewed. Radiographic parameters, including local and global Cobb angle, sagittal vertical axis, and T-1 slope, were measured. The visual analog scale score, Japanese Orthopaedic Association score, Neck Disability Index, Patient Satisfaction Index, and complications were evaluated.

RESULTS

The average follow-up was 50.6 months. The local and global Cobb angle improved from the preoperative average of 82.0° and 54.9° to an average of 35.6° and 29.8°, respectively, at the time of final follow-up. The C2-7 sagittal vertical axis averaged 5.8 mm before surgery and 8.9 mm at the final follow-up. The average T1 slope was -12.3° before surgery and -1.6° at the final follow-up. The visual analog scale score, Japanese Orthopaedic Association score, and Neck Disability Index improved significantly, and the overall satisfaction rate was 90.0%. One death and 4 instrumentation failures occurred, 3 patients showed progression of the kyphosis, and 2 fusion failures were observed.

CONCLUSIONS

Surgical correction, specifically the combined anteroposterior procedure, is essential and effective for management of NF-1-related severe dystrophic cervical kyphosis. However, high incidences of instrumentation failure, kyphosis progression, and fusion failure were observed. NF-1-related continuous skeletal dystrophy caused by multiple metabolic factors remarkably affected the midterm outcomes. Early prevention and targeted pharmacotherapy may be necessary.

Trabecular Bone Score (TBS) and Bone Metabolism in Patients Affected with Type 1 Neurofibromatosis (NF1)

In patients with neurofibromatosis type 1 (NF1), decreased bone mineral density (BMD) and low levels of 25-hydroxy vitamin D3 (25OHD) have been reported. Recently, the trabecular bone score (TBS) measurement has been proposed as index of bone microarchitecture and fracture risk. In 74 NF1 patients (48 females, 26 males, age 41 ± 12), we measured TBS and investigated clinical stage, lifestyle, vitamin D, serum bone turnover markers, vertebral and femoral BMD. A homogenous cohort of 61 healthy subjects was used as control group. TBS was lower in NF1 patients (1.266 ± 0.113 vs. 1.346 ± 0.105) without differences between sexes. No correlations with 25OHD, low exercise, low calcium intake, reduced sun exposure, and number of skin neurofibromas were observed. As expected, hypovitaminosis D was common (98.6%), as well as BMD reduction in hip and spine sites: In NF1 patients, bone texture evaluated by TBS was low in both sexes without any correlation with clinical or metabolic parameters, suggesting a direct role of the fibromin mutation.

Progressive bone impairment with age and pubertal development in neurofibromatosis type I

Bone density impairment represents an established complication in adults with neurofibromatosis type 1, while few data exist in the pediatric population. Age- and gender-adjusted bone mass decreases with age and pubertal development, identifying childhood as the best time frame to introduce prevention strategies aiming at peak bone mass achievement.

PURPOSE

The present study aims at evaluating bone mineral density (BMD) in a population of children with neurofibromatosis type I (NF-1), with particular focus on changes occurring during growth and pubertal development.

METHODS

Bone metabolic markers and bone status [by dual-energy X-ray absorptiometry scans (DXA) of the total body and lumbar spine with morphometric analysis] were assessed in 50 children (33 males; mean age ± SD, 11.6 ± 4 years). Bone mineral apparent density (BMAD), trabecular bone score (TBS), and bone strain (BS) of the lumbar spine (LS) DXA were also obtained.

RESULTS

In our cohort areal BMD (aBMD) Z-score was below the mean in 88% of the patients at LS (70% after correction for bone size) and in 86% considering total body (TB) DXA. However, aBMD Z-score was < - 2 in 12% after correction for bone size at LS and TB, respectively. Lumbar spine aBMD Z-score (r = - 0.54, P < 0.0001), LS BMAD Z-score (r = - 0.53, P < 0.0001), and TB Z-score (r = - 0.39, P = 0.005) showed a negative correlation with growth and pubertal development (P = 0.007, P = 0.02, P = 0.01, respectively), suggesting that patients failed to gain as much as expected for age.

CONCLUSION

Bone density impairment becomes more evident with growth and pubertal development in NF-1 patients, thus identifying childhood as the best time frame to introduce prevention strategies aiming at peak bone mass achievement. TBS and BS, providing bone DXA qualitative information, could be useful during longitudinal follow-up for better characterizing bone impairment in these patients.

Possible modifier genes in the variation of neurofibromatosis type 1 clinical phenotypes

Neurofibromatosis type 1 (NF1) is the most common neurogenetic disorder worldwide, caused by mutations in the (NF1) gene. Although NF1 is a single-gene disorder with autosomal-dominant inheritance, its clinical expression is highly variable and unpredictable. NF1 patients have the highest known mutation rate among all human disorders, with no clear genotype-phenotype correlations. Therefore, variations in NF1 mutations may not correlate with the variations in clinical phenotype. Indeed, for the same mutation, some NF1 patients may develop severe clinical symptoms whereas others will develop a mild phenotype. Variations in the mutant NF1 allele itself cannot account for all of the disease variability, indicating a contribution of modifier genes, environmental factors, or their combination. Considering the gene structure and the interaction of neurofibromin protein with cellular components, there are many possible candidate modifier genes. This review aims to provide an overview of the potential modifier genes contributing to NF1 clinical variability.

Growing Rods Are an Effective Fusionless Method of Controlling Early-Onset Scoliosis Associated With Neurofibromatosis Type 1 (NF1): A Multicenter Retrospective Case Series

BACKGROUND

Spinal deformities associated with neurofibromatosis type 1 (NF1) often have an early onset. These curves frequently develop dysplastic features. Rapid progression is common, and is often difficult to control with casting or bracing. Spinal fusion at a young age can potentially interfere with chest and trunk growth. Growing rods (GRs) have been used in early-onset scoliosis (EOS) effectively. The purpose of this study was to evaluate GR use in NF1.

METHODS

Retrospective data collection was performed from a multicenter EOS database with additional patients from our own institute. Each patient had a genetic diagnosis of NF1 and was treated with GR. Results were compared with reported results of GR in EOS in the literature.

RESULTS

Fourteen patients from 5 centers underwent a total of 71 procedures with an average follow-up of 54 months. Mean age at surgery was 6.8 years. Means of initial and final curves were 74 and 36 degrees, respectively (51% correction). Spine grew at an average of 39 mm (11.2 mm per year). Implant-related complications were the most common (8/14, 57%), including failure of proximal construct (5/14), rod breakage (2/14), and prominent implants (1/14). There was no significant difference between screws and hooks as proximal anchors (Fischer test). Two patients had deep infection that needed debridement.

CONCLUSIONS

This retrospective pooled data study is the first report on the treatment of early-onset NF1 scoliosis with GRs. The use of GRs in these patients effectively controls the spinal deformity and facilitates growth of the spine. The complications were no greater than those seen in other conditions causing EOS. Failure of proximal anchors was found to be the most common complication.

LEVEL OF EVIDENCE

Level IV-retrospective case series.

Effect of higher implant density on curve correction in dystrophic thoracic scoliosis secondary to neurofibromatosis Type 1

OBJECTIVE The aim of this study was to investigate how implant density affects radiographic results and clinical outcomes in patients with dystrophic scoliosis secondary to neurofibromatosis Type 1 (NF1). METHODS A total of 41 patients with dystrophic scoliosis secondary to NF1 who underwent 1-stage posterior correction between June 2011 and December 2013 were included. General information about patients was recorded, as were preoperative and postoperative scores from Scoliosis Research Society (SRS)-22 questionnaires. Pearson correlation analysis was used to analyze the associations among implant density, coronal Cobb angle correction rate and correction loss at last follow-up, change of sagittal curve, and apical vertebral translation. Patients were then divided into 2 groups: those with low-density and those with high-density implants. Independent-sample t-tests were used to compare demographic data, radiographic findings, and clinical outcomes before surgery and at last follow-up between the groups. RESULTS Significant correlations were found between the implant density and the coronal correction rate of the main curve (r = 0.505, p < 0.01) and the coronal correction loss at final follow-up (r = -0.379, p = 0.015). There was no significant correlation between implant density and change of sagittal profile (p = 0.662) or apical vertebral translation (p = 0.062). The SRS-22 scores improved in the appearance, activity, and mental health domains within both groups, but there was no difference between the groups in any of the SRS-22 domains at final follow-up (p > 0.05 for all). CONCLUSIONS Although no significant differences between the high- and low-density groups were found in any of the SRS-22 domains at final follow-up, higher implant density was correlated with superior coronal correction and less postoperative correction loss in patients with dystrophic NF1-associated scoliosis.

A lateral cephalometry study of patients with neurofibromatosis type 1

PURPOSE

Neurofibromatosis type 1 (NF1) is an autosomal dominant transmitted tumour suppressor syndrome and also a bone disease. Osseous dysplasia affecting the craniofacial region is characteristic of NF1. The aim of this study was to analyse the lateral cephalograms of NF1 patients in comparison to individuals who were not affected by this condition in order to describe the skeletal phenotype of NF1 in more detail.

MATERIALS AND METHODS

The study comprises the lateral cephalograms of 172 patients with established NF1 diagnoses (female = 85, male = 87). NF1 patients were distinguished by radiological and/or histological findings of the facial region suggestive of plexiform neurofibroma (PNF) or disseminated cutaneous NF (DNF). The analysed radiographs of a collection of 29 healthy volunteers with ideal occlusion served as controls. The focus of this analysis was cephalometrically defined angles.

RESULTS

Cephalometric analyses of patients with DNF did not differ from those of controls for the vast majority of parameters. However, the measurement results of patients with PNF differed significantly from those of healthy volunteers and patients with DNF. The number of trigeminal nerve branches affected in PNF patients had an effect on the measurement results.

CONCLUSION

Lateral cephalograms revealed no significant alteration of the facial skeleton in NF1 patients as compared to controls. Indeed, the stigma of a so-called 'NF1 facies' cannot be derived from the cephalometric findings presented. Notably, a wide range of deviating readings were recorded for individuals with facial PNF. Clinicians who treat patients with NF1 should be aware of deviations from cephalometric standards on lateral cephalograms in NF1 patients, especially when craniofacial surgical procedures are planned. Some of these findings, particularly asymmetries of the facial skeleton, could be indicators of an associated PNF.

Bone mineral density and bone metabolic markers' status in children with neurofibromatosis type 1

BACKGROUND

Neurofibromatosis type 1 (NF1) is a multisystem disorder characterized by progressive manifestations, which is inherited in an autosomal dominant manner. The majority of patients with NF1 experience a diffuse, significant reduction in bone mass over time, with osteoporosis, osteopenia in the absence of severe scoliosis, or gross bone deformities. This study aimed to determine the bone mineral density (BMD) status, evaluate bone metabolism, and to determine the relevant factors in children with NF1.

METHODS

The study population included 33 pediatric NF1 patients (20 males and 13 females). Bone metabolic markers, such as total calcium, phosphorus, magnesium, alkaline phosphatase, parathyroid hormone, and 25-OH vitamin D, the urinary calcium/creatine ratio were measured. In addition, BMD was measured at both the lumbar spine (LS) and the femoral neck in all the patients.

RESULTS

All the patients had a low 25-OH vitamin D level, but it was significantly lower in the females than in the males (p<0.009). Overall, 18.2% of the patients had skeletal abnormalities. The lumbar Z-score was ≤2 in 21.2% of the patients, whereas the femoral neck Z-score was ≤2 in 9.1%. The urinary calcium/creatine ratio was significantly higher in the female than in the male patients (p<0.027). In all, six patients had skeletal abnormalities.

CONCLUSIONS

It is widely known that bone mineral metabolism markers and BMD are significantly affected in NF1 patients; however, the present study did not identify any effective parameters that could be used to predict skeletal abnormalities, or diagnose early osteoporosis and osteopenia in pediatric NF1 patients.

Halo Gravity Traction Is Associated with Reduced Bone Mineral Density of Patients with Severe Kyphoscoliosis

Background. Halo gravity traction (HGT) is one of the most commonly used perioperative techniques for the treatment of severe kyphoscoliosis. This study was to explore the influence of HGT on the BMD of these patients. Methods. Patients with severe kyphoscoliosis treated by preoperative HGT for at least 2 months were included. Patients' BMD were assessed by dual-energy X-ray absorptiometry at lumbar spine (LS, L2–L4) and femur neck (FN) of the nondominant side. The weight and duration of traction, as well as baseline characteristics, were recorded. Results. Twenty patients were recruited. The average traction duration was 77.9 ± 13.0 days while the mean traction weight was 39.9% ± 11.1% of total body weight. Remarkable decrease of BMD was observed at LS of 17 (85%) patients and at FN of 18 (90%) patients. After HGT, 75% of patients were found to have osteoporosis, the incidence of which was significantly higher than that before HGT (35%). The correlation analysis revealed BMD reduction was only significantly correlated with the traction duration. Conclusions. The current study showed that preoperative HGT can have obvious impact on the BMD. The BMD reduction is associated with traction duration, suggesting that long traction duration may bring more bone mineral loss.

Aberrant Myeloid Differentiation Contributes to the Development of Osteoporosis in Neurofibromatosis Type 1

Neurofibromatosis type 1 (NF1), also known as von Recklinghausen disease, is a common autosomal dominant genetic disorder affecting approximately 1 in 3000 individuals worldwide. NF1 results from heritable or spontaneous mutations of the NF1 tumor suppressor gene. NF1 encodes the protein neurofibromin, which functions to negatively regulate Ras-activity. Approximately 50 % of NF1 patients develop osteopenia or osteoporosis, resulting in significantly increased rates of long-bone fracture and morbidity. While defective osteoblast bone anabolism has been implicated as a central factor in the pathogenesis of NF1 associated skeletal deficits, recent data suggest that NF1 (Nf1) haploinsufficiency within the hematopoietic compartment, particularly in osteoclasts and myeloid progenitors, plays a pivotal role in engendering NF1 osseous manifestations. In this chapter, we review the latest data from clinical studies and murine models delineating a critical role for hematopoietic compartment, myeloid progenitors of NF1 (Nf1) haploinsufficient and their progeny-osteoclasts, in the pathogenesis of NF1 associated osteopenia/osteoporosis and discuss putative targets for future therapeutics.

Nf1 Haploinsufficiency Alters Myeloid Lineage Commitment and Function, Leading to Deranged Skeletal Homeostasis

Although nullizygous loss of NF1 leads to myeloid malignancies, haploinsufficient loss of NF1 (Nf1) has been shown to contribute to osteopenia and osteoporosis which occurs in approximately 50% of neurofibromatosis type 1 (NF1) patients. Bone marrow mononuclear cells of haploinsufficient NF1 patients and Nf1(+/-) mice exhibit increased osteoclastogenesis and accelerated bone turnover; however, the culprit hematopoietic lineages responsible for perpetuating these osteolytic manifestations have yet to be elucidated. Here we demonstrate that conditional inactivation of a single Nf1 allele within the myeloid progenitor cell population (Nf1-LysM) is necessary and sufficient to promote multiple osteoclast gains-in-function, resulting in enhanced osteoclastogenesis and accelerated osteoclast bone lytic activity in response to proresorptive challenge in vivo. Surprisingly, mice conditionally Nf1 heterozygous in mature, terminally differentiated osteoclasts (Nf1-Ctsk) do not exhibit any of these skeletal phenotypes, indicating a critical requirement for Nf1 haploinsufficiency at a more primitive/progenitor stage of myeloid development in perpetuating osteolytic activity. We further identified p21Ras-dependent hyperphosphorylation of Pu.1 within the nucleus of Nf1 haploinsufficient myelomonocytic osteoclast precursors, providing a novel therapeutic target for the potential treatment of NF1 associated osteolytic manifestations.

Hyperactive RAS/PI3-K/MAPK Signaling Cascade in Migration and Adhesion of Nf1 Haploinsufficient Mesenchymal Stem/Progenitor Cells

Neurofibromatosis type 1 (NF1) is an autosomal dominant disease caused by mutations in the NF1 tumor suppressor gene, which affect approximately 1 out of 3000 individuals. Patients with NF1 suffer from a range of malignant and nonmalignant manifestations such as plexiform neurofibromas and skeletal abnormalities. We previously demonstrated that Nf1 haploinsufficiency in mesenchymal stem/progenitor cells (MSPCs) results in impaired osteoblastic differentiation, which may be associated with the skeletal manifestations in NF1 patients. Here we sought to further ascertain the role of Nf1 in modulating the migration and adhesion of MSPCs of the Nf1 haploinsufficient (Nf1^+/−) mice. Nf1^+/− MSPCs demonstrated increased nuclear-cytoplasmic ratio, increased migration, and increased actin polymerization as compared to wild-type (WT) MSPCs. Additionally, Nf1^+/− MSPCs were noted to have significantly enhanced cell adhesion to fibronectin with selective affinity for CH271 with an overexpression of its complimentary receptor, CD49e. Nf1^+/− MSPCs also showed hyperactivation of phosphoinositide 3-kinase (PI3-K) and mitogen activated protein kinase (MAPK) signaling pathways when compared to WT MSPCs, which were both significantly reduced in the presence of their pharmacologic inhibitors, LY294002 and PD0325901, respectively. Collectively, our study suggests that both PI3-K and MAPK signaling pathways play a significant role in enhanced migration and adhesion of Nf1 haploinsufficient MSPCs.

Treatment of dystrophic scoliosis in neurofibromatosis Type 1 with one-stage posterior pedicle screw technique

BACKGROUND CONTEXT

Corrective surgery for dystrophic scoliosis in neurofibromatosis Type 1 (NF-1) is challenging. There are various surgical methods, all with unsatisfactory outcomes.

PURPOSE

The purpose of the study was to evaluate the clinical outcomes of the treatment of dystrophic scoliosis in NF-1 with one-stage posterior pedicle screw approach.

STUDY DESIGN

This is a retrospective clinical study.

PATIENT SAMPLE

Sixteen patients with dystrophic scoliosis in NF-1 underwent one-stage posterior surgery with pedicle screw system.

OUTCOME MEASUREMENT

We used preoperative and postoperative whole-spine radiographs to determine coronal and sagittal Cobb angles (curve correction); distance between apex vertebra and central sacral vertical line (DAC), pelvic obliquity, and shoulder tilt (coronal balance improvement); and sagittal vertical axis and pelvic tilt angle (sagittal balance improvement). We assessed the fusion rate using fusion segment computed tomography scan.

METHODS

Patients underwent surgery with or without osteotomy according to spinal flexibility. Fusion segment selection method of fusion segments selection which mean fusing from one or two levels proximal to upper end vertebra to one or two levels distal to the lower end vertebra (EV+1 or 2) or stable vertebrae fusion. There were no study-specific conflict of interest-associated biases.

RESULTS

The average follow-up time was 40.9 months. Mean scoliosis and kyphosis improved from 83.2° to 27.6° and 58.5° to 26.8°, respectively; at the last follow-up, it was 30.4° and 27.4°, respectively. Mean DAC, pelvic obliquity, and shoulder tilt improved from 53.0 to 23.9, 8.1 to 4.9, and 9.8 to 7.5 mm, respectively. Sagittal vertical axis and pelvic tilt angle improved from -5.8 to 1.6 mm and 17.9° to -5.8°, respectively. During follow-up, mean coronal and sagittal correction losses were 2.8° and 0.7°, respectively. Two EV+1 or 2 patients had decompensation. No pseudoarthrosis was identified.

CONCLUSIONS

The one-stage posterior pedicle screw approach is safe and effective in the treatment of dystrophic scoliosis in NF-1. Posterior vertebral column resection is recommended if flexibility is less than 35%. Stable vertebrae fusing is recommended.

Dystrophic spinal deformities in a neurofibromatosis type 1 murine model

Despite the high prevalence and significant morbidity of spinal anomalies in neurofibromatosis type 1 (NF1), the pathogenesis of these defects remains largely unknown. Here, we present two murine models: Nf1^flox/−;PeriCre and Nf1^flox/−;Col.2.3Cre mice, which recapitulate spinal deformities seen in the human disease. Dynamic histomorphometry and microtomographic studies show recalcitrant bone remodeling and distorted bone microarchitecture within the vertebral spine of Nf1^flox/−;PeriCre and Nf1^flox/−;Col2.3Cre mice, with analogous histological features present in a human patient with dystrophic scoliosis. Intriguingly, 36–60% of Nf1^flox/−;PeriCre and Nf1^flox/−;Col2.3Cre mice exhibit segmental vertebral fusion anomalies with boney obliteration of the intervertebral disc (IVD). While analogous findings have not yet been reported in the NF1 patient population, we herein present two case reports of IVD defects and interarticular vertebral fusion in patients with NF1. Collectively, these data provide novel insights regarding the pathophysiology of dystrophic spinal anomalies in NF1, and provide impetus for future radiographic analyses of larger patient cohorts to determine whether IVD and vertebral fusion defects may have been previously overlooked or underreported in the NF1 patient population.

Vitamin D Status and VDR Genotype in NF1 Patients: A Case-Control Study from Southern Brazil

Neurofibromatosis type 1 (NF1) patients are more likely to have vitamin D deficiency when compared to the general population. This study aimed to determine the levels of 25-OH-vitamin D [25(OH)D] in individuals with NF1 and disease-unaffected controls and analyze FokI and BsmI VDR gene polymorphisms in a case and in a control group. Vitamin D levels were compared between a group of 45 NF1 patients from Southern Brazil and 45 healthy controls matched by sex, skin type, and age. Genotypic and allelic frequencies of VDR gene polymorphisms were obtained from the same NF1 patients and 150 healthy controls. 25(OH)D deficiency or insufficiency was not more frequent in NF1 patients than in controls (p = 0.074). We also did not observe an association between FokI and BsmI VDR gene polymorphisms and vitamin D levels in NF1 patients, suggesting that their deficient or insufficient biochemical phenotypes are not associated with these genetic variants. The differences between the groups in genotypic and allelic frequencies for FokI and BsmI VDR gene polymorphisms were small and did not reach statistical significance. These polymorphisms are in partial linkage disequilibrium and the haplotype frequencies also did not differ in a significant way between the two groups (p = 0.613).

Neurofibromin inactivation impairs osteocyte development in Nf1Prx1 and Nf1Col1 mouse models

Neurofibromin has been identified as a critical regulator of osteoblast differentiation. Osteoblast specific inactivation of neurofibromin in mice results in a high bone mass phenotype and hyperosteoidosis. Here, we show that inactivation of the Nf1 gene also impairs osteocyte development. We analyzed cortical bone tissue in two conditional mouse models, Nf1Prx1 and Nf1Col1, for morphological and molecular effects. Backscattered electron microscopy revealed significantly enlarged osteocyte lacunae in Nf1Prx1 and Nf1Col1 mice (level E2: ctrl=1.90±0.52%, Nf1Prx1=3.40±0.95%; ctrl 1.60±0.47%, Nf1Col1 2.46±0.91%). Moreover, the osteocyte lacunae appeared misshaped in Nf1Prx1 and Nf1Col1 mice as indicated by increased Feret ratios. Strongest osteocyte and dendritic network disorganization was observed in proximity of muscle attachment sites in Nf1Prx1 humeri. In contrast to control cells, Nf1Prx1 osteocytes contained abundant cytosolic vacuoles and accumulated immature organic matrix within the perilacunar space, a phenotype reminiscent of the hyperosteoidosis shown Nf1 deficient mice. Cortical bone lysates further revealed approx. twofold upregulated MAPK signalling in osteocytes of Nf1Prx1 mice. This was associated with transcriptional downregulation of collagens and genes involved in mechanical sensing in Nf1Prx1 and Nf1Col1 bone tissue. In contrast, matrix gla protein (MGP), phosphate regulating endopeptidase homolog, X-linked (PHEX), and genes involved in lipid metabolism were upregulated. In line with previously described hyperactivation of Nf1 deficient osteoblasts, systemic plasma levels of the bone formation markers osteocalcin (OCN) and procollagen typ I N-propeptide (PINP) were approx. twofold increased in Nf1Prx1 mice. Histochemical and molecular analysis ascertained that osteocytes in Nf1Prx1 cortical bone were viable and did not undergo apoptosis or autophagy. We conclude that loss of neurofibromin is not only critical for osteoblasts but also hinders normal osteocyte development. These findings expand the effect of neurofibromin onto yet another cell type where it is likely involved in the regulation of mechanical sensing, bone matrix composition and mechanical resistance of bone tissue.

Maximizing bone formation in posterior spine fusion using rhBMP-2 and zoledronic acid in wild type and NF1 deficient mice

Spinal pseudarthrosis is a well described complication of spine fusion surgery in NF1 patients. Reduced bone formation and excessive resorption have been described in NF1 and anti-resorptive agents may be advantageous in these individuals. In this study, 16 wild type and 16 Nf1(+/-) mice were subjected to posterolateral fusion using collagen sponges containing 5 µg rhBMP-2 introduced bilaterally. Mice were dosed twice weekly with 0.02 mg/kg zoledronic acid (ZA) or sterile saline. The fusion mass was assessed for bone volume (BV) and bone mineral density (BMD) by microCT. Co-treatment using rhBMP-2 and ZA produced a significant increase (p < 0.01) in BV of the fusion mass compared to rhBMP-2 alone in both wild type mice (+229%) and Nf1(+/-) mice (+174%). Co-treatment also produced a significantly higher total BMD of the fusion mass compared to rhBMP-2 alone in both groups (p < 0.01). Despite these gains with anti-resorptive treatment, Nf1(+/-) deficient mice still generated less bone than wild type controls. TRAP staining on histological sections indicated an increased osteoclast surface/bone surface (Oc.S/BS) in Nf1(+/-) mice relative to wild type mice, and this was reduced with ZA treatment.

Differences of 25-hydroxyvitamin D3 concentrations in children and adults with neurofibromatosis type 1

OBJECTIVES

Neurofibromatosis type 1 (NF1) is an autosomal dominant genetic disorder, frequently associated with reduced bone mineral density. Serum 25-hydroxyvitamin D3 concentrations in NF1 adults are lower than in healthy controls in autumn respectively winter and are inversely correlated with the number of dermal neurofibromas. We investigated 25-hydroxyvitamin D3 levels in children and adults with neurofibromatosis type 1 in winter and summer and compared them to healthy controls to get more pathogenic insights in vitamin D3 metabolism in NF1 patients.

DESIGN AND METHODS

NF1 patients were clinically examined and serum 25-hydroxyvitamin D3 concentrations were measured in 58 NF1 adults and 46 children in winter as well as in summer and compared to sex-, age- and month-matched controls.

RESULTS

52 adults suffered from 10 to 5000 dermal neurofibromas, whereas none of the children presented neurofibromas. 25-Hydroxyvitamin D3 increased from winter to summer (mean: 21.0 to 46.5nmol/l) in NF1 adults. This increase was even larger (p=0.0001) than in healthy controls (mean: 50.5 to 60.5nmol/l). However, there were no differences of 25-hydroxyvitamin D3 concentrations in NF1 children and healthy controls both in winter and in summer.

CONCLUSIONS

Only adults with NF1 showed lower 25-hydroxyvitamin D3 levels in winter and summer, which are unlikely due to impaired UV-dependent dermal synthesis, but rather might be caused by an accelerated catabolism.

Multiscale, converging defects of macro-porosity, microstructure and matrix mineralization impact long bone fragility in NF1

Bone fragility due to osteopenia, osteoporosis or debilitating focal skeletal dysplasias is a frequent observation in the Mendelian disease Neurofibromatosis type 1 (NF1). To determine the mechanisms underlying bone fragility in NF1 we analyzed two conditional mouse models, Nf1Prx1 (limb knock-out) and Nf1Col1 (osteoblast specific knock-out), as well as cortical bone samples from individuals with NF1. We examined mouse bone tissue with micro-computed tomography, qualitative and quantitative histology, mechanical tensile analysis, small-angle X-ray scattering (SAXS), energy dispersive X-ray spectroscopy (EDX), and scanning acoustic microscopy (SAM). In cortical bone of Nf1Prx1 mice we detected ectopic blood vessels that were associated with diaphyseal mineralization defects. Defective mineral binding in the proximity of blood vessels was most likely due to impaired bone collagen formation, as these areas were completely devoid of acidic matrix proteins and contained thin collagen fibers. Additionally, we found significantly reduced mechanical strength of the bone material, which was partially caused by increased osteocyte volume. Consistent with these observations, bone samples from individuals with NF1 and tibial dysplasia showed increased osteocyte lacuna volume. Reduced mechanical properties were associated with diminished matrix stiffness, as determined by SAM. In line with these observations, bone tissue from individuals with NF1 and tibial dysplasia showed heterogeneous mineralization and reduced collagen fiber thickness and packaging. Collectively, the data indicate that bone fragility in NF1 tibial dysplasia is partly due to an increased osteocyte-related micro-porosity, hypomineralization, a generalized defect of organic matrix formation, exacerbated in the regions of tensional and bending force integration, and finally persistence of ectopic blood vessels associated with localized macro-porotic bone lesions.

Hyperactive transforming growth factor-β1 signaling potentiates skeletal defects in a neurofibromatosis type 1 mouse model

Dysregulated transforming growth factor beta (TGF-β) signaling is associated with a spectrum of osseous defects as seen in Loeys-Dietz syndrome, Marfan syndrome, and Camurati-Engelmann disease. Intriguingly, neurofibromatosis type 1 (NF1) patients exhibit many of these characteristic skeletal features, including kyphoscoliosis, osteoporosis, tibial dysplasia, and pseudarthrosis; however, the molecular mechanisms mediating these phenotypes remain unclear. Here, we provide genetic and pharmacologic evidence that hyperactive TGF-β1 signaling pivotally underpins osseous defects in Nf1(flox/-) ;Col2.3Cre mice, a model which closely recapitulates the skeletal abnormalities found in the human disease. Compared to controls, we show that serum TGF-β1 levels are fivefold to sixfold increased both in Nf1(flox/-) ;Col2.3Cre mice and in a cohort of NF1 patients. Nf1-deficient osteoblasts, the principal source of TGF-β1 in bone, overexpress TGF-β1 in a gene dosage-dependent fashion. Moreover, Nf1-deficient osteoblasts and osteoclasts are hyperresponsive to TGF-β1 stimulation, potentiating osteoclast bone resorptive activity while inhibiting osteoblast differentiation. These cellular phenotypes are further accompanied by p21-Ras-dependent hyperactivation of the canonical TGF-β1-Smad pathway. Reexpression of the human, full-length neurofibromin guanosine triphosphatase (GTPase)-activating protein (GAP)-related domain (NF1 GRD) in primary Nf1-deficient osteoblast progenitors, attenuated TGF-β1 expression levels and reduced Smad phosphorylation in response to TGF-β1 stimulation. As an in vivo proof of principle, we demonstrate that administration of the TGF-β receptor 1 (TβRI) kinase inhibitor, SD-208, can rescue bone mass deficits and prevent tibial fracture nonunion in Nf1(flox/-) ;Col2.3Cre mice. In sum, these data demonstrate a pivotal role for hyperactive TGF-β1 signaling in the pathogenesis of NF1-associated osteoporosis and pseudarthrosis, thus implicating the TGF-β signaling pathway as a potential therapeutic target in the treatment of NF1 osseous defects that are refractory to current therapies.

NF1 is a critical regulator of muscle development and metabolism

There is emerging evidence for reduced muscle function in children with neurofibromatosis type 1 (NF1). We have examined three murine models featuring NF1 deficiency in muscle to study the effect on muscle function as well as any underlying pathophysiology. The Nf1(+/-) mouse exhibited no differences in overall weight, lean tissue mass, fiber size, muscle weakness as measured by grip strength or muscle atrophy-recovery with limb disuse, although this model lacks many other characteristic features of the human disease. Next, muscle-specific knockout mice (Nf1muscle(-/-)) were generated and they exhibited a failure to thrive leading to neonatal lethality. Intramyocellular lipid accumulations were observed by electron microscopy and Oil Red O staining. More mature muscle specimens lacking Nf1 expression taken from the limb-specific Nf1Prx1(-/-) conditional knockout line showed a 10-fold increase in muscle triglyceride content. Enzyme assays revealed a significant increase in the activities of oxidative metabolism enzymes in the Nf1Prx1(-/-) mice. Western analyses showed increases in the expression of fatty acid synthase and the hormone leptin, as well as decreased expression of a number of fatty acid transporters in this mouse line. These data support the hypothesis that NF1 is essential for normal muscle function and survival and are the first to suggest a direct link between NF1 and mitochondrial fatty acid metabolism.

Approaches to treating NF1 tibial pseudarthrosis: consensus from the Children's Tumor Foundation NF1 Bone Abnormalities Consortium

BACKGROUND

Neurofibromatosis 1 (NF1) is an autosomal dominant disorder with various skeletal abnormalities occurring as part of a complex phenotype. Tibial dysplasia, which typically presents as anterolateral bowing of the leg with subsequent fracture and nonunion (pseudarthrosis), is a serious but infrequent osseous manifestation of NF1. Over the past several years, results from clinical and experimental studies have advanced our knowledge of the role of NF1 in bone. On the basis of current knowledge, we propose a number of concepts to consider as a theoretical approach to the optimal management of tibial pseudarthrosis.

METHODS

A literature review for both clinical treatment and preclinical models for tibial dysplasia in NF1 was performed. Concepts were discussed and developed by experts who participated in the Children's Tumor Foundation sponsored International Bone Abnormalities Consortium meeting in 2011.

RESULTS

Concepts for a theoretical approach to treating tibial pseudarthrosis include: bone fixation appropriate to achieve stability in any given case; debridement of the "fibrous pseudarthrosis tissue" between the bone segments associated with the pseudarthrosis; creating a healthy vascular bed for bone repair; promoting osteogenesis; controlling overactive bone resorption (catabolism); prevention of recurrence of the "fibrous pseudarthrosis tissue"; and achievement of long-term bone health to prevent recurrence.

CONCLUSIONS

Clinical trials are needed to assess effectiveness of the wide variation of surgical and pharmacologic approaches currently in practice for the treatment of tibial pseudarthrosis in NF1.

LEVEL OF EVIDENCE

Level V, expert opinion.

Hyperactive Ras/MAPK signaling is critical for tibial nonunion fracture in neurofibromin-deficient mice

Neurofibromatosis type 1 (NF1) is a common genetic disorder affecting 1 in 3500 individuals. Patients with NF1 are predisposed to debilitating skeletal manifestations, including osteopenia/osteoporosis and long bone pseudarthrosis (nonunion fracture). Hyperactivation of the Ras/mitogen-activated protein kinase (MAPK) pathway in NF1 is known to underlie aberrant proliferation and differentiation in cell lineages, including osteoclast progenitors and mesenchymal stem cells (MSCs) also known as osteoblast progenitors (pro-OBLs). Our current study demonstrates the hyper Ras/MAPK as a critical pathway underlying the pathogenesis of NF1-associated fracture repair deficits. Nf1-deficient pro-OBLs exhibit Ras/MAPK hyperactivation. Introduction of the NF1 GTPase activating-related domain (NF1 GAP-related domain) in vitro is sufficient to rescue hyper Ras activity and enhance osteoblast (OBL) differentiation in Nf1(-/-) pro-OBLs and NF1 human (h) MSCs cultured from NF1 patients with skeletal abnormalities, including pseudarthrosis or scoliosis. Pharmacologic inhibition of mitogen-activated protein kinase kinase (MEK) signaling with PD98059 partially rescues aberrant Erk activation while enhancing OBL differentiation and expression of OBL markers, osterix and osteocalcin, in Nf1-deficient murine pro-OBLs. Similarly, MEK inhibition enhances OBL differentiation of hMSCs. In addition, PD98059 rescues aberrant osteoclast maturation in Nf1 haploinsufficient bone marrow mononuclear cells (BMMNCs). Importantly, MEK inhibitor significantly improves fracture healing in an NF1 murine model, Col2.3Cre;Nf1(flox/-). Collectively, these data indicate the Ras/MAPK cascade as a critical pathway in the pathogenesis of bone loss and pseudarthrosis related to NF1 mutations. These studies provide evidence for targeting the MAPK pathway to improve bone mass and treat pseudarthrosis in NF1.

The generalized bone phenotype in children with neurofibromatosis 1: a sibling matched case-control study

People with neurofibromatosis 1 (NF1) have low bone mineralization, but the natural history and pathogenesis are poorly understood. We performed a sibling-matched case-control study of bone mineral status, morphology, and metabolism. Eighteen children with NF1 without focal bony lesions were compared to unaffected siblings and local population controls. Bone mineral content at the lumbar spine and proximal femur (dual energy X-ray absorptiometry (DXA)) was lower in children with NF1; this difference persisted after adjusting for height and weight. Peripheral quantitative computed tomography (pQCT) of the distal tibia showed that trabecular density was more severely compromised than cortical. Peripheral QCT-derived estimates of bone strength and resistance to bending and stress were poorer among children with NF1 although there was no difference in fracture frequencies. There were no differences in the size or shape of bones after adjusting for height. Differences in markers of bone turnover between cases and controls were in the directions predicted by animal studies, but did not reach statistical significance. Average serum calcium concentration was higher (although within the normal range) in children with NF1; serum 25-OH vitamin D, and PTH levels did not differ significantly between cases and controls. Children with NF1 were less mature (assessed by pubertal stage) than unaffected siblings or population controls. Children with NF1 have a generalized difference of bone metabolism that predominantly affects trabecular bone. Effects of decreased neurofibromin on bone turnover, calcium homeostasis, and pubertal development may contribute to the differences in bone mineral content observed among people with NF1.