Central cholinergic dysfunction in the adult form of Niemann Pick disease type C: a further link with Alzheimer's disease?

A comprehensive review of transcranial magnetic stimulation in secondary dementia

Although primary degenerative diseases are the main cause of dementia, a non-negligible proportion of patients is affected by a secondary and potentially treatable cognitive disorder. Therefore, diagnostic tools able to early identify and monitor them and to predict the response to treatment are needed. Transcranial magnetic stimulation (TMS) is a non-invasive neurophysiological technique capable of evaluating in vivo and in “real time” the motor areas, the cortico-spinal tract, and the neurotransmission pathways in several neurological and neuropsychiatric disorders, including cognitive impairment and dementia. While consistent evidence has been accumulated for Alzheimer’s disease, other degenerative cognitive disorders, and vascular dementia, to date a comprehensive review of TMS studies available in other secondary dementias is lacking. These conditions include, among others, normal-pressure hydrocephalus, multiple sclerosis, celiac disease and other immunologically mediated diseases, as well as a number of inflammatory, infective, metabolic, toxic, nutritional, endocrine, sleep-related, and rare genetic disorders. Overall, we observed that, while in degenerative dementia neurophysiological alterations might mirror specific, and possibly primary, neuropathological changes (and hence be used as early biomarkers), this pathogenic link appears to be weaker for most secondary forms of dementia, in which neurotransmitter dysfunction is more likely related to a systemic or diffuse neural damage. In these cases, therefore, an effort toward the understanding of pathological mechanisms of cognitive impairment should be made, also by investigating the relationship between functional alterations of brain circuits and the specific mechanisms of neuronal damage triggered by the causative disease. Neurophysiologically, although no distinctive TMS pattern can be identified that might be used to predict the occurrence or progression of cognitive decline in a specific condition, some TMS-associated measures of cortical function and plasticity (such as the short-latency afferent inhibition, the short-interval intracortical inhibition, and the cortical silent period) might add useful information in most of secondary dementia, especially in combination with suggestive clinical features and other diagnostic tests. The possibility to detect dysfunctional cortical circuits, to monitor the disease course, to probe the response to treatment, and to design novel neuromodulatory interventions in secondary dementia still represents a gap in the literature that needs to be explored.

Patient-Specific iPSC-Derived Neural Differentiated and Hepatocyte-like Cells, Carrying the Compound Heterozygous Mutation p.V1023Sfs*15/p.G992R, Present the "Variant" Biochemical Phenotype of Niemann-Pick Type C1 Disease

Niemann–Pick disease type C1 (NP-C1) is a rare lysosomal storage disorder caused by autosomal recessive mutations in the NPC1 gene. Patients display a wide spectrum on the clinical as well as on the molecular level, wherein a so-called “variant” biochemical phenotype can be observed. Here, we report an in vitro analysis of fibroblasts obtained from an NP-C1 patient carrying the undescribed compound heterozygous mutation p.V1023Sfs*15/p.G992R. Since NP-C1 is a neurovisceral disease and the patient suffers from severe neurological as well as hepatic symptoms, we extended our study to neural differentiated and hepatocyte-like cells derived from patient-specific induced pluripotent stem cells. We detected slightly increased intracellular cholesterol levels compared to the control cell line in fibroblasts, neural differentiated and hepatocyte-like cells, suggesting a “variant” biochemical phenotype. Furthermore, the total NPC1 protein, as well as post-ER glycoforms of the NPC1 protein, tended to be reduced. In addition, colocalization analysis revealed a mild reduction of the NPC1 protein in the lysosomes. The patient was diagnosed with NP-C1 at the age of 34 years, after an initial misdiagnosis of schizophrenia. After years of mild and unspecific symptoms, such as difficulties in coordination and concentration, symptoms progressed and the patient finally presented with ataxia, dysarthria, dysphagia, vertical supranuclear gaze palsy, and hepatosplenomegaly. Genetic testing finally pointed towards an NP-C1 diagnosis, revealing the so-far undescribed compound heterozygous mutation p.V1023Sfs*15/p.G992R in the NPC1 gene. In light of these findings, this case provides support for the p.G992R mutation being causative for a “variant” biochemical phenotype leading to an adult-onset type of NP-C1 disease.

Diagnostic contribution and therapeutic perspectives of transcranial magnetic stimulation in dementia

Transcranial magnetic stimulation (TMS) is a powerful tool to probe in vivo brain circuits, as it allows to assess several cortical properties such asexcitability, plasticity and connectivity in humans. In the last 20 years, TMS has been applied to patients with dementia, enabling the identification of potential markers of thepathophysiology and predictors of cognitive decline; moreover, applied repetitively, TMS holds promise as a potential therapeutic intervention. The objective of this paper is to present a comprehensive review of studies that have employed TMS in dementia and to discuss potential clinical applications, from the diagnosis to the treatment. To provide a technical and theoretical framework, we first present an overview of the basic physiological mechanisms of the application of TMS to assess cortical excitability, excitation and inhibition balance, mechanisms of plasticity and cortico-cortical connectivity in the human brain. We then review the insights gained by TMS techniques into the pathophysiology and predictors of progression and response to treatment in dementias, including Alzheimer's disease (AD)-related dementias and secondary dementias. We show that while a single TMS measure offers low specificity, the use of a panel of measures and/or neurophysiological index can support the clinical diagnosis and predict progression. In the last part of the article, we discuss the therapeutic uses of TMS. So far, only repetitive TMS (rTMS) over the left dorsolateral prefrontal cortex and multisite rTMS associated with cognitive training have been shown to be, respectively, possibly (Level C of evidence) and probably (Level B of evidence) effective to improve cognition, apathy, memory, and language in AD patients, especially at a mild/early stage of the disease. The clinical use of this type of treatment warrants the combination of brain imaging techniques and/or electrophysiological tools to elucidate neurobiological effects of neurostimulation and to optimally tailor rTMS treatment protocols in individual patients or specific patient subgroups with dementia or mild cognitive impairment.

Neuropsychological assessment in Niemann-Pick disease type C: a systematic review

BACKGROUND

The neuropsychological profile of Niemann-Pick type C (NP-C) patients is characterized by an early deterioration in executive functions and attention. There are few studies on cognitive impairment and on neuropsychological assessment of NP-C disease. The purpose of this review is to analyze the studies on a psychological assessment for NP-C patients.

METHOD

This review aims to identify a neuropsychological assessment to evaluate cognitive domains and neuropsychological changes in these patients. There were a total of 73 articles. The search terms were identified as titles and abstracts. All articles were evaluated by title, abstract, and text.

RESULTS

Only four of the 73 articles were included because they met the criteria of our review. Furthermore, in these studies, possible diagnostic protocols are proposed on NP-C subjects.

DISCUSSION AND CONCLUSION

The cognitive impairment in NP-C has a negative impact on daily functioning and quality of life. Early diagnosis could identify cognitive deficits and promote cognitive interventions to improve the neuropsychological profile. The management of NP-C disease should be based on a multidisciplinary approach, to treating symptoms, preserving neurological functions, and guaranteeing the best possible quality of life. Early identification of neurological and psychological symptoms of the disease is necessary in order to decrease the progression of neurological disease and improve patient care and treatment outcomes. Furthermore, research should focus more on cognitive aspects, not only in the diagnostic process but also in the rehabilitation process.

Long-term normalization of cognitive and psychopathological alterations in a juvenile Niemann-Pick type C case

Niemann-Pick type C (NP-C) disease is a neurovisceral atypical lysosomal lipid storage disorder with a poor prognosis. We present the 5-year neuropsychological follow-up of a patient with juvenile onset NP-C, spanning the pre-diagnostic stage to the period after treatment with miglustat (Actelion Pharmaceuticals Inc., CA, US). In the initial stages of the disease, the patient presented behavioral dysexecutive symptoms resembling those frequently observed in adult-onset forms and frontotemporal dementia, which frequently makes early diagnosis difficult in children. After 4 years of treatment, the impaired cognitive function and behavioral dysexecutive syndrome had been completely reversed. The variability of NP-C disease makes early diagnosis challenging. Evaluations of long-term neuropsychological development can help diagnose this neurodegenerative disease and document its progression.

Sphingolipids in Alzheimer's disease, how can we target them?

Altered levels of sphingolipids and their metabolites in the brain, and the related downstream effects on neuronal homeostasis and the immune system, provide a framework for understanding mechanisms in neurodegenerative disorders and for developing new intervention strategies. In this review we will discuss: the metabolites of sphingolipids that function as second messengers; and functional aberrations of the pathway resulting in Alzheimer's disease (AD) pathophysiology. Focusing on the central product of the sphingolipid pathway ceramide, we describ approaches to pharmacologically decrease ceramide levels in the brain and we argue on how the sphingolipid pathway may represent a new framework for developing novel intervention strategies in AD. We also highlight the possible use of clinical and non-clinical drugs to modulate the sphingolipid pathway and sphingolipid-related biological cascades.

In vivo evidence of cortical amyloid deposition in the adult form of Niemann Pick type C

Background

Niemann Pick disease type C (NPC) is a lysosomal lipid storage disorder presenting visceral and neurological impairment with cognitive decline. Neurodegeneration in NPC is associated to deposition of amyloid-β and abnormal tau aggregations likewise Alzheimer disease (AD). Dementia is also related to intracortical circuiting abnormalities that can be detected by neurophysiological procedures both in NPC and in AD. Aim of this study is to find the in vivo evidence of amyloid deposition in NPC patients with cognitive impairment and to investigate the pathophysiology of dementia according to similarities with AD.

Methods

Two sisters affected by NPC and cognitive decline underwent neuropsychological tests, PET scans with ¹⁸F- Florbetaben and neurophysiological protocols to assess cortex excitability by means of transcranial magnetic stimulation (TMS), such as short-latency afferent inhibition (SAI), short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF).

Results

Both patients presented a multidomain cognitive impairment. ¹⁸F- Florbetaben uptake was detected in brain frontal areas, while SAI and SICI were abnormal in both patients.

Discussion

Cognitive impairment in NPC is associated to cortical amyloid deposition as revealed by ¹⁸F- Florbetaben PET scan. Amyloid imaging data, together with specific abnormalities found at TMS studies, suggest similar mechanisms underlying NPC and AD dementia.

Different cortical excitability profiles in hereditary brain iron and copper accumulation

BACKGROUND AND AIM

Neurodegeneration with brain iron accumulation (NBIA) and Wilson's disease (WD) is considered the prototype of neurodegenerative disorders characterised by the overloading of iron and copper in the central nervous system. Growing evidence has unveiled the involvement of these metals in brain cortical neurotransmission. Aim of this study was to assess cortical excitability profile due to copper and iron overload.

METHODS

Three patients affected by NBIA, namely two patients with a recessive hereditary parkinsonism (PARK9) and one patient with aceruloplasminemia and 7 patients with neurological WD underwent transcranial magnetic stimulation (TMS) protocols to assess cortical excitability. Specifically, we evaluated the motor thresholds that reflect membrane excitability related to the voltage-gated sodium channels in the neurons of the motor system and the ease of activation of motor cortex via glutamatergic networks, and ad hoc TMS protocols to probe inhibitory-GABAergic (short interval intracortical inhibition, SICI; short-latency afferent inhibition, SAI; cortical silent period, CSP) and excitatory intracortical circuitry (intracortical facilitation, ICF).

RESULTS

Patients with NBIA exhibited an abnormal prolongation of CSP respect to HC and WD patients. On the contrary, neurological WD displayed higher motor thresholds and reduced CSP and SICI.

CONCLUSION

Hereditary conditions due to overload of copper and iron exhibited peculiar cortical excitability profiles that can help during differential diagnosis between these conditions. Moreover, such results can give us more clues about the role of metals in acquired neurodegenerative disorders, such as Parkinson disease, Alzheimer disease, and multiple sclerosis.

Clinical and neurophysiological characteristics of heterozygous NPC1 carriers

Niemann-Pick disease type C (NPC) is an uncommon lysosomal storage disorder, which is characterized neuropathologically by cholinergic dysfunction and presents clinically with a broad series of neurological signs and symptoms. NPC is inherited as an autosomal recessive trait, caused by mutations in the NPC1 or NPC2 genes. However, recent reports have raised concerns on heterozygous NPC1 gene mutation carriers, which historically have been considered as clinically unaffected, occasionally presenting with clinical parkinsonian syndromes or dementia. In the present study, we aimed at comprehensively assessing clinical, biochemical, and neurophysiological features in heterozygous NPC1 gene mutation carriers. We assessed cholinergic intracortical circuits with transcranial magnetic stimulation, executive functions and plasma oxysterol levels in two families comprising two monozygotic twins with a homozygous NPC1 p.P888S mutation, four patients with a compound heterozygous p.E451K and p.G992W mutation, 10 heterozygous NPC1 p.P888S carriers, 1 heterozygous NPC1 p.E451K carrier, and 11 noncarrier family members. We observed a significant impairment in cholinergic circuits, evaluated with short-latency afferent inhibition (SAI), and executive abilities in homozygous/compound heterozygous patients and heterozygous asymptomatic NPC1 carriers, compared to noncarriers. Moreover, we reported a significant correlation between executive functions performances and both plasma oxysterol levels and neurophysiological parameters. These data suggest that heterozygous NPC1 carriers show subclinical deficits in cognition, possibly mediated by an impairment of cholinergic circuits, which in turn may mediate the onset of neurological disorders in a subset of patients.

Fast Intracortical Sensory-Motor Integration: A Window Into the Pathophysiology of Parkinson's Disease

Parkinson's Disease (PD) is a prototypical basal ganglia disorder. Nigrostriatal dopaminergic denervation leads to progressive dysfunction of the cortico-basal ganglia-thalamo-cortical sensorimotor loops, causing the classical motor symptoms. Although the basal ganglia do not receive direct sensory input, they are important for sensorimotor integration. Therefore, the basal ganglia dysfunction in PD may profoundly affect sensory-motor interaction in the cortex. Cortical sensorimotor integration can be probed with transcranial magnetic stimulation (TMS) using a well-established conditioning-test paradigm, called short-latency afferent inhibition (SAI). SAI probes the fast-inhibitory effect of a conditioning peripheral electrical stimulus on the motor response evoked by a TMS test pulse given to the contralateral primary motor cortex (M1). Since SAI occurs at latencies that match the peaks of early cortical somatosensory potentials, the cortical circuitry generating SAI may play an important role in rapid online adjustments of cortical motor output to changes in somatosensory inputs. Here we review the existing studies that have used SAI to examine how PD affects fast cortical sensory-motor integration. Studies of SAI in PD have yielded variable results, showing reduced, normal or even enhanced levels of SAI. This variability may be attributed to the fact that the strength of SAI is influenced by several factors, such as differences in dopaminergic treatment or the clinical phenotype of PD. Inter-individual differences in the expression of SAI has been shown to scale with individual motor impairment as revealed by UPDRS motor score and thus, may reflect the magnitude of dopaminergic neurodegeneration. The magnitude of SAI has also been linked to cognitive dysfunction, and it has been suggested that SAI also reflects cholinergic denervation at the cortical level. Together, the results indicate that SAI is a useful marker of disease-related alterations in fast cortical sensory-motor integration driven by subcortical changes in the dopaminergic and cholinergic system. Since a multitude of neurobiological factors contribute to the magnitude of inhibition, any mechanistic interpretation of SAI changes in PD needs to consider the group characteristics in terms of phenotypical spectrum, disease stage, and medication.

Miglustat in Niemann-Pick disease type C patients: a review

OBJECTIVE

Niemann-Pick disease type C (NP-C) is a rare, autosomal recessive, neurodegenerative disease associated with a wide variety of progressive neurological manifestations. Miglustat is indicated for the treatment of progressive neurological manifestations in both adults and children. Since approval in 2009 there has been a vast growth in clinical experience with miglustat. The effectiveness of miglustat has been assessed using a range of measures.

METHODS

Comprehensive review of published data from studies of cellular neuropathological markers and structural neurological indices in the brain, clinical impairment/disability, specific clinical neurological manifestations, and patient survival.

RESULTS

Cranial diffusion tensor imaging and magnetic resonance spectroscopy studies have shown reduced levels of choline (a neurodegeneration marker), and choline/N-acetyl aspartate ratio (indicating increased neuronal viability) in the brain during up to 5 years of miglustat therapy, as well as a slowing of reductions in fractional anisotropy (an axonal/myelin integrity marker). A 2-year immunoassay study showed significant reductions in CSF-calbindin during treatment, indicating reduced cerebellar Purkinje cell loss. Magnetic resonance imaging studies have demonstrated a protective effect of miglustat on cerebellar and subcortical structure that correlated with clinical symptom severity. Numerous cohort studies assessing core neurological manifestations (impaired ambulation, manipulation, speech, swallowing, other) using NP-C disability scales indicate neurological stabilization over 2-8 years, with a trend for greater benefits in patients with older (non-infantile) age at neurological onset. A randomized controlled trial and several cohort studies have reported improvements or stabilization of saccadic eye movements during 1-5 years of therapy. Swallowing was also shown to improve/remain stable during the randomized trial (up to 2 years), as well as in long-term observational cohorts (up to 6 years). A meta-analysis of dysphagia - a potent risk factor for aspiration pneumonia and premature death in NP-C - demonstrated a survival benefit with miglustat due to improved/stabilized swallowing function.

CONCLUSIONS

The effects of miglustat on neurological NP-C manifestations has been assessed using a range of approaches, with benefits ranging from cellular changes in the brain through to visible clinical improvements and improved survival.

Distinguishing neurocognitive deficits in adult patients with NP-C from early onset Alzheimer's dementia

BACKGROUND

Niemann-Pick disease type C (NP-C) is a rare, progressive neurodegenerative disease caused by mutations in the NPC1 or the NPC2 gene. Neurocognitive deficits are common in NP-C, particularly in patients with the adolescent/adult-onset form. As a disease-specific therapy is available, it is important to distinguish clinically between the cognitive profiles in NP-C and primary dementia (e.g., early Alzheimer's disease; eAD).

METHODS

In a prospective observational study, we directly compared the neurocognitive profiles of patients with confirmed NP-C (n = 7) and eAD (n = 15). All patients underwent neurocognitive assessment using dementia screening tests (mini-mental status examination [MMSE] and frontal assessment battery [FAB]) and an extensive battery of tests assessing verbal memory, visuoconstructive abilities, visual memory, executive functions and verbal fluency.

RESULTS

Overall cognitive impairment (MMSE) was significantly greater in eAD vs. NP-C (p = 0.010). The frequency of patients classified as cognitively 'impaired' was also significantly greater in eAD vs. NP-C (p = 0.025). Patients with NP-C showed relatively preserved verbal memory, but frequent impairment in visual memory, visuoconstruction, executive functions and in particular, verbal fluency. In the eAD group, a wider profile of more frequent and more severe neurocognitive deficits was seen, primarily featuring severe verbal and visual memory deficits along with major executive impairment. Delayed verbal memory recall was a particularly strong distinguishing factor between the two groups.

CONCLUSION

A combination of detailed yet easy-to-apply neurocognitive tests assessing verbal memory, executive functions and verbal fluency may help distinguish NP-C cases from those with primary dementia due to eAD.

Long-term therapy with miglustat and cognitive decline in the adult form of Niemann-Pick disease type C: a case report

Niemann-Pick disease type C (NPC) is a recessive lysosomal lipid storage disorder characterized by central nervous system involvement. Miglustat treatment might improve or stabilize neurological manifestations but there is still limited data on the long-term efficacy. The aim of our study was to report a four-year clinical, neuropsychological and electrophysiological follow-up of two sisters under treatment with miglustat. We report data at basal (T0) and after 4 years (T4) of treatment with miglustat from two sisters (P1 and P2) affected by NPC disease. During the follow-up period, P1 was not adherent to treatment. Both patients underwent neurological evaluation, neuropsychological assessment, nerve conduction study and motor (MEP), visual (VEP), somatosensory, and brainstem auditory evoked potentials. In the patient P2, neurological and electrophysiological evaluations at T4 were stable. Instead, the patient P1, with poor adherence to therapy, developed spasticity, psychiatric disturbances, and alterations of MEP and VEP. Neuropsychological examination showed in both patients a worsening of cognitive impairment. Our findings suggest that long-term therapy with miglustat does not arrest cognitive decline; otherwise, it stabilizes other neurological manifestations.

Recent neuroimaging, neurophysiological, and neuropathological advances for the understanding of NPC

Niemann–Pick disease type C (NPC) is a rare autosomal recessive lysosomal storage disorder with extensive biological, molecular, and clinical heterogeneity. Recently, numerous studies have tried to shed light on the pathophysiology of the disease, highlighting possible disease pathways common to other neurodegenerative disorders, such as Alzheimer’s disease and frontotemporal dementia, and identifying possible candidate biomarkers for disease staging and response to treatment. Miglustat, which reversibly inhibits glycosphingolipid synthesis, has been licensed in the European Union and elsewhere for the treatment of NPC in both children and adults. A number of ongoing clinical trials might hold promise for the development of new treatments for NPC. The objective of the present work is to review and evaluate recent literature data in order to highlight the latest neuroimaging, neurophysiological, and neuropathological advances for the understanding of NPC pathophysiology. Furthermore, ongoing developments in disease-modifying treatments will be briefly discussed.

Cognition and anatomy of adult Niemann-Pick disease type C: Insights for the Alzheimer field

Niemann-Pick disease type C (NPC) is a rare lysosomal storage disorder causing an intracellular lipid trafficking defect and varying damage to the spleen, liver, and central nervous system. The adult form, representing approximately 20% of the cases, is associated with progressive cognitive decline. Intriguingly, brains of adult NPC patients exhibit neurofibrillary tangles, a characteristic hallmark of Alzheimer's disease (AD). However, the cognitive, psychiatric, and neuropathological features of adult NPC and their relation to AD have yet to be explored. We systematically reviewed the literature on adult NPC with a particular focus on cognitive and neuroanatomical abnormalities. The careful study of cognition in adult NPC allows drawing critical insights in our understanding of the pathophysiology of AD as well as normal cognition.

Disruption of GABA(A)-mediated intracortical inhibition in patients with chorea-acanthocytosis

Chorea-acanthocytosis (Ch-Ac) is an autosomal recessive neurodegenerative disorder characterized by adult-onset chorea, acanthocytes in the peripheral blood, and Huntington's disease-like neuropsychiatric symptoms. Animal studies have shown mutation-related dysregulated cortical gamma-aminobutyric acid (GABA)ergic inhibitory networks in its pathophysiology. Herein we found that in patients with Ch-Ac there is a striking alteration of intracortical inhibitory circuits detected by using paired pulse transcranial magnetic stimulation protocols. Our findings show in vivo the functional disruption of GABA(A)-mediated networks in humans with Ch-Ac supporting the existing data in mice models with this condition.

Preliminary Results on Long-Term Potentiation-Like Cortical Plasticity and Cholinergic Dysfunction After Miglustat Treatment in Niemann-Pick Disease Type C

Niemann-Pick disease type C (NPC) is a rare autosomal recessive lysosomal storage disorder, which manifests clinically with a wide range of neurological signs and symptoms. We assessed multiple neurological, neuropsychological and neurophysiological biomarkers using a transcranial magnetic stimulation (TMS) multi-paradigm approach in two patients with NPC carrying a homozygous mutation in the NPC1 gene, and in two heterozygous family members.We assessed short-interval intracortical inhibition (SICI), intracortical facilitation (ICF), long-interval intracortical inhibition (LICI), short-latency afferent inhibition (SAI) and long-term potentiation (LTP)-like cortical plasticity with a paired associative stimulation (PAS) protocol.Baseline SAI and LTP-like plasticity were impaired in both patients with NPC and in the symptomatic heterozygous NPC1 gene mutation carrier. Only a limited decrease in SICI and ICF was observed, while LICI was within normal range in all subjects at baseline. After 12 months of treatment with miglustat, a considerable improvement in SAI and LTP-like plasticity was observed in both patients with NPC. In conclusion, these biomarkers could help to confirm the diagnosis of NPC, and may give an indication of prognostic outcomes in pharmacological trials.

Menin: a tumor suppressor that mediates postsynaptic receptor expression and synaptogenesis between central neurons of Lymnaea stagnalis

Neurotrophic factors (NTFs) support neuronal survival, differentiation, and even synaptic plasticity both during development and throughout the life of an organism. However, their precise roles in central synapse formation remain unknown. Previously, we demonstrated that excitatory synapse formation in Lymnaea stagnalis requires a source of extrinsic NTFs and receptor tyrosine kinase (RTK) activation. Here we show that NTFs such as Lymnaea epidermal growth factor (L-EGF) act through RTKs to trigger a specific subset of intracellular signalling events in the postsynaptic neuron, which lead to the activation of the tumor suppressor menin, encoded by Lymnaea MEN1 (L-MEN1) and the expression of excitatory nicotinic acetylcholine receptors (nAChRs). We provide direct evidence that the activation of the MAPK/ERK cascade is required for the expression of nAChRs, and subsequent synapse formation between pairs of neurons in vitro. Furthermore, we show that L-menin activation is sufficient for the expression of postsynaptic excitatory nAChRs and subsequent synapse formation in media devoid of NTFs. By extending our findings in situ, we reveal the necessity of EGFRs in mediating synapse formation between a single transplanted neuron and its intact presynaptic partner. Moreover, deficits in excitatory synapse formation following EGFR knock-down can be rescued by injecting synthetic L-MEN1 mRNA in the intact central nervous system. Taken together, this study provides the first direct evidence that NTFs functioning via RTKs activate the MEN1 gene, which appears sufficient to regulate synapse formation between central neurons. Our study also offers a novel developmental role for menin beyond tumour suppression in adult humans.