Sialidoses Franceschetti, Silvana; Canafoglia, Laura
Epileptic disorders,
September 2016, Letnik:
18, Številka:
s2
Journal Article
Recenzirano
Sialidoses are autosomal recessive disorders caused by NEU1 gene mutations and are classified on the basis of their phenotype and onset age. Sialidosis type II, with infantile onset, has a more ...severe phenotype characterized by coarse facial features, hepatomegaly, dysostosis multiplex, and developmental delay while patients with the late and milder type, known as “cherry red spot‐myoclonus syndrome” develop myoclonic epilepsy, visual impairment and ataxia in the second or third decade of life. The diagnosis is usually suggested by increased urinary bound sialic acid excretion. We recently described genetically diagnosed patients with a specially mild phenotype, no retinal abnormalities and normal urinary sialic acid. This observation suggests that genetic analysis or the demonstration of the neuraminidase enzyme deficiency in cultured fibroblasts are needed to detect and diagnose mildest phenotypes.
We performed hypothesis-free linkage analysis and exome sequencing in a family with two siblings who had neuronal ceroid lipofuscinosis (NCL). Two linkage peaks with maximum LOD scores of 3.07 and ...2.97 were found on chromosomes 7 and 17, respectively. Unexpectedly, we found these siblings to be homozygous for a c.813_816del (p.Thr272Serfs∗10) mutation in the progranulin gene (GRN, granulin precursor) in the latter peak. Heterozygous mutations in GRN are a major cause of frontotemporal lobar degeneration with TDP-43 inclusions (FTLD-TDP), the second most common early-onset dementia. Reexamination of progranulin-deficient mice revealed rectilinear profiles typical of NCL. The age-at-onset and neuropathology of FTLD-TDP and NCL are markedly different. Our findings reveal an unanticipated link between a rare and a common neurological disorder and illustrate pleiotropic effects of a mutation in the heterozygous or homozygous states.
Heterozygous mutations in the gene coding for progranulin (GRN) cause frontotemporal lobar degeneration (FTLD) while homozygous mutations are linked to neuronal ceroidolipofuscinosis (NCL). While ...both FTLD/NCL pathological hallmarks were mostly investigated in heterozygous GRN+/− brain tissue or induced pluripotent stem cell (iPSC)-derived neurons, data from homozygous GRN−/− condition are scarce, being limited to a postmortem brain tissue from a single case. Indeed, homozygous GRN−/− is an extremely rare condition reported in very few cases. Our aim was to investigate pathological phenotypes associated with FTLD and NCL in iPSC-derived cortical neurons from a GRN−/− patient affected by NCL. iPSCs were generated from peripheral blood of a GRN wt healthy donor and a GRN−/− patient and subsequently differentiated into cortical neurons. Several pathological changes were investigated, by means of immunocytochemical, biochemical and ultrastructural analyses. GRN−/− patient-derived cortical neurons displayed both TDP-43 and phospho-TDP-43 mislocalization, enlarged autofluorescent lysosomes and electron-dense vesicles containing storage material with granular, curvilinear and fingerprints profiles. In addition, different patterns in the expression of TDP-43, caspase 3 and cleaved caspase 3 were observed by biochemical analysis at different time points of cortical differentiation. At variance with previous findings, the present data highlight the existence of both FTLD- and NCL-linked pathological features in GRN−/− iPSC-derived cortical neurons from a NCL patient. They also suggest an evolution in the appearance of these features: firstly, FTLD-related TDP-43 alterations and initial NCL storage materials were detected; afterwards, mainly well-shaped NCL storage materials were present, while some FTLD features were not observed anymore.
•GRN−/− iPSC-derived cortical neurons are a good model to study pathological features•GRN−/− cortical neurons display both FTLD and NCL pathological hallmarks•FTLD and NCL pathological features seem to be subjected to temporal evolution.
Lafora disease (LD) is a rare, lethal, progressive myoclonus epilepsy for which no targeted therapy is currently available. Studies on a mouse model of LD showed a good response to metformin, a drug ...with a well known neuroprotective effect. For this reason, in 2016, the European Medicines Agency granted orphan designation to metformin for the treatment of LD. However, no clinical data is available thus far.
We retrospectively collected data on LD patients treated with metformin referred to three Italian epilepsy centres.
Twelve patients with genetically confirmed LD (6 EPM2A, 6 NHLRC1) at middle/late stages of disease were treated with add-on metformin for a mean period of 18 months (range: 6-36). Metformin was titrated to a mean maintenance dose of 1167 mg/day (range: 500-2000 mg). In four patients dosing was limited by gastrointestinal side-effects. No serious adverse events occurred. Three patients had a clinical response, which was temporary in two, characterized by a reduction of seizure frequency and global clinical improvement.
Metformin was overall safe in our small cohort of LD patients. Even though the clinical outcome was poor, this may be related to the advanced stage of disease in our cases and we cannot exclude a role of metformin in slowing down LD progression. Therefore, on the grounds of the preclinical data, we believe that treatment with metformin may be attempted as early as possible in the course of LD.
The causes of genetic epilepsies are unknown in the majority of patients. HCN ion channels have a widespread expression in neurons and increasing evidence demonstrates their functional involvement in ...human epilepsies. Among the four known isoforms, HCN1 is the most expressed in the neocortex and hippocampus and de novo HCN1 point mutations have been recently associated with early infantile epileptic encephalopathy. So far, HCN1 mutations have not been reported in patients with idiopathic epilepsy. Using a Next Generation Sequencing approach, we identified the de novo heterozygous p.Leu157Val (c.469C > G) novel mutation in HCN1 in an adult male patient affected by genetic generalized epilepsy (GGE), with normal cognitive development. Electrophysiological analysis in heterologous expression model (CHO cells) and in neurons revealed that L157V is a loss-of-function, dominant negative mutation causing reduced HCN1 contribution to net inward current and responsible for an increased neuronal firing rate and excitability, potentially predisposing to epilepsy. These data represent the first evidence that autosomal dominant missense mutations of HCN1 can also be involved in GGE, without the characteristics of epileptic encephalopathy reported previously. It will be important to include HCN1 screening in patients with GGE, in order to extend the knowledge of the genetic causes of idiopathic epilepsies, thus paving the way for the identification of innovative therapeutic strategies.
•We have identified a new heterozygous de novo mutation of HCN1 (p.L157V) in a patient with genetic generalized epilepsy (GGE).•The L157V mutation reduces the HCN1 current in both CHO cell and neonatal neurons, in a dominant manner.•When expressed in neurons, mutant channels reduce the firing threshold and increase excitability.•This is the first evidence that loss-of-function HCN1 mutations can predispose to GGE.
We report the clinical and EEG data of two patients harboring heterozygous
mutations, who presented with typical absence seizures at 3 Hz spike and wave as well as with mild cognitive disability. ...Neuroradiological and other laboratory investigations were normal. Our observations suggest that
mutations can be suspected in children with typical absences as the only seizure type, especially if associated with, even mild, cognitive deficits.
Progressive myoclonus epilepsy (PME) of Unverricht–Lundborg type (EPM1) is an autosomal recessive neurodegenerative disorder with the highest incidence of PME worldwide. Mutations in the gene ...encoding cystatin B (CSTB) are the primary genetic cause of EPM1. Here, we investigate the role of CSTB during neurogenesis in vivo in the developing mouse brain and in vitro in human cerebral organoids (hCOs) derived from EPM1 patients. We find that CSTB (but not one of its pathological variants) is secreted into the mouse cerebral spinal fluid and the conditioned media from hCOs. In embryonic mouse brain, we find that functional CSTB influences progenitors’ proliferation and modulates neuronal distribution by attracting interneurons to the site of secretion via cell‐non‐autonomous mechanisms. Similarly, in patient‐derived hCOs, low levels of functional CSTB result in an alteration of progenitor's proliferation, premature differentiation, and changes in interneurons migration. Secretion and extracellular matrix organization are the biological processes particularly affected as suggested by a proteomic analysis in patients’ hCOs. Overall, our study sheds new light on the cellular mechanisms underlying the development of EPM1.
Synopsis
Mutations in the cystatin B (CSTB) gene cause EPM1 epilepsy in patients. CSTB secretion induces the recruitment of migrating interneurons and promotes progenitor cells expansion in the mouse cortex and human cerebral organoids (hCOs). Both functions are impaired in EPM1‐derived hCOs.
CSTB overexpression induces progenitor cells expansion in hCOs and in the developing mouse cortex.
CSTB is secreted and induces recruitment of migrating interneurons.
Downregulation of Cstb and R68X overexpression result in decreased number of progenitors and migrating interneurons in the developing mouse cortex.
Proliferation is reduced in EPM1‐derived cerebral organoids in a cell non‐autonomous manner.
EPM1‐derived cerebral organoids exhibit premature differentiation.
Mutations in the cystatin B (CSTB) gene cause EPM1 epilepsy in patients. CSTB secretion induces the recruitment of migrating interneurons and promotes progenitor cells expansion in the mouse cortex and human cerebral organoids (hCOs). Both functions are impaired in EPM1‐derived hCOs.
Frontotemporal lobar degeneration (FTLD) is a complex disease, characterized by progressive degeneration of frontal and temporal lobes. Mutations in progranulin (
) gene have been found in up to 50% ...of patients with familial FTLD. Abnormal deposits of post-translationally-modified TAR DNA-binding protein of 43 kDa (TDP-43) represent one of the main hallmarks of the brain pathology. To investigate in peripheral cells the presence of the different TDP-43 forms, especially the toxic 25 kDa fragments, we analyzed lymphoblastoid cell lines (LCLs) and the derived extracellular vesicles (EVs) from patients carrying a
mutation, together with wild-type (WT) healthy controls. After characterizing EV sizes and concentrations by nanoparticle tracking analysis, we investigated the levels of different forms of the TDP-43 protein in LCLs and respective EVs by Western blot. Our results showed a trend of concentration decreasing in EVs derived from
-mutated LCLs, although not reaching statistical significance. A general increase in p-TDP-43 levels in
-mutated LCLs and EVs was observed. In particular, the toxic 25 kDa fragments of p-TDP-43 were only present in GRN-mutated LCLs and were absent in the WT controls. Furthermore, these fragments appeared to be more concentrated in EVs than in LCLs, suggesting a relevant role of EVs in spreading pathological molecules between cells.
Emerging data suggest the roles of endo-lysosomal dysfunctions in frontotemporal lobar degeneration (FTLD) and in other dementias. Cathepsin D is one of the major lysosomal proteases, mediating the ...degradation of unfolded protein aggregates. In this retrospective study, we investigated cathepsin D levels in human plasma and in the plasma small extracellular vesicles (sEVs) of 161 subjects (40 sporadic FTLD, 33 intermediate/pathological C9orf72 expansion carriers, 45 heterozygous/homozygous GRN mutation carriers, and 43 controls). Cathepsin D was quantified by ELISA, and nanoparticle tracking analysis data (sEV concentration for the cathepsin D level normalization) were extracted from our previously published dataset or were newly generated. First, we revealed a positive correlation of the cathepsin D levels with the age of the patients and controls. Even if no significant differences were found in the cathepsin D plasma levels, we observed a progressive reduction in plasma cathepsin D moving from the intermediate to C9orf72 pathological expansion carriers. Observing the sEVs nano-compartment, we observed increased cathepsin D sEV cargo (ng/sEV) levels in genetic/sporadic FTLD. The diagnostic performance of this biomarker was fairly high (AUC = 0.85). Moreover, sEV and plasma cathepsin D levels were positively correlated with age at onset. In conclusion, our study further emphasizes the common occurrence of endo-lysosomal dysregulation in GRN/C9orf72 and sporadic FTLD.
Purpose
To describe cerebral glucose metabolism pattern as assessed by
18
F-fluorodeoxyglucose positron emission tomography (FDG-PET) in Lafora disease (LD), a rare, lethal form of progressive ...myoclonus epilepsy caused by biallelic mutations in
EPM2A
or
NHLRC1
.
Methods
We retrospectively included patients with genetically confirmed LD who underwent FDG-PET scan referred to three Italian epilepsy centers. FDG-PET images were evaluated both visually and using SPM12 software. Subgroup analysis was performed on the basis of genetic and clinical features employing SPM. Moreover, we performed a systematic literature review of LD cases that underwent FDG-PET assessment.
Results
Eight Italian patients (3M/5F, 3
EPM2A
/5
NHLRC1
) underwent FDG-PET examination after a mean of 6 years from disease onset (range 1–12 years). All patients showed bilateral hypometabolic areas, more diffuse and pronounced in advanced disease stages. Most frequently, the hypometabolic regions were the temporal (8/8), parietal (7/8), and frontal lobes (7/8), as well as the thalamus (6/8). In three cases, the FDG-PET repeated after a mean of 17 months (range 7–36 months) showed a metabolic worsening compared with the baseline examination. The SPM subgroup analysis found no significant differences based on genetics, whereas it showed a more significant temporoparietal hypometabolism in patients with visual symptoms compared with those without. In nine additional cases identified from eight publications, FDG-PET showed heterogeneous findings, ranging from diffusely decreased cerebral glucose metabolism to unremarkable examinations in two cases.
Conclusions
FDG-PET seems highly sensitive to evaluate LD at any stage and may correlate with disease progression. Areas of decreased glucose metabolism in LD are extensive, often involving multiple cortical and subcortical regions, with thalamus, temporal, frontal, and parietal lobes being the most severely affected. Prospective longitudinal collaborative studies are needed to validate our findings.
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