Towards a neurobiological understanding of pain in neurofibromatosis type 1: mechanisms and implications for treatment

Pain Related Quality of Life in Neurofibromatosis Type 1: A Narrative Review

PURPOSE OF REVIEW

The purpose of this narrative review is to summarize pain symptomatology and mechanisms in neurofibromatosis type 1 (NF1), discuss the pain related quality of life impacts of NF1, and discuss the literature exploring interventions to improve quality of life.

RECENT FINDINGS

Chronic pain in NF1 is described as headache and non-headache pain. The literature describes mechanisms contributing to neuronal hyperexcitability in the setting of reduced neurofibromin as key contributors to pain in NF1. Pain in NF1 negatively impacts quality of life with pain interference, depression, anxiety, and cognitive functioning acting as important mediators. Mitogen-activated protein kinase (MEK) inhibitors are pharmacologic agents that interfere with pain mechanisms. Mind-body interventions improve coping skills to improve quality of life. Chronic pain in NF1 is heterogeneous with negative impacts on quality of life. New developments in pharmacological and non-pharmacological interventions offer promising approaches to pain management and quality of life improvement. Additional research is necessary to validate the use of MEK inhibitors and mind-body interventions in the treatment of NF1.

Quality of Life in Children with Neurofibromatosis Type 1: Agreement between Parents and Patients, and the Role of Disease Severity and Visibility

BACKGROUND

Neurofibromatosis type 1 (NF1) is a genetic disorder that affects multiple systems in the body, often leading to physical disfigurements and a wide range of clinical symptoms. This study aims to investigate the relationship between NF1 severity and visibility and the quality of life (QoL) in children.

METHODS

The Pediatric Quality of Life Inventory (PedsQL) and a modified version of the Ablon scale were used to assess QoL and NF1 severity and visibility, respectively. Self-reported and parent-reported QoL scores were compared, and the associations between NF1 severity/visibility and QoL were explored.

RESULTS

Thirty-eight pediatric NF1 patients and their parents were enrolled. QoL scores did not differ significantly between patient self-reports and parent reports. However, correlational analyses revealed that higher NF1 severity was associated with lower physical QoL in patients, and greater NF1 visibility was linked to lower physical and social QoL. For parents, higher NF1 severity correlated with lower school functioning, whereas NF1 visibility did not show a significant correlation with QoL.

CONCLUSION

The severity and visibility of NF1 have distinct impacts on various aspects of QoL in children, highlighting the need for tailored interventions that address both physical and psychological challenges. These findings underscore the importance of comprehensive care approaches in managing NF1 in pediatric populations.

Association of sociodemographic and clinical factors with the quality of life of Brazilian individuals with Neurofibromatosis type 1: a cross-sectional study

BACKGROUND

Neurofibromatosis type 1 (NF1) is a rare genetic disorder with a wide range of clinical manifestations, notably neurocutaneous features, that can lead to emotional and physical consequences.

OBJECTIVES

This study assessed the influence of sociodemographic factors and clinical features of the disease on the quality of life of Brazilian individuals with NF1.

METHODS

This is a descriptive cross-sectional study. Data were collected from 101 individuals with NF1 using the Brazilian version of the Impact of NF1 on Quality of Life Questionnaire (INF1-QoL), a form with information on sociodemographic characteristics, and an NF1 visibility self-evaluation scale. The relationship between variables was evaluated through statistical testing, and the significance level was defined as 0.05.

RESULTS

The study included 101 adults with NF1 aged 18 to 59 years, with a mean age of 35.54 years (±9.63) and a female predominance (n = 84, 83.17%). The mean total INF1-QoL score was 10.62 (±5.63), with a median of 10, minimum value of 0, and maximum of 31 points. Two characteristics of the participants were significantly associated with the quality of life: educational level (p = 0.003) and familial history of NF1 (p = 0.019). There was a statistically significant correlation between the INF1-QoL score and the degree of disease visibility (rho = 0.218; p = 0.028).

STUDY LIMITATIONS

Cross-sectional study, conducted with a convenience sample and using self-reported measures.

CONCLUSIONS

The findings support the significant impact of NF1 on quality of life. The authors recommend multidisciplinary follow-up for patients, with adherence to anticipatory clinical care measures, adequate pain control, psychological assistance, and genetic counseling.

Understanding chronic pain in Neurofibromatosis Type 1 using the Neurofibromatosis Pain Module (NFPM)

Neurofibromatosis Type 1 (NF1) is an autosomal dominant genetic disorder that can cause an individual significant chronic pain (CP). CP affects quality of life and daily functioning, yet there are limited effective treatments for CP within NF1. The current study describes the impact of CP using the Neurofibromatosis Pain Module (NFPM). The NFPM is a self-reported clinical assessment that evaluates the impact of CP across multiple domains (e.g., interference, severity, tolerance, and symptomology) and three prioritized pain regions. A cross-sectional study (N = 242) asked adults with NF1 to describe and rate their pain using the NFPM. The results indicated that they reported moderate pain severity (M = 6.6, SD = 2.0) on a 0-10 scale, that 54% (n = 131) had been in pain at least 24 days in the last 30, for 75% (n = 181) sleep was affected, and 16% reported that nothing was effective in reducing their CP for their primary pain region. The current results extend previously published work on CP within adults with NF1 and indicate that more emphasis on understanding and ameliorating CP is required. The NFPM is a sensitive clinical measure that provides qualitative and quantitative responses to inform medical providers about changes in CP.

Successful Treatment of Peripheral Nerve Sheath Tumor-related Pain with Perineural Steroid Injection: a case report

Pain associated with Neurofibromatosis Type 1 (NF1) is poorly understood. To date, no treatment options have been approved for NF1-related pain. We present the case of a young female NF1 patient with intermittent buttock pain radiating down the leg who presented with positive dural tension signs. The patient was diagnosed with neurofibroma sciatic nerve compression, which was successfully managed with ultrasound-guided perineural steroid injection. There is sparse literature regarding the efficacy of ultrasound-guided perineural steroid injection in NF1 patients for treatment of benign peripheral nerve sheath tumor compressions. This case describes the utility of perineural steroid injections for symptomatic relief of NF1 neurofibroma-related pain. Perineural steroid injections should be considered when neurofibroma-related pain fails to respond to other conservative treatment. Steroid injections provide an alternative to oral medicinal management and avoid the often morbid risks of surgical intervention.

Schwann cells modulate nociception in neurofibromatosis 1

Pain of unknown etiology is frequent in individuals with the tumor predisposition syndrome neurofibromatosis 1 (NF1), even when tumors are absent. Nerve Schwann cells (SCs) were recently shown to play roles in nociceptive processing, and we find that chemogenetic activation of SCs is sufficient to induce afferent and behavioral mechanical hypersensitivity in wild-type mice. In mouse models, animals showed afferent and behavioral hypersensitivity when SCs, but not neurons, lacked Nf1. Importantly, hypersensitivity corresponded with SC-specific upregulation of mRNA encoding glial cell line-derived neurotrophic factor (GDNF), independently of the presence of tumors. Neuropathic pain-like behaviors in the NF1 mice were inhibited by either chemogenetic silencing of SC calcium or by systemic delivery of GDNF-targeting antibodies. Together, these findings suggest that alterations in SCs directly modulate mechanical pain and suggest cell-specific treatment strategies to ameliorate pain in individuals with NF1.

Human genetics and molecular genomics of Chiari malformation type 1

Chiari malformation type 1 (CM1) is the most common structural brain disorder involving the craniocervical junction, characterized by caudal displacement of the cerebellar tonsils below the foramen magnum into the spinal canal. Despite the heterogeneity of CM1, its poorly understood patho-etiology has led to a 'one-size-fits-all' surgical approach, with predictably high rates of morbidity and treatment failure. In this review we present multiplex CM1 families, associated Mendelian syndromes, and candidate genes from recent whole exome sequencing (WES) and other genetic studies that suggest a significant genetic contribution from inherited and de novo germline variants impacting transcription regulation, craniovertebral osteogenesis, and embryonic developmental signaling. We suggest that more extensive WES may identify clinically relevant, genetically defined CM1 subtypes distinguished by unique neuroradiographic and neurophysiological endophenotypes.

ERN GENTURIS tumour surveillance guidelines for individuals with neurofibromatosis type 1

BACKGROUND

Neurofibromatosis type 1 (NF1) is a multisystem genetic disorder, predisposing development of benign and malignant tumours. Given the oncogenic potential, long-term surveillance is important in patients with NF1. Proposals for NF1 care and its specific manifestations have been developed, but lack integration within routine care. This guideline aims to assimilate available information on NF1 associated tumours (based on evidence and/or expert opinion) to assist healthcare professionals in undertaking tumour surveillance of NF1 individuals.

METHODS

By comprehensive literature review, performed March 18th 2020, guidelines were developed by a NF1 expert group and patient representatives, conversant with clinical care of the wide NF1 disease spectrum. We used a modified Delphi procedure to overcome issues of variability in recommendations for specific (national) health care settings, and to deal with recommendations based on indirect (scarce) evidence.

FINDINGS

We defined proposals for personalised and targeted tumour management in NF1, ensuring appropriate care for those in need, whilst reducing unnecessary intervention. We also incorporated the tumour-related psychosocial and quality of life impact of NF1.

INTERPRETATION

The guideline reflects the current care for NF1 in Europe. They are not meant to be prescriptive and may be adjusted to local available resources at the treating centre, both within and outside EU countries.

FUNDING

This guideline has been supported by the European Reference Network on Genetic Tumour Risk Syndromes (ERN GENTURIS). ERN GENTURIS is funded by the European Union. DGE is supported by the Manchester NIHRBiomedical Research Centre (IS-BRC-1215-20007).

Loss of NF1 in Drosophila Larvae Causes Tactile Hypersensitivity and Impaired Synaptic Transmission at the Neuromuscular Junction

Autism spectrum disorder (ASD) is a neurodevelopmental condition in which the mechanisms underlying its core symptomatology are largely unknown. Studying animal models of monogenic syndromes associated with ASD, such as neurofibromatosis type 1 (NF1), can offer insights into its etiology. Here, we show that loss of function of the Drosophila NF1 ortholog results in tactile hypersensitivity following brief mechanical stimulation in the larva (mixed sexes), paralleling the sensory abnormalities observed in individuals with ASD. Mutant larvae also exhibit synaptic transmission deficits at the glutamatergic neuromuscular junction (NMJ), with increased spontaneous but reduced evoked release. While the latter is homeostatically compensated for by a postsynaptic increase in input resistance, the former is consistent with neuronal hyperexcitability. Indeed, diminished expression of NF1 specifically within central cholinergic neurons induces both excessive neuronal firing and tactile hypersensitivity, suggesting the two may be linked. Furthermore, both impaired synaptic transmission and behavioral deficits are fully rescued via knock-down of Ras proteins. These findings validate NF1 -/- Drosophila as a tractable model of ASD with the potential to elucidate important pathophysiological mechanisms.SIGNIFICANCE STATEMENT Autism spectrum disorder (ASD) affects 1-2% of the overall population and can considerably impact an individual's quality of life. However, there are currently no treatments available for its core symptoms, largely because of a poor understanding of the underlying mechanisms involved. Examining how loss of function of the ASD-associated NF1 gene affects behavior and physiology in Drosophila may shed light on this. In this study, we identify a novel, ASD-relevant behavioral phenotype in NF1 -/- larvae, namely an enhanced response to mechanical stimulation, which is associated with Ras-dependent synaptic transmission deficits indicative of neuronal hyperexcitability. Such insights support the use of Drosophila neurofibromatosis type 1 (NF1) models in ASD research and may provide outputs for genetic or pharmacological screens in future studies.

Mapping the Landscape of Neurofibromatosis: A Bibliometric Evaluation Highlighting Our Current Understanding, Emerging Therapies, and Global Research Trends

BACKGROUND

The literature on neurofibromatosis (NF) has never been systematically assessed using bibliometric analytic methodologies. We quantitatively analyzed the major trends and scientific output regarding NF, highlighting potential avenues for research.

METHODS

An Elsevier's Scopus database search was performed for all indexed studies related to NF from 1898 to 2021. Validated bibliometric parameters were analyzed using productivity, citation, and keyword analysis, including text mining, content analysis, and collaboration network mapping from inception to date on R 4.1.2.

RESULTS

Our search yielded 15,024 documents. Annual scientific production has grown at a compounded rate of 5.86%, with the largest occurring in 2021 (n = 626). Journals with the most publications on NF include the Journal of Medical Genetics (n = 117) and Neurology (n = 113). The topmost cited author was Gutmann DH (n = 295). The United States had the most international collaboration (n = 435; multiple country publications). Identification of citation classics revealed a shift in recent decades towards understanding genetic and molecular pathways of NF tumorigenesis. Macro-level and micro-level text mining revealed the top 20 genetic and molecular pathways, and syndromes, associated with NF.

CONCLUSIONS

Our study exemplifies a quantitative method for understanding the historical and current state of academic efforts regarding NF. There has been a shift of treatment strategies towards targeting specific pathways involved in tumorigenesis. We highlight the top 20 genetic and molecular pathways in the literature as well as the top 20 associated syndromes. This data is encouraging as increased research in molecular targeted therapies aimed at NF pathogenesis may allow advances in disease control.

Understanding the Neurofibromatosis Type 1 (NF1) experience and the priorities of individuals with NF1 and their caregivers for cognitive and social-emotional research

BACKGROUND

Patient engagement is increasingly recognized as a valuable, essential aspect of Neurofibromatosis research given the unique experiences and morbidities associated with the diagnosis. Engaging patients and families can enhance the relevance, methodology, and feasibility of clinical trials.

METHODS

A REDCap survey ascertaining information on NF-related morbidities, priorities, and interests in cognitive and social-emotional research, and willingness to participate in research was dispensed to 4,565 individuals consented to the Children's Tumor Foundation (CTF) Registry with NF1. This included children and adults with NF1 and parents/caregivers of children with NF1.

RESULTS

525 individuals fully completed the survey: 295 parents/caregivers (M_{age child} = 10.12, range = 3-24), 194 adults with NF1 (M_age = 45.73, range = 19-81), and 36 children with NF1 (M_age = 12.61, range = 10-17). Less than 10% of respondents have participated in cognitive research, while 42.4-49.5% indicated having sought opportunities for cognitive research. Most (79.4-82.4%) respondents reported that cognitive research is very/extremely important, with learning/academics and emotional functioning were priorities. Willingness to participate in research aligned with areas of importance.

CONCLUSION

Analysis highlights that most survey respondents believe cognitive and social-emotional research is very important, but a relatively small number have participated. This finding may highlight poor dissemination of information of research opportunities to the broader NF community and limitations to access based on geography or other factors. Respondents indicate that learning/academic problems and emotional challenges to be research priorities. Continuing to engage patients and families with NF is expected to enhance the value and engagement in cognitive research.

A Systematic Review of Recent and Ongoing Clinical Trials in Patients With the Neurofibromatoses

INTRODUCTION

The neurofibromatoses comprise three different genetic conditions causing considerable morbidity and mortality: neurofibromatosis type 1 (NF1), neurofibromatosis type 2 (NF2), and schwannomatosis (SWN). This review summarizes recent and ongoing clinical trials involving patients with neurofibromatoses to better understand the current state of clinical trial research centered around these conditions and inform areas of need.

METHODS

A search was conducted using the Cochrane Central Register of Controlled Trials and clinicaltrials.gov databases. Inclusion and exclusion criteria were designed to identify clinical trials focused on patients with NF1, NF2, or SWN completed in or after 2010 and in process as of December 31, 2021. Information was collected using standardized guidelines.

RESULTS

A total of 134 clinical trials were included, with 75 (56%) completed and 59 (44%) in process. For completed trials, 74% (n = 56) involved patients with NF1, and of those based on specific tumors (n = 26, 46%), the majority focused on plexiform neurofibromas (PNs) (n = 12, 46%). For ongoing trials, 79% (n = 47) involve patients with NF1, and of those based on specific tumors (n = 29, 61%), the majority are focused on PNs (n = 13, 45%).

CONCLUSION

Both recent and ongoing clinical trials have primarily focused on patients with NF1 and the treatment of PNs. This research has led to the first FDA-approved drug for NF1-PN and has changed management of these tumors, allowing for systemic therapy rather than reliance on only a surgical modality. Trials evaluating comorbid psychiatric conditions and quality of life among patients with any of the neurofibromatoses appear less common. These areas may warrant focus in future studies to improve clinical management.

Burden Among Caregivers of Pediatric Patients with Neurofibromatosis Type 1 (NF1) and Plexiform Neurofibroma (PN) in the United States: A Cross-Sectional Study

Introduction

Patients with neurofibromatosis type 1 (NF1) may develop plexiform neurofibromas (PNs) that can cause disfigurement, pain, and dysfunction, and may even be life-threatening. Studies have indicated NF1-PN can substantially impact the quality of life (QoL) of pediatric patients. However, research on caregiver burden is scarce.

Methods

Caregivers of pediatric patients ages 2–18 years with NF1-PN in the USA were recruited through the Children’s Tumor Foundation to participate in an online cross-sectional survey (December 2020–January 2021). Caregiver burden was measured using the Zarit Burden Interview (ZBI), and productivity loss from patientcare was measured using the Work Productivity and Activity Impairment questionnaire, adapted for caregiving (WPAI:CG).

Results

Ninety-five caregivers were recruited with a median age of 44.0 years. Most were female (88.4%), white/Caucasian (85.3%), and did not have NF1 or PN (86.3% and 89.5%, respectively). Commonly reported health conditions among caregivers include anxiety (48.4%) and depression (34.7%). On the ZBI (range 0–88; higher = greater burden), mean (SD) scores were 23.0 (13.8) and 12.7% of caregivers reported moderate–severe (scores 41–60) or severe burden (scores 61–88). Fifty-six caregivers were employed and working in the 7 days prior to completing the WPAI:CG. They reported missing an average of 6.9% of their working hours and an average reduction of 17.3% of on-the-job effectiveness, contributing to 22.3% loss in work productivity. Among all 95 caregivers, an average of 17.2% of regular daily activities were impaired.

Conclusions

The burden among caregivers of pediatric patients with NF1-PN is considerable and underscores an unmet need for better disease management.

Neurofibromin and suppression of tumorigenesis: beyond the GAP

Neurofibromatosis type 1 (NF1) is an autosomal dominant genetic disease and one of the most common inherited tumor predisposition syndromes, affecting 1 in 3000 individuals worldwide. The NF1 gene encodes neurofibromin, a large protein with RAS GTP-ase activating (RAS-GAP) activity, and loss of NF1 results in increased RAS signaling. Neurofibromin contains many other domains, and there is considerable evidence that these domains play a role in some manifestations of NF1. Investigating the role of these domains as well as the various signaling pathways that neurofibromin regulates and interacts with will provide a better understanding of how neurofibromin acts to suppress tumor development and potentially open new therapeutic avenues. In this review, we discuss what is known about the structure of neurofibromin, its interactions with other proteins and signaling pathways, its role in development and differentiation, and its function as a tumor suppressor. Finally, we discuss the latest research on potential therapeutics for neurofibromin-deficient neoplasms.

Clinical and humanistic burden among pediatric patients with neurofibromatosis type 1 and plexiform neurofibroma in the USA

PURPOSE

To assess clinical and humanistic burden among pediatric patients with neurofibromatosis type 1 (NF1) and plexiform neurofibroma (PN) in the USA.

METHODS

NF1-PN patients aged 8-18 years (treatment-naïve or ≤ 1 month of selumetinib treatment) and their caregivers and caregivers of similar patients aged 2-7 years were recruited through the Children's Tumor Foundation to participate in an online cross-sectional survey (December 2020-January 2021). Caregivers provided data on patients' demographic and clinical characteristics and burden of debulking surgeries. Patients and caregivers provided self-reported or proxy responses to health-related quality of life (HRQoL) questions using validated instruments.

RESULTS

Sixty-one patients and 82 caregivers responded to the survey. Median (range) age of patients was 11.5 (3-18) years, and 53.7% were female. Most were treatment-naïve (97.6%), with NF1-PN diagnosis for > 5 years (68.3%). Most patients (59.8%) had > 1 PN and 11.0% reporting > 5 PNs. Common NF1-PN symptoms included pain (64.6%), disfigurement (32.9%), and motor dysfunction (28.0%). Patients and caregiver proxies reported low overall HRQoL and reduced physical, emotional, social, and school functioning. Patients also reported considerable pain severity, interference, daily activity impairments, and movement difficulty. Few patients had received complete resections of their tumors (12.2%). 39.0% reported ≥ 1 debulking surgery, among whom, 15.6% had complications, and debulking surgery-related hospitalizations were common (53.1%).

CONCLUSIONS

The clinical and humanistic burden among pediatric NF1-PN patients is substantial. While debulking surgeries are used for symptom management, they are associated with considerable clinical sequelae. Results highlight a need for improved disease management strategies.

A systematic review of porcine models in translational pain research

Translating basic pain research from rodents to humans has proven to be a challenging task. Efforts have been made to develop preclinical large animal models of pain, such as the pig. However, no consistent overview and comparison of pig models of pain are currently available. Therefore, in this review, our primary aim was to identify the available pig models in pain research and compare these models in terms of intensity and duration. First, we systematically searched Proquest, Scopus and Web of Science and compared the duration for which the pigs were significantly sensitized as well as the intensity of mechanical sensitization. We searched models within the specific field of pain and adjacent fields in which pain induction or assessment is relevant, such as pig production. Second, we compared assessment methodologies in surrogate pain models in humans and pigs to identify areas of overlap and possible improvement. Based on the literature search, 23 types of porcine pain models were identified; 13 of which could be compared quantitatively. The induced sensitization lasted from hours to months and intensities ranged from insignificant to the maximum attainable. We also found a near to complete overlap of assessment methodologies between human and pig models within the area of peripheral neurophysiology, which allows for direct comparison of results obtained in the two species. In spite of this overlap, further development of pain assessment methodologies is still needed. We suggest that central nervous system electrophysiology, such as electroencephalography, electrocorticography or intracortical recordings, may pave the way for future objective pain assessment.

Left to themselves: Time to target chronic pain in childhood rare diseases

BACKGROUND

Chronic pain is prevalent among patients with rare diseases (RDs). However, little is understood about how biopsychosocial mechanisms may be integrated in the unique set of clinical features and therapeutic challenges inherent in their pain conditions.

METHODS

This review presents examples of major categories of RDs with particular pain conditions. In addition, we provide translational evidence on clinical and scientific rationale for psychosocially- and neurodevelopmentally-informed treatment of pain in RD patients.

RESULTS

Neurobiological and functional overlap between various RD syndromes and pain states suggests amalgamation and mutual modulation of the respective conditions. Emotional sequelae could be construed as an emotional homologue of physical pain mediated via overlapping brain circuitry. Given their clearly defined genetic and molecular etiologies, RDs may serve as heuristic models for unraveling pathophysiological processes inherent in chronic pain.

CONCLUSIONS

Systematic evaluation of chronic pain in patients with RD contributes to sophisticated insight into both pain and their psychosocial correlates, which could transform treatment.

P2X Receptors: Potential Therapeutic Targets for Symptoms Associated With Lung Cancer - A Mini Review

Symptoms associated with lung cancer mainly consist of cancer-associated pain, cough, fatigue, and dyspnea. However, underlying mechanisms of lung cancer symptom clusters remain unclear. There remains a paucity of effective treatment to ameliorate debilitating symptoms and improve the quality of life of lung cancer survivors. Recently, extracellular ATP and its receptors have attracted increasing attention among researchers in the field of oncology. Extracellular ATP in the tumor microenvironment is associated with tumor cell metabolism, proliferation, and metastasis by driving inflammation and neurotransmission via P2 purinergic signaling. Accordingly, ATP gated P2X receptors expressed on tumor cells, immune cells, and neurons play a vital role in modulating tumor development, invasion, progression, and related symptoms. P2 purinergic signaling is involved in the development of different lung cancer-related symptoms. In this review, we summarize recent findings to illustrate the role of P2X receptors in tumor proliferation, progression, metastasis, and lung cancer- related symptoms, providing an outline of potential anti-neoplastic activity of P2X receptor antagonists. Furthermore, compared with opioids, P2X receptor antagonists appear to be innovative therapeutic interventions for managing cancer symptom clusters with fewer side effects.

The role of cyclin-dependent kinase 5 in neuropathic pain

The chronification of pain can be attributed to changes in membrane receptors and channels underlying neuronal plasticity and signal transduction largely within nociceptive neurons that initiate and maintain pathological pain states. These proteins are subject to dynamic modification by posttranslational modifications, creating a code that controls protein function in time and space. Phosphorylation is an important posttranslational modification that affects ∼30% of proteins in vivo. Increased phosphorylation of various nociceptive ion channels and of their modulators underlies sensitization of different pain states. Cyclin-dependent kinases are proline-directed serine/threonine kinases that impact various biological and cellular systems. Cyclin-dependent kinase 5 (Cdk5), one member of this kinase family, and its activators p35 and p39 are expressed in spinal nerves, dorsal root ganglia, and the dorsal horn of the spinal cord. In neuropathic pain conditions, expression and/or activity of Cdk5 is increased, implicating Cdk5 in nociception. Experimental evidence suggests that Cdk5 is regulated through its own phosphorylation, through increasing p35's interaction with Cdk5, and through cleavage of p35 into p25. This narrative review discusses the molecular mechanisms of Cdk5-mediated regulation of target proteins involved in neuropathic pain. We focus on Cdk5 substrates that have been linked to nociceptive pathways, including channels (eg, transient receptor potential cation channel and voltage-gated calcium channel), proteins involved in neurotransmitter release (eg, synaptophysin and collapsin response mediator protein 2), and receptors (eg, glutamate, purinergic, and opioid). By altering the phosphoregulatory "set point" of proteins involved in pain signaling, Cdk5 thus appears to be an attractive target for treating neuropathic pain conditions.

Spontaneous and Engineered Large Animal Models of Neurofibromatosis Type 1

Animal models are crucial to understanding human disease biology and developing new therapies. By far the most common animal used to investigate prevailing questions about human disease is the mouse. Mouse models are powerful tools for research as their small size, limited lifespan, and defined genetic background allow researchers to easily manipulate their genome and maintain large numbers of animals in general laboratory spaces. However, it is precisely these attributes that make them so different from humans and explains, in part, why these models do not accurately predict drug responses in human patients. This is particularly true of the neurofibromatoses (NFs), a group of genetic diseases that predispose individuals to tumors of the nervous system, the most common of which is Neurofibromatosis type 1 (NF1). Despite years of research, there are still many unanswered questions and few effective treatments for NF1. Genetically engineered mice have drastically improved our understanding of many aspects of NF1, but they do not exemplify the overall complexity of the disease and some findings do not translate well to humans due to differences in body size and physiology. Moreover, NF1 mouse models are heavily reliant on the Cre-Lox system, which does not accurately reflect the molecular mechanism of spontaneous loss of heterozygosity that accompanies human tumor development. Spontaneous and genetically engineered large animal models may provide a valuable supplement to rodent studies for NF1. Naturally occurring comparative models of disease are an attractive prospect because they occur on heterogeneous genetic backgrounds and are due to spontaneous rather than engineered mutations. The use of animals with naturally occurring disease has been effective for studying osteosarcoma, lymphoma, and diabetes. Spontaneous NF-like symptoms including neurofibromas and malignant peripheral nerve sheath tumors (MPNST) have been documented in several large animal species and share biological and clinical similarities with human NF1. These animals could provide additional insight into the complex biology of NF1 and potentially provide a platform for pre-clinical trials. Additionally, genetically engineered porcine models of NF1 have recently been developed and display a variety of clinical features similar to those seen in NF1 patients. Their large size and relatively long lifespan allow for longitudinal imaging studies and evaluation of innovative surgical techniques using human equipment. Greater genetic, anatomic, and physiologic similarities to humans enable the engineering of precise disease alleles found in human patients and make them ideal for preclinical pharmacokinetic and pharmacodynamic studies of small molecule, cellular, and gene therapies prior to clinical trials in patients. Comparative genomic studies between humans and animals with naturally occurring disease, as well as preclinical studies in large animal disease models, may help identify new targets for therapeutic intervention and expedite the translation of new therapies. In this review, we discuss new genetically engineered large animal models of NF1 and cases of spontaneous NF-like manifestations in large animals, with a special emphasis on how these comparative models could act as a crucial translational intermediary between specialized murine models and NF1 patients.

Assessment of nociception and related quality-of-life measures in a porcine model of neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is an autosomal dominant genetic disorder resulting from germline mutations in the NF1 gene, which encodes neurofibromin. Patients experience a variety of symptoms, but pain in the context of NF1 remains largely underrecognized. Here, we characterize nociceptive signaling and pain behaviors in a miniswine harboring a disruptive NF1 mutation (exon 42 deletion). We present the first characterization of pain-related behaviors in a pig model of NF1, identifying unchanged agitation scores, lower tactile thresholds (allodynia), and decreased response latencies to thermal laser stimulation (hyperalgesia) in NF1 (females only) pigs. Male NF1 pigs with tumors showed reduced sleep quality and increased resting, 2 health-related quality-of-life symptoms found to be comorbid in people with NF1 pain. We explore these phenotypes in relationship to suppression of the increased activity of the N-type voltage-gated calcium (CaV2.2) channel by pharmacological antagonism of phosphorylation of a regulatory protein-the collapsin response mediator protein 2 (CRMP2), a known interactor of neurofibromin, and by targeting the interface between the α subunit of CaV2.2 and the accessory β-subunits with small molecules. Our data support the use of NF1 pigs as a large animal model for studying NF1-associated pain and for understanding the pathophysiology of NF1. Our findings demonstrate the translational potential of 2 small molecules in reversing ion channel remodeling seen in NF1. Interfering with CaV2.2, a clinically validated target for pain management, might also be a promising therapeutic strategy for NF1-related pain management.

Cannabidiol (CBD) for Treatment of Neurofibromatosis-related Pain and Concomitant Mood Disorder: A Case Report

Neurofibromatosis type 1 (NF1) is a common genetic disorder. Pain is a major symptom of this disease which can be secondary to the development of plexiform and subcutaneous neurofibromas, musculoskeletal symptoms (such as scoliosis and pseudoarthrosis), and headaches. Visible neurofibromas add significant psychosocial distress for NF1 patients. Along with the chronic pain, psychosocial distress contributes to associated mood disorders, such as depression and anxiety. Cannabis has been the focus of many studies for treating multiple conditions, including epilepsy, multiple sclerosis, Parkinsonism disease, and many chronic pain conditions. Cannabidiol (CBD) is the major non-psychotropic component of cannabis. CBD has shown anti-inflammatory and analgesic properties, as well as having mood stabilizer and anxiolytic effects. In this report, we present the use of cannabidiol (CBD) for the management of chronic pain and concomitant mood disorder in an NF1 patient.