Novel compound heterozygous mutations of the NPC1 gene associated with Niemann-pick disease type C: a case report and review of the literature.

BACKGROUND: Niemann-Pick Disease type C is a fatal autosomal recessive lipid storage disorder caused by NPC1 or NPC2 gene mutations and characterized by progressive, disabling neurological deterioration and hepatosplenomegaly. Herein, we identified a novel compound heterozygous mutations of the NPC1 gene in a Chinese pedigree. CASE PRESENTATION: This paper describes an 11-year-old boy with aggravated walking instability and slurring of speech who presented as Niemann-Pick Disease type C. He had the maternally inherited c.3452 C > T (p. Ala1151Val) mutation and the paternally inherited c.3557G > A (p. Arg1186His) mutation using next-generation sequencing. The c.3452 C > T (p. Ala1151Val) mutation has not previously been reported. CONCLUSIONS: This study predicted that the c.3452 C > T (p. Ala1151Val) mutation is pathogenic. This data enriches the NPC1 gene variation spectrum and provides a basis for familial genetic counseling and prenatal diagnosis.

Npc1 gene mutation abnormally activates the classical Wnt signalling pathway in mouse kidneys and promotes renal fibrosis.

Niemann-Pick disease type C1 (NPC1) is a lysosomal lipid storage disease caused by NPC1 gene mutation. Our previous study found that, compared with wild-type (Npc1+/+ ) mice, the renal volume and weight of Npc1 gene mutant (Npc1-/- ) mice were significantly reduced. We speculate that Npc1 gene mutations may affect the basic structure of the kidneys of Npc1-/- mice, and thus affect their function. Therefore, we randomly selected postnatal Day 28 (P28) and P56 Npc1+/+ and Npc1-/- mice, and observed the renal structure and pathological changes by haematoxylin-eosin staining. The level of renal fibrosis was detected by immunofluorescence histochemical techniques, and western blotting was used to detect the expression levels of apoptosis-related proteins and canonical Wnt signalling pathway related proteins. The results showed that compared with Npc1+/+ mice, the kidneys of P28 and P56 Npc1-/- mice underwent apoptosis and fibrosis; furthermore, there were obvious vacuoles in the cytoplasm of renal tubular epithelial cells of P56 Npc1-/- mice, the cell bodies were loose and foam-like, and the canonical Wnt signalling pathway was abnormally activated. These results showed that Npc1 gene mutation can cause pathological changes in the kidneys of mice. As age increased, vacuoles developed in the cytoplasm of renal tubular epithelial cells, and apoptosis of renal cells, abnormal activation of the Wnt signalling pathway, and promotion of renal fibrosis increased.

Familial Alzheimer's disease associated with heterozygous NPC1 mutation.

INTRODUCTION: NPC1 mutations are responsible for Niemann-Pick disease type C (NPC), a rare autosomal recessive neurodegenerative disease. Patients harbouring heterozygous NPC1 mutations may rarely show parkinsonism or dementia. Here, we describe for the first time a large family with an apparently autosomal dominant late-onset Alzheimer's disease (AD) harbouring a novel heterozygous NPC1 mutation. METHODS: All the five living siblings belonging to the family were evaluated. We performed clinical evaluation, neuropsychological tests, assessment of cerebrospinal fluid markers of amyloid deposition, tau pathology and neurodegeneration (ATN), structural neuroimaging and brain amyloid-positron emission tomography. Oxysterol serum levels were also tested. A wide next-generation sequencing panel of genes associated with neurodegenerative diseases and a whole exome sequencing analysis were performed. RESULTS: We detected the novel heterozygous c.3034G>T (p.Gly1012Cys) mutation in NPC1, shared by all the siblings. No other point mutations or deletions in NPC1 or NPC2 were found. In four siblings, a diagnosis of late-onset AD was defined according to clinical characterisation and ATN biomarkers (A+, T+, N+) and serum oxysterol analysis showed increased 7-ketocholesterol and cholestane-3ß,5α,6ß-triol. DISCUSSION: We describe a novel NPC1 heterozygous mutation harboured by different members of a family with autosomal dominant late-onset amnesic AD without NPC-associated features. A missense mutation in homozygous state in the same aminoacidic position has been previously reported in a patient with NPC with severe phenotype. The alteration of serum oxysterols in our family corroborates the pathogenic role of our NPC1 mutation. Our work, illustrating clinical and biochemical disease hallmarks associated with NPC1 heterozygosity in patients affected by AD, provides relevant insights into the pathogenetic mechanisms underlying this possible novel association.

A Novel Small NPC1 Promoter Enhances AAV-Mediated Gene Therapy in Mouse Models of Niemann-Pick Type C1 Disease.

Niemann-Pick disease type C1 (NP-C) is a prematurely lethal genetic lysosomal storage disorder with neurological and visceral pathology resulting from mutations in the NPC1 gene encoding the lysosomal transmembrane protein NPC1. There is currently no cure for NP-C, and the only disease modifying treatment, miglustat, slows disease progression but does not significantly attenuate neurological symptoms. AAV-mediated gene therapy is an attractive option for NP-C, but due to the large size of the human NPC1 gene, there may be packaging and truncation issues during vector manufacturing. One option is to reduce the size of DNA regulatory elements that are essential for gene expression, such as the promoter sequence. Here, we describe a novel small truncated endogenous NPC1 promoter that leads to high gene expression both in vitro and in vivo and compare its efficacy to other commonly used promoters. Following neonatal intracerebroventricular (ICV) injection into the CNS, this novel promoter provided optimal therapeutic efficacy compared to all other promoters including increased survival, improved behavioural phenotypes, and attenuated neuropathology in mouse models of NP-C. Taken together, we propose that this novel promoter can be extremely efficient in designing an optimised AAV9 vector for gene therapy for NP-C.

The point mutation of the cholesterol trafficking membrane protein NPC1 may affect its proper function in more than a single step: Molecular dynamics simulation study.

The Niemann-Pick type C1 (NPC1) protein is one of the key players of cholesterol trafficking from the lysosome and its function is closely coupled with the Niemann-Pick type C2 (NPC2) protein. The dysfunction of one of these proteins can cause problems in the overall cholesterol homeostasis and leads to a disease, which is called the Niemann-Pick type C (NPC) disease. The parts of the cholesterol transport mechanism by NPC1 have begun to recently emerge, especially after the full-length NPC1 structure was determined from a cryo-EM study. However, many details about the overall cholesterol trafficking process by NPC1 still remain to be elucidated. Notably, the NPC1 could act as one of the target proteins for the control of infectious diseases due to its role as the virus entry point into the cells as well as for cancer treatment due to the inhibitory effect of tumor growth. A mutation of NPC1 can leads to dysfunctions and understanding this process can provide valuable insights into the mechanisms of the corresponding protein and the therapeutic strategies against the disease that are caused by the mutation. It has been found that patients with the point mutation R518W (or R518Q) on the NPC1 show the accumulation of lipids within the lysosomal lumen. In this paper, we report how the corresponding mutation can affect the cholesterol transport process by NPC1 in the different stages by the molecular dynamics simulations. The simulation results show that the point mutation intervenes at least at two different steps during the cholesterol transport by NPC1 and NPC2 in combination, which includes the association step of NPC2 with the NPC1, the cholesterol transfer step from NPC2 to NPC1-NTD while the cholesterol passage within the NPC1 via a channel is relatively unaffected by R518W mutation. The detailed analysis of the resulting simulation trajectories reveals the important structural features that are essential for the proper functioning of the NPC1 for the cholesterol transport, and it shows how the overall structure, which thereby includes the function, can be affected by a single mutation.

Potential Composite Digenic Contribution of NPC1 and NOD2 Leading to Atypical Lethal Niemann-Pick Type C with Initial Crohn's Disease-like Presentation: Genotype-Phenotype Correlation Study.

Niemann-Pick disease type C (NPC) is an autosomal recessive neurovisceral disease characterized by progressive neurodegeneration with variable involvement of multisystemic abnormalities. Crohn's disease (CD) is an inflammatory bowel disease (IBD) with a multifactorial etiology influenced by variants in NOD2. Here, we investigated a patient with plausible multisystemic overlapping manifestations of both NPC and CD. Her initial hospitalization was due to a prolonged fever and non-bloody diarrhea. A few months later, she presented with recurrent skin tags and anal fissures. Later, her neurological and pulmonary systems progressively deteriorated, leading to her death at the age of three and a half years. Differential diagnosis of her disease encompassed a battery of clinical testing and genetic investigations. The patient's clinical diagnosis was inconclusive. Specifically, the histopathological findings were directed towards an IBD disease. Nevertheless, the diagnosis of IBD was not consistent with the patient's subsequent neurological and pulmonary deterioration. Consequently, we utilized a genetic analysis approach to guide the diagnosis of this vague condition. Our phenotype-genotype association attempts led to the identification of candidate disease-causing variants in both NOD2 and NPC1. In this study, we propose a potential composite digenic impact of these two genes as the underlying molecular etiology. This work lays the foundation for future functional and mechanistic studies to unravel the digenic role of NOD2 and NPC1.

Variants in the Niemann-pick type C genes are not associated with Alzheimer's disease: a large case-control study in the Chinese population.

Despite the similar clinical and pathological features between Niemann-Pick type C (NPC) disease and Alzheimer's disease (AD), few studies have investigated the role of NPC genes in AD. To elucidate the role of NPC genes in AD, we sequenced NPC1 and NPC2 in 1192 AD patients and 2412 controls. Variants were divided into common variants and rare variants according to minor allele frequency (MAF). Common variant (MAF≥0.01) based association analysis was conducted by PLINK 1.9. Gene-based aggregation testing of rare variants was performed by Sequence Kernel Association Test-Optimal (SKAT-O test), respectively. Age at onset (AAO) and mini-mental state examination (MMSE) association studies were also performed with PLINK 1.9. Six common variants were identified and exhibited no association with AD. Gene-based aggregation testing revealed that both NPC1 and NPC2 were not associated with AD risk. Additionally, AAO and MMSE association studies revealed that no common variants were linked with AD endophenotypes. Taken together, our study indicated that NPC1 and NPC2 may not be implicated in AD pathogenesis in the Chinese population.

Saturation variant interpretation using CRISPR prime editing.

High-throughput functional characterization of genetic variants in their endogenous locus has so far been possible only with methods that rely on homology-directed repair, which are limited by low editing efficiencies. Here, we adapted CRISPR prime editing for high-throughput variant classification and combined it with a strategy that allows for haploidization of any locus, which simplifies variant interpretation. We demonstrate the utility of saturation prime editing (SPE) by applying it to the NPC intracellular cholesterol transporter 1 gene (NPC1), mutations in which cause the lysosomal storage disorder Niemann-Pick disease type C. Our data suggest that NPC1 is very sensitive to genetic perturbation, with 410 of 706 assayed missense mutations being classified as deleterious, and that the derived function score of variants is reflective of diverse molecular defects. We further applied our approach to the BRCA2 gene, demonstrating that SPE is translatable to other genes with an appropriate cellular assay. In sum, we show that SPE allows for efficient, accurate functional characterization of genetic variants.

Assessment of FDA-Approved Drugs as a Therapeutic Approach for Niemann-Pick Disease Type C1 Using Patient-Specific iPSC-Based Model Systems.

Niemann-Pick type C1 (NP-C1) is a fatal, progressive neurodegenerative disease caused by mutations in the NPC1 gene. Mutations of NPC1 can result in a misfolded protein that is subsequently marked for proteasomal degradation. Such loss-of-function mutations lead to cholesterol accumulation in late endosomes and lysosomes. Pharmacological chaperones (PCs) are described to protect misfolded proteins from proteasomal degradation and are being discussed as a treatment strategy for NP-C1. Here, we used a combinatorial approach of high-throughput in silico screening of FDA-approved drugs and in vitro biochemical assays to identify potential PCs. The effects of the hit compounds identified by molecular docking were compared in vitro with 25-hydroxycholesterol (25-HC), which is known to act as a PC for NP-C1. We analyzed cholesterol accumulation, NPC1 protein content, and lysosomal localization in patient-specific fibroblasts, as well as in neural differentiated and hepatocyte-like cells derived from patient-specific induced pluripotent stem cells (iPSCs). One compound, namely abiraterone acetate, showed comparable results to 25-HC and restored NPC1 protein level, corrected the intracellular localization of NPC1, and consequently decreased cholesterol accumulation in NPC1-mutated fibroblasts and iPSC-derived neural differentiated and hepatocyte-like cells. The discovered PC altered not only the pathophysiological phenotype of cells carrying the I1061T mutation- known to be responsive to treatment with PCs-but an effect was also observed in cells carrying other NPC1 missense mutations. Therefore, we hypothesize that the PCs studied here may serve as an effective treatment strategy for a large group of NP-C1 patients.

Whole-exome sequencing analysis to identify novel potential pathogenetic NPC1 mutations in two Chinese families with Niemann-Pick disease type C.

BACKGROUND: Niemann-Pick disease type C (NPC) is an autosomal recessive lipid storage disorder, affecting the nervous system and the internal organs. It is characterized by the presence of foam cells in bone marrow, liver, and spleen biopsies. Although many mutations in NPC1 have been identified to be related to disease onset, the relationship between genotype and phenotype remains unclear. To elucidate the genetic heterogeneity of NPC, we described the clinical manifestations and possible genetic pathogenesis of two patients from unrelated families with NPC. METHODS: DNA was extracted from the peripheral blood of the two patients and their families and from healthy individuals. Whole-exome sequencing followed by Sanger sequencing was performed to verify the mutations identified in their families. RESULTS: We identified four mutations in NPC1 in the two patients from different families: c.1290delC (p.F431Lfs*18)/c.2807G > A(p.G936D) in family A and c.3604_3605insA (p.I1202Nfs*56)/c.881 + 3A > G in family B from their parents. Bioinformatics analysis predicted these mutations to be deleterious, suggesting that mutations in exons are highly conservative. The patient in family A presented with a developmental delay that was different from the typical symptoms of developmental regression in family B. CONCLUSION: Our study identified three novel mutations and one known mutation in NPC1 and evaluated their pathogenicity, enriching the NPC1 mutation and phenotype spectrum and providing a new basis for the genetic and prenatal diagnosis of this disease.

Loading of cell cultures with cholesterol-dextran particles as a new functional test for Niemann-Pick type C disease.

Deuterium-labeled cholesterol-dextran particles (d4-CholDex), prepared by co-precipitation, were internalized by cultured human skin fibroblasts and HEK293 cells. Subcellular particles from d4-CholDex-treated HEK293 cells were fractionated on iodixanol gradients. More than 60% of d4-cholesterol (d4-UC) in the gradient co-fractionated with lysosomal markers and NPC1. This and formation of d4-cholesteryl esters (d4-CE) in the cells suggests that d4-CholDex is lysosomally processed. In accordance with these findings, we observed an increase in lysosomal cholesterol content by fluorescence microscopy in CholDex-loaded cells. Fibroblast cultures including 13 NPC1-deficient, four heterozygous and six control lines were treated with d4-CholDex at final d4-UC concentration of 0.05 mg/ml (127.98 µmol/L) for 3 h and chased for 48 h in medium without d4-CholDex. Concentrations of d4-UC and d4-CE in harvested cells were measured by tandem mass spectrometry (MS/MS). d4-UC/d4-CE ratios were elevated in NP-C lines compared to controls (n = 6, mean = 4.36, range = 1.89-8.91), with the highest ratios in severe NP-C1 phenotypes and the lowest in adolescent/adult type patients. There were overlaps between NP-C1 forms: early infantile (n = 1, mean = 48.6), late infantile (n = 4, mean = 36.3, range = 20.6-54.0), juvenile (n = 5, mean = 24.7, range = 13.4-38.3), adolescent/adult (n = 3, mean = 14.5, range = 11.7-19.8). The ratios in NP-C1 heterozygotes were mildly elevated (n = 4, mean = 16.4, range = 14.9-17.4) and comparable to patients with adolescent/adult NP-C1. The test can be useful in evaluation of suspected NP-C patients with inconclusive results of biomarker or molecular tests. Its advantages include standardized preparation of particles with longer shelf life at 4 °C, quantitative results, and no requirement for radioactive chemicals.

Additive effect of frequent polymorphism and rare synonymous variant alters splicing in twin patients with Niemann-Pick disease type C.

Niemann-Pick disease type C (NP-C) (OMIM#257220) is a rare lysosomal storage disorder caused by pathogenic variants in either the NPC1 or NPC2 genes. It manifests with a wide spectrum of clinical symptoms and variable age of onset. We studied the impact of the frequent polymorphic variant c.2793 C > T (p.Asn931 = ), located in the donor splice site (SS) of NPC1 exon 18 on the penetrance of the rare synonymous variant c.2727 C > T (p.Cys909 = ), identified in two 55 y.o. twins with an adult onset form of NP-C. The patients' diagnosis was supported by biochemical analysis and positive filipin test. Analysis of the patients' cDNA showed that the c.2727 C > T variant leads to cryptic donor SS activation and frameshift deletion in the NPC1 exon 18. However, the minigene assay demonstrated that this exon shortening takes place only in the presence of the frequent polymorphic variant c.2793 C > T. Results of the transcript specific qPCR showed that only the presence in the NPC1 exon 18 of both variants leads to significant decrease of wild type (WT) transcript isoform.

Niemann-Pick type C disease with a novel intronic mutation: three Turkish cases from the same family.

OBJECTIVES: Niemann-Pick type C (NPC) disease is a rare progressive neurodegenerative condition that is characterized by the accumulation of cholesterol, glycosphingolipids, and sphingosine in lysosomes. Patients have various systemic and neurological findings depending on their age at onset. This disease is caused by the autosomal recessive transmission of mutations in the NPC1 and NPC2 genes; patients have mutations mainly in the NPC1 gene (95%) and the majority of them are point mutations located in the exonic regions. CASE PRESENTATION: Here, we presented three cousins with hepatosplenomegaly and progressive neurodegeneration who were diagnosed with visceral-neurodegenerative NPC disease. Their parents were relatives, and they had a history of sibling death with similar complaints. Bone marrow smear showed foamy cells in patient 1. Vertical supranuclear gaze palsy was not present in all cases. Sphingomyelinase (SM) activities were almost normal to exclude NPA or NPB. Filipin staining was performed in patient 2 and showed a massive accumulation of unesterified cholesterol The NPC1 gene analysis of the three patients showed a novel homozygous c.1553+5G>A intronic mutation. cDNA analysis was performed from the patient 3 and both parents. It was observed that exon 9 was completely skipped in the homozygous mutant baby. Both the normal and the exon 9-skipped transcripts have been detected in the parents. CONCLUSIONS: When combined with the filipin staining and the patients' clinical outcomes, this mutation is likely to be deleterious. Moreover, cDNA sequencing supports the pathogenicity of this novel variant.

Pharmacologically induced endolysosomal cholesterol imbalance through clinically licensed drugs itraconazole and fluoxetine impairs Ebola virus infection in vitro.

Ebola virus disease (EVD) is a severe and frequently lethal disease caused by Ebola virus (EBOV). The latest occasional EVD outbreak (2013-2016) in Western African, which was accompanied by a high fatality rate, showed the great potential of epidemic and pandemic spread. Antiviral therapies against EBOV are very limited, strain-dependent (only antibody therapies are available) and mostly restricted to symptomatic treatment, illustrating the urgent need for novel antiviral strategies. Thus, we evaluated the effect of the clinically widely used antifungal itraconazole and the antidepressant fluoxetine for a repurposing against EBOV infection. While itraconazole, similar to U18666A, directly binds to and inhibits the endosomal membrane protein Niemann-Pick C1 (NPC1), fluoxetine, which belongs to the structurally unrelated group of weakly basic, amphiphile so-called "functional inhibitors of acid sphingomyelinase" (FIASMA) indirectly acts on the lysosome-residing acid sphingomyelinase via enzyme detachment leading to subsequent lysosomal degradation. Both, the drug-induced endolysosomal cholesterol accumulation and the altered endolysosomal pH, might interfere with the fusion of viral and endolysosomal membrane, preventing infection with EBOV. We further provide evidence that cholesterol imbalance is a conserved cross-species mechanism to hamper EBOV infection. Thus, exploring the endolysosomal host-pathogen interface as a suitable antiviral treatment may offer a general strategy to combat EBOV infection.

Impaired Retromer Function in Niemann-Pick Type C Disease Is Dependent on Intracellular Cholesterol Accumulation.

Niemann-Pick type C disease (NPC) is a rare inherited neurodegenerative disorder characterized by an accumulation of intracellular cholesterol within late endosomes and lysosomes due to NPC1 or NPC2 dysfunction. In this work, we tested the hypothesis that retromer impairment may be involved in the pathogenesis of NPC and may contribute to increased amyloidogenic processing of APP and enhanced BACE1-mediated proteolysis observed in NPC disease. Using NPC1-null cells, primary mouse NPC1-deficient neurons and NPC1-deficient mice (BALB/cNctr-Npc1m1N), we show that retromer function is impaired in NPC. This is manifested by altered transport of the retromer core components Vps26, Vps35 and/or retromer receptor sorLA and by retromer accumulation in neuronal processes, such as within axonal swellings. Changes in retromer distribution in NPC1 mouse brains were observed already at the presymptomatic stage (at 4-weeks of age), indicating that the retromer defect occurs early in the course of NPC disease and may contribute to downstream pathological processes. Furthermore, we show that cholesterol depletion in NPC1-null cells and in NPC1 mouse brains reverts retromer dysfunction, suggesting that retromer impairment in NPC is mechanistically dependent on cholesterol accumulation. Thus, we characterized retromer dysfunction in NPC and propose that the rescue of retromer impairment may represent a novel therapeutic approach against NPC.

Two Distinct Lysosomal Targeting Strategies Afford Trojan Horse Antibodies With Pan-Filovirus Activity.

Multiple agents in the family Filoviridae (filoviruses) are associated with sporadic human outbreaks of highly lethal disease, while others, including several recently identified agents, possess strong zoonotic potential. Although viral glycoprotein (GP)-specific monoclonal antibodies have demonstrated therapeutic utility against filovirus disease, currently FDA-approved molecules lack antiviral breadth. The development of broadly neutralizing antibodies has been challenged by the high sequence divergence among filovirus GPs and the complex GP proteolytic cleavage cascade that accompanies filovirus entry. Despite this variability in the antigenic surface of GP, all filoviruses share a site of vulnerability-the binding site for the universal filovirus entry receptor, Niemann-Pick C1 (NPC1). Unfortunately, this site is shielded in extracellular GP and only uncovered by proteolytic cleavage by host proteases in late endosomes and lysosomes, which are generally inaccessible to antibodies. To overcome this obstacle, we previously developed a 'Trojan horse' therapeutic approach in which engineered bispecific antibodies (bsAbs) coopt viral particles to deliver GP:NPC1 interaction-blocking antibodies to their endo/lysosomal sites of action. This approach afforded broad protection against members of the genus Ebolavirus but could not neutralize more divergent filoviruses. Here, we describe next-generation Trojan horse bsAbs that target the endo/lysosomal GP:NPC1 interface with pan-filovirus breadth by exploiting the conserved and widely expressed host cation-independent mannose-6-phosphate receptor for intracellular delivery. Our work highlights a new avenue for the development of single therapeutics protecting against all known and newly emerging filoviruses.

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.

Estimated prevalence of Niemann-Pick type C disease in Quebec.

Niemann-Pick type C (NP-C) disease is an autosomal recessive disease caused by variants in the NPC1 or NPC2 genes. It has a large range of symptoms depending on age of onset, thus making it difficult to diagnose. In adults, symptoms appear mainly in the form of psychiatric problems. The prevalence varies from 0.35 to 2.2 per 100,000 births depending on the country. The aim of this study is to calculate the estimated prevalence of NP-C in Quebec to determine if it is underdiagnosed in this population. The CARTaGENE database is a unique database that regroups individuals between 40 and 69 years old from metropolitan regions of Quebec. RNA-sequencing data was available for 911 individuals and exome sequencing for 198 individuals. We used a bioinformatic pipeline on those individuals to extract the variants in the NPC1/2 genes. The prevalence in Quebec was estimated assuming Hardy-Weinberg Equilibrium. Two pathogenic variants were used. The variant p.Pro543Leu was found in three heterozygous individuals that share a common haplotype, which suggests a founder French-Canadian pathogenic variant. The variant p.Ile1061Thr was found in two heterozygous individuals. Both variants have previously been reported and are usually associated with infantile onset. The estimated prevalence calculated using those two variants is 0.61:100,000 births. This study represents the first estimate of NP-C in Quebec. The estimated prevalence for NP-C is likely underestimated due to misdiagnosis or missed cases. It is therefore important to diagnose all NP-C patients to initiate early treatment.