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Hereditary spastic paraplegias (HSPs) are a diverse set of neurological disorders characterized by progressive spasticity and weakness in the lower limbs caused by damage to the axons of the corticospinal tract. More than 88 genetic mutations have been associated with HSP, yet the mechanisms underlying these disorders are not well understood. We replicated the pathophysiology of one form of HSP known as spastic paraplegia 15 (SPG15) in zebrafish. This disorder is caused in humans by mutations in the ZFYVE26 gene, which codes for a protein called SPASTIZIN. We show that, in zebrafish, the significant reduction of Spastizin caused degeneration of large motor neurons. Motor neuron degeneration is associated with axon demyelination in the spinal cord and impaired locomotion in the spastizin mutants. Our findings reveal that the reduction in Spastizin compromises axonal integrity and affects the myelin sheath, ultimately recapitulating the pathophysiology of HSPs.

Purpose: Spastic paraplegia, intellectual disability, nystagmus, and obesity syndrome (SINO) is a rare autosomal dominant condition caused by heterozygous variants in KIDINS220. A total of 12 individuals are reported, comprising 8 with SINO and 4 with an autosomal recessive condition attributed to biallelic KIDINS220 variants., Methods: In our international cohort, we have included 14 individuals, carrying 13 novel pathogenic KIDINS220 variants in heterozygous form. We assessed the clinical and molecular data of our cohort and previously reported individuals and, based on functional experiments, reached a better understanding of the pathogenesis behind the KIDINS220-related disease., Results: Using fetal tissue and in vitro assays, we demonstrate that the variants generate KIDINS220 truncated forms that mislocalize in punctate intracellular structures, with decreased levels of the full-length protein, suggesting a trans-dominant negative effect. A total of 92% had their diagnosis within 3 years, with symptoms of developmental delay, spasticity, hypotonia, lack of eye contact, and nystagmus. We identified a KIDINS220 variant associated with fetal hydrocephalus and show that 58% of examined individuals present brain ventricular dilatation. We extend the phenotypic spectrum of SINO syndrome to behavioral manifestations not previously highlighted., Conclusion: Our study provides further insights into the clinical spectrum, etiology, and predicted functional impact of KIDINS220 variants., Competing Interests: Conflict of Interest The authors declare no conflicts of interest., (Copyright © 2024 American College of Medical Genetics and Genomics. Published by Elsevier Inc. All rights reserved.)

Hereditary spastic paraplegias are rare genetic disorders characterized by corticospinal tract impairment. Spastic paraplegia 83 (SPG83) is associated with biallelic mutations in the HPDL gene, leading to varied severities from neonatal to juvenile onset. The function of HPDL is unclear, though it is speculated to play a role in alternative coenzyme Q10 biosynthesis. Here, we report the generation of hiPS lines from primary skin fibroblasts derived from three SPG83 patients with different HPDL mutations, using episomal reprogramming. The patients' clinical characteristics are carefully listed. The hiPS lines were meticulously characterized, demonstrating typical pluripotent characteristics through immunofluorescence assays for stemness markers (OCT4, TRA1-60, NANOG, and SSEA4) and RT-PCR for endogenous gene expression. Genetic integrity and identity were confirmed via Sanger sequencing and short tandem repeat analysis. These hiPS cells displayed typical pluripotent characteristics and were able to differentiate into neocortical neurons via a dual SMAD inhibition protocol. In addition, HPDL mutant neurons assessed via long-term culturing were able to achieve effective maturation, similarly to their wild-type counterparts. The HPDL hiPS lines we generated will provide a valuable model for studying SPG83, offering insights into its molecular mechanisms and potential for developing targeted therapies.

Hereditary Spastic Paraplegia (HSP) is a group of rare inherited disorders characterized by progressive weakness and spasticity of the legs. Recent newly discovered biallelic variants in the gene FICD were found in patients with a highly similar phenotype to early onset HSP. FICD encodes filamentation induced by cAMP domain protein. FICD is involved in the AMPylation and deAMPylation protein modifications of the endoplasmic reticulum (ER) chaperone BIP, a major constituent of the ER that regulates the unfolded protein response. Although several biochemical properties of FICD have been characterized, the neurological function of FICD and the pathological mechanism underlying HSP are unknown. We established a Drosophila model to gain mechanistic understanding of the function of FICD in HSP pathogenesis, and specifically the role of BIP in neuromuscular physiology. Our studies on Drosophila Fic null mutants uncovered that loss of Fic resulted in locomotor impairment and reduced levels of BIP in the motor neuron circuitry, as well as increased reactive oxygen species (ROS) in the ventral nerve cord of Fic null mutants. Finally, feeding Drosophila Fic null mutants with chemical chaperones PBA or TUDCA, or treatment of patient fibroblasts with PBA, reduced the ROS accumulation. The neuronal phenotypes of Fic null mutants recapitulate several clinical features of HSP patients and further reveal cellular patho-mechanisms. By modeling FICD in Drosophila, we provide potential targets for intervention for HSP, and advance fundamental biology that is important for understanding related rare and common neuromuscular diseases., Competing Interests: Declaration of competing interest Authors declare that they have no competing interests., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Background: Hereditary spastic paraplegia (HSP) is a rare genetically heterogeneous neurodegenerative disorder. The most common type of HSP is caused by pathogenic variants in the SPAST gene. Various hypotheses regarding the pathogenic mechanisms of HSP-SPAST have been proposed. However, a single hypothesis may not be sufficient to explain HSP-SPAST., Objective: To determine the causative gene of autosomal dominant HSP-SPAST in a pure pedigree and to study its underlying pathogenic mechanism., Methods: A four-generation Chinese family was investigated. Genetic testing was performed for the causative gene, and a splice site variant was identified. In vivo and in vitro experiments were conducted separately. Western blotting and immunofluorescence were performed after transient transfection of cells with the wild-type (WT) or mutated plasmid. The developmental expression pattern of zebrafish spasts was assessed via whole-mount in situ hybridization. The designed guide RNA (gRNA) and an antisense oligo spast-MO were microinjected into Tg(hb9:GFP) zebrafish embryos, spinal cord motor neurons were observed, and a swimming behavioral analysis was conducted., Results: A novel heterozygous intron variant, c.1004 + 5G > A, was identified in a pure HSP-SPAST pedigree and shown to cosegregate with the disease phenotypes. This intron splice site variant skipped exon 6, causing a frameshift mutation that resulted in a premature termination codon. In vitro, the truncated protein was evenly distributed throughout the cytoplasm, formed filamentous accumulations around the nucleus, and colocalized with microtubules. Truncated proteins diffusing in the cytoplasm appeared denser. No abnormal microtubule structures were observed, and the expression levels of α-tubulin remained unchanged. In vivo, zebrafish larvae with this mutation displayed axon pathfinding defects, impaired outgrowth, and axon loss. Furthermore, spast-MO larvae exhibited unusual behavioral preferences and increased acceleration., Conclusion: The adverse effects of premature stop codon mutations in SPAST result in insufficient levels of functional protein, and the potential toxicity arising from the intracellular accumulation of spastin serves as a contributing factor to HSP-SPAST., (© 2024. The Author(s).)

Background and objectives: Hereditary spastic paraplegia (HSP) is characterized by unsteady gait, motor incoordination, speech impairment, abnormal eye movement, progressive spasticity and lower limb weakness. Spastic paraplegia 75 (SPG75) results from a mutation in the gene that encodes myelin associated glycoprotein (MAG). Only a limited number of MAG variants associated with SPG75 in families of European, Middle Eastern, North African, Turkish and Palestinian ancestry have been documented so far. This study aims to provide further insight into the clinical and molecular manifestations of HSP. Methods: Using whole-exome sequencing, we investigated a consanguineous Pakistani family where three individuals presented with clinical signs of HSP. Sanger sequencing was used to carry out segregation analysis on available family members, and a minigene splicing assay was utilized to evaluate the effect of the splicing variant. Results: We identified a novel homozygous pathogenic splice donor variant in MAG (c.46 + 1G > T) associated with SPG75. RNA analysis revealed exon skipping that resulted in the loss of a start codon for ENST00000361922.8 isoform. Affected individuals exhibited variable combinations of nystagmus, developmental delay, cognitive impairments, spasticity, dysarthria, delayed gait and ataxia. The proband displayed a quadrupedal stride, and his siblings experienced frequent falls and ataxic gait as one of the prominent features that have not been previously reported in SPG75. Conclusions: Thus, the present study presents an uncommon manifestation of SPG75, the first from the Pakistani population, and broadens the spectrum of MAG variants.

Mutation of the ATL1 gene is one of the most common causes of hereditary spastic paraplegia (HSP), a group of genetic neurodegenerative conditions characterised by distal axonal degeneration of the corticospinal tract axons. Atlastin-1, the protein encoded by ATL1, is one of three mammalian atlastins, which are homologous dynamin-like GTPases that control endoplasmic reticulum (ER) morphology by fusing tubules to form the three-way junctions that characterise ER networks. However, it is not clear whether atlastin-1 is required for correct ER morphology in human neurons and if so what the functional consequences of lack of atlastin-1 are. Using CRISPR-inhibition we generated human cortical neurons lacking atlastin-1. We demonstrate that ER morphology was altered in these neurons, with a reduced number of three-way junctions. Neurons lacking atlastin-1 had longer endosomal tubules, suggestive of defective tubule fission. This was accompanied by reduced lysosomal proteolytic capacity. As well as demonstrating that atlastin-1 is required for correct ER morphology in human neurons, our results indicate that lack of a classical ER-shaping protein such as atlastin-1 may cause altered endosomal tubulation and lysosomal proteolytic dysfunction. Furthermore, they strengthen the idea that defective lysosome function contributes to the pathogenesis of a broad group of HSPs, including those where the primary localisation of the protein involved is not at the endolysosomal system., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Evan Reid reports a relationship with SwanBio Therapeutics, Inc. that includes: consulting or advisory. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: Autosomal Recessive Spastic Ataxia of Charlevoix-Saguenay (ARSACS) and Spastic Paraplegia Type 7 (SPG7) are paradigmatic spastic ataxias (SPAX) with suggested white matter (WM) involvement. Aim of this work was to thoroughly disentangle the degree of WM involvement in these conditions, evaluating both macrostructure and microstructure via the analysis of diffusion MRI (dMRI) data., Material and Methods: In this multi-center prospective study, ARSACS and SPG7 patients and Healthy Controls (HC) were enrolled, all undergoing a standardized dMRI protocol and a clinimetrics evaluation including the Scale for the Assessment and Rating of Ataxia (SARA). Differences in terms of WM volume or global microstructural WM metrics were probed, as well as the possible occurrence of a spatially defined microstructural WM involvement via voxel-wise analyses, and its correlation with patients' clinical status., Results: Data of 37 ARSACS (M/F = 21/16; 33.4 ± 12.4 years), 37 SPG7 (M/F = 24/13; 55.7 ± 10.7 years), and 29 HC (M/F = 13/16; 42.1 ± 17.2 years) were analyzed. While in SPG7, only a mild mean microstructural damage was found compared to HC, ARSACS patients present a severe WM involvement, with a reduced global volume (p < 0.001), an alteration of all microstructural metrics (all with p < 0.001), without a spatially defined pattern of damage but with a prominent involvement of commissural fibers. Finally, in ARSACS, a correlation between microstructural damage and SARA scores was found (p = 0.004)., Conclusion: In ARSACS, but not SPG7 patients, we observed a complex and multi-faced involvement of brain WM, with a clinically meaningful widespread loss of axonal and dendritic integrity, secondary demyelination and, overall, a reduction in cellularity and volume., (© 2024. The Author(s).)

Background and Purpose: White matter (WM) damage is the main target of hereditary spastic paraplegia (HSP), but mounting evidence indicates that genotype-specific grey matter (GM) damage is not uncommon. Our aim was to identify and compare brain GM and WM damage patterns in HSP subtypes and investigate how gene expression contributes to these patterns, and explore the relationship between GM and WM damage., Methods: In this prospective single-centre cohort study from 2019 to 2022, HSP patients and controls underwent magnetic resonance imaging evaluations. The alterations of GM and WM patterns were compared between groups by applying a source-based morphometry approach. Spearman rank correlation was used to explore the associations between gene expression and GM atrophy patterns in HSP subtypes. Mediation analysis was conducted to investigate the interplay between GM and WM damage., Results: Twenty-one spastic paraplegia type 4 (SPG4) patients (mean age 50.7 years ± 12.0 SD, 15 men), 21 spastic paraplegia type 5 (SPG5) patients (mean age 29.1 years ± 12.8 SD, 14 men) and 42 controls (sex- and age-matched) were evaluated. Compared to controls, SPG4 and SPG5 showed similar WM damage but different GM atrophy patterns. GM atrophy patterns in SPG4 and SPG5 were correlated with corresponding gene expression (ρ = 0.30, p = 0.008, ρ = 0.40, p < 0.001, respectively). Mediation analysis indicated that GM atrophy patterns were mediated by WM damage in HSP., Conclusions: Grey matter atrophy patterns were distinct between SPG4 and SPG5 and were not only secondary to WM damage but also associated with disease-related gene expression., Clinical Trial Registration No: NCT04006418., (© 2024 The Authors. European Journal of Neurology published by John Wiley & Sons Ltd on behalf of European Academy of Neurology.)

Hereditary spastic paraplegia (HSP) comprises a large group of neurogenetic disorders characterized by progressive lower extremity spasticity. Neurological evaluation and genetic testing were completed in a Malian family with early-onset HSP. Three children with unaffected consanguineous parents presented with symptoms consistent with childhood-onset complicated HSP. Neurological evaluation found lower limb weakness, spasticity, dysarthria, seizures, and intellectual disability. Brain MRI showed corpus callosum thinning with cortical and spinal cord atrophy, and an EEG detected slow background in the index patient. Whole exome sequencing identified a homozygous missense variant in the adaptor protein (AP) complex 2 alpha-2 subunit (AP2A2) gene. Western blot analysis showed reduced levels of AP2A2 in patient-iPSC derived neuronal cells. Endocytosis of transferrin receptor (TfR) was decreased in patient-derived neurons. In addition, we observed increased axon initial segment length in patient-derived neurons. Xenopus tropicalis tadpoles with ap2a2 knockout showed cerebral edema and progressive seizures. Immunoprecipitation of the mutant human AP-2-appendage alpha-C construct showed defective binding to accessory proteins. We report AP2A2 as a novel genetic entity associated with HSP and provide functional data in patient-derived neuron cells and a frog model. These findings expand our understanding of the mechanism of HSP and improve the genetic diagnosis of this condition., Competing Interests: Declaration of competing interest The authors report no conflicts of interest., (Published by Elsevier Inc.)

Spastic paraplegia type 4 (SPG4), caused by SPAST mutations, is the most predominant subtype of hereditary spastic paraplegia. Most documented SPG4 patients present as pure form, with the complex form rarely reported. We described the clinical and genetic features of 20 patients with complex phenotypes of SPG4 and further explored the genotype-phenotype correlations. We collected detailed clinical data of all SPG4 patients and assessed their phenotypes. SPAST gene mutations were identified by Multiplex ligation-dependent probe amplification in combination with whole exome sequencing. We further performed statistical analysis in genotype and phenotype among patients with various manifestations and different variants. Out of 90 SPG4 patients, 20 patients (male:female = 16:4) with additional neurologic deficits, namely complex form, were included in our study. The bimodal distribution of age of onset at 0-10 and 21-40 years old is concluded. On cranial MRI, obvious white matter lesions can be observed in five patients. We identified 9 novel and 8 reported SPAST mutations, of which 11 mutations were located in AAA (ATPase associated with various cellular activities) domain. The AAA cassette of spastin is the hottest mutated region among complex SPG4. All patients with cognitive impairment (CI) are males (n = 9/9). Additionally, 80% patients with ataxia are due to frameshift mutations (n = 4/5). Overall, our study summarized and analyzed the genetic and phenotypic characteristics of complex SPG4, making up over 1/5 of in-house SPG4 cohort, among which CI and ataxia are the most common features. Further studies are expected to explore the underlying mechanisms., (© 2024 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: Spastic paraplegia 11 (SPG11) is the most prevalent form of autosomal recessive hereditary spastic paraplegia, resulting from biallelic pathogenic variants in the SPG11 gene (MIM *610844)., Methods: The proband is a 36-year-old female referred for genetic evaluation due to cognitive dysfunction, gait impairment, and corpus callosum atrophy (brain MRI was normal at 25-years-old). Diagnostic approaches included CGH array, next-generation sequencing, and whole transcriptome sequencing., Results: CGH array revealed a 180 kb deletion located upstream of SPG11. Sequencing of SPG11 uncovered two rare single nucleotide variants: the novel variant c.3143C>T in exon 17 (in cis with the deletion), and the previously reported pathogenic variant c.6409C>T in exon 34 (in trans). Whole transcriptome sequencing revealed that the variant c.3143C>T caused exon 17 skipping., Conclusion: We report a novel sequence variant in the SPG11 gene resulting in exon 17 skipping, which, along with a nonsense variant, causes Spastic Paraplegia 11 in our proband. In addition, a deletion upstream of SPG11 was identified in the patient, whose implication in the phenotype remains uncertain. Nonetheless, the deletion apparently affects cis-regulatory elements of the gene, suggesting a potential new pathogenic mechanism underlying the disease in a subset of undiagnosed patients. Our findings further support the hypothesis that the origin of thin corpus callosum in patients with SPG11 is of progressive nature., (© 2024 The Author(s). Molecular Genetics & Genomic Medicine published by Wiley Periodicals LLC.)

Selenoprotein I (SELENOI) catalyzes the final reaction of the CDP-ethanolamine branch of the Kennedy pathway, generating the phospholipids phosphatidylethanolamine (PE) and plasmenyl-PE. Plasmenyl-PE is a key component of myelin and is characterized by a vinyl ether bond that preferentially reacts with oxidants, thus serves as a sacrificial antioxidant. In humans, multiple loss-of-function mutations in genes affecting plasmenyl-PE metabolism have been implicated in hereditary spastic paraplegia, including SELENOI. Herein, we developed a mouse model of nervous system-restricted SELENOI deficiency that circumvents embryonic lethality caused by constitutive deletion and recapitulates phenotypic features of hereditary spastic paraplegia. Resulting mice exhibited pronounced alterations in brain lipid composition, which coincided with motor deficits and neuropathology including hypomyelination, elevated reactive gliosis, and microcephaly. Further studies revealed increased lipid peroxidation in oligodendrocyte lineage cells and disrupted oligodendrocyte maturation both in vivo and in vitro. Altogether, these findings detail a critical role for SELENOI-derived plasmenyl-PE in myelination that is of paramount importance for neurodevelopment., Competing Interests: Conflict of interest The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: Mutations in the tropomyosin receptor kinase fused ( TFG ) gene are associated with various neurological disorders, including autosomal recessive hereditary spastic paraplegia (HSP), autosomal dominant hereditary motor and sensory neuropathy with proximal dominant involvement (HMSN-P) and autosomal dominant type of Charcot-Marie-Tooth disease type 2., Methods: Whole genome sequencing and whole-exome sequencing were used, followed by Sanger sequencing for validation. Haplotype analysis was performed to confirm the inheritance mode of the novel TFG mutation in a large Chinese family with HSP. Additionally, another family diagnosed with HMSN-P and carrying the reported TFG mutation was studied. Clinical data and muscle pathology comparisons were drawn between patients with HSP and patients with HMSN-P. Furthermore, functional studies using skin fibroblasts derived from patients with HSP and patients with HMSN-P were conducted to investigate the pathomechanisms of TFG mutations., Results: A novel heterozygous TFG variant (NM&#95;006070.6: c.125G>A (p.R42Q)) was identified and caused pure HSP. We further confirmed that the well-documented recessively inherited spastic paraplegia, caused by homozygous TFG mutations, exists in a dominantly inherited form. Although the clinical features and muscle pathology between patients with HSP and patients with HMSN-P were distinct, skin fibroblasts derived from both patient groups exhibited reduced levels of autophagy-related proteins and the presence of TFG-positive puncta., Conclusions: Our findings suggest that autophagy impairment may serve as a common pathomechanism among different clinical phenotypes caused by TFG mutations. Consequently, targeting autophagy may facilitate the development of a uniform treatment for TFG-related neurological disorders., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2024. No commercial re-use. See rights and permissions. Published by BMJ.)

Hereditary spastic paraplegia (HSP) is a group of inherited neurodegenerative disorders characterized by progressive lower limb spasticity and weakness. One subtype of HSP, known as SPG54, is caused by biallelic mutations in the DDHD2 gene. The primary pathological feature observed in patients with SPG54 is the massive accumulation of lipid droplets (LDs) in the brain. However, the precise mechanisms and roles of DDHD2 in regulating lipid homeostasis are not yet fully understood. Through Affinity Purification-Mass Spectroscopy (AP-MS) analysis, we identify that DDHD2 interacts with multiple members of the ATG8 family proteins (LC3, GABARAPs), which play crucial roles in lipophagy. Mutational analysis reveals the presence of two authentic LIR motifs in DDHD2 protein that are essential for its binding to LC3/GABARAPs. We show that DDHD2 deficiency leads to LD accumulation, while enhanced DDHD2 expression reduces LD formation. The LC3/GABARAP-binding capacity of DDHD2 and the canonical autophagy pathway both contribute to its LD-eliminating activity. Moreover, DDHD2 enhances the colocalization between LC3B and LDs to promote lipophagy. LD·ATTEC, a small molecule that tethers LC3 to LDs to enhance their autophagic clearance, effectively counteracts DDHD2 deficiency-induced LD accumulation. These findings provide valuable insights into the regulatory roles of DDHD2 in LD catabolism and offer a potential therapeutic approach for treating SPG54 patients., (© 2024. The Author(s), under exclusive licence to ADMC Associazione Differenziamento e Morte Cellulare.)

Biallelic loss of SPG11 function constitutes the most frequent cause of complicated autosomal recessive hereditary spastic paraplegia (HSP) with thin corpus callosum, resulting in progressive multisystem neurodegeneration. While the impact of neuroinflammation is an emerging and potentially treatable aspect in neurodegenerative diseases and leukodystrophies, the role of immune cells in SPG11-HSP patients is unknown. Here, we performed a comprehensive immunological characterization of SPG11-HSP, including examination of three human postmortem brain donations, immunophenotyping of patients' peripheral blood cells and patient-specific induced pluripotent stem cell-derived microglia-like cells (iMGL). We delineate a previously unknown role of innate immunity in SPG11-HSP. Neuropathological analysis of SPG11-HSP patient brain tissue revealed profound microgliosis in areas of neurodegeneration, downregulation of homeostatic microglial markers and cell-intrinsic accumulation of lipids and lipofuscin in IBA1 + cells. In a larger cohort of SPG11-HSP patients, the ratio of peripheral classical and intermediate monocytes was increased, along with increased serum levels of IL-6 that correlated with disease severity. Stimulation of patient-specific iMGLs with IFNγ led to increased phagocytic activity compared to control iMGL as well as increased upregulation and release of proinflammatory cytokines and chemokines, such as CXCL10. On a molecular basis, we identified increased STAT1 phosphorylation as mechanism connecting IFNγ-mediated immune hyperactivation and SPG11 loss of function. STAT1 expression was increased both in human postmortem brain tissue and in an Spg11 -/- mouse model. Application of an STAT1 inhibitor decreased CXCL10 production in SPG11 iMGL and rescued their toxic effect on SPG11 neurons. Our data establish neuroinflammation as a novel disease mechanism in SPG11-HSP patients and constitute the first description of myeloid cell/ microglia activation in human SPG11-HSP. IFNγ/ STAT1-mediated neurotoxic effects of hyperreactive microglia upon SPG11 loss of function indicate that immunomodulation strategies may slow down disease progression., (© 2024. The Author(s).)

Objective: Haploinsufficiency is widely accepted as the pathogenic mechanism of hereditary spastic paraplegias type 4 (SPG4). However, there are some cases that cannot be explained by reduced function of the spastin protein encoded by SPAST. The aim of this study was to identify the causative variant of SPG4 in a large Chinese family and explore its pathological mechanism., Materials and Methods: A five-generation family with 49 members including nine affected (4 males and 5 females) and 40 unaffected individuals in Mongolian nationality was recruited. Whole exome sequencing was employed to investigate the genetic etiology. Western blotting and immunofluorescence were used to analyze the effects of the mutant proteins in vitro., Results: A novel frameshift variant NM&#95;014946.4: c.483&#95;484delinsC (p.Val162Leufs*2) was identified in SPAST from a pedigree with SPG4. The variant segregated with the disease in the family and thus determined as the disease-causing variant. The c.483&#95;484delinsC variant produced two truncated mutants (mutant M1 and M87 isoforms). They accumulated to a higher level and presented increased stability than their wild-type counterparts and may lost the microtubule severing activity., Conclusion: SPAST mutations leading to premature stop codons do not always act through haploinsufficiency. The potential toxicity to the corticospinal tract caused by the intracellular accumulation of truncated spastin should be considered as the pathological mechanism of SPG4., (© 2023. The Author(s).)

For a long time, technical obstacles have hampered the acquisition of high-resolution images and the development of reliable processing protocols for spinal cord (SC) MRI. Fortunately, this scenario has changed in the past 5-10 years, due to hardware and software improvements. Nowadays, with advanced protocols, SC MRI is considered a useful tool for several inherited and acquired neurologic diseases, not only for diagnosis approach but also for pathophysiological unraveling and as a biomarker for disease monitoring and clinical trials. In this review, we address advanced SC MRI sequences for macrostructural and microstructural evaluation, useful semiautomatic and automatic processing tools and clinical applications on several neurologic conditions such as hereditary cerebellar ataxia, hereditary spastic paraplegia, motor neuron diseases and multiple sclerosis., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Objective: Hereditary spastic paraplegias (HSPs) are a group of inherited neurodegenerative disorders characterized by slowly progressive lower limb spasticity and weakness. HSP type 54 (SPG54) is autosomal recessively inherited and caused by mutations in the DDHD2 gene. This study investigated the clinical characteristics and molecular features of DDHD2 mutations in a cohort of Taiwanese patients with HSP., Methods: Mutational analysis of DDHD2 was performed for 242 unrelated Taiwanese patients with HSP. The clinical, neuroimaging, and genetic features of the patients with biallelic DDHD2 mutations were characterized. A cell-based study was performed to assess the effects of the DDHD2 mutations on protein expression., Results: SPG54 was diagnosed in three patients. Among them, two patients carried compound heterozygous DDHD2 mutations, p.[R112Q];[Y606*] and p.[R112Q];[p.D660H], and the other one was homozygous for the DDHD2 p.R112Q mutation. DDHD2 p.Y606* is a novel mutation, whereas DDHD2 p.D660H and p.R112Q have been reported in the literature. All three patients manifested adult onset complex HSP with additional cerebellar ataxia, polyneuropathy, or cognitive impairment. Brain proton magnetic resonance spectroscopy revealed an abnormal lipid peak in thalamus of all three patients. In vitro studies demonstrated that all the three DDHD2 mutations were associated with a considerably lower DDHD2 protein level., Interpretation: SPG54 was detected in approximately 1.2% (3 of 242) of the Taiwanese HSP cohort. This study expands the known mutational spectrum of DDHD2, provides molecular evidence of the pathogenicity of the DDHD2 mutations, and underlines the importance of considering SPG54 as a potential diagnosis of adult-onset HSP., (© 2023 The Authors. Annals of Clinical and Translational Neurology published by Wiley Periodicals LLC on behalf of American Neurological Association.)

Introduction: Hereditary spastic paraplegias (HSPs) are a group of inherited neurodegenerative disorders characterized by progressive spasticity and weakness of the lower limbs. These conditions are caused by lesions in the neuronal pyramidal tract and exhibit clinical and genetic variability. Ongoing research focuses on understanding the underlying mechanisms of HSP onset, which ultimately lead to neuronal degeneration. Key molecular mechanisms involved include axonal transport, cytoskeleton dynamics, myelination abnormalities, membrane trafficking, organelle morphogenesis, ER homeostasis, mitochondrial dysfunction, and autophagy deregulation., Areas Covered: This review aims to provide an overview of the shared pathogenetic mechanisms in various forms of HSPs. By examining disease-causing gene products and their associated functional pathways, this understanding could lead to the discovery of new therapeutic targets and the development of treatments to modify the progression of the disease., Expert Opinion: Investigating gene functionality is crucial for identifying shared pathogenetic pathways underlying different HSP subtypes. Categorizing protein function and identifying pathways aids in finding biomarkers, predicting early onset, and guiding treatment for a better quality of life. Targeting shared mechanisms enables efficient and cost-effective therapies. Prospects involve identifying new disease-causing genes, refining molecular processes, and implementing findings in diagnosis, key for advancing HSP understanding and developing effective treatments.

Neuronal endoplasmic reticulum (ER) appears continuous throughout the cell. Its shape and continuity are influenced by ER-shaping proteins, mutations in which can cause distal axon degeneration in Hereditary Spastic Paraplegia (HSP). We therefore asked how loss of Rtnl1, a Drosophila ortholog of the human HSP gene RTN2 (SPG12), which encodes an ER-shaping protein, affects ER organization and the function of presynaptic terminals. Loss of Rtnl1 depleted ER membrane markers at Drosophila presynaptic motor terminals and appeared to deplete narrow tubular ER while leaving cisternae largely unaffected, thus suggesting little change in resting Ca2+ storage capacity. Nevertheless, these changes were accompanied by major reductions in activity-evoked Ca2+ fluxes in the cytosol, ER lumen, and mitochondria, as well as reduced evoked and spontaneous neurotransmission. We found that reduced STIM-mediated ER-plasma membrane contacts underlie presynaptic Ca2+ defects in Rtnl1 mutants. Our results show the importance of ER architecture in presynaptic physiology and function, which are therefore potential factors in the pathology of HSP., (© 2023 Pérez-Moreno et al.)

Background: KIF1A (kinesin family member 1A)-related disorders encompass a variety of diseases. KIF1A variants are responsible for autosomal recessive and dominant spastic paraplegia 30 (SPG, OMIM610357), autosomal recessive hereditary sensory and autonomic neuropathy type 2 (HSN2C, OMIM614213), and autosomal dominant neurodegeneration and spasticity with or without cerebellar atrophy or cortical visual impairment (NESCAV syndrome), formerly named mental retardation type 9 (MRD9) (OMIM614255). KIF1A variants have also been occasionally linked with progressive encephalopathy with brain atrophy, progressive neurodegeneration, PEHO-like syndrome (progressive encephalopathy with edema, hypsarrhythmia, optic atrophy), and Rett-like syndrome., Materials and Methods: The first Polish patients with confirmed heterozygous pathogenic and potentially pathogenic KIF1A variants were analyzed. All the patients were of Caucasian origin. Five patients were females, and four were males (female-to-male ratio = 1.25). The age of onset of the disease ranged from 6 weeks to 2 years., Results: Exome sequencing identified three novel variants. Variant c.442G>A was described in the ClinVar database as likely pathogenic. The other two novel variants, c.609G>C; p.(Arg203Ser) and c.218T>G, p.(Val73Gly), were not recorded in ClinVar., Conclusions: The authors underlined the difficulties in classifying particular syndromes due to non-specific and overlapping signs and symptoms, sometimes observed only temporarily.

Hereditary spastic paraplegia (HSP) comprises a group of hereditary and neurodegenerative diseases that are characterized by axonal degeneration or demyelination of bilateral corticospinal tracts in the spinal cord; affected patients exhibit progressive spasticity and weakness in the lower limbs. The most common manifestation of HSP is spastic paraplegia type 4 (SPG4), which is caused by mutations in the spastin ( SPAST ) gene. The present study reports the clinical characteristics of affected individuals and sequencing analysis of a mutation that caused SPG4 in a family. All affected family members exhibited spasticity and weakness of the lower limbs and, notably, only male members of the family were affected. Whole‑exome sequencing revealed that all affected individuals had a novel c.1785C>A (p. Ser595Arg) missense mutation in SPAST . Bioinformatics analysis revealed changes in both secondary and tertiary structures of the mutated protein. The novel missense mutation in SPAST supported the diagnosis of SPG4 in this family and expands the spectrum of pathogenic mutations that cause SPG4. Analysis of SPAST sequences revealed that most pathogenic mutations occurred in the AAA domain of the protein, which may have a close relationship with SPG4 pathogenesis.

Objective: Spastic paraplegia type 2 (SPG2) is an X-linked recessive (XLR) form of hereditary spastic paraplegia (HSP) caused by mutations in proteolipid protein 1 (PLP1) gene. We described the clinical and genetic features of three unrelated families with PLP1 mutations and reviewed PLP1-related cases worldwide to summarize the genotype-phenotype correlations., Methods: The three probands were 23, 26, and 27 years old, respectively, with progressively aggravated walking difficulty as well as lower limb spasticity. Detailed physical examination showed elevated muscle tone, hyperreflexia, and Babinski signs in lower limbs. Brain MRI examinations were investigated for all cases. PLP1 mutations were identified by whole exome sequencing, followed by Sanger sequencing, family co-segregation, and phenotypic reevaluation., Results: A total of eight patients with SPG2 were identified in these three families. The probands additionally had cognitive impairment, urinary or fecal incontinence, ataxia, and white matter lesions (WML) in periventricular regions, with or without kinetic tremor. Three hemizygous mutations in PLP1 were identified, including c.453+159G>A, c.834A>T (p.*278C), and c.434G>A (p.W145*), of which c.834A>T was first associated with HSP., Interpretation: We identified three families with complicated SPG2 due to three PLP1 mutations. Our study supports the clinically inter-and intra-family heterogeneity of SPG2. The periventricular region WML and cognitive impairment are the most common characteristics. The kinetic tremor in upper limbs was observed in 2/3 families, suggesting the spectrum of PLP1-related disorders is still expanding., (© 2023 The Authors. Annals of Clinical and Translational Neurology published by Wiley Periodicals LLC on behalf of American Neurological Association.)

Pathogenic variants in ATL1 are a known cause of autosomal-dominantly inherited hereditary spastic paraplegia (HSP-ATL1, SPG3A) with a predominantly 'pure' HSP phenotype. Although a relatively large number of patients have been reported, no genotype-phenotype correlations have been established for specific ATL1 variants. Confronted with five children carrying de novo ATL1 variants showing early, complex and severe symptoms, we systematically investigated the molecular and phenotypic spectrum of HSP-ATL1. Through a cross-sectional analysis of 537 published and novel cases, we delineate a distinct phenotype observed in patients with de novo variants. Guided by this systematic phenotyping approach and structural modelling of disease-associated variants in atlastin-1, we demonstrate that this distinct phenotypic signature is also prevalent in a subgroup of patients with inherited ATL1 variants and is largely explained by variant localization within a three-dimensional mutational cluster. Establishing genotype-phenotype correlations, we find that symptoms that extend well beyond the typical pure HSP phenotype (i.e. neurodevelopmental abnormalities, upper limb spasticity, bulbar symptoms, peripheral neuropathy and brain imaging abnormalities) are prevalent in patients with variants located within this mutational cluster., (© The Author(s) 2022. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

The hereditary spastic paraplegia (HSP) is a rare hereditary disease in nervous system due to the damage of corticospinal tract. HSP has various inheritance modes, including autosomal dominant inheritance, autosomal recessive inheritance, X-linked inheritance, and mitochondrial inheritance in some cases. At present, there are at least 80 subtypes of HSP. Hereditary spastic paraplegia type 11 (SPG11) is the most common subtype in autosomal recessive inheritance, and its pathogenic factor is KIAA1840 gene, which encodes spatacsin protein. A total of 52 SPG11 patients aged from 4-24 years old have been reported. Their initial symptoms were gait disturbance and/or mental retardation. As the disease develops, they may present with mental retardation, sphincter disturbance, decreased vision, ataxia, amyotrophy, pes arcuatus, ophthalmoplegia, peripheral neuropathy, and others. Except agenesis of the corpus callosum and periventricular white matter changes, patients might show cortical atrophy, ventricular dilation, and cerebellar atrophy, and so on. Chinese SPG11 patients manifested significant clinical and genetical heterogeneity and no obvious gender difference. Of them, 37 pathogenic mutations of KIAA1840 gene were detected, which all introduced truncated mutation of spatacsin protein. KIAA1840 gene frameshift mutation is the most common type of mutation.

Hereditary spastic paraplegias are characterized by lower limb spasticity resulting from degeneration of long corticospinal axons. SPG11 is one of the most common autosomal recessive hereditary spastic paraplegias, and the SPG11 protein spatacsin forms a complex with the SPG15 protein spastizin and heterotetrameric AP5 adaptor protein complex, which includes the SPG48 protein AP5Z1. Using the integration-free episomal method, we established SPG11 patient-specific induced pluripotent stem cells (iPSCs) from patient fibroblasts. We differentiated SPG11 iPSCs, as well as SPG48 iPSCs previously established, into cortical projection neurons and examined protective effects by targeting mitochondrial dynamics using P110, a peptide that selectively inhibits mitochondrial fission GTPase Drp1. P110 treatment mitigates mitochondrial fragmentation, improves mitochondrial motility, and restores mitochondrial health and ATP levels in SPG11 and SPG48 neurons. Neurofilament aggregations are increased in SPG11 and SPG48 axons, and these are also suppressed by P110. Similarly, P110 mitigates neurofilament disruption in both SPG11 and SPG48 knockdown cortical projection neurons, confirming the contribution of hereditary spastic paraplegia gene deficiency to subsequent neurofilament and mitochondrial defects. Strikingly, neurofilament aggregations in SPG11 and SPG48 deficient neurons double stain with ubiquitin and autophagy related proteins, resembling the pathological hallmark observed in SPG11 autopsy brain sections. To confirm the cause-effect relationship between the SPG11 mutations and disease phenotypes, we knocked-in SPG11 disease mutations to human embryonic stem cells (hESCs) and differentiated these stem cells into cortical projection neurons. Reduced ATP levels and accumulated neurofilament aggregations along axons are observed, and both are mitigated by P110. Furthermore, rescue experiment with expression of wild-type SPG11 in cortical projection neurons derived from both SPG11 patient iPSCs and SPG11 disease mutation knock-in hESCs leads to rescue of mitochondrial dysfunction and neurofilament aggregations in these SPG11 neurons. Finally, in SPG11 and SPG48 long-term cultures, increased release of phosphoNF-H, a biomarker for nerve degeneration, is significantly reduced by inhibiting mitochondrial fission pharmacologically using P110 and genetically using Drp1 shRNA. Taken together, our results demonstrate that impaired mitochondrial dynamics underlie both cytoskeletal disorganization and axonal degeneration in SPG11 and SPG48 neurons, highlighting the importance of targeting these pathologies therapeutically., (© The Author(s) 2022. Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Background: Pathogenic variants in SPG11 cause the most common autosomal recessive complicated hereditary spastic paraplegia. Besides the prototypical combination of spastic paraplegia with a thin corpus callosum, obesity has increasingly been reported in this multisystem neurodegenerative disease. However, a detailed analysis of the metabolic state is lacking., Methods: In order to characterize metabolic alterations, a cross-sectional analysis was performed comparing SPG11 patients (n = 16) and matched healthy controls (n = 16). We quantified anthropometric parameters, body composition as determined by bioimpedance spectroscopy, and serum metabolic biomarkers, and we measured hypothalamic volume by high-field MRI., Results: Compared to healthy controls, SPG11 patients exhibited profound changes in body composition, characterized by increased fat tissue index, decreased lean tissue index, and decreased muscle mass. The presence of lymphedema correlated with increased extracellular fluid. The serum levels of the adipokines leptin, resistin, and progranulin were significantly altered in SPG11 while adiponectin and C1q/TNF-related protein 3 (CTRP-3) were unchanged. MRI volumetry revealed a decreased hypothalamic volume in SPG11 patients., Conclusions: Body composition, adipokine levels, and hypothalamic volume are altered in SPG11. Our data indicate a link between obesity and hypothalamic neurodegeneration in SPG11 and imply that specific metabolic interventions may prevent obesity despite severely impaired mobility in SPG11.

Hereditary spastic paraplegia (HSP) is a heterogeneous group of genetic neurodegenerative disorders, characterized by progressive lower limb spasticity and weakness resulting from retrograde axonal degeneration of motor neurons (MNs). Here, we generated in vitro human neuromuscular junctions (NMJs) from five HSP patient-specific induced pluripotent stem cell (hiPSC) lines, by means of microfluidic strategy, to model disease-relevant neuropathologic processes. The strength of our NMJ model lies in the generation of lower MNs and myotubes from autologous hiPSC origin, maintaining the genetic background of the HSP patient donors in both cell types and in the cellular organization due to the microfluidic devices. Three patients characterized by a mutation in the SPG3a gene, encoding the ATLASTIN GTPase 1 protein, and two patients with a mutation in the SPG4 gene, encoding the SPASTIN protein, were included in this study. Differentiation of the HSP-derived lines gave rise to lower MNs that could recapitulate pathological hallmarks, such as axonal swellings with accumulation of Acetyl-α-TUBULIN and reduction of SPASTIN levels. Furthermore, NMJs from HSP-derived lines were lower in number and in contact point complexity, denoting an impaired NMJ profile, also confirmed by some alterations in genes encoding for proteins associated with microtubules and responsible for axonal transport. Considering the complexity of HSP, these patient-derived neuronal and skeletal muscle cell co-cultures offer unique tools to study the pathologic mechanisms and explore novel treatment options for rescuing axonal defects and diverse cellular processes, including membrane trafficking, intracellular motility and protein degradation in HSP.

Pharmacological targeting of neuroinflammation in distinct models of genetically mediated disorders of the central nervous system (CNS) has been shown to attenuate disease outcome significantly. These include mouse models mimicking distinct subtypes of neuronal ceroid lipofuscinoses (NCL, CLN diseases) as well as hereditary spastic paraplegia type 2 (HSP/SPG2). We here show in a model of another, complicated HSP form (SPG11) that there is neuroinflammation in distinct compartments of the diseased CNS. Using a proof-of-principle experiment, we provide evidence that genetically targeting the adaptive immune system dampens disease progression including gait disturbance, demonstrating a pathogenic impact of neuroinflammation. Translating these studies into a clinically applicable approach, we show that the established immunomodulators fingolimod and teriflunomide significantly attenuate the neurodegenerative phenotype and improve gait performance in the SPG11 model, even when applied relatively late during disease progression. Particularly abnormalities in gait coordination, representing ataxia, could be attenuated, while features indicative of reduced strength during walking did not respond to treatment. Our study identifies neuroinflammation by the adaptive immune system as a robust and targetable disease amplifier in a mouse model of SPG11 and may thus pave the way for a translational approach in humans implicating approved immunomodulators., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Background: SPG11-linked hereditary spastic paraplegia is characterized by multisystem neurodegeneration leading to a complex clinical and yet incurable phenotype of progressive spasticity and weakness. Severe cognitive symptoms are present in the majority of SPG11 patients, but a systematic and multidimensional analysis of the neuropsychological phenotype in a larger cohort is lacking. While thinning of the corpus callosum is a well-known structural hallmark observed in SPG11 patients, the neuroanatomical pattern of cortical degeneration is less understood. We here aimed to integrate neuropsychological and brain morphometric measures in SPG11., Methods: We examined the neuropsychological profile in 16 SPG11 patients using a defined neuropsychological testing battery. Long-term follow up testing was performed in 7 patients. Cortical and subcortical degeneration was analyzed using an approved, artificial intelligence based magnetic resonance imaging brain morphometry, comparing patients to established reference values and to matched controls., Results: In SPG11 patients, verbal fluency and memory as well as frontal-executive functions were severely impaired. Later disease stages were associated with a global pattern of impairments. Interestingly, reaction times correlated significantly with disease progression. Brain morphometry showed a significant reduction of cortical and subcortical parenchymal volume following a rostro-caudal gradient in SPG11. Whereas performance in memory tasks correlated with white matter damage, verbal fluency measures showed strong associations with frontal and parietal cortical volumes., Conclusions: The present data will help define neuropsychological and imaging read out parameters in early as well as in advanced clinical stages for future interventional trials in SPG11., (© 2022. The Author(s).)

PNS and CNS myelin contain large amounts of galactocerebroside and sulfatide with 2-hydroxylated fatty acids. The underlying hydroxylation reaction is catalyzed by fatty acid 2-hydroxylase (FA2H). Deficiency in this enzyme causes a complicated hereditary spastic paraplegia, SPG35, which is associated with leukodystrophy. Mass spectrometry-based proteomics of purified myelin isolated from sciatic nerves of Fa2h-deficient (Fa2h -/- ) mice revealed an increase in the concentration of the three proteins Cadm4, Mpp6 (Pals2), and protein band 4.1G (Epb41l2) in 17-month-old, but not in young (4 to 6-month-old), Fa2h -/- mice. These proteins are known to form a complex, together with the protein Lin7, in Schmidt-Lanterman incisures (SLIs). Accordingly, the number of SLIs was significantly increased in 17-month-old but not 4-month-old Fa2h -/- mice compared to age-matched wild-type mice. On the other hand, the relative increase in the SLI frequency was less pronounced than expected from Cadm4, Lin7, Mpp6 (Pals2), and band 4.1G (Epb41l2) protein levels. This suggests that the latter not only reflect the higher SLI frequency but that the concentration of the Cadm4 containing complex itself is increased in the SLIs or compact myelin of Fa2h -/- mice and may potentially play a role in the pathogenesis of the disease. The proteome data are available via ProteomeXchange with identifier PXD030244., (© 2022. The Author(s).)

Hereditary spastic paraplegia (HSP) is a genetically and clinically heterogeneous genetic disease characterized by progressive weakness and spasticity predominantly affecting the lower limbs. Complex HSP is a subset of HSP presenting with additional neuronal and/or non-neuronal phenotypes. Here, we identify a homozygous ABHD16A nonsense variant in two affected children in a Chilean family. Very recently, two groups reported patients with biallelic ABHD16A whose clinical presentation was similar to that of our patients. By reviewing the clinical features of these reports and our patients, ABHD16A-related HSP can be characterized by early childhood onset, developmental delay, intellectual disability, speech disturbance, extrapyramidal signs, psychiatric features, no sphincter control, skeletal involvement, thin corpus callosum, and high-intensity signals in white matter on T2-weighted brain MRI. In addition, our affected siblings showed a characteristic face, sleep disturbance, and nodular and hyperpigmented skin lesions, which have not previously been reported in this condition., (© 2021 John Wiley & Sons A/S . Published by John Wiley & Sons Ltd.)

Introduction: Hereditary spastic paraplegias (HSPs) are uncommon but not rare neurodegenerative diseases. More than 100 pathogenic genes and loci related to spastic paraplegia symptoms have been reported. HSPs have the same core clinical features, including progressive spasticity in the lower limbs, though HSPs are heterogeneous (eg, clinical signs, MRI features, gene mutation). The age of onset varies greatly, from infant to adulthood. In addition, the slow and variable rates of disease progression in patients with HSP represent a substantial challenge for informative assessment of therapeutic efficacy. To address this, we are undertaking a prospective cohort study to investigate genetic-clinical characteristics, find surrogates for monitoring disease progress and identify clinical readouts for treatment., Methods and Analysis: In this case-control cohort study, we will enrol 200 patients with HSP and 200 healthy individuals in parallel. Participants will be continuously assessed for 3 years at 12-month intervals. Six aspects, including clinical signs, genetic spectrum, cognitive competence, MRI features, potential biochemical indicators and nerve electrophysiological factors, will be assessed in detail. This study will observe clinical manifestations and disease severity based on different molecular mechanisms, including oxidative stress, cholesterol metabolism and microtubule dynamics, all of which have been proposed as potential treatment targets or modalities. The analysis will also assess disease progression in different types of HSPs and cellular pathways with a longitudinal study using t tests and χ 2 tests., Ethics and Dissemination: The study was granted ethics committee approval by the first affiliated hospital of Fujian Medical University (MRCTA, ECFAH of FMU (2019)194) in 2019. Findings will be disseminated via presentations and peer-reviewed publications. Dissemination will target different audiences, including national stakeholders, researchers from different disciplines and the general public., Trial Registration Number: NCT04006418., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2022. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Hereditary spastic paraplegia (HSP) denotes genetically heterogeneous disorders characterized by leg spasticity due to degeneration of corticospinal axons. SPG11 and SPG15 have a similar clinical course and together are the most prevalent autosomal recessive HSP entity. The respective proteins play a role for macroautophagy/autophagy and autophagic lysosome reformation (ALR). Here, we report that spg11 and zfyve26 KO mice developed motor impairments within the same course of time. This correlated with enhanced accumulation of autofluorescent material in neurons and progressive neuron loss. In agreement with defective ALR, tubulation events were diminished in starved KO mouse embryonic fibroblasts (MEFs) and lysosomes decreased in neurons of KO brain sections. Confirming that both proteins act in the same molecular pathway, the pathologies were not aggravated upon simultaneous disruption of both. We further show that PI4K2A (phosphatidylinositol 4-kinase type 2 alpha), which phosphorylates phosphatidylinositol to phosphatidylinositol-4-phosphate (PtdIns4P), accumulated in autofluorescent deposits isolated from KO but not WT brains. Elevated PI4K2A abundance was already found at autolysosomes of neurons of presymptomatic KO mice. Immunolabelings further suggested higher levels of PtdIns4P at LAMP1-positive structures in starved KO MEFs. An increased association with LAMP1-positive structures was also observed for clathrin and DNM2/dynamin 2, which are important effectors of ALR recruited by phospholipids. Because PI4K2A overexpression impaired ALR, while its knockdown increased tubulation, we conclude that PI4K2A modulates phosphoinositide levels at autolysosomes and thus the recruitment of downstream effectors of ALR. Therefore, PI4K2A may play an important role in the pathogenesis of SPG11 and SPG15. Abbreviations : ALR: autophagic lysosome reformation; AP-5: adaptor protein complex 5; BFP: blue fluorescent protein; dKO: double knockout; EBSS: Earle's balanced salt solution; FBA: foot base angle; GFP: green fluorescent protein; HSP: hereditary spastic paraplegia; KO: knockout; LAMP1: lysosomal-associated membrane protein 1; MAP1LC3B/LC3: microtubule-associated protein 1 light chain 3 beta; MEF: mouse embryonic fibroblast; SQSTM1/p62: sequestosome 1; PI4K2A: phosphatidylinositol 4-kinase type 2 alpha; PtdIns3P: phosphatidylinositol-3-phosphate; PtdIns4P: phosphatidylinositol-4-phosphate; RFP: red fluorescent protein; SPG: spastic paraplegia gene; TGN: trans-Golgi network; WT: wild type.

The endoplasmic reticulum (ER) is the most abundant and widespread organelle in cells. Its peculiar membrane architecture, formed by an intricate network of tubules and cisternae, is critical to its multifaceted function. Regulation of ER morphology is coordinated by a few ER-specific membrane proteins and is thought to be particularly important in neurons, where organized ER membranes are found even in the most distant neurite terminals. Mutation of ER-shaping proteins has been implicated in the neurodegenerative disease hereditary spastic paraplegia (HSP). In this review we discuss the involvement of these proteins in the pathogenesis of HSP, focusing on the experimental evidence linking their molecular function to disease onset. Although the precise biochemical activity of some ER-related HSP proteins has been elucidated, the pathological mechanism underlying ER-linked HSP is still undetermined and needs to be further investigated.

ABHD16A (abhydrolase domain-containing protein 16A, phospholipase) encodes the major phosphatidylserine (PS) lipase in the brain. PS lipase synthesizes lysophosphatidylserine, an important signaling lipid that functions in the mammalian central nervous system. ABHD16A has not yet been associated with a human disease. In this report, we present a cohort of 11 affected individuals from six unrelated families with a complicated form of hereditary spastic paraplegia (HSP) who carry bi-allelic deleterious variants in ABHD16A. Affected individuals present with a similar phenotype consisting of global developmental delay/intellectual disability, progressive spasticity affecting the upper and lower limbs, and corpus callosum and white matter anomalies. Immunoblot analysis on extracts from fibroblasts from four affected individuals demonstrated little to no ABHD16A protein levels compared to controls. Our findings add ABHD16A to the growing list of lipid genes in which dysregulation can cause complicated forms of HSP and begin to describe the molecular etiology of this condition., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.)

In recent years, the tropomyosin-receptor kinase fused gene (TFG) has been linked to diverse hereditary neurodegenerative disorders, including a very rare complex hereditary spastic paraplegia, named spastic paraplegia type 57 (SPG57). Until now, four pathogenic homozygous variants of the TFG gene have been reported associated with SPG57. Two consanguineous Iranian families (1 and 2), the first one with two affected members and the second one with one, all with an early-onset progressive muscle weakness, spasticity, and several neurological symptoms were examined via the whole-exome sequencing. Two homozygous missense variants including c.41A>G (p.Lys14Arg) and c.316C>T (p.Arg106Cys) have been found in the related families. The candidate variants were confirmed by Sanger sequencing and found to co-segregate with the disease in families. The bioinformatics analysis showed the deleterious effects of these nucleotide changes and the variants were classified as pathogenic according to ACMG guidelines. A comparison of the clinical presentation of the patients harboring c.41A>G (p.Lys14Arg) with previously reported SPG57 revealed variability in the severity state and unreported clinical presentation, including, facial atrophy, nystagmus, hyperelastic skin, cryptorchidism, hirsutism, kyphoscoliosis, and pectus excavatum. The affected member of the second family carried a previously reported homozygous c.316C>T (p.Arg106Cys) variant and displayed a complex HSP including optic atrophy. Remarkable clinical differences were observed between the family 1 and 2 harboring the c.41A>G (p.Lys14Arg) and c.316C>T (p.Arg106Cys) variants, which could be attributed to the distinct affected domains (PB1 domains and coiled-coil domains), and therefore, SPG57 might have been representing phenotype vs. variant position correlation., (© 2021. The Author(s), under exclusive licence to The Japan Society of Human Genetics.)

Spastic paraplegias (SPGs) are a group of clinically and genetically heterogeneous neurodegenerative diseases. Mutations in 78 genes have been identified in autosomal dominant hereditary SPG (AD-HSP) and autosomal recessive hereditary SPG (AR-HSP). Compared to familial HSP, much less is known about the genetic and clinical profiles of sporadic SPGs. In this study, we have screened mutations for 18 sporadic SPGs or AR-HSP patients (mainly Northern Chinese) by whole-exome sequencing. We identified 12 mutations in five genes in 9 (50%) patients, including 9 novel ones: SPG5A/CYP7B1 (c.851C > A; c.122 + 2 T > G), SPG11/KIAA1840 (c.1735 + 3&#95; 1735 + 6del AAGT); SPG7/SPG7 (c.1454G > A; c.1892&#95; 1906dup GAGGACGGGCCTCGG); SPG39/PNPLA6 (c.1591G > A; c. 2990C > T); SPG15/ ZFYVE26 (c. 4804C > T; c. 4278 G > A). Among all the mutations, 7 were detected in the SPG5A and SPG11. Age at onset was significantly younger in cases with mutations (15.45 ± 6.78 years) than those without mutations (25.56 ± 10.90 years) (P = 0.03). Except for two cases with the SPG5A mutations, all cases presented with complicated SPGs. Three cases carrying mutations in SPG7, SPG15, SPG39 showed symptoms and signs of ataxia. One case carrying the homozygous c.259 + 2 T > C mutation in CYP7B1 showed serum parameters indicating liver impairment. Magnetic resonance imaging showed significantly thinned corpus callosum in cases with SPG11 and SPG15, but not in those with SPG5A, SPG7 or SPG39. In contrast, cerebellar atrophy was prominent in the SPG7 and SPG39 cases. These findings expand the spectrum of genetic, clinical and imaging features of sporadic SPG and AR-HSP, and have important implications in genetic counselling, molecular mechanisms and precise diagnosis of the disease., (Copyright © 2021 Elsevier B.V. All rights reserved.)

A central need for neurodegenerative diseases is to find curative drugs for the many clinical subtypes, the causative gene for most cases being unknown. This requires the classification of disease cases at the genetic and cellular level, an understanding of disease aetiology in the subtypes and the development of phenotypic assays for high throughput screening of large compound libraries. Herein we describe a method that facilitates these requirements based on cell morphology that is being increasingly used as a readout defining cell state. In patient-derived fibroblasts we quantified 124 morphological features in 100,000 cells from 15 people with two genotypes (SPAST and SPG7) of Hereditary Spastic Paraplegia (HSP) and matched controls. Using machine learning analysis, we distinguished between each genotype and separated them from controls. Cell morphologies changed with treatment with noscapine, a tubulin-binding drug, in a genotype-dependent manner, revealing a novel effect on one of the genotypes (SPG7). These findings demonstrate a method for morphological profiling in fibroblasts, an accessible non-neural cell, to classify and distinguish between clinical subtypes of neurodegenerative diseases, for drug discovery, and potentially for biomarkers of disease severity and progression., (© 2021. The Author(s).)

Hereditary spastic paraplegia (HSP) refers to a group of neurological disorders involving the degeneration of motor neurons. Due to their clinical and genetic heterogeneity, finding common effective therapeutics is difficult. Therefore, a better understanding of the common pathological mechanisms is necessary. The role of several HSP genes/proteins is linked to the endolysosomal and autophagic pathways, suggesting a functional convergence. Furthermore, impairment of these pathways is particularly interesting since it has been linked to other neurodegenerative diseases, which would suggest that the nervous system is particularly sensitive to the disruption of the endolysosomal and autophagic systems. In this review, we will summarize the involvement of HSP proteins in the endolysosomal and autophagic pathways in order to clarify their functioning and decipher some of the pathological mechanisms leading to HSP.

Hereditary spastic paraplegias (HSPs) are clinically and genetically heterogeneous neurodegenerative disorders characterized by progressive weakness and spasticity in the lower limbs due to pyramidal tract dysfunction. REEP2 mutations have been identified as a cause of "pure" HSP, SPG72, with both autosomal dominant and autosomal recessive inheritance. We describe a rare Nepalese family with early-onset pure-type HSP harboring a heterozygous REEP2 missense mutation (c.119T>G, p.Met40Arg). This is only the second SPG72 family with autosomal dominant inheritance. The proband presented slow and spastic gait at age 2 years and the symptoms progressed slowly. The proband's father and uncle presented even milder symptoms of pure spastic paraplegia. Our study may provide an opportunity to further study the genotype-phenotype correlation of SPG72.

Objective: Hereditary spastic paraplegias (HSP) is a clinically and genetically heterogeneous group of neurodegenerative disorders. We describe the genetic and clinical features of a cohort of five HSP families from central-southern China., Methods: Using targeted exome-sequencing technology, we investigated the genetic and clinical features in five HSP families. We reviewed the clinical histories of these patients as well as the molecular and functional characterization of the associated gene variants. We also performed functional analysis of an intron variant of SPAST in vitro., Results: We identified a known SPAST mutation (p.Pro435Leu) in a family with autosomal dominant HSP (AD-HSP) and four novel variants in two HSP families and a sporadic case. These identified four novel variants included a variant in SPG11 (p.Val1979Ter), two variants in B4GALNT1 (p.Ser475Phe and c.1002 + 2 T > G), and a splicing site variant in SPAST (c.1245+5G>A). Minigene analysis of the splicing variant in SPAST (c.1245+5G>A) revealed that the mutation resulted in mRNAs with a loss of exon 9. The SPG4 family carrying c.1245+5G>A variant in SPAST exhibited genetic anticipation, with a decreased age at onset and increased severity in successive generations. The proband with p.Val1979Ter variant in SPG11 showed characteristic clinical features of early-onset, severe spasticity, and corpus callosum atrophy which were highly suggestive of the diagnosis of SPG11-associated HSP., Conclusions: Our findings strongly support variable phenotype of B4GALNT1-related SPG26 and also expand the clinical and mutation spectrum of HSP caused by mutations in SPAST, SPG11, and B4GALNT1. These results will help to improve the efficiency of early diagnosis in patients clinically suspected of HSP., (© 2021 The Authors. Molecular Genetics & Genomic Medicine published by Wiley Periodicals LLC.)

Purpose: Pseudoxanthoma elasticum (PXE) is a recessive disorder involving skin, eyes and arteries, mainly caused by ABCC6 pathogenic variants. However, almost one fifth of patients remain genetically unsolved despite extensive genetic screening of ABCC6, as illustrated in a large French PXE series of 220 cases. We searched for new PXE gene(s) to solve the ABCC6-negative patients., Methods: First, family-based exome sequencing was performed, in one ABCC6-negative PXE patient with additional neurological features, and her relatives. CYP2U1, involved in hereditary spastic paraplegia type 56 (SPG56), was selected based on this complex phenotype, and the presence of two candidate variants. Second, CYP2U1 sequencing was performed in a retrospective series of 46 additional ABCC6-negative PXE probands. Third, six additional SPG56 patients were evaluated for PXE skin and eye phenotype. Additionally, plasma pyrophosphate dosage and functional analyses were performed in some of these patients., Results: 6.4% of ABCC6-negative PXE patients (n = 3) harboured biallelic pathogenic variants in CYP2U1. PXE skin lesions with histological confirmation, eye lesions including maculopathy or angioid streaks, and various neurological symptoms were present. CYP2U1 missense variants were confirmed to impair protein function. Plasma pyrophosphate levels were normal. Two SPG56 patients (33%) presented some phenotypic overlap with PXE., Conclusion: CYP2U1 pathogenic variants are found in unsolved PXE patients with neurological findings, including spastic paraplegia, expanding the SPG56 phenotype and highlighting its overlap with PXE. The pathophysiology of ABCC6 and CYP2U1 should be explored to explain their respective role and potential interaction in ectopic mineralization., (© 2020 The Association for the Publication of the Journal of Internal Medicine.)

Background and Purpose: Spinal cord damage is a hallmark of hereditary spastic paraplegias, but it is still not clear whether specific subtypes of the disease have distinctive patterns of spinal cord gray (GM) and white (WM) matter involvement. We compared cervical cross-sectional GM and WM areas in patients with distinct hereditary spastic paraplegia subtypes. We also assessed whether these metrics correlated with clinical parameters., Materials and Methods: We analyzed 37 patients (17 men; mean age, 47.3 [SD, 16.5] years) and 21 healthy controls (7 men; mean age, 42.3 [SD, 13.2] years). There were 7 patients with spastic paraplegia type 3A (SPG3A), 12 with SPG4, 10 with SPG7, and 8 with SPG11. Image acquisition was performed on a 3T MR imaging scanner, and T2*-weighted 2D images were assessed by the Spinal Cord Toolbox. Statistical analyses were performed in SPSS using nonparametric tests and false discovery rate-corrected P values < .05., Results: The mean disease duration for the hereditary spastic paraplegia group was 22.4 [SD, 13.8] years and the mean Spastic Paraplegia Rating Scale score was 22.8 [SD, 11.0]. We failed to identify spinal cord atrophy in SPG3A and SPG7. In contrast, we found abnormalities in patients with SPG4 and SPG11. Both subtypes had spinal cord GM and WM atrophy. SPG4 showed a strong inverse correlation between GM area and disease duration (ρ = -0.903, P  < .001)., Conclusions: Cervical spinal cord atrophy is found in some but not all hereditary spastic paraplegia subtypes. Spinal cord damage in SPG4 and 11 involves both GM and WM., (© 2021 by American Journal of Neuroradiology.)

Hereditary spastic paraplegia type 11 (SPG11) is the most common subtype of autosomal recessive hereditary spastic paraplegia (HSP), to date, there are more than 181 different KIAA1840 gene mutations detected, and yet the genetic landscape of SPG11 is far from complete. To find the clinical and genetic characteristics of SPG11, we performed a reanalysis of the clinical features and genotype-phenotype correlations in all reported studies exhibiting SPG11 mutations. A total of 339 patients were collected, their mean age at onset was 13.10 ± 3.65 years, with initial symptoms like gait disturbance (107/195, 54.87%) and mental retardation (47/195, 24.10%). Cognitive decline (228/270, 84.44%) was the most common complex manifestation stepped by dysarthria (134/195, 68.72%), neuropathy (112/177, 63.28%), amyatrophy, sphincter disturbance (60/130, 46.15%) and ataxia (90/194, 46.39%). The most common brain MRI abnormality is thinning of the corpus callosum (TCC) (173/190, 91.05%), followed by periventricular white matter changes (130/158, 82.28%), cerebral or cerebellar cortical atrophy (55/107, 51.40%). The mutational spectrum associated with KIAA1840 gene is wide, and frameshift mutations are the most common type followed by nonsense mutations. Our reanalysis demonstrated that SPG11 exhibited significant clinical and genetic heterogeneity, and no clear genotype-phenotype correlation was observed. There is no mutational hot spot in the KIAA1840 gene, which emphasizes the need to analyse the whole gene in clinical practice. In addition to conventional genetic testing methods, further mRNA analysis should be conducted on some cases to yield a definitive diagnosis., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)