Littérature scientifique sur le sujet « SPG52 »

Abstract Deficiency of the adaptor protein complex 4 (AP-4) leads to childhood-onset hereditary spastic paraplegia (AP-4-HSP): SPG47 (AP4B1), SPG50 (AP4M1), SPG51 (AP4E1) and SPG52 (AP4S1). This study aims to evaluate the impact of loss-of-function variants in AP-4 subunits on intracellular protein trafficking using patient-derived cells. We investigated 15 patient-derived fibroblast lines and generated six lines of induced pluripotent stem cell (iPSC)-derived neurons covering a wide range of AP-4 variants. All patient-derived fibroblasts showed reduced levels of the AP4E1 subunit, a surrogate for levels of the AP-4 complex. The autophagy protein ATG9A accumulated in the trans-Golgi network and was depleted from peripheral compartments. Western blot analysis demonstrated a 3–5-fold increase in ATG9A expression in patient lines. ATG9A was redistributed upon re-expression of AP4B1 arguing that mistrafficking of ATG9A is AP-4-dependent. Examining the downstream effects of ATG9A mislocalization, we found that autophagic flux was intact in patient-derived fibroblasts both under nutrient-rich conditions and when autophagy is stimulated. Mitochondrial metabolism and intracellular iron content remained unchanged. In iPSC-derived cortical neurons from patients with AP4B1-associated SPG47, AP-4 subunit levels were reduced while ATG9A accumulated in the trans-Golgi network. Levels of the autophagy marker LC3-II were reduced, suggesting a neuron-specific alteration in autophagosome turnover. Neurite outgrowth and branching were reduced in AP-4-HSP neurons pointing to a role of AP-4-mediated protein trafficking in neuronal development. Collectively, our results establish ATG9A mislocalization as a key marker of AP-4 deficiency in patient-derived cells, including the first human neuron model of AP-4-HSP, which will aid diagnostic and therapeutic studies.

Hereditary spastic paraplegia (HSP) is among the most genetically diverse of all monogenic diseases. The aim was to analyze the genetic causes of HSP among adult Serbian patients. The study comprised 74 patients from 65 families clinically diagnosed with HSP during a nine-year prospective period. A panel of thirteen genes was analyzed: L1CAM (SPG1), PLP1 (SPG2), ATL1 (SPG3A), SPAST (SPG4), CYP7B1 (SPG5A), SPG7 (SPG7), KIF5A (SPG10), SPG11 (SPG11), ZYFVE26 (SPG15), REEP1 (SPG31), ATP13A2 (SPG78), DYNC1H1, and BICD2 using a next generation sequencing-based technique. A copy number variation (CNV) test for SPAST, SPG7, and SPG11 was also performed. Twenty-three patients from 19 families (29.2%) had conclusive genetic findings, including 75.0% of families with autosomal dominant and 25.0% with autosomal recessive inheritance, and 15.7% of sporadic cases. Twelve families had mutations in the SPAST gene, usually with a pure HSP phenotype. Three sporadic patients had conclusive findings in the SPG11 gene. Two unrelated patients carried a homozygous pathogenic mutation c.233T>A (p.L78*) in SPG7 that is a founder Roma mutation. One patient had a heterozygous de novo variant in the KIF5A gene, and one had a compound heterozygous mutation in the ZYFVE26 gene. The combined genetic yield of our gene panel and CNV analysis for HSP was around 30%. Our findings broaden the knowledge on the genetic epidemiology of HSP, with implications for molecular diagnostics in this region.

ObjectiveUniparental isodisomy can lead to blended phenotypes of imprinting disorders and autosomal recessive diseases. To determine whether a complex neurodevelopmental disorder was caused by uniparental isodisomy, a detailed clinical and molecular characterization was performed.MethodsA combination of clinical, molecular, and imaging data and functional studies in patient-derived fibroblasts.ResultsWe report a 4-year-old female with a blended, complex phenotype of Silver-Russell syndrome (SRS) and hereditary spastic paraplegia type 50 (SPG50) caused by total maternal isodisomy of chromosome 7 (UPiD(7)mat) and a loss-of-function variant in AP4M1 (NM_00472.3: c.59-1G>C, IVS1-1G>C). Functional studies in patient-derived fibroblasts confirmed the loss of adaptor protein complex 4 function. Distinctive facial features, intrauterine growth restriction, short stature, feeding difficulties, and severe gastroesophageal reflux were consistent with SRS. Features associated with SPG50 included early-onset epilepsy, episodes of stereotypical laughter, and thinning of the corpus callosum and ventriculomegaly on brain MRI. Symptoms shared by both syndromes such as developmental delay, short stature, and axial and appendicular hypotonia were also present. Notably, other common manifestations of SPG50 such as microcephaly or spasticity had not developed yet.ConclusionsThis case highlights that atypical clinical features in patients with well-described imprinting disorders should lead to investigations for recessive conditions caused by variants in genes that localize to the region of homozygosity.

Objectives:To characterize at clinical and molecular levels a family presenting with X-linked recessive Hereditary Spastic Paraplegia (HSP).Background:HSPs are a large group of genetically heterogeneous neurodegenerative disorders characterized by progressive upper motor neuron signs. Mutations in the proteolipid protein (PLP1) gene have been identified in families linked to the SPG2 locus on chromosome Xq22. However, Pelizaeus-Merzbacher disease (PMD) is also an X-linked recessive neurological disorder caused by PLP1 mutations.Methods:The SPG2 locus was investigated by linkage analysis in the family. The PLP1 gene was screened by sequencing. We present findings in a large French-Canadian family with an X-linked recessive HSP. The proband presented early with developmental delay and developed progressive spastic paraplegia. He has been wheelchair-bound since the age of three years. At the latest follow-up, he was 20 years-old and had severe spasticity predominantly affecting the lower extremities, moderate cerebellar dysfunction, and optic atrophy.Results:Linkage to SPG2 was established and a G to A mutation (M1R) in the initiation codon of the PLP1 gene was identified, likely resulting in the complete absence of proteolipid protein.Conclusion:We report a new PLP1 gene mutation in a patient with a clinical phenotype consistent with a PLP1 null syndrome.

The term Hereditary spastic paraplegia (HSP) refers to a group of genetically heterogeneous neurodegenerative motor neuron disorders characterized by progressive age-dependent loss of corticospinal motor tract function, lower limb spasticity, and weakness. Recent clinical use of next generation sequencing (NGS) methodologies suggests that NGS facilitates the diagnostic approach to HSP, but the power of this method as a first-tier diagnostic procedure is unclear. The larger-than-expected genetic heterogeneity— there are over 80 potential disease-associated genes— and frequent overlap with other clinical conditions affecting the motor system make a molecular diagnosis in HSP cumbersome and time consuming. In a single-center, cross-sectional study, spanning 5 years, 242 subjects with a clinical diagnosis of HSP underwent molecular screening of a large set of genes, using two different customized NGS panels. The latest version of our targeted sequencing panel (SpastiSure3.0) comprises 118 genes known to be associated with HSP or syndromic conditions. Using an in-house validated bioinformatics pipeline and several in silico tools to predict mutation pathogenicity, we gathered a positive diagnostic yield of 30% (73/242), whereas variants of unknown significance (VUS) were found in 86 patients (36%), and 83 (34%) cases remained unsolved. This study is among the largest screening of consecutive HSP index cases enrolled in real-life clinical-diagnostic settings. Its results corroborate NGS as a modern, first-step procedure for molecular diagnosis of HSP. It also disclosed a significant number of new mutations in ultra-rare genes, expanding the clinical spectrum, and genetic landscape of HSP, at least in Italy. Interestingly, we identified new unreported mutations in the AP4S1 gene (SPG52), the smallest of the four subunits that form the AP-4 complex, a heterotetrameric protein complex which participates in membrane sorting between the trans-Golgi network and the endosomes, and plays a key role in signal-mediated tracking of integral membrane proteins. Mutations in AP4 subunits have been associated with alterations in neurodevelopment, epilepsy and complicated spastic paraplegia and the relative rarity of patients with mutations in subunits of the AP4 complex makes useful to report additional cases. In this study we described clinical presentations of three additional unrelated patients and their mutations. To improve our understating on to how AP4S1 operates during neurodevelopment, we knocked-down ap4s1 in zebrafish (Danio rerio), using morpholino antisense oligonucleotide technique. Our results showed that morphant embryos displayed an impairment of the neuronal excitability, locomotor defects, development delay, and altered neurogenesis, which are also phenotypic traits of AP4-HSP patients. Whilst we expanded the allelic heterogeneity in AP4-related diseases, we modeled in the simple vertebrate system zebrafish the early steps of abnormal neurodevelopment associated with AP4S1 defects offering a new tool for future therapeutic opportunities. Importantly, AP-complex served as an example for similar strategies in genes associated with HSP.

Le paraparesi spastiche ereditarie (HSPs) rappresentano un gruppo eterogeneo di disturbi neurologici con interessamento del motoneurone superiore (UMND) la cui caratteristica clinica prevalente è la spasticità e l’ipostenia piramidale degli arti inferiori. HSP può essere classificata clinicamente in accordo alla modalità di ereditarietà, età di insorgenza o il fenotipo clinico. Questo disturbo è ereditato più spesso secondo la modalità autosomica dominante, meno frequentemente con ereditarietà autosomica recessiva e raramente secondo modalità di trasmissione X-linked. Pochi studi epidemiologici sono stati condotti sulle HSPs, ma la prevalenza è stimata tra 3-10:100 000, di cui le forme di HSP ad ereditarietà autosomica dominante costituiscono circa l’80% dei casi nei paesi Occidentali (con le forme più comuni in SPG4 e SPG3A). A dispetto di una eterogeneità genetica con 46 loci genetici (di cui 5 riservati) e 20 geni identificati, è più difficile separare le diverse entità nosografiche sul piano clinico. Questa uniformità fenotipica forse riflette un pathway finale comune nei processi della malattia da cui esita una degenerazione retrograda assonale dei tratti cortico-spinali e delle colonne posteriori. Studi recenti hanno permesso di identificare i geni di circa la metà di questi loci, suggerendo un’interruzione a più livelli come possibile causa di danno assonale: nel trasporto assonale e nella regolazione citoscheletrica, nelle funzioni mitocondriali, nel mantenimento e assemblaggio della mielina e nella migrazione neuronale. Questo studio ha l’obiettivo di effettuare un’indagine genetico-molecolare di famiglie affette da forme ad esordio precoce di ADHSP, ARHSP e casi apparentemente sporadici, sia con fenotipo clinico “non complicato” che “complicato”. Uno studio di linkage a 2 punti è stato effettuato in una famiglia ADHSP per 8 loci noti autosomico dominanti (SPG3A, SPG4, SPG6, SPG8, SPG10, SPG12, SPG13, SPG31). I risultati indicano che il disturbo in questa famiglia era legato al locus noto SPG3A. Attraverso il sequenziamento diretto degli esoni codificanti e delle regioni fiancheggianti gli introni del gene SPG3A è stata individuata una nuova mutazione missenso nell’esone 12 al nucleotide c.1246 C>T (p.R416C). La Arginina 416 è altamente conservata tra le specie. Ho analizzato i 3 geni HSP ad esordio precoce, SPG3A, SPG5A and SPG42, attraverso l’analisi di sequenziamento diretto nel restante campione composto dai probandi di 9 famiglie non imparentate autosomico dominanti, 3 autosomico recessive e 18 pazienti con paraplegia spastica apparentemente sporadica, con forme pure e complesse di malattia. L’analisi MLPA effettuata nei pazienti candidati per SPG3A (kit P165-HSP-B1, MRC-Holland) non ha individuato nessun cambiamento patogenetico. Attraverso il sequenziamento diretto ho evidenziato cinque mutazioni, di cui tre nuove, una che segrega in due famiglie non imparentate e le altre in casi apparentemente sporadici. Quattro di queste mutazioni sono missenso: c.1246 C>T (p.R416C) e c.1243 C>T (p.R415W) nel gene SPG3A, c.995 T>C (p.F264S) e c.344C>T (p.S115F) nel gene SPG5A. Una è un’inserzione che esita in un frameshift con l’introduzione di uno stop prematuro al codone C-terminale della proteina: c.1362insT (p.A453CfsX470) nel gene SPG5A. Nessun cambio patogenetico è stato individuato nel gene SPG42. È interessante che sia l’esordio precoce sia possibili fenomeni di anticipazione genetica siano stati osservati nelle due famiglie che presentano la mutazione p.R416C in ATL1. Questi risultati confermano i dati osservati in letteratura per cui i geni SPG3A e SPG5A mostrano un’alta frequenza mutazionale nelle forme ad esordio precoce di ADHSP e ARHSP (rispettivamente il 20 e il 7%) e nei casi apparentemente sporadici.
The hereditary spastic paraplegias (HSPs) are an etiologically heterogeneous group of neurological disorders which results from the selective degeneration of upper motor neurons (UMNs), of which key diagnostic clinical findings are spasticity and pyramidal weakness of lower limbs. HSP can be classified clinically according to mode of inheritance, age of onset or clinical phenotype. The disorder is inherited most often as an autosomal dominant trait, with autosomal recessive and X-linked inheritance occurring rarely and very rarely, respectively. Few epidemiological studies of HSP have been done, but prevalence is estimated at 3–10 cases per 100 000 population in western countries, in which approximately ADHSPs account for 80% of all HSPs (with SPG4 and SPG3A being the most common forms). Although genetically diverse with 46 genetic loci for HSP (of which 5 reserved) and 20 genes identified, it is often difficult to separate the disorders on clinical grounds. This phenotypic uniformity perhaps reflects a final common pathway in the disease process which results in degeneration of the corticospinal tracts and posterior columnes. Advances in recent years identifying the genes at half of these loci have suggested that disruption in any of the following: axonal transport, cytoskeleton regulation, mitochondrial function, myelin maintenance and assembly and neuronal migration may cause axonal damage in HSP. This study aims at genetic-molecular investigation of families affected by early onset forms of ADHSP, ARHSP, and apparently sporadic cases, as with “uncomplicated” or “complicated” clinical phenotype. Two point linkage analyses were performed in a ADHSP family to 8 known autosomal dominant loci (SPG3A, SPG4, SPG6, SPG8, SPG10, SPG12, SPG13, SPG31). The data indicated that the disorder in this kindred was linked to the known HSP locus SPG3A. Sequencing the SPG3A gene coding exons and flanking intronic regions disclosed a novel heterozygous missense mutation in exon 12 at nucleotide c.1246 C>T (p.Arg416Cys). The Arginine 416 is highly conserved among species. I analysed the coding region and exon–intron boundaries of 3 “early onset” HSP genes, SPG3A, SPG5A and SPG42, by direct sequencing in a total serie of 9 unrelated autosomal dominant and 3 autosomal recessive hereditary spastic paraplegia index patients, and in 18 unrelated index patients with apparently sporadic hereditary spastic paraplegia, manifesting either pure or complex forms of the disease. Multiplex ligation-dependent probe amplification performed in SPG3A candidate patients (probe mixtures P165-HSP-B1, MRC-Holland, The Netherlands) did not detect any pathogenic changes. By direct sequencing I identified five, including three novel, mutations, one segregating in two unrelated families, the others in apparently sporadic cases. Four of these mutations were missense: c.1246 C>T (p.R416C) and c.1243 C>T (p.R415W) in SPG3A gene, c. 995 T>C (p.F264S) and c.344C>T (p.S115F) in SPG5A gene. One resulted in a frameshift with the introduction of a premature stop codon at the C-terminal of the protein: c.1362insT (p.A453CfsX470) in SPG5A gene. Any pathogenic changes was detected in SPG42 gene. Interestingly, both early-age onset and possible anticipatory phenomena were observed in the two families showing mutation p.R416C in ATL1. These results confirm data observed in literature according to which the SPG3A and SPG5A genes show an high mutational frequency in early onset forms of ADHSP and ARHSP (respectively 20% and 7%) and apparently sporadic cases.

This thesis examines the excimer-laser-induced melting of ELA-prepared silicon films using in situ transient reflectance and transmission analysis. The results clearly show that these polycrystalline films, which consist of columnar grains in contact with SiO₂, can melt in a largely and remarkably 2-D manner. Based on the presently and previously obtained experimental results, as well as considering the thermal, thermodynamic, and kinetic aspects of the melting-transition-relevant details, we suggest a model that consists of grain-boundary-initiated melting, followed by lateral melting proceeding into the transiently superheated interior of the grains. Additional experiments are performed which demonstrate how this 2-D melting behavior at least stems intrinsically from the presence in the material of melt-prone grain boundaries and superheating-permitting Si/SiO₂ interfaces. Next, the phase and temperature evolutions of the irradiated films are investigated using a numerical simulation program, which incorporates key material, thermodynamic, and kinetic parameters. We find that the center portion of the grains during (partial) melting (1) corresponds to, especially at the SiO₂-passivated surface, the hottest regions of the films during rapid heating, and (2) remains entirely solid throughout the thickness of the film, as the maximum temperature sustained in these unmelted solids remains well below the superheating limit of silicon at the Si/SiO₂ interface. Lastly, we discuss, and substantiate with results obtained from numerical simulations, the role that the manifested dimensionality of melting plays in dictating the efficiency with which the ELA crystallization technique can generate microstructurally uniform polycrystalline materials. The current discovery regarding the 2-D nature of melting should be recognized and appreciated as a critical process-enabling element for ELA, as the scenario permits microstructure evolution of the grains to take place in an effective manner.

Chapter 1 Cerebrotendinous xanthomatosis (CTX) and spastic paraplegia type 5 (SPG5) are autosomal recessive bile acid disorders characterized by accumulation of neurotoxic oxysterols which leads to central nervous system damage causing significant disability if the disorders are not early treated. CTX patients are treated with chenodeoxycholic acid (CDCA), while SPG5 subjects may benefit from a cholesterol lowering-therapy. Chapter 2 Since CTX is a chronic disorder leading to progressive deterioration and premature death if not treated, all authors agree on the need for early diagnosis and timely introduction of CDCA therapy. However, as there is considerable variation in disease onset, systemic involvement and neurological impairment, its recognition at an initial stage may be challenging in the clinical setting. This prompted us to develop a simple practical diagnostic algorithm for early identification of CTX patients.We reviewed the largest available series of CTX cases analyzed together, and we developed a suspicion index to achieve early diagnosis of this treatable metabolic disorder. Our results show that the present suspicion index could allow early diagnosis of CTX, so that treatment can be started before disability occurs. We therefore propose its use in clinical practice. Chapter 3 We evaluated the serum profile of bile acids intermediates (cholestanol and its precursor 7αC4, 27-OHC, 24S-hydroxycholesterol), cholesterol, lathosterol, and plant sterols (campesterol, sitosterol) in a significantly large CTX population: we performed a baseline assessment and a long-term follow up during therapy with oral CDCA, comparing biochemical data with neurological outcome. Our metabolic evaluation of CTX patients allowed us to clarify some pathogenetic aspects of the disease, to specify the role of the various biochemical parameters in the diagnostic setting, and to better assess the effects of CDCA treatment on cholesterol metabolism, also in the light of clinical evolution. Chapter 4 We report the clinical and MRI findings of 38 CTX patients, and the follow up data of 16 of them who were untreated at baseline. Our detailed description of the complex spectrum of MRI abnormalities in CTX brains should contribute to the earlier recognition. Infratentorial lesions involving the dentate nuclei and surrounding white matter, and less frequently the brainstem, should lead to suspect CTX. However, this finding is not invariably present, since cerebellar signal alterations can be subtle or absent in some patients. The variable appearance of cerebellar abnormalities seems to provide a snapshot into the neuropathology underlying CTX. Notably, patients showing MRI evidence of cerebellar vacuolation should be monitored more strictly over time and could be the ones to select for additional or experimental therapies. Chapter 5 We report a case of a child presenting with neonatal cholestasis and diagnosed as CTX in the first year of life. She was promptly treated with CDCA and presented a normal neurological development. The early beginning of the therapy with CDCA, with the declining of the toxic bile acid intermediates, prevented clinical deterioration. Our long term experience, with an early beginning of the treatment with CDCA, not only confirms the efficacy of the drug in preventing neurologic damage, but also demonstrates its total safety. Chapter 6 SPG5 patients have increased levels of 27-hydroxycholesterol (27OHC), and its accumulation in the brain may be the key pathogenetic event, with relevant therapeutic implications. We describe four SPG5 patients and report the follow up data including evaluation of response to therapy with cholesterol-lowering drugs. Therapy of HSPs essentially focuses on symptomatic treatment. In this regard, SPG5 may represent the first form with an available disease-modifying therapy. In our patients simvastatin and ezetimibe strongly reduced serum levels of 27OHC. Our findings support the use of this drugs in SPG5, which however should be further evaluated with a double-blind, placebo-controlled clinical trial.

Spastic paraplegia type 5 (SPG5) is an autosomal recessive hereditary spastic paraplegia due to mutations in CYP7B1, which encodes oxysterol 7α‎-hydroxylase. Oxysterol 7α‎-hydroxylase is involved in the synthesis of bile acids from cholesterol. CYP7B1 mutations are responsible for rare forms of liver failure in infancy as well as lower motor neuron degeneration in adults with no obvious genotype-phenotype correlation. SPG5 is mostly characterized by spastic paraplegia with prominent posterior column sensory impairment that can lead to sensory ataxia and bladder dysfunction. SPG5 can easily be diagnosed thanks to the significant elevation of two plasma oxysterols: 27- and 25-hydroxycholesterol. Accordingly, plasma oxysterols are biomarkers that should be included in the screening of any spastic paraplegia of unknown etiology. Furthermore, the dramatic therapeutic response of a child with liver failure due to CYP7B1 mutations using chenodeoxycholic acid opens promising therapeutic perspectives for SPG5 patients, possibly as in cerebrotendinous xanthomatosis.