Identification of 25 new mutations in 40 unrelated Spanish Niemann-Pick type C patients: genotype-phenotype correlations

Development and validation of a new genotype-phenotype correlation for Niemann-Pick disease type C1

Hundreds of NPC1 variants cause highly heterogeneous phenotypes. This study aims to explore the genotype-phenotype correlation of NPC1, especially for missense variants. In a well-characterized cohort, phenotypes are graded into three clinical forms: mild, intermediate, and severe. Missense residue structural location was stratified into three categories: surface, partially, and fully buried. The association of phenotypes with the topography of the amino acid substitution in the protein structure was investigated in our cohort and validated in two reported cohorts. One hundred six unrelated NPC1 patients were enrolled. A significant correlation of genotype-phenotype was found in 81 classified individuals with two or one (the second was null variant) missense variant (p < 0.001): of 25 patients with at least one missense variant of surface (group A), 19 (76%) mild, six (24%) intermediate, and none severe; of 31 cases with at least one missense variant of partially buried without surface variants (group B), 11 (35%) mild, 16 (52%) intermediate, and four (13%) severe; of the remaining 25 patients with two or one buried missense variants (group C), eight (32%) mild, nine (36%) intermediate, and eight (32%) severe. Additionally, 7-ketocholesterol, the biomarker, was lower in group A than in group B (p = 0.024) and group C (p = 0.029). A model was proposed that accurately predicted phenotypes of 72 of 90 (80%), 73 of85 (86%), and 64 of 69 (93%) patients in our cohort, Italian, and UK cohort, respectively. This study proposed a novel genotype-phenotype correlation in NPC1, linking the underlying molecular pathophysiology with clinical phenotype and aiding genetic counseling and evaluation in clinical practice.

Challenges in the Definitive Diagnosis of Niemann-Pick Type C-Leaky Variants and Alternative Transcripts

Niemann-Pick type C (NPC, ORPHA: 646) is a neuro-visceral, psychiatric disease caused predominantly by pathogenic variants in the NPC1 gene or seldom in NPC2. The rarity of the disease, and its wide range of clinical phenotypes and ages of onset, turn the diagnosis into a significant challenge. Other than the detailed clinical history, the typical diagnostic work-up for NPC includes the quantification of pathognomonic metabolites. However, the molecular basis diagnosis is still of utmost importance to fully characterize the disorder. Here, the authors provide an overview of splicing variants in the NPC1 and NPC2 genes and propose a new workflow for NPC diagnosis. Splicing variants cover a significant part of the disease-causing variants in NPC. The authors used cDNA analysis to study the impact of such variants, including the collection of data to classify them as leaky or non-leaky pathogenic variants. However, the presence of naturally occurring spliced transcripts can misdiagnose or mask a pathogenic variant and make the analysis even more difficult. Analysis of the NPC1 cDNA in NPC patients in parallel with controls is vital to assess and detect alternatively spliced forms. Moreover, nonsense-mediated mRNA decay (NMD) analysis plays an essential role in evaluating the naturally occurring transcripts during cDNA analysis and distinguishing them from other pathogenic variants' associated transcripts.

Elucidating the mutational impact in causing Niemann-Pick disease type C: an in silico approach

Niemann-Pick disease type C is a rare autosomal recessive of lysosomal storage disorder characterized by impaired intracellular lipid transport and has a tendency to accumulate the fatty acids and glycosphingolipids in a variety of neurovisceral tissues. This work includes computational tools to deciphere the mutational effect in NPC protein. The study initiated with the collection of 471 missense mutations from various databases, which were then analyzed using computational tools. The mutations (G549V, F703S, Q775P and L1244P) were said to be disease associated, altering the biophysical properties, in highly conserved regions and reduces the stability using several in silico methods and were subjected to molecular docking analysis. To analyze the ligand (Itraconazole: a small molecule of antifungal drug class, which is known to inhibit cholesterol export from lysosomes) activity Molecular docking study was performed for all the complex proteins. The average binding affinity was taken and found to be -10.76 kcal/mol (native) and -11.06 kcal/mol (Q775P was located in transmembrane region IV which impacts the sterol-sensing domain of the NPC1 protein and associated with a severe infantile neurological form). Finally, molecular dynamic simulation was performed in duplicate and trajectories were built for the backbone of the RMSD, RMSF, the number of intramolecular hydrogen bonds, the radius of gyration and the SSE percent for both the complex proteins. This work contributes to understand the effectiveness and may provide an insight on the stability of the drug with the complex variant structures.Communicated by Ramaswamy H. Sarma.

At a glance: the largest Niemann-Pick type C1 cohort with 602 patients diagnosed over 15 years

Niemann-Pick type C1 disease (NPC1 [OMIM 257220]) is a rare and severe autosomal recessive disorder, characterized by a multitude of neurovisceral clinical manifestations and a fatal outcome with no effective treatment to date. Aiming to gain insights into the genetic aspects of the disease, clinical, genetic, and biomarker PPCS data from 602 patients referred from 47 countries and diagnosed with NPC1 in our laboratory were analyzed. Patients' clinical data were dissected using Human Phenotype Ontology (HPO) terms, and genotype-phenotype analysis was performed. The median age at diagnosis was 10.6 years (range 0-64.5 years), with 287 unique pathogenic/likely pathogenic (P/LP) variants identified, expanding NPC1 allelic heterogeneity. Importantly, 73 P/LP variants were previously unpublished. The most frequent variants detected were: c.3019C > G, p.(P1007A), c.3104C > T, p.(A1035V), and c.2861C > T, p.(S954L). Loss of function (LoF) variants were significantly associated with earlier age at diagnosis, highly increased biomarker levels, and a visceral phenotype (abnormal abdomen and liver morphology). On the other hand, the variants p.(P1007A) and p.(S954L) were significantly associated with later age at diagnosis (p < 0.001) and mildly elevated biomarker levels (p ≤ 0.002), consistent with the juvenile/adult form of NPC1. In addition, p.(I1061T), p.(S954L), and p.(A1035V) were associated with abnormality of eye movements (vertical supranuclear gaze palsy, p ≤ 0.05). We describe the largest and most heterogenous cohort of NPC1 patients published to date. Our results suggest that besides its utility in variant classification, the biomarker PPCS might serve to indicate disease severity/progression. In addition, we establish new genotype-phenotype relationships for "frequent" NPC1 variants.

Effects of miglustat therapy on neurological disorder and survival in early-infantile Niemann-Pick disease type C: a national French retrospective study

BACKGROUND

Niemann-Pick disease type C (NP-C) is a rare neurovisceral lysosomal lipid storage disease characterized by progressive neurodegeneration and premature death. While miglustat can stabilize neurological manifestations in later onset forms of NP-C, its efficacy in the early-infantile neurological form has not been demonstrated. In this observational retrospective study, we compared long-term neurodevelopmental outcome and survival between an untreated and a treated group of early infantile NP-C patients.

METHODS

Data available on all NP-C patients with early infantile neurological onset diagnosed in France between 1990 and 2013 were compiled. Patients with incomplete data or who had died from a systemic perinatal, rapidly fatal form were excluded.

RESULTS

Ten patients were included in the treated group (year of birth: 2006-2012), and 16 patients in the untreated group [born 1987-2005 (n = 15), 2012 (n = 1)]. The median age at neurological onset was 9 months (5-18) in the treated group, and 12 months (3-18) in the untreated group (p = 0.22). Miglustat therapy was started at a median age of 24.5 months (9-29) and median duration was 30 months (11-56). Gastrointestinal adverse events were reported in 7/10 patients on miglustat. All patients developed loss of psychomotor acquisitions or additional neurological symptoms despite miglustat therapy. The ages of developmental milestones and neurological involvement did not significantly differ between the two groups. Four patients in the untreated group were lost to follow up. The 22 remaining patients had died by the end of the study and no patient survived beyond the age of 7.4 years. The median survival age was 4.42 years in the untreated group and 5.56 years in the treated group; the Kaplan-Meier survival curves were not significantly different (log-rank test: p = 0.11).

CONCLUSIONS

Miglustat allowed no significant long-term neurodevelopmental improvement nor significant increase of survival in patients with early infantile NP-C.

Molecular profile and peripheral markers of neurodegeneration in patients with Niemann-Pick type C: Decrease in Plasminogen Activator Inhibitor type 1 and Platelet-Derived Growth Factor type AA

Niemann-Pick type C1 (NPC1) is a fatal inherited disease, caused by pathogenic variants in NPC1 gene, which leads to intracellular accumulation of non-esterified cholesterol and glycosphingolipids. This accumulation leads to a wide range of clinical manifestations, including neurological and cognitive impairment as well as psychiatric disorders. The pathophysiology of cerebral damage involves loss of Purkinje cells, synaptic disturbance, and demyelination. Miglustat, a reversible inhibitor of glucosylceramide synthase, is an approved treatment for NPC1 and can slow neurological damage. The aim of this study was to assess the levels of peripheric neurodegeneration biomarkers of NPC1 patients, namely brain-derived neurotrophic factor (BDNF), platelet-derived growth factors (PDGF-AA and PDGF-AB/BB), neural cell adhesion molecule (NCAM), PAI-1 Total and Cathepsin-D, as well as the levels of cholestane-3β,5α,6β-triol (3β,5α,6β-triol), a biomarker for NPC1. Molecular analysis of the NPC1 patients under study was performed by next generation sequencing (NGS) in cultured fibroblasts. We observed that NPC1 patients treated with miglustat have a significant decrease in PAI-1 total and PDGF-AA concentrations, and no alteration in BDNF, NCAM, PDGF-AB/BB and Cathepsin D. We also found that NPC1 patients treated with miglustat have normalized levels of 3β,5α,6β-triol. The molecular analysis showed four described mutations, and for two patients was not possible to identify the second mutated allele. Our results indicate that the decrease of PAI-1 and PDGF-AA in NPC1 patients could be involved in the pathophysiology of this disease. This is the first work to analyze those plasmatic markers of neurodegenerative processes in NPC1 patients.

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.

Probability of high-risk genetic matching with oocyte and semen donors: complete gene analysis or genotyping test?

PURPOSE

To estimate the probability of high-risk genetic matching when assisted reproductive techniques (ART) are applied with double gamete donation, following an NGS carrier test based on a complete study of the genes concerned. We then determine the results that would have been obtained if the genotyping tests most widely used in Spanish gamete banks had been applied.

METHODS

In this descriptive observational study, 1818 gamete donors were characterised by NGS. The pathogenic variants detected were analysed to estimate the probability of high-risk genetic matching and to determine the results that would have been obtained if the three most commonly used genotyping tests in ART had been applied.

RESULTS

The probability of high-risk genetic matching with gamete donation, screened by NGS and complete gene analysis, was 5.5%, versus the 0.6-2.7% that would have been obtained with the genotyping test. A total of 1741 variants were detected, including 607 different variants, of which only 22.6% would have been detected by all three genotyping tests considered and 44.7% of which would not have been detected by any of these tests.

CONCLUSION

Our study highlights the considerable heterogeneity of the genotyping tests, which present significant differences in their ability to detect pathogenic variants. The complete study of the genes by NGS considerably reduces reproductive risks when genetic matching is performed with gamete donors. Accordingly, we recommend that carrier screening in gamete donors be carried out using NGS and a complete study with nontargeted analysis of the variants of the screened genes.

Identification of novel mutations among Iranian NPC1 patients: a bioinformatics approach to predict pathogenic mutations

Background

Niemann-Pick disease type C (NPC) is a rare lysosomal neurovisceral storage disease caused by mutations in the NPC 1 (95%) or NPC2 (5%) genes. The products of NPC1 and NPC2 genes play considerable roles in glycolipid and cholesterol trafficking, which could consequently lead to NPC disease with variable phenotypes displaying a broad spectrum of symptoms.

Materials

In the present study 35 Iranian NPC unrelated patients were enrolled. These patients were first analysed by the Filipin Staining test of cholesterol deposits in cells for NPC diagnostics. Genomic DNA was extracted from the samples of peripheral blood leukocytes in EDTA following the manufacturer's protocol. All exon–intron boundaries and coding exons of the NPC1gene were amplified by polymerase chain reaction (PCR) using appropriate sets of primers. Thereafter, the products of PCR were sequenced and analysed using the NCBI database (https://blast.ncbi.nlm.nih.gov/Blast.cgi). The variants were reviewed by some databases including the Human Gene Mutation Database (HGMD) (http://www.hgmd.cf.ac.uk/ac/index.php) and ClinVar (https://www.ncbi.nlm.nih.gov/clinvar (. Moreover, all the variants were manually classified in terms of the American College of Medical Genetics and Genomics (ACMG) guideline.

Results

The sequence analysis revealed 20 different variations, 10 of which are new, including one nonsense mutation (c.406C > T); three small deletions, (c.3126delC, c.2920_2923delCCTG, and c.2037delG); and six likely pathogenic missense mutations, (c.542C > A, c.1970G > A, c.1993C > G, c.2821 T > C, c.2872C > G, and c.3632 T > A). Finally, the pathogenicity of these new variants was determined using the ACMG guidelines.

Conclusion

The present study aimed to facilitate the prenatal diagnosis of NPC patients in the future. In this regard, we identified 10 novel mutations, and verified that the majority of them occurred in six NPC1 exons (5, 8, 9, 13, 19, and 21), that should be considered with a high priority for Iranian patients' cost-effective evaluation.

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.

Neonatal cholestasis and Niemann-pick type C disease: A literature review

BACKGROUND

Neonatal cholestasis (NC) is one of the most serious diseases in newborns and infants and results from metabolic disorders, such as Niemann-Pick type C (NPC), among other causes.

OBJECTIVE

We evaluated the incidence of NPC in our NC plus lysosomal storage disease (LSD) suspicious neonates and infants series.

METHODS

The study included children (≤3 years old) with a history of NC together with a suspicion of LSD, referred from Spanish Hospitals during the period 2011-2020. Screening for NPC was done by plasma biomarker assay (chitotriosidase activity and 7-ketocholesterol), and Sanger sequencing for NPC1 and NPC2 genes.

RESULTS

We screened NPC disease in 17 patients with NC plus organomegaly and that were LSD suspicious, finding 5 NPC patients (29.4%) and 2 carriers.

CONCLUSIONS

Our results emphasize the need to study NPC when NC and visceral enlargement arise in a newborn or infant.

HSP90 inhibitors reduce cholesterol storage in Niemann-Pick type C1 mutant fibroblasts

Niemann-Pick type C1 (NPC1) disease is a lysosomal lipid storage disorder caused by mutations of the NPC1 gene. More than 300 disease-associated mutations are reported in patients, resulting in abnormal accumulation of unesterified cholesterol, glycosphingolipids, and other lipids in late endosomes and lysosomes (LE/Ly) of many cell types. Previously, we showed that treatment of many different NPC1 mutant fibroblasts with histone deacetylase inhibitors resulted in reduction of cholesterol storage, and we found that this was associated with enhanced exit of the NPC1 protein from the endoplasmic reticulum and delivery to LE/Ly. This suggested that histone deacetylase inhibitors may work through changes in protein chaperones to enhance the folding of NPC1 mutants, allowing them to be delivered to LE/Ly. In this study, we evaluated the effect of several HSP90 inhibitors on NPC1I1061T skin fibroblasts. We found that HSP90 inhibition resulted in clearance of cholesterol from LE/Ly, and this was associated with enhanced delivery of the mutant NPC1I1061T protein to LE/Ly. We also observed that inhibition of HSP90 increased the expression of HSP70, and overexpression of HSP70 also reduced cholesterol storage in NPC1I1061T fibroblasts. However, we did not see correction of cholesterol storage by arimoclomol, a drug that is reported to increase HSP70 expression, at doses up to 0.5 mM. The increase in other chaperones as a consequence of HSP90 improves folding of NPC1 protein and relieves cholesterol accumulation in NPC1 mutant fibroblasts.

Inhibition of Histone Deacetylases 1, 2, and 3 Enhances Clearance of Cholesterol Accumulation in Niemann-Pick C1 Fibroblasts

Niemann-Pick disease type C1 (NPC1) is a rare genetic cholesterol storage disorder caused by mutations in the NPC1 gene. Mutations in this transmembrane late endosome protein lead to loss of normal cholesterol efflux from late endosomes and lysosomes. It has been shown that broad spectrum histone deacetylase inhibitors (HDACi's) such as Vorinostat correct the cholesterol accumulation phenotype in the majority of NPC1 mutants tested in cultured cells. In order to determine the optimal specificity for HDACi correction of the mutant NPC1s, we screened 76 HDACi's of varying specificity. We tested the ability of these HDACi's to correct the excess accumulation of cholesterol in patient fibroblast cells that homozygously express NPC1^I1061T, the most common mutation. We determined that inhibition of HDACs 1, 2, and 3 is important for correcting the defect, and combined inhibition of all three is needed to achieve the greatest effect, suggesting a need for multiple effects of the HDACi treatments. Identifying the specific HDACs involved in the process of regulating cholesterol trafficking in NPC1 will help to focus the search for more specific druggable targets.

A phase 1/2 open label nonrandomized clinical trial of intravenous 2-hydroxypropyl-β-cyclodextrin for acute liver disease in infants with Niemann-Pick C1

Introduction

Niemann-Pick C (NPC) is an autosomal recessive disease due to defective NPC1 or NPC2 proteins resulting in endo-lysosomal storage of unesterified cholesterol in the central nervous system and liver. Acute liver disease in the newborn period may be self-limited or fatal. 2-hydroxypropyl-β-cyclodextrin (2HPBCD) is a cholesterol-binding agent that reduces lysosomal cholesterol storage. We have enrolled 3 infants 0–6 months old with direct hyperbilirubinemia due to NPC1 or NPC2 liver disease in a Phase I/II open label clinical trial of intravenous 2HPBCD.

Methods

Infants received intravenous 2HPBCD twice a week for 6 weeks, followed by monthly infusion for 6-months. Primary outcome measure was reduction of plasma (3β,5α,6β-trihydroxy-cholan-24-oyl) glycine (TCG), a bile acid generated from cholesterol sequestered in lysosome.

Results

Three participants completed this protocol. A fourth patient received intravenous 2HPBCD under an emergency investigational new drug study but later expired from her underlying condition. The three protocol patients are living and have improved liver enzymes and TCG. No patient has experienced a drug-related adverse event.

Conclusion

Intravenous 2HPBCD was tolerated in three infants with liver disease due to NPC.

NPC1 silent variant induces skipping of exon 11 (p.V562V) and unfolded protein response was found in a specific Niemann-Pick type C patient

Background

Niemann‐Pick type C (NPC, MIM #257220) is a neuro‐visceral disease, caused predominantly by pathogenic variants in the NPC1 gene. Here we studied patients with clinical diagnosis of NPC but inconclusive results regarding the molecular analysis.

Methods

We used a Next‐Generation Sequencing (NGS)‐panel followed by cDNA analysis. Latter, we used massively parallel single‐cell RNA‐seq (MARS‐Seq) to address gene profiling changes and finally the effect of different variants on the protein and cellular levels.

Results

We identified novel variants and cDNA analysis allowed us to establish the functional effect of a silent variant, previously reported as a polymorphism. We demonstrated that this variant induces the skipping of exon 11 leading to a premature stop codon and identified it in NPC patients from two unrelated families. MARS‐Seq analysis showed that a number of upregulated genes were related to the unfolded protein response (UPR) and endoplasmic reticulum (ER) stress in one specific patient. Also, for all analyzed variants, the NPC1 protein was partially retained in the ER.

Conclusion

We showed that the NPC1 silent polymorphism (p.V562V) is a disease‐causing variant in NPC and that the UPR is upregulated in an NPC patient.

Clinical and Molecular Features of Early Infantile Niemann Pick Type C Disease

Niemann Pick disease type C (NPC) is a neurovisceral disorder due to mutations in NPC1 or NPC2. This review focuses on poorly characterized clinical and molecular features of early infantile form of NPC (EIF) and identified 89 cases caused by NPC1 (NPC1) and 16 by NPC2 (NPC2) mutations. Extra-neuronal features were common; visceromegaly reported in 80/89 NPC1 and in 15/16 NPC2, prolonged jaundice in 30/89 NPC1 and 7/16 NPC2. Early lung involvement was present in 12/16 NPC2 cases. Median age of neurological onset was 12 (0-24) and 7.5 (0-24) months in NPC1 and NPC2 groups, respectively. Developmental delay and hypotonia were the commonest first detected neurological symptoms reported in 39/89 and 18/89 NPC1, and in 8/16 and 10/16 NPC2, respectively. Additional neurological symptoms included vertical supranuclear gaze palsy, dysarthria, cataplexy, dysphagia, seizures, dystonia, and spasticity. The following mutations in homozygous state conferred EIF: deletion of exon 1+promoter, c.3578_3591 + 9del, c.385delT, p.C63fsX75, IVS21-2delATGC, c. 2740T>A (p.C914S), c.3584G>T (p.G1195V), c.3478-6T>A, c.960_961dup (p.A321Gfs*16) in NPC1 and c.434T>A (p.V145E), c.199T>C (p.S67P), c.133C>T (p.Q45X), c.141C>A (p.C47X) in NPC2. This comprehensive analysis of the EIF type of NPC will benefit clinical patient management, genetic counselling, and assist design of novel therapy trials.

Inherited disorders of lysosomal membrane transporters

Disorders caused by defects in lysosomal membrane transporters form a distinct subgroup of lysosomal storage disorders (LSDs). To date, defects in only 10 lysosomal membrane transporters have been associated with inherited disorders. The clinical presentations of these diseases resemble the phenotypes of other LSDs; they are heterogeneous and often present in children with neurodegenerative manifestations. However, for pathomechanistic and therapeutic studies, lysosomal membrane transport defects should be distinguished from LSDs caused by defective hydrolytic enzymes. The involved proteins differ in function, localization, and lysosomal targeting, and the diseases themselves differ in their stored material and therapeutic approaches. We provide an overview of the small group of disorders of lysosomal membrane transporters, emphasizing discovery, pathomechanism, clinical features, diagnostic methods and therapeutic aspects. We discuss common aspects of lysosomal membrane transporter defects that can provide the basis for preclinical research into these disorders.

Pre-mRNA splicing defects and RNA binding protein involvement in Niemann Pick type C disease

Niemann-Pick type C (NPC) is an autosomal recessive lysosomal storage disorder due to mutations in NPC1 (95 % cases) or NPC2 genes, encoding NPC1 and NPC2 proteins, respectively. Both NPC1 and NPC2 proteins are involved in transport of intracellular cholesterol and their alteration leads to the accumulation of unesterified cholesterol and other lipids within the lysosomes. The disease is characterized by visceral, neurological and psychiatric symptoms. However, the pathogenic mechanisms that lead to the fatal neurodegeneration are still unclear. To date, several mutations leading to the generation of aberrant splicing variants or mRNA degradation in NPC1 and NPC2 genes have been reported. In addition, different lines of experimental evidence have highlighted the possible role of RNA-binding proteins and RNA-metabolism, in the onset and progression of many neurodegenerative disorders, that could explain NPC neurological features and in general, the disease pathogenesis. In this review, we will provide an overview of the impact of mRNA processing and metabolism on NPC disease pathology.

Transcript, protein, metabolite and cellular studies in skin fibroblasts demonstrate variable pathogenic impacts of NPC1 mutations

Background

Niemann-Pick type C (NP-C) is a rare neurovisceral genetic disorder caused by mutations in the NPC1 or the NPC2 gene. NPC1 is a multipass-transmembrane protein essential for egress of cholesterol from late endosomes/lysosomes. To evaluate impacts of NPC1 mutations, we examined fibroblast cultures from 26 NP-C1 patients with clinical phenotypes ranging from infantile to adult neurologic onset forms. The cells were tested with multiple assays including NPC1 mRNA expression levels and allele expression ratios, assessment of NPC1 promoter haplotypes, NPC1 protein levels, cellular cholesterol staining, localization of the mutant NPC1 proteins to lysosomes, and cholesterol/cholesteryl ester ratios. These results were correlated with phenotypes of the individual patients.

Results

Overall we identified 5 variant promoter haplotypes. Three of them showed reporter activity decreased down to 70% of the control sequence. None of the haplotypes were consistently associated with more severe clinical presentation of NP-C. Levels of transcripts carrying null NPC1 alleles were profoundly lower than levels of the missense variants. Low levels of the mutant NPC1 protein were identified in most samples. The protein localised to lysosomes in cultures expressing medium to normal NPC1 levels. Fibroblasts from patients with severe infantile phenotypes had higher cholesterol levels and higher cholesterol/cholesteryl ester ratios. On the contrary, cell lines from patients with juvenile and adolescent/adult phenotypes showed values comparable to controls.

Conclusion

No single assay fully correlated with the disease severity. However, low residual levels of NPC1 protein and high cholesterol/cholesteryl ester ratios associated with severe disease. The results suggest not only low NPC1 expression due to non-sense mediated decay or low mutant protein stability, but also dysfunction of the stable mutant NPC1 as contributors to the intracellular lipid transport defect.

Molecular Genetics of Niemann-Pick Type C Disease in Italy: An Update on 105 Patients and Description of 18 NPC1 Novel Variants

Niemann-Pick type C (NPC) disease is an autosomal recessive lysosomal storage disorder caused by mutations in NPC1 or NPC2 genes. In 2009, the molecular characterization of 44 NPC Italian patients has been published. Here, we present an update of the genetic findings in 105 Italian NPC patients belonging to 83 unrelated families (77 NPC1 and 6 NPC2). NPC1 and NPC2 genes were studied following an algorithm recently published. Eighty-four different NPC1 and five NPC2 alleles were identified. Only two NPC1 alleles remained non detected. Sixty-two percent of NPC1 alleles were due to missense variants. The most frequent NPC1 mutation was the p.F284Lfs*26 (5.8% of the alleles). All NPC2 mutations were found in the homozygous state, and all but one was severe. Among newly diagnosed patients, 18 novel NPC1 mutations were identified. The pathogenic nature of 7/9 missense alleles and 3/4 intronic variants was confirmed by filipin staining and NPC1 protein analysis or mRNA expression in patient’s fibroblasts. Taken together, our previous published data and new results provide an overall picture of the molecular characteristics of NPC patients diagnosed so far in Italy.

Modeling Niemann-Pick disease type C in a human haploid cell line allows for patient variant characterization and clinical interpretation

The accurate clinical interpretation of human sequence variation is foundational to personalized medicine. This remains a pressing challenge, however, as genome sequencing becomes routine and new functionally undefined variants rapidly accumulate. Here, we describe a platform for the rapid generation, characterization, and interpretation of genomic variants in haploid cells focusing on Niemann–Pick disease type C (NPC) as an example. NPC is a fatal neurodegenerative disorder characterized by a lysosomal accumulation of unesterified cholesterol and glycolipids. In 95% of cases, NPC is caused by mutations in the NPC1 gene, for which more than 200 unique disease-causing variants have been reported to date. Furthermore, the majority of patients with NPC are compound heterozygotes that often carry at least one private mutation, presenting a challenge for the characterization and classification of individual variants. Here, we have developed the first haploid cell model of NPC. This haploid cell model recapitulates the primary biochemical and molecular phenotypes typically found in patient-derived fibroblasts, illustrating its utility in modeling NPC. Additionally, we show the power of CRISPR/Cas9-mediated base editing in quickly and efficiently generating haploid cell models of individual patient variants in NPC. These models provide a platform for understanding the disease mechanisms underlying individual NPC1 variants while allowing for definitive clinical variant interpretation for NPC.

Different Niemann-Pick C1 Genotypes Generate Protein Phenotypes that Vary in their Intracellular Processing, Trafficking and Localization

Niemann-Pick Type C (NP-C) is an inherited neurovisceral lysosomal storage disease characterized by a defect in the trafficking of endocytosed cholesterol. In 95% of patients the gene encoding NPC1 is affected. The correlation of the genetic background in NP-C with the clinical phenotype such as, severity and onset of liver dysfunction, ataxia, dystonia and vertical gaze palsy, has not been elucidated at the molecular level. We have designed strategies to investigate the effect of different mutations in the NPC1 gene at the protein and cellular levels. The NPC1 mutants were expressed in mammalian cells and their structural features, maturation pathways and subcellular localization elucidated. Interestingly, three classes of NPC1 mutants could be identified and further characterized. The first group comprised mutants in which the NPC1 protein revealed virtually similar structural features to the wild type species. It was trafficked to the lysosomes and colocalized with the lysosomal protein marker Lamp2. The second class of NPC1 mutants was only partially trafficked to the lysosomes, but predominantly localized to the endoplasmic reticulum (ER). In the third group with the most severe phenotype, NPC1 mutants were entirely retained in the ER, colocalizing with the ER-protein marker calnexin. In conclusion, this study relates NPC1 mutations to the trafficking behavior of the NPC1 mutants along the secretory pathway. The findings are essential for a comprehensive understanding of the pathogenesis of NP-C and propose a mutation-based personalized therapeutical approach.

Niemann-Pick Disease Type C: Mutation Spectrum and Novel Sequence Variations in the Human NPC1 Gene

Niemann-Pick type C (NP-C) is a rare autosomal recessive disorder characterized by storage of unesterified glycolipids and cholesterol in lysosome and/or late endosome due to mutations in either NPC1 or NPC2 gene. This study aims to identify the spectrum of sequence alterations associated to NP-C in individuals with clinical suspicion of this disease. The entire coding region and flanking sequences of both genes associated to NP-C were evaluated in a total of 265 individuals that were referred to our laboratory. Clinical and/or biochemical suspicion of NP-C was confirmed by molecular analysis in 54 subjects. In this cohort, 33 different sequence alterations were identified in NPC1 and one in NPC2. Among those, 5 novel alterations in NPC1 gene were identified as follows: one deletion (p.Lys38_Tyr40del), one frameshift (p.Asn195Lysfs*2), and three missense mutations (p.Cys238Arg, p.Ser365Pro and, p.Val694Met) that are likely to be pathogenic through different approaches, including in silico tools as well as multiple sequence alignment throughout different species. We have also reported main clinical symptoms of patients with novel alterations and distribution of frequent symptoms in the cohort. Findings reported here contribute to the knowledge of mutation spectrum of NP-C, defining frequent mutations as well as novel sequence alterations associated to the disease.

Consensus clinical management guidelines for Niemann-Pick disease type C

Niemann-Pick Type C (NPC) is a progressive and life limiting autosomal recessive disorder caused by mutations in either the NPC1 or NPC2 gene. Mutations in these genes are associated with abnormal endosomal-lysosomal trafficking, resulting in the accumulation of multiple tissue specific lipids in the lysosomes. The clinical spectrum of NPC disease ranges from a neonatal rapidly progressive fatal disorder to an adult-onset chronic neurodegenerative disease. The age of onset of the first (beyond 3 months of life) neurological symptom may predict the severity of the disease and determines life expectancy.

NPC has an estimated incidence of ~ 1: 100,000 and the rarity of the disease translate into misdiagnosis, delayed diagnosis and barriers to good care. For these reasons, we have developed clinical guidelines that define standard of care for NPC patients, foster shared care arrangements between expert centres and family physicians, and empower patients. The information contained in these guidelines was obtained through a systematic review of the literature and the experiences of the authors in their care of patients with NPC. We adopted the Appraisal of Guidelines for Research & Evaluation (AGREE II) system as method of choice for the guideline development process. We made a series of conclusive statements and scored them according to level of evidence, strengths of recommendations and expert opinions. These guidelines can inform care providers, care funders, patients and their carers of best practice of care for patients with NPC. In addition, these guidelines have identified gaps in the knowledge that must be filled by future research. It is anticipated that the implementation of these guidelines will lead to a step change in the quality of care for patients with NPC irrespective of their geographical location.

The Extending Spectrum of NPC1-Related Human Disorders: From Niemann-Pick C1 Disease to Obesity

The Niemann-Pick type C1 (NPC1) protein regulates the transport of cholesterol and fatty acids from late endosomes/lysosomes and has a central role in maintaining lipid homeostasis. NPC1 loss-of-function mutations in humans cause NPC1 disease, a rare autosomal-recessive lipid-storage disorder characterized by progressive and lethal neurodegeneration, as well as liver and lung failure, due to cholesterol infiltration. In humans, genome-wide association studies and post-genome-wide association studies highlight the implication of common variants in NPC1 in adult-onset obesity, body fat mass, and type 2 diabetes. Heterozygous human carriers of rare loss-of-function coding variants in NPC1 display an increased risk of morbid adult obesity. These associations have been confirmed in mice models, showing an important interaction with high-fat diet. In this review, we describe the current state of knowledge for NPC1 variants in relationship to pleiotropic effects on metabolism. We provide evidence that NPC1 gene variations may predispose to common metabolic diseases by modulating steroid hormone synthesis and/or lipid homeostasis. We also propose several important directions of research to further define the complex roles of NPC1 in metabolism. This review emphasizes the contribution of NPC1 to obesity and its metabolic complications.

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

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

Genome sequencing in a case of Niemann-Pick type C

Adult-onset Niemann–Pick disease type C (NPC) is an infrequent presentation of a rare neurovisceral lysosomal lipid storage disorder caused by autosomal recessive mutations in NPC1 (∼95%) or NPC2 (∼5%). Our patient was diagnosed at age 33 when he presented with a 10-yr history of difficulties in judgment, concentration, speech, and coordination. A history of transient neonatal jaundice and splenomegaly with bone marrow biopsy suggesting a lipid storage disorder pointed to NPC; biochemical (“variant” level cholesterol esterification) and ultrastructural studies in adulthood confirmed the diagnosis. Genetic testing revealed two different missense mutations in the NPC1 gene—V950M and N1156S. Symptoms progressed over >20 yr to severe ataxia and spasticity, dementia, and dysphagia with aspiration leading to death. Brain autopsy revealed mild atrophy of the cerebrum and cerebellum. Microscopic examination showed diffuse gray matter deposition of balloon neurons, mild white matter loss, extensive cerebellar Purkinje cell loss with numerous “empty baskets,” and neurofibrillary tangles predominantly in the hippocampal formation and transentorhinal cortex. We performed whole-genome sequencing to examine whether the patient harbored variants outside of the NPC1 locus that could have contributed to his late-onset phenotype. We focused analysis on genetic modifiers in pathways related to lipid metabolism, longevity, and neurodegenerative disease. We identified no rare coding variants in any of the pathways examined nor was the patient enriched for genome-wide association study (GWAS) single-nucleotide polymorphisms (SNPs) associated with longevity or altered lipid metabolism. In light of these findings, this case provides support for the V950M variant being sufficient for adult-onset NPC disease.

Rapid whole-genome sequencing identifies a novel homozygous NPC1 variant associated with Niemann-Pick type C1 disease in a 7-week-old male with cholestasis

Niemann–Pick type C disease (NPC; OMIM #257220) is an inborn error of intracellular cholesterol trafficking. It is an autosomal recessive disorder caused predominantly by mutations in NPC1. Although characterized as a progressive neurological disorder, it can also cause cholestasis and liver dysfunction because of intrahepatocyte lipid accumulation. We report a 7-wk-old infant who was admitted with neonatal cholestasis, and who was diagnosed with a novel homozygous stop-gain variant in NPC1 by rapid whole-genome sequencing (WGS). WGS results were obtained 16 d before return of the standard clinical genetic test results and prompted initiation of targeted therapy.

Novel NPC1 mutations with different segregation in two related Greek patients with Niemann-Pick type C disease: molecular study in the extended pedigree and clinical correlations

BACKGROUND

Niemann-Pick type C disease (NPC) is an autosomal recessive, neurovisceral, lysosomal storage disorder with protean and progressive clinical manifestations, resulting from mutations in either of the two genes, NPC1 (~95% of families) and NPC2. Contrary to other populations, published evidence regarding NPC disease in Greece is sparse.

METHODS

The study population consisted of two Greek NPC patients and their extended pedigree. Patients' clinical, biochemical, molecular profiles and the possible correlations are presented. Genotyping was performed by direct sequencing. Mutations' origin was investigated through selected exonic NPC1 polymorphisms encountered more frequently in a group of 37 Greek patients with clinical suspicion of NPC disease and in a group of 90 healthy Greek individuals, by the use of Haplore software.

RESULTS

Two novel NPC1 mutations, [IVS23 + 3insT (c.3591 + 3insT) and p. K1057R (c.3170A > C)] were identified and each mutation was associated with a specific haplotype. One of the patients was entered to early treatment with miglustat and has presented no overt neurological impairment after 11.5 years.

CONCLUSIONS

The splicing mutation IVS23 + 3insT was associated in homozygocity with a severe biochemical and clinical phenotype. A possible founder effect for this mutation was demonstrated in the Greek Island, as well as a different origin for each novel mutation. Longitudinal follow-up may contribute to clarify the possible effect of early miglustat therapy on the patient compound heterozygous for the two novel mutations.

The hidden Niemann-Pick type C patient: clinical niches for a rare inherited metabolic disease

BACKGROUND

Niemann-Pick disease type C (NP-C) is a rare, inherited neurodegenerative disease of impaired intracellular lipid trafficking. Clinical symptoms are highly heterogeneous, including neurological, visceral, or psychiatric manifestations. The incidence of NP-C is under-estimated due to under-recognition or misdiagnosis across a wide range of medical fields. New screening and diagnostic methods provide an opportunity to improve detection of unrecognized cases in clinical sub-populations associated with a higher risk of NP-C. Patients in these at-risk groups ("clinical niches") have symptoms that are potentially related to NP-C, but go unrecognized due to other, more prevalent clinical features, and lack of awareness regarding underlying metabolic causes.

METHODS

Twelve potential clinical niches identified by clinical experts were evaluated based on a comprehensive, non-systematic review of literature published to date. Relevant publications were identified by targeted literature searches of EMBASE and PubMed using key search terms specific to each niche. Articles published in English or other European languages up to 2016 were included.

FINDINGS

Several niches were found to be relevant based on available data: movement disorders (early-onset ataxia and dystonia), organic psychosis, early-onset cholestasis/(hepato)splenomegaly, cases with relevant antenatal findings or fetal abnormalities, and patients affected by family history, consanguinity, and endogamy. Potentially relevant niches requiring further supportive data included: early-onset cognitive decline, frontotemporal dementia, parkinsonism, and chronic inflammatory CNS disease. There was relatively weak evidence to suggest amyotrophic lateral sclerosis or progressive supranuclear gaze palsy as potential niches.

CONCLUSIONS

Several clinical niches have been identified that harbor patients at increased risk of NP-C.

Precision Medicine in Cats: Novel Niemann-Pick Type C1 Diagnosed by Whole-Genome Sequencing

State‐of‐the‐art health care includes genome sequencing of the patient to identify genetic variants that contribute to either the cause of their malady or variants that can be targeted to improve treatment. The goal was to introduce state‐of‐the‐art health care to cats using genomics and a precision medicine approach. To test the feasibility of a precision medicine approach in domestic cats, a single cat that presented to the University of Missouri, Veterinary Health Center with an undiagnosed neurologic disease was whole‐genome sequenced. The DNA variants from the cat were compared to the DNA variant database produced by the 99 Lives Cat Genome Sequencing Consortium. Approximately 25× genomic coverage was produced for the cat. A predicted p.H441P missense mutation was identified in NPC1, the gene causing Niemann‐Pick type C1 on cat chromosome D3.47456793 caused by an adenine‐to‐cytosine transversion, c.1322A>C. The cat was homozygous for the variant. The variant was not identified in any other 73 domestic and 9 wild felids in the sequence database or 190 additionally genotyped cats of various breeds. The successful effort suggested precision medicine is feasible for cats and other undiagnosed cats may benefit from a genomic analysis approach. The 99 Lives DNA variant database was sufficient but would benefit from additional cat sequences. Other cats with the mutation may be identified and could be introduced as a new biomedical model for NPC1. A genetic test could eliminate the disease variant from the population.

Assessment of plasma chitotriosidase activity, CCL18/PARC concentration and NP-C suspicion index in the diagnosis of Niemann-Pick disease type C: a prospective observational study

BACKGROUND

Niemann-Pick disease type C (NP-C) is a rare, autosomal recessive neurodegenerative disease caused by mutations in either the NPC1 or NPC2 genes. The diagnosis of NP-C remains challenging due to the non-specific, heterogeneous nature of signs/symptoms. This study assessed the utility of plasma chitotriosidase (ChT) and Chemokine (C-C motif) ligand 18 (CCL18)/pulmonary and activation-regulated chemokine (PARC) in conjunction with the NP-C suspicion index (NP-C SI) for guiding confirmatory laboratory testing in patients with suspected NP-C.

METHODS

In a prospective observational cohort study, incorporating a retrospective determination of NP-C SI scores, two different diagnostic approaches were applied in two separate groups of unrelated patients from 51 Spanish medical centers (n = 118 in both groups). From Jan 2010 to Apr 2012 (Period 1), patients with ≥2 clinical signs/symptoms of NP-C were considered 'suspected NP-C' cases, and NPC1/NPC2 sequencing, plasma chitotriosidase (ChT), CCL18/PARC and sphingomyelinase levels were assessed. Based on findings in Period 1, plasma ChT and CCL18/PARC, and NP-C SI prediction scores were determined in a second group of patients between May 2012 and Apr 2014 (Period 2), and NPC1 and NPC2 were sequenced only in those with elevated ChT and/or elevated CCL18/PARC and/or NP-C SI ≥70. Filipin staining and 7-ketocholesterol (7-KC) measurements were performed in all patients with NP-C gene mutations, where possible.

RESULTS

In total across Periods 1 and 2, 10/236 (4%) patients had a confirmed diagnosis o NP-C based on gene sequencing (5/118 [4.2%] in each Period): all of these patients had two causal NPC1 mutations. Single mutant NPC1 alleles were detected in 8/236 (3%) patients, overall. Positive filipin staining results comprised three classical and five variant biochemical phenotypes. No NPC2 mutations were detected. All patients with NPC1 mutations had high ChT activity, high CCL18/PARC concentrations and/or NP-C SI scores ≥70. Plasma 7-KC was higher than control cut-off values in all patients with two NPC1 mutations, and in the majority of patients with single mutations. Family studies identified three further NP-C patients.

CONCLUSION

This approach may be very useful for laboratories that do not have mass spectrometry facilities and therefore, they cannot use other NP-C biomarkers for diagnosis.

Diagnostic tests for Niemann-Pick disease type C (NP-C): A critical review

Niemann-Pick disease type C (NP-C) is a neurovisceral lysosomal cholesterol trafficking and lipid storage disorder caused by mutations in one of the two genes, NPC1 or NPC2. Diagnosis has often been a difficult task, due to the wide range in age of onset of NP-C and clinical presentation of the disease, combined with the complexity of the cell biology (filipin) laboratory testing, even in combination with genetic testing. This has led to substantial delays in diagnosis, largely depending on the access to specialist centres and the level of knowledge about NP-C of the physician in the area. In recent years, advances in mass spectrometry has allowed identification of several sensitive plasma biomarkers elevated in NP-C (e.g. cholestane-3β,5α,6β-triol, lysosphingomyelin isoforms and bile acid metabolites), which, together with the concomitant progress in molecular genetic technology, have greatly impacted the strategy of laboratory testing. Specificity of the biomarkers is currently under investigation and other pathologies are being found to also result in elevations. Molecular genetic testing also has its limitations, notably with unidentified mutations and the classification of new variants. This review is intended to increase awareness on the currently available approaches to laboratory diagnosis of NP-C, to provide an up to date, comprehensive and critical evaluation of the various techniques (cell biology, biochemical biomarkers and molecular genetics), and to briefly discuss ongoing/future developments. The use of current tests in proper combination enables a rapid and correct diagnosis in a large majority of cases. However, even with recent progress, definitive diagnosis remains challenging in some patients, for whom combined genetic/biochemical/cytochemical markers do not provide a clear answer. Expertise and reference laboratories thus remain essential, and further work is still required to fulfill unmet needs.

Structure of glycosylated NPC1 luminal domain C reveals insights into NPC2 and Ebola virus interactions

Niemann‐pick type C1 (NPC1) is an endo/lysosomal membrane protein involved in intracellular cholesterol trafficking, and its luminal domain C is an essential endosomal receptor for Ebola and Marburg viruses. We have determined the crystal structure of glycosylated NPC1 luminal domain C and find all seven possible sites are glycosylated. Mapping the disease mutations onto the glycosylated structure reveals a potential binding face for NPC2. Knowledge‐based docking of NPC1 onto Ebola viral glycoprotein and sequence analysis of filovirus susceptible and refractory species reveals four critical residues, H418, Q421, F502 and F504, some or all of which are likely responsible for the species‐specific susceptibility to the virus infection.

Role of STARD4 and NPC1 in intracellular sterol transport

Cholesterol plays an important role in determining the biophysical properties of membranes in mammalian cells, and the concentration of cholesterol in membranes is tightly regulated. Cholesterol moves among membrane organelles by a combination of vesicular and nonvesicular transport pathways, but the details of these transport pathways are not well understood. In this review, we discuss the mechanisms for nonvesicular sterol transport with an emphasis on the role of STARD4, a small, soluble, cytoplasmic sterol transport protein. STARD4 can rapidly equilibrate sterol between membranes, especially membranes with anionic lipid headgroups. We also discuss the sterol transport in late endosomes and lysosomes, which is mediated by a soluble protein, NPC2, and a membrane protein, NPC1. Homozygous mutations in these proteins lead to a lysosomal lipid storage disorder, Niemann-Pick disease type C. Many of the disease-causing mutations in NPC1 are associated with degradation of the mutant NPC1 proteins in the endoplasmic reticulum. Several histone deacetylase inhibitors have been found to rescue the premature degradation of the mutant NPC1 proteins, and one of these is now in a small clinical trial.

Identification of lysosomal Npc1-binding proteins: Cathepsin D activity is regulated by NPC1

Niemann-Pick type C (NPC) disease is an inherited lysosomal storage disorder, characterized by severe neurodegeneration. It is mostly produced by mutations in the NPC1 gene, encoding for a protein of the late endosomes/lysosomes membrane, involved in cholesterol metabolism. However, the specific role of this protein in NPC disease still remains unknown. We aimed to identify Npc1-binding proteins in order to define new putative NPC1 lysosomal functions. By affinity chromatography using an Npc1 peptide (amino acids 1032-1066 of loop I), as bait, we fished 31 lysosomal proteins subsequently identified by LC-MS/MS. Most of them were involved in proteolysis and lipid catabolism and included the protease cathepsin D. Cathepsin D and NPC1 interaction was validated by immunoprecipitation and the functional relevance of this interaction was studied. We found that fibroblasts from NPC patients with low levels of NPC1 protein have high amounts of procathepsin D but reduced quantities of the mature protein, thus showing a diminished cathepsin D activity. The increase of NPC1 protein levels in NPC cells by treatment with the proteasome inhibitor bortezomib, induced an elevation of cathepsin D activity. All these results suggest a new lysosomal function of NPC1 as a regulator of cathepsin D processing and activity.

Cholestane-3β,5α,6β-triol: high levels in Niemann-Pick type C, cerebrotendinous xanthomatosis, and lysosomal acid lipase deficiency

Niemann-Pick type C (NPC) is a progressive neurodegenerative disease characterized by lysosomal/endosomal accumulation of unesterified cholesterol and glycolipids. Recent studies have shown that plasma cholestane-3β,5α,6β-triol (CT) and 7-ketocholesterol (7-KC) could be potential biomarkers for the diagnosis of NPC patients. We aimed to know the sensitivity and specificity of these biomarkers for the diagnosis of NPC compared with other diseases that can potentially lead to oxysterol alterations. We studied 107 controls and 122 patients including 16 with NPC, 3 with lysosomal acid lipase (LAL) deficiency, 8 with other lysosomal diseases, 5 with galactosemia, 11 with cerebrotendinous xanthomatosis (CTX), 3 with Smith-Lemli-Opitz, 14 with peroxisomal biogenesis disorders, 19 with unspecific hepatic diseases, 13 with familial hypercholesterolemia, and 30 with neurological involvement and no evidence of an inherited metabolic disease. CT and 7-KC were analyzed by HPLC-ESI-MS/MS as mono-dimethylglycine derivatives. Levels of 7-KC were high in most of the studied diseases, whereas those of CT were only high in NPC, LAL, and CTX patients. Consequently, although CT is a sensitive biomarker of NPC disease, including those cases with doubtful filipin staining, it is not specific. 7-KC is a very unspecific biomarker.

Genetic and laboratory diagnostic approach in Niemann Pick disease type C

Niemann Pick disease type C (NP-C) is a rare autosomal recessive disorder that results from mutations in either the NPC1 or the NPC2 gene. The estimated incidence of NP-C is 1 in 120,000 live births, although the frequency of cases is higher in some isolated populations. More than 350 different NPC1 and NPC2 gene mutations have been reported in patients with confirmed diagnoses. Approximately 95 % of patients harbour mutations in NPC1, with most of the remaining patients having NPC2 mutations. The traditional methods for diagnosing patients with NP-C include histopathological analysis of bone marrow aspirate, liver and skin biopsies, fluorescent and electron microscopy, and cholesterol esterification assays. New laboratory methods that use mass spectroscopy for detection of cholesterol metabolism products are promising to become part of the routine diagnostic and screening tests in the near future, but further evaluation is required to determine the sensitivity and specificity of these analyses in patients with different age-at-onset forms of NP-C. Although filipin staining and cholesterol esterification studies performed in patient skin fibroblasts can, in experienced hands, provide a robust approach to diagnosing NP-C, they are only available in a few specialist laboratories. Thus, sequencing of NPC1 and NPC2 is currently the most universally accessible diagnostic technique in this disorder.

Miglustat: a review of its use in Niemann-Pick disease type C

Miglustat (Zavesca®, Brazaves®), a small iminosugar molecule that reversibly inhibits glycosphingolipid synthesis, is the only disease-specific drug approved for the treatment of progressive neurological manifestations of Niemann-Pick disease type C (NP-C) in adult and paediatric patients. NP-C is a rare, autosomal-recessive lipid storage disorder characterized by impaired intracellular lipid trafficking and progressive neurological symptoms leading to premature death. In a randomized clinical trial, long-term extension studies and a retrospective observational cohort study, treatment with oral miglustat stabilized key neurological manifestations of NP-C (including horizontal saccadic eye movement peak velocity, ambulation, manipulation, language and swallowing) in paediatric and adult patients with the disease. The therapeutic effects of miglustat in stabilizing or slowing disease progression have been confirmed in other reports in the clinical experience setting. The primary tolerability issues associated with miglustat are mild to moderate gastrointestinal effects (e.g. diarrhoea, flatulence and abdominal pain/discomfort) and weight loss, which usually occur during initial therapy and are generally manageable. In the absence of a cure, miglustat is a valuable agent to reduce the progression of clinically relevant neurological symptoms in paediatric and adult patients with NP-C, which is considered a significant achievement in the treatment of this disease.

Differential Association of Niemann-Pick C1 Gene Polymorphisms with Maternal Prepregnancy Overweight and Gestational Diabetes

A genome-wide association study (GWAS) and subsequent replication studies in diverse ethnic groups indicate that common Niemann-Pick C1 gene (NPC1) polymorphisms are associated with morbid-adult obesity or diabetes independent of body weight. The objectives for this prospective cross-sectional study were to determine allele frequencies for NPC1 polymorphisms (644A>G, 1926C>G, 2572A>G, and 3797G>A) and association with metabolic disease phenotypes in an ethnically diverse New Mexican obstetric population. Allele frequencies for 1926C>G, 2572A>G, and 3797G>A were significantly different between race/ethnic groups (non-Hispanic white, Hispanic, and Native American). The results also indicated a significant pairwise linkage-disequilibrium between each of the four NPC1 polymorphisms in race/ethnic groups. Moreover, the derived and major allele for 1926C>G was associated (OR 2.11, 95% CI 1.10–3.96, P = 0.022) with increased risk for maternal prepregnancy overweight (BMI 25.0–29.9kg/m²) while the ancestral and major allele for 2572A>G was associated (OR 4.68, 95% CI 1.23–17.8, P = 0.024) with increased risk for gestational diabetes in non-Hispanic whites, but not Hispanics or Native Americans. In summary, this is the first transferability study to investigate common NPC1 polymorphisms in a multiethnic population and demonstrate a differential association with increased risk for maternal prepregnancy overweight and gestational diabetes.

Observational, retrospective study of a large cohort of patients with Niemann-Pick disease type C in the Czech Republic: a surprisingly stable diagnostic rate spanning almost 40 years

Background

Niemann-Pick disease type C (NPC) is a rare, fatal neurovisceral disorder with autosomal recessive inheritance, and featuring striking clinical variability dependent on the age at onset of neurological symptoms. We report data from a large cohort of 56 Czech patients with NPC diagnosed over a period of 37 years.

Methods

An observational, retrospective analysis of historic and current clinical and laboratory information was performed among all NPC patients originating from the area of the contemporary Czech Republic and diagnosed between 1975 and 2012. All patients with ≥1 positive diagnostic test and relevant clinical information were included. Data on diagnostic methods (histopathological and/or ultrastructural; biochemical; genetic), clinical status and general information on treatment were collated. Data were examined in accordance with international guidelines for the management of NPC.

Results

Between 1975 and 1985 diagnoses were based exclusively on specific histopathological findings, often at autopsy. Bone marrow smear (BMS) analyses have proved to be a very specific indicator for NPC and have become an important part of our diagnostic algorithm. Filipin staining and cholesterol esterification assays became the definitive diagnostic tests after 1985 and were applied in 24 of our patients. Since 2005, more and more patients have been assessed using NPC1/NPC2 gene sequencing. Twelve patients were diagnosed with neonatal/early-infantile onset NPC, 13 with the late-infantile onset form, 20 with the juvenile onset form, and nine with the adolescent/adult onset form. Two diagnosed patients remained neurologically asymptomatic at study completion. Nineteen patients were siblings. Causal NPC1 mutations were determined in 38 patients; two identical NPC2 mutations were identified in one patient. In total, 30 different mutations were identified, 14 of which have been confirmed as novel. The frequency of individual mutated NPC1 alleles in our cohort differs compared with previous published data: the most frequent mutant NPC1 allele was p.R1186H (n = 13), followed by p.P1007A (n = 8), p.S954L (n = 8) and p.I1061T (n = 4).

Conclusions

These data demonstrate the evolution of the diagnostic process in NPC over the last four decades. We estimate the contemporary birth prevalence of NPC in the Czech Republic at 0.93 per 100,000.

[Niemann-Pick type C disease and psychosis: Two siblings]

INTRODUCTION

Niemann-Pick type C disease (NPC) is a rare, neurovisceral, autosomal recessive disease, with an extremely heterogeneous clinical presentation. The adult form of the disease is usually expressed as a neurological form. Non-specific psychiatric symptoms are often associated with NPC. For some cases, it can also be expressed as an isolated psychiatric disorder form. Since 2009, the launching of a medicine called miglustat has helped to improve the disease evolution.

CASE HISTORIES

We report two siblings followed-up in the same department of psychiatry and with an atypical psychotic symptomatology. Case 1 is a 27-year-old French male. He was hospitalised several times due to disordered behaviour, psychomotor excitation, mood instability and wandering. He was originally diagnosed with schizophrenia. However, the patient's psychosis proved refractory to treatment. He also exhibited a number of neurological signs (pyramidal signs and abnormal movements of the hands, head and limbs), which were considered related to his antipsychotic medication. Three years later, a full physical, neurological and neuropsychological examination revealed various neurological and visceral symptoms. He was diagnosed with NPC based on a classical biochemical NPC-phenotype following filipin staining in cultured skin fibroblasts. NPC1 gene sequencing revealed that he was a compound heterozygote for the p.S954L and p.N1156S mutations. The patient's psychiatric and neurological symptoms are currently stabilized by miglustat, allowing the patient to cease antipsychotic medication. Case 2 is the elder sister of Case 1. She was hospitalised several times due to acute delirium, hallucinations and suicidal tendencies. She was diagnosed with paranoid schizophrenia at 22 years of age. She has received a variety of typical and atypical antipsychotics. Many of these drugs proved initially effective but the patient's symptoms repeatedly returned. The patient shows persistent and worsening gait disorder and abnormal arm movements. A follow-up neurological examination at age 29 did not detect any ataxia, cataplexy or vertical supra-nuclear gaze palsy. Direct NPC1 gene sequencing detected a mutant NPC1 allele held in common with her brother, but full sequencing of both the NPC1 and NPC2 genes and multiplex ligation-dependent probe amplification (MLPA) did not detect any other pathogenic mutation or other anomalies.

DISCUSSION

Because NPC is an autosomal recessive condition, heterozygous individuals carrying only one causal gene mutation are usually asymptomatic. Thus, while the accepted wisdom would suggest that patient 2 is not affected by the disease, it is interesting to consider why she has developed neurological and psychiatric disorders like her brother. Several hypotheses are discussed: mental expression in heterozygous genetic factor predisposing to schizophrenia, comorbidity or fortuitous association. It is not currently known whether a patient with a single NPC gene mutation can express NPC in full, partially, or perhaps just to a minimal degree. This case of a patient with a heterozygous "carrier" NPC genotype and neuropsychiatric disorders suggestive of the disease raises the possibility that symptomatic heterozygous NPC patients may exist. On the other hand, if the heterozygous genotype of patient 2 does not give rise to symptomatic disease, it is pertinent to question whether it could be a predisposing factor for the development of psychiatric pathologies. There are currently no published data on the occurrence of heterozygous NPC1 or NPC2 mutations among patients with atypical psychiatric presentations combined with neurological symptoms. Conversely, there are no published data demonstrating an increased frequency of psychiatric disorders in families affected by NPC. Finally, in view of the history of psychiatric disorders in this family, it is possible that psychosis simply occurred concomitantly with symptomatic NPC in patient 1 by chance, and that schizophrenia occurred simultaneously with an asymptomatic NPC carrier genotype in patient 2. To investigate this further, NPC patients' carrier family members (parents and siblings) should be fully screened for signs suggestive of the disease.

The proteasome inhibitor bortezomib reduced cholesterol accumulation in fibroblasts from Niemann-Pick type C patients carrying missense mutations

Niemann-Pick disease type C (NPC) is a lipid storage disorder mainly caused by mutations in the NPC1 gene. Approximately 60% of these mutations are missense changes that may induce reduced NPC1 protein levels by increased degradation via ubiquitin-proteasome. This is the case for the most prevalent worldwide mutation, p.Ile1061Thr, as well as for other three missense changes. In the present study, we analyzed the NPC1 levels in fibroblasts from eighteen NPC patients presenting missense mutations. We found that fourteen of these cells lines showed decreased levels of NPC1. Six of these cell lines were homozygous, whereas the other eight were associated with a frame shifting mutation. We focused our attention in the NPC homozygous samples and demonstrated that, in most of the cases, NPC1 reduction was a consequence of a decrease of its half-life. NPC cells were treated not only with the proteasome inhibitors carbobenzoxy-l-leucyl-l-leucyl-l-leucinal or N-acetyl-leucyl-leucyl-norleucinal, both widely used as a research tools, but also with bortezomib, the first proteasome inhibitor to reach clinical applications, although it has never been used in NPC disease. We observed that, after treatment, the mutant NPC1 protein levels were partially recovered in most of the cell lines. Importantly, these mutant proteins partially recovered their activity and substantially reduced free cholesterol levels. These results suggest that by enhancing the NPC1 protein stability with the use of proteasome inhibitors, their functionality might be recovered and this might represent a therapeutical approach for future treatments of NPC disease resulting from specific missense mutations.

Characterisation of two deletions involving NPC1 and flanking genes in Niemann-Pick type C disease patients

Niemann-Pick type C (NPC) disease is an autosomal recessive lysosomal disorder characterised by the accumulation of a complex pattern of lipids in the lysosomal-late endosomal system. More than 300 disease-causing mutations have been identified so far in the NPC1 and NPC2 genes, including indel, missense, nonsense and splicing mutations. Only one genomic deletion, of more than 23 kb, has been previously reported. We describe two larger structural variants, encompassing NPC1 and flanking genes, as a cause of the disease. QMPSF, SNP inheritance and CytoScan® HD Array were used to confirm and further characterise the presence of hemizygous deletions in two patients. One of the patients (NPC-57) bore a previously described missense mutation (p.T1066N) and an inherited deletion that included NPC1, C18orf8 and part of ANKRD29 gene. The second patient (NPC-G1) had a 1-bp deletion (c.852delT; p.F284Lfs*26) and a deletion encompassing the promoter region and exons 1-10 of NPC1 and the adjacent ANKRD29 and LAMA3. This study characterised two novel chromosomal microdeletions at 18q11-q12 that cause NPC disease and provide insight into missing NPC1 mutant alleles.