Stochastic Optical Reconstruction Microscopy Imaging of Multiple System Atrophy Inclusions Suggests Stepwise α-Synuclein Aggregation.

BACKGROUND: The architecture and composition of glial (GCI) and neuronal (NCI) α-synuclein inclusions observed in multiple system atrophy (MSA) remain to be precisely defined to better understand the disease. METHODS: Here, we used stochastic optical reconstruction microscopy (STORM) to characterize the nanoscale organization of glial (GCI) and neuronal (NCI) α-synuclein inclusions in cryopreserved brain sections from MSA patients. RESULTS: STORM revealed a dense cross-linked internal structure of α-synuclein in all GCI and NCI. The internal architecture of hyperphosphorylated α-synuclein (p-αSyn) inclusions was similar in glial and neuronal cells, suggesting a common aggregation mechanism. A similar sequence of p-αSyn stepwise intracellular aggregation was defined in oligodendrocytes and neurons, starting from the perinuclear area and growing inside the cells. Consistent with this hypothesis, we found a higher mitochondrial density in GCI and NCI compared to oligodendrocytes and neurons from unaffected donors (P < 0.01), suggesting an active recruitment of the organelles during the aggregation process. CONCLUSIONS: These first STORM images of GCI and NCI suggest stepwise α-synuclein aggregation in MSA. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

The top 10 most frequently involved genes in hereditary optic neuropathies in 2186 probands.

Hereditary optic neuropathies are caused by the degeneration of retinal ganglion cells whose axons form the optic nerves, with a consistent genetic heterogeneity. As part of our diagnostic activity, we retrospectively evaluated the combination of Leber hereditary optic neuropathy mutations testing with the exon sequencing of 87 nuclear genes on 2186 patients referred for suspected hereditary optic neuropathies. The positive diagnosis rate in individuals referred for Leber hereditary optic neuropathy testing was 18% (199/1126 index cases), with 92% (184/199) carrying one of the three main pathogenic variants of mitochondrial DNA (m.11778G>A, 66.5%; m.3460G>A, 15% and m.14484T>C, 11%). The positive diagnosis rate in individuals referred for autosomal dominant or recessive optic neuropathies was 27% (451/1680 index cases), with 10 genes accounting together for 96% of this cohort. This represents an overall positive diagnostic rate of 30%. The identified top 10 nuclear genes included OPA1, WFS1, ACO2, SPG7, MFN2, AFG3L2, RTN4IP1, TMEM126A, NR2F1 and FDXR. Eleven additional genes, each accounting for less than 1% of cases, were identified in 17 individuals. Our results show that 10 major genes account for more than 96% of the cases diagnosed with our nuclear gene panel.

Dominant ACO2 mutations are a frequent cause of isolated optic atrophy.

Biallelic mutations in ACO2, encoding the mitochondrial aconitase 2, have been identified in individuals with neurodegenerative syndromes, including infantile cerebellar retinal degeneration and recessive optic neuropathies (locus OPA9). By screening European cohorts of individuals with genetically unsolved inherited optic neuropathies, we identified 61 cases harbouring variants in ACO2, among whom 50 carried dominant mutations, emphasizing for the first time the important contribution of ACO2 monoallelic pathogenic variants to dominant optic atrophy. Analysis of the ophthalmological and clinical data revealed that recessive cases are affected more severely than dominant cases, while not significantly earlier. In addition, 27% of the recessive cases and 11% of the dominant cases manifested with extraocular features in addition to optic atrophy. In silico analyses of ACO2 variants predicted their deleterious impacts on ACO2 biophysical properties. Skin derived fibroblasts from patients harbouring dominant and recessive ACO2 mutations revealed a reduction of ACO2 abundance and enzymatic activity, and the impairment of the mitochondrial respiration using citrate and pyruvate as substrates, while the addition of other Krebs cycle intermediates restored a normal respiration, suggesting a possible short-cut adaptation of the tricarboxylic citric acid cycle. Analysis of the mitochondrial genome abundance disclosed a significant reduction of the mitochondrial DNA amount in all ACO2 fibroblasts. Overall, our data position ACO2 as the third most frequently mutated gene in autosomal inherited optic neuropathies, after OPA1 and WFS1, and emphasize the crucial involvement of the first steps of the Krebs cycle in the maintenance and survival of retinal ganglion cells.

Novel CCM2 missense variants abrogating the CCM1-CCM2 interaction cause cerebral cavernous malformations.

BACKGROUND: Cerebral cavernous malformations (CCMs) are vascular malformations mostly located within the central nervous system. Most deleterious variants are loss of function mutations in one of the three CCM genes. These genes code for proteins that form a ternary cytosolic complex with CCM2 as a hub. Very few CCM2 missense variants have been shown to be deleterious by modifying the ternary CCM complex stability. OBJECTIVES: To investigate the causality of novel missense CCM2 variants detected in patients with CCM. METHODS: The three CCM genes were screened in 984 patients referred for CCM molecular screening. Interaction between CCM1 and CCM2 proteins was tested using co-immunoprecipitation experiments for the CCM2 missense variants located in the phosphotyrosine binding (PTB) domain. RESULTS: 11 distinct CCM2 rare missense variants were found. Six variants predicted to be damaging were located in the PTB domain, four of them were novel. When co-transfected with CCM1 in HEK293T cells, a loss of interaction between CCM1 and CCM2 was observed for all six variants. CONCLUSION: We showed, using co-immunoprecipitation experiments, that CCM2 missense variants located in the PTB domain were actually damaging by preventing the normal interaction between CCM1 and CCM2. These data are important for diagnosis and genetic counselling, which are challenging in patients harbouring such variants.

Primary fibroblasts derived from sporadic amyotrophic lateral sclerosis patients do not show ALS cytological lesions.

OBJECTIVE: Sporadic amyotrophic lateral sclerosis (sALS) is a fatal neurodegenerative disorder affecting upper and lower motor neurons. In view of the heterogeneous presentation of the disease, one of the current challenges is to identify diagnostic and prognostic markers in order to diagnose sALS at early stage and to stratify patients in trials. In this study, we sought to identify cytological hallmarks of sALS in patient-derived fibroblasts with the aim of finding new clinical-related markers of the disease. METHODS: Primary fibroblasts were prospectively collected from patients affected with classical, rapid, and slow forms of sALS. TDP-43 localization, cytoskeleton distribution, mitochondrial network architecture, and stress granules formation were analyzed using 3D fluorescence microscopy and new super-resolution imaging. Intracellular reactive oxygen species (ROS) production was assessed using live imaging techniques. RESULTS: Six sALS patients (two classical, two rapid, and two slow) and four age-matched controls were included. No difference in fibroblasts cell growth, morphology, and distribution was noticed. The analysis of TDP-43 did not reveal any mislocalization nor aggregation of the protein. The cytoskeleton was harmoniously distributed among the cells, without any inclusion noticed, and no difference was observed regarding the mitochondrial network architecture. Basal ROS production and response to induced stress were similar among patient and control fibroblasts. CONCLUSIONS: ALS cytological lesions are absent in patient-derived fibroblasts and thus cannot contribute as diagnostic nor prognostic markers of the disease.

A Plasma Metabolomic Signature Involving Purine Metabolism in Human Optic Atrophy 1 (OPA1)-Related Disorders.

Purpose: Dominant optic atrophy (DOA; MIM [Mendelian Inheritance in Man] 165500), resulting in retinal ganglion cell degeneration, is mainly caused by mutations in the optic atrophy 1 (OPA1) gene, which encodes a dynamin guanosine triphosphate (GTP)ase involved in mitochondrial membrane processing. This work aimed at determining whether plasma from OPA1 pathogenic variant carriers displays a specific metabolic signature. Methods: We applied a nontargeted clinical metabolomics pipeline based on ultra-high-pressure liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HRMS) allowing the exploration of 500 polar metabolites in plasma. We compared the plasma metabolic profiles of 25 patients with various OPA1 pathogenic variants and phenotypes to those of 20 healthy controls. Statistical analyses were performed using univariate and multivariate (principal component analysis [PCA], orthogonal partial least-squares discriminant analysis [OPLS-DA]) methods and a machine learning approach, the Biosigner algorithm. Results: A robust and relevant predictive model characterizing OPA1 individuals was obtained, based on a complex panel of metabolites with altered concentrations. An impairment of the purine metabolism, including significant differences in xanthine, hypoxanthine, and inosine concentrations, was at the foreground of this signature. In addition, the signature was characterized by differences in urocanate, choline, phosphocholine, glycerate, 1-oleoyl-rac-glycerol, rac-glycerol-1-myristate, aspartate, glutamate, and cystine concentrations. Conclusions: This first metabolic signature reported in the plasma of patient carrying OPA1 pathogenic variants highlights the unexpected involvement of purine metabolism in the pathophysiology of DOA.

A randomized, double-blind, placebo-controlled trial evaluating cysteamine in Huntington's disease.

BACKGROUND: Cysteamine has been demonstrated as potentially effective in numerous animal models of Huntington's disease. METHODS: Ninety-six patients with early-stage Huntington's disease were randomized to 1200 mg delayed-release cysteamine bitartrate or placebo daily for 18 months. The primary end point was the change from baseline in the UHDRS Total Motor Score. A linear mixed-effects model for repeated measures was used to assess treatment effect, expressed as the least-squares mean difference of cysteamine minus placebo, with negative values indicating less deterioration relative to placebo. RESULTS: At 18 months, the treatment effect was not statistically significant - least-squares mean difference, -1.5 ± 1.71 (P = 0.385) - although this did represent less mean deterioration from baseline for the treated group relative to placebo. Treatment with cysteamine was safe and well tolerated. CONCLUSIONS: Efficacy of cysteamine was not demonstrated in this study population of patients with Huntington's disease. Post hoc analyses indicate the need for definitive future studies. © 2017 International Parkinson and Movement Disorder Society.

Assembly defects induce oxidative stress in inherited mitochondrial complex I deficiency.

Complex I (CI) deficiency is the most common respiratory chain defect representing more than 30% of mitochondrial diseases. CI is an L-shaped multi-subunit complex with a peripheral arm protruding into the mitochondrial matrix and a membrane arm. CI sequentially assembled into main assembly intermediates: the P (pumping), Q (Quinone) and N (NADH dehydrogenase) modules. In this study, we analyzed 11 fibroblast cell lines derived from patients with inherited CI deficiency resulting from mutations in the nuclear or mitochondrial DNA and impacting these different modules. In patient cells carrying a mutation located in the matrix arm of CI, blue native-polyacrylamide gel electrophoresis (BN-PAGE) revealed a significant reduction of fully assembled CI enzyme and an accumulation of intermediates of the N module. In these cell lines with an assembly defect, NADH dehydrogenase activity was partly functional, even though CI was not fully assembled. We further demonstrated that this functional N module was responsible for ROS production through the reduced flavin mononucleotide. Due to the assembly defect, the FMN site was not re-oxidized leading to a significant oxidative stress in cell lines with an assembly defect. These findings not only highlight the relationship between CI assembly and oxidative stress, but also show the suitability of BN-PAGE analysis in evaluating the consequences of CI dysfunction. Moreover, these data suggest that the use of antioxidants may be particularly relevant for patients displaying a CI assembly defect.

Longitudinal study of informed consent in innovative therapy research: experience and provisional recommendations from a multicenter trial of intracerebral grafting.

BACKGROUND: There is an urgent need to assess and improve the consent process in clinical trials of innovative therapies for neurodegenerative disorders. METHODS: We performed a longitudinal study of the consent of Huntington's disease patients during the Multicenter Fetal Cell Intracerebral Grafting Trial in Huntington's Disease (MIG-HD) in France and Belgium. Patients and their proxies completed a consent questionnaire at inclusion, before signing the consent form and after one year of follow-up, before randomization and transplantation. The questionnaire explored understanding of the protocol, satisfaction with the information delivered, reasons for participating in the trial and expectations regarding the transplant. Forty-six Huntington's disease patients and 27 proxies completed the questionnaire at inclusion, and 27 Huntington's disease patients and 16 proxies one year later. RESULTS: The comprehension score was high and similar for Huntington's disease patients and proxies at inclusion (72.6% vs 77.8%; P > 0.1) but only decreased in HD patients after one year. The information satisfaction score was high (73.5% vs 66.5%; P > 0.1) and correlated with understanding in both patients and proxies. The motivation and expectation profiles were similar in patients and proxies and remained unchanged after one year. CONCLUSIONS: Cognitively impaired patients with Huntington's disease were capable of consenting to participation in this trial. This consent procedure has presumably strengthened their understanding and should be proposed before signing the consent form in future gene or cell therapy trials for neurodegenerative disorders. Because of the potential cognitive decline, proxies should be designated as provisional surrogate decision-makers, even in competent patients.

A Case of Type I Sialidosis With Osteonecrosis Revealing a New Mutation in NEU1

Abstract Sialidosis is a rare lysosomal storage disease. The 2 forms described are as follows: the early-onset form, or type II, presents with dysostosis multiplex, while the late-onset form, or type I, does not involve bone in the literature. We report the case of a 42-year-old woman with type I sialidosis who presents with osteonecrosis of both humeral and femoral heads. Molecular study reveals a never listed mutation of NEU1 in exon 5, p.Gly273Asp (c.818G>A), and a second known missense mutation.

Phenotypic spectrum of probable and genetically-confirmed idiopathic basal ganglia calcification.

Idiopathic basal ganglia calcification is characterized by mineral deposits in the brain, an autosomal dominant pattern of inheritance in most cases and genetic heterogeneity. The first causal genes, SLC20A2 and PDGFRB, have recently been reported. Diagnosing idiopathic basal ganglia calcification necessitates the exclusion of other causes, including calcification related to normal ageing, for which no normative data exist. Our objectives were to diagnose accurately and then describe the clinical and radiological characteristics of idiopathic basal ganglia calcification. First, calcifications were evaluated using a visual rating scale on the computerized tomography scans of 600 consecutively hospitalized unselected controls. We determined an age-specific threshold in these control computerized tomography scans as the value of the 99th percentile of the total calcification score within three age categories: <40, 40-60, and >60 years. To study the phenotype of the disease, patients with basal ganglia calcification were recruited from several medical centres. Calcifications that rated below the age-specific threshold using the same scale were excluded, as were patients with differential diagnoses of idiopathic basal ganglia calcification, after an extensive aetiological assessment. Sanger sequencing of SLC20A2 and PDGFRB was performed. In total, 72 patients were diagnosed with idiopathic basal ganglia calcification, 25 of whom bore a mutation in either SLC20A2 (two families, four sporadic cases) or PDGFRB (one family, two sporadic cases). Five mutations were novel. Seventy-one per cent of the patients with idiopathic basal ganglia calcification were symptomatic (mean age of clinical onset: 39 ± 20 years; mean age at last evaluation: 55 ± 19 years). Among them, the most frequent signs were: cognitive impairment (58.8%), psychiatric symptoms (56.9%) and movement disorders (54.9%). Few clinical differences appeared between SLC20A2 and PDGFRB mutation carriers. Radiological analysis revealed that the total calcification scores correlated positively with age in controls and patients, but increased more rapidly with age in patients. The expected total calcification score was greater in SLC20A2 than PDGFRB mutation carriers, beyond the effect of the age alone. No patient with a PDGFRB mutation exhibited a cortical or a vermis calcification. The total calcification score was more severe in symptomatic versus asymptomatic individuals. We provide the first phenotypical description of a case series of patients with idiopathic basal ganglia calcification since the identification of the first causative genes. Clinical and radiological diversity is confirmed, whatever the genetic status. Quantification of calcification is correlated with the symptomatic status, but the location and the severity of the calcifications don't reflect the whole clinical diversity. Other biomarkers may be helpful in better predicting clinical expression.

Association between caffeine intake and age at onset in Huntington's disease.

Habitual consumption of caffeine, a non-selective adenosine receptor (AR) antagonist, has been suggested to be beneficial in Parkinson's and Alzheimer's diseases. Experimental evidence support that ARs play a role in Huntington's disease (HD) raising the hypothesis that caffeine may be a life-style modifier in HD. To determine a possible relationship between caffeine consumption and age at onset (AAO) in HD, we retrospectively assessed caffeine consumption in 80 HD patients using a dietary survey and determined relationship with AAO. Following adjustment for gender, smoking status and CAG repeat length, caffeine consumption greater than 190mg/day was significantly associated with an earlier AAO. These data support an association between habitual caffeine intake and AAO in HD patients, but further studies are warranted to understand the link between these variables.

G51D α-synuclein mutation causes a novel parkinsonian-pyramidal syndrome.

OBJECTIVE: To date, 3 rare missense mutations in the SNCA (α-synuclein) gene and the more frequent duplications or triplications of the wild-type gene are known to cause a broad array of clinical and pathological symptoms in familial Parkinson disease (PD). Here, we describe a French family with a parkinsonian-pyramidal syndrome harboring a novel heterozygous SNCA mutation. METHODS: Whole exome sequencing of DNA from 3 patients in a 3-generation pedigree was used to identify a new PD-associated mutation in SNCA. Clinical and pathological features of the patients were analyzed. The cytotoxic effects of the mutant and wild-type proteins were assessed by analytical ultracentrifugation, thioflavin T binding, transmission electron microscopy, cell viability assay, and caspase-3 activation. RESULTS: We identified a novel SNCA G51D (c.152 G>A) mutation that cosegregated with the disease and was absent from controls. G51D was associated with an unusual PD phenotype characterized by early disease onset, moderate response to levodopa, rapid progression leading to loss of autonomy and death within a few years, marked pyramidal signs including bilateral extensor plantar reflexes, occasionally spasticity, and frequently psychiatric symptoms. Pathological lesions predominated in the basal ganglia and the pyramidal tracts and included fine, diffuse cytoplasmic inclusions containing phospho-α-synuclein in superficial layers of the cerebral cortex, including the entorhinal cortex. Functional studies showed that G51D α-synuclein oligomerizes more slowly and its fibrils are more toxic than those of the wild-type protein. INTERPRETATION: We have identified a novel SNCA G51D mutation that causes a form of PD with unusual clinical, neuropathological, and biochemical features.

A genetic variation in the ADORA2A gene modifies age at onset in Huntington's disease.

Based on the pathophysiological role of adenosine A(2A) receptors in HD, we have evaluated the association of the 1976C/T single-nucleotide polymorphism in the ADORA2A gene (rs5751876) with residual age at onset (AAO) in HD. The study population consisted of 791 unrelated patients belonging to the Huntington French Speaking Network. The variability in AAO attributable to the CAG repeats number was calculated by linear regression using the log (AAO) as the dependent variable, and the respective rs5751876 genotypes as independent variables. We show that the rs5751876 variant significantly influences the variability in AAO. The R(2) statistic rose slightly but significantly (p=0.019) when rs5751876 T/T genotype was added to the regression model. Patients harbouring T/T genotype have an earlier AAO of 3.8 years as compared to C/C genotype (p=0.02). Our data thus strengthens the pathophysiological role of A(2A) receptors in Huntington's disease.

Mitochondrial coupling defect in Charcot-Marie-Tooth type 2A disease.

OBJECTIVE: Mutations of the mitofusin 2 gene (MFN2) may account for at least a third of the cases of Charcot-Marie-Tooth disease type 2 (CMT2). This study investigates mitochondrial cellular bioenergetics in MFN2-related CMT2A. METHODS: Mitochondrial network morphology and metabolism were studied in cultures of skin fibroblasts obtained from four CMT2A patients harboring novel missense mutations of the MFN2 gene. RESULTS: Although the mitochondrial network appeared morphologically unaltered, there was a significant defect of mitochondrial coupling associated with a reduction of the mitochondrial membrane potential. INTERPRETATION: Our results suggest that the sharply reduced efficacy of oxidative phosphorylation in MFN2-related CMT2A may contribute to the pathophysiology of the axonal neuropathy.

OPA1 R445H mutation in optic atrophy associated with sensorineural deafness.

The heterozygous R445H mutation in OPA1 was found in five patients with optic atrophy and deafness. Audiometry suggested that the sensorineural deafness resulted from auditory neuropathy. Skin fibroblasts showed hyperfragmentation of the mitochondrial network, decreased mitochondrial membrane potential, and adenosine triphosphate synthesis defect. In addition, OPA1 was found to be widely expressed in the sensory and neural cochlear cells of the guinea pig. Thus, optic atrophy and deafness may be related to energy defects due to a fragmented mitochondrial network.