Neuronal intranuclear inclusion disease: recognition and update

Autophagy Dysfunction and Neurodegeneration: Where Does It Go Wrong?

An infamous hallmark of neurodegenerative diseases is the accumulation of misfolded or unfolded proteins forming inclusions in the brain. The accumulation of these abnormal structures is a mysterious one, given that cells devote significant resources to integrate complementary pathways to ensure proteome integrity and proper protein folding. Aberrantly folded protein species are rapidly targeted for disposal by the ubiquitin-proteasome system (UPS), and even if this should fail, and the species accumulates, the cell can also rely on the lysosome-mediated degradation pathways of autophagy. Despite the many safeguards in place, failure to maintain protein homeostasis commonly occurs during, or preceding, the onset of disease. Over the last decade and a half, studies suggest that the failure of autophagy may explain the disruption in protein homeostasis observed in disease. In this review, we will examine how the highly complex cells of the brain can become vulnerable to failure of aggregate clearance at specific points during the processive pathway of autophagy, contributing to aggregate accumulation in brains with neurodegenerative disease.

Clinical Reasoning: Juvenile-Onset Dopa-Responsive Dystonia-Until It Isn't

Dopa-responsive dystonia (DRD) encompasses a broad spectrum of phenotypically diverse conditions, offering unique diagnostic challenges. We describe the case of a 24-year-old woman with dystonic gait and jerky position-sensitive limb tremor that initially responded exquisitely well to low-dose levodopa, suggesting DRD. Two years later, she developed parkinsonian features, ultimately leading to a diagnostic reclassification. Despite extensive investigations, the underlying etiology remained elusive until 10 years after symptom onset. We discuss this DRD mimic and briefly review the disorders from which it must be distinguished.

Spatial and Temporal Distribution of White Matter Lesions in NOTCH2NLC-Related Neuronal Intranuclear Inclusion Disease

BACKGROUND AND OBJECTIVES

NOTCH2NLC-related neuronal intranuclear inclusion disease (NIID) is a neurodegenerative disease with characteristic white matter lesions (WMLs) visible on MRI. However, the distribution of WMLs and their clinical correlations remain poorly understood in NIID. This study aims to investigate the spatial and temporal distribution of WMLs in the brain of patients with NOTCH2NLC-related NIID.

METHODS

We retrospectively evaluated patients diagnosed with NOTCH2NLC-related NIID in Zhongshan Hospital, Fudan University. Detailed clinical information, including retrospective MRI data, was collected. Spatial distribution of WMLs with fluid-attenuated inversion recovery (FLAIR) and diffusion-weighted imaging (DWI) hyperintensities was quantified, and the relationship between WML distribution and clinical presentations was analyzed by the Fisher exact test. The volume of whole-brain WMLs was quantified using ITK-SNAP software. The relationship between phenotypes and WML volume was analyzed by the Student t test, Mann-Whitney test, or correlation analysis. WML development patterns were summarized based on the longitudinal observation of MRI characteristics.

RESULTS

This study evaluated 45 patients with NOTCH2NLC-related NIID, with a median age of 66 years (range 55-82 years) and consisting of 30 women. Patients exhibited diverse clinical manifestations, with cognitive decline, autonomic dysfunction, and tremor being the 3 most frequent presentations. Severe WMLs were observed in 43 patients, with FLAIR hyperintensities predominantly in the corona radiata, centrum semiovale, and other brain regions. The presence of DWI hyperintensities was common in the corticomedullary junction (91.1%) and corpus callosum (53.3%). Analysis showed significant correlations between FLAIR hyperintensity volume and both age (r = 0.312, p = 0.042) and Montreal Cognitive Assessment scores (r = -0.371, p = 0.048). Longitudinal MRI retrospection in 7 patients over an average of 9.6 ± 2.9 years revealed 3 gradually progressed WML patterns: periventricular-subcortical, periventricular-dominant, and corticomedullary junction-dominant. In addition, 3 patients experienced rapid WML expansion associated with mitochondrial encephalomyopathy with lactic acidosis and stroke (MELAS)-like episodes.

DISCUSSION

Our analysis revealed the radiologic characteristics and spatial distribution of WMLs and demonstrated significant correlations between FLAIR hyperintensity volume and age/cognitive levels in NIID. Long-term retrospection revealed 3 types of gradual WML expansion patterns while MELAS-like episodes cause rapid WML aggravation. Although results should be confirmed in a larger cohort, these insights enhance understanding of NIID's clinical-radiologic relationships and pathogenesis.

Clinical and multimodal imaging features of adult-onset neuronal intranuclear inclusion disease

OBJECTIVES

This study aimed to analyze the clinical and multimodal imaging manifestations of adult-onset neuronal intranuclear inclusion disease (NIID) patients and to investigate NIID-specific neuroimaging biomarkers.

METHODS

Forty patients were retrospectively enrolled from the Qilu Hospital of Shandong University. We analyzed the clinical and imaging characteristics of 40 adult-onset NIID patients and investigated the correlation between these characteristics and genetic markers and neuropsychological scores. We further explored NIID-specific alterations using multimodal imaging indices, including diffusion tensor imaging (DTI), magnetic resonance spectroscopy (MRS), and brain age estimation. In addition, we summarized the dynamic evolution pattern of NIID by examining the changes in diffusion weighted imaging (DWI) signals over time.

RESULTS

The NIID patients' ages ranged from 31 to 77 years. Cognitive impairment was the most common symptom (30/40, 75.0%), while some patients (18/40, 45.0%) initially presented with episodic symptoms such as headache (10/40, 25.0%). Patients with cognitive impairment symptoms had more cerebral white matter damage (χ2 = 11.475, P = 0.009). The most prevalent imaging manifestation was a high signal on DWI in the corticomedullary junction area, which was observed in 80.0% (32/40) of patients. In addition, the DWI dynamic evolution patterns could be classified into four main patterns. Diffusion tensor imaging (DTI) revealed extensive thinning of cerebral white matter fibers. The estimated brain age surpassed the patient's chronological age, signifying advanced brain aging in NIID patients.

CONCLUSIONS

The clinical manifestations of NIID exhibit significant variability, usually leading to misdiagnosis. Our results provided new imaging perspectives for accurately diagnosing and exploring this disease's neuropathological mechanisms.

Neuronal intranuclear inclusion disease with subclinical peripheral neuropathy: A case report

RATIONALE

Neuronal intranuclear inclusion disease (NIID) is a slowly progressing neurodegenerative disease with various manifestations and high heterogeneity. Clinical characteristics, imaging, skin biopsy, and genetic testing are necessary for its diagnosis. Electromyography may also be a useful tool for diagnosing NIID. In this study, we report a patient with motor and sensory nerve demyelination changes accompanied by axonal damage.

PATIENT CONCERNS

A 64-year-old woman was admitted to our department with gradually worsening forgetfulness for over a year. After 6 years of follow-up, the symptoms progressively deteriorated.

DIAGNOSES

Cerebrospinal fluid analysis revealed increased protein levels. Brain magnetic resonance imaging showed characteristic "ribbon-like" high signals in the corticomedullary junction area on diffusion-weighted imaging. High-intensity signals in the white matter were also observed on T2 and fluid-attenuated inversion recovery imaging. Electromyography revealed multiple peripheral nerve damage and conduction changes, including motor and sensory nerve demyelination changes, accompanied by axonal damage. Skin biopsy revealed inclusion bodies with strong positive staining for P62 and ubiquitin antibodies in the nuclei of sweat gland cells, adipocytes, and fibroblasts. Genetic testing indicated that the number of GGC repeats in NOTCH2NLC alleles were 14 and 134, respectively. Consequently, the patient was diagnosed with NIID.

INTERVENTIONS

Currently, no effective treatment is available to delay the progression of the disease.

LESSONS

We report a case of NIID with subclinical peripheral neuropathy, although the patient did not experience sensory symptoms such as numbness in the extremities. Electromyography can be used to detect subclinical peripheral nerve damage.

Familial adult-onset neuronal intranuclear inclusion disease: A case report and literature review

RATIONALE

Neuronal intranuclear inclusion disease (NIID) is a rare neurodegenerative disorder with highly variable clinical manifestations, making diagnosis challenging. Recent advancements in genetic and pathological testing, such as the identification of GGC repeat expansions in the NOTCH2NLC gene, have improved diagnostic accuracy, but familial cases remain underreported.

PATIENT CONCERNS

This report details 3 cases of familial adult-onset NIID in 2 sisters and 1 brother. The older sister experienced episodic encephalopathy and autonomic dysfunction for over 40 years, while the younger sister presented similar symptoms 5 years ago. The brother also developed episodic encephalopathy 5 years ago. Brain diffusion-weighted imaging (DWI) for all 3 patients revealed hyperintensity at the corticomedullary junction and corpus callosum. Skin biopsies from the older sister and brother confirmed the presence of p62 antibody-positive intranuclear inclusion bodies in sweat gland cells and fibroblasts. Genetic testing showed 146 and 133 GGC repeats in the NOTCH2NLC gene in the older sister and brother, respectively.

DIAGNOSES

All 3 patients were diagnosed with NIID based on clinical, radiological, and genetic findings.

INTERVENTIONS

The patients received hormonal therapy, circulation-enhancing treatments, and rehydration therapy during acute episodes.

OUTCOMES

All 3 patients showed significant improvement in symptoms following treatment, with a return to baseline function after hospital discharge.

LESSONS

Proper management of NIID includes prompt recognition of symptoms, adequate rest, and avoidance of triggers such as fatigue, infections, and stress, which may reduce the frequency of episodic attacks. Early diagnosis and targeted symptomatic treatment are essential for improving patient outcomes.

Neuronal Intranuclear Inclusion Disease Presenting with Acute-Onset Dementia and Cortical Edema: A Case Report

Background

Neuronal Intranuclear Inclusion Disease (NIID) is a neurodegenerative disorder characterized by the formation of eosinophilic inclusions in the neurons, visceral and skin cells. The cause is associated with the GGC nucleotide repeat expansion in the NOTCH2NLC gene. The imaging hallmark of NIID is hyperintensities on diffusion-weighted imaging (DWI) at the corticomedullary junction. Clinical manifestations of NIID are highly heterogeneous. Here, we report a case of NIID presenting with acute-onset dementia and cortical edema.

Case presentation

We describe an elderly male patient who presented with sudden dementia within a day. Considering the abrupt onset and the stroke history, we initially diagnosed vascular disease. However, further imaging revealed cortical edema in the temporo-parieto-occipital lobes. Blood and cerebrospinal fluid tests ruled out immunological, metabolic, infectious, or neoplastic etiologies. Genetic testing ultimately confirmed the diagnosis of NIID. Intravenous immunoglobulin (IVIG) therapy did not improve the patient's symptoms; However, about 1 month after treatment, spontaneous improvement was observed. It is noteworthy that 22 months before the onset of cognitive impairment, the patient's MRI for headaches already exhibited the typical imaging lesions of this disease in the cerebellum paravermal region.

Conclusion

Patients with encephalopathy syndrome exhibiting imaging features resembling mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome or Creutzfeldt-Jakob disease should consider the NIID as differential diagnosis. Chronic headaches and symmetric lesions in the cerebellar paravermal region on MRI may be noteworthy indicators of NIID during non-episodic phases.

Neuronal Intranuclear Inclusion Disease with a Corneal Disorder: A Case Report

Background: Neuronal intranuclear inclusion disease (NIID) is a progressive neurodegenerative disorder characterized by the formation of intranuclear inclusions in cells. Adult-type NIID usually develops in elderly patients with various clinical manifestations and is sometimes accompanied by ocular symptoms. A case of adult-onset NIID with early and unique manifestations, including a progressive corneal defect and retinal changes, which are concerning at a young age, is reported. Case Presentation: A 29-year-old woman with adult sporadic NIID presented to our department with a progressive corneal disorder. Her neurological symptoms started at the age of 22 years, and she was diagnosed with NIID by skin biopsy and genetic testing. Ocular examination revealed bilateral corneal superficial punctate keratitis, right corneal opacity, decreased vision, nocturnal lagophthalmos, and early retinal changes. Corneal nerve fiber atrophy was detected by in vivo confocal microscopy. With a Cochet-Bonnet aesthesiometer, the progression of NIID and decreased corneal sensation were confirmed. Findings consistent with neurotrophic keratitis and keratoconjunctivitis due to nocturnal lagophthalmos were both suggested as being complications of her underlying NIID. Treatment with punctal plugs, sodium hyaluronate eye drops, diquafosol sodium eye drops, systemic and local antivirals, and local steroid medications resulted in the gradual improvement in the irregularity and opacity of the epithelium. Conclusions: NIID may lead to neurotrophic keratopathy due to impairment of the corneal sensory nerves. Nocturnal lagophthalmos is a remarkable finding in a case of NIID. The findings in the present case highlight the complex and multifaceted nature of NIID, with neurological and ocular manifestations requiring a multidisciplinary approach to management.

Encephalitis-like episodes with cortical edema and enhancement in patients with neuronal intranuclear inclusion disease

OBJECTIVES

Neuronal intranuclear inclusion disease (NIID) exhibited significant clinical heterogeneities. However, the clinical features, radiographic changes, and prognosis of patients with encephalitis-like NIID have yet to be systematically elucidated.

METHODS

Clinical data including medical history, physical examination, and laboratory examinations were collected and analyzed. Skin and sural nerve biopsies were conducted on the patient. Repeat-primed PCR (RP-PCR) and fluorescence amplicon length PCR (AL-PCR) were used to detect the expansion of CGG repeat. We also reviewed the clinical and genetic data of NIID patients with cortical enhancement.

RESULTS

A 54-year-old woman presented with encephalitis-like NIID, characterized by severe headache and agitative psychiatric symptoms. The brain MRI showed cortical swelling in the temporo-occipital lobes and significant enhancement of the cortical surface and dura, but without hyperintensities along the corticomedullary junction on diffusion-weighted image (DWI). A biopsy of the sural nerve revealed a demyelinating pathological change. The intranuclear inclusions were detected in nerve and skin tissues using the p62 antibody and electron microscopy. RP-PCR and AL-PCR unveiled the pathogenic expansion of CGG repeats in the NOTCH2NLC gene. A review of the literature indicated that nine out of the 16 patients with cortical lesions and linear enhancement exhibited encephalitis-like NIID.

CONCLUSION

This study indicated that patients with encephalitis-like NIID typically exhibited headache and excitatory psychiatric symptoms, often accompanied by cortical edema and enhancement of posterior lobes, and responded well to glucocorticoid treatment. Furthermore, some patients may not exhibit hyperintensities along the corticomedullary junction on DWI, potentially leading to misdiagnosis.

Case report: Sacral neuromodulation for neurogenic lower urinary tract dysfunction in patient with neuronal intranuclear inclusion disease

Neuronal intranuclear inclusion disease is an uncommon neurodegenerative disorder. The diagnosis of this condition has become more definitive based on current research. However, treatment options remain limited. Neurogenic lower urinary tract dysfunction is one of the prevalent and significant complications, which is the result of its multi-system effects. Here, we present the case of a 48-year-old man diagnosed with neuronal intranuclear inclusion disease based on existing evidence and was complicated by neurogenic lower urinary tract dysfunction. Despite undergoing some medical treatments, his lower urinary tract symptoms, including urinary incontinence, incomplete or intermittent voiding, etc, continued to worsen while upper urinary tract injury developed. Based on careful consideration of the patient's condition and the available findings, we performed an unprecedented sacral neuromodulation on him. Implementation of sacral neuromodulation led to significant improvement in his urination function and alleviate kidney function damage. Our case suggests a potential therapeutic role for sacral neuromodulation in the treatment of neurogenic lower urinary tract dysfunction associated with neuronal intranuclear inclusion disease. Additional research is required to determine the effectiveness of sacral neuromodulation in managing neurogenic lower urinary tract dysfunction caused by various etiologies.

Reversible encephalitis-like episodes in fragile X-associated tremor/ataxia syndrome: a case report

BACKGROUND

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a neurodegenerative disorder caused by CGG repeat expansion of FMR1 gene. Both FXTAS and neuronal intranuclear inclusion disease (NIID) belong to polyglycine diseases and present similar clinical, radiological, and pathological features, making it difficult to distinguish these diseases. Reversible encephalitis-like attacks are often observed in NIID. It is unclear whether they are presented in FXTAS and can be used for differential diagnosis of NIID and FXTAS.

CASE PRESENTATION

A 63-year-old Chinese male with late-onset gait disturbance, cognitive decline, and reversible attacks of fever, consciousness impairment, dizziness, vomiting, and urinary incontinence underwent neurological assessment and examinations, including laboratory tests, electroencephalogram test, imaging, skin biopsy, and genetic test. Brain MRI showed T2 hyperintensities in middle cerebellar peduncle and cerebrum, in addition to cerebellar atrophy and DWI hyperintensities along the corticomedullary junction. Lesions in the brainstem were observed. Skin biopsy showed p62-positive intranuclear inclusions. The possibilities of hypoglycemia, lactic acidosis, epileptic seizures, and cerebrovascular attacks were excluded. Genetic analysis revealed CGG repeat expansion in FMR1 gene, and the number of repeats was 111. The patient was finally diagnosed as FXTAS. He received supportive treatment as well as symptomatic treatment during hospitalization. His encephalitic symptoms were completely relieved within one week.

CONCLUSIONS

This is a detailed report of a case of FXTAS with reversible encephalitis-like episodes. This report provides new information for the possible and rare features of FXTAS, highlighting that encephalitis-like episodes are common in polyglycine diseases and unable to be used for differential diagnosis.

Clinical features of neuronal intranuclear inclusion disease with seizures: a systematic literature review

Background

Infant, junior, and adult patients with neuronal intranuclear inclusion disease (NIID) present with various types of seizures. We aimed to conduct a systematic literature review on the clinical characteristics of NIID with seizures to provide novel insight for early diagnosis and treatment and to improve prognosis of these patients.

Methods

We used keywords to screen articles related to NIID and seizures, and data concerning the clinical characteristics of patients, including demographic features, disease characteristics of the seizures, treatment responses, imaging examinations, and other auxiliary examination results were extracted.

Results

The included studies comprised 21 patients with NIID with seizures. The most common clinical phenotypes were cognitive impairment (76.20%) and impaired consciousness (57.14%), and generalized onset motor seizures (46.15%) represented the most common type. Compared with infantile and juvenile cases, the use of antiepileptic drugs in adults led to significant seizure control and symptom improvement, in addition to providing a better prognosis. The number of GGC sequence repeats in the NOTCH2NLC gene in six NIID patients with seizures who underwent genetic testing ranged 72-134.

Conclusion

The most common clinical phenotypes in patients with NIID with seizures were cognitive impairment and consciousness disorders. Patients with NIID presented with various types of seizures, with the most common being generalized onset motor seizures. Adult patients had a better prognosis and were relatively stable. The early diagnosis of NIID with seizures is of great significance for treatment and to improve prognosis.

Plasma neurofilament light as a promising biomarker in neuronal intranuclear inclusion disease

Neuronal intranuclear inclusion disease (NIID) is a rare neurodegenerative disorder lacking reliable biomarkers. This study investigates plasma protein levels as potential biomarkers of disease severity and progression in NIID. In this study, we enrolled 30 NIID patients and 36 age- and sex-matched controls, following them for 1-2 years. Plasma neurofilament light (NfL), glial fibrillary acidic protein (GFAP), ubiquitin carboxy-terminal hydrolase L1 (UCH-L1), and tau were measured using ultrasensitive single molecule array (Simoa) assays. Disease severity was evaluated with the Mini-Mental State Examination (MMSE), Montreal Cognitive Assessment (MoCA), Activities of Daily Living (ADL), and CNS symptom counts, in addition to neuroimaging data. Our study revealed that NIID patients has significantly higher plasma NfL (median, 35.2 vs. 8.61 pg/mL, p < 0.001) and GFAP (102 vs. 79.0 pg/mL, p = 0.010) levels compared to controls, with NfL emerging as a robust diagnostic marker (AUC = 0.956). NfL levels were notably higher in acute-onset NIID (77.5 vs. 28.8 pg/mL, p = 0.001). NfL correlated strongly with disease severity, including MMSE (ρ = - 0.687, p < 0.001), MoCA (ρ = - 0.670, p < 0.001), ADL (ρ = 0.587, p = 0.001), CNS symptoms (ρ = 0.369, p = 0.045), and white matter hyperintensity volume (ρ = 0.620, p = 0.004). Higher baseline NfL (≥ 35.2 pg/mL) associated with increased ADL scores, CNS symptoms, and white matter hyperintensity at follow-up. UCH-L1 and total tau levels showed no significant differences. Our results suggested the potential of NfL as a promising biomarker of disease severity and progression in NIID.

Non-coding CGG repeat expansion in LOC642361/NUTM2B-AS1 is associated with a phenotype of oculopharyngodistal myopathy

BACKGROUND

Oculopharyngodistal myopathy (OPDM) is a rare adult-onset neuromuscular disease, associated with CGG repeat expansions in the 5' untranslated region of LRP12, GIPC1, NOTCH2NLC and RILPL1. However, the genetic cause of a proportion of pathoclinically confirmed cases remains unknown.

METHODS

A total of 26 OPDM patients with unknown genetic cause(s) from 4 tertiary referral hospitals were included in this study. Clinical data and laboratory findings were collected. Muscle samples were observed by histological and immunofluorescent staining. Long-read sequencing was initially conducted in six patients with OPDM. Repeat-primed PCR was used to screen the CGG repeat expansions in LOC642361/NUTM2B-AS1 in all 26 patients.

RESULTS

We identified CGG repeat expansion in the non-coding transcripts of LOC642361/NUTM2B-AS1 in another two unrelated Chinese cases with typical pathoclinical features of OPDM. The repeat expansion was more than 70 times in the patients but less than 40 times in the normal controls. Both patients showed no leucoencephalopathy but one showed mild cognitive impairment detected by Montreal Cognitive Assessment. Rimmed vacuoles and p62-positive intranuclear inclusions (INIs) were identified in muscle pathology, and colocalisation of CGG RNA foci with p62 was also found in the INIs of patient-derived fibroblasts.

CONCLUSIONS

We identified another two unrelated cases with CGG repeat expansion in the long non-coding RNA of the LOC642361/NUTM2B-AS1 gene, presenting with a phenotype of OPDM. Our cases broadened the recognised phenotypic spectrum and pathogenesis in the disease associated with CGG repeat expansion in LOC642361/NUTM2B-AS1.

Neuronal Intranuclear Inclusion Disease with NOTCH2NLC GGC Repeat Expansion: A Systematic Review and Challenges of Phenotypic Characterization

Neuronal intranuclear inclusion disease (NIID) is a highly clinically heterogeneous neurodegenerative disorder primarily attributed to abnormal GGC repeat expansions in the NOTCH2NLC gene. This study aims to comprehensively explore its phenotypic characteristics and genotype-phenotype correlation. A literature search was conducted in PubMed, Embase, and the Cochrane Library from September 1, 2019, to December 31, 2022, encompassing reported NIID cases confirmed by pathogenic NOTCH2NLC mutations. Linear regressions and trend analyses were performed. Analyzing 635 cases from 85 included studies revealed that familial cases exhibited significantly larger GGC repeat expansions than sporadic cases (p < 0.001), and this frequency significantly increased with expanding GGC repeats (p trend < 0.001). Age at onset (AAO) showed a negative correlation with GGC repeat expansions (p < 0.001). The predominant initial symptoms included tremor (31.70%), cognitive impairment (14.12%), and muscle weakness (10.66%). The decreased or absent tendon reflex (DTR/ATR) emerged as a notable clinical indicator of NIID due to its high prevalence. U-fiber was observed in 79.11% of patients, particularly prominent in paroxysmal disease-dominant (87.50%) and dementia-dominant cases (81.08%). Peripheral neuropathy-dominant cases exhibited larger GGC repeat expansions (median = 123.00) and an earlier AAO (median = 33.00) than other phenotypes. Moreover, a significant genetic anticipation of 3.5 years was observed (p = 0.039). This study provides a comprehensive and up-to-date compilation of genotypic and phenotypic information on NIID since the identification of the causative gene NOTCH2NLC. We contribute a novel diagnostic framework for NIID to support clinical practice.

Skin biopsy and neuronal intranuclear inclusion disease

Neuronal intranuclear inclusion disease (NIID) is a rare neurodegenerative disease with variable clinical phenotypes. There is a considerable delay in the definite diagnosis, which primarily depends on postmortem brain pathological examination. Although CGG repeat expansion in the 5'-untranslated region of NOTCH2NLC has been identified as a disease-associated variant, the pathological diagnosis is still required in certain NIID cases. Intranuclear inclusions found in the skin tissue of patients with NIID dramatically increased its early detection rate. Skin biopsy, as a minimally invasive method, has become widely accepted as a routine examination to confirm the pathogenicity of the repeat expansion in patients with suspected NIID. In addition, the shared developmental origin of the skin and nerve system provided a new insight into the pathological changes observed in patients with NIID. In this review, we systematically discuss the role of skin biopsy for NIID diagnosis, the procedure of skin biopsy, and the pathophysiological mechanism of intranuclear inclusion in the skin.

Case report: Neuronal intranuclear inclusion disease presenting with acute encephalopathy

Neuronal intranuclear inclusion disease (NIID), a neurodegenerative disease previously thought to be rare, is increasingly recognized despite heterogeneous clinical presentations. NIID is pathologically characterized by ubiquitin and p-62 positive intranuclear eosinophilic inclusions that affect multiple organ systems, including the brain, skin, and other tissues. Although the diagnosis of NIID is challenging due to phenotypic heterogeneity, a greater understanding of the clinical and imaging presentations can improve accurate and early diagnosis. Here, we present three cases of pathologically proven adult-onset NIID, all presenting with episodes of acute encephalopathy with protracted workups and lengthy time between symptom onset and diagnosis. Case 1 highlights challenges in the diagnosis of NIID when MRI does not reveal classic abnormalities and provides a striking example of hyperperfusion in the setting of acute encephalopathy, as well as unique pathology with neuronal central chromatolysis, which has not been previously described. Case 2 highlights the progression of MRI findings associated with multiple NIID-related encephalopathic episodes over an extended time period, as well as the utility of skin biopsy for antemortem diagnosis.

Neuronal intranuclear inclusion disease mimicking progressive supranuclear palsy

BACKGROUND

Given the variable nature of clinical manifestations, neuronal intranuclear inclusion disease (NIID) is regarded as a heterogeneous disease which is challenging to diagnose early. To the present, progressive supranuclear palsy (PSP)-like symptoms have never been listed in the performance of NIID.

CASE PRESENTATION

A 58-year-old man presented with progressive Parkinsonism and postural instability for 3 years. Initially, he was considered as probable PSP due to vertical supranuclear gaze palsy, postural instability, and hummingbird sign. No high-intensity signal on diffusion-weighted imaging (DWI) was revealed. Eventually, the diagnosis was revised to NIID by Notch 2 N-terminal like C (NOTCH2NLC) GGC repeat expansions and skin biopsy showing intranuclear eosinophilic inclusions in the vesicles and ductal epithelial cells of sweat glands.

CONCLUSION

Even if the typical high-intensity along the corticomedullary junction (CMJ) on DWI is lacking, clinicians should be alert to the possibility of NIID when PSP-like symptoms develop. This case report offers new features of NIID and expands its clinical spectrum.

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.

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.

Clinical-neuroimaging-pathological relationship analysis of adult onset Neuronal Intranuclear Inclusion Disease (NIID)

BACKGROUND

Neuronal Intranuclear Inclusion Disease (NIID) is a degenerative disease with heterogeneous clinical manifestations. We aim to analysis the relationship between clinical manifestations, neuroimaging and skin pathology in a Chinese NIID cohort.

METHODS

Patients were recruited from a Chinese cohort. Detail clinical information were collected. Visual rating scale was used for evaluation of neuroimaging. The relationship between clinical presentations and neuroimaging, as well as skin pathology was statistically analyzed.

RESULTS

Thirty-two patients were recruited. The average onset age was 54.3 y/o. 28.1% had positive family history. Dementia, autonomic nervous system dysfunction, episodic attacks were three main presentations. CSF analysis including Aβ₄₂ and tau level was almost normal. The most frequently involved on MRI was periventricular white matter (100%), frontal subcortical and deep white matter (96.6%), corpus callosum (93.1%) and external capsule (72.4%). Corticomedullary junction DWI high intensity was found in 87.1% patients. Frontal and external capsule DWI high intensity connected to form a "kite-like" specific image. Severity of dementia was significantly related to leukoencephalopathy (r = 0.465, p = 0.0254), but not cortical atrophy and ventricular enlargement. Grey matter lesions were significantly associated with encephalopathy like attacks (p = 0.00077) but not stroke like attacks. The density of intranuclear inclusions in skin biopsy was not associated with disease duration, severity of leukoencephalopathy and dementia.

CONCLUSIONS

Specific distribution of leukoencephalopathy and DWI high intensity were indicative. Leukoencephalopathy and subcortical mechanism were critical in pathogenesis of NIID. Irrelevant of inclusion density and clinical map suggested the direct pathogenic factor need further investigation.

Clinical characteristics of two patients with neuronal intranuclear inclusion disease and literature review

Background

Neuronal intranuclear inclusion disease (NIID) is a rare chronic progressive neurodegenerative disease, with complex and diverse clinical manifestations and pathological eosinophilic hyaline intranuclear inclusions in the central and peripheral nervous systems and visceral organs. Improvements in diagnostic methods such as skin biopsy and gene testing are helpful in revealing the clinical and genetic characters of NIID.

Materials and methods

We presented two cases of NIID diagnosed by using NOTCH2NLC gene testing and skin biopsy. Diffusion weighted imaging (DWI) showed high linear intensity in corticomedullary junction. We also reviewed all the published NIID cases with positive NOTCH2NLC GGC repeat expansion and skin biopsy results in PubMed.

Results

Patient 1 was a 63-year-old male who carried 148 GGC repeats and presented with progressive tremor and limb weakness. Patient 2 was a 62-year-old woman who carried 131 GGC repeats and presented with tremors, memory loss and headaches. The most common clinical manifestation of 63 NIID patients in this study was cognitive impairment, followed by tremors. In our study, almost all the patients were from East Asia, the male to female ratio was 1:1.26, with an age of onset of 54.12 ± 14.12 years, and an age of diagnosis of 60.03 ± 12.21 years. Symmetrical high signal intensity at the corticomedullary junction on DWI were revealed in 80.96% of the patients. For the GGC repeat numbers, the majority of GGC repeats were in the 80-119 intervals, with few GGC repeats above 160. The number of GGC repetitions was significantly higher in patients presented with muscle weakness than in other clinical manifestations.

Conclusion

NIID is a neurodegenerative disease caused by aberrant polyglycine (polyG) protein aggregation. NIID mostly occurs in the elderly population in East Asia, with cognitive dysfunction as the most common symptom. Staging NIID based on clinical presentation is inappropriate because most patients with NIID have overlapping symptoms. In our study, there was no significant correlation between the number of GGC repeats and different phenotypes except for muscle weakness. Abnormal trinucleotides repeat and PolyG protein aggregation maybe common pathogenic mechanism in neurodegenerative diseases and cerebrovascular diseases, which needs to be confirmed by more studies.

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.

Oculopharyngodistal myopathy

PURPOSE OF REVIEW

Oculopharyngodistal myopathy (OPDM) is a rare adolescent or adult-onset neuromuscular disease that is characterized by progressive ocular, facial, pharyngeal and distal limb muscle weakness. The rimmed vacuoles and intranuclear inclusions in myofibers constitute the pathological hallmark of OPDM. In this review, the latest findings related to the genetic, molecular and clinical features of OPDM, as well as the diagnosis and management are summarized.

RECENT FINDINGS

Four gene mutations, CGG repeats in the 5'-untranslated region of LRP12 , GIPC1 , NOTCH2NLC and RILPL1 have been reported to be disease-causing genes in OPDM, namely OPDM1, OPDM2, OPDM3 and OPDM4, accordingly. So far, limited studies have suggested that CGG repeat expansion within the pathogenic range may play a key role in the pathogenesis of OPDM with the gain-of-function mechanism at the RNA and/or protein level, while repeat expansion over a threshold limit may cause hypermethylation, leading to the transcriptional silencing of the CGG repeats in the expanded allele, which results in the existence of mild phenotype or asymptomatic carriers.

SUMMARY

Novel gene mutations, possible molecular mechanisms and the clinical features related to different causative genes are discussed in this review. More studies on the exact pathogenic mechanism are needed.

Urine cytological study in patients with clinicopathologically confirmed neuronal intranuclear inclusion disease

Objective

The diagnosis of neuronal intranuclear inclusion disease (NIID) is currently based on CGG repeat expansion in the 5′UTR of the NOTCH2NLC gene, or p62-positive intranuclear inclusions in skin biopsy. The purpose of this study is to explore the value of non-invasive pathological findings in urine sediment cells from NIID patients.

Materials and methods

Ten patients with clinically suspected NIID were enrolled for skin biopsy and gene screening. Morning urine (500 ml) was collected from each patient, and cell sediment was obtained by centrifugation. Urine cytology, including Giemsa staining, p62 immunostaining, and electron microscopic examination, were conducted on cell sediment.

Results

The main clinical symptoms of 10 patients included episodic disturbance of consciousness, cognitive impairment, tremor, limb weakness, and so on. Cerebral MRI showed that 9 patients had linear DWI high signal in the corticomedullary junction. Genetic testing found that the number of CGG repeat ranged from 96 to 158 in the NOTCH2NLC gene. Skin biopsy revealed that all patients showed p62-positive intranuclear inclusions in 18.5 ± 6.3% of the duct epithelial cells of sweat gland. In contrast, urine sediment smears revealed that only 3 patients had p62 positive intranuclear inclusions in 3.5 ± 1.2% of the sedimentary cells. Ultrastructural examinations showed that intranuclear inclusions were also identified in the cell sediment of the 3 patients.

Conclusion

Urine cytology may be a new and non-invasive pathological diagnosis technique for some NIID patients, although the positive rate is not as high as that of skin biopsy, which is a sensitive and reliable pathological method for NIID.

Case report: Adult-onset neuronal intranuclear inclusion disease with an amyotrophic lateral sclerosis phenotype

Amyotrophic lateral sclerosis (ALS) is one of the differential diagnoses of diseases that occur in adulthood and lead to progressive generalized muscle weakness. Neuronal intranuclear inclusion disease (NIID) is a disease in which histopathologically eosinophilic nuclear inclusion bodies are found in various systems. Both familial and sporadic forms of the disease have been reported. Most cases of sporadic NIID are of the dementia type, in which the main symptom is dementia at the first onset. Familial NIID is more diverse, with the main dominant symptoms being muscle weakness (NIID-M), dementia (NIID-D), and parkinsonism (NIID-P). Furthermore, recently, a GGC-repeat expansion in the Notch 2 N-terminal like C (NOTCH2NLC) gene, which produces a toxic polyglycine-containing protein (uN2CpolyG) in patients with NIID, has been associated with the pathogenesis of ALS. These results suggest that sporadic NIIDs may have more diverse forms. To date, no autopsy cases of NIID patients with an ALS phenotype have been reported. Here, we describe the first autopsy case report of a patient with sporadic NIID who had been clinically diagnosed with ALS. A 65-year-old Japanese man with no family history of neuromuscular disease developed progressive muscle atrophy and weakness in all limbs. The patient was diagnosed with ALS (El Escoriral diagnostic criteria: probable ALS, laboratory-supported ALS). He had no cognitive dysfunction or neuropathies suggestive of NIID. He required respiratory assistance 48 months after onset. He died of pneumonia at the age of 79 years. Postmortem examinations revealed neuronal loss in the spinal anterior horns and motor cortex. In these affected regions, eosinophilic, round neuronal intranuclear inclusions were evident, which were immunopositive for ubiquitin, p62, and uN2CpolyG. No Bunina bodies or TDP-43-positive inclusions were observed in the brain or spinal cord. Our findings suggest that a small proportion of patients with NIID can manifest a clinical phenotype of ALS. Although skin biopsy is commonly used for the clinical diagnosis of NIID, it may also be useful to identify cases of NIID masquerading as ALS.

Neuronal Intranuclear Inclusion Disease-Related Neurotrophic Keratitis: A Case Report

Neuronal intranuclear inclusion disease (NIID) is a rare and slowly progressive neurodegenerative disease characterized by the presence of eosinophilic neuronal intranuclear inclusions. The clinical manifestations of NIID are diverse, and the most common initial feature in cases of sporadic NIID is dementia. Herein, we report an adult female with keratitis as the initial presentation with subsequent bilateral limb tremor, gait disturbances, overemotional behavior, sweating and constipation. Diffusion-weighted imaging (DWI) showed hyperintensity in the bilateral fronto-parieto-occipital corticomedullary junction. Skin biopsy specimens revealed eosinophilic hyaline intranuclear inclusions in fibroblast cells, sweat gland cells and adipose cells. In vivo confocal microscopy of the cornea indicated the absence of corneal nerves in both affected eyes. The patient’s diagnosis of NIID was based on the presence of intranuclear inclusions in biopsied skin and the characteristic high-intensity signal in the corticomedullary junction obtained with DWI. This case report emphasizes that the clinical heterogeneity of NIID and an examination of the corneal nerves may offer valuable clues to its early diagnosis in some patients.

The polyG diseases: a new disease entity

Recently, inspired by the similar clinical and pathological features shared with fragile X-associated tremor/ataxia syndrome (FXTAS), abnormal expansion of CGG repeats in the 5' untranslated region has been found in neuronal intranuclear inclusion disease (NIID), oculopharyngeal myopathy with leukoencephalopathy (OPML), and oculopharyngodistal myopathy (OPDMs). Although the upstream open reading frame has not been elucidated in OPML and OPDMs, polyglycine (polyG) translated by expanded CGG repeats is reported to be as a primary pathogenesis in FXTAS and NIID. Collectively, these findings indicate a new disease entity, the polyG diseases. In this review, we state the common clinical manifestations, pathological features, mechanisms, and potential therapies in these diseases, and provide preliminary opinions about future research in polyG diseases.

A Case Report of Neuronal Intranuclear Inclusion Disease Presenting With Recurrent Migraine-Like Attacks and Cerebral Edema: A Mimicker of MELAS

Background

Neuronal intranuclear inclusion disease (NIID) is a progressive neurodegenerative disease associated with the GGC repeats in the 5'-untranslated region (5'UTR) of NOTCH2NLC. NIID exhibits a wide range of clinical manifestations. However, patients presenting with recurrent migraine-like attacks and cerebral edema have only rarely been reported.

Case Presentation

A Chinese female suffered probable migraines with aura for 10 years. At age of 51, aggravating migraine-like attacks co-occurred with a sudden encephalopathy-like episode. Brain MRI showed right cerebral edema and cortical enhancement. Serum lactic acid level was elevated at rest and significantly increased after a simplified serum lactic acid exercise test. The initial diagnosis was MELAS, while NIID was suspected after faint DWI high-intensity signals in the corticomedullary junction was retrospectively recognized. Mitochondrial genome sequencing and gene panel analysis of nuclear genes related to mitochondrial diseases failed to find any causative variants. Repeat-primed PCR and fluorescence amplicon length PCR of NOTCH2NLC gene identified an abnormal expansion of 118 GGC repeats in the 5'UTR of NOTCH2NLC gene.

Conclusion

NIID should be taken into account for differential diagnosis of migraines and MELAS-like episodes. Besides the corticomedullary hyperintensity on DWI, cortical enhancement in contrast-enhanced brain MRI may also be a brain image marker for the differential diagnosis between MELAS and NIID with MELAS-like episodes.

Upstream open reading frame with NOTCH2NLC GGC expansion generates polyglycine aggregates and disrupts nucleocytoplasmic transport: implications for polyglycine diseases

Neuronal intranuclear inclusion disease (NIID) is neurodegenerative disease characterized by widespread inclusions. Despite the identification of GGC repeat expansion in 5'UTR of NOTCH2NLC gene in adult-onset NIIDs, its pathogenic mechanism remains unclear. Gain-of-function poly-amino-acid proteins generated by unconventional translation have been revealed in nucleotide repeat expansion disorders, inspiring us to explore the possibility of unconventional translation in NIID. Here we demonstrated that NOTCH2NLC 5'UTR triggers the translation of a polyglycine (polyG)-containing protein, N2NLCpolyG. N2NLCpolyG accumulates in p62-positive inclusions in cultured cells, mouse models, and NIID patient tissues with NOTCH2NLC GGC expansion. Translation of N2NLCpolyG is initiated by an upstream open reading frame (uORF) embedding the GGC repeats. N2NLCpolyG tends to aggregate with the increase of GGC repeat units, and displays phase separation properties. N2NLCpolyG aggregation impairs nuclear lamina and nucleocytoplasmic transport but does not necessarily cause acute death on neuronal cells. Our study suggests a similarity of pathogenic mechanisms between NIID and another GGC-repeat disease, fragile X-associated tremor ataxia syndrome. These findings expand our knowledge of protein gain-of-function in NIID, and further highlight evidence for a novel spectrum of diseases caused by aberrant polyG protein aggregation, namely the polyG diseases.

Characteristics of ocular findings of patients with neuronal intranuclear inclusion disease

PURPOSE

This study aimed to explore the ocular characteristics of neuronal intranuclear inclusion disease (NIID), caused by GGC repeat expansion in the NOTCH2NLC gene, combined with the systemic clinical manifestations, and propose early diagnostic features of NIID.

METHODS

Six patients (12 eyes) were enrolled in this study. In vivo corneal confocal microscopy (IVCCM), fundus photography, fundus autofluorescence (FAF) imaging, optical coherence tomography (OCT), full-field electroretinography (ERG), and electromyography were performed.

RESULTS

The average corneal nerve fiber density (CNFD) was 6.83 ± 4.96 number/mm², and the corneal nerve fiber length (CNFL) was 6.76 ± 1.96 mm/mm². The nerves were looser and more curved in affected individuals. Dendritic cells were observed in patients with NIID. Chorioretinal atrophy, hyper-AF spots, and outer retinal abnormalities were observed during FAF imaging and OCT examinations. In full-field ERGs, the amplitudes of the a-wave and b-wave reduced or extinguished over time. The compound muscle action potential and motor nerve conduction velocity of the left common peroneal nerve decreased substantially.

CONCLUSION

The findings of IVCCM and retinal changes should be included in the diagnostic criteria for NIID. Corneal confocal characteristics may precede the systemic neurological manifestations and provide a clinical basis for the early treatment and staging of the disease. ClincalTrials.gov. Identifier: ChiCTR21000500227.

GGC Repeat Expansion in the NOTCH2NLC Gene Is Associated With a Phenotype of Predominant Motor-Sensory and Autonomic Neuropathy

There is still a considerable proportion of patients with inherited peripheral neuropathy (IPN) whose pathogenic genes are unknown. This study was intended to investigate whether the GGC repeat expansion in the NOTCH2NLC is presented in some patients with IPN. A total of 142 unrelated mainland Chinese patients with highly suspected diagnosis of IPN without any known causative gene were recruited. Repeat-primed polymerase chain reaction (RP-PCR) was performed to screen GGC repeat expansion in NOTCH2NLC, followed by fluorescence amplicon length analysis-PCR (AL-PCR) to determine the GGC repeat size. Detailed clinical data as well as nerve, muscle, and skin biopsy were reviewed and analyzed in the NOTCH2NLC-related IPN patients. In total, five of the 142 patients (3.52%) were found to have pathogenic GGC expansion in NOTCH2NLC, with repeat size ranging from 126 to 206 repeats. All the NOTCH2NLC-related IPN patients presented with adult-onset motor-sensory and autonomic neuropathy that predominantly affected the motor component of peripheral nerves. While tremor and irritating dry cough were noted in four-fifths of the patients, no other signs of the central nervous system were presented. Electrophysiological studies revealed both demyelinating and axonal changes of polyneuropathy that were more severe in lower limbs and asymmetrically in upper limbs. Sural nerve pathology was characterized by multiple fibers with thin myelination, indicating a predominant demyelinating process. Muscle pathology was consistent with neuropathic changes. P62-positive intranuclear inclusions were observed in nerve, skin, and muscle tissues. Our study has demonstrated that GGC expansion in NOTCH2NLC is associated with IPN presenting as predominant motor-sensory and autonomic neuropathy, which expands the phenotype of the NOTCH2NLC-related repeat expansion spectrum. Screening of GGC repeat expansions in the NOTCH2NLC should be considered in patients presenting with peripheral neuropathy with tremor and irritating dry cough.

GGC repeat expansions in NOTCH2NLC causing a phenotype of distal motor neuropathy and myopathy

Background

The expansion of GGC repeat in the 5' untranslated region of the NOTCH2NLC has been associated with various neurogenerative disorders of the central nervous system and, more recently, oculopharyngodistal myopathy. This study aimed to report patients with distal weakness with both neuropathic and myopathic features on electrophysiology and pathology who present GGC repeat expansions in the NOTCH2NLC.

Methods

Whole‐exome sequencing (WES) and long‐read sequencing were implemented to identify the candidate genes. In addition, the available clinical data and the pathological changes associated with peripheral nerve and muscle biopsies were reviewed and studied.

Results

We identified and validated GGC repeat expansions of NOTCH2NLC in three unrelated patients who presented with progressive weakness predominantly affecting distal lower limb muscles, following negative results in an initial WES. We found intranuclear inclusions with multiple proteins deposits in the nuclei of both myofibers and Schwann cells. The clinical features of these patients are compatible with the diagnosis of distal motor neuropathy and rimmed vacuolar myopathy.

Interpretation

These phenotypes enrich the class of features associated with NOTCH2NLC‐related repeat expansion disorders (NRED), and provide further evidence that the neurological symptoms of NRED include not only brain, spinal cord, and peripheral nerves damage, but also myopathy, and that overlapping symptoms might exist.