No genetic evidence for the involvement of GGC repeat expansions of the NOTCH2NLC gene in Chinese patients with multiple system atrophy

Advances of NOTCH2NLC Repeat Expansions and Associated Diseases: A Bibliometric and Meta-analysis

The unclear pathogenic mechanisms of neurodegenerative disorders stemming from NOTCH2NLC GGC repeat expansions drive focused research. Thus, a bibliometric and meta-analysis was conducted to uncover research trends and positivity rates in NOTCH2NLC. We conducted systematic searches in the Web of Science, PubMed, Embase, and Scopus databases for studies related to NOTCH2NLC up until August 2, 2023. Information regarding countries, institutions, authors, journals, and keywords of studies included in the Web of Science was analyzed and visualized. The positivity rates of NOTCH2NLC GGC repeat expansions across all screened patients and patients' families were pooled under the random-effects model. Publication bias and its impact were examined using funnel plots, Egger's linear regression, and trim-and-fill method. The bibliometric analysis, revealing pronounced publication growth, comprised 119 studies, which came from China and Japan particularly. "Neuronal intranuclear inclusion disease" emerged as a frequently used keyword. The meta-analysis comprised 36 studies, indicating global positivity rates of 1.79% (95% CI, 0.75-3.17) for all patients and 2.00% (95% CI, 0.26-4.78) for patients' families. Subgroup analyses based on region and phenotype suggested the highest NOTCH2NLC positivity rates in Taiwan population (5.42%, 95% CI 0.08-16.89) and in leukoencephalopathy-dominant patients (8.25%, 95% CI, 3.01-15.60). Sensitivity analysis affirmed the robustness of results. In conclusion, NOTCH2NLC GGC repeat expansions exhibit rare globally, primarily in East Asia, and leukoencephalopathy-dominant patients, emphasizing regional and phenotypic distinctions. Emerging focal points in NOTCH2NLC researches underscore the need for collaborative exploration.

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.

NOTCH2NLC GGC repeats are not expanded in Italian amyotrophic lateral sclerosis patients

Repeat expansions in genes other than C9orf72 and ATXN2 have been recently associated with Amyotrophic Lateral Sclerosis (ALS). Indeed, an abnormal number of GGC repeats in NOTCH2NLC has been recently reported in 0.7% of sporadic ALS patients from mainland China. This finding was not confirmed in an ALS cohort of subjects from Taiwan. As the involvement of expanded NOTCH2NLC alleles in ALS is debated, we addressed this point by evaluating NOTCH2NLC repeat expansions in an Italian cohort of ALS patients. A screening analysis of NOTCH2NLC GGC repeats was performed by repeat-primed polymerase chain reaction (RP-PCR) in a cohort of 385 probable/definite ALS Italian patients. Mean age at onset was 60.5 years (SD 13.7), and 60.9% were males. Sporadic cases were 357 (92.7%), and most patients had a spinal onset (71.8%). None of our patients showed the typical sawtooth tail pattern on RP-PCR, thus excluding abnormal repeat expansion in NOTCH2NLC. Overall, we suggest that NOTCH2NLC expanded alleles might be absent or at least extremely rare in ALS Italian patients. Further investigations in larger cohorts with different ethnic backgrounds are required to support the involvement of NOTCH2NLC in ALS.

The genetic basis of multiple system atrophy

Multiple system atrophy (MSA) is a heterogenous, uniformly fatal neurodegenerative ɑ-synucleinopathy. Patients present with varying degrees of dysautonomia, parkinsonism, cerebellar dysfunction, and corticospinal degeneration. The underlying pathophysiology is postulated to arise from aberrant ɑ-synuclein deposition, mitochondrial dysfunction, oxidative stress and neuroinflammation. Although MSA is regarded as a primarily sporadic disease, there is a possible genetic component that is poorly understood. This review summarizes current literature on genetic risk factors and potential pathogenic genes and loci linked to both sporadic and familial MSA, and underlines the biological mechanisms that support the role of genetics in MSA. We discuss a broad range of genes that have been associated with MSA including genes related to Parkinson's disease (PD), oxidative stress, inflammation, and tandem gene repeat expansions, among several others. Furthermore, we highlight various genetic polymorphisms that modulate MSA risk, including complex gene-gene and gene-environment interactions, which influence the disease phenotype and have clinical significance in both presentation and prognosis. Deciphering the exact mechanism of how MSA can result from genetic aberrations in both experimental and clinical models will facilitate the identification of novel pathophysiologic clues, and pave the way for translational research into the development of disease-modifying therapeutic targets.

NOTCH2NLC-related disorders: the widening spectrum and genotype-phenotype correlation

GGC repeat expansion in the 5' untranslated region of NOTCH2NLC is the most common causative factor in neuronal intranuclear inclusion disease (NIID) in Asians. Such expanded GGC repeats have been identified in patients with leukoencephalopathy, essential tremor (ET), multiple system atrophy, Parkinson's disease (PD), amyotrophic lateral sclerosis and oculopharyngodistal myopathy (OPDM). Herein, we review the recently reported NOTCH2NLC-related disorders and potential disease-causing mechanisms. We found that visual abnormalities may be NOTCH2NLC-specific and should be investigated in other patients with NOTCH2NLC mutations. NOTCH2NLC GGC repeat expansion was rarely identified in patients of European ancestry, whereas the actual prevalence of the expansion in European patients may be potentially higher than reported, and the CGG repeats in LRP12/GIPC1 are suggested to be screened in European patients with NIID. The repeat size and interruptions in NOTCH2NLC GGC expansion confer pleiotropic effects on clinical phenotype, a pure and stable ET phenotype may be an early symptom of NIID, and GGC repeats in NOTCH2NLC possibly give rise to ET. An association may also exist between intermediate-length NOTCH2NLC GGC repeat expansion and patients affected by PD and ET. NOTCH2NLC-OPDM highly resembles NOTCH2NLC-NIID, the two disorders may be the variations of a single neurodegenerative disease, and there may be a disease-causing upper limit in size of GGC repeats in NOTCH2NLC, repeats over which may be non-pathogenic. The haploinsufficiency of NOTCH2NLC may not be primarily involved in NOTCH2NLC-related disorders and a toxic gain-of-function mechanism possibly drives the pathogenesis of neurodegeneration in patients with NOTCH2NLC-associated disorders.

NOTCH2NLC-related repeat expansion disorders: an expanding group of neurodegenerative disorders

The NOTCH2NLC gene 5' untranslated region (UTR) GGC repeat expansion mutations were identified as a genetic contributor of neuronal intranuclear inclusion disease (NIID) in 2019. Since then, the number of reported cases with NOTCH2NLC GGC repeat expansion in Asian and European populations has increased rapidly, indicating that the expanded mutation not only leads to the onset or progression of the NIID, but also may play an important role in multiple progressive neurological disorders, including Parkinson's disease, essential tremor, multiple system atrophy, Alzheimer's disease, frontotemporal dementia, amyotrophic lateral sclerosis, leukoencephalopathy, and oculopharyngodistal myopathy type 3. Nevertheless, the underlying pathogenic mechanism of the NOTCH2NLC 5' UTR region GGC repeat expansion in these disorders remains largely unknown. This review aims to present recent breakthroughs on this mutation and improve our knowledge of a newly defined spectrum of disease: NOTCH2NLC-related repeat expansion disorder.