Plasma oxysterols: biomarkers for diagnosis and treatment in spastic paraplegia type 5

What can pediatricians learn from adult inherited metabolic diseases?

The field of inherited metabolic diseases (IMD) has initially emerged and developed over decades in pediatric departments. Still, today, about 50% of patients with IMD are adults, and adult metabolic medicine (AMM) is getting more structured at national and international levels. There are several domains in which pediatricians can learn from AMM. First, long-term evolution of IMD patients, especially those treated since childhood, is critical to determine nutritional and neuropsychiatric outcomes in adults so that these outcomes can be better monitored, and patient care adjusted as much as possible from childhood. Conversely, the observation of attenuated phenotypes in adults of IMD known to present with severe phenotypes in children calls for caution in the development of newborn screening programs and, more largely, in the interpretation of next-generation sequencing data. Third, it is important for pediatricians to be familiar with adult-onset IMD as they expand our understanding of metabolism, including in children, such as oxysterols and glycogen metabolism. Last, the identification of common molecular and cellular mechanisms in neurodevelopment and neurodegeneration opens the way to synergistic therapeutic developments that will benefit both fields of pediatric and adult medicine. Overall, these observations underline the need of strong interdisciplinarity between pediatricians and adult specialists for the diagnosis and the treatment of IMD well beyond the issues of patient transition from pediatric to adult medicine.

Oxy- and Phytosterols as Biomarkers: Current Status and Future Perspectives

Oxysterols and phytosterols are sterol compounds present at markedly low levels in tissues and serum of healthy individuals. A wealth of evidence suggests that they could be employed as biomarkers for human diseases or for cholesterol absorption.An increasing number of reports suggest circulating or tissue oxysterols as putative biomarkers for cardiovascular and neurodegenerative diseases or cancers. Thus far most of the studies have been carried out on small study populations. To achieve routine biomarker use, large prospective cohort studies are absolutely required. This, again, would necessitate thorough standardization of the oxysterol analytical methodology across the different laboratories, which now employ different technologies resulting in inconsistencies in the measured oxysterol levels. Routine use of oxysterol biomarkers would also necessitate the development of a new targeted analytical methodology suitable for high-throughput platforms.The most important use of phytosterols as biomarkers involves their use as markers for cholesterol absorption. For this to be achieved, (1) their quantitative analyses should be available in routine lipid laboratories, (2) it should be generally acknowledgment that the profile of cholesterol metabolism can reveal the risk of the development of atherosclerotic cardiovascular diseases (ASCVD), and (3) screening of the profile of cholesterol metabolism should be included in the ASCVD risk surveys. This should be done e.g. in families with a history of early onset or frequent ASCVD and in young adults aged 18-20 years, to exclude the presence of high cholesterol absorption. Individuals in high cholesterol absorption families need preventive measures from young adulthood to inhibit the possible development and progression of atherosclerosis.

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.

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.

AMFR dysfunction causes autosomal recessive spastic paraplegia in human that is amenable to statin treatment in a preclinical model

Hereditary spastic paraplegias (HSP) are rare, inherited neurodegenerative or neurodevelopmental disorders that mainly present with lower limb spasticity and muscle weakness due to motor neuron dysfunction. Whole genome sequencing identified bi-allelic truncating variants in AMFR, encoding a RING-H2 finger E3 ubiquitin ligase anchored at the membrane of the endoplasmic reticulum (ER), in two previously genetically unexplained HSP-affected siblings. Subsequently, international collaboration recognized additional HSP-affected individuals with similar bi-allelic truncating AMFR variants, resulting in a cohort of 20 individuals from 8 unrelated, consanguineous families. Variants segregated with a phenotype of mainly pure but also complex HSP consisting of global developmental delay, mild intellectual disability, motor dysfunction, and progressive spasticity. Patient-derived fibroblasts, neural stem cells (NSCs), and in vivo zebrafish modeling were used to investigate pathomechanisms, including initial preclinical therapy assessment. The absence of AMFR disturbs lipid homeostasis, causing lipid droplet accumulation in NSCs and patient-derived fibroblasts which is rescued upon AMFR re-expression. Electron microscopy indicates ER morphology alterations in the absence of AMFR. Similar findings are seen in amfra-/- zebrafish larvae, in addition to altered touch-evoked escape response and defects in motor neuron branching, phenocopying the HSP observed in patients. Interestingly, administration of FDA-approved statins improves touch-evoked escape response and motor neuron branching defects in amfra-/- zebrafish larvae, suggesting potential therapeutic implications. Our genetic and functional studies identify bi-allelic truncating variants in AMFR as a cause of a novel autosomal recessive HSP by altering lipid metabolism, which may potentially be therapeutically modulated using precision medicine with statins.

Chenodeoxycholic acid rescues axonal degeneration in induced pluripotent stem cell-derived neurons from spastic paraplegia type 5 and cerebrotendinous xanthomatosis patients

BACKGROUND

Biallelic mutations in CYP27A1 and CYP7B1, two critical genes regulating cholesterol and bile acid metabolism, cause cerebrotendinous xanthomatosis (CTX) and hereditary spastic paraplegia type 5 (SPG5), respectively. These rare diseases are characterized by progressive degeneration of corticospinal motor neuron axons, yet the underlying pathogenic mechanisms and strategies to mitigate axonal degeneration remain elusive.

METHODS

To generate induced pluripotent stem cell (iPSC)-based models for CTX and SPG5, we reprogrammed patient skin fibroblasts into iPSCs by transducing fibroblast cells with episomal vectors containing pluripotency factors. These patient-specific iPSCs, as well as control iPSCs, were differentiated into cortical projection neurons (PNs) and examined for biochemical alterations and disease-related phenotypes.

RESULTS

CTX and SPG5 patient iPSC-derived cortical PNs recapitulated several disease-specific biochemical changes and axonal defects of both diseases. Notably, the bile acid chenodeoxycholic acid (CDCA) effectively mitigated the biochemical alterations and rescued axonal degeneration in patient iPSC-derived neurons. To further examine underlying disease mechanisms, we developed CYP7B1 knockout human embryonic stem cell (hESC) lines using CRISPR-cas9-mediated gene editing and, following differentiation, examined hESC-derived cortical PNs. Knockout of CYP7B1 resulted in similar axonal vesiculation and degeneration in human cortical PN axons, confirming a cause-effect relationship between gene deficiency and axonal degeneration. Interestingly, CYP7B1 deficiency led to impaired neurofilament expression and organization as well as axonal degeneration, which could be rescued with CDCA, establishing a new disease mechanism and therapeutic target to mitigate axonal degeneration.

CONCLUSIONS

Our data demonstrate disease-specific lipid disturbances and axonopathy mechanisms in human pluripotent stem cell-based neuronal models of CTX and SPG5 and identify CDCA, an established treatment of CTX, as a potential pharmacotherapy for SPG5. We propose this novel treatment strategy to rescue axonal degeneration in SPG5, a currently incurable condition.

Elevated oxysterol and N-palmitoyl-O-phosphocholineserine levels in congenital disorders of glycosylation

Congenital disorders of glycosylation (CDG) and Niemann-Pick type C (NPC) disease are inborn errors of metabolism that can both present with infantile-onset severe liver disease and other multisystemic manifestations. Plasma bile acid and N-palmitoyl-O-phosphocholineserine (PPCS) are screening biomarkers with proposed improved sensitivity and specificity for NPC. We report an infant with ATP6AP1-CDG who presented with cholestatic liver failure and elevated plasma oxysterols and bile acid, mimicking NPC clinically and biochemically. On further investigation, PPCS, but not the bile acid derivative N-(3β,5α,6β-trihydroxy-cholan-24-oyl) glycine (TCG), were elevated in plasma samples from individuals with ATP6AP1-, ALG1-, ALG8-, and PMM2-CDG. These findings highlight the importance of keeping CDG within the diagnostic differential when evaluating children with early onset severe liver disease and elevated bile acid or PPCS to prevent delayed diagnosis and treatment.

Childhood-onset hereditary spastic paraplegia and its treatable mimics

Early-onset forms of hereditary spastic paraplegia and inborn errors of metabolism that present with spastic diplegia are among the most common "mimics" of cerebral palsy. Early detection of these heterogenous genetic disorders can inform genetic counseling, anticipatory guidance, and improve outcomes, particularly where specific treatments exist. The diagnosis relies on clinical pattern recognition, biochemical testing, neuroimaging, and increasingly next-generation sequencing-based molecular testing. In this short review, we summarize the clinical and molecular understanding of: 1) childhood-onset and complex forms of hereditary spastic paraplegia (SPG5, SPG7, SPG11, SPG15, SPG35, SPG47, SPG48, SPG50, SPG51, SPG52) and, 2) the most common inborn errors of metabolism that present with phenotypes that resemble hereditary spastic paraplegia.

The Puzzle of Hereditary Spastic Paraplegia: From Epidemiology to Treatment

Inherited neurodegenerative pathology characterized by lower muscle tone and increasing spasticity in the lower limbs is termed hereditary spastic paraplegia (HSP). HSP is associated with changes in about 80 genes and their products involved in various biochemical pathways, such as lipid droplet formation, endoplasmic reticulum shaping, axon transport, endosome trafficking, and mitochondrial function. With the inheritance patterns of autosomal dominant, autosomal recessive, X-linked recessive, and mitochondrial inheritance, HSP is prevalent around the globe at a rate of 1–5 cases in every 100,000 individuals. Recent technology and medical interventions somewhat aid in recognizing and managing the malaise. However, HSP still lacks an appropriate and adequate therapeutic approach. Current therapies are based on the clinical manifestations observed in the patients, for example, smoothing the relaxant spastic muscle and physiotherapies. The limited clinical trial studies contribute to the absence of specific pharmaceuticals for HSPs. Our current work briefly explains the causative genes, epidemiology, underlying mechanism, and the management approach undertaken to date. We have also mentioned the latest approved drugs to summarise the available knowledge on therapeutic strategies for HSP.

Plasma oxysterols in drug-free patients with schizophrenia

Evidence from clinical, genetic, and medical studies has shown the neuronal developmental disorder aspect of schizophrenia (SZ). Whereas oxysterols are vital factors in neurodevelopment, it is still unknown whether they are involved in the pathophysiology of SZ. The current study aims to explore the profile of oxysterols in plasma, ratio to total cholesterol (Tchol) and the association with clinical factors in patients with SZ. Forty men diagnosed with SZ and forty healthy controls matched for age and sex were included in the study. The ratios of cholestane-3β,5α,6β-triol, 27-hydroxycholesterol (27-OHC) and Cholestanol to Tchol increased in the schizophrenic group compared to controls. However, levels of 24S-hydroxycholesterol (24-OHC) were not significantly different between patients and controls. For the SZ patients, the plasma 24-OHC levels were positively correlated with the positive and negative syndrome total scores (PANSS) but negatively correlated with the Montreal Cognitive Assessment scores (MOCA). Moreover, the ratio Cholestanol to Tchol was negatively correlated with MOCA scores and positively correlated with PANSS general. The binary logistic regression analysis revealed that the ratio Cholestane-3β,5α,6β-triol/TChol could be considered as an independent risk factor for SZ. On the other hand, the receiver's operating characteristics analysis corresponding to potential biomarkers on SZ showed Areas Under the Curve (AUCs) of 82.1%; 69.7% and 77.6% for the ratio of Cholestane-3β,5α,6β-triol/TChol, 27-OHC/TChol and Cholestanol/TChol respectively. The relevance of Cholestane-3β,5α,6β-triol, 27-OHC and Cholestanol assays as biomarkers of this disease deserves further investigation.

25-Hydroxycholesterol as a Signaling Molecule of the Nervous System

Cholesterol is an essential component of plasma membrane and precursor of biological active compounds, including hydroxycholesterols (HCs). HCs regulate cellular homeostasis of cholesterol; they can pass across the membrane and vascular barriers and act distantly as para- and endocrine agents. A small amount of 25-hydroxycholesterol (25-HC) is produced in the endoplasmic reticulum of most cells, where it serves as a potent regulator of the synthesis, intracellular transport, and storage of cholesterol. Production of 25-HC is strongly increased in the macrophages, dendrite cells, and microglia at the inflammatory response. The synthesis of 25-HC can be also upregulated in some neurological disorders, such as Alzheimer’s disease, amyotrophic lateral sclerosis, spastic paraplegia type 5, and X-linked adrenoleukodystrophy. However, it is unclear whether 25-HC aggravates these pathologies or has the protective properties. The molecular targets for 25-HC are transcriptional factors (LX receptors, SREBP2, ROR), G protein-coupled receptor (GPR183), ion channels (NMDA receptors, SLO1), adhesive molecules (α5β1 and ανβ3 integrins), and oxysterol-binding proteins. The diversity of 25-HC-binding proteins points to the ability of HC to affect many physiological and pathological processes. In this review, we focused on the regulation of 25-HC production and its universal role in the control of cellular cholesterol homeostasis, as well as the effects of 25-HC as a signaling molecule mediating the influence of inflammation on the processes in the neuromuscular system and brain. Based on the evidence collected, it can be suggested that 25-HC prevents accumulation of cellular cholesterol and serves as a potent modulator of neuroinflammation, synaptic transmission, and myelinization. An increased production of 25-HC in response to a various type of damage can have a protective role and reduce neuronal loss. At the same time, an excess of 25-HC may exert the neurotoxic effects.

New Function of Cholesterol Oxidation Products Involved in Osteoporosis Pathogenesis

Osteoporosis (OP) is a systemic bone disease characterized by decreased bone strength, microarchitectural changes in bone tissues, and increased risk of fracture. Its occurrence is closely related to various factors such as aging, genetic factors, living habits, and nutritional deficiencies as well as the disturbance of bone homeostasis. The dysregulation of bone metabolism is regarded as one of the key influencing factors causing OP. Cholesterol oxidation products (COPs) are important compounds in the maintenance of bone metabolic homeostasis by participating in several important biological processes such as the differentiation of mesenchymal stem cells, bone formation in osteoblasts, and bone resorption in osteoclasts. The effects of specific COPs on mesenchymal stem cells are mainly manifested by promoting osteoblast genesis and inhibiting adipocyte genesis. This review aims to elucidate the biological roles of COPs in OP development, starting from the molecular mechanisms of OP, pointing out opportunities and challenges in current research, and providing new ideas and perspectives for further studies of OP pathogenesis.

25-Hydroxycholesterol suppress IFN-γ-induced inflammation in microglia by disrupting lipid raft formation and caveolin-mediated signaling endosomes

Acute microglial activation plays an important role in neuroprotection. However, dysregulated, prolonged microgliosis exacerbates neurodegeneration through excessive release of pro-inflammatory cytokines and cytotoxic factors. Interferon-gamma (IFN-γ), an inflammatory cytokine, exacerbates the detrimental microglial response. Although various anti-inflammatory drugs have been evaluated as interventions for microglia-mediated neuroinflammation, no anti-inflammatories are in clinical use for microgliosis. The present study evaluated the anti-inflammatory mechanisms of oxysterols, blood brain barrier (BBB) penetrable bioactive lipids, revealing that this intervention suppresses neuroinflammation by disrupting membrane lipid raft formation and caveolae-mediated endosomal IFN-γ signaling. We find that 25-hydroxycholesterol (25-HC) rapidly repressed IFN-γ receptor trafficking to lipid rafts in microglia by disrupting raft formation, thereby suppressing microglial inflammatory response. IFN-γ treatment upregulated expression of Cav-1, a major component of caveolae, and IFN-γ signaling was sustained through Cav-1+ signaling endosomes. 25-HC repressed IFN-γ induction of Cav-1 expression in microglia, and subsequently suppressed the chronic inflammatory response. Taken together, these findings demonstrated that 25-HC effectively regulate the inflammatory status of microglia by mediating the formation of rafts and caveolae-dependent signaling endosomes. Given the important roles of IFN-γ and microglia in the pathology of neurodegenerative brain diseases, a novel anti-inflammatory mechanism of 25-HC that is not receptor-dependent, but rather is related to the regulation of membrane rafts and caveolae, suggests a new therapeutic target for inflammatory neurodegenerations.

Insights into Clinical, Genetic, and Pathological Aspects of Hereditary Spastic Paraplegias: A Comprehensive Overview

Hereditary spastic paraplegias (HSP) are a heterogeneous group of motor neurodegenerative disorders that have the core clinical presentation of pyramidal syndrome which starts typically in the lower limbs. They can present as pure or complex forms with all classical modes of monogenic inheritance reported. To date, there are more than 100 loci/88 spastic paraplegia genes (SPG) involved in the pathogenesis of HSP. New patterns of inheritance are being increasingly identified in this era of huge advances in genetic and functional studies. A wide range of clinical symptoms and signs are now reported to complicate HSP with increasing overall complexity of the clinical presentations considered as HSP. This is especially true with the emergence of multiple HSP phenotypes that are situated in the borderline zone with other neurogenetic disorders. The genetic diagnostic approaches and the utilized techniques leave a diagnostic gap of 25% in the best studies. In this review, we summarize the known types of HSP with special focus on those in which spasticity is the principal clinical phenotype ("SPGn" designation). We discuss their modes of inheritance, clinical phenotypes, underlying genetics, and molecular pathways, providing some observations about therapeutic opportunities gained from animal models and functional studies. This review may pave the way for more analytic approaches that take into consideration the overall picture of HSP. It will shed light on subtle associations that can explain the occurrence of the disease and allow a better understanding of its observed variations. This should help in the identification of future biomarkers, predictors of disease onset and progression, and treatments for both better functional outcomes and quality of life.

Phenoconversion from Spastic Paraplegia to ALS/FTD Associated with CYP7B1 Compound Heterozygous Mutations

Biallelic mutations in the CYP7B1 gene lead to spastic paraplegia-5 (SPG5). We report herein the case of a patient whose clinical symptoms began with progressive lower limb spasticity during childhood, and who secondly developed amyotrophic lateral sclerosis/frontotemporal dementia (ALS/FTD) at the age of 67 years. Hereditary spastic paraplegia (HSP) gene analysis identified the compound heterozygous mutations c.825T>A (pTyr275*) and c.1193C>T (pPro398Leu) in CYP7B1 gene. No other pathogenic variant in frequent ALS/FTD causative genes was found. The CYP7B1 gene seems, therefore, to be the third gene associated with the phenoconversion from HSP to ALS, after the recently described UBQLN2 and ERLIN2 genes. We therefore expand the phenotype associated with CYP7B1 biallelic mutations and make an assumption about a link between cholesterol dyshomeostasis and ALS/FTD.

Potential markers for sample size estimations in hereditary spastic paraplegia type 5

Background

Aim to identify potential biomarkers to assess therapeutic efficacy for hereditary spastic paraplegias type 5 (SPG5) by investigating the clinical, cerebrospinal fluid (CSF) and magnetic resonance imaging (MRI) features.

Methods

We performed a cross-sectional study to compare SPG5 patients with age- and sex-matched healthy controls who underwent conventional and quantitative MRI techniques of spinal cord (C1-T9) and brain. SPG5 patients also underwent assessment for clinical status and CSF biomarkers (27-hydroxycholesterol, neurofilament light). We identified a set of markers with standardized effect sizes (|t|> 0.5) to estimate sample sizes for disease progression (disease duration > 14 years vs. ≤ 14 years).

Results

Seventeen genetically confirmed SPG5 patients (11 men, 6 women; age range, 13–49 years; median disease duration, 14 years) were enrolled. Compared to healthy controls, the total spinal cord area (SCA) of SPG5 patients was reduced particularly at the thoracic levels (cervical levels: 12–27%; thoracic levels 41–60%). Patients did not show significant alterations of brain signal abnormalities or atrophy relative to controls. A total of 10 surrogate markers were selected and a minimum sample size was achieved with the measurement of SCA on T9 (n = 22) much less that what would be required if using clinical disability assessment (n = 124).

Conclusions

SPG5 patients showed distinct MRI features of spinal cord atrophy without significant brain alterations. Our finding supports the measurements of spinal cord on T9 level as potential endpoint for SPG5 clinical trials.

Trial registration ClinicalTrials.gov, NCT04006418. Registered 05 July 2019, https://clinicaltrials.gov/ct2/show/NCT04006418?term=NCT04006418&draw=2&rank=1.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-02014-w.

A Transcriptomic Meta-Analysis Shows Lipid Metabolism Dysregulation as an Early Pathological Mechanism in the Spinal Cord of SOD1 Mice

Amyotrophic lateral sclerosis (ALS) is a multifactorial and complex fatal degenerative disorder. A number of pathological mechanisms that lead to motor neuron death have been identified, although there are many unknowns in the disease aetiology of ALS. Alterations in lipid metabolism are well documented in the progression of ALS, both at the systemic level and in the spinal cord of mouse models and ALS patients. The origin of these lipid alterations remains unclear. This study aims to identify early lipid metabolic pathways altered before systemic metabolic symptoms in the spinal cord of mouse models of ALS. To do this, we performed a transcriptomic analysis of the spinal cord of SOD1^G93A mice at an early disease stage, followed by a robust transcriptomic meta-analysis using publicly available RNA-seq data from the spinal cord of SOD1 mice at early and late symptomatic disease stages. The meta-analyses identified few lipid metabolic pathways dysregulated early that were exacerbated at symptomatic stages; mainly cholesterol biosynthesis, ceramide catabolism, and eicosanoid synthesis pathways. We present an insight into the pathological mechanisms in ALS, confirming that lipid metabolic alterations are transcriptionally dysregulated and are central to ALS aetiology, opening new options for the treatment of these devastating conditions.

Genetics in hereditary spastic paraplegias: Essential but not enough

Hereditary spastic paraplegias consist of a group of rare neurodegenerative diseases characterized by lower limb spasticity. These inherited Mendelian disorders show high genetic variability associated with wide clinical diversity. Pathophysiological investigations have suggested that mutations in genes affecting the same cellular pathway generally lead to similar clinical symptoms, highlighting the importance of genetic mutation in these diseases. However, phenotype-genotype correlations have failed to explain the observed large inter-individual variability linked to mutations in a single gene, suggesting that genetics alone is not sufficient to explain symptom diversity. The identification of biomarkers, such as neurofilament light chain, could fill the gap and predict disease evolution.

High rate of hypomorphic variants as the cause of inherited ataxia and related diseases: study of a cohort of 366 families

PURPOSE

Diagnosis of inherited ataxia and related diseases represents a real challenge given the tremendous heterogeneity and clinical overlap of the various causes. We evaluated the efficacy of molecular diagnosis of these diseases by sequencing a large cohort of undiagnosed families.

METHODS

We analyzed 366 unrelated consecutive patients with undiagnosed ataxia or related disorders by clinical exome-capture sequencing. In silico analysis was performed with an in-house pipeline that combines variant ranking and copy-number variant (CNV) searches. Variants were interpreted according to American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) guidelines.

RESULTS

We established the molecular diagnosis in 46% of the cases. We identified 35 mildly affected patients with causative variants in genes that are classically associated with severe presentations. These cases were explained by the occurrence of hypomorphic variants, but also rarely suspected mechanisms such as C-terminal truncations and translation reinitiation.

CONCLUSION

A significant fraction of the clinical heterogeneity and phenotypic overlap is explained by hypomorphic variants that are difficult to identify and not readily predicted. The hypomorphic C-terminal truncation and translation reinitiation mechanisms that we identified may only apply to few genes, as it relies on specific domain organization and alterations. We identified PEX10 and FASTKD2 as candidates for translation reinitiation accounting for mild disease presentation.

Plasma oxysterols: Altered level of plasma 24-hydroxycholesterol in patients with bipolar disorder

Cholesterol and its oxygenated metabolites, including oxysterols, are intensively investigated as potential players in the pathophysiology of brain disorders. Altered oxysterol levels have been described in patients with numerous neuropsychiatric disorders. Recent studies have shown that Bipolar disorder (BD) is associated with the disruption of cholesterol metabolism. The present study was aimed at investigating the profile of oxysterols in plasma, their ratio to total cholesterol and their association with clinical parameters in patients with BD. Thirty three men diagnosed with BD and forty healthy controls matched for age and sex were included in the study. Oxysterol levels were measured by isotope-dilution ultra-performance liquid chromatography-tandem mass spectrometry. Significantly higher levels were observed for cholestane-3β,5α,6β-triol, 27-hydroxycholesterol (27-OHC) and Cholestanol in patients with BD. The concentration of 24-hydroxycholesterol (24-OHC) was significantly lower in patients compared to controls. 24-OHC was also negatively correlated to MAS subscale score (r =-0.343; p = 0.049). In patients, 24-OHC was inversely correlated with age (r = -0.240; p = 0.045). Multivariate analysis found that BD acute decompensation was independently related to the rise in plasma 24-OHC (p = 0.002; OR = 0.966, 95 % CI [0.945 - 0.987]). However, the 24-OHC assay relevance as a biomarker of this disease deserves further investigation in other studies.

Successful treatment of infantile oxysterol 7α-hydroxylase deficiency with oral chenodeoxycholic acid

BACKGROUND

Deficiency of oxysterol 7α-hydroxylase, encoded by CYP7B1, is associated with fatal infantile progressive intrahepatic cholestasis and hereditary spastic paraplegia type 5. Most reported patients with CYP7B1 mutations presenting with liver disease in infancy have died of liver failure. However, it was recently reported that two patients treated with chenodeoxycholic acid survived. Correlations between the phenotype and genotype of CYP7B1 deficiency have not been clearly established.

CASE PRESENTATION

A 5-month-7-day-old Chinese baby from non-consanguineous parents was referred for progressive cholestasis and prolonged prothrombin time from one month of age. Genetic testing revealed compound heterozygous mutations c.187C > T(p.R63X)/c.334C > T(p.R112X) in CYP7B1, and fast atom bombardment mass spectrometry analysis of the urinary bile acid confirmed the presence of atypical hepatotoxic 3β-hydroxy-Δ⁵-bile acids. While awaiting liver transplantation she was orally administered chenodeoxycholic acid. Her liver function rapidly improved, urine atypical bile acids normalized, and she thrived well until the last follow-up at 23 months of age. Her 15-year-old brother, with no history of infantile cholestasis but harboring the same mutations in CYP7B1, had gait abnormality from 13 years of age. Neurological examination revealed hyper-reflexia and spasticity of the lower limbs. Brain MRI revealed enlarged perivascular space in the bilateral basal ganglia and white matter of frontal parietal.

CONCLUSIONS

In summary, these findings highlight that the phenotype of CYP7B1 deficiency varies widely, even in siblings and that early administration of chenodeoxycholic acid may improve prognosis.

Disturbances of brain cholesterol metabolism: A new excitotoxic process associated with status epilepticus

The understanding of the excitotoxic processes associated with a severe status epilepticus (SE) is of major importance. Changes of brain cholesterol homeostasis is an emerging candidate for excitotoxicity. We conducted an overall analysis of the cholesterol homeostasis both (i) in fluids and tissues from patients with SE: blood (n = 63, n = 87 controls), CSF (n = 32, n = 60 controls), and post-mortem brain tissues (n = 8, n = 8 controls) and (ii) in a mouse model of SE induced by an intrahippocampal injection of kainic acid. 24-hydroxycholesterol levels were decreased in kainic acid mouse hippocampus and in human plasma and post-mortem brain tissues of patients with SE when compared with controls. The decrease of 24-hydroxycholesterol levels was followed by increased cholesterol levels and by an increase of the cholesterol synthesis. Desmosterol levels were higher in human CSF and in mice and human hippocampus after SE. Lanosterol and dihydrolanosterol levels were higher in plasma from SE patients. Our results suggest that a CYP46A1 inhibition could occur after SE and is followed by a brain cholesterol accumulation. The excess of cholesterol is known to be excitotoxic for neuronal cells and may participate to neurological sequelae observed after SE. This study highlights a new pathophysiological pathway involved in SE excitotoxicity.

The History of Gene Hunting in Hereditary Spinocerebellar Degeneration: Lessons From the Past and Future Perspectives

Hereditary spinocerebellar degeneration (SCD) encompasses an expanding list of rare diseases with a broad clinical and genetic heterogeneity, complicating their diagnosis and management in daily clinical practice. Correct diagnosis is a pillar for precision medicine, a branch of medicine that promises to flourish with the progressive improvements in studying the human genome. Discovering the genes causing novel Mendelian phenotypes contributes to precision medicine by diagnosing subsets of patients with previously undiagnosed conditions, guiding the management of these patients and their families, and enabling the discovery of more causes of Mendelian diseases. This new knowledge provides insight into the biological processes involved in health and disease, including the more common complex disorders. This review discusses the evolution of the clinical and genetic approaches used to diagnose hereditary SCD and the potential of new tools for future discoveries.

Inherited Neuromuscular Disorders: Which Role for Serum Biomarkers?

Inherited neuromuscular disorders (INMD) are a heterogeneous group of rare diseases that involve muscles, motor neurons, peripheral nerves or the neuromuscular junction. Several different lab abnormalities have been linked to INMD: sometimes they are typical of the disorder, but they usually appear to be less specific. Sometimes serum biomarkers can point out abnormalities in presymtomatic or otherwise asymptomatic patients (e.g., carriers). More often a biomarker of INMD is evaluated by multiple clinicians other than expert in NMD before the diagnosis, because of the multisystemic involvement in INMD. The authors performed a literature search on biomarkers in inherited neuromuscular disorders to provide a practical approach to the diagnosis and the correct management of INMD. A considerable number of biomarkers have been reported that support the diagnosis of INMD, but the role of an expert clinician is crucial. Hence, the complete knowledge of such abnormalities can accelerate the diagnostic workup supporting the referral to specialists in neuromuscular disorders.

Challenges and Controversies in the Genetic Diagnosis of Hereditary Spastic Paraplegia

Purpose of Review

The hereditary spastic paraplegias (HSPs) are a group of disorders characterised by progressive lower limb weakness and spasticity. We address the challenges and controversies involved in the genetic diagnosis of HSP.

Recent Findings

There is a large and rapidly expanding list of genes implicated in HSP, making it difficult to keep gene testing panels updated. There is also a high degree of phenotypic overlap between HSP and other disorders, leading to problems in choosing the right panel to analyse. We discuss genetic testing strategies for overcoming these diagnostic hurdles, including the use of targeted sequencing gene panels, whole-exome sequencing and whole-genome sequencing. Personalised treatments for HSP are on the horizon, and a genetic diagnosis may hold the key to access these treatments.

Summary

Developing strategies to overcome the challenges and controversies in HSP may hold the key to a rapid and accurate genetic diagnosis.

27-Hydroxycholesterol regulates human SLC22A12 gene expression through estrogen receptor action

The excretion and reabsorption of uric acid both to and from urine are tightly regulated by uric acid transporters. Metabolic syndrome conditions, such as obesity, hypercholesterolemia, and insulin resistance, are believed to regulate the expression of uric acid transporters and decrease the excretion of uric acid. However, the mechanisms driving cholesterol impacts on uric acid transporters have been unknown. Here, we show that cholesterol metabolite 27‐hydroxycholesterol (27HC) upregulates the uric acid reabsorption transporter URAT1 encoded by SLC22A12 via estrogen receptors (ER). Transcriptional motif analysis showed that the SLC22A12 gene promoter has more estrogen response elements (EREs) than other uric acid reabsorption transporters such as SLC22A11 and SLC22A13, and 27HC‐activated SLC22A12 gene promoter via ER through EREs. Furthermore, 27HC increased SLC22A12 gene expression in human kidney organoids. Our results suggest that in hypercholesterolemic conditions, elevated levels of 27HC derived from cholesterol induce URAT1/SLC22A12 expression to increase uric acid reabsorption, and thereby, could increase serum uric acid levels.

Insulin resistance dysregulates CYP7B1 leading to oxysterol accumulation: a pathway for NAFL to NASH transition

NAFLD is an important public health issue closely associated with the pervasive epidemics of diabetes and obesity. Yet, despite NAFLD being among the most common of chronic liver diseases, the biological factors responsible for its transition from benign nonalcoholic fatty liver (NAFL) to NASH remain unclear. This lack of knowledge leads to a decreased ability to find relevant animal models, predict disease progression, or develop clinical treatments. In the current study, we used multiple mouse models of NAFLD, human correlation data, and selective gene overexpression of steroidogenic acute regulatory protein (StarD1) in mice to elucidate a plausible mechanistic pathway for promoting the transition from NAFL to NASH. We show that oxysterol 7α-hydroxylase (CYP7B1) controls the levels of intracellular regulatory oxysterols generated by the "acidic/alternative" pathway of cholesterol metabolism. Specifically, we report data showing that an inability to upregulate CYP7B1, in the setting of insulin resistance, results in the accumulation of toxic intracellular cholesterol metabolites that promote inflammation and hepatocyte injury. This metabolic pathway, initiated and exacerbated by insulin resistance, offers insight into approaches for the treatment of NAFLD.

Neuro-oxysterols and neuro-sterols as ligands to nuclear receptors, GPCRs, ligand-gated ion channels and other protein receptors

The brain is the most cholesterol rich organ in the body containing about 25% of the body's free cholesterol. Cholesterol cannot pass the blood-brain barrier and be imported or exported; instead, it is synthesised in situ and metabolised to oxysterols, oxidised forms of cholesterol, which can pass the blood-brain barrier. 24S-Hydroxycholesterol is the dominant oxysterol in the brain after parturition, but during development, a myriad of other oxysterols are produced, which persist as minor oxysterols after birth. During both development and in later life, sterols and oxysterols interact with a variety of different receptors, including nuclear receptors, membrane bound GPCRs, the oxysterol/sterol sensing proteins INSIG and SCAP, and the ligand-gated ion channel NMDA receptors found in nerve cells. In this review, we summarise the different oxysterols and sterols found in the CNS whose biological activity is transmitted via these different classes of protein receptors. LINKED ARTICLES: This article is part of a themed issue on Oxysterols, Lifelong Health and Therapeutics. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.16/issuetoc.

Lipid metabolic pathways converge in motor neuron degenerative diseases

Motor neuron diseases (MNDs) encompass an extensive and heterogeneous group of upper and/or lower motor neuron degenerative disorders, in which the particular clinical outcomes stem from the specific neuronal component involved in each condition. While mutations in a large number of molecules associated with lipid metabolism are known to be implicated in MNDs, there remains a lack of clarity regarding the key functional pathways involved, and their inter-relationships. This review highlights evidence that defines defects within two specific lipid (cholesterol/oxysterol and phosphatidylethanolamine) biosynthetic cascades as being centrally involved in MND, particularly hereditary spastic paraplegia. We also identify how other MND-associated molecules may impact these cascades, in particular through impaired organellar interfacing, to propose ‘subcellular lipidome imbalance’ as a likely common pathomolecular theme in MND. Further exploration of this mechanism has the potential to identify new therapeutic targets and management strategies for modulation of disease progression in hereditary spastic paraplegias and other MNDs.

Clinical characteristics of Taiwanese patients with Hereditary spastic paraplegia type 5

Objectives

To investigate the clinical, electrophysiological, neuroimaging characteristics and genetic features of SPG5 in Taiwan.

Methods

Mutational analysis of the coding regions of CYP7B1 was performed by utilizing targeted resequencing analysis of the 187 unrelated Taiwanese HSP patients. The diagnosis of SPG5 was ascertained by the presence of biallelic CYP7B1 mutations. The SPG5 patients received clinical, electrophysiological, and neuroimaging evaluations. Disease severity was assessed by using the Spastic Paraplegia Rating Scale (SPRS) and the disability score. Two microsatellite markers as well as 18 single‐nucleotide polymorphism (SNP) markers flanking CYP7B1 were genotyped to assess the founder effect of the CYP7B1 p.R112* mutation.

Results

Nineteen SPG5 patients from 17 families were identified. They typically presented an insidious onset progressive spastic paraparesis with proprioception involvement beginning at age 8 to 40 years. Their MRIs often showed white matter abnormalities in bilateral occipito‐parietal regions, spinal cord atrophy, and mild cerebellar atrophy. Six different mutations in CYP7B1 were recognized, including three novel ones (p.N131Ifs*4, p.A295V, and p.L439R). CYP7B1 p.R112* was the most common mutation and present in 88.2% of the 17 SPG5 pedigrees. The patients with homozygous CYP7B1 p.R112* mutations had a milder clinical severity. Detailed haplotype analyses demonstrated a shared haplotype in the 25 individuals carrying at least one single allele of CYP7B1 p.R112*, suggesting a founder effect.

Interpretation

This study delineates the distinct clinical and genetic features of SPG5 in Taiwan and provides useful information for the diagnosis and management of SPG5, especially in patients of Chinese descent.

Lipids in the Physiopathology of Hereditary Spastic Paraplegias

Hereditary spastic paraplegias (HSP) are a group of neurodegenerative diseases sharing spasticity in lower limbs as common symptom. There is a large clinical variability in the presentation of patients, partly underlined by the large genetic heterogeneity, with more than 60 genes responsible for HSP. Despite this large heterogeneity, the proteins with known function are supposed to be involved in a limited number of cellular compartments such as shaping of the endoplasmic reticulum or endolysosomal function. Yet, it is difficult to understand why alteration of such different cellular compartments can lead to degeneration of the axons of cortical motor neurons. A common feature that has emerged over the last decade is the alteration of lipid metabolism in this group of pathologies. This was first revealed by the identification of mutations in genes encoding proteins that have or are supposed to have enzymatic activities on lipid substrates. However, it also appears that mutations in genes affecting endoplasmic reticulum, mitochondria, or endolysosome function can lead to changes in lipid distribution or metabolism. The aim of this review is to discuss the role of lipid metabolism alterations in the physiopathology of HSP, to evaluate how such alterations contribute to neurodegenerative phenotypes, and to understand how this knowledge can help develop therapeutic strategy for HSP.

Sterolomics in biology, biochemistry, medicine

In mammalian systems "sterolomics" can be regarded as the quantitative or semi-quantitative profiling of all metabolites derived from cholesterol and its cyclic precursors. The system can be further complicated by metabolites derived from ingested phytosterols or pharmaceuticals, but this is beyond the scope of this article. "Sterolomics" can be performed on either an unbiased global format, or more usually, exploiting a targeted format. Here we discuss the different mass spectrometry-based analytical techniques used in "sterolomics" giving specific examples in the context of neurodegenerative disease and for the diagnosis of inborn errors of metabolism. We pay particular attention to the profiling of cholesterol metabolites in the bile acid biosynthesis pathways, although the analytical techniques discussed are also appropriate for analysis of hormonal steroids.

mRNA as a Novel Treatment Strategy for Hereditary Spastic Paraplegia Type 5

Hereditary spastic paraplegia type 5 is a neurodegenerative disease caused by loss-of-function mutations in the CYP7B1 gene encoding the oxysterol 7-α-hydroxylase involved in bile acid synthesis in the liver. Lack of CYP7B1 leads to an accumulation of its oxysterol substrates, in particular 25-hydroxycholesterol and 27-hydroxycholesterol that are able to cross the blood-brain barrier and have neurotoxic properties. A potential therapeutic strategy for SPG5 is the replacement of CYP7B1 by administration of mRNA. Here, we studied the intravenous application of formulated mouse and human CYP7B1 mRNA in mice lacking the endogenous Cyp7b1 gene. A single-dose injection of either mouse or human CYP7B1 mRNA led to a pronounced degradation of oxysterols in liver and serum within 2 days of treatment. Pharmacokinetics indicate a single injection of human CYP7B1 mRNA to be effective in reducing oxysterols for at least 5 days. Repetitive applications of mRNA were safe for at least 17 days and resulted in a significant reduction of neurotoxic oxysterols not only in liver and serum but also to some extent in the brain. Our study highlights the potential to use mRNA as a novel therapy to treat patients with SPG5 disease.

Motor Evoked Potentials in Hereditary Spastic Paraplegia-A Systematic Review

Background: Hereditary Spastic Paraplegia (HSP) is a slowly progressive neurodegenerative disorder with no disease modifying treatment. Potential therapeutic approaches are emerging and large-scale clinical drug trials for patients with HSP are imminent. A sensitive biomarker to measure the drug efficacy in these trials is required. Motor evoked potentials (MEPs) are a potential biomarker for HSP as they assess the central motor pathways and can be standardized with set protocols and guidelines.

Objectives: We performed a systematic review to investigate the utility of MEPs as a diagnostic and disease severity biomarker for HSP.

Search Methods: Systematic searches of PubMed, Embase, Medline, and Scopus were performed.

Selection Criteria: Studies reporting on central motor conduction time measured with MEPs in adult and pediatric patients with HSP were included. We excluded studies in non-HSP patient cohorts, not in English, not original research, and unpublished journal articles.

Data Collection and analysis: Search results were de-duplicated and screened according to the inclusion and exclusion criteria. The included papers were reviewed independently by two reviewers and data was collected on patient cohorts, test methods, results, and study quality. Results were analyzed using descriptive methods.

Results: Of the 882 search results, 32 studies were included in the review. The most common finding was absent or prolonged lower limb (LL) central motor conduction time (CMCT) in patients with HSP (78% of patients studied). Quality assessment revealed variability in study methodology and reporting of results. Variations included patient cohorts of various genotypes as well as variations in equipment and techniques used. Aside from CMCT, none of the MEP parameter measures correlated with disease severity and many did not show significant difference between HSP patients and controls.

Conclusion: Systematic review of MEP studies in HSP patient cohorts demonstrated mixed findings. Lower limb CMCT was the most promising parameter in terms of differentiating HSP patients from controls, with one study demonstrating a weak correlation with clinical disease severity. It is possible that the lack of consistency in study methodologies and small patient cohorts have contributed to the variable findings. A longitudinal study of MEPs in a large cohort of HSP patients with the same genotype will help clarify the utility of MEPs as a biomarker for disease severity and use in clinical trials.

25-hydroxycholesterol impairs neuronal and muscular development in zebrafish

Oxysterols have essential effects on brain homeostasis and their levels are often altered in neurodegenerative and neuroinflammatory diseases. Several studies have demonstrated the cytotoxic effects of 25-HC on different cell lines, however, not much is known about its effects on neurons in vivo. In this study, we examined the effects of 25-HC exposure on the nervous system development in the zebrafish. We showed that survival rate of zebrafish embryos/larvae is significantly decreased at doses of 25-HC above 40 μM. 25-HC was found to affect the motility of zebrafish larvae, primary motor axon and muscle morphology. Furthermore, larvae treated with 25-HC showed a reduced neuronal network and number of HuC-positive cells in the brain. An increased cell death was also observed in both the brain and spinal cord of zebrafish treated with 25-HC. Interestingly, administration of 25-HC at later stages of development (24 and 48 h post fertilization) had no detrimental effects on motor axons. Altogether, our findings show that elevated levels of 25-HC may have important consequences on neuronal development and cell survival.

Hereditary spastic paraplegia: from diagnosis to emerging therapeutic approaches

Hereditary spastic paraplegia (HSP) describes a heterogeneous group of genetic neurodegenerative diseases characterised by progressive spasticity of the lower limbs. The pathogenic mechanism, associated clinical features, and imaging abnormalities vary substantially according to the affected gene and differentiating HSP from other genetic diseases associated with spasticity can be challenging. Next generation sequencing-based gene panels are now widely available but have limitations and a molecular diagnosis is not made in most suspected cases. Symptomatic management continues to evolve but with a greater understanding of the pathophysiological basis of individual HSP subtypes there are emerging opportunities to provide targeted molecular therapies and personalised medicine.

Diagnosis and management of progressive ataxia in adults

Progressive ataxia in adults can be difficult to diagnose, owing to its heterogeneity and the rarity of individual causes. Many patients remain undiagnosed (‘idiopathic’ ataxia). This paper provides suggested diagnostic pathways for the general neurologist, based on Ataxia UK’s guidelines for professionals. MR brain scanning can provide diagnostic clues, as well as identify ‘structural’ causes such as tumours and multiple sclerosis. Advances in molecular genetics, including the wider and cheaper availability of ‘next-generation sequencing’, have enabled clinicians to identify many more cases with a genetic cause. Finally, autoimmunity is probably an under-recognised cause of progressive ataxia: as well as patients with antigliadin antibodies there are smaller numbers with various antibodies, including some associated with cancer. There are a few treatable ataxias, but also symptomatic treatments to help people with the spectrum of complications that might accompany progressive ataxias. Multidisciplinary team involvement and allied health professionals’ input are critical to excellent patient care, including in the palliative phase. We can no longer justify a nihilistic approach to the management of ataxia.

Hereditary spastic paraplegias: time for an objective case definition and a new nosology for neurogenetic disorders to facilitate biomarker/therapeutic studies

INTRODUCTION

Hereditary spastic paraplegias (HSPs) are heterogeneous neurodegenerative disorders characterized by progressive lower limb weakness and spasticity as core symptoms of the degeneration of the corticospinal motor neurons. Even after exclusion of infectious and toxic mimickers of these disorders, the definitive diagnosis remains tricky, mainly in sporadic forms, as there is significant overlap with other disorders. Since their first description, various attempts failed to reach an appropriate classification. This was due to the constant expansion of the clinical spectrum of these diseases and the discovery of new genes, a significant number of them was involved in overlapping diseases. Areas covered: In this perspective review, an extensive literature study was conducted on the historical progress of HSP research. We also revised the previous and the current classifications of HSP and the closely related neurogenetic disorders and analyzed the areas of overlap. Expert opinion: There is undeniable need for objective case definition and reclassification of all neurogenetic disorders including HSPs, a prerequisite to improve patient follow-up, biomarker identification and develop therapeutics. The challenge is to understand why mutations can give rise to multiple phenotypic presentations along this spectrum of diseases in which the corticospinal tract is affected.

Mining for Oxysterols in Cyp7b1-/- Mouse Brain and Plasma: Relevance to Spastic Paraplegia Type 5

Deficiency in cytochrome P450 (CYP) 7B1, also known as oxysterol 7α-hydroxylase, in humans leads to hereditary spastic paraplegia type 5 (SPG5) and in some cases in infants to liver disease. SPG5 is medically characterized by loss of motor neurons in the corticospinal tract. In an effort to gain a better understanding of the fundamental biochemistry of this disorder, we have extended our previous profiling of the oxysterol content of brain and plasma of Cyp7b1 knockout (-/-) mice to include, amongst other sterols, 25-hydroxylated cholesterol metabolites. Although brain cholesterol levels do not differ between wild-type (wt) and knockout mice, we find, using a charge-tagging methodology in combination with liquid chromatography-mass spectrometry (LC-MS) and multistage fragmentation (MSⁿ), that there is a build-up of the CYP7B1 substrate 25-hydroxycholesterol (25-HC) in Cyp7b1-/- mouse brain and plasma. As reported earlier, levels of (25R)26-hydroxycholesterol (26-HC), 3β-hydroxycholest-5-en-(25R)26-oic acid and 24S,25-epoxycholesterol (24S,25-EC) are similarly elevated in brain and plasma. Side-chain oxysterols including 25-HC, 26-HC and 24S,25-EC are known to bind to INSIG (insulin-induced gene) and inhibit the processing of SREBP-2 (sterol regulatory element-binding protein-2) to its active form as a master regulator of cholesterol biosynthesis. We suggest the concentration of cholesterol in brain of the Cyp7b1-/- mouse is maintained by balancing reduced metabolism, as a consequence of a loss in CYP7B1, with reduced biosynthesis. The Cyp7b1-/- mouse does not show a motor defect; whether the defect in humans is a consequence of less efficient homeostasis of cholesterol in brain has yet to be uncovered.

Oxysterol research: a brief review

In the present study, we discuss the recent developments in oxysterol research. Exciting results have been reported relating to the involvement of oxysterols in the fields of neurodegenerative disease, especially in Huntington's disease, Parkinson's disease and Alzheimer's disease; in signalling and development, in particular, in relation to Hedgehog signalling; and in cancer, with a special focus on (25R)26-hydroxycholesterol. Methods for the measurement of oxysterols, essential for understanding their mechanism of action in vivo, and valuable for diagnosing rare diseases of cholesterol biosynthesis and metabolism are briefly considered.

Exome Sequencing Reveals a Novel Homozygous Frameshift Mutation in the CYP7B1 Gene in a Japanese Patient with SPG5

SPG5 is a rare subtype of autosomal recessive hereditary spastic paraplegia caused by a homozygous mutation in the oxysterol 7α-hydroxylase gene, CYP7B1. We describe the first Japanese patient with SPG5 with a novel mutation in the CYP7B1 gene. On exome sequencing, we identified a homozygous frameshift mutation, c.741delA, p.K247fs, in exon 3 of the CYP7B1 gene. The patient showed spastic paraparesis with white matter hyperintensities in the bilateral corona radiata and periventricular and subcortical regions on brain magnetic resonance imaging. The present study expands the mutation spectrum of CYP7B1 and provides an opportunity to study the genotype-phenotype correlation in SPG5.

Spinal cord involvement in adult-onset metabolic and genetic diseases

In adulthood, spinal cord MRI abnormalities such as T2-weighted hyperintensities and atrophy are commonly associated with a large variety of causes (inflammation, infections, neoplasms, vascular and spondylotic diseases). Occasionally, they can be due to rare metabolic or genetic diseases, in which the spinal cord involvement can be a prominent or even predominant feature, or a secondary one. This review focuses on these rare diseases and associated spinal cord abnormalities, which can provide important but over-ridden clues for the diagnosis. The review was based on a PubMed search (search terms: 'spinal cord' AND 'leukoencephalopathy' OR 'leukodystrophy'; 'spinal cord' AND 'vitamin'), further integrated according to the authors' personal experience and knowledge. The genetic and metabolic diseases of adulthood causing spinal cord signal alterations were identified and classified into four groups: (1) leukodystrophies; (2) deficiency-related metabolic diseases; (3) genetic and acquired toxic/metabolic causes; and (4) mitochondrial diseases. A number of genetic and metabolic diseases of adulthood causing spinal cord atrophy without signal alterations were also identified. Finally, a classification based on spinal MRI findings is presented, as well as indications about the diagnostic work-up and differential diagnosis. Some of these diseases are potentially treatable (especially if promptly recognised), while others are inherited as autosomal dominant trait. Therefore, a timely diagnosis is needed for a timely therapy and genetic counselling. In addition, spinal cord may be the main site of pathology in many of these diseases, suggesting a tempting role for spinal cord abnormalities as surrogate MRI biomarkers.

Oxysterols as a biomarker in diseases

Cholesterol is one of the most important chemical substances as a structural element in human cells, and it is very susceptible to oxidation reactions that form oxysterol. Oxysterols exhibit almost the exact structure as cholesterol and a cholesterol precursor (7-dehydrocholesterol) with an additional hydroxyl, epoxy or ketone moiety. The oxidation reaction is performed via an enzymatic or non-enzymatic mechanism. The wide array of enzymatic oxysterols encountered in the human body varies in origin and function. Oxysterols establish a concentration equilibrium in human body fluids. Disease may alter the equilibrium, and oxysterols may be used as a diagnostic tool. The current review presents the possibility of using non-enzymatic oxysterols and disturbances in enzymatic oxysterol equilibrium in the human body as a potential biomarker for diagnosing and/or monitoring of the progression of various diseases.

Management of Hereditary Spastic Paraplegia: A Systematic Review of the Literature

The term hereditary spastic paraplegia (HSP) embraces a clinically and genetically heterogeneous group of neurodegenerative diseases characterized by progressive spasticity and weakness of the lower limbs. There currently exist no specific therapies for HSP, and treatment is exclusively symptomatic, aimed at reducing muscle spasticity, and improving strength and gait. The authors set out to perform a comprehensive systematic review of the available scientific literature on the treatment of HSP, applying Cochrane Collaboration methods. The Google Scholar, PubMed and Scopus electronic databases were searched to find relevant randomized control trials (RCTs) and open-label interventional studies, prospective, and retrospective observational studies of supplements, medications, and physical therapy, as well as case reports and case series. Two authors independently analyzed 27 articles selected on the basis of a series of inclusion criteria. Applying a best-evidence synthesis approach, they evaluated these articles for methodological quality. A standardized scoring system was used to obtain interrater assessments. Disagreements were resolved by discussion. The 27 articles focused on pharmacological treatment (n = 17 articles), physical therapy (n = 5), surgical treatment (n = 5). The drugs used in the 17 articles on pharmacological therapy were: gabapentin, progabide, dalfampridine, botulinum toxin, L-Dopa, cholesterol-lowering drugs, betaine, and folinic acid. Gabapentin, progabide, dalfampridine, and botulinum toxin were used as antispastic agents; the study evaluating gabapentin efficacy was well-designed, but failed to demonstrate any significant improvement. L-Dopa, cholesterol-lowering drugs, betaine, and folinic acid were only used in specific HSP subtypes. Two of the three studies evaluating cholesterol-lowering drugs (in SPG5 patients) were well-designed and showed a significant reduction of specific serum biomarkers (oxysterols), but clinical outcomes were not evaluated. The articles focusing on physical treatment and surgical therapy were found to be of low/medium quality and, accordingly, failed to clarify the role of these approaches in HSP. Despite recent advances in understanding of the pathogenesis of HSP and the possibility, in several centers, of obtaining more precise and rapid molecular diagnoses, there is still no adequate evidence base for recommending the various published therapies. Well-designed RCTs are needed to evaluate the efficacy of both symptomatic and pathogenetic treatments.

Clinical Trial Designs and Measures in Hereditary Spastic Paraplegias

Hereditary spastic paraplegias (HSPs) are a large group of genetically-diverse neurologic disorders characterized clinically by a common feature of lower extremity spasticity and gait difficulties. Current therapies are predominantly symptomatic, and even then usually provide inadequate relief of symptoms. Going forward, HSP therapeutics development requires a systematic analysis of quantifiable measures and tools to assess treatment response. This review summarizes promising therapeutic targets, assessment measures, and previous clinical trials for the HSPs. Oxidative stress, signaling pathways, microtubule dynamics, and gene rescue/replacement have been proposed as potential treatment targets or modalities. Quantitative evaluation of pre-clinical rodent HSP models emphasize rotarod performance, foot base angle, grip strength, stride length, beam walking, critical speed, and body weight. Clinical measures of HSP in humans include 10-m gait velocity, the Spastic Paraplegia Rating Scale (SPRS), Ashworth Spasticity Scale, Fugl-Meyer Scale, timed up-and-go, and the Gillette Functional Assessment Questionnaire. We conducted a broad search for past clinical trials in HSPs and identified trials that investigated pharmacological agents including atorvastatin, gabapentin, L-threonine, botulinum toxin, dalfampridine, methylphenidate, and baclofen. We provide recommendations for future HSP treatment directions based on these prior research experiences as well as regulatory insight.

Next Generation Molecular Diagnosis of Hereditary Spastic Paraplegias: An Italian Cross-Sectional Study

Hereditary spastic paraplegia (HSP) refers to a group of genetically heterogeneous neurodegenerative motor neuron disorders characterized by progressive age-dependent loss of corticospinal motor tract function, lower limb spasticity, and weakness. Recent clinical use of next generation sequencing (NGS) methodologies suggests that they facilitate the diagnostic approach to HSP, but the power of NGS as a first-tier diagnostic procedure is unclear. The larger-than-expected genetic heterogeneity-there are over 80 potential disease-associated genes-and frequent overlap with other clinical conditions affecting the motor system make a molecular diagnosis in HSP cumbersome and time consuming. In a single-center, cross-sectional study, spanning 4 years, 239 subjects with a clinical diagnosis of HSP underwent molecular screening of a large set of genes, using two different customized NGS panels. The latest version of our targeted sequencing panel (SpastiSure3.0) comprises 118 genes known to be associated with HSP. Using an in-house validated bioinformatics pipeline and several in silico tools to predict mutation pathogenicity, we obtained a positive diagnostic yield of 29% (70/239), whereas variants of unknown significance (VUS) were found in 86 patients (36%), and 83 cases remained unsolved. This study is among the largest screenings of consecutive HSP index cases enrolled in real-life clinical-diagnostic settings. Its results corroborate NGS as a modern, first-step procedure for molecular diagnosis of HSP. It also disclosed a significant number of new mutations in ultra-rare genes, expanding the clinical spectrum, and genetic landscape of HSP, at least in Italy.

Treatment with chenodeoxycholic acid in cerebrotendinous xanthomatosis: clinical, neurophysiological, and quantitative brain structural outcomes

BACKGROUND

Cerebrotendinous xanthomatosis (CTX) is a rare neurodegenerative disease related to sterols metabolism. It affects both central and peripheral nervous systems but treatment with chenodeoxycholic acid (CDCA) has been reported to stabilize clinical scores and improve nerve conduction parameters. Few quantitative brain structural studies have been conducted to assess the effect of CDCA in CTX.

METHODS AND RESULTS

We collected retrospectively clinical, neurophysiological, and quantitative brain structural data in a cohort of 14 patients with CTX treated by CDCA over a mean period of 5 years. Plasma cholestanol levels normalized under treatment with CDCA within a few months. We observed a significant clinical improvement in patients up to 25 years old, whose treatment was initiated less than 15 years after the onset of neurological symptoms. Conversely, patients whose treatment was initiated more than 25 years after neurological disease onset continued their clinical deterioration. Eleven patients presented with a length-dependent peripheral neuropathy, whose electrophysiological parameters improved significantly under CDCA. Volumetric analyses in a subset of patients showed no overt volume loss under CDCA. Moreover, diffusion weighted imaging showed improved fiber integrity of the ponto-cerebellar and the internal capsule with CDCA. CDCA was well tolerated in all patients with CTX.

CONCLUSION

CDCA may reverse the pathophysiological process in patients with CTX, especially if treatment is initiated early in the disease process. Besides tendon xanthoma, this study stresses the need to consider plasma cholestanol measurement in any patient with infantile chronic diarrhea and/or jaundice, juvenile cataract, learning disability and/or autism spectrum disorder, pyramidal signs, cerebellar syndrome or peripheral neuropathy.