Bone health and fracture rate in individuals with neurofibromatosis 1 (NF1)

Epidemiology and Outcomes of Neurofibromatosis Type 1 (NF-1): Multicenter Tertiary Experience

Purpose

The aim of this manuscript was to assess the epidemiology and clinical features of Neurofibromatosis type 1 (NF-1) based on the newly published revised NF-1 diagnostic criteria and to evaluate complications of NF-1 including neurodevelopmental disorders.

Patients and methods

A retrospective cross-sectional observational study was conducted in the Ministry of National Guard Health Affairs (MNGHA) healthcare organization branches including four tertiary hospitals and 51 primary health care centers in different regions in Saudi Arabia. This study included all patients diagnosed with NF1 using the revised NIH diagnostic criteria published in 2021 that were registered at the electronic medical records (EMR) from 2015 to 2021.

Results

A total of 184 patients fulfilled the diagnostic criteria and were included in this study. The median age at diagnosis was 11 years (IQR: 4.00-20.25). The most encountered diagnostic criteria in this study were Café-au-lait macules (85.3%), and (42.9%) were found to have two or more neurofibromas with plexiform neurofibroma being the most common subtype (23.36%), approximately (36.4%) of the patient with optic pathway glioma. Nearby (26.6%) of the patients displayed different type of tumors. Iris Lisch nodules were presented in 36.4% of patients at a median age of 12 years (IQR: 9.0-21.8). Cardiovascular abnormality was encountered in 9.8% of the patients. Around 27.7% of the patients reported headache and 11.4% of the patient suffered from different type of epilepsy. Besides, 10.5% of the patients had intellectual disability, 33.8% suffered from communication disorders, and 4.9% patients had ADHD.

Conclusion

The results of this study will enable practitioners to adopt a more holistic approach and prioritize numerous attributes, which they can subsequently incorporate into their therapeutic methodologies. Furthermore, the identification of these attributes will facilitate an expeditious and accurate diagnosis. Hence, the implementation of intervention during its nascent phase may result in a more advantageous consequence.

Endocrine and non-endocrine causes of fatigue in adults with Neurofibromatosis type 1

Context

Neurofibromatosis type 1 (NF1) is a complex system disorder, caused by alterations in RAS pathways. NF1 adults often suffer from chronic and severe fatigue, for which they are frequently referred to Internal Medicine/Endocrinology. Seeking medical help often leads to (invasive) diagnostic procedures. To prevent the personal and financial burden of this disabling fatigue, it is crucial to know the causes.

Objective

To explore somatic causes and provide practical recommendations for the approach to fatigue in adults with NF1.

Design

Cross-sectional. All adults with NF1 (N = 133) who visited our Endocrinology department underwent a systematic health screening, including a medical questionnaire, structured interview, complete physical examination, biochemical measurements and additional tests if indicated.

Main outcome measure

Prevalence of endocrine and non-endocrine health problems between NF1 adults with and without fatigue.

Results

In our cohort, 75% of NF1 adults experienced fatigue. The most frequent endocrine disorders were vitamin D deficiency (28%), obesity (18%) and hypothyroidism (8%). The most frequent non-endocrine internal disorder was high blood pressure (42%). None of the disorders differed significantly between adults with and without fatigue.

Conclusions

Endocrine and non-endocrine disorders were equally present in our cohort of NF1 adults with and without fatigue. This suggests that the high prevalence of fatigue in NF1 adults is not explained by these somatic disorders. An alternative explanation for fatigue might be deficits in cognitive functioning and other neuropsychological processes in NF1. Based on our results and review of the literature, we provide a clinical algorithm for the approach to fatigue in NF1 adults, including somatic and psychological assessment.

Bone mineral density, vitamin D and osseous metabolism indices in neurofibromatosis type 1: A systematic review and meta-analysis

BACKGROUND

Neurofibromatosis type 1 (NF1) is a genetic autosomal neurocutaneous syndrome correlated with skeletal dysplasia and defects in the osseous microarchitecture. The physiological mechanism for the development of NF1-related bone abnormal turnover is still unclear.

OBJECTIVES

A meta-analysis was performed to investigate the effects of NF1 on bone mineral density (BMD) and osseous metabolic indices in order to provide clinical evidence for the pathogenesis of the associated skeletal deformities.

METHODS

A systematic literature review search was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines in the PubMed/Medline and Web of Science databases from the date of inception of each database through to 10 September 2023. Specific inclusion and exclusion criteria were applied for the identification of studies examining the effects of NF1 on bone strength and metabolism. The Newcastle-Ottawa and Jadad scales were applied to assess the quality of the included studies. RevMan 5.3 software was used for the analysis of the data, and MedCalc was applied to examine publication bias.

RESULTS

Overall, 13 studies met the inclusion criteria comprised of 5 cross-sectional, 6 case-control and 2 retrospective studies. 703 patients and 973 healthy subjects formed the NF1 and control group, respectively. The results of the meta-analysis displayed that lumbar (SMD = -3.85, 95%CI = -7.53 to -0.18, Z = 2.05, p = 0.04) and femoral (SMD = -4.78, 95%CI = -8.86 to -0.69, Z = 2.29, p = 0.02) BMD was reduced in the NF1 group. Both in children and adults the serum levels of 25 hydroxyvitamin D3 were also decreased in NF1 group, but without any statistical significance (SMD = -0.62, 95%CI = -1.34 to -0.11, Z = 1.66, p = 0.10). Serum Parathyroid hormone (PTH) (SMD = 0.73, 95%CI = 0.31 to 1.15, Z = 3.43, p = 0.0006) and C-telopeptide of type 1 collagen (CTX) (SMD = 0.82, 95%CI = 0.33 to 1.30, Z = 3.29, p = 0.001) were elevated in NF1 patients, while serum calcium (SMD = -0.10, 95%CI = -0.74 to 0.53, Z = 0.32, p = 0.75) phosphorous (SMD = 0.33, 95%CI = -0.38 to 1.05, Z = 0.92, p = 0.36), alkaline phosphatase (ALP) (SMD = -0.36, 95%CI = -0.77 to 0.05, Z = 1.71, p = 0.09), osteocalcin (SMD = 1.81, 95%CI = -0.37 to -3.98, Z = 1.63, p = 0.10) and bone formation markers (SMD = 0.28, 95%CI = -0.37 to -0.94, Z = 0.85, p = 0.39) were not.

CONCLUSION

NF1 is associated with decreased BMD at the lumbar spine and femur. Taking into account that the serum levels of PTH, CTX were increased whereas the concentrations of vitamin D, calcium, phosphorous, ALP, osteocalcin and bone formation markers were not altered significantly in the NF1 patients compared with the healthy subjects, a vitamin D independent dysregulated bone cellular activity could be considered.

STUDY REGISTRATION

Registered on PROSPERO (CRD42023424751).

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.

Endocrine morbidity in neurofibromatosis 1: a nationwide, register-based cohort study

OBJECTIVE

Previous studies have found that neurofibromatosis 1 (NF1) is associated with an increased risk for endocrine disorders, but no comprehensive overview of the risk for specific endocrine disorders has been published. We assessed endocrine morbidity in individuals with NF1 from information on hospital admissions, surgery for endocrine disorders, and relevant medication.

DESIGN

A nationwide population registry-based cohort study.

METHODS

We identified 2467 individuals with NF1 diagnosed between 1977 and 2013 from the Danish National Patient Register and the RAREDIS database and 20 132 randomly sampled age- and sex-matched population comparisons. Information on endocrine diseases was identified using registrations of discharge diagnoses, surgery, and medication prescriptions. The rates of endocrine disorders in individuals with NF1 were compared with those in the comparison cohort in Cox proportional hazard models.

RESULTS

Individuals with NF1 had a higher rate than the comparison group of any endocrine discharge diagnosis (hazard ratio [HR] 1.72, 95% confidence interval [CI]: 1.58-1.87), endocrine-related surgery (2.03, 1.39-2.96), and prescribed medications (1.32, 1.23-1.42). Increased HRs were observed for diseases and surgical operations of several glands, including pheochromocytoma, and for osteoporosis, and osteoporotic fractures. Decreased rates were observed with drugs for type 2 diabetes. Women with NF1 had higher HRs for surgery of the ovaries, uterus, and sterilization, but lower rates of surgeries of cervix and prescriptions for birth control pills.

CONCLUSIONS

Neurofibromatosis 1 is associated with a variety of endocrine disorders, surgery, and medication related to endocrine disease. Awareness of endocrine morbidity is important in the clinical follow-up of individuals with NF1.

Icariin Promotes Osteogenic Differentiation in a Cell Model with NF1 Gene Knockout by Activating the cAMP/PKA/CREB Pathway

Neurofibromatosis type 1 is a rare autosomal dominant genetic disorder, with up to 50% of patients clinically displaying skeletal defects. Currently, the pathogenesis of bone disorders in NF1 patients is unclear, and there are no effective preventive and treatment measures. In this study, we found that knockout of the NF1 gene reduced cAMP levels and osteogenic differentiation in an osteoblast model, and icariin activated the cAMP/PKA/CREB pathway to promote osteoblast differentiation of the NF1 gene knockout cell model by increasing intracellular cAMP levels. The PKA selective inhibitor H89 significantly impaired the stimulatory effect of icariin on osteogenesis in the NF1 cell model. In this study, an osteoblast model of NF1 was successfully constructed, and icariin was applied to the cell model for the first time. The results will help to elucidate the molecular mechanism of NF1 bone disease and provide new ideas for the clinical prevention and treatment of NF1 bone disease and drug development in the future.

Bone Mineral Density in Neurofibromatosis Type 1: A Systematic Review and Meta-Analysis

To assess BMD in patients with neurofibromatosis type 1 (NF1) using systematic review and meta-analysis technique. Potentially eligible studies were identified from Medline and EMBASE databases from inception to February 2023 using search strategy that comprised terms for "Bone mineral density" and Neurofibromatosis type 1″. Eligible study must include adult or pediatric patients with NF1. The study must report mean Z-score with variance of total body, lumbar spine, femoral neck or total hip BMD of the studied patients. Point estimates with standard errors were retrieved from each study and were combined using the generic inverse variance method. A total of 1,165 articles were identified. After systematic review, 19 studies were included. The meta-analysis revealed that patients with NF1 had negative mean Z-scores for total body BMD (pooled mean Z-score -0.808; 95%CI, -1.025 to -0.591) and BMD at lumbar spine (pooled mean Z-score -1.104; 95%CI, -1.376 to -0.833), femoral neck (pooled mean Z-score -0.726; 95%CI, -0.893 to -0.560) and total hip (pooled mean Z-score -1.126; 95%CI, -2.078 to -0.173). The subgroup meta-analysis in pediatric patients aged < 18 years revealed that patients with NF1 had negative mean Z-scores for lumbar spine BMD (pooled mean Z-score -0.938; 95%CI, -1.299 to -0.577) and femoral neck BMD (pooled mean Z-score -0.585; 95%CI, -0.872 to -0.298). The current meta-analysis found that patients with NF1 had low Z-scores although the degree of low BMD may not be of clinical significance. The results do not support the role of early BMD screening in children and young adults with NF1.

Vitamin D and Bone Metabolism in Adult Patients with Neurofibromatosis Type 1

Neurofibromatosis type 1 (NF1) is a genetic multisystemic autosomal dominant disorder determining reduced life expectancy due to higher risk of developing benign and malignant tumors. Low levels of vitamin D and reduced bone mineral density (BMD) have been reported in young patients with NF1. However, correlation between vitamin D and NF1 phenotype needs to be elucidated. Aim of this study was to assess vitamin D levels and bone metabolism in NF1 patients, analyzing potential correlations with clinical phenotype. A cross-sectional study was carried out in a monocentric series of NF1 patients, evaluating genotype, clinical phenotype, BMD, biochemical evaluation with focus on serum 25OH-vitamin D, parathyroid hormone (PTH), calcium and phosphate levels. Correlations between clinical manifestations, neurofibromas, and vitamin D status have been studied in comparison with healthy controls. 31 NF1 adult patients were matched for sex, age and body mass index with 31 healthy controls. A significantly difference in vitamin D level emerged in NF1 patients compared to controls. Interestingly low vitamin D levels correlated with a more aggressive phenotype and with a bigger size of neurofibromas. These data underline that vitamin D deficiency/insufficiency may play a role in clinical severity of neurofibromas in patients with NF1, suggesting the need to check bone status and replace vitamin D in these patients.

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.

Bone deformities in patients with neurofibromatosis type 1: Single-center experience

BACKGROUND

Neurofibromatosis type 1 (NF-1) is the most common neurocutaneous syndrome with an autosomal dominant inheritance. However, half of the cases are de novo mutations. Involvement of bone, skin (cafe au lait macules), as well as ocular and tumoral formations is also associated with NF-1. Here, we present our case series of patients with bone deformities.

METHODS

The medical files of patients with NF-1 who were followed up by the same doctor in the pediatric neurology outpatient clinic over 2 years were retrospectively analyzed.

RESULTS

Overall, 19 girls and 13 boys were diagnosed with NF-1. Of these 32 patients, 12 (nine girls, three boys) were found to have bone pathologies. The average age was of these patients with bone pathology was 7.5 and 9.5 years. Scoliosis, bowing, short stature, and long bone cysts were found in descending order of frequency. Severe adhesions in the hands and feet as well as phalangeal hypoplasia were noted in one patient.

CONCLUSION

NF-1 requires a multidisciplinary approach. Routine follow-up is very important as it is known that deformities that affect different systems may appear or increase with age. Severe hand and foot anomalies seen in one of our patients did not seem to be associated with NF-1.

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.

Are Children Suffering From Congenital Pseudarthrosis of the Tibia Associated With Decreased Bone Strength?

BACKGROUND

Congenital pseudarthrosis of the tibia (CPT) is a rare and difficult-to-treat congenital disease in neonates. Our previous study found that exosomes derived from serum of children with CPT inhibit bone formation. In this study, we used ultrasound bone densitometry to detect the bone strength differences between hospitalized children with CPT and with non-metabolic diseases to determine the bone strength of children with CPT.

METHODS

A total of 37 children with CPT with a mean age of 3.14 ± 1.81 years and 40 hospitalized children with a mean age of 3.32 ± 2.66 years with supracondylar fracture of the humerus and without a bone metabolic disease (control group) were recruited in our hospital. The ultrasonic bone densitometer was used to examine the bilateral calcaneus of the subjects. We collected the broadband ultrasonic attenuation (BUA), speed of sound (SOS), quantitative ultrasound index (QUI), bone strength index (STI) and bone mineral density estimation (BMDe) values. Multivariable regression was used to examine the associations between quantitative ultrasound measurement differences and age, body mass index (BMI), neurofibromatosis type 1 (NF1) and CPT Crawford type. Intra-class correlation coefficient (ICC) was calculated to estimate intra- and inter-rater agreements.

RESULTS

74 calcaneus scans were taken from CPT patients (23 boys and 14 girls) and 80 calcaneus scans were taken from the control (24 boys and 16 girls). The CPT patients exhibited significantly lower SOS (1,368.75 ± 136.78 m/s), STI (7.2319 ± 38.6525), QUI (8.2532 ± 56.1720), and BMDe (-0.0241 ± 0.3552 g/cm³) than the control (SOS: 1,416.02 ± 66.15 m/s, STI: 7.96 ± 16.884, QUI: 28.8299 ± 25.461, BMDe: 0.0180 ± 0.1610 g/cm³). Multiple regression revealed that SOS, STI and QUI were statistically significant and negatively correlated with CPT Crawford classification.

CONCLUSIONS

We found the incidence of decreased bone strength in CPT group was higher than that in the non-bone metabolic disease group. This phenomenon was not related to NF1 but related to CPT Crawford classification, which suggested that the higher the grade of the CPT Crawford classification, the lower the bone strength and the higher the risk of fracture.

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.

RASopathies: The musculoskeletal consequences and their etiology and pathogenesis

The RASopathies comprise an ever-growing number of clinical syndromes resulting from germline mutations in components of the RAS/MAPK signaling pathway. While multiple organs and tissues may be affected by these mutations, this review will focus on how these mutations specifically impact the musculoskeletal system. Herein, we review the genetics and musculoskeletal phenotypes of these syndromes in humans. We discuss how mutations in the RASopathy syndromes have been studied in translational mouse models. Finally, we discuss how signaling molecules within the RAS/MAPK pathway are involved in normal and abnormal bone biology in the context of osteoblasts, osteoclasts and chondrocytes.

Phenotyping spinal abnormalities in patients with Neurofibromatosis type 1 using whole-body MRI

Neurofibromatosis Type 1 (NF1) has been reported to be associated with a variety of spinal abnormalities. The purpose of this study was to quantify the prevalence of spinal abnormalities in a collective of NF1 patients that is representative for the general NF1 population, to associate the co-appearance of spinal abnormalities with both NF1 and clinical symptoms and to investigate if different mutations of the NF1 gene affect the prevalence of these abnormalities. Retrospectively, 275 patients with NF1 and an age- and sex-matched collective of 262 patients were analyzed. The prevalence of spinal abnormalities was recorded. Mutational analysis of the NF1 gene was obtained in 235 NF1 patients. Associations between spinal abnormalities, clinical symptoms and genotype were investigated by binary logistic regression analysis. Prevalence of all spinal abnormalities was higher in NF1 patients than in the control group. Six characteristics of spinal abnormalities were significantly associated with NF1 (all p < 0.05). An influence of scalloping on scoliosis (OR 3.01; p = 0.002); of meningoceles (OR 7.63) and neuroforaminal tumors (OR 2.96) on scalloping, and of dural ectasia on neuroforaminal tumors (OR 1.93) was identified. Backpain and loss of motor function were associated with neuroforaminal tumors, spinal tumors and scalloping of vertebral bodies (all p < 0.05). Specific mutations of the NF1 gene were not relevantly associated with the development of spinal abnormalities. These findings can aid clinicians to improve clinical care of NF1 patients by creating awareness for co-appearences of specific spinal abnormalities and associated symptoms.

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.

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.

The Neurofibromatoses

BACKGROUND

Neurofibromatosis of types 1 and 2 (NF1, NF2) and schwannomatosis are the diseases that make up the neurofibromatosis spectrum. With respective incidences of 1 in 3000, 1 in 33 000, and 1 in 60 000 births, they form part of the group of rare tumor-suppressor syndromes. They give rise to a greater tumor burden for the nervous system than any other type of neoplastic disease. New approaches to symptomatic treatment are emerging.

METHODS

This review is based on articles retrieved by a selective literature search on the pathogenesis, diagnosis, and treatment of the neurofibromatoses.

RESULTS

NF1 and NF2 are monogenic diseases, while the genetics of schwannomatosis is complex. The three entities are clinically and pathophysiologically distinct. An important aspect of their tumor biology is the alternation of growth phases and growth pauses. Correlations between genotypes and phenotypes are variable, while new mutations and genetic mosaics are common. Ninety-nine percent of patients with NF1 have six or more café-au-lait spots by the age of 12 months; 90-95% of patients with NF2 develop bilateral vestibular schwannomas. In schwannomatosis, pain is the most prominent symptom; two-thirds of those affected develop spinal schwannomas. The severity and prognosis of these disorders are not closely correlated with the radiological findings; rather, neurologic deficits, malignant transformation, and psychosocial stress are of greater clinical importance. Advances in knowledge of pathophysiology have led to the development of targeted treatment approaches. Examples include the off-label treatment of vestibular schwannomas with bevacizumab and of plexiform neurofibromas with MEK inhibitors.

CONCLUSION

Patients with neurofibromatoses need individualized care. They should be treated in centers of expertise where interdisciplinary consultation is available and new types of pharmacotherapy can be provided.

Phenotypic heterogeneity of neurofibromatosis type 1 in a large international registry

Neurofibromatosis type 1 (NF1) is a rare genetic disorder, characterized by the development of benign and malignant nerve tumors. Although all individuals with NF1 harbor genetic alterations in the same gene, the clinical manifestations of NF1 are extremely heterogeneous even among individuals who carry identical genetic defects. In order to deepen the understanding of phenotypic manifestations in NF1, we comprehensively characterized the prevalence of 18 phenotypic traits in 2051 adults with NF1 from the Children's Tumor Foundation's NF1 registry. We further investigated the coassociation of traits and found positive correlations between spinal neurofibromas and pain, spinal neurofibromas and scoliosis, spinal neurofibromas and optic gliomas, and optic gliomas and sphenoid wing dysplasia. Furthermore, with increasing numbers of cutaneous neurofibromas, the odds ratio of malignant peripheral nerve sheath tumor increased. Phenotypic clustering revealed 6 phenotypic patient cluster subtypes: mild, freckling predominant, neurofibroma predominant, skeletal predominant, late-onset neural severe, and early-onset neural severe, highlighting potential phenotypic subtypes within NF1. Together, our results support potential shared molecular pathogenesis for certain clinical manifestations and illustrate the utility of disease registries for understanding rare diseases.

Phakomatoses

Phakomatoses present with characteristic findings on the skin, central or peripheral nervous system, and tumors. Neurofibromatosis type 1 is the most common syndrome and is characterized by Café-au-lait macules, intertriginous freckling, Lisch nodules, and tumors including neurofibromas, malignant peripheral nerve sheath tumors, and gliomas. Tuberous Sclerosis Complex is characterized by benign hamartomas presenting with hypomelanotic macules, shagreen patches, angiofibromas, confetti lesions and tumors including cortical tubers, subependymal nodules, subependymal giant cell astrocytomas and tumors of the kidney, lung, and heart. Managing these disorders requires disease specific supportive care, tumor monitoring, surveillance for selected cancers, and treatment of comorbid conditions.

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.

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.

Neurofibromin haploinsufficiency results in altered spermatogenesis in a mouse model of neurofibromatosis type 1

The fertility of men with neurofibromatosis 1 (NF1) is reduced. Despite this observation, gonadal function has not been examined in patients with NF1. In order to assess the role of reduced neurofibromin in the testes, we examined testicular morphology and function in an Nf1+/- mouse model. We found that although Nf1+/- male mice are able to reproduce, they have significantly fewer pups per litter than Nf1+/+ control males. Reduced fertility in Nf1+/- male mice is associated with disorganization of the seminiferous epithelium, with exfoliation of germ cells and immature spermatids into the tubule lumen. Morphometric analysis shows that these alterations are associated with decreased Leydig cell numbers and increased spermatid cell numbers. We hypothesized that hyper-activation of Ras in Nf1+/- males affects ectoplasmic specialization, a Sertoli-spermatid adherens junction involved in spermiation. Consistent with this idea, we found increased expression of phosphorylated ERK, a downstream effector of Ras that has been shown to alter ectoplasmic specialization, in Nf1+/- males in comparison to control Nf1+/+ littermates. These data demonstrate that neurofibromin haploinsufficiency impairs spermatogenesis and fertility in a mouse model of NF1.

Neurocutaneous Disorders

PURPOSE OF REVIEW

This article presents an up-to-date summary of the genetic etiology, diagnostic criteria, clinical features, and current management recommendations for the most common neurocutaneous disorders encountered in clinical adult and pediatric neurology practices.

RECENT FINDINGS

The phakomatoses are a phenotypically and genetically diverse group of multisystem disorders that primarily affect the skin and central nervous system. A greater understanding of the genetic and biological underpinnings of numerous neurocutaneous disorders has led to better clinical characterization, more refined diagnostic criteria, and improved treatments in neurofibromatosis type 1, Legius syndrome, neurofibromatosis type 2, Noonan syndrome with multiple lentigines, tuberous sclerosis complex, Sturge-Weber syndrome, and incontinentia pigmenti.

SUMMARY

Neurologists require a basic knowledge of and familiarity with a wide variety of neurocutaneous disorders because of the frequent involvement of the central and peripheral nervous systems. A simple routine skin examination can often open a broad differential diagnosis and lead to improved patient care.

Efficacy of denosumab therapy for neurofibromatosis type 1 with osteoporosis and history of fractures: a case report

Background

The natural history and pathogenesis of the skeletal abnormalities found in neurofibromatosis type 1 (NF1) are poorly understood, and the therapeutic options for these manifestations remain limited. This report first describes the clinical outcomes of denosumab treatment for a patient with NF1 suffering from osteoporosis.

Methods

We enrolled a patient with NF1 under denosumab treatment for osteoporosis, prior fractures, and no improvement in bone mineral density (BMD) over 3 years of alendronate therapy. BMD was monitored by dual-energy X-ray absorptiometry. Tested laboratory data included bone-specific alkaline phosphatase, urinary type I collagen amino-terminal telopeptide, tartrate-resistant acid phosphatase 5b, 1-alpha, 25-dihydroxyvitamin D₃, and parathyroid hormone. BMD and laboratory data were evaluated before, between 2 and 4 months, and at 6, 12, 18, and 24 months of treatment.

Case presentation

During 2 years of denosumab therapy for osteoporosis in a 58-year-old female NF1 patient with prior fractures, BMD increased by 6.5% in the lumbar spine and 10.6% in the total hips, and bone turnover markers were notably improved. No fractures occurred during the latter half of treatment.

Conclusion

Denosumab represents an effective treatment option for osteoporosis in NF1 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.

Neurofibromatosis: A Review of NF1, NF2, and Schwannomatosis

The neurofibromatoses are a heterogeneous group of hereditary cancer syndromes that lead to tumors of the central and peripheral nervous systems, as well as other organ systems. By far the most common form is neurofibromatosis 1 (96%), followed by neurofibromatosis 2 (3%), and a more recently recognized, lesser known form, schwannomatosis. The diagnostic criteria, pathogenesis, molecular considerations, and clinical manifestations are discussed in this review article.

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.

Risedronate therapy for neurofibromatosis Type 1-related low bone mass: a stitch in time saves nine

Neurofibromatosis Type 1 (NF1) is a common hereditary disease characterized by disorders regarding the skin, neural, and skeletal systems. Osteoporosis is one of the skeletal manifestations of NF1, which is associated with increased fracture risk. The management of NF1-related low bone mass has been less studied in the literature. We present a 19-year-old patient with severe low bone mass complicating NF1. The patient received 1-year course of 35 mg risedronate sodium once per week along with a daily regimen of 1200 mg calcium and 800 IU vitamin D. Significant improvement with regard to the Z-scores and bone mineral density values was achieved. Besides, rapid favourable biochemical response was obtained. The patient experienced 24·4 and 15·0% improvements in bone mineral density at the lumbar site and hip, respectively, at the first year of therapy. No adverse effect was observed. Since increased bone turnover is the primary contributor of osteoporosis in NF1, antiresorptive agents such as bisphosphonates can be considered for treatment. Despite the lack of consensus on the treatment of osteoporosis in NF1, risedronate may hold a promise as a potential therapy for osteoporosis complicating NF1. This is the first report of risedronate therapy in a case with NF1-associated low bone mass in the literature.

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).

Neurofibromatosis type 1: a multidisciplinary approach to care

Neurofibromatosis type 1 is a relatively common inherited disorder. Patients have a high predisposition to develop both benign and malignant tumours. Although many manifestations of neurofibromatosis type 1 affect the nervous system, other organs and tissues can also be affected. Because of the varying features and clinical heterogeneity inherent to this disorder, patients can present to different medical and surgical specialists and, therefore, the association of clinical symptoms with neurofibromatosis type 1 might not be appreciated. Thus, for prompt diagnosis and to provide optimum care for patients with neurofibromatosis type 1, clinicians must be aware of the diverse clinical features of this disorder. We advocate a multidisciplinary approach to care, entailing a dedicated team of specialists throughout the lifetime of the patient. As our understanding of this disorder deepens through basic laboratory and clinical investigations, swift implementation of new effective treatments becomes feasible.

Follow-up of six patients with neurofibromatosis 1-related osteoporosis treated with alendronate for 23 months

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

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.

Decreased bone mineral density in Costello syndrome

INTRODUCTION

Costello syndrome (CS) is a multisystemic disorder characterized by postnatal reduced growth, facial dysmorphism, cardiac defects, cognitive impairment, skin and musculo-skeletal anomalies, and predisposition to certain cancers. CS is caused by activating germline mutations in the HRAS proto-oncogene. Similar to what is observed in other RASopathies, CS causative HRAS mutations promote enhanced signal flow through the RAF-MEK-ERK and PI3K-AKT signaling cascades. While decreased bone mineralization has been documented in other RASopathies, such as neurofibromatosis type 1 and Noonan syndrome, systematic studies investigating bone mineral density (BMD) are lacking in CS.

MATERIALS AND METHODS

Dual-energy X-ray absorptiometry (DXA) was utilized to assess BMD and body composition (fat and fat-free mass) in a cohort of subjects with molecularly confirmed diagnosis of CS (n = 9) and age-matched control individuals (n = 29). Using general linear regression, subtotal body (total body less head), lumbar, femoral neck and femur BMD parameters were compared considering age, sex, body mass index (BMI) and Tanner stage. Blood and urine biomarkers of bone metabolism were also assessed.

RESULTS

All individuals with CS showed significantly lower mean values of subtotal, lumbar and femoral neck BMD compared to the control group (p ≤ 0.01). Similarly, mean total body mass and fat-free mass parameters were lower among the CS patients than in controls (p < 0.01). Low 25-OH vitamin D concentration was documented in all individuals with CS, with values below the reference range in two patients. No significant correlation between vitamin D levels and BMD parameters was observed.

DISCUSSION

CS belongs to a family of developmental disorders, the RASopathies, that share skeletal defects as a common feature. The present data provide evidence that, similar to what is recently seen in NF1 and NS, bone homeostasis is impaired in CS. The significant decrease in BMD and low levels of vitamin D documented in the present cohort, along with the risk for pathologic fractures reported in adult individuals with CS, testifies the requirement for a preventive treatment to alleviate evolutive complications resulting from dysregulated bone metabolism.

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.

Neurofibromatosis and fibrous dysplasia manifesting in the same patient: a rare case report

Neurofibromatosis and fibrous dysplasia show the presence of café-au-lait spots, bone lesions, and endocrinopathies. There has been speculation whether neurofibromatosis and fibrous dysplasia are different manifestations of the same disease or if these conditions are in some way related. We provide a case of whether neurofibromatosis and fibrous dysplasia complicated by hyperparathyroidism and osteoporosis.

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.

Calvarial defects and skeletal dysplasia in patients with neurofibromatosis Type 1

OBJECT

Skull defects, including sphenoid dysplasia and calvarial defects, are rare but distinct findings in patients with neurofibromatosis Type 1 (NF1). The underlying pathophysiology is unclear. The goal of this study was to identify the clinical characteristics and natural history of skull defects in patients with NF1.

METHODS

An electronic search engine of medical records was used to identify patients with NF1 and bony skull anomalies. All clinical, radiographic, pathology, and operative reports were reviewed. The relationship between bony anomalies and significant clinical associations was evaluated. This study received institutional review board approval.

RESULTS

Twenty-one patients were identified. The mean age at NF1 diagnosis was 4.2 years. The mean age at skull defect diagnosis was 8.8 years (9.7 years in the sphenoid wing dysplasia group and 11.9 years in the calvarial defect group). Sphenoid dysplasia was associated with a plexiform neurofibroma or dural ectasia in 73.3% and 80.0% of cases, respectively. Calvarial defects were associated with a plexiform neurofibroma or dural ectasia in 66.7% and 33.3% of patients, respectively. An absence of either an associated neurofibroma or ectasia was not noted in any patient with sphenoid wing dysplasia or 25.0% of those with calvarial defects. In 6 patients, both types of skull defects presented simultaneously. Serial imaging studies were obtained for a mean follow-up time of 7.5 years (range 0.4-20.0 years). Of these patients with serial imaging, radiographic progression was found in 60% of cases of calvarial defects and 56% of cases of sphenoid wing dysplasia. Two patients underwent surgical repair of a skull defect, and both required repeat procedures.

CONCLUSIONS

The majority of skull defects in patients with NF1 were associated with an adjacent structural lesion, such as a plexiform neurofibroma or dural ectasia. This findings from this cohort also support the concept of progression in defect size in more than half of the patients. Potential mechanisms by which these secondary lesions contribute to pathogenesis of the bony defect may include changes in the bony microenvironment. A better understanding of the pathophysiology of skull defects will help guide detection, improve treatment and outcome, and may contribute to the understanding of the pathogenesis of bony lesions in NF1.