GGC repeat expansion in NOTCH2NLC induces dysfunction in ribosome biogenesis and translation.

GGC repeat expansion in the 5' untranslated region (UTR) of NOTCH2NLC is associated with a broad spectrum of neurological disorders, especially neuronal intranuclear inclusion disease (NIID). Studies have found that GGC repeat expansion in NOTCH2NLC induces the formation of polyglycine (polyG)-containing protein, which is involved in the formation of neuronal intranuclear inclusions. However, the mechanism of neurotoxicity induced by NOTCH2NLC GGC repeats is unclear. Here, we used NIID patient-specific induced pluripotent stem cell (iPSC)-derived 3D cerebral organoids (3DCOs) and cellular models to investigate the pathophysiological mechanisms of NOTCH2NLC GGC repeat expansion. IPSC-derived 3DCOs and cellular models showed the deposition of polyG-containing intranuclear inclusions. The NOTCH2NLC GGC repeats could induce the upregulation of autophagic flux, enhance integrated stress response and activate EIF2α phosphorylation. Bulk RNA sequencing for iPSC-derived neurons and single-cell RNA sequencing (scRNA-seq) for iPSC-derived 3DCOs revealed that NOTCH2NLC GGC repeats may be associated with dysfunctions in ribosome biogenesis and translation. Moreover, NOTCH2NLC GGC repeats could induce the NPM1 nucleoplasm translocation, increase nucleolar stress, impair ribosome biogenesis and induce ribosomal RNA sequestration, suggesting dysfunction of membraneless organelles in the NIID cellular model. Dysfunctions in ribosome biogenesis and phosphorylated EIF2α and the resulting increase in the formation of G3BP1-positive stress granules may together lead to whole-cell translational inhibition, which may eventually cause cell death. Interestingly, scRNA-seq revealed that NOTCH2NLC GGC repeats may be associated with a significantly decreased proportion of immature neurons while 3DCOs were developing. Together, our results underscore the value of patient-specific iPSC-derived 3DCOs in investigating the mechanisms of polyG diseases, especially those caused by repeats in human-specific genes.

Subclinical peripheral neuropathy is common in neuronal intranuclear inclusion disease with dominant encephalopathy.

BACKGROUND AND PURPOSE: Neuronal intranuclear inclusion disease (NIID) is associated with CGG repeat expansion in the NOTCH2NLC gene. Although pure or dominant peripheral neuropathy has been described as a subtype of NIID in a few patients, most NIID patients predominantly show involvements of the central nervous system (CNS). It is necessary to further explore whether these patients have subclinical peripheral neuropathy. METHODS: Twenty-eight NIID patients, clinically characterized by CNS-dominant involvements, were recruited from two tertiary hospitals. Standard nerve conduction studies were performed in all patients. Skin and sural nerve biopsies were performed in 28 and 15 patients, respectively. Repeat-primed polymerase chain reaction and amplicon length polymerase chain reaction were used to screen the CGG repeat expansion in NOTCH2NLC. RESULTS: All 28 patients can be diagnosed with NIID based on skin pathological and genetic changes. All patients predominantly showed CNS symptoms mainly characterized by episodic encephalopathy and cognitive impairments, but no clinical symptoms of peripheral neuropathy could be observed initially. Electrophysiological abnormalities were found in 96.4% (27/28) of these patients, indicating that subclinical peripheral neuropathy is common in NIID patients with CNS-dominant type. Electrophysiological and neuropathological studies revealed that demyelinating degeneration was the main pathological pattern in these patients, although mild axonal degeneration was also observed in some patients. No significant association between CGG repeat size and the change of nerve conduction velocity was found in these patients. CONCLUSIONS: This study demonstrated that most patients with CNS-dominant NIID had subclinical peripheral neuropathy. Electrophysiological examination should be the routinely diagnostic workflow for every NIID patient.

Recurrent headache and visual symptoms in a young man: a rare neuronal intranuclear inclusion disease case report.

BACKGROUND: Neuronal intranuclear inclusion disease (NIID) is a progressive neurodegenerative disease. Patients with NIID may present with heterogeneous clinical symptoms, including episodic encephalopathy, dementia, limb weakness, cerebellar ataxia, and autonomic dysfunction. Among the NIID cases reported in China, patients often have complicated and severe manifestations. Therefore, many clinicians do not consider the disease when the patient presents with relatively minor complaints. CASE PRESENTATION: We present the case of a 39-year-old man showing migraine-aura-like symptoms for the past 3 years. Brain magnetic resonance imaging (MRI) revealed hyperintense signals in the splenium of the corpus callosum and corticomedullary junction on diffusion-weighted imaging (DWI) over time. In addition, brain atrophy that was not concomitant with the patient's age was detected while retrospectively reviewing the patient's imaging results. Genetic analysis and skin biopsy confirmed a diagnosis of NIID. The patient was treated with sibelium, and the symptoms did not recur. DISCUSSION AND CONCLUSIONS: Migraine-aura-like symptoms may be the predominant clinical presentation in young patients with NIID. Persistent high-intensity signals on DWI in the brain and early-onset brain atrophy might be clues for the diagnosis of NIID.

Adult-onset autosomal dominant leukodystrophy and neuronal intranuclear inclusion disease: lessons from two new Chinese families.

INTRODUCTION: Adult-onset autosomal dominant leukodystrophy (ADLD) is a rare genetic leukoencephalopathy caused by duplication of the lamin B1 gene (LMNB1) or LMNB1 upstream deletions. Neuronal intranuclear inclusion disease (NIID) is another leukoencephalopathy due to GGC repeat expansion in the 5'-untranslated region of the NOTCH2NLC gene. Here, we report two Chinese ADLD families with neuroimaging and clinical features mimicking NIID. METHODS: We conducted detailed medical history inquiry, neurological examinations, and magnetic resonance imaging in the two families. Candidate gene sequencing and whole exome sequencing (WES) with copy number variation analysis were used to screen the genetic variations. The special points on the clinical and neuroimaging findings in the current families and differential diagnosis of ADLD with NIID are discussed. RESULTS: The two families presented with slowly progressive, multiple central nervous system symptoms, including spastic paraplegia, autonomic dysfunction, ataxia, deep sensory loss, and tremor. Clinical phenotypes were consistent within the family. Transient hypoglycemia and transient dilated pupils indicating autonomic dysfunctions were recorded for the first time in ADLD. Brain MRI showed band-like hyperintensities at the cortico-medullary junction on DWI, typical for NIID. Skin biopsy and genetic sequencing of the NOTCH2NCL gene did not support the diagnosis of NIID. Further whole exome sequencing (WES) identified the duplication mutation spanning the entire LMNB1 gene. CONCLUSIONS: The novel feature of transient hypoglycemia and dilated pupils broadens the spectrum of autonomic dysfunction in ADLD. Clinical manifestations and neuroimaging of ADLD can mimic NIID. Although ADLD is even rarer than NIID, the differential diagnosis of these two diseases should not be confused.

Unraveling rare form of adult-onset NIID by characteristic brain MRI features: A single-center retrospective review.

Adult-onset neuronal intranuclear inclusion disease (NIID) is a rare neurodegenerative disorder with high clinical heterogeneity. Previous studies indicated that the high-intensity signals in the corticomedullary junction on diffusion-weighted imaging (DWI) on brain MRI, known as the "ribbon sign," could serve as a strong diagnostic clue. Here we used the explorative approach to study the undiagnosed rate of adult-onset NIID in a single center in China via searching for the ribbon sign in picture archive and communication system (PACS) and report the clinical and radiological features of initially undiagnosed NIID patients. Consecutive brain MRI of 21,563 adult individuals (≥18 years) in the PACS database in 2019 from a tertiary hospital were reviewed. Of them, 4,130 were screened out using the keywords "leukoencephalopathy" and "white matter demyelination." Next, all 4,130 images were read by four neurologists. The images with the suspected ribbon sign were reanalyzed by two neuroradiologists. Those with the ribbon sign but without previously diagnosed NIID were invited for skin biopsy and/or genetic testing for diagnostic confirmation. The clinical features of all NIID patients were retrospectively reviewed. Five patients with high-intensity in the corticomedullary junction on DWI were enrolled. Three patients were previously diagnosed with NIID confirmed by genetic or pathological findings and presented with episodic encephalopathy or cognitive impairment. The other two patients were initially diagnosed with limb-girdle muscular dystrophy (LGMD) with rimmed vacuoles (RVs) and normal pressure hydrocephalus (NPH) in one each. Genetic analysis demonstrated GGC repeat expansion in the NOTCH2NLC gene of both, and skin biopsy of the first patient showed the presence of intranuclear hyaline inclusion bodies. Thus, five of the 21,563 adult patients (≥18 years) were diagnosed with NIID. The distinctive subcortical high-intensity signal on DWI was distributed extensively throughout the lobes, corpus callosum, basal ganglia, and brainstem. In addition, T2-weighted imaging revealed white matter hyperintensity of Fazekas grade 2 or 3, atrophy, and ventricular dilation. Distinctive DWI hyperintensity in the junction between the gray and white matter can help identify atypical NIID cases. Our findings highly suggest that neurologists and radiologists should recognize the characteristic neuroimaging pattern of NIID.

Distinctive diffusion-weighted imaging features in late-onset genetic leukoencephalopathies.

Genetic leukoencephalopathies are inherited disorders characterized by progressive white matter involvement. Although most are paediatric conditions, late-onset adult leukoencephalopathies are being increasingly recognized. Adult leukoencephalopathies may present as neurodegenerative diseases with cognitive decline and motor symptoms. Similar to their paediatric counterparts, different adult leukoencephalopathies often have distinctive MRI appearances. In particular, DWI has been recently shown to demonstrate specific patterns of persistent diffusion restriction in several adult-onset leukoencephalopathies. As such, DWI may provide important clues to the diagnosis of adult-onset leukoencephalopathy. The purpose of this review is to discuss characteristic DWI features in some late-onset leukoencephalopathies.

Identifying patients with neuronal intranuclear inclusion disease in Singapore using characteristic diffusion-weighted MR images.

PURPOSE: Adult-onset neuronal intranuclear inclusion disease (NIID) is a rare neurodegenerative disorder described mainly in the Japanese population, with characteristic DWI abnormalities at the junction between gray and white matter. We identify possible cases of NIID in the picture archive and communication system (PACS) of a tertiary neurological referral hospital in Singapore and describe their radiological features. METHODS: The neuroradiology imaging database was reviewed using keyword search of radiological reports to identify patients who had "subcortical U fibre" abnormalities on DWI. MRI were retrospectively reviewed, and those fulfilling inclusion criteria were invited for skin biopsy to detect nuclear inclusions by light and electron microscopy. RESULTS: Twelve Chinese patients (nine female; median age 70.5 years) were enrolled. Seven patients were being assessed for dementia and five for other neurological indications. In all patients, DWI showed distinctive subcortical high signal with increased average apparent diffusion coefficient (ADC), involving frontal, parietal, and temporal more than occipital lobes; the corpus callosum and external capsule were affected in some patients. On T2-weighted images, cerebral and cerebellar atrophy and white matter hyperintensity of Fazekas grade 2 and above were seen in all patients. Three patients underwent skin biopsy; all were positive for intranuclear hyaline inclusion bodies on either p62 staining or electron microscopy, which are pathognomonic for NIID. CONCLUSION: Previously undiagnosed patients with NIID can be identified by searching for abnormalities at the junction between gray and white matter on DWI in PACS and subsequently confirmed by skin biopsy. Radiologists should recognize the distinctive neuroimaging pattern of this dementing disease.