Clinical Trial Designs and Measures in Hereditary Spastic Paraplegias

Hereditary spastic paraplegia: Novel insights into the pathogenesis and management

Hereditary spastic paraplegia is a genetically heterogeneous neurodegenerative disorder characterised primarily by muscle stiffness in the lower limbs. Neurodegenerative disorders are conditions that result from cellular and metabolic abnormalities, many of which have strong genetic ties. While ageing is a known contributor to these changes, certain neurodegenerative disorders can manifest early in life, progressively affecting a person's quality of life. Hereditary spastic paraplegia is one such condition that can appear in individuals of any age. In hereditary spastic paraplegia, a distinctive feature is the degeneration of long nerve fibres in the corticospinal tract of the lower limbs. This degeneration is linked to various cellular and metabolic processes, including mitochondrial dysfunction, remodelling of the endoplasmic reticulum membrane, autophagy, abnormal myelination processes and alterations in lipid metabolism. Additionally, hereditary spastic paraplegia affects processes like endosome membrane trafficking, oxidative stress and mitochondrial DNA polymorphisms. Disease-causing genetic loci and associated genes influence the progression and severity of hereditary spastic paraplegia, potentially affecting various cellular and metabolic functions. Although hereditary spastic paraplegia does not reduce a person's lifespan, it significantly impairs their quality of life as they age, particularly with more severe symptoms. Regrettably, there are currently no treatments available to halt or reverse the pathological progression of hereditary spastic paraplegia. This review aims to explore the metabolic mechanisms underlying the pathophysiology of hereditary spastic paraplegia, emphasising the interactions of various genes identified in recent network studies. By comprehending these associations, targeted molecular therapies that address these biochemical processes can be developed to enhance treatment strategies for hereditary spastic paraplegia and guide clinical practice effectively.

Gait analysis patterns and rehabilitative interventions to improve gait in persons with hereditary spastic paraplegia: a systematic review and meta-analysis

Background

Hereditary spastic paraplegias (HSPs) are a group of inheritance diseases resulting in gait abnormalities, which may be detected using instrumented gait analysis. The aim of this systematic review was 2-fold: to identify specific gait analysis patterns and interventions improving gait in HSP subjects.

Methods

A systematic review was conducted in PubMed, Cochrane Library, REHABDATA, and PEDro databases, in accordance with reporting guidelines of PRISMA statement and Cochrane's recommendation. The review protocol was recorded on the PROSPERO register. Patients with pure and complicated HSP of any age were included. All types of studies were included. Risk of bias, quality assessment, and meta-analysis were performed.

Results

Forty-two studies were included: 19 were related to gait analysis patterns, and 24 were intervention studies. The latter ones were limited to adults. HSP gait patterns were similar to cerebral palsy in younger subjects and stroke in adults. Knee hyperextension, reduced range of motion at knee, ankle, and hip, reduced foot lift, and increased rapid trunk and arm movements were reported. Botulinum injections reduced spasticity but uncovered weakness and improved gait velocity at follow-up. Weak evidence supported intrathecal baclofen, active intensive physical therapy (i.e., robot-assisted gait training, functional exercises, and hydrotherapy), and functional electrical stimulation. Some improvements but adverse events were reported after transcranial magnetic stimulation, transcutaneous spinal direct current stimulation, and spinal cord stimulation implant.

Conclusion

Knee hyperextension, non-sagittal pelvic movements, and reduced ROM at the knee, ankle, and hip represent the most peculiar patterns in HSP, compared to diplegic cerebral palsy and stroke. Botulinum improved comfortable gait velocity after 2 months. Nonetheless, interventions reducing spasticity might result in ineffective functional outcomes unveiling weakness. Intensive active physical therapy and FES might improve gait velocity in the very short term.

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.

Trials for Slowly Progressive Neurogenetic Diseases Need Surrogate Endpoints

Heritable neurological disorders provide insights into disease mechanisms that permit development of novel therapeutic approaches including antisense oligonucleotides, RNA interference, and gene replacement. Many neurogenetic diseases are rare and slowly progressive making it challenging to measure disease progression within short time frames. We share our experience developing clinical outcome assessments and disease biomarkers in the inherited peripheral neuropathies. We posit that carefully developed biomarkers from imaging, plasma, or skin can predict meaningful progression in functional and patient reported outcome assessments such that clinical trials of less than 2 years will be feasible for these rare and ultra-rare disorders. ANN NEUROL 2023;93:906-910.

Hereditary Spastic Paraplegia in Koreans: Clinical Characteristics and Factors Influencing the Disease Severity

Background and Purpose

Hereditary spastic paraplegia (HSP) progresses over time and is associated with locomotive dysfunction. Understanding the factors affecting disease severity and locomotive function is important in HSP. This study investigated the factors influencing disease severity and ambulation status of HSP.

Methods

We consecutively enrolled 109 Korean patients (64 males, and 45 females)from 84 families with a clinical diagnosis of HSP. HSP was primarily diagnosed based on clinical criteria including clinical findings, family history, and supported by genetic studies. Epidemiological and clinical features of the patients were analyzed, and the Spastic Paraplegia Rating Scale (SPRS) score and ambulatory status were used to evaluate disease severity.

Results

Ninety-two (84.4%) patients had pure HSP, and 55 (50.4%) had a dominant family history. Thirty-one (28.4%) patients required a mobility aid for locomotion. A Kaplan-Meier analysis showed that HSP patients lost their independent gait ability after a median disease duration of 34 years. Those with an age at onset of ≤18 years had a longer median independent walking time. Pure HSP is characterized by predominant bilateral lower extremity weakness and spasticity, whereas complicated HSP presents more complex neurological findings such as ocular and bulbar symptoms, ataxia, and cognitive impairment. Complicated HSP was significantly correlated with the SPRS mobility score (β=3.70, 95% confidence interval=0.45–6.94). The age at onset and disease duration were significantly correlated with disease severity, and they were significant predictors of the use of a mobility aid (p<0.05).

Conclusions

These findings suggest that a later age at onset and longer disease duration are significant factors affecting the disease severity and ambulatory function in patients with HSP. These findings can help clinicians to identify subjects at risk of locomotive impairment.

Biallelic variants in HPDL cause pure and complicated hereditary spastic paraplegia

Human 4-hydroxyphenylpyruvate dioxygenase-like (HPDL) is a putative iron-containing non-heme oxygenase of unknown specificity and biological significance. We report 25 families containing 34 individuals with neurological disease associated with biallelic HPDL variants. Phenotypes ranged from juvenile-onset pure hereditary spastic paraplegia to infantile-onset spasticity and global developmental delays, sometimes complicated by episodes of neurological and respiratory decompensation. Variants included bona fide pathogenic truncating changes, although most were missense substitutions. Functionality of variants could not be determined directly as the enzymatic specificity of HPDL is unknown; however, when HPDL missense substitutions were introduced into 4-hydroxyphenylpyruvate dioxygenase (HPPD, an HPDL orthologue), they impaired the ability of HPPD to convert 4-hydroxyphenylpyruvate into homogentisate. Moreover, three additional sets of experiments provided evidence for a role of HPDL in the nervous system and further supported its link to neurological disease: (i) HPDL was expressed in the nervous system and expression increased during neural differentiation; (ii) knockdown of zebrafish hpdl led to abnormal motor behaviour, replicating aspects of the human disease; and (iii) HPDL localized to mitochondria, consistent with mitochondrial disease that is often associated with neurological manifestations. Our findings suggest that biallelic HPDL variants cause a syndrome varying from juvenile-onset pure hereditary spastic paraplegia to infantile-onset spastic tetraplegia associated with global developmental delays.

Hereditary Spastic Paraplegia and Future Therapeutic Directions: Beneficial Effects of Small Compounds Acting on Cellular Stress

Hereditary spastic paraplegia (HSP) is a group of inherited neurodegenerative conditions that share a characteristic feature of degeneration of the longest axons within the corticospinal tract, which leads to progressive spasticity and weakness of the lower limbs. Mutations of over 70 genes produce defects in various biological pathways: axonal transport, lipid metabolism, endoplasmic reticulum (ER) shaping, mitochondrial function, and endosomal trafficking. HSPs suffer from an adequate therapeutic plan. Currently the treatments foreseen for patients affected by this pathology are physiotherapy, to maintain the outgoing tone, and muscle relaxant therapies for spasticity. Very few clinical studies have been conducted, and it's urgent to implement preclinical animal studies devoted to pharmacological test and screening, to expand the rose of compounds potentially attractive for clinical trials. Small animal models, such as Drosophila melanogaster and zebrafish, have been generated, analyzed, and used as preclinical model for screening of compounds and their effects. In this work, we briefly described the role of HSP-linked proteins in the organization of ER endomembrane system and in the regulation of ER homeostasis and stress as a common pathological mechanism for these HSP forms. We then focused our attention on the pharmacodynamic and pharmacokinetic features of some recently identified molecules with antioxidant property, such as salubrinal, guanabenz, N-acetyl cysteine, methylene blue, rapamycin, and naringenin, and on their potential use in future clinical studies. Expanding the models and the pharmacological screening for HSP disease is necessary to give an opportunity to patients and clinicians to test new molecules.

Brain Magnetic Spectroscopy Imaging and Hereditary Spastic Paraplegia: A Focused Systematic Review on Current Landmarks and Future Perspectives

Magnetic resonance spectroscopy (MRS) is a non-invasive neuroimaging technique used to investigate in vivo brain metabolites. MRS could provide a sensitive tool for the study of hereditary spastic paraplegia (HSP) by helping to unveil the underlying biochemical mechanisms and monitoring response to treatment. This focused systematic review aimed to summarize the brain metabolite findings in studies performed in genetically determined HSP. The second aim was to provide a critical analysis and recommendations for well-designed protocols for future studies. Fourteen MRS studies have been analyzed with overall 61 HSP patients, falling within a wide range of age at onset, disease duration, and age at the MRS scan, including children and adults. The genetic diagnosis included several subtypes (SPG2/3/4/5/10/11/28/31/54). SPG11 and SPG54 have been more frequently investigated. The MRS methodology included different MR field strength, not easily comparable spectra areas varying from whole brain to various cortical areas, brain stem and cerebellum sampling. No consistency in disease severity and other outcome measures was observed. The main MRS findings corresponded to the white matter metabolite abnormalities in the corticospinal tracts. In summary, this focused review provides insights on the current knowledge of brain metabolites in HSP and, in particular, in SPG11 and SPG54. Despite the inhomogeneity of the studies to date reported, brain metabolites as assessed by MRS could represent potentially useful diagnostic markers and prognostic indicators of disease progression in HSP. Specific recommendations regarding the MRS technical protocol, CNS area sampling, study design, and applicability of findings are given.

CAPN1 and hereditary spastic paraplegia: a novel variant in an Iranian family and overview of the genotype-phenotype correlation

PURPOSE

SPG76 is one of the rare forms of hereditary spastic paraplegia (HSP) which causes by mutations in the CAPN1 gene. The mode of inheritance of SPG76 is autosomal recessive (AR) and so far, only 24 families and 25 mutations in this gene have been reported worldwide. These mutations have been associated with a spectrum of disorders from pure HSP to spastic ataxia. HSP genetically is one of the most heterogeneous neurological disorders and to date, 79 types of HSP (SPG1-SPG79) have been identified, however, it has been suggested that many HSP-genes, particularly in AR-HSPs, remained unknown. AR-HSPs clinically overlap with other neurodegenerative disorders, making an accurate diagnosis of the disease difficult. Therefore, in addition to clinical examination, a high throughout genetic method like whole exome sequencing (WES) may be necessary for the diagnosis of this type of neurodegenerative disorders.

METHODS AND RESULTS

Herein, we present the clinical features and results of WES in the first Iranian family with a novel CAPN1 variant, c.C853T:p.R285* and pure HSP.

CONCLUSION

Some of the previous studies have mentioned that the "spasticity-ataxia phenotype might be conducted to the diagnosis of SPG76" but recently the number of pure HSP patients with CAPN1 mutation is increasing. The present study also expands the mutation spectrum of pure CAPN1-related SPG76; emphasizing that CAPN1 screening is required in both pure HSP and spasticity-ataxia phenotypes. As noted in some other literature, we suggest the clinical spectrum of this disorder to be considered as "CAPN1-associated neurodegeneration".