Dopamine deficiency underlies learning deficits in neurofibromatosis-1 mice

Unraveling neuronal and metabolic alterations in neurofibromatosis type 1

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

Drosophila Contributions towards Understanding Neurofibromatosis 1

Neurofibromatosis 1 (NF1) is a multisymptomatic disorder with highly variable presentations, which include short stature, susceptibility to formation of the characteristic benign tumors known as neurofibromas, intense freckling and skin discoloration, and cognitive deficits, which characterize most children with the condition. Attention deficits and Autism Spectrum manifestations augment the compromised learning presented by most patients, leading to behavioral problems and school failure, while fragmented sleep contributes to chronic fatigue and poor quality of life. Neurofibromin (Nf1) is present ubiquitously during human development and postnatally in most neuronal, oligodendrocyte, and Schwann cells. Evidence largely from animal models including Drosophila suggests that the symptomatic variability may reflect distinct cell-type-specific functions of the protein, which emerge upon its loss, or mutations affecting the different functional domains of the protein. This review summarizes the contributions of Drosophila in modeling multiple NF1 manifestations, addressing hypotheses regarding the cell-type-specific functions of the protein and exploring the molecular pathways affected upon loss of the highly conserved fly homolog dNf1. Collectively, work in this model not only has efficiently and expediently modelled multiple aspects of the condition and increased understanding of its behavioral manifestations, but also has led to pharmaceutical strategies towards their amelioration.

Early-life immune activation is a vulnerability factor for adult epileptogenesis in neurofibromatosis type 1 in male mice

Introduction

Patients with Neurofibromatosis type 1 (NF1), the most common neurocutaneous disorder, can develop several neurological manifestations that include cognitive impairments and epilepsy over their lifetime. It is unclear why certain patients with NF1 develop these conditions while others do not. Early-life immune activation promotes later-life seizure susceptibility, neurocognitive impairments, and leads to spontaneous seizures in some animal models of neurodevelopmental disorders, but the central nervous system immune profile and the enduring consequences of early-life immune activation on the developmental trajectory of the brain in NF1 have not yet been explored. We tested the hypothesis that early-life immune activation promotes the development of spatial memory impairments and epileptogenesis in a mouse model of NF1.

Methods

Male wild-type (WT) and Nf1+/- mice received systemic lipopolysaccharide (LPS) or saline at post-natal day 10 and were assessed in adulthood for learning and memory deficits in the Barnes maze and underwent EEG recordings to look for spontaneous epileptiform abnormalities and susceptibility to challenge with pentylenetetrazole (PTZ).

Results

Whereas early-life immune activation by a single injection of LPS acutely elicited a comparable brain cytokine signature in WT and Nf1+/- mice, it promoted spontaneous seizure activity in adulthood only in the Nf1+/- mice. Early-life immune activation affected susceptibility to PTZ-induced seizures similarly in both WT and Nf1+/-mice. There was no effect on spatial learning and memory regardless of mouse genotype.

Discussion

Our findings suggest second-hit environmental events such as early-life immune activation may promote epileptogenesis in the Nf1+/- mouse and may be a risk-factor for NF1-associated epilepsy.

Gender-Specific Fine Motor Skill Learning Is Impaired by Myelin-Targeted Neurofibromatosis Type 1 Gene Mutation

Neurofibromatosis type 1 (NF1) is caused by mutations in the NF1 gene. The clinical presentation of NF1 includes diverse neurological issues in pediatric and adult patients, ranging from learning disabilities, motor skill issues, and attention deficit disorder, to increased risk of depression and dementia. Preclinical research suggests that abnormal neuronal signaling mediates spatial learning and attention issues in NF1; however, drugs that improve phenotypes in models show inconclusive results in clinical trials, highlighting the need for a better understanding of NF1 pathophysiology and broader therapeutic options. Most NF1 patients show abnormalities in their brain white matter (WM) and myelin, and links with NF1 neuropathophysiology have been suggested; however, no current data can clearly support or refute this idea. We reported that myelin-targeted Nf1 mutation impacts oligodendrocyte signaling, myelin ultrastructure, WM connectivity, and sensory-motor behaviors in mice; however, any impact on learning and memory remains unknown. Here, we adapted a voluntary running test-the complex wheel (CW; a wheel with unevenly spaced rungs)-to delineate fine motor skill learning curves following induction of an Nf1 mutation in pre-existing myelinating cells (pNf1 mice). We found that pNf1 mutant females experience delayed or impaired learning in the CW, while proper learning in pNf1 males is predominantly disrupted; these phenotypes add complexity to the gender-dependent learning differences in the mouse strain used. No broad differences in memory of acquired CW skills were detected in any gender, but gene-dose effects were observed at the studied time points. Finally, nitric oxide signaling regulation differentially impacted learning in wild type (WT)/pNf1, male/female mice. Our results provide evidence for fine motor skill learning issues upon induction of an Nf1 mutation in mature myelinating cells. Together with previous connectivity, cellular, and molecular analyses, these results diversify the potential treatments for neurological issues in NF1.

A new era for myelin research in Neurofibromatosis type 1

Evidence for myelin regulating higher-order brain function and disease is rapidly accumulating; however, defining cellular/molecular mechanisms remains challenging partially due to the dynamic brain physiology involving deep changes during development, aging, and in response to learning and disease. Furthermore, as the etiology of most neurological conditions remains obscure, most research models focus on mimicking symptoms, which limits understanding of their molecular onset and progression. Studying diseases caused by single gene mutations represents an opportunity to understand brain dys/function, including those regulated by myelin. Here, we discuss known and potential repercussions of abnormal central myelin on the neuropathophysiology of Neurofibromatosis Type 1 (NF1). Most patients with this monogenic disease present with neurological symptoms diverse in kind, severity, and onset/decline, including learning disabilities, autism spectrum disorders, attention deficit and hyperactivity disorder, motor coordination issues, and increased risk for depression and dementia. Coincidentally, most NF1 patients show diverse white matter/myelin abnormalities. Although myelin-behavior links were proposed decades ago, no solid data can prove or refute this idea yet. A recent upsurge in myelin biology understanding and research/therapeutic tools provides opportunities to address this debate. As precision medicine moves forward, an integrative understanding of all cell types disrupted in neurological conditions becomes a priority. Hence, this review aims to serve as a bridge between fundamental cellular/molecular myelin biology and clinical research in NF1.

Polysomnographic study in pediatric neurofibromatosis type 1

Background

Neurofibromatosis type 1 (NF1) is a genetic disease that alters neurodevelopment. We aimed to analyze the sleep macrostructure of a sample of children affected by NF1 without neurocognitive co-morbidities and MRI reports of unidentified bright objects (UBOs).

Methods

A 100 pre-pubertal children participated in the cross-sectional study: 50 subjects were children diagnosed with NF1 and 50 subjects were typically developing healthy children (TDC). All participants underwent polysomnographic evaluation through which conventional sleep parameters were collected: Total sleep time (TST), Sleep latency (SOL), first REM latency (FRL), number of stage shifts/h (SS/h), number of awakenings/h (AWN/h), wake after sleep onset (WASO%), sleep efficiency percentage (SE%), percentage of sleep time spent in sleep stages 1 (N1%) and 2 (N2%), slow-wave sleep (N3%), and REM sleep (REM%). Additionally, nocturnal respiratory events such as apnea/hypopnea index (AHI), oxygen desaturation index (ODI), and periodic limb movement index (PLMI) were recorded.

Results

Neurofibromatosis type 1 children showed a reduction in sleep duration parameters (TST; p < 0.001), sleep efficiency (SE%; p < 0.001), and stage N2% (p < 0.001). Moreover, the number of awakenings per hour (AWN/h), wake after sleep onset (WASO%), and respiratory events such as AHI, ODI, and PLMI resulted higher in NF1 vs. TDC children.

Conclusion

The data showed that the sleep macrostructure differs between NF1 and TDC children. These findings suggest that the evaluation of sleep may provide useful support in corroborating the diagnosis and offers additional therapeutic management perspectives in NF1 and genetic neurodevelopmental disorders in general.

The therapeutic potential of neurofibromin signaling pathways and binding partners

Neurofibromin controls many cell processes, such as growth, learning, and memory. If neurofibromin is not working properly, it can lead to health problems, including issues with the nervous, skeletal, and cardiovascular systems and cancer. This review examines neurofibromin's binding partners, signaling pathways and potential therapeutic targets. In addition, it summarizes the different post-translational modifications that can affect neurofibromin's interactions with other molecules. It is essential to investigate the molecular mechanisms that underlie neurofibromin variants in order to provide with functional connections between neurofibromin and its associated proteins for possible therapeutic targets based on its biological function.

Non-invasive brain stimulation modulates GABAergic activity in neurofibromatosis 1

Neurofibromatosis 1 (NF1) is a single-gene disorder associated with cognitive phenotypes common to neurodevelopmental conditions such as autism. GABAergic dysregulation underlies working memory impairments seen in NF1. This mechanistic experimental study investigates whether application of anodal transcranial direct current stimulation (atDCS) can modulate GABA and working memory in NF1. Thirty-one NF1 adolescents 11-18 years, were recruited to this single-blind sham-controlled cross-over randomized trial. AtDCS or sham stimulation was applied to the left Dorsolateral Prefrontal Cortex (DLPFC) and MR Spectroscopy was collected before and after intervention in the left DLPFC and occipital cortex. Task-related functional MRI was collected before, during, and after stimulation. Higher baseline GABA+ in the left DLPFC was associated with faster response times on baseline working memory measures. AtDCS was seen to significantly reduced GABA+ and increase brain activation in the left DLPFC as compared to sham stimulation. Task performance was worse in the aTDCS group during stimulation but no group differences in behavioural outcomes were observed at the end of stimulation. Although our study suggests aTDCS modulates inhibitory activity in the DLPFC, further work is needed to determine whether repeated sessions of atDCS and strategies such as alternating current stimulation offer a better therapeutic approach.

Mechanistic insights from animal models of neurofibromatosis type 1 cognitive impairment

Neurofibromatosis type 1 (NF1) is an autosomal-dominant neurogenetic disorder caused by mutations in the gene neurofibromin 1 (NF1). NF1 predisposes individuals to a variety of symptoms, including peripheral nerve tumors, brain tumors and cognitive dysfunction. Cognitive deficits can negatively impact patient quality of life, especially the social and academic development of children. The neurofibromin protein influences neural circuits via diverse cellular signaling pathways, including through RAS, cAMP and dopamine signaling. Although animal models have been useful in identifying cellular and molecular mechanisms that regulate NF1-dependent behaviors, translating these discoveries into effective treatments has proven difficult. Clinical trials measuring cognitive outcomes in patients with NF1 have mainly targeted RAS signaling but, unfortunately, resulted in limited success. In this Review, we provide an overview of the structure and function of neurofibromin, and evaluate several cellular and molecular mechanisms underlying neurofibromin-dependent cognitive function, which have recently been delineated in animal models. A better understanding of neurofibromin roles in the development and function of the nervous system will be crucial for identifying new therapeutic targets for the various cognitive domains affected by NF1.

Summary: Neurofibromin influences neural circuits through RAS, cAMP and dopamine signaling. Exploring the mechanisms underlying neurofibromin-dependent behaviors in animal models might enable future treatment of the various cognitive deficits that are associated with neurofibromatosis type 1.

A systematic review and meta-analysis of intellectual, neuropsychological, and psychoeducational functioning in neurofibromatosis type 1

Neurofibromatosis Type 1 (NF1) is a common genetic disorder frequently associated with cognitive deficits. Despite cognitive deficits being a key feature of NF1, the profile of such impairments in NF1 has been shown to be heterogeneous. Thus, we sought to quantitatively synthesize the extant literature on cognitive functioning in NF1. A random-effects meta-analysis of cross-sectional studies was carried out comparing cognitive functioning of patients with NF1 to typically developing or unaffected sibling comparison subjects of all ages. Analyses included 50 articles (Total N_NF1 = 1,522; M_Age = 15.70 years, range = 0.52-69.60), yielding 460 effect sizes. Overall moderate deficits were observed [g = -0.64, 95% CI = (-0.69, -0.60)] wherein impairments differed at the level of cognitive domain. Deficits ranged from large [general intelligence: g = -0.95, 95% CI = (-1.12, -0.79)] to small [emotion: g = -0.37, 95% CI = (-0.63, -0.11)]. Moderation analyses revealed nonsignificant contributions of age, sex, educational attainment, and parental level of education to outcomes. These results illustrate that cognitive impairments are diffuse and salient across the lifespan in NF1. Taken together, these results further demonstrate efforts should be made to evaluate and address cognitive morbidity in patients with NF1 in conjunction with existing best practices.

RAS and beyond: the many faces of the neurofibromatosis type 1 protein

Neurofibromatosis type 1 is a rare neurogenetic syndrome, characterized by pigmentary abnormalities, learning and social deficits, and a predisposition for benign and malignant tumor formation caused by germline mutations in the NF1 gene. With the cloning of the NF1 gene and the recognition that the encoded protein, neurofibromin, largely functions as a negative regulator of RAS activity, attention has mainly focused on RAS and canonical RAS effector pathway signaling relevant to disease pathogenesis and treatment. However, as neurofibromin is a large cytoplasmic protein the RAS regulatory domain of which occupies only 10% of its entire coding sequence, both canonical and non-canonical RAS pathway modulation, as well as the existence of potential non-RAS functions, are becoming apparent. In this Special article, we discuss our current understanding of neurofibromin function.

The Use of Drosophila to Understand Psychostimulant Responses

The addictive properties of psychostimulants such as cocaine, amphetamine, methamphetamine, and methylphenidate are based on their ability to increase dopaminergic neurotransmission in the reward system. While cocaine and methamphetamine are predominately used recreationally, amphetamine and methylphenidate also work as effective therapeutics to treat symptoms of disorders including attention deficit and hyperactivity disorder (ADHD) and autism spectrum disorder (ASD). Although both the addictive properties of psychostimulant drugs and their therapeutic efficacy are influenced by genetic variation, very few genes that regulate these processes in humans have been identified. This is largely due to population heterogeneity which entails a requirement for large samples. Drosophila melanogaster exhibits similar psychostimulant responses to humans, a high degree of gene conservation, and allow performance of behavioral assays in a large population. Additionally, amphetamine and methylphenidate reduce impairments in fly models of ADHD-like behavior. Therefore, Drosophila represents an ideal translational model organism to tackle the genetic components underlying the effects of psychostimulants. Here, we break down the many assays that reliably quantify the effects of cocaine, amphetamine, methamphetamine, and methylphenidate in Drosophila. We also discuss how Drosophila is an efficient and cost-effective model organism for identifying novel candidate genes and molecular mechanisms involved in the behavioral responses to psychostimulant drugs.

Feedback-Based Learning of Timing in Attention-Deficit/Hyperactivity Disorder and Neurofibromatosis Type 1

OBJECTIVE

Patients with Neurofibromatosis Type 1 (NF1) frequently display symptoms resembling those of Attention Deficit/Hyperactivity Disorder (ADHD). Importantly, these disorders are characterised by distinct changes in the dopaminergic system, which plays an important role in timing performance and feedback-based adjustments in timing performance. In a transdiagnostic approach, we examine how far NF1 and ADHD show distinct or comparable profiles of timing performance and feedback-based adjustments in timing.

METHOD

We examined time estimation and learning processes in healthy control children (HC), children with ADHD with predominantly inattentive symptoms and those with NF1 using a feedback-based time estimation paradigm.

RESULTS

Healthy controls consistently responded closer to the correct time window than both patient groups, were less variable in their reaction times and displayed intact learning-based adjustments across time. The patient groups did not differ from each other regarding the number of in-time responses. In ADHD patients, the performance was rather unstable across time. No performance changes could be observed in patients with NF1 across the entire task.

CONCLUSIONS

Children with ADHD and NF1 differ in feedback learning-based adjustments of time estimation processes. ADHD is characterised by behavioural fluctuations during the learning process. These are likely to be associated with inefficiencies in the dopaminergic system. NF1 is characterised by impairments of feedback learning which could be due to various neurotransmitter alterations occurring in addition to deficits in dopamine synthesis. Results show that despite the strong overlap in clinical phenotype and neuropsychological deficits between NF1 and ADHD, the underlying cognitive mechanisms are different.

Assessing Psychiatric Comorbidity and Pharmacologic Treatment Patterns Among Patients With Neurofibromatosis Type 1

Background and objective

Neurofibromatosis 1 (NF1) is a genetic disorder that is accompanied by psychiatric comorbidities such as depression, anxiety, and attention-deficit hyperactivity disorder (ADHD) in more than half of the patients. However, there are limited data describing optimal treatment strategies for these conditions. This study aimed to address that gap in understanding and explore the neurobiological basis of psychiatric comorbidities in NF1.

Materials and methods

A retrospective cohort study was conducted among NF1 patients with a comorbid diagnosis of depression, anxiety, and/or ADHD. These disease states were chosen based on their relatively high reported prevalence in NF1 and shared pathophysiological mechanisms via monoaminergic dysfunction. Information regarding demographics, psychotherapeutic medication use, and clinical outcomes was gathered from electronic medical records. Relationships between patient- and medication-related factors and outcome measures were assessed using statistical analysis.

Results

The study population (n = 82) consisted of NF1 patients with a comorbid diagnosis of depression (76.8%), anxiety (53.7%), and/or ADHD (23.2%). The use of second-generation antipsychotic agent augmentation therapy or hydroxyzine monotherapy was associated with significantly more behavioral health (BH)-related emergency department (ED) visits, admissions, and inpatient days in the study population. Conversely, the use of bupropion augmentation therapy, buspirone augmentation therapy, and stimulants was associated with improved clinical outcomes, though these results were not statistically significant.

Conclusions

Based on our findings in this real-world study setting, patients with NF1 and psychiatric comorbidities appear to experience significant benefits from medications that enhance dopaminergic neurotransmission (e.g., bupropion, stimulants) when compared to drugs that oppose it (e.g., second-generation antipsychotics).

Visuospatial but Not Verbal Working Memory Deficits in Adult Patients With Neurofibromatosis Type 1

Background: Cognitive dysfunction is one of the main symptoms of neurofibromatosis type 1 (NF1). As an important cognitive function, working memory (WM) has rarely been systematically analyzed in NF1 by isolating the particular domain of WM, and existing data involving WM in adult patients with NF1 are insufficient. This study aimed to investigate the characteristics of different types of WM in NF1 from the perspective of the adult population. Method: We comprehensively analyzed WM in both verbal and visuospatial WM domains by using the N-back task (including the verbal N-back task and the visuospatial N-back task) in 31 adults with NF1 and 34 healthy controls matched for age, gender, education levels, and general cognitive status. The accuracy and reaction times (RTs) in the N-back task were entered into mixed-design ANOVA. Results: Compared with healthy controls, adults with NF1 presented significantly lower mean accuracy and longer RTs in the visuospatial N-back task. However, no significant difference was found between the NF1 group and healthy controls in the verbal N-back task. Conclusions: The present study suggested that adults with NF1 might have deficits in visuospatial WM. We did not find evidence for verbal WM deficits in adult patients with NF1. Our findings supplement and refine the existing data on WM in the context of NF1.

Neurofibromin regulates metabolic rate via neuronal mechanisms in Drosophila

Neurofibromatosis type 1 is a chronic multisystemic genetic disorder that results from loss of function in the neurofibromin protein. Neurofibromin may regulate metabolism, though the underlying mechanisms remain largely unknown. Here we show that neurofibromin regulates metabolic homeostasis in Drosophila via a discrete neuronal circuit. Loss of neurofibromin increases metabolic rate via a Ras GAP-related domain-dependent mechanism, increases feeding homeostatically, and alters lipid stores and turnover kinetics. The increase in metabolic rate is independent of locomotor activity, and maps to a sparse subset of neurons. Stimulating these neurons increases metabolic rate, linking their dynamic activity state to metabolism over short time scales. Our results indicate that neurofibromin regulates metabolic rate via neuronal mechanisms, suggest that cellular and systemic metabolic alterations may represent a pathophysiological mechanism in neurofibromatosis type 1, and provide a platform for investigating the cellular role of neurofibromin in metabolic homeostasis.

Neurofibromatosis type 1 (NF1) is a genetic disorder caused by mutations in neurofibromin and associated with disruptions in physiology and behavior. Here the authors show that neurofibromin regulates metabolic homeostasis via a discrete brain circuit in a Drosophila model of NF1.

Associative Learning Requires Neurofibromin to Modulate GABAergic Inputs to Drosophila Mushroom Bodies

Cognitive dysfunction is among the hallmark symptoms of Neurofibromatosis 1, and accordingly, loss of the Drosophila melanogaster ortholog of Neurofibromin 1 (dNf1) precipitates associative learning deficits. However, the affected circuitry in the adult CNS remained unclear and the compromised mechanisms debatable. Although the main evolutionarily conserved function attributed to Nf1 is to inactivate Ras, decreased cAMP signaling on its loss has been thought to underlie impaired learning. Using mixed sex populations, we determine that dNf1 loss results in excess GABAergic signaling to the central for associative learning mushroom body (MB) neurons, apparently suppressing learning. dNf1 is necessary and sufficient for learning within these non-MB neurons, as a dAlk and Ras1-dependent, but PKA-independent modulator of GABAergic neurotransmission. Surprisingly, we also uncovered and discuss a postsynaptic Ras1-dependent, but dNf1-independnet signaling within the MBs that apparently responds to presynaptic GABA levels and contributes to the learning deficit of the mutants.

Attention and Executive Disorders in Neurofibromatosis 1: Comparison Between NF1 With ADHD Symptomatology (NF1 + ADHD) and ADHD Per Se

Objective: To compare children with Neurofibromatosis type 1 and associated ADHD symptomatology (NF1 + ADHD) with children having received a diagnosis of ADHD without NF1. The idea was that performance differences in tasks of attention between these two groups would be attributable not to the ADHD symptomatology, but to NF1 alone. Method: One group of children with NF1 + ADHD (N = 32), one group of children with ADHD (N = 31), and one group of healthy controls (N = 40) participated in a set of computerized tasks assessing intensive, selective, and executive aspects of attention. Results: Differences were found between the two groups of patients in respect of several aspects of attention. Children with NF1 + ADHD did not always perform worse than children with ADHD. Several double dissociations can be established between the two groups of patients. Conclusion: ADHD symptomatology in NF1 does not contribute to all attention deficits, and ADHD cannot account for all attention impairments in NF1.

Neurofibromin Structure, Functions and Regulation

Neurofibromin is a large and multifunctional protein encoded by the tumor suppressor gene NF1, mutations of which cause the tumor predisposition syndrome neurofibromatosis type 1 (NF1). Over the last three decades, studies of neurofibromin structure, interacting partners, and functions have shown that it is involved in several cell signaling pathways, including the Ras/MAPK, Akt/mTOR, ROCK/LIMK/cofilin, and cAMP/PKA pathways, and regulates many fundamental cellular processes, such as proliferation and migration, cytoskeletal dynamics, neurite outgrowth, dendritic-spine density, and dopamine levels. The crystallographic structure has been resolved for two of its functional domains, GRD (GAP-related (GTPase-activating protein) domain) and SecPH, and its post-translational modifications studied, showing it to be localized to several cell compartments. These findings have been of particular interest in the identification of many therapeutic targets and in the proposal of various therapeutic strategies to treat the symptoms of NF1. In this review, we provide an overview of the literature on neurofibromin structure, function, interactions, and regulation and highlight the relationships between them.

Neurofibromatosis type 1: New developments in genetics and treatment

Neurofibromatosis type 1 is the most common neurocutaneous syndrome, with a frequency of 1 in 2500 persons. Diagnosis is paramount in the pretumor stage to provide proper anticipatory guidance for a number of neoplasms, both benign and malignant. Loss-of-function mutations in the NF1 gene result in truncated and nonfunctional production of neurofibromin, a tumor suppressor protein involved in downregulating the RAS signaling pathway. New therapeutic and preventive options include tyrosine kinase inhibitors, mTOR inhibitors, interferons, and radiofrequency therapy. This review summarizes recent updates in genetics, mutation analysis assays, and treatment options targeting aberrant genetic pathways. We also propose modified diagnostic criteria and provide an algorithm for surveillance of patients with neurofibromatosis type 1.

Developmental loss of neurofibromin across distributed neuronal circuits drives excessive grooming in Drosophila

Neurofibromatosis type 1 is a monogenetic disorder that predisposes individuals to tumor formation and cognitive and behavioral symptoms. The neuronal circuitry and developmental events underlying these neurological symptoms are unknown. To better understand how mutations of the underlying gene (NF1) drive behavioral alterations, we have examined grooming in the Drosophila neurofibromatosis 1 model. Mutations of the fly NF1 ortholog drive excessive grooming, and increased grooming was observed in adults when Nf1 was knocked down during development. Furthermore, intact Nf1 Ras GAP-related domain signaling was required to maintain normal grooming. The requirement for Nf1 was distributed across neuronal circuits, which were additive when targeted in parallel, rather than mapping to discrete microcircuits. Overall, these data suggest that broadly-distributed alterations in neuronal function during development, requiring intact Ras signaling, drive key Nf1-mediated behavioral alterations. Thus, global developmental alterations in brain circuits/systems function may contribute to behavioral phenotypes in neurofibromatosis type 1.

An update on the central nervous system manifestations of neurofibromatosis type 1

Neurofibromatosis 1 (NF1) is an autosomal dominant genetic disorder that presents with variable phenotypes as a result of mutations in the neurofibromatosis type 1 (NF1) gene and subsequently, abnormal function of the protein product, neurofibromin. Patients with NF1 are at increased risk for central nervous system (CNS) manifestations including structural, functional, and neoplastic disease. The mechanisms underlying the varied manifestations of NF1 are incompletely understood, but the loss of functional neurofibromin, resulting in sustained activation of the oncoprotein RAS, is responsible for tumorigenesis throughout the body, including the CNS. Much of our understanding of NF1-related CNS manifestations is from a combination of data from animal models and natural history studies of people with NF1 and CNS disease. Data from animal models suggest the importance of both Nf1 mutations and somatic genetic alterations, such as Tp53 loss, for development of neoplasms, as well as the role of the timing of the acquisition of such alterations on the variability of CNS manifestations. A variety of non-neoplastic structural (macrocephaly, hydrocephalus, aqueductal stenosis, and vasculopathy) and functional (epilepsy, impaired cognition, attention deficits, and autism spectrum disorder) abnormalities occur with variable frequency in individuals with NF1. In addition, there is increasing evidence that similar appearing CNS neoplasms in people with and without the NF1 syndrome are due to distinct oncogenic pathways. Gliomas in people with NF1 show alterations in the RAS/MAPK pathway, generally in the absence of BRAF alterations (common to sporadic pilocytic astrocytomas) or IDH or histone H3 mutations (common to diffuse gliomas subsets). A subset of low-grade astrocytomas in these patients remain difficult to classify using standard criteria, and occasionally demonstrate morphologic features resembling subependymal giant cell astrocytomas that afflict patients with tuberous sclerosis complex ("SEGA-like astrocytomas"). There is also emerging evidence that NF1-associated high-grade astrocytomas have frequent co-existing alterations such as ATRX mutations and an alternative lengthening of telomeres (ALT) phenotype responsible for unique biologic properties. Ongoing efforts are seeking to improve diagnostic accuracy for CNS neoplasms in the setting of NF1 versus sporadic tumors. In addition, MEK inhibitors, which act on the RAS/MAPK pathway, continue to be studied as rational targets for the treatment of NF1-associated tumors, including CNS tumors.

Validating indicators of CNS disorders in a swine model of neurological disease

Genetically modified swine disease models are becoming increasingly important for studying molecular, physiological and pathological characteristics of human disorders. Given the limited history of these model systems, there remains a great need for proven molecular reagents in swine tissue. Here, to provide a resource for neurological models of disease, we validated antibodies by immunohistochemistry for use in examining central nervous system (CNS) markers in a recently developed miniswine model of neurofibromatosis type 1 (NF1). NF1 is an autosomal dominant tumor predisposition disorder stemming from mutations in NF1, a gene that encodes the Ras-GTPase activating protein neurofibromin. Patients classically present with benign neurofibromas throughout their bodies and can also present with neurological associated symptoms such as chronic pain, cognitive impairment, and behavioral abnormalities. As validated antibodies for immunohistochemistry applications are particularly difficult to find for swine models of neurological disease, we present immunostaining validation of antibodies implicated in glial inflammation (CD68), oligodendrocyte development (NG2, O4 and Olig2), and neuron differentiation and neurotransmission (doublecortin, GAD67, and tyrosine hydroxylase) by examining cellular localization and brain region specificity. Additionally, we confirm the utility of anti-GFAP, anti-Iba1, and anti-MBP antibodies, previously validated in swine, by testing their immunoreactivity across multiple brain regions in mutant NF1 samples. These immunostaining protocols for CNS markers provide a useful resource to the scientific community, furthering the utility of genetically modified miniswine for translational and clinical applications.

Guanfacine treatment improves ADHD phenotypes of impulsivity and hyperactivity in a neurofibromatosis type 1 mouse model

Background

Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder with a mutation in one copy of the neurofibromin gene (NF1^+/−). Even though approximately 40–60% of children with NF1 meet the criteria for attention deficit hyperactivity disorder (ADHD), very few preclinical studies, if any, have investigated alterations in impulsivity and risk-taking behavior. Mice with deletion of a single NF1 gene (Nf1^+/−) recapitulate many of the phenotypes of NF1 patients.

Methods

We compared wild-type (WT) and Nf1^+/− mouse strains to investigate differences in impulsivity and hyperactivity using the delay discounting task (DDT), cliff avoidance reaction (CAR) test, and open field. We also investigated whether treatment with the clinically effective alpha-2A adrenergic receptor agonist, guanfacine (0.3 mg/kg, i.p.), would reverse deficits observed in behavioral inhibition.

Results

Nf1^+/− mice chose a higher percentage of smaller rewards when both 10- and 20-s delays were administered compared to WT mice, suggesting Nf1^+/− mice are more impulsive. When treated with guanfacine (0.3 mg/kg, i.p.), Nf1^+/− mice exhibited decreased impulsive choice by waiting for the larger, delayed reward. Nf1^+/− mice also exhibited deficits in behavioral inhibition compared to WT mice in the CAR test by repetitively entering the outer edge of the platform where they risk falling. Treatment with guanfacine ameliorated these deficits. In addition, Nf1^+/− mice exhibited hyperactivity as increased distance was traveled compared to WT controls in the open field. This hyperactivity in Nf1^+/− mice was reduced with guanfacine pre-treatment.

Conclusions

Overall, our study confirms that Nf1^+/− mice exhibit deficits in behavioral inhibition in multiple contexts, a key feature of ADHD, and can be used as a model system to identify alterations in neural circuitry associated with symptoms of ADHD in children with NF1.

Attention Deficit Predicts Intellectual Functioning in Children with Neurofibromatosis Type 1

Aims

Attention deficit hyperactivity disorder (ADHD) is one of the most frequent neurocognitive impairments in neurofibromatosis type 1 (NF1) and a well-known risk factor for intellectual dysfunction in general. Since NF1 is per se associated with intellectual difficulties, this comorbidity may be crucial for the cognitive development of affected patients. In our study, we investigated if attention deficits are associated with intellectual functioning in NF1 and if children with NF1 plus ADHD differ in their intellectual and attention profiles from children affected by NF1-only or ADHD only.

Methods

111 children aged between 6 and 12 years (53 NF1 plus ADHD, 28 NF1-only, 30 ADHD-only) performed the German version of the intelligence test WISC-IV and a continuous performance test (T.O.V.A.) to assess attention functions. Parents completed questionnaires about everyday attention and executive functions (Conners 3®, BRIEF).

Results

Children with NF1 plus ADHD showed significantly lower intelligence test scores (full-scale IQ: 89.39 [1.40]) than patients with NF1-only (full-scale IQ: 101.14 [1.98]; p < .001), and intellectual functioning correlated significantly with attention performance in NF1 (p < .001). As compared to NF1-only, attention, and executive functioning were impaired on several dimensions (T.O.V.A., Conners 3® and BRIEF) in NF1 plus ADHD. ADHD-only was associated with significantly higher problem scores regarding hyperactivity/impulsivity and inattention (Conners 3®). NF1-only was associated with inattentiveness when compared to the normative sample of the T.O.V.A.

Conclusion

NF1 is associated with variable attention problems. Severe attention deficits appear to be a risk factor for intellectual dysfunction in NF1, more than NF1 without attention deficit. NF1 plus ADHD presents a specific cognitive profile, which differs from that of NF1 and from neurotypical ADHD.

NF1-cAMP signaling dissociates cell type-specific contributions of striatal medium spiny neurons to reward valuation and motor control

The striatum plays a fundamental role in motor learning and reward-related behaviors that are synergistically shaped by populations of D1 dopamine receptor (D1R)- and D2 dopamine receptor (D2R)-expressing medium spiny neurons (MSNs). How various neurotransmitter inputs converging on common intracellular pathways are parsed out to regulate distinct behavioral outcomes in a neuron-specific manner is poorly understood. Here, we reveal that distinct contributions of D1R-MSNs and D2R-MSNs towards reward and motor behaviors are delineated by the multifaceted signaling protein neurofibromin 1 (NF1). Using genetic mouse models, we show that NF1 in D1R-MSN modulates opioid reward, whereas loss of NF1 in D2R-MSNs delays motor learning by impeding the formation and consolidation of repetitive motor sequences. We found that motor learning deficits upon NF1 loss were associated with the disruption in dopamine signaling to cAMP in D2R-MSN. Restoration of cAMP levels pharmacologically or chemogenetically rescued the motor learning deficits seen upon NF1 loss in D2R-MSN. Our findings illustrate that multiplex signaling capabilities of MSNs are deployed at the level of intracellular pathways to achieve cell-specific control over behavioral outcomes.

A mouse genetic study reveals that the multifaceted signaling protein neurofibromin (known for its role in the human genetic disease neurofibromatosis type 1) plays a key role in differential routing of motor and reward signals in populations of striatal medium spiny neurons.

Optical dopamine monitoring with dLight1 reveals mesolimbic phenotypes in a mouse model of neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder whose neurodevelopmental symptoms include impaired executive function, attention, and spatial learning and could be due to perturbed mesolimbic dopaminergic circuitry. However, these circuits have never been directly assayed in vivo. We employed the genetically encoded optical dopamine sensor dLight1 to monitor dopaminergic neurotransmission in the ventral striatum of NF1 mice during motivated behavior. Additionally, we developed novel systemic AAV vectors to facilitate morphological reconstruction of dopaminergic populations in cleared tissue. We found that NF1 mice exhibit reduced spontaneous dopaminergic neurotransmission that was associated with excitation/inhibition imbalance in the ventral tegmental area and abnormal neuronal morphology. NF1 mice also had more robust dopaminergic and behavioral responses to salient visual stimuli, which were independent of learning, and rescued by optogenetic inhibition of non-dopaminergic neurons in the VTA. Overall, these studies provide a first in vivo characterization of dopaminergic circuit function in the context of NF1 and reveal novel pathophysiological mechanisms.

Neurofibromatosis type 1 (Nf1)-mutant mice exhibit increased sleep fragmentation

Neurofibromatosis type 1 (NF1) is a neurodevelopmental disorder in which affected children and adults are at a higher risk of sleep disorders. In an effort to identify potential sleep disturbances in a small animal model, we used a previously reported Nf1 conditional knockout (Nf1^CKO ) mouse strain. In contrast to Nf1 mutant flies, the distribution of vigilance states was intact in Nf1^CKO mice. However, Nf1^CKO mice exhibited increased non-REM sleep (NREM)-to-wake and wake-to-NREM transitions. This sleep disruption was accompanied by decreased bout durations during awake and NREM sleep states under both light and dark conditions. Moreover, Nf1^CKO mice have higher percentage delta power during awake and NREM sleep states under all light conditions. Taken together, Nf1^CKO mice phenocopy some of the sleep disturbances observed in NF1 patients and provide a tractable platform to explore the molecular mechanisms governing sleep abnormalities in NF1.

Neurofibromatosis type 1 as a model system to study molecular mechanisms of autism spectrum disorder symptoms

Neurofibromatosis type 1 (NF1) is monogenic neurodevelopmental disorder caused by mutation of NF1 gene, which leads to increased susceptibility to various tumors formations. Additionally, majority of patients with NF1 are experience high incidence of cognitive deficits. Particularly, we review the growing number of reports demonstrated a higher incidence of autism spectrum disorder (ASD) in individuals with NF1. In this review we also discuss face validity of preclinical Nf1 mouse models. Then we describe discoveries from these animal models that have uncovered the deficiencies in the regulation of Ras and other intracellular pathways as critical mechanisms underlying the Nf1 cognitive problems. We also summarize and interpret recent preclinical and clinical studies that point toward potential pharmacological therapies for NF1 patients.

Height Growth Impairment in Children With Neurofibromatosis Type 1 Is Characterized by Decreased Pubertal Growth Velocity in Both Sexes

Previous studies have suggested that children with neurofibromatosis type 1 are shorter than their unaffected counterparts as an effect of a germline NF1 gene mutation. The pathophysiology of this effect is still uncertain. The purpose of this study was to characterize longitudinal growth in children with neurofibromatosis type 1 in order to assess growth velocity and its influence on stature. Longitudinal height data were collected for 188 patients with a confirmed clinical diagnosis of neurofibromatosis type 1. Children with neurofibromatosis type 1 had population mean heights statistically different from the general population, with a reduced peak height velocity during pubertal growth. In addition, there were no significant differences in the timing of peak height velocity during puberty between the general population and those with neurofibromatosis type 1. These data demonstrate that short stature in neurofibromatosis type 1 is due in part to subnormal height acquisition during puberty.

Effects of methylphenidate on cognition and behaviour in children with neurofibromatosis type 1: a study protocol for a randomised placebo-controlled crossover trial

INTRODUCTION

Dopamine dysregulation has been identified as a key modulator of behavioural impairment in neurofibromatosis type 1 (NF1) and a potential therapeutic target. Preclinical research demonstrates reduced dopamine in the brains of genetically engineered NF1 mouse strains is associated with reduced spatial-learning and attentional dysfunction. Methylphenidate, a stimulant medication that increases dopaminergic and noradrenergic neurotransmission, rescued the behavioural and dopamine abnormalities. Although preliminary clinical trials have demonstrated that methylphenidate is effective in treating attention deficit hyperactivity disorder (ADHD) symptoms in children with NF1, its therapeutic effect on cognitive performance is unclear. The primary aim of this clinical trial is to assess the efficacy of methylphenidate for reducing attention deficits, spatial working memory impairments and ADHD symptoms in children with NF1.

METHODS AND ANALYSIS

A randomised, double-blind, placebo-controlled trial of methylphenidate with a two period crossover design. Thirty-six participants with NF1 aged 7-16 years will be randomised to one of two treatment sequences: 6 weeks of methylphenidate followed by 6 weeks of placebo or; 6 weeks of placebo followed by 6 weeks of methylphenidate. Neurocognitive and behavioural outcomes as well as neuroimaging measures will be completed at baseline and repeated at the end of each treatment condition (week 6, week 12). Primary outcome measures are omission errors on the Conners Continuous Performance Test-II (attention), between-search errors on the Spatial Working Memory task from the Cambridge Neuropsychological Test Automated Battery (spatial working memory) and the Inattentive and Hyperactivity/Impulsivity Symptom Scales on the Conners 3-Parent. Secondary outcomes will examine the effect of methylphenidate on executive functions, attention, visuospatial skills, behaviour, fine-motor skills, language, social skills and quality of life.

ETHICS AND DISSEMINATION

This trial has hospital ethics approval and the results will be disseminated through peer-reviewed publications and international conferences.

TRIAL REGISTRATION NUMBER

ACTRN12611000765921.

Emerging therapeutic targets for neurofibromatosis type 1

INTRODUCTION

Neurofibromatosis type 1 (NF1) is an autosomal dominantly inherited tumor predisposition syndrome with an incidence of one in 3000-4000 individuals with no currently effective therapies. The NF1 gene encodes neurofibromin, which functions as a negative regulator of RAS. NF1 is a chronic multisystem disorder affecting many different tissues. Due to cell-specific complexities of RAS signaling, therapeutic approaches for NF1 will likely have to focus on a particular tissue and manifestation of the disease. Areas covered: We discuss the multisystem nature of NF1 and the signaling pathways affected due to neurofibromin deficiency. We explore the cell-/tissue-specific molecular and cellular consequences of aberrant RAS signaling in NF1 and speculate on their potential as therapeutic targets for the disease. We discuss recent genomic, transcriptomic, and proteomic studies combined with molecular, cellular, and biochemical analyses which have identified several targets for specific NF1 manifestations. We also consider the possibility of patient-specific gene therapy approaches for NF1. Expert opinion: The emergence of NF1 genotype-phenotype correlations, characterization of cell-specific signaling pathways affected in NF1, identification of novel biomarkers, and the development of sophisticated animal models accurately reflecting human pathology will continue to provide opportunities to develop therapeutic approaches to combat this multisystem disorder.

Neurological comorbidity in children with neurofibromatosis type 1

BACKGROUND

The aim of this study was to determine the frequency of central nervous system comorbidities in children with neurofibromatosis type 1 (NF1).

METHODS

We performed a nationwide survey to investigate neurological comorbidities in 3-15-year-old children with NF1 in Japan by sending questionnaires to pediatricians and pediatric neurologists. A secondary questionnaire was sent to the parents of identified NF1 patients to assess neurological comorbidities including headache, attention deficit-hyperactivity disorder (ADHD) Rating Scale (RS), and the Social Responsiveness Scale 2.

RESULTS

The primary survey identified 760 NF1 patients, and the parents of 565 patients were sent the secondary questionnaire. The parental response rate was 25.7% (145; 63 girls, 81 boys, one unspecified). Among the patients, 42.9% (55/128; 35 girls, 20 boys) were reported to exhibit intellectual problems. On the ADHD-RS, 40.2% (47/117) of NF1 patients aged 6-15 had ADHD (RS score >93rd percentile), with a rate of 47.7% in boys and 30.8% in girls. Furthermore, 20.2% of patients had suspected autism spectrum disorder (29/143; 10 girls, 19 boys), with Social Responsiveness Scale score ≥76. Headache was reported by 49.6% (61/123) of children over 5 years old, and 25.2% (31/123; 10 girls, 21 boys) reported migraine. Other neurological comorbidities included 20 cases of epilepsy (13.8%), 11 cases of optic nerve glioma (7.6%), five cases of brain tumor (3.4%), six cases of cerebrovascular disease (4.1%), and two cases of hydrocephalus (1.4%).

CONCLUSION

Intellectual problems, ADHD, autism spectrum disorder, and migraine are major neurological comorbidities in NF1.

Early development of infants with neurofibromatosis type 1: a case series

Background

Prospective studies of infants at familial risk for autism spectrum disorder (ASD) have yielded insights into the earliest signs of the disorder but represent heterogeneous samples of unclear aetiology. Complementing this approach by studying cohorts of infants with monogenic syndromes associated with high rates of ASD offers the opportunity to elucidate the factors that lead to ASD.

Methods

We present the first report from a prospective study of ten 10-month-old infants with neurofibromatosis type 1 (NF1), a monogenic disorder with high prevalence of ASD or ASD symptomatology. We compared data from infants with NF1 to a large cohort of infants at familial risk for ASD, separated by outcome at age 3 of ASD (n = 34), atypical development (n = 44), or typical development (n = 89), and low-risk controls (n = 75). Domains assessed at 10 months by parent report and examiner observation include cognitive and adaptive function, sensory processing, social engagement, and temperament.

Results

Infants with NF1 showed striking impairments in motor functioning relative to low-risk infants; this pattern was seen in infants with later ASD from the familial cohort (HR-ASD). Both infants with NF1 and the HR-ASD group showed communication delays relative to low-risk infants.

Conclusions

Ten-month-old infants with NF1 show a range of developmental difficulties that were particularly striking in motor and communication domains. As with HR-ASD infants, social skills at this age were not notably impaired. This is some of the first information on early neurodevelopment in NF1. Strong inferences are limited by the sample size, but the findings suggest implications for early comparative developmental science and highlight motor functioning as an important domain to inform the development of relevant animal models. The findings have clinical implications in indicating an important focus for early surveillance and remediation in this early diagnosed genetic disorder.

Characterization of early communicative behavior in mouse models of neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is a monogenic neurodevelopmental disease caused by germline loss-of-function mutations in the NF1 tumor suppressor gene. Cognitive impairments are observed in approximately 80% of children with this disease, with 45-60% exhibiting autism spectrum disorder (ASD) symptomatology. In light of the high comorbidity rate between ASD and NF1, we assessed early communicative behavior by maternal-separation induced pup ultrasonic vocalizations (USV) and developmental milestones in two distinct Nf1 genetically engineered models, one modeling clinical germline heterozygous loss of Nf1 function (Nf1^+/- mice), and a second with somatic biallelic Nf1 inactivation in neuroglial progenitor cells (Nf1^GFAP CKO mice). We observed altered USV production in both models: Nf1^+/- mice exhibited both increased USVs across development and alterations in aspects of pitch, while Nf1^GFAP CKO mice demonstrated a decrease in USVs. Developmental milestones, such as weight, pinnae detachment, and eye opening, were not disrupted in either model, indicating the USV deficits were not due to gross developmental delay, and likely reflected more specific alterations in USV circuitry. In this respect, increased whole-brain serotonin was observed in Nf1^+/- mice, but whole-brain levels of dopamine and its metabolites were unchanged at the age of peak USV disruption, and USV alterations did not correlate with overall level of neurofibromin loss. The early communicative phenotypes reported herein should motivate further studies into the risks mediated by haploinsufficiency and biallelic deletion of Nf1 across a full battery of ASD-relevant behavioral phenotypes, and a targeted analysis of underlying circuitry disruptions. Autism Res 2018, 11: 44-58. © 2017 International Society for Autism Research, Wiley Periodicals, Inc.

LAY SUMMARY

Neurofibromatosis type 1 (NF1) is a common neurogenetic disorder caused by mutation of the NF1 gene, in which 80% of affected children exhibit cognitive and behavioral issues. Based on emerging evidence that NF1 may be an autism predisposition gene, we examined autism spectrum disorder (ASD)-relevant early communicative behavior in Nf1 mouse models and observed alterations in both models. The changes in early communicative behavior in Nf1 mutant mice should motivate further studies into the causative factors and potential treatments for ASD arising in the context of NF1.

Dissecting Clinical Heterogeneity in Neurofibromatosis Type 1

Neurofibromatosis type 1 (NF1) is a common neurogenetic disorder in which affected children and adults are predisposed to the development of benign and malignant nervous system tumors. Caused by a germline mutation in the NF1 tumor suppressor gene, individuals with NF1 are prone to optic gliomas, malignant gliomas, neurofibromas, and malignant peripheral nerve sheath tumors, as well as behavioral, cognitive, motor, bone, cardiac, and pigmentary abnormalities. Although NF1 is a classic monogenic syndrome, the clinical features of the disorder and their impact on patient morbidity are variable, even within individuals who bear the same germline NF1 gene mutation. As such, NF1 affords unique opportunities to define the factors that contribute to disease heterogeneity and to develop therapies personalized to a given individual (precision medicine). This review highlights the clinical features of NF1 and the use of genetically engineered mouse models to define the molecular and cellular pathogenesis of NF1-associated nervous system tumors.

Risky Decision Making in Neurofibromatosis Type 1: An Exploratory Study

BACKGROUND

Neurofibromatosis type 1 (NF1) is a monogenic disorder affecting cognitive function. About one third of children with NF1 have attentional disorders, and the cognitive phenotype is characterized by impairment in prefrontally-mediated functions. Mouse models of NF1 show irregularities in GABA release and striatal dopamine metabolism. We hypothesized that youth with NF1 would show abnormal behavior and neural activity on a task of risk-taking reliant on prefrontal-striatal circuits.

METHODS

Youth with NF1 (N=29) and demographically comparable healthy controls (N=22), ages 8-19, were administered a developmentally sensitive gambling task, in which they chose between low-risk gambles with a high probability of obtaining a small reward, and high-risk gambles with a low probability of obtaining a large reward. We used functional magnetic resonance imaging (fMRI) to investigate neural activity associated with risky decision making, as well as age-associated changes in these behavioral and neural processes.

RESULTS

Behaviorally, youth with NF1 tended to make fewer risky decisions than controls. Neuroimaging analyses revealed significantly reduced neural activity across multiple brain regions involved in higher-order semantic processing and motivation (i.e., anterior cingulate, paracingulate, supramarginal, and angular gyri) in patients with NF1 relative to controls during the task. We also observed atypical age-associated changes in neural activity in patients with NF1, such that during risk taking, neural activity tended to decrease with age in controls, whereas it tended to increase with age in patients with NF1.

CONCLUSIONS

Findings suggest that developmental trajectories of neural activity during risky decision-making may be disrupted in youth with NF1.

Oligodendrocyte Nf1 Controls Aberrant Notch Activation and Regulates Myelin Structure and Behavior

The RASopathy neurofibromatosis type 1 (NF1) is one of the most common autosomal dominant genetic disorders. In NF1 patients, neurological issues may result from damaged myelin, and mice with a neurofibromin gene (Nf1) mutation show white matter (WM) defects including myelin decompaction. Using mouse genetics, we find that altered Nf1 gene-dose in mature oligodendrocytes results in progressive myelin defects and behavioral abnormalities mediated by aberrant Notch activation. Blocking Notch, upstream mitogen-activated protein kinase (MAPK), or nitric oxide signaling rescues myelin defects in hemizygous Nf1 mutants, and pharmacological gamma secretase inhibition rescues aberrant behavior with no effects in wild-type (WT) mice. Concomitant pathway inhibition rescues myelin abnormalities in homozygous mutants. Notch activation is also observed in Nf1^+/− mouse brains, and cells containing active Notch are increased in NF1 patient WM. We thus identify Notch as an Nf1 effector regulating myelin structure and behavior in a RASopathy and suggest that inhibition of Notch signaling may be a therapeutic strategy for NF1.

Human stem cell modeling in neurofibromatosis type 1 (NF1)

The future of precision medicine is heavily reliant on the use of human tissues to identify the key determinants that account for differences between individuals with the same disorder. This need is exemplified by the neurofibromatosis type 1 (NF1) neurogenetic condition. As such, individuals with NF1 are born with a germline mutation in the NF1 gene, but may develop numerous distinct neurological problems, ranging from autism and attention deficit to brain and peripheral nerve sheath tumors. Coupled with accurate preclinical mouse models, the availability of NF1 patient-derived induced pluripotent stem cells (iPSCs) provides new opportunities to define the critical factors that underlie NF1-associated nervous system disease pathogenesis and progression. In this review, we discuss the generation and potential applications of iPSC technology to the study of NF1.

Response inhibition in Attention deficit disorder and neurofibromatosis type 1 - clinically similar, neurophysiologically different

There are large overlaps in cognitive deficits occurring in attention deficit disorder (ADD) and neurodevelopmental disorders like neurofibromatosis type 1 (NF1). This overlap is mostly based on clinical measures and not on in-depth analyses of neuronal mechanisms. However, the consideration of such neuronal underpinnings is crucial when aiming to integrate measures that can lead to a better understanding of the underlying mechanisms. Inhibitory control deficits, for example, are a hallmark in ADD, but it is unclear how far there are similar deficits in NF1. We thus compared adolescent ADD and NF1 patients to healthy controls in a Go/Nogo task using behavioural and neurophysiological measures. Clinical measures of ADD-symptoms were not different between ADD and NF1. Only patients with ADD showed increased Nogo errors and reductions in components reflecting response inhibition (i.e. Nogo-P3). Early perceptual processes (P1) were changed in ADD and NF1. Clinically, patients with ADD and NF1 thus show strong similarities. This is not the case in regard to underlying cognitive control processes. This shows that in-depth analyses of neurophysiological processes are needed to determine whether the overlap between ADD and NF1 is as strong as assumed and to develop appropriate treatment strategies.

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.

Conflict processing in juvenile patients with neurofibromatosis type 1 (NF1) and healthy controls - Two pathways to success

Neurofibromatosis Type 1 (NF1) is a monogenetic autosomal-dominant disorder with a broad spectrum of clinical symptoms and is commonly associated with cognitive deficits. Patients with NF1 frequently exhibit cognitive impairments like attention problems, working memory deficits and dysfunctional inhibitory control. The latter is also relevant for the resolution of cognitive conflicts. However, it is unclear how conflict monitoring processes are modulated in NF1. To examine this question in more detail, we used a system neurophysiological approach combining high-density ERP recordings with source localisation analyses in juvenile patients with NF1 and controls during a flanker task. Behaviourally, patients with NF1 perform significantly slower than controls. Specifically on trials with incompatible flanker-target pairings, however, the patients with NF1 made significantly fewer errors than healthy controls. Yet, importantly, this overall successful conflict resolution was reached via two different routes in the two groups. The healthy controls seem to arrive at a successful conflict monitoring performance through a developing conflict recognition via the N2 accompanied by a selectively enhanced N450 activation in the case of perceived flanker-target conflicts. The presumed dopamine deficiency in the patients with NF1 seems to result in a reduced ability to process conflicts via the N2. However, NF1 patients show an increased N450 irrespective of cognitive conflict. Activation differences in the orbitofrontal cortex (BA11) and anterior cingulate cortex (BA24) underlie these modulations. Taken together, juvenile patients with NF1 and juvenile healthy controls seem to accomplish conflict monitoring via two different cognitive neurophysiological pathways.

RASopathies: unraveling mechanisms with animal models

RASopathies are developmental disorders caused by germline mutations in the Ras-MAPK pathway, and are characterized by a broad spectrum of functional and morphological abnormalities. The high incidence of these disorders (∼1/1000 births) motivates the development of systematic approaches for their efficient diagnosis and potential treatment. Recent advances in genome sequencing have greatly facilitated the genotyping and discovery of mutations in affected individuals, but establishing the causal relationships between molecules and disease phenotypes is non-trivial and presents both technical and conceptual challenges. Here, we discuss how these challenges could be addressed using genetically modified model organisms that have been instrumental in delineating the Ras-MAPK pathway and its roles during development. Focusing on studies in mice, zebrafish and Drosophila, we provide an up-to-date review of animal models of RASopathies at the molecular and functional level. We also discuss how increasingly sophisticated techniques of genetic engineering can be used to rigorously connect changes in specific components of the Ras-MAPK pathway with observed functional and morphological phenotypes. Establishing these connections is essential for advancing our understanding of RASopathies and for devising rational strategies for their management and treatment.

Summary: Developmental disorders caused by germline mutations in the Ras-MAPK pathway are called RASopathies. Studies with animal models, including mice, zebrafish and Drosophila, continue to enhance our understanding of these diseases.

Neurofibromin Loss of Function Drives Excessive Grooming in Drosophila

Neurofibromatosis I is a common genetic disorder that results in tumor formation, and predisposes individuals to a range of cognitive/behavioral symptoms, including deficits in attention, visuospatial skills, learning, language development, and sleep, and autism spectrum disorder-like traits. The nf1-encoded neurofibromin protein (Nf1) exhibits high conservation, from the common fruit fly, Drosophila melanogaster, to humans. Drosophila provides a powerful platform to investigate the signaling cascades upstream and downstream of Nf1, and the fly model exhibits similar behavioral phenotypes to mammalian models. In order to understand how loss of Nf1 affects motor behavior in flies, we combined traditional activity monitoring with video analysis of grooming behavior. In nf1 mutants, spontaneous grooming was increased up to 7x. This increase in activity was distinct from previously described dopamine-dependent hyperactivity, as dopamine transporter mutants exhibited slightly decreased grooming. Finally, we found that relative grooming frequencies can be compared in standard activity monitors that measure infrared beam breaks, enabling the use of activity monitors as an automated method to screen for grooming phenotypes. Overall, these data suggest that loss of nf1 produces excessive activity that is manifested as increased grooming, providing a platform to dissect the molecular genetics of neurofibromin signaling across neuronal circuits.

ADHD-associated dopamine transporter, latrophilin and neurofibromin share a dopamine-related locomotor signature in Drosophila

Attention-deficit/hyperactivity disorder (ADHD) is a common, highly heritable neuropsychiatric disorder with hyperactivity as one of the hallmarks. Aberrant dopamine signaling is thought to be a major theme in ADHD, but how this relates to the vast majority of ADHD candidate genes is illusive. Here we report a Drosophila dopamine-related locomotor endophenotype that is shared by pan-neuronal knockdown of orthologs of the ADHD-associated genes Dopamine transporter (DAT1) and Latrophilin (LPHN3), and of a gene causing a monogenic disorder with frequent ADHD comorbidity: Neurofibromin (NF1). The locomotor signature was not found in control models and could be ameliorated by methylphenidate, validating its relevance to symptoms of the disorder. The Drosophila ADHD endophenotype can be further exploited in high throughput to characterize the growing number of candidate genes. It represents an equally useful outcome measure for testing chemical compounds to define novel treatment options.

Skeletal muscle and motor deficits in Neurofibromatosis Type 1

Neurofibromatosis Type 1 (NF1) is a genetic neurocutaneous disorder with multisystem manifestations, including a predisposition to tumor formation and bone dysplasias. Studies over the last decade have shown that NF1 can also be associated with significant motor deficits, such as poor coordination, low muscle tone, and easy fatigability. These have traditionally been ascribed to developmental central nervous system and cognitive deficits. However, recent preclinical studies have also illustrated a primary role for the NF1 gene product in muscle growth and metabolism; these findings are consistent with clinical studies demonstrating reduced muscle size and muscle weakness in individuals with NF1. Currently there is no evidence-based intervention for NF1 muscle and motor deficiencies; this review identifies key research areas where improved mechanistic understanding could unlock new therapeutic options.

Elucidating the impact of neurofibromatosis-1 germline mutations on neurofibromin function and dopamine-based learning

Neurofibromatosis type 1 (NF1) is a common autosomal dominant neurologic condition characterized by significant clinical heterogeneity, ranging from malignant cancers to cognitive deficits. Recent studies have begun to reveal rare genotype-phenotype correlations, suggesting that the specific germline NF1 gene mutation may be one factor underlying disease heterogeneity. The purpose of this study was to define the impact of the germline NF1 gene mutation on brain neurofibromin function relevant to learning. Herein, we employ human NF1-patient primary skin fibroblasts, induced pluripotent stem cells and derivative neural progenitor cells (NPCs) to demonstrate that NF1 germline mutations have dramatic effects on neurofibromin expression. Moreover, while all NF1-patient NPCs exhibit increased RAS activation and reduced cyclic AMP generation, there was a neurofibromin dose-dependent reduction in dopamine (DA) levels. Additionally, we leveraged two complementary Nf1 genetically-engineered mouse strains in which hippocampal-based learning and memory is DA-dependent to establish that neuronal DA levels and signaling as well as mouse spatial learning are controlled in an Nf1 gene dose-dependent manner. Collectively, this is the first demonstration that different germline NF1 gene mutations differentially dictate neurofibromin function in the brain.

Neurofibromatosis type 1 and chronic neurological conditions in the United States: an administrative claims analysis

PURPOSE

Neurofibromatosis type 1 has been linked to several neurological conditions, including epilepsy, Parkinson disease, headache, multiple sclerosis, and sleep disturbances, predominantly through case reports and patient series that lack comparison groups. Our objective was to assess whether specific neurological conditions occur more frequently in individuals with neurofibromatosis type 1 versus those without neurofibromatosis type 1.

METHODS

We used the 2006-2010 MarketScan Commercial Claims and Encounters database to examine associations between neurological conditions and neurofibromatosis type 1. The neurofibromatosis type 1 group was identified through ≥2 International Classification of Diseases, Ninth Revision, Clinical Modification neurofibromatosis codes (237.70, 237.71) occurring ≥30 days apart or one inpatient neurofibromatosis code. A nonneurofibromatosis type 1 comparison group was frequency matched to the neurofibromatosis type 1 group on age and enrollment length at a 10:1 ratio. Unconditional logistic regression was employed to calculate adjusted odds ratios and 95% confidence intervals for associations between neurofibromatosis and neurological conditions.

RESULTS

Compared with the nonneurofibromatosis type 1 group (n = 85,790), the neurofibromatosis type 1 group (n = 8,579) had significantly higher odds of health insurance claims for epilepsy (odds ratio: 7.3; 95% confidence interval: 6.4-8.3), Parkinson disease (odds ratio: 3.1; 95% confidence interval: 1.3-7.5), headache (odds ratio: 2.9; 95% confidence interval: 2.6-3.1), multiple sclerosis (odds ratio: 1.9; 95% confidence interval: 1.2-2.9), and sleep disturbances/disorder (odds ratio: 1.4; 95% confidence interval: 1.2-3.6).

CONCLUSION

This large study provides strong evidence for positive associations between several neurological conditions and neurofibromatosis type 1.