Evaluation of the basal ganglia in neurofibromatosis type 1

T2 Hyperintensities in Children with Neurofibromatosis Type 1

OBJECTIVE

Areas of increased signal intensity, known as T2 hyperintensities (T2Hs), observed on T2-weighted magnetic resonance imaging (MRI) scans, are linked to a spectrum of brain abnormalities in children with neurofibromatosis type 1 (NF1). Defining the radiological characteristics that distinguish non-neoplastic from neoplastic T2Hs in children with NF1 is crucial. Then, we could identify lesions that were most likely to require oncologic surveillance.

METHODS

We conducted a single-center retrospective review of all available brain MRIs from 98 children with NF1 and 50 healthy pediatric controls. All T2Hs identified on MRI were characterized based on location, imaging features, and the presence of lesion-related symptoms. Subsequently, all T2Hs were classified using newly established criteria and categorized into 3 distinct groups: low-risk tumor lesions, medium-risk tumor lesions, and high-risk tumor lesions. Lesions deemed to be high-risk will be recommended for surgical treatment.

RESULTS

T2Hs were present in 61 (62.2%) individuals of the NF1 cohort. T2Hs were a highly sensitive (100%; 95% confidence interval 92.9%-100.0%) and specific (62.2%; 95% confidence interval 51.9%-71.8%) marker for the diagnosis of NF1. In children aged 4-10, the detection rate of T2Hs is significantly higher than in children under 4 years old and those aged between 10 and 18 (P < 0.05). T2Hs were most frequently located in basal ganglia, cerebellar hemispheres, and brainstem. During the follow-up process, none of the lesions categorized as low-risk or medium-risk tumor lesions progressed to high-risk tumor lesions. Seven patients had high-risk tumor lesions and underwent surgical treatment. The pathological assessment identified 5 cases of glioma among the 7 patients, along with 1 case of gliosis and 1 case of vascular dysplasia.

CONCLUSIONS

Low-risk and medium-risk tumor lesions can both be classified as unidentified bright objects . Unidentified bright objects constituted the majority of T2Hs in children with NF1. High-risk tumor lesions should be considered as probable tumors. With the application of standardized radiologic criteria, a high prevalence of probable brain tumors will be identified in this at-risk population of children, which underscores the importance of vigilant and appropriate oncological surveillance to ensure timely detection and intervention for these tumors.

Social Communication in Ras Pathway Disorders: A Comprehensive Review from Genetics to Behavior in Neurofibromatosis Type 1 and Noonan Syndrome

Neurofibromatosis type 1 (NF1) and Noonan syndrome (NS) are neurogenetic syndromes caused by pathogenetic variants encoding components of the Ras-ERK-MAPK signaling pathway (Ras pathway). NF1 and NS are associated with differences in social communication and related neuropsychiatric risks. During the last decade, there has been growing interest in Ras-linked syndromes as models to understand social communication deficits and autism spectrum disorders. We systematically review the literature between 2010-2023 focusing on the social communication construct of the RDoC framework. We provide an integrative summary of the research on facial and non-facial social communication processes in NF1 and NS across molecular, cellular, neural circuitry, and behavioral domains. At the molecular and cellular levels, dysregulation in the Ras pathway is intricately tied to variations in social communication through changes in GABAergic, glutamatergic, and serotonergic transmission, as well as inhibitory/excitatory imbalance. Neural circuitry typically associated with learning, attention, and memory in NF1 and NS (e.g., cortico-striatal connectivity), is also implicated in social communication. We highlight less researched, potential mechanisms for social communication, such as white matter connectivity and the default mode network. Finally, key gaps in NF1 and NS literature are identified and a roadmap for future research is provided. By leveraging genetic syndromes research, we can understand the mechanisms associated with behaviors and psychiatric disorders.

Joubert Syndrome: Diagnostic Evaluation and Follow-up

The follow-up of a child with genetic syndrome is necessarily multidisciplinary because of the multiplicity of problems and calls for close collaboration between different specialists. The primary objective is the total care of the child and his family, regardless of the rarity and complexity of the disease, to obtain the highest possible degree of mental and physical health and autonomy.

Age-Related Neurodevelopmental Features in Children with Joubert Syndrome

Joubert syndrome (JS) is a rare inherited disorder of central nervous system with neonatal/infantile onset, mainly affecting cerebellum and brainstem, and clinically characterized by agenesis or dysgenesis of the cerebellar vermis with accompanying brainstem malformations. More than 20 disease-causing genes have been associated with JS but a clear genotype–phenotype correlation has not been assessed yet. Diagnosis is usually confirmed by detection of the JS neuroradiological hallmark, the molar tooth sign. Patients with JS typically present with neurological manifestations, moreover, a heterogeneous spectrum of multisystemic anomalies may be observed. Signs and symptoms onset varies according to the age range and clinical diagnosis might become complicated. Moreover, specific neurodevelopmental disorders can be associated with JS such as autism spectrum disorders, attention deficit with hyperactivity, and a wide range of behavioral disturbances. Here, we examined the main neurological and neurodevelopmental features of JS according to an age-dependent mode of presentation. Furthermore, differential diagnosis with other neurological syndromes was closely reviewed.

Atypical connectivity in the cortico-striatal network in NF1 children and its relationship with procedural perceptual-motor learning and motor skills

INTRODUCTION

Neurofibromatosis type 1 (NF1) is considered a model of neurodevelopmental disorder because of the high frequency of learning deficits, especially developmental coordination disorder. In neurodevelopmental disorder, Nicolson and Fawcett formulated the hypothesis of an impaired procedural learning system that has its origins in cortico-subcortical circuits. Our aim was to investigate the relationship between cortico-striatal connectivity and procedural perceptual-motor learning performance and motor skills in NF1 children.

METHODS

Seventeen NF1 and 18 typically developing children aged between 8 and 12 years old participated in the study. All were right-handed and did not present intellectual or attention deficits. In all children, procedural perceptual-motor learning was assessed using a bimanual visuo-spatial serial reaction time task (SRTT) and motor skills using the Movement Assessment Battery for Children (M-ABC). All participants underwent a resting-state functional MRI session. We used a seed-based approach to explore cortico-striatal connectivity in somatomotor and frontoparietal networks. A comparison between the groups' striato-cortical connectivity and correlations between connectivity and learning (SRTT) and motor skills (M-ABC) were performed.

RESULTS

At the behavioral level, SRTT scores are not significantly different in NF1 children compared to controls. However, M-ABC scores are significantly impaired within 9 patients (scores below the 15th percentile). At the cerebral level, NF1 children present a higher connectivity in the cortico-striatal regions mapping onto the right angular gyrus compared to controls. We found that the higher the connectivity values between these regions, differentiating NF1 and controls, the lower the M-ABC scores in the whole sample. No correlation was found for the SRTT scores.

CONCLUSION

NF1 children present atypical hyperconnectivity in cortico-striatal connections. The relationship with motor skills could suggest a sensorimotor dysfunction already found in children with developmental coordination disorder. These abnormalities are not linked to procedural perceptual-motor learning assessed by SRTT.

Focal Areas of High Signal Intensity in Children with Neurofibromatosis Type 1: Expected Evolution on MRI

BACKGROUND AND PURPOSE

Focal areas of high signal intensity are T2WI/T2-FLAIR hyperintensities frequently found on MR imaging of children diagnosed with neurofibromatosis type 1, often thought to regress spontaneously during adolescence or puberty. Due to the risk of tumor in this population, some focal areas of high signal intensity may pose diagnostic problems. The objective of this study was to assess the characteristics and temporal evolution of focal areas of high signal intensity in children with neurofibromatosis type 1 using long-term follow-up with MR imaging.

MATERIALS AND METHODS

We retrospectively examined the MRIs of children diagnosed with neurofibromatosis type 1 using the National Institutes of Health Consensus Criteria (1987), with imaging follow-up of at least 4 years. We recorded the number, size, and surface area of focal areas of high signal intensity according to their anatomic distribution on T2WI/T2-FLAIR sequences. A generalized mixed model was used to analyze the evolution of focal areas of high signal intensity according to age, and separate analyses were performed for girls and boys.

RESULTS

Thirty-nine patients (ie, 285 MR images) with a median follow-up of 7 years were analyzed. Focal areas of high signal intensity were found in 100% of patients, preferentially in the infratentorial white matter (35% cerebellum, 30% brain stem) and in the capsular lenticular region (22%). They measured 15 mm in 95% of cases. They appeared from the age of 1 year; increased in number, size, and surface area to a peak at the age of 7; and then spontaneously regressed by 17 years of age, similarly in girls and boys.

CONCLUSIONS

Focal areas of high signal intensity are mostly small (<15 mm) abnormalities in the posterior fossa or capsular lenticular region. Our results suggest that the evolution of focal areas of high signal intensity is not related to puberty with a peak at the age of 7 years. Knowledge of the predictive evolution of focal areas of high signal intensity is essential in the follow-up of children with neurofibromatosis type 1.

Can the Cognitive Phenotype in Neurofibromatosis Type 1 (NF1) Be Explained by Neuroimaging? A Review

Neurofibromatosis type 1 (NF1) is one of the most frequent monogenetic disorders. It can be associated with cognitive dysfunctions in several domains such as executive functioning, language, visual perception, motor skills, social skills, memory and/or attention. Neuroimaging is becoming more and more important for a clearer understanding of the neural basis of these deficits. In recent years, several studies have used different imaging techniques to examine structural, morphological and functional alterations in NF1 disease. They have shown that NF1 patients have specific brain characteristics such as Unidentified Bright Objects (UBOs), macrocephaly, a higher volume of subcortical structures, microstructure integrity alterations, or connectivity alterations. In this review, which focuses on the studies published after the last 2 reviews of this topic (in 2010 and 2011), we report on recent structural, morphological and functional neuroimaging studies in NF1 subjects, with special focus on those that examine the neural basis of the NF1 cognitive phenotype. Although UBOs are one of the most obvious and visible elements in brain imaging, correlation studies have failed to establish a robust and reproducible link between major cognitive deficits in NF1 and their presence, number or localization. In the same vein, the results among structural studies are not consistent. Functional magnetic resonance imaging (fMRI) studies appear to be more sensitive, especially for understanding the executive function deficit that seems to be associated with a dysfunction in the right inferior frontal areas and the middle frontal areas. Similarly, fMRI studies have found that visuospatial deficits could be associated with a dysfunction in the visual cortex and especially in the magnocellular pathway involved in the processing of low spatial frequency and high temporal frequency. Connectivity studies have shown a reduction in anterior-posterior “long-range” connectivity and a deficit in deactivation in default mode network (DMN) during cognitive tasks. In conclusion, despite the contribution of new imaging techniques and despite relative advancement, the cognitive phenotype of NF1 patients is not totally understood.

Autism-associated Nf1 deficiency disrupts corticocortical and corticostriatal functional connectivity in human and mouse

Children with the autosomal dominant single gene disorder, neurofibromatosis type 1 (NF1), display multiple structural and functional changes in the central nervous system, resulting in neuropsychological cognitive abnormalities. Here we assessed the pathological functional organization that may underlie the behavioral impairments in NF1 using resting-state functional connectivity MRI. Coherent spontaneous fluctuations in the fMRI signal across the entire brain were used to interrogate the pattern of functional organization of corticocortical and corticostriatal networks in both NF1 pediatric patients and mice with a heterozygous mutation in the Nf1 gene (Nf1^+/-). Children with NF1 demonstrated abnormal organization of cortical association networks and altered posterior-anterior functional connectivity in the default network. Examining the contribution of the striatum revealed that corticostriatal functional connectivity was altered. NF1 children demonstrated reduced functional connectivity between striatum and the frontoparietal network and increased striatal functional connectivity with the limbic network. Awake passive mouse functional connectivity MRI in Nf1^+/- mice similarly revealed reduced posterior-anterior connectivity along the cingulate cortex as well as disrupted corticostriatal connectivity. The striatum of Nf1^+/- mice showed increased functional connectivity to somatomotor and frontal cortices and decreased functional connectivity to the auditory cortex. Collectively, these results demonstrate similar alterations across species, suggesting that NF1 pathogenesis is linked to striatal dysfunction and disrupted corticocortical connectivity in the default network.

Imaging genetics in neurodevelopmental psychopathology

Neurodevelopmental disorders are defined by highly heritable problems during development and brain growth. Attention-deficit/hyperactivity disorder (ADHD), autism spectrum disorders (ASDs), and intellectual disability (ID) are frequent neurodevelopmental disorders, with common comorbidity among them. Imaging genetics studies on the role of disease-linked genetic variants on brain structure and function have been performed to unravel the etiology of these disorders. Here, we reviewed imaging genetics literature on these disorders attempting to understand the mechanisms of individual disorders and their clinical overlap. For ADHD and ASD, we selected replicated candidate genes implicated through common genetic variants. For ID, which is mainly caused by rare variants, we included genes for relatively frequent forms of ID occurring comorbid with ADHD or ASD. We reviewed case-control studies and studies of risk variants in healthy individuals. Imaging genetics studies for ADHD were retrieved for SLC6A3/DAT1, DRD2, DRD4, NOS1, and SLC6A4/5HTT. For ASD, studies on CNTNAP2, MET, OXTR, and SLC6A4/5HTT were found. For ID, we reviewed the genes FMR1, TSC1 and TSC2, NF1, and MECP2. Alterations in brain volume, activity, and connectivity were observed. Several findings were consistent across studies, implicating, for example, SLC6A4/5HTT in brain activation and functional connectivity related to emotion regulation. However, many studies had small sample sizes, and hypothesis-based, brain region-specific studies were common. Results from available studies confirm that imaging genetics can provide insight into the link between genes, disease-related behavior, and the brain. However, the field is still in its early stages, and conclusions about shared mechanisms cannot yet be drawn.

GABA deficiency in NF1: A multimodal [11C]-flumazenil and spectroscopy study

OBJECTIVE

To provide a comprehensive investigation of the γ-aminobutyric acid (GABA) system in patients with neurofibromatosis type 1 (NF1) that allows understanding the nature of the GABA imbalance in humans at pre- and postsynaptic levels.

METHODS

In this cross-sectional study, we employed multimodal imaging and spectroscopy measures to investigate GABA type A (GABAA) receptor binding, using [(11)C]-flumazenil PET, and GABA concentration, using magnetic resonance spectroscopy (MRS). Fourteen adult patients with NF1 and 13 matched controls were included in the study. MRS was performed in the occipital cortex and in a frontal region centered in the functionally localized frontal eye fields. PET and MRS acquisitions were performed in the same day.

RESULTS

Patients with NF1 have reduced concentration of GABA+ in the occipital cortex (p = 0.004) and frontal eye fields (p = 0.026). PET results showed decreased binding of GABAA receptors in patients in the parieto-occipital cortex, midbrain, and thalamus, which are not explained by decreased gray matter levels.

CONCLUSIONS

Abnormalities in the GABA system in NF1 involve both GABA concentration and GABAA receptor density suggestive of neurodevelopmental synaptopathy with both pre- and postsynaptic involvement.

Abnormal relationship between GABA, neurophysiology and impulsive behavior in neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is a neurodevelopmental disorder characterized by a broad spectrum of cognitive deficits. In particular, executive dysfunction is recognized as a core deficit of NF1, including impairments in executive attention and inhibitory control. Yet, the neural mechanisms behind these important deficits are still unknown. Here, we studied inhibitory control in a visual go/no-go task in children and adolescents with NF1 and age- and gender-matched controls (n = 16 per group). We applied a multimodal approach using high-density electroencephalography (EEG), to study the evoked brain responses, and magnetic resonance spectroscopy (MRS) to measure the levels of GABA and glutamate + glutamine in the medial frontal cortex, a brain region that plays a pivotal role in inhibitory control, and also in a control region, the occipital cortex. Finally, we run correlation analyses to identify the relationship between inhibitory control, levels of neurotransmitters, and EEG markers of neural function. Individuals with NF1 showed impaired impulse control and reduced EEG correlates of early visual processing (parieto-occipital P1) and inhibitory control (frontal P3). MRS data revealed a reduction in medial frontal GABA+/tCr (total Creatine) levels in the NF1 group, in parallel with the already reported reduced occipital GABA levels. In contrast, glutamate + glutamine/tCr levels were normal, suggesting the existence of abnormal inhibition/excitation balance in this disorder. Notably, medial frontal but not occipital GABA levels correlated with general intellectual abilities (IQ) in NF1, and inhibitory control in both groups. Surprisingly, the relationship between inhibitory control and medial frontal GABA was reversed in NF1: higher GABA was associated with a faster response style whereas in controls it was related to a cautious strategy. Abnormal GABAergic physiology appears, thus, as an important factor underlying impaired cognition in NF1, in a level and region dependent manner.

Is magnetic resonance spectroscopy capable of detecting metabolic abnormalities in neurofibromatosis type 1 that are not revealed in brain parenchyma of normal appearance?

BACKGROUND

Results of magnetic resonance spectroscopy studies in normal-appearing brain and in non-neoplastic brain lesions in individuals with neurofibromatosis type 1 (NF1) have been discrepant.

OBJECTIVE

We used magnetic resonance spectroscopy to analyze the metabolic patterns in the basal ganglia of patients with NF1 and examine their correlation with focal hyperintense lesions in T2-weighted images (T2-weighted hyperintensities).

METHODS

We used magnetic resonance spectroscopy data of 42 individuals with NF1 (18 with and 24 without T2- weighted hyperintensities) and 25 controls matched for gender and age. A single-voxel technique was employed by manually placing a region of interest with a uniform size over a predetermined anatomical region including the globus pallidum and putamen (capsulolenticular region). We further analyzed the ratios of choline/creatine, N-acetyl aspartate (NAA)/creatine, and myoinositol/creatine metabolites and the occurrence of T2-weighted hyperintensities in these regions in individuals with NF1.

RESULTS

There was a significant difference between the NF1 and control groups with regard to the mean values of myoinositol/creatine and choline/creatine, with higher metabolite values observed in the NF1 group (P < 0.001). Only the myoinositol/creatine ratio was able to discriminate between NF1 subgroups with and without T2-weighted hyperintensities. For the NAA/creatine ratio, there was no significant difference between the NF1 and the control groups.

CONCLUSION

Magnetic resonance spectroscopy allows the characterization of tissue abnormalities not demonstrable in the structural images of individuals with NF1 through choline and myoinositol metabolite analysis. Yet the preserved NAA values argue against demyelination and axonal degeneration occurring in the region, suggesting instead a functional neuronal stability. Taken in association with the findings of lack of clinical manifestations and the known transient nature of T2-weighted hyperintensities in NF1 as demonstrated by other studies, our results support the current histopathologically driven hypothesis that such T2-weighted hyperintensities may be related to intramyelinic edema.