Clinical and genetic spectra of 1550 index patients with hereditary spastic paraplegia

Presynaptic perspective: Axonal transport defects in neurodevelopmental disorders

Disruption of synapse assembly and maturation leads to a broad spectrum of neurodevelopmental disorders. Presynaptic proteins are largely synthesized in the soma, where they are packaged into precursor vesicles and transported into distal axons to ensure precise assembly and maintenance of presynapses. Due to their morphological features, neurons face challenges in the delivery of presynaptic cargos to nascent boutons. Thus, targeted axonal transport is vital to build functional synapses. A growing number of mutations in genes encoding the transport machinery have been linked to neurodevelopmental disorders. Emerging lines of evidence have started to uncover presynaptic mechanisms underlying axonal transport defects, thus broadening the view of neurodevelopmental disorders beyond postsynaptic mechanisms. In this review, we discuss presynaptic perspectives of neurodevelopmental disorders by focusing on impaired axonal transport and disturbed assembly and maintenance of presynapses. We also discuss potential strategies for restoring axonal transport as an early therapeutic intervention.

Identification of novel variations in three cases with rare inherited neuromuscular disorder

Inherited neuromuscular disorder (IND) is a broad-spectrum, clinically diverse group of diseases that are caused due to defects in the neurosystem, muscles and related tissue. Since IND may originate from mutations in hundreds of different genes, the resulting heterogeneity of IND is a great challenge for accurate diagnosis and subsequent management. Three pediatric cases with IND were enrolled in the present study and subjected to a thorough clinical examination. Next, a genetic investigation was conducted using whole-exome sequencing (WES). The suspected variants were validated through Sanger sequencing or quantitative fluorescence PCR assay. A new missense variant of the Spastin (SPAST) gene was found and analyzed at the structural level using molecular dynamics (MD) simulations. All three cases presented with respective specific clinical manifestations, which reflected the diversity of IND. WES detected the diagnostic variants in all 3 cases: A compound variation comprising collagen type VI α3 chain (COL6A3) (NM_004369; exon19):c.6322G>T(p.E1208*) and a one-copy loss of COL6A3:exon19 in Case 1, which are being reported for the first time; a de novo SPAST (NM_014946; exon8):c.1166C>A(p.T389K) variant in Case 2; and a de novo Duchenne muscular dystrophy (NM_004006; exon11):c.1150-17_1160delACTTCCTTCTTTGTCAGGGGTACATGATinsC variant in Case 3. The structural and MD analyses revealed that the detected novel SPAST: c.1166C>A(p.T389K) variant mainly altered the intramolecular hydrogen bonding status and the protein segment's secondary structure. In conclusion, the present study expanded the IND mutation spectrum. The study not only detailed the precise diagnoses of these cases but also furnished substantial grounds for informed consultations. The approach involving the genetic evaluation strategy using WES for variation screening followed by validation using appropriate methods is beneficial due to the considerable heterogeneity of IND.

The Role of Structural Variants in the Genetic Architecture of Parkinson's Disease

Parkinson's disease (PD) significantly impacts millions of individuals worldwide. Although our understanding of the genetic foundations of PD has advanced, a substantial portion of the genetic variation contributing to disease risk remains unknown. Current PD genetic studies have primarily focused on one form of genetic variation, single nucleotide variants (SNVs), while other important forms of genetic variation, such as structural variants (SVs), are mostly ignored due to the complexity of detecting these variants with traditional sequencing methods. Yet, these forms of genetic variation play crucial roles in gene expression and regulation in the human brain and are causative of numerous neurological disorders, including forms of PD. This review aims to provide a comprehensive overview of our current understanding of the involvement of coding and noncoding SVs in the genetic architecture of PD.

Relationship between brain white matter damage and grey matter atrophy in hereditary spastic paraplegia types 4 and 5

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.

Whole exome sequencing in Serbian patients with hereditary spastic paraplegia

Hereditary spastic paraplegia (HSP) is a group of neurodegenerative diseases with a high genetic and clinical heterogeneity. Numerous HSP patients remain genetically undiagnosed despite screening for known genetic causes of HSP. Therefore, identification of novel variants and genes is needed. Our previous study analyzed 74 adult Serbian HSP patients from 65 families using panel of the 13 most common HSP genes in combination with a copy number variation analysis. Conclusive genetic findings were established in 23 patients from 19 families (29%). In the present study, nine patients from nine families previously negative on the HSP gene panel were selected for the whole exome sequencing (WES). Further, 44 newly diagnosed adult HSP patients from 44 families were sent to WES directly, since many studies showed WES may be used as the first step in HSP diagnosis. WES analysis of cohort 1 revealed a likely genetic cause in five (56%) of nine HSP families, including variants in the ETHE1, ZFYVE26, RNF170, CAPN1, and WASHC5 genes. In cohort 2, possible causative variants were found in seven (16%) of 44 patients (later updated to 27% when other diagnosis were excluded), comprising six different genes: SPAST, SPG11, WASCH5, KIF1A, KIF5A, and ABCD1. These results expand the genetic spectrum of HSP patients in Serbia and the region with implications for molecular genetic diagnosis and future causative therapies. Wide HSP panel can be the first step in diagnosis, alongside with the copy number variation (CNV) analysis, while WES should be performed after.

A Retrospective Review of 18 Patients With Childhood-Onset Hereditary Spastic Paraplegia, Nine With Novel Variants

BACKGROUND

Hereditary spastic paraplegias (HSPs) are a group of genetically heterogeneous neurodegenerative disorders. Our objective was to determine the clinical and molecular characteristics of patients with genetically confirmed childhood-onset HSPs and to expand the genetic spectrum for some rare subtypes of HSP.

METHODS

We reviewed the charts of subjects with genetically confirmed childhood-onset HSP. The age at the disease onset was defined as the point at which the delayed motor milestones were observed. Delayed motor milestones were defined as being unable to hold the head up by four months, sitting unassisted by nine months, and walking independently by 17 months. If there were no delayed motor milestones, age at disease onset was determined by leg stiffness, frequent falls, or unsteady gait. Genetic testing was performed based on delayed motor milestones, progressive leg spasticity, and gait difficulty. The variant classification was determined based on the American College of Medical Genetics standard guidelines for variant interpretation. Variants of uncertain significance (VUS) were considered disease-associated when clinical findings were consistent with the previously described disease phenotypes for pathogenic variants. In addition, in the absence of another pathogenic, likely pathogenic, or VUS variant that could explain the phenotype of our cases, we concluded that the disease is associated with VUS in the HSP-causing gene. Segregation analysis was also performed on the parents of some patients to demonstrate the inheritance model.

RESULTS

There were a total of 18 patients from 17 families. The median age of symptom onset was 18 months (2 to 84 months). The mean delay between symptom onset and genetic diagnosis was 5.8 years (5 months to 17 years). All patients had gait difficulty caused by progressive leg spasticity and weakness. Independent walking was not achieved at 17 months for 67% of patients (n = 12). In our cohort, there were two subjects each with SPG11, SPG46, and SPG 50 followed by single subject each with SPG3A, SPG4, SPG7, SPG8, SPG30, SPG35, SPG43, SPG44, SPG57, SPG62, infantile-onset ascending spastic paralysis (IAHSP), and spastic paraplegia and psychomotor retardation with or without seizures (SPPRS). Eight novel variants in nine patients were described. Two affected siblings had a novel variant in the GBA2 gene (SPG46), and one subject each had a novel variant in WASHC5 (SPG8), SPG11 (SPG11), KIF1A (SPG30), GJC2 (SPG44), ERLIN1 (SPG62), ALS2 (IAHSP), and HACE1 (SPPRS). Among the novel variants, the variant in the SPG11 was pathogenic and the variants in the KIF1A, GJC2, and HACE1 were likely pathogenic. The variants in the GBA2, ALS2, ERLIN1, and WASHC5 were classified as VUS.

CONCLUSIONS

There was a significant delay between symptom onset and genetic diagnosis of HSP. An early diagnosis may be possible by examining patients with delayed motor milestones, progressive spasticity, gait difficulties, and neuromuscular weakness in the context of HSP. Eight novel variants in nine patients were described, clinically similar to the previously described disease phenotype associated with pathogenic variants. This study contributes to expanding the genetic spectrum of some rare subtypes of HSP.

Familial motor neuron disease: co-occurrence of PLS and ALS (-FTD)

OBJECTIVE

To report the frequency and characteristics of patients diagnosed with primary lateral sclerosis (PLS) with a positive family history for motor neuron diseases (MND) in the Netherlands and to compare our findings to the literature.

METHODS

Patients were identified through our ongoing, prospective population-based study on MND in The Netherlands, which also includes a standardized collection of patient characteristics, genetic testing, and family history. Only patients meeting the latest consensus criteria for definite PLS were included. The family history was considered positive for MND if any family members had been diagnosed with PLS, amyotrophic lateral sclerosis (ALS)(-FTD), or progressive muscular atrophy (PMA). Additionally, the literature was reviewed on PLS cases in which MND co-occurred within the same family.

RESULTS

We identified 392 definite PLS cases, resulting in 9 families with a PLS patient and a positive family history for MND (2.3%). In only one of these pedigrees, a pathogenic variant (C9orf72 repeat expansion) was found. Our literature review revealed 23 families with a co-occurrence of PLS and MND, with 12 of them having a potentially pathogenic genetic variant.

CONCLUSIONS

The consistent observation of PLS patients with a positive family history for MND, evident in both our study and the literature, implies the presence of shared underlying genetic factors between PLS and ALS. However, these factors are yet to be elucidated.

Primary Lateral Sclerosis: An Overview

Primary lateral sclerosis (PLS) is a rare neurodegenerative disorder which causes the selective deterioration of the upper motor neurons (UMNs), sparing the lower motor neuron (LMN) system. The clinical course is defined by a progressive motor disability due to muscle spasticity which typically involves lower extremities and bulbar muscles. Although classically considered a sporadic disease, some familiar cases and possible causative genes have been reported. Despite it having been recognized as a rare but distinct entity, whether it actually represents an extreme end of the motor neuron diseases continuum is still an open issue. The main knowledge gap is the lack of specific biomarkers to improve the clinical diagnostic accuracy. Indeed, the diagnostic imprecision, together with some uncertainty about overlap with UMN-predominant ALS and Hereditary Spastic Paraplegia (HSP), has become an obstacle to the development of specific therapeutic trials. In this study, we provided a comprehensive analysis of the existing literature, including neuropathological, clinical, neuroimaging, and neurophysiological features of the disease, and highlighting the controversies still unsolved in the differential diagnoses and the current diagnostic criteria. We also discussed the current knowledge gaps still present in both diagnostic and therapeutic fields when approaching this rare condition.

Biallelic COQ4 Variants in Hereditary Spastic Paraplegia: Clinical and Molecular Characterization

BACKGROUND

Hereditary spastic paraplegias (HSP) are neurologic disorders characterized by progressive lower-extremity spasticity. Despite the identification of several HSP-related genes, many patients lack a genetic diagnosis.

OBJECTIVES

The aims were to confirm the pathogenic role of biallelic COQ4 mutations in HSP and elucidate the clinical, genetic, and functional molecular features of COQ4-associated HSP.

METHODS

Whole exome sequences of 310 index patients with HSP of unknown cause from three distinct populations were analyzed to identify potential HSP causal genes. Clinical data obtained from patients harboring candidate causal mutations were examined. Functional characterization of COQ4 variants was performed using bioinformatic tools, single-cell RNA sequencing, biochemical assays in cell lines, primary fibroblasts, induced pluripotent stem cell-derived pyramidal neurons, and zebrafish.

RESULTS

Compound heterozygous variants in COQ4, which cosegregated with HSP in pedigrees, were identified in 7 patients from six unrelated families. Patients from four of the six families presented with pure HSP, whereas probands of the other two families exhibited complicated HSP with epilepsy or with cerebellar ataxia. In patient-derived fibroblasts and COQ4 knockout complementation lines, stable expression of these missense variants exerted loss-of-function effects, including mitochondrial reactive oxygen species accumulation, decreased mitochondrial membrane potential, and lower ubiquinone biosynthesis. Whereas differentiated pyramidal neurons expressed high COQ4 levels, coq4 knockdown zebrafish displayed severe motor dysfunction, reflecting motor neuron dysregulation.

CONCLUSIONS

Our study confirms that loss-of-function, compound heterozygous, pathogenic COQ4 variants are causal for autosomal recessive pure and complicated HSP. Moreover, reduced COQ4 levels attributable to variants correspond with decreased ubiquinone biosynthesis, impaired mitochondrial function, and higher phenotypic disease severity. © 2023 International Parkinson and Movement Disorder Society.

A Young Woman With Hypertonia, Severe Scoliosis, and Encephalopathy

A 31-year-old woman was seen with contractures in her fingers and toes, carpal inversion, dysarthria, dysphagia, hypertonia, decreased tendon reflexes, absence of Babinski sign, and no psychiatric problems and significant global atrophy. What is your diagnosis?

Pharmacological rescue of mitochondrial and neuronal defects in SPG7 hereditary spastic paraplegia patient neurons using high throughput assays

SPG7 is the most common form of autosomal recessive hereditary spastic paraplegia (HSP). There is a lack of HSP-SPG7 human neuronal models to understand the disease mechanism and identify new drug treatments. We generated a human neuronal model of HSP-SPG7 using induced pluripotent stem (iPS) cell technology. We first generated iPS cells from three HSP-SPG7 patients carrying different disease-causing variants and three healthy controls. The iPS cells were differentiated to form neural progenitor cells (NPCs) and then from NPCs to mature cortical neurons. Mitochondrial and neuronal defects were measured using a high throughout imaging and analysis-based assay in live cells. Our results show that compared to control NPCs, patient NPCs had aberrant mitochondrial morphology with increased mitochondrial size and reduced membrane potential. Patient NPCs develop to form mature cortical neurons with amplified mitochondrial morphology and functional defects along with defects in neuron morphology - reduced neurite complexity and length, reduced synaptic gene, protein expression and activity, reduced viability and increased axonal degeneration. Treatment of patient neurons with Bz-423, a mitochondria permeability pore regulator, restored the mitochondrial and neurite morphological defects and mitochondrial membrane potential back to control neuron levels and rescued the low viability and increased degeneration in patient neurons. This study establishes a direct link between mitochondrial and neuronal defects in HSP-SPG7 patient neurons. We present a strategy for testing mitochondrial targeting drugs to rescue neuronal defects in HSP-SPG7 patient neurons.

Outcome Measures and Biomarkers for Clinical Trials in Hereditary Spastic Paraplegia: A Scoping Review

Hereditary spastic paraplegia (HSP) is characterized by progressive lower limb spasticity. There is no disease-modifying treatment currently available. Therefore, standardized, validated outcome measures to facilitate clinical trials are urgently needed. We performed a scoping review of outcome measures and biomarkers for HSP to provide recommendations for future studies and identify areas for further research. We searched Embase, Medline, Scopus, Web of Science, and the Central Cochrane database. Seventy studies met the inclusion criteria, and eighty-three outcome measures were identified. The Spastic Paraplegia Rating Scale (SPRS) was the most widely used (27 studies), followed by the modified Ashworth Scale (18 studies) and magnetic resonance imaging (17 studies). Patient-reported outcome measures (PROMs) were infrequently used to assess treatment outcomes (28% of interventional studies). Diffusion tensor imaging, gait analysis and neurofilament light chain levels were the most promising biomarkers in terms of being able to differentiate patients from controls and correlate with clinical disease severity. Overall, we found variability and inconsistencies in use of outcome measures with a paucity of longitudinal data. We highlight the need for (1) a standardized set of core outcome measures, (2) validation of existing biomarkers, and (3) inclusion of PROMs in HSP clinical trials.

Individual perception of environmental factors that influence lower limbs spasticity in inherited spastic paraparesis

BACKGROUND

Phenotypic variability is a consistent finding in neurogenetics and therefore applicable to hereditary spastic paraparesis. Identifying reasons for this variability is a challenge. We hypothesized that, in addition to genetic modifiers, extrinsic factors influence variability.

OBJECTIVES

Our aim was to describe the clinical variability in hereditary spastic paraparesis from the person's perspective. Our goals were to identify individual and environmental factors that influence muscle tone disorders and derive interventions which could improve spasticity.

METHODS

This study was based on self-assessments with questions on nominal and ordinal scales completed by participants with hereditary spastic paraparesis. A questionnaire was completed either in-person in the clinic or electronically via lay organization websites.

RESULTS

Among the 325 responders, most had SPG4/SPAST (n = 182, 56%) with a mean age at onset of 31.7 (SD 16.7) years and a mean disease duration of 23 (SD 13.6) years at the time of participation. The 2 factors identified as improving spasticity for > 50% of the responders were physiotherapy (193/325, 59%), and superficial warming (172/308, 55%). Half of the responders (n = 164, 50%) performed physical activity at least once a month and up to once a week. Participants who reported physiotherapy as effective were significantly more satisfied with ≥ 3 sessions per week. Psychologically stressful situations (246/319, 77%) and cold temperatures (202/319, 63%) exacerbated spasticity for most participants.

CONCLUSION

Participants perceived that physiotherapy reduced spasticity and that the impact of physiotherapy on spasticity was much greater than other medical interventions. Therefore, people should be encouraged to practice physical activity at least 3 times per week. This study reported participants' opinions: in hereditary spastic paraparesis only functional treatments exist, therefore the participant's expertise is of particular importance.

Biallelic DDHD2 mutations in patients with adult-onset complex hereditary spastic paraplegia

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.

Valosin containing protein (VCP): initiator, modifier, and potential drug target for neurodegenerative diseases

The AAA+ ATPase valosin containing protein (VCP) is essential for cell and organ homeostasis, especially in cells of the nervous system. As part of a large network, VCP collaborates with many cofactors to ensure proteostasis under normal, stress, and disease conditions. A large number of mutations have revealed the importance of VCP for human health. In particular, VCP facilitates the dismantling of protein aggregates and the removal of dysfunctional organelles. These are critical events to prevent malfunction of the brain and other parts of the nervous system. In line with this idea, VCP mutants are linked to the onset and progression of neurodegeneration and other diseases. The intricate molecular mechanisms that connect VCP mutations to distinct brain pathologies continue to be uncovered. Emerging evidence supports the model that VCP controls cellular functions on multiple levels and in a cell type specific fashion. Accordingly, VCP mutants derail cellular homeostasis through several mechanisms that can instigate disease. Our review focuses on the association between VCP malfunction and neurodegeneration. We discuss the latest insights in the field, emphasize open questions, and speculate on the potential of VCP as a drug target for some of the most devastating forms of neurodegeneration.

Power of NGS-based tests in HSP diagnosis: analysis of massively parallel sequencing in clinical practice

Hereditary spastic paraplegia (HSP) refers to a group of heterogeneous neurological disorders mainly characterized by corticospinal degeneration (pure forms), but sometimes associated with additional neurological and extrapyramidal features (complex HSP). The advent of next-generation sequencing (NGS) has led to huge improvements in knowledge of HSP genetics and made it possible to clarify the genetic etiology of hundreds of "cold cases," accelerating the process of reaching a molecular diagnosis. The different NGS-based strategies currently employed as first-tier approaches most commonly involve the use of targeted resequencing panels and exome sequencing, whereas genome sequencing remains a second-tier approach because of its high costs. The question of which approach is the best is still widely debated, and many factors affect the choice. Here, we aim to analyze the diagnostic power of different NGS techniques applied in HSP, by reviewing 38 selected studies in which different strategies were applied in different-sized cohorts of patients with genetically uncharacterized HSP.

Upregulation of Heat-Shock Protein (hsp)-27 in a Patient with Heterozygous SPG11 c.1951C>T and SYNJ1 c.2614G>T Mutations Causing Clinical Spastic Paraplegia

We report a 49-year-old patient suffering from spastic paraplegia with a novel heterozygous mutation and analyzed the levels of heat shock proteins (hsp)-27, dopamine (DA), and its metabolites in their cerebrospinal fluid (CSF). The hsp27 protein concentration in the patient's CSF was assayed by an ELISA kit, while DA levels and its metabolites in the CSF, 3,4-dihydroxyphenylacetic acid (DOPAC), Cys-DA, and Cys-DOPA were measured by HPLC. Whole exome sequencing demonstrated SPG-11 c.1951C>T and novel SYNJ1 c.2614G>T mutations, both heterozygous recessive. The patient's DA and DOPAC levels in their CSF were significantly decreased (53.0 ± 6.92 and 473.3 ± 72.19, p < 0.05, respectively) while no differences were found in their Cys-DA. Nonetheless, Cys-DA/DOPAC ratio (0.213 ± 0.024, p < 0.05) and hsp27 levels (1073.0 ± 136.4, p < 0.05) were significantly higher. To the best of our knowledge, the c.2614G>T SYNJ1 mutation has not been previously reported. Our patient does not produce fully functional spatacsin and synaptojanin-1 proteins. In this line, our results showed decreased DA and DOPAC levels in the patient's CSF, indicating loss of DAergic neurons. Many factors have been described as being responsible for the increased cys-DA/DOPAC ratio, such as MAO inhibition and decreased antioxidant activity in DAergic neurons which would increase catecholquinones and consequently cysteinyl-catechols. In conclusion, haploinsufficiency of spatacsin and synaptojanin-1 proteins might be the underlying cause of neurodegeneration produced by protein trafficking defects, DA vesicle trafficking/recycling processes, autophagy dysfunction, and cell death leading to hsp27 upregulation as a cellular mechanism of protection and/or to balance impaired protein trafficking.

Spastin is required for human immunodeficiency virus-1 efficient replication through cooperation with the endosomal sorting complex required for transport (ESCRT) protein

Human immunodeficiency virus-1 (HIV-1) encodes simply 15 proteins and thus depends on multiple host cellular factors for virus reproduction. Spastin, a microtubule severing protein, is an identified HIV-1 dependency factor, but the mechanism regulating HIV-1 is unclear. Here, the study showed that knockdown of spastin inhibited the production of the intracellular HIV-1 Gag protein and new virions through enhancing Gag lysosomal degradation. Further investigation showed that increased sodium tolerance 1 (IST1), the subunit of endosomal sorting complex required for transport (ESCRT), could interact with the MIT domain of spastin to regulate the intracellular Gag production. In summary, spastin is required for HIV-1 replication, while spastin-IST1 interaction facilitates virus production by regulating HIV-1 Gag intracellular trafficking and degradation. Spastin may serve as new target for HIV-1 prophylactic and therapy.

Genetic characterization of primary lateral sclerosis

BACKGROUND AND OBJECTIVES

Primary lateral sclerosis (PLS) is a motor neuron disease characterised by loss of the upper motor neurons. Most patients present with slowly progressive spasticity of the legs, which may also spread to the arms or bulbar regions. It is challenging to distinguish between PLS, early-stage amyotrophic lateral sclerosis (ALS) and hereditary spastic paraplegia (HSP). The current diagnostic criteria advise against extensive genetic testing. This recommendation is, however, based on limited data.

METHODS

We aim to genetically characterize a PLS cohort using whole exome sequencing (WES) for genes associated with ALS, HSP, ataxia and movement disorders (364 genes) and C9orf72 repeat expansions. Patients fulfilling the definite PLS criteria by Turner et al. and with available DNA samples of sufficient quality were recruited from an on-going, population-based epidemiological study. Genetic variants were classified according to the ACMG criteria and assigned to groups based on disease association.

RESULTS

WES was performed in 139 patients and the presence of repeat expansions in C9orf72 was analysed separately in 129 patients. This resulted in 31 variants of which 11 were (likely) pathogenic. (Likely) pathogenic variants resulted in 3 groups based on disease association: ALS-FTD (C9orf72, TBK1), pure HSP (SPAST, SPG7), "ALS-HSP-CMT overlap" (FIG4, NEFL, SPG11).

DISCUSSION

In a cohort of 139 PLS patients, genetic analyses resulted in 31 variants (22%) of which 10 (7%) (likely) pathogenic associated with different diseases (predominantly ALS and HSP). Based on these results and the literature, we advise to consider genetic analyses in the diagnostic work-up for PLS.

The clinical and molecular spectrum of ZFYVE26-associated hereditary spastic paraplegia: SPG15

In the field of hereditary spastic paraplegia (HSP), progress in molecular diagnostics needs to be translated into robust phenotyping studies to understand genetic and phenotypic heterogeneity and to support interventional trials. ZFYVE26-associated hereditary spastic paraplegia (HSP-ZFYVE26, SPG15) is a rare, early-onset complex HSP, characterized by progressive spasticity and a variety of other neurological symptoms. While prior reports, often in populations with high rates of consanguinity, have established a general phenotype, there is a lack of systematic investigations and a limited understanding of age-dependent manifestation of symptoms. Here we delineate the clinical, neuroimaging and molecular features of 44 individuals from 36 families, the largest cohort assembled to date. Median age at last follow-up was 23.8 years covering a wide age range (11-61 years). While symptom onset often occurred in early childhood [median: 24 months, interquartile range (IQR) = 24], a molecular diagnosis was reached at a median age of 18.8 years (IQR = 8), indicating significant diagnostic delay. We demonstrate that most patients present with motor and/or speech delay or learning disabilities. Importantly, these developmental symptoms preceded the onset of motor symptoms by several years. Progressive spasticity in the lower extremities, the hallmark feature of HSP-ZFYVE26, typically presents in adolescence and involves the distal lower limbs before progressing proximally. Spasticity in the upper extremities was seen in 64%. We found a high prevalence of extrapyramidal movement disorders including cerebellar ataxia (64%) and dystonia (11%). Parkinsonism (16%) was present in a subset and showed no sustained response to levodopa. Cognitive decline and neurogenic bladder dysfunction progressed over time in most patients. A systematic analysis of brain MRI features revealed a common diagnostic signature consisting of thinning of the anterior corpus callosum, signal changes of the anterior forceps and non-specific cortical and cerebellar atrophy. The molecular spectrum included 45 distinct variants, distributed across the protein structure without mutational hotspots. Spastic Paraplegia Rating Scale scores, SPATAX Disability Scores and the Four Stage Functional Mobility Score showed moderate strength in representing the proportion of variation between disease duration and motor dysfunction. Plasma neurofilament light chain levels were significantly elevated in all patients (Mann-Whitney U-test, P < 0.0001) and were correlated inversely with age (Spearman's rank correlation coefficient r = -0.65, P = 0.01). In summary, our systematic cross-sectional analysis of HSP-ZFYVE26 patients across a wide age-range, delineates core clinical, neuroimaging and molecular features and identifies markers of disease severity. These results raise awareness to this rare disease, facilitate an early diagnosis and create clinical trial readiness.

Clinical phenotyping and genetic diagnosis of a large cohort of Sudanese families with hereditary spinocerebellar degenerations

Hereditary spinocerebellar degenerations (SCDs) is an umbrella term that covers a group of monogenic conditions that share common pathogenic mechanisms and include hereditary spastic paraplegia (HSP), cerebellar ataxia, and spinocerebellar ataxia. They are often complicated with axonal neuropathy and/or intellectual impairment and overlap with many neurological conditions, including neurodevelopmental disorders. More than 200 genes and loci inherited through all modes of Mendelian inheritance are known. Autosomal recessive inheritance predominates in consanguineous communities; however, autosomal dominant and X-linked inheritance can also occur. Sudan is inhabited by genetically diverse populations, yet it has high consanguinity rates. We used next-generation sequencing, genotyping, bioinformatics analysis, and candidate gene approaches to study 90 affected patients from 38 unrelated Sudanese families segregating multiple forms of SCDs. The age-at-onset in our cohort ranged from birth to 35 years; however, most patients manifested childhood-onset diseases (the mean and median ages at onset were 7.5 and 3 years, respectively). We reached the genetic diagnosis in 63% and possibly up to 73% of the studied families when considering variants of unknown significance. Combining the present data with our previous analysis of 25 Sudanese HSP families, the success rate reached 52-59% (31-35/59 families). In this article we report candidate variants in genes previously known to be associated with SCDs or other phenotypically related monogenic disorders. We also highlight the genetic and clinical heterogeneity of SCDs in Sudan, as we did not identify a major causative gene in our cohort, and the potential for discovering novel SCD genes in this population.

Stem Cell-Based Organoid Models of Neurodevelopmental Disorders

The past decade has seen an explosion in the identification of genetic causes of neurodevelopmental disorders, including Mendelian, de novo, and somatic factors. These discoveries provide opportunities to understand cellular and molecular mechanisms as well as potential gene-gene and gene-environment interactions to support novel therapies. Stem cell-based models, particularly human brain organoids, can capture disease-associated alleles in the context of the human genome, engineered to mirror disease-relevant aspects of cellular complexity and developmental timing. These models have brought key insights into neurodevelopmental disorders as diverse as microcephaly, autism, and focal epilepsy. However, intrinsic organoid-to-organoid variability, low levels of certain brain-resident cell types, and long culture times required to reach maturity can impede progress. Several recent advances incorporate specific morphogen gradients, mixtures of diverse brain cell types, and organoid engraftment into animal models. Together with nonhuman primate organoid comparisons, mechanisms of human neurodevelopmental disorders are emerging.

Reduced acetylated α-tubulin in SPAST hereditary spastic paraplegia patient PBMCs

HSP-SPAST is the most common form of hereditary spastic paraplegia (HSP), a neurodegenerative disease causing lower limb spasticity. Previous studies using HSP-SPAST patient-derived induced pluripotent stem cell cortical neurons have shown that patient neurons have reduced levels of acetylated α-tubulin, a form of stabilized microtubules, leading to a chain of downstream effects eventuating in increased vulnerability to axonal degeneration. Noscapine treatment rescued these downstream effects by restoring the levels of acetylated α-tubulin in patient neurons. Here we show that HSP-SPAST patient non-neuronal cells, peripheral blood mononuclear cells (PBMCs), also have the disease-associated effect of reduced levels of acetylated α-tubulin. Evaluation of multiple PBMC subtypes showed that patient T cell lymphocytes had reduced levels of acetylated α-tubulin. T cells make up to 80% of all PBMCs and likely contributed to the effect of reduced acetylated α-tubulin levels seen in overall PBMCs. We further showed that mouse administered orally with increasing concentrations of noscapine exhibited a dose-dependent increase of noscapine levels and acetylated α-tubulin in the brain. A similar effect of noscapine treatment is anticipated in HSP-SPAST patients. To measure acetylated α-tubulin levels, we used a homogeneous time resolved fluorescence technology-based assay. This assay was sensitive to noscapine-induced changes in acetylated α-tubulin levels in multiple sample types. The assay is high throughput and uses nano-molar protein concentrations, making it an ideal assay for evaluation of noscapine-induced changes in acetylated α-tubulin levels. This study shows that HSP-SPAST patient PBMCs exhibit disease-associated effects. This finding can help expedite the drug discovery and testing process.

Toward the Definition of Patient-Reported Outcome Measurements in Hereditary Spastic Paraplegia

Background and Objectives

Hereditary spastic paraplegias (HSPs) are a heterogeneous group of rare neurodegenerative diseases, characterized by a progressive spastic paraparesis. Currently, there is a HSP-specific clinician-reported outcome measure (CROM) called Spastic Paraplegia Rating Scale (SPRS). There are, however, no specific patient-reported outcome measures (PROMs) for HSP. In the present cohort study, we prospectively follow up a well-examined Austrian HSP cohort using validated rating scales and compared PROM with disease-specific and non-disease-specific CROM.

Methods

Patients were recruited and followed up at the Center for Rare Movement Disorders, Innsbruck, Austria. CROM included the SPRS, Scale for the Assessment and Rating of Ataxia (SARA), Barthel Index (BI), and Mini-Mental State Examination (MMSE). PROM included the EQ-5D questionnaire and the Patient Health Questionnaire 9 (PHQ-9). Standardized response means (SRMs) were calculated for all scales at follow-up (FU) after 1 year.

Results

A total of 55 patients (36 males) with HSP were included in the study. FU was performed for 30 patients (21 males). Apart from females reporting more problems in the EQ-5D domain of anxiety and depression (p = 0.008), other clinician-reported outcomes (CROs) or patient-reported outcomes (PROs) did not differ significantly across sex. SPRS showed significant correlations with SARA (p < 0.001), mainly driven by the gait item, as well as the BI. Although SPRS did not correlate with EQ-5D visual analogue scale and PHQ-9 scores, several EQ-5D domains correlated significantly with SPRS. At FU, SPRS showed the highest responsiveness (SRM 1.11), followed by SARA (SRM 0.47). Neither MMSE nor PRO significantly increased at FU.

Discussion

In this study, we present an Austrian cohort of patients with HSP and a prospective study evaluating correlations of CRO and PRO as well as their progression. Demographics from our cohort are comparable with several other European cohort studies. Our data highlight the capabilities of the SPRS to show clinical progression and warrant consideration of ataxia rating scales such as SARA in HSP cohorts. We also show that the generic PROMs are not suitable to detect change in HSP, and thus, we propose to create a disease-specific PROM fully depicting the effect of HSP on the patients' lives.

De novo variants cause complex symptoms in HSP-ATL1 (SPG3A) and uncover genotype-phenotype correlations

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.

Clinical features and genetic spectrum of Chinese patients with hereditary spastic paraplegia: A 14-year study

Background: Hereditary spastic paraplegia (HSP) constitutes a group of clinically and genetically rare neurodegenerative diseases characterized by progressive corticospinal tract degeneration. The phenotypes and genotypes of HSP are still expanding. In this study, we aimed to analyse the differential diagnosis, clinical features, and genetic distributions of a Chinese HSP patients in a 14-year cohort and to improve our understanding of the disease. Methods: The clinical data of patients with a primary diagnosis of HSP at the initial visit to the Department of the Neurology, Peking University Third Hospital, from 2008 to 2022 were retrospectively collected. Next-generation sequencing gene panels (NGS) combined with a multiplex ligation-amplification assay (MLPA) were conducted. Epidemiological and clinical features and candidate variants in HSP-related genes were analyzed and summarized. Results: 54 cases (probands from 25 different pedigrees and 29 sporadic cases) from 95 patients with a primary diagnosis of HSP were finally confirmed to have a clinical diagnosis of HSP based on clinical criteria, including their clinical findings, family history and long-term follow-up. Earlier disease onset was associated with longer diagnostic delay and longer disease duration and was associated with a lower risk of loss of ability to walk independently. In addition, 20 candidate variants in reported HSP-related genes were identified in these clinically diagnosed HSP patients, including variants in SPAST, ALT1, WASHC5, SPG11, B4GALNT1, and REEP1. The genetic diagnostic rate in these 54 patients was 35.18%. Conclusion: Hereditary spastic paraplegia has high clinical and genetic heterogeneity and is prone to misdiagnosis. Long-term follow-up and genetic testing can partially assist in diagnosing HSP. Our study summarized the clinical features of Chinese HSP patients in a 14-year cohort, expanded the genotype spectrum, and improved our understanding of the disease.

The REEP family of proteins: molecular targets and role in pathophysiology

Receptor expression-enhancing proteins (REEPs) are an evolutionarily conserved protein family that is pivotal to the structure and function of the endoplasmic reticulum (ER). The REEP family can be classified into two major subfamilies in higher species, the REEP1-4 and REEP5-6 subfamilies. Within the REEP1-4 subfamily, REEP1 and REEP2 are closely related, and REEP3 and REEP4 are similarly related. The REEP family is widely distributed in various tissues. Recent studies indicate that the REEP family is involved in many pathological and physiological processes, such as ER morphogenesis and remodeling, microtubule cytoskeleton regulation, and the trafficking and expression of G protein-coupled receptors (GPCRs). Moreover, the REEP family plays crucial roles in the occurrence and development of many diseases, including neurological diseases, diabetes, retinal diseases, cardiac diseases, infertility, obesity, oligoarticular juvenile idiopathic arthritis (OJIA), COVID-19, and cancer. In the present review, we describe the distribution and structure of the REEP family. Furthermore, we summarize the functions and the associated diseases of this family. Based on the pleiotropic actions of the REEP family, the study of its family members is crucial to understanding the relevant pathophysiological processes and developing strategies to modulate and control these related diseases. AVAILABILITY OF DATA AND MATERIAL: The datasets used or analyzed during the current study are available from the corresponding author on reasonable request.

Investigating KIF1A mutations in a Taiwanese cohort with hereditary spastic paraplegia

BACKGROUND

Hereditary spastic paraplegia (HSP) is a heterogeneous group of inherited neurodegenerative disorders characterized by slowly progressive lower limbs spasticity and weakness. HSP type 30 (SPG30) is a HSP subtype caused by mutations in the kinesin family member 1A gene (KIF1A) and could be either autosomal dominantly or recessively inherited. The aim of this study was to investigate the clinical and genetic features of KIF1A mutations in a Taiwanese HSP cohort.

METHODS

Mutational analysis of KIF1A was performed in 242 unrelated Taiwanese patients of Han Chinese ethnicity with clinically suspected HSP using targeted resequencing panel covering the entire coding regions of KIF1A. Clinical, electrophysiological and neuroimaging features of the HSP patients carrying a KIF1A mutation were characterized.

RESULTS

Three different KIF1A mutations were identified in three patients with autosomal dominantly inherited HSP. Among them, KIF1A p.E19K was a novel mutation. The patient harboring KIF1A p.G321D presented with pure HSP, while the individuals carrying KIF1A p.E19K or p.R316Q manifested complex HSP with additional axonal sensorimotor polyneuropathy. The patients carrying KIF1A p.R316Q also had thoracic cord atrophy, thin corpus callosum and white matter hyperintensity.

CONCLUSION

SPG30 accounts for 1.2% (3/242) of patients in the Taiwanese HSP cohort, suggesting that it is an uncommon HSP subtype in Taiwan. This study delineates the clinical and genetic features of SPG30 in Taiwan and provides useful information for the diagnosis and management of SPG30, especially in patients of Han Chinese descent.

Phenotypic and Genetic Heterogeneity of Adult Patients with Hereditary Spastic Paraplegia from Serbia

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.