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

Neurofibromatosis Type 1: Diagnostic Timelines in Children

BACKGROUND AND OBJECTIVES

The neurofibromatosis 1 (NF1) diagnosis is challenging in young children without a family history of NF1. The aims of this study were to estimate diagnostic delays in children without a family history of NF1 and to examine the effects of using café au lait macules and skin fold freckling as a single diagnostic criterion.

PATIENTS AND METHODS

Retrospective, descriptive, observational study of all patients diagnosed with NF1 before the age of 18 years who were seen at our hospital. The medical records of those included were reviewed to identify the date on which the diagnostic criteria of NF1 were objectified. The patients were categorized into 2 groups: those with a known parental history of NF1 and those without. Café au lait macules and skin fold freckling were assessed as a single diagnostic criterion, and genetic evidence was considered to confirm highly suspicious cases.

RESULTS

We studied 108 patients younger than the age of 18 years with a diagnosis of NF1. Mean (SD) age at diagnosis was 3.94 (±3.8) years for the overall group, 1 year for patients with a parental history of NF1, and 4 years and 8 months for those without. Diagnosis was therefore delayed by 3 years and 8 months in patients without a family history.

CONCLUSION

Skin lesions were the first clinical manifestation of NF1 in most patients. We believe that the National Institutes of Health's diagnostic criteria for NF1 should be updated to aid diagnosis in young children.

[Translated article] Neurofibromatosis Type 1: Diagnostic Timelines in Children

BACKGROUND AND OBJECTIVES

Diagnosis of neurofibromatosis 1 (NF1) diagnosis is challenging in young children without a family history of NF1. The aims of this study were to estimate diagnostic delays in children without a family history of NF1 and to examine the effects of considering café-au-lait macules and skinfold freckling as a single diagnostic criterion.

PATIENTS AND METHODS

Retrospective, descriptive, observational study of all patients diagnosed with NF1 before the age of 18 years who were seen at our hospital. The medical records of those included were reviewed to identify the date on which the diagnostic criteria of NF1 were objectified. The patients were categorized into 2 groups: those with a known parental history of NF1 and those without. Café-au-lait macules and skinfold freckling were assessed as a single diagnostic criterion, and genetic evidence was considered to confirm highly suspicious cases.

RESULTS

We studied 108 patients younger than the age of 18 years with a diagnosis of NF1. Mean (SD) age at diagnosis was 3.94 (±3.8) years for the overall group, 1 year for patients with a parental history of NF1, and 4 years and 8 months for those without. Diagnosis was therefore delayed by 3 years and 8 months in patients without a family history.

CONCLUSION

Skin lesions were the first clinical manifestation of NF1 in most patients. We believe that the National Institutes of Health's diagnostic criteria for NF1 should be updated to aid diagnosis in young children.

Anterolateral Tibial Bowing and Congenital Pseudoarthrosis of the Tibia: Current Concept Review and Future Directions

PURPOSE OF REVIEW

Congenital pseudarthrosis of the tibia (CPT) is a rare condition closely associated with neurofibromatosis type I. Affected children are born with anterolateral bowing of the tibia which progresses to pathologic fracture, pseudarthrosis, and high risk of refracture even after initial union has been attained. There is currently no consensus on the classification of this disease or consensus on its treatment. The purpose of this review is to (1) review the clinical presentation, etiology, epidemiology, classification, and natural history of congenital pseudarthrosis of the tibia and (2) review the existing trends in treatment of congenital pseudarthrosis of the tibia and its associated complications.

RECENT FINDINGS

Current treatment protocols focus primarily on combining intramedullary fixation with external or internal fixation to achieve union rates between 74 and 100%. Intramedullary devices should be retained as long as possible to prevent refracture. Cross-union techniques, though technically difficult, have a reported union rate of 100% and no refractures at mid- to long-term follow-up. Vascularized fibular grafting and induced membrane technique can be successful, but at the cost of numerous surgical procedures. Growth modulation is a promising new approach to preventing fracture altogether, though further study with larger patient series is necessary. The primary consideration in treatment of CPT is expected union rate and refracture risk. Combined intramedullary and external or internal fixation, especially with cross-union techniques, show most promise. Perhaps most exciting is further research on preventing fracture through guided growth, which may reduce the morbidity of multiple surgical procedures which have been the mainstay of treatment for CPT thus far.

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.

Identifying Bone Matrix Impairments in a Mouse Model of Neurofibromatosis Type 1 (NF1) by Clinically Translatable Techniques

Three-to-four percent of children with neurofibromatosis type 1 (NF1) present with unilateral tibia bowing, fracture, and recalcitrant healing. Alkaline phosphatase (ALP) enzyme therapy prevented poor bone mineralization and poor mechanical properties in mouse models of NF1 skeletal dysplasia; but transition to clinical trials is hampered by the lack of a technique that (i) identifies NF1 patients at risk of tibia bowing and fracture making them eligible for trial enrollment and (ii) monitors treatment effects on matrix characteristics related to bone strength. Therefore, we assessed the ability of matrix-sensitive techniques to provide characteristics that differentiate between cortical bone from mice characterized by postnatal loss of Nf1 in Osx-cre^Tet-Off ;Nf1^flox/flox osteoprogenitors (cKO) and from wild-type (WT) mice. Following euthanasia at two time points of bone disease progression, femur and tibia were harvested from both genotypes (n ≥ 8/age/sex/genotype). A reduction in the mid-diaphysis ultimate force during three-point bending at 20 weeks confirmed deleterious changes in bone induced by Nf1 deficiency, regardless of sex. Pooling females and males, low bound water (BW), and low cortical volumetric bone mineral density (Ct.vBMD) were the most accurate outcomes in distinguishing cKO from WT femurs with accuracy improving with age. Ct.vBMD and the average unloading slope (Avg-US) from cyclic reference point indentation tests were the most sensitive in differentiating WT from cKO tibias. Mineral-to-matrix ratio and carbonate substitution from Raman spectroscopy were not good classifiers. However, when combined with Ct.vBMD and BW (femur), they helped predict bending strength. Nf1 deficiency in osteoprogenitors negatively affected bone microstructure and matrix quality with deficits in properties becoming more pronounced with duration of Nf1 deficiency. Clinically measurable without ionizing radiation, BW and Avg-US are sensitive to deleterious changes in bone matrix in a preclinical model of NF1 bone dysplasia and require further clinical investigation as potential indicators of an onset of bone weakness in children with NF1. © 2022 American Society for Bone and Mineral Research (ASBMR).

The Number of Surgical Interventions and Specialists Involved in the Management of Patients with Neurofibromatosis Type I: A 25-Year Analysis

Objective: In this study, we aim to present a single institution’s 25-year experience of employing a comprehensive multidisciplinary team-based surgical approach for treating patients with NF-1. Summary Background Data: All patients (n = 106) with a confirmed diagnosis of NF-1 who were treated using a multidisciplinary surgical treatment algorithm at Chang Gung Memorial Hospital between 1994 and 2019 were retrospectively enrolled. Patients were categorized into groups according to the anatomy involved (craniofacial and noncraniofacial groups) and the type of clinical presentation (plexiform and cutaneous neurofibromas groups) for comparative analysis. Methods: The number of surgical interventions and number of specialists involved in surgical care were assessed. Results: Most of the patients exhibited craniofacial involvement (69.8%) and a plexiform type of NF-1 (58.5%), as confirmed through histology. A total of 332 surgical interventions (3.1 ± 3.1 procedures per patient) were performed. The number of specialists involved in surgical care of the included patients was 11 (1.6 ± 0.8 specialists per patient). Most of the patients (62.3%) underwent two or more surgical interventions, and 40.6% of the patients received treatment from two or more specialists. No significant differences were observed between the craniofacial and noncraniofacial groups in terms of the average number of surgical interventions (3.3 ± 3.2 vs. 2.7 ± 2.7, respectively) and number of specialists involved (1.7 ± 0.9 vs. 1.4 ± 0.6). Patients with plexiform craniofacial involvement underwent a significantly higher average number of surgical interventions (4.3 ± 3.6 vs. 1.6 ± 1.1; p < 0.001) and received treatment by more specialists (1.9 ± 0.9 vs. 1.2 ± 0.5; p < 0.001) compared with those having cutaneous craniofacial involvement. Conclusions: In light of the potential benefits of employing the multidisciplinary team-based surgical approach demonstrated in this study, such an approach should be adopted to provide comprehensive individualized care to patients with NF-1.

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.

MEK inhibitors - novel targeted therapies of neurofibromatosis associated benign and malignant lesions

MAP/ERK kinase 1 and 2 (MEK 1/2) inhibitors (MEKi) are investigated in several trials to treat lesions that arise from pathogenic variants of the Neurofibromatosis type 1 and type 2 genes (NF1, NF2). These trials showed that MEKi are capable to shrink volume of low grade gliomas and plexiform neurofibromas in NF1. Targeting other lesions being associated with a high morbidity in NF1 seems to be promising. Due to involvement of multiple pathways in NF2 associated lesions as well as in malignant tumors, MEKi are also used in combination therapies. This review outlines the current state of MEKi application in neurofibromatosis and associated benign and malignant lesions.

Congenital Forearm Pseudarthrosis, a Systematic Review for a Treatment Algorithm on a Rare Condition

BACKGROUND

A congenital forearm pseudarthrosis is a rare condition and is strongly associated with neurofibromatosis type 1. Several surgical techniques are described in the literature, but the most optimal treatment strategy remains unclear. This systematic review aims to develop a treatment algorithm that may aid in clinical decision making.

METHODS

The PROSPERO registration number for this study was CRD42018099602 and adheres to the PRISMA guidelines for systematic reviews. Embase, MEDLINE, Cochrane Central, Web of Science, and Google Scholar databases were searched for published studies reporting on congenital forearm pseudarthrosis not related to other underlying pathologies like bacterial infection or fibrous dysplasia. Results were not restricted by date or study type, only English literature was allowed. Studies were assessed for quality using the critical appraisal checklist for case reports from the Joanna Briggs Institute. Patient characteristics, underlying disease, type of surgery, union rate, and functional outcome were extracted from included studies.

RESULTS

Of 829 studies identified, 47 were included in this review (17 case series and 30 case reports, a total of 84 cases). A one-bone forearm procedure showed highest union rates (92%), however, it results in loss of forearm rotation. Free vascularized fibula grafting showed high union rates (87%) and was related to good functional outcome of elbow flexion and forearm rotations. Other procedures showed disappointing outcomes.

CONCLUSIONS

Congenital forearm pseudarthrosis is best treated with a free vascularized fibula grafting, a one-bone forearm procedure should be used as a salvage procedure. Evidence extracted from the case reports was sufficient to generate a treatment algorithm to be used in clinical pediatric practice.

LEVEL OF EVIDENCE

Level IV-therapeutic.

The Diagnosis and Management of Neurofibromatosis Type 1

Neurofibromatosis type 1 (NF1), NF2, and schwannomatosis are related, but distinct, tumor suppressor syndromes characterized by a predilection for tumors in the central and peripheral nervous systems. NF1 is one of the most common autosomal dominant conditions of the nervous system. NF1 has a high degree of variability in clinical presentation, which may include multiple neoplasms as well as cutaneous, vascular, bony, and cognitive features. Some of these manifestations overlap with other genetic conditions. Accurate diagnosis of NF1 is important for individualizing clinical care and genetic counseling. This article summarizes the clinical features, diagnostic work-up, and management of NF1.

Dysfunctional coping is related to impaired skin-related quality of life and psychological distress in patients with neurofibromatosis type 1 with major skin involvement

BACKGROUND

Low skin-related quality of life (QoL) is usually associated with low levels of self-confidence and self-esteem and with high levels of anxiety and depression symptoms. The way patients cope with a physical disease impacts significantly on their psychosocial adjustment to the disorder and on their emotional functioning.

OBJECTIVES

To explore how coping strategies, skin-related QoL, psychological distress and self-esteem interact in a sample of individuals with neurofibromatosis type 1 (NF1).

METHODS

Seventy-two adult patients with NF1 completed the following questionnaires: Coping Orientation to Problem Experiences (COPE), Skindex-29, Padua Skin-Related QoL questionnaire (PSRQ), State-Trait Anxiety Inventory-X2 form (STAI-X2), Depression Questionnaire (DQ) and Rosenberg Self-Esteem Scale (RSES). The k-modes algorithm was used to identify clusters of patients based on four variables: sex, NF1 severity, number and distribution of cutaneous neurofibromas. Individuals in different clusters were compared with regard to their scores; correlations between scores were analysed within each cluster.

RESULTS

Two main clusters were identified: individuals in Cluster 1 had a larger number and more widespread distribution of neurofibromas compared with Cluster 2. Patients in Cluster 1 scored higher only on several PSRQ and Skindex-29 scales. Among patients in Cluster 1, the COPE 'avoidance strategies' scale was significantly correlated with the PSRQ 'physical distress and impairments' scale, the Skindex-29 'physical symptoms' and 'functioning' scales, the STAI-X2, the DQ and the RSES.

CONCLUSIONS

Patients with major skin involvement have reduced skin-related QoL. Among them, current findings tentatively suggest that the higher the use of dysfunctional coping, the more impaired are QoL, psychological distress and self-esteem. What's already known about this topic? Neurofibromatosis type 1 (NF1) can affect the quality of life (QoL) in adolescent and adult patients. Low skin-related QoL is usually associated with low levels of self-confidence and self-esteem and with high levels of anxiety and depression symptoms. Questionnaires evaluating skin-related QoL, anxiety, depression, self-esteem and coping are available. What does this study add? Patients with a large number and a widespread distribution of cutaneous neurofibromas have reduced skin-related QoL compared with patients with minor skin involvement. The newly developed Padua Skin-Related QoL questionnaire allows the simultaneous evaluation of discomfort and comfort skin-related QoL dimensions in patients with NF1. Among patients with major skin involvement, the higher the use of dysfunctional coping, the more impaired are skin-related QoL, psychological distress and self-esteem. Our data suggest that patients with NF1 with major skin involvement who endorse dysfunctional beliefs about their own coping abilities might benefit from psychological counselling and coping skills treatments aiming to both improve perceived self-efficacy and learn more adaptive coping strategies.

Identification and characterization of NF1 and non-NF1 congenital pseudarthrosis of the tibia based on germline NF1 variants: genetic and clinical analysis of 75 patients

Background

Congenital pseudarthrosis of the tibia (CPT) is a rare disease. Some patients present neurofibromatosis type 1 (NF1), while some others do not manifest NF1 (non-NF1). The etiology of CPT, particularly non-NF1 CPT, is not well understood. Here we screened germline variants of 75 CPT cases, including 55 NF1 and 20 non-NF1. Clinical data were classified and analyzed based on NF1 gene variations to investigate the genotype-phenotype relations of the two types of patients.

Results

Using whole-exome sequencing and Multiplex Ligation-Dependent Probe Amplification, 44 out of 55 NF1 CPT patients (80.0%) were identified as carrying pathogenic variants of the NF1 gene. Twenty-five variants were novel; 53.5% of variants were de novo, and a higher proportion of their carriers presented bone fractures compared to inherited variant carriers. No NF1 pathogenic variants were found in all 20 non-NF1 patients. Clinical features comparing NF1 CPT to non-NF1 CPT did not show significant differences in bowing or fracture onset, lateralization, tissue pathogenical results, abnormality of the proximal tibial epiphysis, and follow-up tibial union after surgery. A considerably higher proportion of non-NF1 patients have cystic lesion (Crawford type III) and used braces after surgery.

Conclusions

We analyzed a large cohort of non-NF1 and NF1 CPT patients and provided a new perspective for genotype-phenotype features related to germline NF1 variants. Non-NF1 CPT in general had similar clinical features of the tibia as NF1 CPT. Germline NF1 pathogenic variants could differentiate NF1 from non-NF1 CPT but could not explain the CPT heterogeneity of NF1 patients. Our results suggested that non-NF1 CPT was probably not caused by germline NF1 pathogenic variants. In addition to NF1, other genetic variants could also contribute to CPT pathogenesis. Our findings would facilitate the interpretation of NF1 pathogenic variants in CPT genetic counseling.

Supplementary information

The online version of this article (10.1186/s13023-019-1196-0) contains supplementary material, which is available to authorized users.

Management of Congenital Pseudoarthrosis of the Tibia and Fibula

PURPOSE OF REVIEW

Congenital pseudoarthrosis of the tibia and fibula are rare conditions that share common treatment strategies. The purpose of this review is to provide an overview of the recent developments in treatments for both conditions.

RECENT FINDINGS

Recent literature has focused on the use of BMP and on gait analysis as a tool for measuring long-term functional outcomes. Recent study has indicated rhBMP-2 may shorten the time to initial healing of pseudoarthroses, but not guarantee bony union. Children with initial fractures before the age of four have been shown to have long-term gait outcomes that may be ultimately comparable to children with prostheses. Both congenital pseudoarthrosis of the tibia and fibula are challenging conditions to treat, which require comprehensive approaches to account for both the biological and mechanical components of the conditions.

Neurofibromatosis type 1-related pseudarthrosis: Beyond the pseudarthrosis site

Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder affecting approximately 1 in 2,000 newborns. Up to 5% of NF1 patients suffer from pseudarthrosis of a long bone (NF1-PA). Current treatments are often unsatisfactory, potentially leading to amputation. To gain more insight into the pathogenesis we cultured cells from PA tissue and normal-appearing periosteum of the affected bone for NF1 mutation analysis. PA cells were available from 13 individuals with NF1. Biallelic NF1 inactivation was identified in all investigated PA cells obtained during the first surgery. Three of five cases sampled during a later intervention showed biallelic NF1 inactivation. Also, in three individuals, we examined periosteum-derived cells from normal-appearing periosteum proximal and distal to the PA. We identified the same biallelic NF1 inactivation in the periosteal cells outside the PA region. These results indicate that NF1 inactivation is required but not sufficient for the development of NF1-PA. We observed that late-onset NF1-PA occurs and is not always preceded by congenital bowing. Furthermore, the failure to identify biallelic inactivation in two of five later interventions and one reintervention with a known somatic mutation indicates that NF1-PA can persist after the removal of most NF1 negative cells.

Current treatment of congenital pseudarthrosis of the tibia: a systematic review and meta-analysis

To compare the current treatments for congenital pseudarthrosis of tibia, a total of 33 studies were reviewed. Vascularized fibular graft with external fixation or combined fixation had the fastest time till initial union (P<0.05). Bone morphogenetic protein had no advantage in terms of initial union, time till union, and refracture rates. This meta-analysis supports that fixation methods with corticocancellous bone autograft utilizing the combined technique of Ilizarov external fixation and intramedullary rod stabilization ensure a statistically significant reduction in the number of refractures compared with standalone fixation methods and would be the preferred method for preventing long-term complications in patients with congenital pseudarthrosis of tibia.

A 15-Month-Old Girl Presenting With Clitoromegaly and a Chest Mass

A 15-month-old girl was initially referred for endocrine evaluation for clitoromegaly and subsequently found to have an adrenal mass that tracked along the paravertebral region and was associated with increased vascular markings along the skin. Neurologic examination was normal. Magnetic resonance imaging of the chest mass demonstrated a serpiginous lesion along the intercostal margins. Initial differential diagnosis included neuroblastoma, ganglioneuroblastoma, vascular lesion, or nerve sheath tumor. Biopsy was consistent with plexiform neurofibroma. Subsequent examination revealed features consistent with neurofibromatosis type 1. A review of clinical features of NF1 is provided in the case report.

Quantitative Ultrasound and Tibial Dysplasia in Neurofibromatosis Type 1

Neurofibromatosis type 1 (NF1) is a common autosomal dominant disorder associated with unilateral anterolateral bowing with subsequent fracture and nonunion. In infancy, physiologic bowing of the lower leg can be confused with pathologic tibial dysplasia in NF1. Little is known about the bone physiology of the tibiae prior to fracture or predictors of fracture. The aim of this study was to characterize bone quality of bowed tibiae prior to fracture in NF1 using quantitative ultrasound (QUS). Bone quality was assessed on both tibiae (the non-bowed and bowed tibiae) using QUS to measure speed of sound (SOS) at the mid-shaft in 23 individuals with NF1. SOS (m/s) was determined and Z-scores generated using cross-sectional reference data of the same sex and age. The mean difference in SOS Z-scores when comparing the bowed tibia vs the individual's contralateral unaffected tibia was statistically significant with lower mean Z-scores in the bowed tibia (p = 0.001). Radiographs of all individuals with a clinical diagnosis of anterolateral bowing were reviewed, and in 2 individuals the radiographs showed minimal bowing with absence of characteristic cortical thickening and medullary canal narrowing in NF1-related tibial dysplasia, suggesting physiologic bowing. In both individuals, the Z-scores of the bowed leg were not lower than the unaffected leg supporting the suggestion of physiologic bowing rather than pathologic tibial dysplasia. These data show that dysplastic tibiae in NF1 prior to fracture and nonunion have abnormal bone quality with significant decreases in SOS even though radiographically the tibiae show a thickened cortex. These data also suggest that QUS can help distinguish dysplastic bowing vs physiologic bowing in infancy in NF1. QUS is an effective quantitative outcome measure for trials aimed at improving tibial bowing to prevent fracture, and it is a potential aid in diagnosis and clinical management in NF1.

rhBMP-2 and Intramedullary Fixation in Congenital Pseudarthrosis of the Tibia

BACKGROUND

In congenital pseudarthrosis of the tibia, use of intramedullary (IM) fixation and autogenous bone graft has long been the standard of care. This study was undertaken to determine whether the addition of rhBMP-2 to this treatment method further enhances healing potential.

METHODS

Twenty-one patients with congenital pseudarthrosis of the tibia were evaluated. Fifteen of these patients had neurofibromatosis type 1 (NF1). All had IM fixation and autogenous bone graft, followed by a BMP-soaked collagen sponge wrapped around both the fracture site and bone graft. A minimum 2 years' follow-up was required.

RESULTS

Follow-up averaged 7.2 years (range, 2.1 to 12.8 y). Sixteen of 21 tibias achieved bone union following the index surgery, at an average 6.6 months postoperatively. The 5 persistent nonunions occurred in NF1 patients. Further surgery was undertaken in these 5 NF1 patients, including the use of BMP. One of the 5 healed, 1 had persistent nonunion, and 3 eventually had amputation. Of the 16 patients who healed initially following the index surgery, 5 refractured (3 had NF1). Of these 5 patients, the IM fixation at the index surgery did not cross the ankle joint, and refracture occurred at the rod tip in 4. Three of these 5 patients healed following further surgery, 1 had persistent nonunion, and 1 had amputation. All of those with eventual amputation had NF1. No deleterious effects related to the use of BMP-2 were recognized in any patient.

CONCLUSIONS

The addition of rhBMP-2 appears to be helpful in shortening the time required to achieve fracture union in those who healed, but its use does not insure that healing will occur.

LEVEL OF EVIDENCE

Level IV-therapeutic, case series.

Neurofibromatosis type I and multiple myeloma coexistence: A possible link?

The association between Neurofibromatosis type I (NF1) and multiple myeloma (MM), a plasma cell, dyscrasia is very rare. Here we put to the attention of the scientific community two new cases. The first one is a patient with active MM whereas the second with smoldering MM. Both patients present typical features of NF1 but skeletal alterations were present only in the second case including dysplasia, marked scoliosis and osteoporosis. MM osteolytic lesions were absent in both patients. In addition to the clinical diagnosis of NF1, a molecular testing for NF1 gene mutations has been performed finding that patient one was heterozygous for the c.6855C>A (Tyr2285Ter) mutation, while patient two was heterozygous for the c.7838dupC (Lys2614GlufsTer20) mutation. The two mutations were diagnosed both in genomic DNA from peripheral blood and from MM cells. The potential link between NF1 mutation and the increased risk of MM is discussed in the report.

Improved union and bone strength in a mouse model of NF1 pseudarthrosis treated with recombinant human bone morphogenetic protein-2 and zoledronic acid

Tibial pseudarthrosis associated with Neurofibromatosis type 1 (NF1) is an orthopedic condition with consistently poor clinical outcomes. Using a murine model that features localized double inactivation of the Nf1 gene in an experimental tibial fracture, we tested the effects of recombinant human bone morphogenetic protein-2 (rhBMP-2) and/or the bisphosphonate zoledronic acid (ZA). Tibiae were harvested at 3 weeks for analysis, at which time there was negligible healing in un-treated control fractures (7% union). In contrast, rhBMP-2 and rhBMP-2/ZA groups showed significantly greater union (87% and 93%, p < 0.01 for both). Treatment with rhBMP-2 led to a 12-fold increase in callus bone volume and this was further increased in the rhBMP-2/ZA group. Mechanical testing of the healed rhBMP-2 and rhBMP-2/ZA fractures showed that the latter group had significantly higher mechanical strength and was restored to that of the un-fractured contralateral leg. Co-treatment with rhBMP-2/ZA also reduced fibrous tissue infiltration at the fracture site compared to rhBMP alone (p = 0.068). These data support the future clinical investigation of this combination of anabolic and anti-resorptive agents for the treatment of NF1 pseudarthrosis. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:930-936, 2018.

The reduced osteogenic potential of Nf1-deficient osteoprogenitors is EGFR-independent

Neurofibromatosis type 1 (NF1) is a common genetic disorder caused by mutations in the NF1 gene. Recalcitrant bone healing following fracture (i.e. pseudarthrosis) is one of the most problematic skeletal complications associated with NF1. The etiology of this condition is still unclear; thus, pharmacological options for clinical management are limited. Multiple studies have shown the reduced osteogenic potential of Nf1-deficient osteoprogenitors. A recent transcriptome profiling investigation revealed that EREG and EGFR, encoding epiregulin and its receptor Epidermal Growth Factor Receptor 1, respectively, were among the top over-expressed genes in cells of the NF1 pseudarthrosis site. Because EGFR stimulation is known to inhibit osteogenic differentiation, we hypothesized that increased EREG and EGFR expression in NF1-deficient skeletal progenitors may contribute to their reduced osteogenic differentiation potential. In this study, we first confirmed via single-cell mRNA sequencing that EREG over-expression was associated with NF1 second hit somatic mutations in human bone cells, whereas Transforming Growth Factor beta 1 (TGFβ1) expression was unchanged. Second, using ex-vivo recombined Nf1-deficient mouse bone marrow stromal cells (mBMSCs), we show that this molecular signature is conserved between mice and humans, and that epiregulin generated by these cells is overexpressed and active, whereas soluble TGFβ1 expression and activity are not affected. However, blocking either epiregulin function or EGFR signaling by EGFR1 or pan EGFR inhibition (using AG-1478 and Poziotinib respectively) did not correct the differentiation defect of Nf1-deficient mBMSCs, as measured by the expression of Alpl, Ibsp and alkaline phosphatase activity. These results suggest that clinically available drugs aimed at inhibiting EGFR signaling are unlikely to have a significant benefit for the management of bone non-union in children with NF1 PA.

Targeted Disruption of NF1 in Osteocytes Increases FGF23 and Osteoid With Osteomalacia-like Bone Phenotype

Neurofibromatosis type 1 (NF1, OMIM 162200), caused by NF1 gene mutations, exhibits multi-system abnormalities, including skeletal deformities in humans. Osteocytes play critical roles in controlling bone modeling and remodeling. However, the role of neurofibromin, the protein product of the NF1 gene, in osteocytes is largely unknown. This study investigated the role of neurofibromin in osteocytes by disrupting Nf1 under the Dmp1-promoter. The conditional knockout (Nf1 cKO) mice displayed serum profile of a metabolic bone disorder with an osteomalacia-like bone phenotype. Serum FGF23 levels were 4 times increased in cKO mice compared with age-matched controls. In addition, calcium-phosphorus metabolism was significantly altered (calcium reduced; phosphorus reduced; parathyroid hormone [PTH] increased; 1,25(OH)₂ D decreased). Bone histomorphometry showed dramatically increased osteoid parameters, including osteoid volume, surface, and thickness. Dynamic bone histomorphometry revealed reduced bone formation rate and mineral apposition rate in the cKO mice. TRAP staining showed a reduced osteoclast number. Micro-CT demonstrated thinner and porous cortical bones in the cKO mice, in which osteocyte dendrites were disorganized as assessed by electron microscopy. Interestingly, the cKO mice exhibited spontaneous fractures in long bones, as found in NF1 patients. Mechanical testing of femora revealed significantly reduced maximum force and stiffness. Immunohistochemistry showed significantly increased FGF23 protein in the cKO bones. Moreover, primary osteocytes from cKO femora showed about eightfold increase in FGF23 mRNA levels compared with control cells. The upregulation of FGF23 was specifically and significantly inhibited by PI3K inhibitor Ly294002, indicating upregulation of FGF23 through PI3K in Nf1-deficient osteocytes. Taken together, these results indicate that Nf1 deficiency in osteocytes dramatically increases FGF23 production and causes a mineralization defect (ie, hyperosteoidosis) via the alteration of calcium-phosphorus metabolism. This study demonstrates critical roles of neurofibromin in osteocytes for osteoid mineralization. © 2017 American Society for Bone and Mineral Research.

Novel phenotypes of NF1 patients from unrelated Chinese families with tibial pseudarthrosis and anemia

Neurofibromatosis type 1 (NF1) is an autosomal dominant, multi-system, neurocutaneous disorder, manifested with neurofibromas and Cafe´-au-lait spots. Germline mutations in NF1 gene are associated with Neurofibromatosis type 1. NF1 gene encodes neurofibromin, a RAS-specific GTPase activating protein. In our study, we present a clinical molecular study of four Chinese probands with NF1 from four unrelated families, showing extreme phenotypic variation with rare phenotype. In family 1, the proband is a 16 months old girl with multiple café-au-lait spots throughout her whole body. In family 2, the proband is a 6 months old girl with several café-au-lait spots mostly in her trunk and in lower limbs. In family 3, the proband is a 4 months old boy with several café-au-lait spots, tibial pseudarthrosis, and chronic iron deficiency anemia. In family 4, the proband is a 14 years old boy with multiple café-au-lait spots of variable sizes. Targeted exome capture based next generation sequencing and Sanger sequencing identified a novel mutation and three previously reported mutations in these four probands. These four mutations in NF1 gene were causing disease phenotypes in these four probands and was absent in unaffected family members and in healthy controls. According to the variant interpretation guideline of American College of Medical Genetics and Genomics (ACMG), these four mutations, are classified as "likely pathogenic". Our result expands the mutational spectrum of the NF1 gene associated with neurofibromatosis type1.

Utilization of Whole-Exome Next-Generation Sequencing Variant Read Frequency for Detection of Lesion-Specific, Somatic Loss of Heterozygosity in a Neurofibromatosis Type 1 Cohort with Tibial Pseudarthrosis

A subset of neurofibromatosis type 1 patients develop tibial dysplasia, which can lead to pseudarthrosis. The tissue from the tibial pseudarthrosis region commonly has a somatic second hit in NF1: single-nucleotide variants, small deletions, or loss of heterozygosity (LOH). We used exome next-generation sequencing (NGS) variant frequency data (allelic imbalance analysis) to detect somatic LOH in pseudarthrosis tissue from three individuals with clinically and diagnostically confirmed neurofibromatosis type 1, and verified the results with microarray. The variant files were parsed and plotted using python scripts, and the NGS variant frequencies between the affected tissue and blood sample were compared. Individuals without somatic single-nucleotide variants or small insertions/deletions were tested for somatic LOH using the NGS variant allele frequencies. One individual's NGS data indicated no LOH in chromosome 17. The other two individuals demonstrated somatic LOH inclusive of NF1: one had an LOH region of approximately one million bases and Contra (NGS copy number program) indicated a somatic deletion and the other individual had LOH for most of chromosome 17q and Contra indicated no copy number change (microarray data verified this sample as copy neutral somatic LOH). Both LOH and copy number variation detected by NGS data correlated with microarray data, demonstrating the somatic LOH second hit can be detected directly from the NGS data.

Sella turcica measurements on lateral cephalograms of patients with neurofibromatosis type 1

The aim of this study was to measure line segments and areas of sella turcica on lateral cephalograms with respect to the clinical diagnosis of facial phenotype of patients with neurofibromatosis type 1 (NF1). Special attention was given to correlate the measured values with certain tumour types that are typical for this disease.

Material and methods: Lateral cephalograms of 194 individuals were investigated. Patients with NF1 were further divided according to the detection and topography of facial plexiform neurofibromas (PNF) taking into account the distribution pattern of the trigeminal nerve. All patients with PNF showed unilateral tumour localisation. Patients without any facial PNF constituted a separate group. Healthy volunteers with ideal occlusion and no history of any intervention in the maxillofacial region served as a control group. The following items were determined on the radiographs: sella entrance, sella width, sella depths, sella diagonal, and sella area.

Results: Patients with PNF of the first and second trigeminal nerve branch or affected in all branches showed highly statistically significant enlarged sella tucica measurement values. On the other hand, patients with PNF restricted to one branch only or simultaneously in the second and third branches showed measurement values that were not different to those obtained in NF1 patients devoid of facial PNF. The latter group also showed no difference of sella turcica parameters obtained in the control group.

Conclusion: This study provides evidence for the association of a certain NF1 phenotype with distinct skeletal alterations of the skull base, shown here using the example of the representation of the sella turcica in the lateral radiograph. These findings are also relevant in the discussion of NF1 as a disease of bones and in the assessment of brain development in NF1. Both items are discussed in relationship to a facial plexiform neurofibroma. Furthermore, the knowledge of this association of findings provides the clinician with relevant information in the planning of skull base procedures in these patients.

Neurofibromatosis type 1

Neurofibromatosis type 1 is a complex autosomal dominant disorder caused by germline mutations in the NF1 tumour suppressor gene. Nearly all individuals with neurofibromatosis type 1 develop pigmentary lesions (café-au-lait macules, skinfold freckling and Lisch nodules) and dermal neurofibromas. Some individuals develop skeletal abnormalities (scoliosis, tibial pseudarthrosis and orbital dysplasia), brain tumours (optic pathway gliomas and glioblastoma), peripheral nerve tumours (spinal neurofibromas, plexiform neurofibromas and malignant peripheral nerve sheath tumours), learning disabilities, attention deficits, and social and behavioural problems, which can negatively affect quality of life. With the identification of NF1 and the generation of accurate preclinical mouse strains that model some of these clinical features, therapies that target the underlying molecular and cellular pathophysiology for neurofibromatosis type 1 are becoming available. Although no single treatment exists, current clinical management strategies include early detection of disease phenotypes (risk assessment) and biologically targeted therapies. Similarly, new medical and behavioural interventions are emerging to improve the quality of life of patients. Although considerable progress has been made in understanding this condition, numerous challenges remain; a collaborative and interdisciplinary approach is required to manage individuals with neurofibromatosis type1 and to develop effective treatments.

Therapeutic advances for the tumors associated with neurofibromatosis type 1, type 2, and schwannomatosis

Neurofibromatosis type 1 (NF1), neurofibromatosis type 2 (NF2), and schwannomatosis (SWN) are tumor-suppressor syndromes. Each syndrome is an orphan disease; however, the tumors that arise within them represent the most common tumors of the nervous system worldwide. Systematic investigation of the pathways impacted by the loss of function of neurofibromin (encoded byNF1) and merlin (encoded byNF2) have led to therapeutic advances for patients with NF1 and NF2. In the syndrome of SWN, the genetic landscape is more complex, with 2 known causative genes (SMARCB1andLZTR1) accounting for up to 50% of familial SWN patients. The understanding of the molecular underpinnings of these syndromes is developing rapidly and offers more therapeutic options for the patients. In addition, common sporadic cancers harbor somatic alterations inNF1(ie, glioblastoma, breast cancer, melanoma),NF2(ie, meningioma, mesothelioma) andSMARCB1(ie, atypical teratoid/rhabdoid tumors) such that advances in management of syndromic tumors may benefit patients both with and without germline mutations. In this review, we discuss the clinical and genetic features of NF1, NF2 and SWN, the therapeutic advances for the tumors that arise within these syndromes and the interaction between these rare tumor syndromes and the common tumors that share these mutations.

Cephalometry in adults and children with neurofibromatosis type 1: Implications for the pathogenesis of sphenoid wing dysplasia and the "NF1 facies"

BACKGROUND

Neurofibromatosis type 1 (NF1) is a common, autosomal dominant tumor-predisposition disorder that arises secondary to mutations in the tumor suppressor gene NF1. Cephalometry is an inexpensive, readily available and non-invasive technique that is under-utilized in studying the NF1 craniofacial phenotype. An analysis of NF1 cephalometry was first published by Heervä et al. in 2011. We expand here on that first investigation with a larger cohort of adult and pediatric patients affected with NF1 and sought objective insight into the NF1 facies, said to feature hypertelorism and a broad nasal base, from cephalometric analysis.

METHODS

We obtained cephalograms from 101 patients with NF1 (78 adults and 23 children) from two NF1 protocols at the National Institutes of Health. Each subject had an age-, gender- and ethnicity-matched control. We used Dolphin software to make the cephalometric measurements. We assessed the normality of differences between paired samples using the Shapiro-Wilk test and evaluated the significance of mean differences using paired t-tests and adjusted for multiple testing. We explored the relationship between the cephalometric measurements and height, head circumference and interpupillary distance.

RESULTS

In this dataset of American whites with NF1, we confirmed in a modestly larger sample many of the findings found by Heerva et al. in an NF1 Finnish cohort. We found a shorter maxilla, mandible, cranial base, (especially anteriorly, p = 0.0001) and diminished facial height in adults, but not children, with NF1. Only one adult exhibited hypertelorism.

CONCLUSIONS

The cephalometric differences in adults arise in part from cranial base shortening and thus result in a shorter face, mid-face hypoplasia, reduced facial projection, smaller jaw, and increased braincase globularity. In addition, we suggest that NF1 sphenoid bone shortening, a common event, is consistent with an intrinsic NF1 bone cell defect, which renders the bone more vulnerable to a random "second hit" in NF1, leading to sphenoid wing dysplasia, a rare event.

FGFR1 signaling in hypertrophic chondrocytes is attenuated by the Ras-GAP neurofibromin during endochondral bone formation

Aberrant fibroblast growth factor receptor 3 (FGFR3) signaling disrupts chondrocyte proliferation and growth plate size and architecture, leading to various chondrodysplasias or bone overgrowth. These observations suggest that the duration, intensity and cellular context of FGFR signaling during growth plate chondrocyte maturation require tight, regulated control for proper bone elongation. However, the machinery fine-tuning FGFR signaling in chondrocytes is incompletely defined. We report here that neurofibromin, a Ras-GAP encoded by Nf1, has an overlapping expression pattern with FGFR1 and FGFR3 in prehypertrophic chondrocytes, and with FGFR1 in hypertrophic chondrocytes during endochondral ossification. Based on previous evidence that neurofibromin inhibits Ras-ERK signaling in chondrocytes and phenotypic analogies between mice with constitutive FGFR1 activation and Nf1 deficiency in Col2a1-positive chondrocytes, we asked whether neurofibromin is required to control FGFR1-Ras-ERK signaling in maturing chondrocytes in vivo. Genetic Nf1 ablation in Fgfr1-deficient chondrocytes reactivated Ras-ERK1/2 signaling in hypertrophic chondrocytes and reversed the expansion of the hypertrophic zone observed in mice lacking Fgfr1 in Col2a1-positive chondrocytes. Histomorphometric and gene expression analyses suggested that neurofibromin, by inhibiting Rankl expression, attenuates pro-osteoclastogenic FGFR1 signaling in hypertrophic chondrocytes. We also provide evidence suggesting that neurofibromin in prehypertrophic chondrocytes, downstream of FGFRs and via an indirect mechanism, is required for normal extension and organization of proliferative columns. Collectively, this study indicates that FGFR signaling provides an important input into the Ras-Raf-MEK-ERK1/2 signaling axis in chondrocytes, and that this input is differentially regulated during chondrocyte maturation by a complex intracellular machinery, of which neurofibromin is a critical component.

Evaluation of somatic mutations in tibial pseudarthrosis samples in neurofibromatosis type 1

BACKGROUND

Tibial pseudarthrosis is associated with neurofibromatosis type 1 (NF1) and there is wide clinical variability of the tibial dysplasia in NF1, suggesting the possibility of genetic modifiers. Double inactivation of NF1 is postulated to be necessary for the development of tibial pseudarthrosis, but tissue or cell of origin of the 'second hit' mutation remains unclear.

METHODS

Exome sequencing of different sections of surgically resected NF1 tibial pseudarthrosis tissue was performed and compared to germline (peripheral blood).

RESULTS

A germline NF1 splice site mutation (c.61-2A>T, p.L21 M68del) was identified from DNA extracted from peripheral blood. Exome sequencing of DNA extracted from tissue removed during surgery of the tibial pseudarthrosis showed a somatic mutation of NF1 (c.3574G>T, p.E1192*) in the normal germline allele. Further analysis of different regions of the tibial pseudarthrosis sample showed enrichment of the somatic mutation in the soft tissue within the pseudarthrosis site and absence of the somatic mutation in cortical bone. In addition, a germline variant in PTPN11 (c.1658C>T, p.T553M), a gene involved in the RAS signal transduction pathway was identified, although the clinical significance is unknown.

CONCLUSIONS

Given that the NF1 somatic mutation was primarily detected in the proliferative soft tissue at the pseudarthrosis site, it is likely that the second hit occurred in mesenchymal progenitors from the periosteum. These results are consistent with a defect of differentiation, which may explain why the mutation is found in proliferative cells and not within cortical bone tissue, as the latter by definition contains mostly mature differentiated osteoblasts and osteocytes.

Combined MEK inhibition and BMP2 treatment promotes osteoblast differentiation and bone healing in Nf1Osx -/- mice

Neurofibromatosis type I (NF1) is an autosomal dominant disease with an incidence of 1/3000, caused by mutations in the NF1 gene, which encodes the RAS/GTPase-activating protein neurofibromin. Non-bone union after fracture (pseudarthrosis) in children with NF1 remains a challenging orthopedic condition to treat. Recent progress in understanding the biology of neurofibromin suggested that NF1 pseudarthrosis stems primarily from defects in the bone mesenchymal lineage and hypersensitivity of hematopoietic cells to TGFβ. However, clinically relevant pharmacological approaches to augment bone union in these patients remain limited. In this study, we report the generation of a novel conditional mutant mouse line used to model NF1 pseudoarthrosis, in which Nf1 can be ablated in an inducible fashion in osteoprogenitors of postnatal mice, thus circumventing the dwarfism associated with previous mouse models where Nf1 is ablated in embryonic mesenchymal cell lineages. An ex vivo-based cell culture approach based on the use of Nf1(flox/flox) bone marrow stromal cells showed that loss of Nf1 impairs osteoprogenitor cell differentiation in a cell-autonomous manner, independent of developmental growth plate-derived or paracrine/hormonal influences. In addition, in vitro gene expression and differentiation assays indicated that chronic ERK activation in Nf1-deficient osteoprogenitors blunts the pro-osteogenic property of BMP2, based on the observation that only combination treatment with BMP2 and MEK inhibition promoted the differentiation of Nf1-deficient osteoprogenitors. The in vivo preclinical relevance of these findings was confirmed by the improved bone healing and callus strength observed in Nf1osx (-/-) mice receiving Trametinib (a MEK inhibitor) and BMP2 released locally at the fracture site via a novel nanoparticle and polyglycidol-based delivery method. Collectively, these results provide novel evidence for a cell-autonomous role of neurofibromin in osteoprogenitor cells and insights about a novel targeted approach for the treatment of NF1 pseudoarthrosis.

Neurofibromin deficiency-associated transcriptional dysregulation suggests a novel therapy for tibial pseudoarthrosis in NF1

Neurofibromatosis type 1 (NF1) is an autosomal dominant disease caused by mutations in NF1. Among the earliest manifestations is tibial pseudoarthrosis and persistent nonunion after fracture. To further understand the pathogenesis of pseudoarthrosis and the underlying bone remodeling defect, pseudoarthrosis tissue and cells cultured from surgically resected pseudoarthrosis tissue from NF1 individuals were analyzed using whole-exome and whole-transcriptome sequencing as well as genomewide microarray analysis. Genomewide analysis identified multiple genetic mechanisms resulting in somatic biallelic NF1 inactivation; no other genes with recurring somatic mutations were identified. Gene expression profiling identified dysregulated pathways associated with neurofibromin deficiency, including phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) signaling pathways. Unlike aggressive NF1-associated malignancies, tibial pseudoarthrosis tissue does not harbor a high frequency of somatic mutations in oncogenes or other tumor-suppressor genes, such as p53. However, gene expression profiling indicates that pseudoarthrosis tissue has a tumor-promoting transcriptional pattern, despite lacking tumorigenic somatic mutations. Significant overexpression of specific cancer-associated genes in pseudoarthrosis highlights a potential for receptor tyrosine kinase inhibitors to target neurofibromin-deficient pseudoarthrosis and promote proper bone remodeling and fracture healing.

Asfotase-α improves bone growth, mineralization and strength in mouse models of neurofibromatosis type-1

Mineralization of the skeleton depends on the balance between levels of pyrophosphate (PPi), an inhibitor of hydroxyapatite formation, and phosphate generated from PPi breakdown by alkaline phosphatase (ALP). We report here that ablation of Nf1, encoding the RAS/GTPase–activating protein neurofibromin, in bone–forming cells leads to supraphysiologic PPi accumulation, caused by a chronic ERK–dependent increase in genes promoting PPi synthesis and extracellular transport, namely Enpp1 and Ank. It also prevents BMP2–induced osteoprogenitor differentiation and, consequently, expression of ALP and PPi breakdown, further contributing to PPi accumulation. The short stature, impaired bone mineralization and strength in mice lacking Nf1 in osteochondroprogenitors or osteoblasts could be corrected by enzyme therapy aimed at reducing PPi concentration. These results establish neurofibromin as an essential regulator of bone mineralization, suggest that altered PPi homeostasis contributes to the skeletal dysplasiae associated with neurofibromatosis type-1 (NF1), and that some of the NF1 skeletal conditions might be preventable pharmacologically.