Pilot study of a novel computerized task to assess spatial learning in children and adolescents with neurofibromatosis type 1

A Systematic Review on Visual-Processing Deficits in Neurofibromatosis Type 1: What Possible Impact on Learning to Read?

This systematic review aimed to examine the possible implication of visual-perceptual, visuo-attentional and oculomotor processing in the reading deficits frequently experienced by children with Neurofibromatosis type 1 (NF1), as previously shown in dyslexia. Using PRISMA methodological guidelines, we examined 49 studies; most of these reported visual-processing deficits in this population, raising the importance of directly studying the visuo-perceptual and visuo-attentional processes and eye-movement control involved in the learning-to-read process in NF1. The discussion provides a reflection for a better understanding of how visual-processing skills interact with reading deficits in NF1, as well as new avenues for their screening and care.

Neuropsychological factors associated with performance on the rey-osterrieth complex figure test in children with neurofibromatosis type 1

Children with neurofibromatosis type 1 (NF1) are at considerable risk for cognitive difficulties, including visuospatial deficits and executive dysfunction. This study aimed to (1) assess the overall performance of children with NF1 on the Rey-Osterrieth Complex Figure Test (RCFT) compared to unaffected siblings and (2) examine neuropsychological predictors of RCFT performance in children with NF1. A retrospective clinical audit was performed on neuropsychological records from a multidisciplinary NF1 Clinic in Australia. We searched for children that had completed an assessment between 2000 and 2015 which included the RCFT and other neuropsychological outcomes in this study. These included the Wechsler Intelligence Scale for Children, Judgment of Line Orientation (JLO), Tower of London test, Conners ADHD Scales, and the Behavioral Rating Inventory of Executive Function (BRIEF). The study population consisted of 191 children with NF1 aged 6-16 years, and 55 unaffected siblings recruited from a separate study. Results revealed that 62% of children with NF1 performed at or below the first percentile on the RCFT copy, which was significantly worse than their unaffected siblings. Visuospatial skills, parent-rated executive abilities, ADHD symptoms, and intellectual skills all predicted poorer performance on the RCFT copy, however the best fitting multiple regression model only contained the JLO, BRIEF Metacognition Index, and chronological age. The JLO emerged as the strongest predictor of RCFT performance. This study provides evidence that visuospatial deficits are a key driver of reduced RCFT performance in NF1 and that executive skills as well as a younger age are also independent predictors of RCFT performance.

An evaluation of computerized attention and executive function measures for use with school age children with neurofibromatosis type 1

The present study investigated the performance of children with neurofibromatosis type 1 on computerized assessments of attention and executive function. Relations to ADHD symptomatology were also examined. Participants included 37 children (20 male) with NF1 (9-13 years; Mage = 11.02). Participants completed the NIH Toolbox Dimensional Change Card Sort, List Sort Working Memory (LSWM), and Flanker tasks, as well as Cogstate Identification and One Back tests. ADHD symptomatology was assessed using the K-SADS. Average performance was significantly different from the normative mean on every measure, except LSWM. The NIH Toolbox Flanker and Cogstate Identification tasks detected the highest proportion of participants with at least mild difficulty, and the Cogstate Identification task detected the highest proportion of participants with severe difficulty. Analyses revealed significant relations with ADHD symptomatology for two NIH toolbox tasks. The various computerized measures of attention and executive function offer different information when working with school age children with NF1. The NIH Flanker may offer the most room for change and offers face validity, which may be beneficial for clinical trials research. However, the LSWM shows most support for relations with behavioral indicators of attention and executive challenges.

Neurobehavioral sex-related differences in Nf1+/- mice: female show a "camouflaging"-type behavior

BACKGROUND

Neurofibromatosis type 1 (NF1) is an inherited neurocutaneous disorder associated with neurodevelopmental disorders including autism spectrum disorder (ASD). This condition has been associated with an increase of gamma-aminobutyric acid (GABA) neurotransmission and, consequently, an excitation/inhibition imbalance associated with autistic-like behavior in both human and animal models. Here, we explored the influence of biological sex in the GABAergic system and behavioral alterations induced by the Nf1^+/- mutation in a murine model.

METHODS

Juvenile male and female Nf1^+/- mice and their wild-type (WT) littermates were used. Hippocampus size was assessed by conventional toluidine blue staining and structural magnetic resonance imaging (MRI). Hippocampal GABA and glutamate levels were determined by magnetic resonance spectroscopy (MRS), which was complemented by western blot for the GABA(A) receptor. Behavioral evaluation of on anxiety, memory, social communication, and repetitive behavior was performed.

RESULTS

We found that juvenile female Nf1^+/- mice exhibited increased hippocampal GABA levels. Moreover, mutant female displays a more prominent anxious-like behavior together with better memory performance and social behavior. On the other hand, juvenile Nf1^+/- male mice showed increased hippocampal volume and thickness, with a decrease in GABA(A) receptor levels. We observed that mutant males had higher tendency for repetitive behavior.

CONCLUSIONS

Our results suggested a sexually dimorphic impact of Nf1^+/- mutation in hippocampal neurochemistry, and autistic-like behaviors. For the first time, we identified a "camouflaging"-type behavior in females of an animal model of ASD, which masked their autistic traits. Accordingly, like observed in human disorder, in this animal model of ASD, females show larger anxiety levels but better executive functions and production of normative social patterns, together with an imbalance of inhibition/excitation ratio. Contrary, males have more externalizing disorders, such as hyperactivity and repetitive behaviors, with memory deficits. The ability of females to camouflage their autistic traits creates a phenotypic evaluation challenge that mimics the diagnosis difficulty observed in humans. Thus, we propose the study of the Nf1^+/- mouse model to better understand the sexual dimorphisms of ASD phenotypes and to create better diagnostic tools.

A preliminary study of the different memory systems in neurofibromatosis type 1: What is impaired and what is spared?

BACKGROUND

Since 1990's, the cognitive profile of children with a neurofibromatosis type 1 (NF1) has been refined by many different studies. Children with NF1 may exhibit a variety of cognitive dysfunctions. Memory difficulties have been reported, but the results are contradictory and, compared to other cognitive functions, memory has been less evaluated.

OBJECTIVE

The aim of this study was to investigate the memory profile in NF1 with a particular population, children with NF1 without attention deficit hyperactivity disorder (ADHD).

METHODS

Eighteen children with NF1 without ADHD and eighteen typically developing aged from 8 to 12.6 years were compared in terms of both their verbal and visual working memory, anterograde memory, and procedural perceptual-motor memory. We also assessed semantic and autobiographical memory.

RESULTS

Our results indicate the existence of memory difficulties in children with NF1 without ADHD in verbal working and anterograde memory but not in terms of the visual domain. They also experienced difficulties recalling personal memories but these were improved by cueing. However, semantic memory and procedural perceptual-motor memory was preserved.

CONCLUSIONS

These results highlight a difference between memory systems in children with NF1 without ADHD and the importance to assess the different memory systems, the nature of information and the processes in long-term memory in NF1 population. However, our results raise questions about the possible links between these difficulties and the executive functions. The specifics of memory profile in children with NF1 must be taken into consideration in these children's clinical follow-up, in order to understand their learning difficulties and to make adaptations to their care.

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.

Verbal learning and memory in youth with neurofibromatosis type 1 and plexiform neurofibromas: Relationships with disease severity

AIM

To provide a comprehensive characterization of verbal learning and memory (VLM) abilities in youth with neurofibromatosis type 1 (NF1) and plexiform neurofibromas (PNs) and to evaluate disease severity as a predictor of VLM functioning over time.

METHOD

As part of a longitudinal natural history study, youth with NF1 and PNs were administered repeat neuropsychological assessments, including measures of VLM and ratings of NF1 disease severity completed by a medical professional. This sub-study analyzed data from 89 patients (M age baseline = 13.1, SD = 4.3 years, range 6-24 years) who had completed tests of VLM abilities and verbal attention at either baseline and/or 36 months.

RESULTS

VLM scores across the sample fell predominantly within the average range of functioning at both time points. However, relative to peers with mild NF1 disease severity, youth with moderate/severe NF1 disease showed lower functioning across multiple VLM domains at 36 months, even after controlling for the effects of verbal attention.

INTERPRETATION

Exclusive use of overall domain scores does not fully characterize VLM functioning in youth with NF1 and PNs. Additionally, children and adolescents with more severe NF1 disease should be monitored more closely for verbal memory challenges and targeted for interventions.

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.

Adolescents and young adults with neurofibromatosis type 1: A descriptive study of adaptive functioning

Neurofibromatosis type 1 (NF1) is a genetic syndrome affecting about 1 in 3500 individuals; many of those affected have plexiform neurofibroma (pNF) tumors and associated symptoms and complications. Furthermore, learning and attention problems, as well as deficits in adaptive functioning, are common, often beginning in early childhood. This study aimed to describe adaptive functioning and to examine relationships between adaptive functioning and cognitive and academic variables and level of independence among adolescents and young adults (AYA) with NF1 and pNF tumors. Fifty-five AYA aged 16-31 years participated in a series of neuropsychological evaluations while parents completed the Vineland Adaptive Behavior Scales (VABS-II) as part of a larger natural history study. Over one-third (35%) of AYA were neither in school nor employed. Mean VABS-II daily living and socialization scores were low average while mean Verbal and Performance IQ scores were average. VABS-II scores were positively correlated with processing speed, executive functioning, and working memory scores. Verbal IQ was the only significant predictor of work/school status. Identification of the correlates and predictors of adaptive functioning and life achievement can help guide healthcare providers with the early identification of risk factors and possible areas for intervention.

Visual spatial learning outcomes for clinical trials in neurofibromatosis type 1

Cognitive problems are common in children with neurofibromatosis type 1, representing a significant source of lifelong morbidity. Assessment of cognitive function has been challenging in the setting of clinical trials. Spatial learning deficits may be an important target for cognitive interventions. We leveraged a large, international cognitive study in affected children with NF1 treated with lovastatin to assess spatial learning using the “Arena Maze”, a portable, computerized task that allows for retesting in the same environment. As with the parent study, spatial learning assessed with this task did not improve with lovastatin treatment.

Visuoperceptual Impairment in Children with NF1: From Early Visual Processing to Procedural Strategies

Visual-spatial impairment has long been considered a hallmark feature of neurofibromatosis type 1 (NF1). No study investigating the cognitive and neuropsychological profile of NF1 used the Rey Complex Figure Test (RCFT) task as the primary measure of visual-perceptual abilities taking into consideration all functions involved including the strategic processing style. We compared 18 children with NF1, 17 siblings (S), and 18 typically developing children (TD) at intelligence scale and RCFT copy, recall, and recognition trials; we also evaluated the copy strategy as a measure of a visual-processing style. Children with NF1 had normal total IQ, with cognitive weaknesses in the perceptual organization and working memory in line with the existing literature. At the RCFT copy, immediate and delay recall scores are significantly lower in NF1 than S and TD, while recognition is in the normal range in all groups. Copy style was poor and less efficient in children with NF1 and correlated to copy and recall ability, but the effect of the group in the RCFT copy and recall remained significantly controlling for strategic approach. The present study confirms visuospatial impairment in children with NF1, due to a deficit in perceptual analysis of shape and their spatial features, in visuomotor integration efficiency and strategies, in recall memory, while recognition memory is preserved. A more configural/holistic style may facilitate both the visual-perceptual and visuomotor ability and the recall process. Visuoperceptual impairment in NF1 seems to be a unified process from early visual processing to higher order functions (planning, strategy, and executive functioning).

Measurement considerations in pediatric research on autism spectrum disorders

Studying Autism Spectrum Disorders (ASD) in genetic syndromes has gained interest in the scientific community as a way to elucidate mechanisms and symptom profiles to understand ASD more broadly. Appropriate and adequate measurement of constructs, symptomatology, and outcomes in clinical research is of vital importance in establishing the prevalence of such symptoms and measuring change in symptoms in the context of clinical trials. As such, we provide an overview of the prevalence of ASD, present current diagnostic guidelines, discuss important comorbidities to consider, describe current assessment strategies in assessing ASD, and discuss these within the context of a specific genetic condition to highlight how ASD can be best evaluated.

Systematic Review and Meta-analysis of Executive Functions in Preschool and School-Age Children With Neurofibromatosis Type 1

OBJECTIVES

Neurofibromatosis type 1 (NF1) is a genetic disorder in which the most frequent complication in children is learning disabilities. Over the past decade, growing arguments support the idea that executive dysfunction is a core deficit in children with NF1. However, some data remain inconsistent. The aim of this study was to determine the magnitude of impairment for each executive function (EF) and clarify the impact of methodological choices and participant's characteristics on EFs.

METHODS

In this meta-analysis, 19 studies met the selection criteria and were included with data from a total of 805 children with NF1 and 667 controls. Based on the Diamond's model (2013), EF measures were coded separately according to the following EF components: working memory, inhibitory control, cognitive flexibility, planning/problem solving. The review protocol was registered with PROSPERO (International prospective register of systematic reviews; CRD42017068808).

RESULTS

A significant executive dysfunction in children with NF1 is demonstrated. Subgroup analysis showed that the impairment varied as a function of the specific component of executive functioning. The effect size for working memory and planning/problem solving was moderate whereas it was small for inhibitory control and cognitive flexibility. Executive dysfunction seems to be greater with increasing age whereas assessment tool type, intellectual performance, attention deficit hyperactivity disorder and control group composition did not seem to affect EF results.

CONCLUSIONS

EF deficits are a core feature in children with NF1 and an early identification of executive dysfunctions is essential to limit their impact on the quality of life. (JINS, 2018, 24, 977-994).

Neurofibromatosis Clinical Trial Consortium

Neurofibromatosis type 1 and type 2, affecting both children and adults, often results in devastating complications. The rapid unravelling of the genetic underpinnings of these unique disorders has led to the development of novel therapies, especially molecular-targeted therapies. To facilitate clinical trial development, the Neurofibromatosis Clinical Trial Consortium (NFCTC) was established in 2006 by the Department of Defense. Over the past decade, the Consortium has successfully completed studies for children and adults with neurofibromatosis type 1 and plexiform neurofibromas, neurocognitive challenges, low-grade gliomas, and malignant peripheral nerve sheath tumors. In addition, a study for children and adults with neurofibromatosis type 2 and acoustic schwannomas is near completion. The NFCTC has now been expanded to 19 sites in the United Stated and Australia. Mechanisms have been put in place to work closely with other consortia, foundations, and industry to expeditiously translate preclinical discoveries into clinical trials.

Visuoperceptual processing in children with neurofibromatosis type 1: True deficit or artefact?

Impairments in visuoperceptual processing have long been considered a hallmark deficit of individuals with Neurofibromatosis type 1 (NF1). However, it is unclear which specific visuoperceptual subprocesses are impaired and whether impairments on these tasks really result from visuoperceptual impairments or rather from confounding factors like Executive Functioning (EF) impairments, lower intelligence (IQ) and/or co-occurring symptoms of Autism Spectrum Disorder (ASD). To answer these questions, we administered four visuoperceptual tasks and two control tasks in 39 children with NF1, 52 typically developing children and 52 children with ASD (8-18 years), all matched for age and gender. Furthermore, EF, IQ, and symptoms of ASD were assessed. Children with NF1 displayed intact visual form discrimination and intact information integration along the dorsal visual pathway. Moreover, their reduced performance on a task requiring integration of information along the ventral visual stream and their more detail-oriented processing style appeared to result from confounding EF impairments and not from visuoperceptual impairments per se. The co-occurring ASD symptoms and lower IQ of the children with NF1 did not impact substantially upon their visuoperceptual performance. These findings point to the large impact of EF impairments on the performance of visuoperceptual task and suggest that individuals with NF1 show intact visual form discrimination, intact visual integration, and typical visual processing style when potential confounding factors are controlled for. This may have large repercussions for the interpretation of other findings on visuoperceptual processing in individuals with NF1. © 2017 Wiley Periodicals, Inc.

Parent and Teacher Perspectives on Emerging Executive Functioning in Preschoolers With Neurofibromatosis Type 1: Comparison to Unaffected Children and Lab-Based Measures

Objective

Children with neurofibromatosis type 1 (NF1) are at risk for executive functioning (EF) challenges, with little research with preschoolers.

Methods

EF was examined using parent and teacher ratings of preschool-aged children with NF1 ( n  = 26) and parent ratings of unaffected children ( n  = 37) on the Behavior Rating Inventory for Executive Functioning-Preschool Form. Relations to performance on laboratory measures were also examined.

Results

Based on parent ratings, children with NF1 had more dysfunction than the normative mean on the Working Memory (WM) scale and Emergent Metacognition Index (EMI). Teacher ratings indicated greater dysfunction than the normative mean on the WM and Planning/Organization scales, EMI, and General Executive Composite. Children with NF1 showed more difficulties than unaffected children on the WM scale. Teacher report of WM was significantly correlated with Differential Ability Scales-Second Edition Digits Forward performance.

Conclusions

WM emerged as an area of difficulty for young children with NF1.

Executive functioning deficits in children with neurofibromatosis type 1: The influence of intellectual and social functioning

The aim of this study was to provide a broad picture of Executive Functioning (EF) in NF1 children, while taking into account their lower average IQ and increased Autism Spectrum Disorder (ASD) symptoms. This was done by administering an extended battery of tasks and questionnaires, designed to reduce task impurity, that measures five EF domains (inhibition, cognitive flexibility, working memory, generativity and planning) in a laboratory setting and in daily life. Data are presented for 42 age- and gender-matched NF1, 52 typically developing, and 52 ASD children (8-18 years). Our results indicated that although EF is highly influenced by IQ and severity of ASD symptoms, EF deficits seem to be a core feature of NF1 and not merely a secondary effect of a lower IQ and/or increased ASD symptoms. However, additional research is needed to confirm these findings.

Behavioral and cognitive outcomes for clinical trials in children with neurofibromatosis type 1

OBJECTIVE

To evaluate the appropriateness of cognitive and behavioral outcome measures in clinical trials in neurofibromatosis type 1 (NF1) by analyzing the degree of deficits compared to reference groups, test-retest reliability, and how scores correlate between outcome measures.

METHODS

Data were analyzed from the Simvastatin for cognitive deficits and behavioral problems in patients with neurofibromatosis type 1 (NF1-SIMCODA) trial, a randomized placebo-controlled trial of simvastatin for cognitive deficits and behavioral problems in children with NF1. Outcome measures were compared with age-specific reference groups to identify domains of dysfunction. Pearson r was computed for before and after measurements within the placebo group to assess test-retest reliability. Principal component analysis was used to identify the internal structure in the outcome data.

RESULTS

Strongest mean score deviations from the reference groups were observed for full-scale intelligence (-1.1 SD), Rey Complex Figure Test delayed recall (-2.0 SD), attention problems (-1.2 SD), and social problems (-1.1 SD). Long-term test-retest reliability were excellent for Wechsler scales (r > 0.88), but poor to moderate for other neuropsychological tests (r range 0.52-0.81) and Child Behavioral Checklist subscales (r range 0.40-0.79). The correlation structure revealed 2 strong components in the outcome measures behavior and cognition, with no correlation between these components. Scores on psychosocial quality of life correlate strongly with behavioral problems and less with cognitive deficits.

CONCLUSIONS

Children with NF1 show distinct deficits in multiple domains. Many outcome measures showed weak test-retest correlations over the 1-year trial period. Cognitive and behavioral outcomes are complementary. This analysis demonstrates the need to include reliable outcome measures on a variety of cognitive and behavioral domains in clinical trials for NF1.

Cognitive and behavioral problems in children with neurofibromatosis type 1: challenges and future directions

Cognitive and behavioral disorders affect nearly 80% of all children with the neurofibromatosis type 1 inherited cancer syndrome, and are among the most significant clinical manifestations for patients and their families. One of the barriers to successful therapeutic intervention is the wide spectrum of clinical phenotypic expression, ranging from visuospatial learning problems to social perceptual deficits (autism). Leveraging numerous small-animal models of neurofibromatosis type 1, several promising targets have been identified to treat the learning, attention, and autism spectrum phenotypes in this at-risk population. In this review, we provide an up-to-date summary of our current understanding of these disorders in NF1, and propose future research directions aimed at designing more effective therapeutic approaches and clinical trials.

Simvastatin for cognitive deficits and behavioural problems in patients with neurofibromatosis type 1 (NF1-SIMCODA): a randomised, placebo-controlled trial

BACKGROUND

Neurofibromatosis type 1 is a common genetic disorder characterised by neurocutaneous manifestations and cognitive and behavioural problems. Statins were shown to reduce analogous learning deficits in a mouse model of the disease, but a short-term trial in humans was inconclusive. We aimed to assess the use of simvastatin for the improvement of cognitive and behavioural deficits in children with neurofibromatosis type 1 for 12 months.

METHODS

In this randomised, double-masked, placebo-controlled trial, we recruited children with genetically confirmed neurofibromatosis type 1 aged 8-16 years from two national referral centres in the Netherlands and Belgium. Those with symptomatic CNS abnormalities or on neurotropic medication, including stimulants, were excluded. Eligible patients were randomly assigned (1:1) via a computer-generated, permuted-block list to simvastatin (10 mg per day in month 1, 20 mg per day in month 2, and 20-40 mg per day in months 3-12) or placebo for 12 months. Investigators, participants, and parents were masked to treatment assignment. Primary outcome measures were full-scale intelligence (Wechsler intelligence scale for children), attention problems (child behaviour checklist, parent-rated [CBCL]), and internalising behavioural problems (CBCL). We did intention-to-treat analyses (of all patients who had outcome data) using linear regression of the 12 month outcome scores, adjusted for baseline performance. This trial is registered with the Netherlands Trial Register, number NTR2150.

FINDINGS

We randomly assigned 84 children to a treatment group (43 to simvastatin, 41 to placebo) between March 9, 2010, and March 6, 2012. We did not assess outcomes in two patients in the placebo group because they needed additional drug therapy. Simvastatin for 12 months had no effect on full-scale intelligence (treatment effect compared with placebo -1·3 IQ points [95% CI -3·8 to 1·3]; p=0·33), attention problems (-1·6 T-score points [-4·3 to 1·0]; p=0·23), and internalising behavioural problems (-0·1 T-score points [-3·3 to 3·1]; p=0·96). 38 (88%) of 43 patients on simvastatin and 39 (95%) of 41 patients on placebo reported adverse events, which were serious in two and four patients, respectively.

INTERPRETATION

12 month simvastatin treatment did not ameliorate cognitive deficits or behavioural problems in children with neurofibromatosis type 1. The use of 20-40 mg simvastatin per day for cognitive enhancement in children with neurofibromatosis type 1 is not recommended.

FUNDING

The Netherlands Organization for Health Research and Development (ZonMw), Research Foundation Flanders (FWO-Vlaanderen), Marguerite-Marie Delacroix Foundation, and the Dutch Neurofibromatosis Association (NFVN).

Behaviour in children with neurofibromatosis type 1: cognition, executive function, attention, emotion, and social competence

AIM

This systematic review aimed to pull together the findings from research into behavioural systems and attention in children with neurofibromatosis type 1 (NF1) and to identify areas that need further study.

METHOD

Relevant papers were identified through searches of electronic databases (MEDLINE, PsycINFO, EMBASE) and manual searches through reference lists. In total, 5746 articles were identified and 57 met the inclusion criteria. The data were synthesized using the narrative approach, as the studies varied considerably in terms of participants and measures.

RESULTS

The results of the review showed that intelligence, academic skills, visuospatial skills, social competence, and attention are impaired in children with NF1. Evidence of deficits in memory, motor functioning, language, and executive functions was less clear.

INTERPRETATION

Research has made marked progress in outlining the behavioural phenotype of NF1. However, although the general areas of impairment are becoming better known, the exact nature of the impairment is still not understood in many areas of behaviour. Care needs to be taken with the way in which behavioural constructs are defined and measured, and the variability of problems in NF1 is a particular challenge. Nevertheless, research is steadily moving towards comprehensive understanding of behaviour in children with NF1.

Neurofibromatosis type 1: modeling CNS dysfunction

Neurofibromatosis type 1 (NF1) is the most common monogenic disorder in which individuals manifest CNS abnormalities. Affected individuals develop glial neoplasms (optic gliomas, malignant astrocytomas) and neuronal dysfunction (learning disabilities, attention deficits). Nf1 genetically engineered mouse models have revealed the molecular and cellular underpinnings of gliomagenesis, attention deficit, and learning problems with relevance to basic neurobiology. Using NF1 as a model system, these studies have revealed critical roles for the NF1 gene in non-neoplastic cells in the tumor microenvironment, the importance of brain region heterogeneity, novel mechanisms of glial growth regulation, the neurochemical bases for attention deficit and learning abnormalities, and new insights into neural stem cell function. Here we review recent studies, presented at a symposium at the 2012 Society for Neuroscience annual meeting, that highlight unexpected cell biology insights into RAS and cAMP pathway effects on neural progenitor signaling, neuronal function, and oligodendrocyte lineage differentiation.

Paired associate learning in children with neurofibromatosis type 1: implications for clinical trials

Studies investigating behavior in mice with a heterozygous null mutation of the NF1 gene (Nf1 (+/-)) have provided critical insights into the molecular and cellular mechanisms underlying cognitive impairments associated with neurofibromatosis type 1 (NF1). Hyperactivation of the Ras-MAPK signaling cascade, which results in increased GABA-mediated inhibition and significantly reduced long-term potentiation, has been proposed as a core mechanism underlying Nf1 (+/-) mice deficits in visuospatial learning and attention. This assertion has been reinforced by preclinical trials that reveal that these impairments can be rescued both at a cognitive and cellular level. We attempted to demonstrate a phenotypic parallel between Nf1 (+/-) mice and children with NF1 using a well-validated measure of visuospatial learning. Children with NF1 (n = 71) and healthy controls (n = 29) were assessed on a computerized paired associate learning task. Interrelationships between visuospatial learning and other cognitive abilities that may influence performance, such as intelligence, attention and visuospatial function, were explored. Children with NF1 displayed significant impairments in visuospatial learning, with reduced initial retention and poorer learning across repeated trials. Importantly, we demonstrated that visuospatial learning was inferior in NF1 even after accounting for group differences in intelligence, sustained attention and visuospatial abilities. We have thus identified impaired visuospatial learning as a core phenotypic feature in children with NF1. These findings imply that hippocampal-based learning networks are dysfunctional in children with NF1 and provide validation for a primary outcome measure for clinical trials aiming to correct aberrant Ras signaling.

Ultrastructural synaptic changes associated with neurofibromatosis type 1: a quantitative analysis of hippocampal region CA1 in a Nf1(+/-) mouse model

Neurofibromatosis type 1 (NF1) is one of the most frequently diagnosed autosomal dominant inherited disorders resulting in neurological dysfunction, including an assortment of learning disabilities and cognitive deficits. To elucidate the neural mechanisms underlying the disorder, we employed a mouse model (Nf1(+/-) ) to conduct a quantitative analysis of ultrastructural changes associated with the NF1 disorder. Using both serial light and electron microscopy, we examined reconstructions of the CA1 region of the hippocampus, which is known to play a central role in many of the dysfunctions associated with NF1. In general, the morphology of synapses in both the Nf1(+/-) and wild-type groups of animals were similar. No differences were observed in synapse per neuron density, pre- and postsynaptic areas, or lengths. However, concave synapses were found to show a lower degree of curvature in the Nf1(+/-) mutant than in the wild type. These results indicate that the synaptic ultrastructure of Nf1(+/-) mice appears relatively normal with the exception of the degree of synaptic curvature in concave synapses, adding further support to the importance of synaptic curvature in synaptic plasticity, learning, and memory.