Metachromatic leukodystrophy: Disease spectrum and approaches for treatment

Terra incognita of glial cell dynamics in the etiology of leukodystrophies: Broadening disease and therapeutic perspectives

Neuroglial cells, also known as glia, are primarily characterized as auxiliary cells within the central nervous system (CNS). The recent findings have shed light on their significance in numerous physiological processes and their involvement in various neurological disorders. Leukodystrophies encompass an array of rare and hereditary neurodegenerative conditions that were initially characterized by the deficiency, aberration, or degradation of myelin sheath within CNS. The primary cellular populations that experience significant alterations are astrocytes, oligodendrocytes and microglia. These glial cells are either structurally or metabolically impaired due to inherent cellular dysfunction. Alternatively, they may fall victim to the accumulation of harmful by-products resulting from metabolic disturbances. In either situation, the possible replacement of glial cells through the utilization of implanted tissue or stem cell-derived human neural or glial progenitor cells hold great promise as a therapeutic strategy for both the restoration of structural integrity through remyelination and the amelioration of metabolic deficiencies. Various emerging treatment strategies like stem cell therapy, ex-vivo gene therapy, infusion of adeno-associated virus vectors, emerging RNA-based therapies as well as long-term therapies have demonstrated success in pre-clinical studies and show promise for rapid clinical translation. Here, we addressed various leukodystrophies in a comprehensive and detailed manner as well as provide prospective therapeutic interventions that are being considered for clinical trials. Further, we aim to emphasize the crucial role of different glial cells in the pathogenesis of leukodystrophies. By doing so, we hope to advance our understanding of the disease, elucidate underlying mechanisms, and facilitate the development of potential treatment interventions.

Rapid discrimination between deleterious and benign missense mutations in the CAGI 6 experiment

We describe the machine learning tool that we applied in the CAGI 6 experiment to predict whether single residue mutations in proteins are deleterious or benign. This tool was trained using only single sequences, i.e., without multiple sequence alignments or structural information. Instead, we used global characterizations of the protein sequence. Training and testing data for human gene mutations was obtained from ClinVar (ncbi.nlm.nih.gov/pub/ClinVar/), and for non-human gene mutations from Uniprot (www.uniprot.org). Testing was done on post-training data from ClinVar. This testing yielded high AUC and Matthews correlation coefficient (MCC) for well trained examples but low generalizability. For genes with either sparse or unbalanced training data, the prediction accuracy is poor. The resulting prediction server is available online at http://www.mamiris.com/Shoni.cagi6.

Progressive demyelinating polyneuropathy after hematopoietic cell transplantation in metachromatic leukodystrophy: a case series

Metachromatic leukodystrophy (MLD) is a neuro-metabolic disorder due to arylsulfatase A deficiency, causing demyelination of the central and peripheral nervous system. Hematopoietic cell transplantation (HCT) can provide a symptomatic and survival benefit for pre-symptomatic and early symptomatic patients by stabilizing CNS disease. This case series, however, illustrates the occurrence of severely progressive polyneuropathy shortly after HCT in two patients with late-infantile, one with late-juvenile, and one with adult MLD, leading to the inability to walk or sit without support. The patients had demyelinating polyneuropathy before HCT, performed at the ages of 2 years in the first two patients and at 14 and 23 years in the other two patients. The myeloablative conditioning regimen consisted of busulfan, fludarabine and, in one case, rituximab, with anti-thymocyte globulin, cyclosporine, steroids, and/or mycophenolate mofetil for GvHD prophylaxis. Polyneuropathy after HCT progressed parallel with tapering immunosuppression and paralleled bouts of infection and graft-versus-host disease (GvHD). Differential diagnoses included MLD progression, neurological GvHD or another (auto)inflammatory cause. Laboratory, electroneurography and pathology investigations were inconclusive. In two patients, treatment with immunomodulatory drugs led to temporary improvement, but not sustained stabilization of polyneuropathy. One patient showed recovery to pre-HCT functioning, except for a Holmes-like tremor, for which a peripheral origin cannot be excluded. One patient showed marginal response to immunosuppressive treatment and died ten months after HCT due to respiratory failure. The extensive diagnostic and therapeutic attempts highlight the challenge of characterizing and treating progressive polyneuropathy in patients with MLD shortly after HCT. We advise to consider repeat electro-neurography and possibly peripheral nerve biopsy in such patients. Nerve conduction blocks, evidence of the presence of T lymphocytes and macrophages in the neuronal and surrounding nerve tissue, and beneficial effects of immunomodulatory drugs may indicate a partially (auto)immune-mediated pathology. Polyneuropathy may cause major residual disease burden after HCT. MLD patients with progressive polyneuropathy could potentially benefit from a more intensified immunomodulatory drug regime following HCT, especially at times of immune activation.

Experiences of patients with metachromatic leukodystrophy, adrenoleukodystrophy, or Krabbe disease and the experiences of their family members: a qualitative systematic review

OBJECTIVE

This review aimed to synthesize the experiences of patients with metachromatic leukodystrophy, adrenoleukodystrophy, or Krabbe disease and the experiences of their families.

INTRODUCTION

Leukodystrophies are metabolic diseases caused by genetic mutations. There are multiple forms of the disease, varying in age of onset and symptoms. The progression of leukodystrophies worsens central nervous system symptoms and significantly affects the lives of patients and their families.

INCLUSION CRITERIA

Qualitative studies on the experiences of patients with leukodystrophies and their family members were included. These experiences included treatments such as enzyme replacement therapy and hematopoietic stem cell transplantation; effects of tracheostomy and gastrostomy; burdens on the family, coordinating care within the health care system, and family planning due to genetic disorders. This review considered studies in any setting.

METHODS

MEDLINE (Ovid), CINAHL Plus (EBSCOhost), APA PsycINFO (EBSCOhost), Scopus, and MedNar databases were searched on November 18, 2022. Study selection, critical appraisal, data extraction, and data synthesis were conducted in accordance with the JBI methodology for systematic reviews of qualitative evidence, and synthesized findings were evaluated according to the ConQual approach.

RESULTS

Eleven studies were eligible for synthesis, and 45 findings were extracted corresponding with participants' voices. Of these findings, 40 were unequivocal and 5 were credible. The diseases in the included studies were metachromatic leukodystrophy and adrenoleukodystrophy; no studies were identified for patients with Krabbe disease and their families. These findings were grouped into 11 categories and integrated into 3 synthesized findings, including i) providing care by family members and health care providers as physical symptoms progress, which relates to the effects of the characteristics of progressive leukodystrophies; ii) building medical teamwork to provide appropriate support services, comprising categories related to the challenges experienced with the health care system for patients with leukodystrophy and their families; and iii) coordinating family functions to accept and cope with the disease, which included categories related to family psychological difficulties and role divisions within the family. According to the ConQual criteria, the second synthesized finding had a low confidence level, and the first and third synthesized findings had a very low confidence level.

CONCLUSIONS

The synthesized findings of this review provide evidence on the experiences of patients with metachromatic leukodystrophy or adrenoleukodystrophy and their families. These findings indicate that there are challenges in managing a patient's physical condition and coordinating the health care system and family functions.

REVIEW REGISTRATION

PROSPERO CRD42022318805.

SUPPLEMENTAL DIGITAL CONTENT

A Japanese-language version of the abstract of this review is available [ http://links.lww.com/SRX/A49 ].

The effect of intrathecal recombinant arylsulfatase A therapy on structural brain magnetic resonance imaging in children with metachromatic leukodystrophy

This study aimed to evaluate the effect of intrathecal (IT) recombinant human arylsulfatase A (rhASA) on magnetic resonance imaging (MRI)-assessed brain tissue changes in children with metachromatic leukodystrophy (MLD). In total, 510 MRI scans were collected from 12 intravenous (IV) rhASA-treated children with MLD, 24 IT rhASA-treated children with MLD, 32 children with untreated MLD, and 156 normally developing children. Linear mixed models were fitted to analyze the time courses of gray matter (GM) volume and fractional anisotropy (FA) in the posterior limb of the internal capsule. Time courses for demyelination load and FA in the centrum semiovale were visualized using locally estimated scatterplot smoothing regression curves. All assessed imaging parameters demonstrated structural evidence of neurological deterioration in children with MLD. GM volume was significantly lower at follow-up (median duration, 104 weeks) in IV rhASA-treated versus IT rhASA-treated children. GM volume decline over time was steeper in children receiving low-dose (10 or 30 mg) versus high-dose (100 mg) IT rhASA. Similar effects were observed for demyelination. FA in the posterior limb of the internal capsule showed a higher trend over time in IT rhASA-treated versus children with untreated MLD, but FA parameters were not different between children receiving the low doses versus those receiving the high dose. GM volume in IT rhASA-treated children showed a strong positive correlation with 88-item Gross Motor Function Measure score over time. In some children with MLD, IT administration of high-dose rhASA may delay neurological deterioration (assessed using MRI), offering potential therapeutic benefit.

Evaluation of enzyme activity predictions for variants of unknown significance in Arylsulfatase A

Continued advances in variant effect prediction are necessary to demonstrate the ability of machine learning methods to accurately determine the clinical impact of variants of unknown significance (VUS). Towards this goal, the ARSA Critical Assessment of Genome Interpretation (CAGI) challenge was designed to characterize progress by utilizing 219 experimentally assayed missense VUS in the Arylsulfatase A (ARSA) gene to assess the performance of community-submitted predictions of variant functional effects. The challenge involved 15 teams, and evaluated additional predictions from established and recently released models. Notably, a model developed by participants of a genetics and coding bootcamp, trained with standard machine-learning tools in Python, demonstrated superior performance among submissions. Furthermore, the study observed that state-of-the-art deep learning methods provided small but statistically significant improvement in predictive performance compared to less elaborate techniques. These findings underscore the utility of variant effect prediction, and the potential for models trained with modest resources to accurately classify VUS in genetic and clinical research.

Dose-response evaluation of intravenous gene therapy in a symptomatic mouse model of metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is a rare, autosomal recessive neurodegenerative disease caused by deficient activity of the lysosomal enzyme arylsulfatase A (ARSA), resulting in sulfatide accumulation and subsequent demyelination and neuronal damage within the central and peripheral nervous systems. Three clinical forms of MLD have been described, based on age at symptom onset. The most frequent and severe forms have an early onset, with the disease progressing rapidly toward severe motor and cognitive regression and ultimately premature death. There are currently no approved therapies for most of these early-onset patients once symptoms are present. Thus, it is crucial to develop new approaches to treat symptomatic patients. Here, we proposed a gene therapy approach based on the intravenous delivery of AAVPHP.eB encoding ARSA. MLD mice were treated at 6 months for a dose-response study and at 9 months to assess late-treatment efficacy. Therapeutic efficacy was evaluated 3 or 6 months after injection. We demonstrated a broad transduction in the central nervous system, a complete correction of sulfatide storage, and a significant improvement in neuroinflammation at low dose and late treatment. Taken together, this work establishes a strong rationale for proposing a phase I/II clinical trial in MLD patients.

Biochemical and molecular analysis of pediatric patients with metachromatic leukodystrophy in South China: functional characterization of five novel ARSA variants

Metachromatic leukodystrophy (MLD) is a rare hereditary neurodegenerative disease caused by deficiency of the lysosomal enzyme arylsulfatase A (ARSA). This study described the clinical and molecular characteristics of 24 Chinese children with MLD and investigated functional characterization of five novel ARSA variants. A retrospective analysis was performed in 24 patients diagnosed with MLD at Guangzhou Women and Children's Medical Center in South China. Five novel mutations were further characterized by transient expression studies. We recruited 17 late-infantile, 3 early-juvenile, 4 late-juvenile MLD patients. In late-infantile patients, motor developmental delay and gait disturbance were the most frequent symptoms at onset. In juvenile patients, cognitive regression and gait disturbance were the most frequent chief complaints. Overall, 25 different ARSA mutations were identified with 5 novel mutations.The most frequent alleles were p.W320* and p.G449Rfs. The mutation p.W320*, p.Q155=, p.P91L, p.G156D, p.H208Mfs*46 and p.G449Rfs may link to late-infantile type. The novel missense mutations were predicted damaging in silico. The bioinformatic structural analysis of the novel missense mutations showed that these amino acid replacements would cause severe impairment of protein structure and function. In vitro functional analysis of the six mutants, showing a low ARSA enzyme activity, clearly demonstrated their pathogenic nature. The mutation p.D413N linked to R alleles. In western blotting analysis of the ARSA protein, the examined mutations retained reduced amounts of ARSA protein compared to the wild type. This study expands the spectrum of genotype of MLD. It helps to the future studies of genotype-phenotype correlations to estimate prognosis and develop new therapeutic approach.

Exome sequencing reveals genetic heterogeneity and clinically actionable findings in children with cerebral palsy

Cerebral palsy (CP) is the most common motor disability in children. To ascertain the role of major genetic variants in the etiology of CP, we conducted exome sequencing on a large-scale cohort with clinical manifestations of CP. The study cohort comprised 505 girls and 1,073 boys. Utilizing the current gold standard in genetic diagnostics, 387 of these 1,578 children (24.5%) received genetic diagnoses. We identified 412 pathogenic and likely pathogenic (P/LP) variants across 219 genes associated with neurodevelopmental disorders, and 59 P/LP copy number variants. The genetic diagnostic rate of children with CP labeled at birth with perinatal asphyxia was higher than the rate in children without asphyxia (P = 0.0033). Also, 33 children with CP manifestations (8.5%, 33 of 387) had findings that were clinically actionable. These results highlight the need for early genetic testing in children with CP, especially those with risk factors like perinatal asphyxia, to enable evidence-based medical decision-making.

The natural history and burden of illness of metachromatic leukodystrophy: a systematic literature review

BACKGROUND

Metachromatic leukodystrophy (MLD; OMIM 250100 and 249900) is a rare lysosomal storage disease caused by deficient arylsulfatase A activity, leading to accumulation of sulfatides in the nervous system. This systematic literature review aimed to explore the effect of MLD on the lives of patients.

METHODS

The Ovid platform was used to search Embase, MEDLINE, and the Cochrane Library for articles related to the natural history, clinical outcomes, and burden of illness of MLD; congress and hand searches were performed using 'metachromatic leukodystrophy' as a keyword. Of the 531 publications identified, 120 were included for data extraction following screening. A subset of findings from studies relating to MLD natural history and burden of illness (n = 108) are presented here.

RESULTS

The mean age at symptom onset was generally 16-18 months for late-infantile MLD and 6-10 years for juvenile MLD. Age at diagnosis and time to diagnosis varied widely. Typically, patients with late-infantile MLD presented predominantly with motor symptoms and developmental delay; patients with juvenile MLD presented with motor, cognitive, and behavioral symptoms; and patients with adult MLD presented with cognitive symptoms and psychiatric and mood disorders. Patients with late-infantile MLD had more rapid decline of motor function over time and lower survival than patients with juvenile MLD. Commonly reported comorbidities/complications included ataxia, epilepsy, gallbladder abnormalities, incontinence, neuropathy, and seizures.

CONCLUSIONS

Epidemiology of MLD by geographic regions, quantitative cognitive data, data on the differences between early- and late-juvenile MLD, and humanistic or economic outcomes were limited. Further studies on clinical, humanistic (i.e., quality of life), and economic outcomes are needed to help inform healthcare decisions for patients with MLD.

Newborn screening in metachromatic leukodystrophy - European consensus-based recommendations on clinical management

INTRODUCTION

Metachromatic leukodystrophy (MLD) is a rare autosomal recessive lysosomal storage disorder resulting from arylsulfatase A enzyme deficiency, leading to toxic sulfatide accumulation. As a result affected individuals exhibit progressive neurodegeneration. Treatments such as hematopoietic stem cell transplantation (HSCT) and gene therapy are effective when administered pre-symptomatically. Newborn screening (NBS) for MLD has recently been shown to be technically feasible and is indicated because of available treatment options. However, there is a lack of guidance on how to monitor and manage identified cases. This study aims to establish consensus among international experts in MLD and patient advocates on clinical management for NBS-identified MLD cases.

METHODS

A real-time Delphi procedure using eDELPHI software with 22 experts in MLD was performed. Questions, based on a literature review and workshops, were answered during a seven-week period. Three levels of consensus were defined: A) 100%, B) 75-99%, and C) 50-74% or >75% but >25% neutral votes. Recommendations were categorized by agreement level, from strongly recommended to suggested. Patient advocates participated in discussions and were involved in the final consensus.

RESULTS

The study presents 57 statements guiding clinical management of NBS-identified MLD patients. Key recommendations include timely communication by MLD experts with identified families, treating early-onset MLD with gene therapy and late-onset MLD with HSCT, as well as pre-treatment monitoring schemes. Specific knowledge gaps were identified, urging prioritized research for future evidence-based guidelines.

DISCUSSION

Consensus-based recommendations for NBS in MLD will enhance harmonized management and facilitate integration in national screening programs. Structured data collection and monitoring of screening programs are crucial for evidence generation and future guideline development. Involving patient representatives in the development of recommendations seems essential for NBS programs.

Impact on physical, social, and family functioning of patients with metachromatic leukodystrophy and their family members in Japan: A qualitative study

Metachromatic leukodystrophy is a rare autosomal recessive disease. There are three forms of this disease, all of which result in cognitive and motor dysfunctions. Although enzyme replacement and gene therapies have been developed, they are not expected to be effective in patients with advanced diseases. Therefore, it is important to focus on treatment effects and patients' quality of life; however, qualitative findings on the experiences of patients and their families have not been adequately reported. Interviews were conducted with the family members of patients with metachromatic leukodystrophy in Japan. Verbatim transcripts were analyzed using a qualitative content analysis approach. We interviewed the mothers of five patients. Verbatim interview transcripts were classified into 81 codes. The codes were then aggregated into 15 categories and 3 themes: challenges of life for the patients, challenges in the healthcare system, and challenges of family function. Disease progression greatly affects patients' lives. Moreover, social systems supporting patients and their families are inadequate, especially as the disease progresses. Family members face life restrictions and role changes because of the patient's diagnosis. Patients with metachromatic leukodystrophy and their families require comprehensive support.

The burden of disease in metachromatic leukodystrophy: results of a caregiver survey in the UK and Republic of Ireland

BACKGROUND

Metachromatic Leukodystrophy (MLD) is a rare, autosomal recessive lysosomal storage disease characterised by the progressive loss of motor function and severe decline in cognitive function. Limited information is available on the burden MLD places on patients and their families and the medical and social support these patients need. Three UK-based MLD patient organisations commissioned an online survey, and follow-up semi-structured interviews to describe and quantify these burdens across MLD subtypes, stage of disease (including end of life) and treatment status (untreated, gene therapy or hematopoietic stem cell transplant [HSCT]).

RESULTS

A total of 24 patients were included in the study: thirteen late infantile (LI), six early juvenile (EJ), two late juvenile (LJ) and three adult onset (AO). Six patients had received gene therapy and one had received an HSCT. MLD patients receiving no disease modifying treatment bore a high symptom burden: 94% were wheelchair dependent, 88% required tube feeding, 88% were incontinent, 82% had lost their speech and all the children were either unable to attend education or needed specialist provision. Patients were reliant on numerous medical interventions and assistive equipment. All early-onset patients (LI and EJ) were wheelchair dependent, and tube fed, with all EJ patients having lost all speech. The caregiving responsibilities of parents impacted their employment, finances, relationships and health. Patients treated with gene therapy or HSCT were more mobile and were able to eat normally and two thirds of the children were able to attend mainstream school.

CONCLUSIONS

The impact of illness that patients and their caregivers faced was extensive, and the level of care, amount of medication, number of hospital visits and educational support required were substantial. Financial constraints often brought about by inability to work also placed considerable strain on families. The study increases understanding of the burden of MLD on patients and their families, and the level of unmet need in the treatment of the disease.

A systematic review on the birth prevalence of metachromatic leukodystrophy

BACKGROUND

Metachromatic leukodystrophy (MLD) is an autosomal recessive lysosomal storage disease caused by deficiency in arylsulfatase A (ASA) activity arising primarily from ASA gene (ARSA) variants. Late-infantile, juvenile and adult clinical subtypes are defined by symptom onset at ≤ 2.5, > 2.5 to < 16 and ≥ 16 years, respectively. Epidemiological data were sought to address knowledge gaps and to inform decisions regarding the clinical development of an investigational drug.

METHODS

To synthesize all available estimates of MLD incidence and birth prevalence worldwide and in selected countries, Ovid MEDLINE and Embase were searched systematically (March 11, 2022) using a population, intervention, comparator, outcome, time and setting framework, complemented by pragmatic searching to reduce publication bias. Where possible, results were stratified by clinical subtype. Data were extracted from non-interventional studies (clinical trials, non-clinical studies and case reports were excluded; reviews were used for snowballing only).

RESULTS

Of the 31 studies included, 14 reported birth prevalence (13 countries in Asia-Pacific, Europe, the Middle East, North America and South America), one reported prevalence and none reported incidence. Birth prevalence per 100,000 live births ranged from 0.16 (Japan) to 1.85 (Portugal). In the three European studies with estimates stratified by clinical subtypes, birth prevalence was highest for late-infantile cases (0.31-1.12 per 100,000 live births). The distribution of clinical subtypes reported in cases diagnosed over various time periods in 17 studies varied substantially, but late-infantile and juvenile MLD accounted for at least two-thirds of cases in most studies.

CONCLUSIONS

This review provides a foundation for further analysis of the regional epidemiology of MLD. Data gaps indicate the need for better global coverage, increased use of epidemiological measures (e.g. prevalence estimates) and more stratification of outcomes by clinical and genetic disease subtype.

Effects of sulfatide on peripheral nerves in metachromatic leukodystrophy

OBJECTIVE

To evaluate the longitudinal correlations between sulfatide/lysosulfatide levels and central and peripheral nervous system function in children with metachromatic leukodystrophy (MLD) and to explore the impact of intravenous recombinant human arylsulfatase A (rhASA) treatment on myelin turnover.

METHODS

A Phase 1/2 study of intravenous rhASA investigated cerebrospinal fluid (CSF) and sural nerve sulfatide levels, 88-item Gross Motor Function Measure (GMFM-88) total score, sensory and motor nerve conduction, brain N-acetylaspartate (NAA) levels, and sural nerve histology in 13 children with MLD. Myelinated and unmyelinated nerves from an untreated MLD mouse model were also analyzed.

RESULTS

CSF sulfatide levels correlated with neither Z-scores for GMFM-88 nor brain NAA levels; however, CSF sulfatide levels correlated negatively with Z-scores of nerve conduction parameters, number of large (≥7 μm) myelinated fibers, and myelin/fiber diameter slope, and positively with nerve g-ratios and cortical latencies of somatosensory-evoked potentials. Quantity of endoneural litter positively correlated with sural nerve sulfatide/lysosulfatide levels. CSF sulfatide levels decreased with continuous high-dose treatment; this change correlated with improved nerve conduction. At 26 weeks after treatment, nerve g-ratio decreased by 2%, and inclusion bodies per Schwann cell unit increased by 55%. In mice, abnormal sulfatide storage was observed in non-myelinating Schwann cells in Remak bundles of sciatic nerves but not in unmyelinated urethral nerves.

INTERPRETATION

Lower sulfatide levels in the CSF and peripheral nerves correlate with better peripheral nerve function in children with MLD; intravenous rhASA treatment may reduce CSF sulfatide levels and enhance sulfatide/lysosulfatide processing and remyelination in peripheral nerves.

Utilizing hiPSC-derived oligodendrocytes to study myelin pathophysiology in neuropsychiatric and neurodegenerative disorders

Oligodendrocytes play a crucial role in our central nervous system (CNS) by myelinating axons for faster action potential conduction, protecting axons from degeneration, structuring the position of ion channels, and providing nutrients to neurons. Oligodendrocyte dysfunction and/or dysmyelination can contribute to a range of neurodegenerative diseases and neuropsychiatric disorders such as Multiple Sclerosis (MS), Leukodystrophy (LD), Schizophrenia (SCZ), and Autism Spectrum Disorder (ASD). Common characteristics identified across these disorders were either an inability of oligodendrocytes to remyelinate after degeneration or defects in oligodendrocyte development and maturation. Unfortunately, the causal mechanisms of oligodendrocyte dysfunction are still uncertain, and therapeutic targets remain elusive. Many studies rely on the use of animal models to identify the molecular and cellular mechanisms behind these disorders, however, such studies face species-specific challenges and therefore lack translatability. The use of human induced pluripotent stem cells (hiPSCs) to model neurological diseases is becoming a powerful new tool, improving our understanding of pathophysiology and capacity to explore therapeutic targets. Here, we focus on the application of hiPSC-derived oligodendrocyte model systems to model disorders caused by oligodendrocyte dysregulation.

Progress in leukodystrophies with zebrafish

Inherited leukodystrophies are genetic disorders characterized by abnormal white matter in the central nervous system. Although individually rare, there are more than 400 distinct types of leukodystrophies with a cumulative incidence of 1 in 4500 live births. The pathophysiology of most leukodystrophies is poorly understood, there are treatments for only a few, and there is significant morbidity and mortality, suggesting a critical need for improvements in this field. A variety of animal, cell, and induced pluripotent stem cell-derived models have been developed for leukodystrophies, but with significant limitations in all models. Many leukodystrophies lack animal models, and extant models often show no or mixed recapitulation of key phenotypes. Zebrafish (Danio rerio) have become increasingly used as disease models for studying leukodystrophies due to their early onset of disease phenotypes and conservation of molecular and neurobiological mechanisms. Here, we focus on reviewing new zebrafish disease models for leukodystrophy or models with recent progress. This includes discussion of leukodystrophy with vanishing white matter disease, X-linked adrenoleukodystrophy, Zellweger spectrum disorders and peroxisomal disorders, PSAP deficiency, metachromatic leukodystrophy, Krabbe disease, hypomyelinating leukodystrophy-8/4H leukodystrophy, Aicardi-Goutières syndrome, RNASET2-deficient cystic leukoencephalopathy, hereditary diffuse leukoencephalopathy with spheroids-1 (CSF1R-related leukoencephalopathy), and ultra-rare leukodystrophies. Zebrafish models offer important potentials for the leukodystrophy field, including testing of new variants in known genes; establishing causation of newly discovered genes; and early lead compound identification for therapies. There are also unrealized opportunities to use humanized zebrafish models which have been sparsely explored.

Identification and structural characterization of a pathogenic ARSA missense variant in two consanguineous families from Jammu and Kashmir (India) with late infantile metachromatic leukodystrophy

BACKGROUND

Metachromatic leukodystrophy (MLD) is a rare lysosomal storage disorder caused by a deficiency of Arylsulfatase A (ARSA) enzyme activity. Its clinical manifestations include progressive motor and cognitive decline. ARSA gene mutations are frequent in MLD.

METHODS AND RESULTS

In the present study, whole exome sequencing (WES) was employed to decipher the genetic cause of motor and cognitive decline in proband's of two consanguineous families from J&K (India). Clinical investigations using radiological and biochemical analysis revealed MLD-like features. WES confirmed a pathogenic variant in the ARSA gene. Molecular simulation dynamics was applied for structural characterization of the variant.

CONCLUSION

We report the identification of a pathogenic missense variant (c.1174 C > T; p.Arg390Trp) in the ARSA gene in two cases of late infantile MLD from consanguineous families in Jammu and Kashmir, India. Our study utilized genetic analysis and molecular dynamics simulations to identify and investigate the structural consequences of this mutation. The molecular dynamics simulations revealed significant alterations in the structural dynamics, residue interactions, and stability of the ARSA protein harbouring the p.Arg390Trp mutation. These findings provide valuable insights into the molecular mechanisms underlying the pathogenicity of this variant in MLD.

Branched-chain keto acids promote an immune-suppressive and neurodegenerative microenvironment in leptomeningeal disease

Leptomeningeal disease (LMD) occurs when tumors seed into the leptomeningeal space and cerebrospinal fluid (CSF), leading to severe neurological deterioration and poor survival outcomes. We utilized comprehensive multi-omics analyses of CSF from patients with lymphoma LMD to demonstrate an immunosuppressive cellular microenvironment and identified dysregulations in proteins and lipids indicating neurodegenerative processes. Strikingly, we found a significant accumulation of toxic branched-chain keto acids (BCKA) in the CSF of patients with LMD. The BCKA accumulation was found to be a pan-cancer occurrence, evident in lymphoma, breast cancer, and melanoma LMD patients. Functionally, BCKA disrupted the viability and function of endogenous T lymphocytes, chimeric antigen receptor (CAR) T cells, neurons, and meningeal cells. Treatment of LMD mice with BCKA-reducing sodium phenylbutyrate significantly improved neurological function, survival outcomes, and efficacy of anti-CD19 CAR T cell therapy. This is the first report of BCKA accumulation in LMD and provides preclinical evidence that targeting these toxic metabolites improves outcomes.

Identification of a Novel ARSA Gene Mutation Through High-Throughput Molecular Diagnosis Method in Two Girls with Late Infantile Metachromatic Leukodystrophy

Metachromatic leukodystrophy (MLD) is a rare leukoencephalopathy caused by pathogenic mutations in the ARSA gene. It manifests as severe motor symptoms, mental problems, and sometimes, seizures. We aimed to investigate the phenotypic manifestations and genetic causes of MLD in an Iranian family. We present the case of a 3-year-old girl who presented with hypotonia, muscular atrophy, and seizures. Neurological and neuromuscular examinations were performed to evaluate clinical characteristics. Whole exome sequencing (WES) was used to detect disease-causing variants. In silico analysis was performed to predict the pathogenicity of this variant. GROMACS software was utilized for molecular dynamic simulation (MDS). Neurological studies revealed marked slowing of motor conduction velocities and an increased motor unit action potential duration. Brain MRI scan revealed white matter abnormalities. By applying WES, we identified a novel homozygous missense variant (NM_000487.6, c.938G > C, p.R313P) in ARSA. Direct sequencing identified this homozygous variant in her asymptomatic younger sister, whereas both parents carried a heterozygous variant. This mutation has not been reported in genetic databases or in literature. In silico analysis predicted that any variation in this DNA position would cause disease, as it is highly conserved. The c.938G > C variant was classified as a pathogenic variant according to ACMG/AMP guidelines. MDS analysis indicated that c.938G > C had a significant impact on both the structure and stabilization of ARSA, ultimately resulting in impaired protein function. The identification of this variant expands the spectrum of ARSA gene mutations associated with MLD and highlights the importance of genetic testing for the diagnosis of MLD.

Study of lncRNAs in Pediatric Neurological Diseases: Methods, Analysis of the State-of-Art and Possible Therapeutic Implications

Long non-coding RNAs (lncRNAs) have emerged as crucial regulators in various cellular processes, and their roles in pediatric neurological diseases are increasingly being explored. This review provides an overview of lncRNA implications in the central nervous system, both in its physiological state and when a pathological condition is present. We describe the role of lncRNAs in neural development, highlighting their significance in processes such as neural stem cell proliferation, differentiation, and synaptogenesis. Dysregulation of specific lncRNAs is associated with multiple pediatric neurological diseases, such as neurodevelopmental or neurodegenerative disorders and brain tumors. The collected evidence indicates that there is a need for further research to uncover the full spectrum of lncRNA involvement in pediatric neurological diseases and brain tumors. While challenges exist, ongoing advancements in technology and our understanding of lncRNA biology offer hope for future breakthroughs in the field of pediatric neurology, leveraging lncRNAs as potential therapeutic targets and biomarkers.

Gene therapy for neurodegenerative disorders in children: dreams and realities

Gene therapy encompasses the administration of biological medicinal products containing recombinant nucleic acids, mainly DNA, with the aim of treating or curing diseases. This represents a unique therapeutic strategy to reach the brain, in order to prevent or halt a neurodegenerative process. During the past decade, active multidisciplinary research has started to solve many issues for gene therapy in neurodegenerative disorders in terms of vectors, modes of administration, and expression of the therapeutic DNA. The engineering of hematopoietic stem cells (HSC) with lentivirus vectors for ex vivo gene therapy has demonstrated efficiency in reaching the brain through their transformation into microglial/macrophages cells with a long-term gene expression of the therapeutic vector as an alternative to autologous HSC transplants. Two drugs based on this strategy have been approved to date. The first is for metachromatic leukodystrophy (MLD), a severe lysosomal storage disease, and provides high levels of the deficient enzyme; the second one is for cerebral forms of X-linked adrenoleukodystrophy (X-ALD), and works by halting the neuroinflammation process. However, due to the long-lasting effect of the procedure, the therapy is applicable only to pre- or pauci/oligo-symptomatic patients. In vivo gene therapy via direct injection into the brain or the cerebrospinal fluid, but also by intravenous injection, represents a more efficient approach; however, many challenges remain to be solved despite the approval of two drugs: one for the early infantile form of spinal muscular atrophy (SMA), in which the gene product injected intravenously is able to prevent spinal motoneuron neurodegeneration. The second one, for aromatic L-amino acid decarboxylase (AADC) deficiency, provides the defective enzyme to the basal ganglia via intraparenchymal injection. The production of vectors able to reach the brain target cells with a sufficiently high expression remains a major bottleneck. In parallel, efforts must continue in order to better define (i) the natural history and clinical outcomes of many neurodegenerative disorders with childhood onset, and (ii) the mechanisms involved in the neurodegenerative process. © 2023 Published by Elsevier Masson SAS on behalf of French Society of Pediatrics.

Insight into adult-onset metachromatic leukodystrophy with optic atrophy: A comprehensive case report

This abstract provides an overview of metachromatic leukodystrophy (MLD), an autosomal recessive disorder stemming from arylsulfatase A deficiency. MLD leads to cerebroside sulfate accumulation, causing central and peripheral demyelination. Clinical manifestations vary by age group: late-infantile (rapid progression), juvenile (slower progression), and adult-onset (psychiatric symptoms). A case study details a 23-year-old with progressive vision impairment, motor weakness, and cognitive changes. Examination and MRI findings led to suspicion of MLD, later confirmed by enzyme testing. Optic nerve involvement is emphasized, along with diagnostic criteria involving enzyme assays, imaging, and urinary sulfatide excretion tests. While no cure exists, symptomatic and supportive care, including hematopoietic stem cell transplantation, remains key in MLD management.

Chronic Inflammatory Demyelinating Polyneuropathy With Reversible Severe Cognitive Impairment and Gastrointestinal Dysfunction

We treated a patient with an unusual case of reversible rapidly progressive cognitive impairment, gastrointestinal dysfunction, and generalized neuromyopathy in chronic inflammatory demyelinating polyneuropathy (CIDP) with optic neuropathy. A man in his 50s presented with a four-month history of rapidly progressive cognitive decline in addition to a six-month history of proximal greater than distal painful muscle weakness, wasting in all extremities, almost complete loss of deep tendon reflexes in his lower extremities, and slow progressive vision loss. Additionally, he had a 90-pound weight loss over the past two years with loss of appetite and ongoing chronic diarrhea. The exam showed muscle weakness and wasting with absent deep tendon reflexes. Initial Saint Louis University Mental Status (SLUMS) exam score was 16/30. Visual acuity was 20/25 with full extraocular movements; optical coherence tomography revealed superior arcuate bundle thinning bilaterally. Gastrointestinal workup proved nonrevealing. Serologic studies for vitamin deficiencies, heavy metals, and autoantibodies were negative. Whipple, Giardia lamblia, and Campylobacter jejuni stool testing were negative. Imaging studies were unremarkable. Nerve conduction studies showed demyelinating sensorimotor peripheral neuropathy. Muscle biopsy was indicative of denervation with scattered myopathic changes; no evidence of inflammatory myopathy nor glycogen or mitochondrial abnormalities was seen. Intravenous immunoglobulin treatment was begun. The patient was started at a dose of 0.75g/kg every three weeks. Following good but incomplete clinical improvement after the first treatment, his dose was increased to 1g/kg every three weeks. He improved remarkably after four months of infusions, scoring 30/30 on SLUMS with a full return of muscle strength and reflexes. Diarrhea remitted. Visual acuity and conduction delay remained unchanged. Symptom timing and dramatic response to immunoglobulins suggest a common immunological mechanism. In light of extensive differential investigations, unremarkable imaging and serology, and no other systemic disease processes, this case plausibly represents a potential new CIDP phenotypic variant.

Inborn Errors of Metabolism with Ataxia: Current and Future Treatment Options

A number of hereditary ataxias are caused by inborn errors of metabolism (IEM), most of which are highly heterogeneous in their clinical presentation. Prompt diagnosis is important because disease-specific therapies may be available. In this review, we offer a comprehensive overview of metabolic ataxias summarized by disease, highlighting novel clinical trials and emerging therapies with a particular emphasis on first-in-human gene therapies. We present disease-specific treatments if they exist and review the current evidence for symptomatic treatments of these highly heterogeneous diseases (where cerebellar ataxia is part of their phenotype) that aim to improve the disease burden and enhance quality of life. In general, a multimodal and holistic approach to the treatment of cerebellar ataxia, irrespective of etiology, is necessary to offer the best medical care. Physical therapy and speech and occupational therapy are obligatory. Genetic counseling is essential for making informed decisions about family planning.

Advances in therapies for neurological lysosomal storage disorders

Lysosomal Storage Disorders (LSDs) are a diverse group of inherited, monogenic diseases caused by functional defects in specific lysosomal proteins. The lysosome is a cellular organelle that plays a critical role in catabolism of waste products and recycling of macromolecules in the body. Disruption to the normal function of the lysosome can result in the toxic accumulation of storage products, often leading to irreparable cellular damage and organ dysfunction followed by premature death. The majority of LSDs have no curative treatment, with many clinical subtypes presenting in early infancy and childhood. Over two-thirds of LSDs present with progressive neurodegeneration, often in combination with other debilitating peripheral symptoms. Consequently, there is a pressing unmet clinical need to develop new therapeutic interventions to treat these conditions. The blood-brain barrier is a crucial hurdle that needs to be overcome in order to effectively treat the central nervous system (CNS), adding considerable complexity to therapeutic design and delivery. Enzyme replacement therapy (ERT) treatments aimed at either direct injection into the brain, or using blood-brain barrier constructs are discussed, alongside more conventional substrate reduction and other drug-related therapies. Other promising strategies developed in recent years, include gene therapy technologies specifically tailored for more effectively targeting treatment to the CNS. Here, we discuss the most recent advances in CNS-targeted treatments for neurological LSDs with a particular emphasis on gene therapy-based modalities, such as Adeno-Associated Virus and haematopoietic stem cell gene therapy approaches that encouragingly, at the time of writing are being evaluated in LSD clinical trials in increasing numbers. If safety, efficacy and improved quality of life can be demonstrated, these therapies have the potential to be the new standard of care treatments for LSD patients.

A retrospective cohort study of Libmeldy (atidarsagene autotemcel) for MLD: What we have accomplished and what opportunities lie ahead

Metachromatic leukodystrophy (MLD) results from ARSA gene mutations. Affected individuals meet early milestones before neurological deterioration and early death. Atidarsagene autotemcel (arsa-cel), an autologous haematopoietic stem cell gene therapy (HSC-GT) product, has demonstrated sustained clinical benefits in MLD. Arsa-cel was approved for NHS treatment in February 2022 for asymptomatic late infantile or early juvenile disease, or early symptomatic early juvenile MLD. We evaluate the impact of this approval in the largest real-world dataset of MLD HSC-GT. Hospital records were reviewed for all patients referred for NHS treatment following arsa-cel approval. Information was gathered about disease phenotype, presentation, eligibility, and affected siblings. In the year following NHS approval, 17 UK MLD patients were referred for treatment. Four patients met eligibility criteria and have been treated, including 1 infant who weighed 5 kg at leukapheresis. Eleven patients failed screening: 10 symptomatic patients with late infantile disease and 1 with early juvenile disease and cognitive decline. Two further patients with later onset subtypes did not meet the approval criteria. Three out of four treated patients were diagnosed by screening after MLD was diagnosed in a symptomatic older sibling. The success of HSC-GT for MLD has heralded a new era of hope for families affected by this devastating disease, yet currently, most patients are ineligible for treatment at diagnosis. The feasibility of apheresis in infants and the availability of a licenced, effective HSC-GT product highlights the urgent need for newborn screening to ensure that patients can be diagnosed and treated before symptom onset.

Olaparib Attenuates Demyelination and Neuroinflammation in an Organotypic Slice Culture Model of Metachromatic Leukodystrophy

Metachromatic leukodystrophy (MLD) is a severe demyelinating, autosomal recessive genetic leukodystrophy. The disease is underpinned by mutations in the arylsulfatase A gene (ARSA), resulting in deficient activity of the arylsulfatase A lysosomal enzyme and consequential accumulation of galactosylceramide-3-O-sulfate (sulfatide) in the brain. Using an ex vivo murine-derived organotypic cerebellar slice culture model, we demonstrate that sulfatide induces demyelination in a concentration-dependent manner. Interestingly, our novel data demonstrate that sulfatide-induced demyelination is underpinned by PARP-1 activation, oligodendrocyte loss, pro-inflammatory cytokine expression, astrogliosis, and microgliosis. Moreover, such sulfatide-induced effects can be attenuated by the treatment with the poly (ADP-ribose) polymerase 1 (PARP-1) inhibitor Olaparib (IC50∼100 nM) suggesting that this small molecule may be neuroprotective and limit toxin-induced demyelination. Our data support the idea that sulfatide is a key driver of demyelination and neuroinflammation in MLD and suggest that PARP-1 inhibitors have therapeutic utility in the sphere of rare demyelinating disease.

Predicting disease severity in metachromatic leukodystrophy using protein activity and a patient phenotype matrix

BACKGROUND

Metachromatic leukodystrophy (MLD) is a lysosomal storage disorder caused by mutations in the arylsulfatase A gene (ARSA) and categorized into three subtypes according to age of onset. The functional effect of most ARSA mutants remains unknown; better understanding of the genotype-phenotype relationship is required to support newborn screening (NBS) and guide treatment.

RESULTS

We collected a patient data set from the literature that relates disease severity to ARSA genotype in 489 individuals with MLD. Patient-based data were used to develop a phenotype matrix that predicts MLD phenotype given ARSA alleles in a patient's genotype with 76% accuracy. We then employed a high-throughput enzyme activity assay using mass spectrometry to explore the function of ARSA variants from the curated patient data set and the Genome Aggregation Database (gnomAD). We observed evidence that 36% of variants of unknown significance (VUS) in ARSA may be pathogenic. By classifying functional effects for 251 VUS from gnomAD, we reduced the incidence of genotypes of unknown significance (GUS) by over 98.5% in the overall population.

CONCLUSIONS

These results provide an additional tool for clinicians to anticipate the disease course in MLD patients, identifying individuals at high risk of severe disease to support treatment access. Our results suggest that more than 1 in 3 VUS in ARSA may be pathogenic. We show that combining genetic and biochemical information increases diagnostic yield. Our strategy may apply to other recessive diseases, providing a tool to address the challenge of interpreting VUS within genotype-phenotype relationships and NBS.

Evaluating meaningful changes in physical functioning and cognitive declines in metachromatic leukodystrophy: a caregiver interview study

BACKGROUND

Metachromatic leukodystrophy (MLD) is a rare lysosomal storage disease caused by deficient activity of arylsulfatase A (ASA). Treatment options for patients are limited; gene therapy based on haematopoietic stem cell transplantation is the only approved treatment for some subtypes of MLD. Any therapeutic benefit of treatments must be meaningful for patients and their families. We evaluated the clinical meaningfulness of slowing the decline in gross motor function as measured by the Gross Motor Function Classification in MLD (GMFC-MLD) from the caregiver perspective via semi-structured telephone interviews with caregivers of children with late-infantile MLD. We also evaluated the perceived significance of declines in communication abilities measured by the Expressive Language Function Classification in MLD (ELFC-MLD). This work could help to inform the endpoints of a phase 2 clinical trial (NCT03771898) assessing the efficacy of intrathecal recombinant human ASA in MLD.

RESULTS

Twelve caregivers were recruited, reporting on 12 children with MLD. Children had a mean age of 6.1 years; mean age at symptom onset was 17.6 months. Most children (10/12) progressed from walking without support (categories 0-1) to a loss of locomotion (categories 5-6) in ≤ 2 years. Caregivers felt that GMFC-MLD and ELFC-MLD accurately described motor and language declines in their children, respectively. Most caregivers (10/12) reported that the idea of delaying disease progression would be meaningful. Further, a slowing of motor function decline in GMFC-MLD, from category 1 to category 3 or from category 2 to category 4 over 2 years, was seen as meaningful by all caregivers asked; however, only 3/12 caregivers reported that delayed decline would be meaningful if baseline category was ≥ 3. Caregivers also reported that delaying expressive language decline at any level that did not indicate a complete loss of expressive language (indicated by categories 1-3) would be meaningful.

CONCLUSIONS

Caregivers of children with MLD felt that a delayed decline in gross motor function, as assessed by the GMFC-MLD, would be meaningful, supporting the selection of primary and secondary endpoints for the phase 2 clinical trial. Communication abilities were another area of significance for consideration in future clinical trial design.

Neurodegenerative disease after hematopoietic stem cell transplantation in metachromatic leukodystrophy

OBJECTIVE

Metachromatic leukodystrophy is a lysosomal storage disease caused by deficient arylsulfatase A. It is characterized by progressive demyelination and thus mainly affects the white matter. Hematopoietic stem cell transplantation may stabilize and improve white matter damage, yet some patients deteriorate despite successfully treated leukodystrophy. We hypothesized that post-treatment decline in metachromatic leukodystrophy might be caused by gray matter pathology.

METHODS

Three metachromatic leukodystrophy patients treated with hematopoietic stem cell transplantation with a progressive clinical course despite stable white matter pathology were clinically and radiologically analyzed. Longitudinal volumetric MRI was used to quantify atrophy. We also examined histopathology in three other patients deceased after treatment and compared them with six untreated patients.

RESULTS

The three clinically progressive patients developed cognitive and motor deterioration after transplantation, despite stable mild white matter abnormalities on MRI. Volumetric MRI identified cerebral and thalamus atrophy in these patients, and cerebellar atrophy in two. Histopathology showed that in brain tissue of transplanted patients, arylsulfatase A expressing macrophages were clearly present in the white matter, but absent in the cortex. Arylsulfatase A expression within patient thalamic neurons was lower than in controls, the same was found in transplanted patients.

INTERPRETATION

Neurological deterioration may occur after hematopoietic stem cell transplantation in metachromatic leukodystrophy despite successfully treated leukodystrophy. MRI shows gray matter atrophy, and histological data demonstrate absence of donor cells in gray matter structures. These findings point to a clinically relevant gray matter component of metachromatic leukodystrophy, which does not seem sufficiently affected by transplantation.

An in silico approach to identify early damage biomarker candidates in metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is a rare, autosomal recessive lysosomal storage disease. Deficient activity of arylsulfatase A causes sulfatides to accumulate in cells of different tissues, including those in the central and peripheral nervous systems, leading to progressive demyelination and neurodegeneration. Although there is some association between specific arylsulfatase A alleles and disease severity, genotype-phenotype correlations are not fully understood. We aimed to identify biomarker candidates of early tissue damage in MLD using a modeling approach based on systems biology. A review of the literature was performed in an initial disease characterization step, allowing identification of pathophysiological processes involved in MLD and proteins relating to these processes. Three mathematical models were generated to simulate different stages of MLD at the molecular level: an early pro-inflammatory stage model (including only processes considered to be active in the early stages of disease), a pre-demyelination stage model (including additional processes that are active after some disease progression), and a demyelination stage model (in which all pathophysiological processes are active). The models evaluated 3457 proteins of interest, individually and by pairs through data mining techniques, applying five filters to prioritize biomarkers that could differentiate between the models. Sixteen potential biomarkers were identified, including effectors relating to mitochondrial dysfunction, remyelination, and neurodegeneration. The findings were corroborated in a gene expression data set from T lymphocytes of patients with MLD; all candidates formed combinations that were able to distinguish patients with MLD from controls, and all but one candidate distinguished late-infantile MLD from juvenile MLD as part of a combinatorial biomarker pair. In particular, pro-neuregulin-1 appeared as differential on all comparisons (patients with MLD vs controls and within clinical subtypes); casein kinase II subunit alpha was detected as a potential individual marker within clinical subtypes. These findings provide a panel of biomarker candidates suitable for experimental validation and highlight the utility of mathematical models to identify biomarker candidates of early tissue damage in MLD with a high degree of accuracy and sensitivity.

Preserving Ambulation in a Gene Therapy-Treated Girl Affected by Metachromatic Leukodystrophy: A Case Report

(1) Background: Atidarsagene autotemcel is a hematopoietic stem and progenitor cell gene therapy (HSPC-GT) approved to treat early-onset metachromatic leukodystrophy (MLD). The purpose of this case report is to describe the long-term management of residual gait impairment of a child with late infantile MLD treated with HSPC-GT. (2) Methods: Assessment included Gross Motor Function Measure-88, nerve conduction study, body mass index (BMI), Modified Tardieu Scale, passive range of motion, modified Medical Research Council scale, and gait analysis. Interventions included orthoses, a walker, orthopedic surgery, physiotherapy, and botulinum. (3) Results: Orthoses and a walker were fundamental to maintaining ambulation. Orthopedic surgery positively influenced gait by reducing equinovarus. Nonetheless, unilateral recurrence of varo-supination was observed, attributable to spasticity and muscle imbalance. Botulinum improved foot alignment but induced transient overall weakness. A significant increase in BMI occurred. Finally, a shift to bilateral valgopronation was observed, more easily managed with orthoses. (4) Conclusions: HSPC-GT preserved survival and locomotor abilities. Rehabilitation was then considered fundamental as a complementary treatment. Muscle imbalance and increased BMI contributed to gait deterioration in the growing phase. Caution is recommended when considering botulinum in similar subjects, as the risk of inducing overall weakness can outweigh the benefits of spasticity reduction.

Novel in-frame duplication variant characterization in late infantile metachromatic leukodystrophy using whole-exome sequencing and molecular dynamics simulation

Metachromatic leukodystrophy (MLD) is a neurodegenerative lysosomal storage disease caused by a deficiency in the arylsulfatase A (ARSA). ARSA deficiency leads to sulfatide accumulation, which involves progressive demyelination. The profound impact of early diagnosis on MLD treatment options necessitates the development of new or updated analysis tools and approaches. In this study, to identify the genetic etiology in a proband from a consanguineous family with MLD presentation and low ARSA activity, we employed Whole-Exome Sequencing (WES) followed by co-segregation analysis using Sanger sequencing. Also, MD simulation was utilized to study how the variant alters the structural behavior and function of the ARSA protein. GROMACS was applied and the data was analyzed by RMSD, RMSF, Rg, SASA, HB, atomic distance, PCA, and FEL. Variant interpretation was done based on the American College of Medical Genetics and Genomics (ACMG) guidelines. WES results showed a novel homozygous insertion mutation, c.109_126dup (p.Asp37_Gly42dup), in the ARSA gene. This variant is located in the first exon of ARSA, fulfilling the criteria of being categorized as likely pathogenic, according to the ACMG guidelines and it was also found to be co-segregating in the family. The MD simulation analysis revealed this mutation influenced the structure and the stabilization of ARSA and led to the protein function impairment. Here, we report a useful application of WES and MD to identify the causes of a neurometabolic disorder.

Childhood Dementia: A Collective Clinical Approach to Advance Therapeutic Development and Care

Childhood dementias are a group of over 100 rare and ultra-rare pediatric conditions that are clinically characterized by chronic global neurocognitive decline. This decline is associated with a progressive loss of skills and shortened life expectancy. With an estimated incidence of one in 2800 births and less than 5% of the conditions having disease-modifying therapies, the impact is profound for patients and their families. Traditional research, care, and advocacy efforts have focused on individual disorders, or groups classified by molecular pathogenesis, and this has established robust foundations for further progress and collaboration. This review describes the shared and disease-specific clinical changes contributing to childhood dementia and considers these as potential indicators of underlying pathophysiologic processes. Like adult neurodegenerative syndromes, the heterogeneous phenotypes extend beyond cognitive decline and may involve changes in eating, motor function, pain, sleep, and behavior, mediated by physiological changes in neural networks. Importantly, these physiological phenotypes are associated with significant carer stress, anxiety, and challenges in care. These phenotypes are also pertinent for the development of therapeutics and optimization of best practice management. A collective approach to childhood dementia is anticipated to identify relevant biomarkers of prognosis or therapeutic efficacy, streamline the path from preclinical studies to clinical trials, increase opportunities for the development of multiple therapeutics, and refine clinical care.

Lysosomal storage disorders: Clinical and therapeutic aspects

The lysosomal storage disorders are hereditary metabolic disorders characterized by autosomal recessive inheritance, mainly caused by deficiency of an enzyme responsible for the intra-lysosomal breakdown of various substrates and products of cellular metabolism. This chapter examines the underlying defects, clinical manifestations, and provides context for the expected clinical outcome of various available therapy options employing enzyme replacement therapy, hematopoietic stem cell transplantation, substrate reduction, and enzyme enhancement therapies.

Ataxia in Neurometabolic Disorders

Ataxia is a movement disorder that manifests during the execution of purposeful movements. It results from damage to the structures of the cerebellum and its connections or the posterior cords of the spinal cord. It should be noted that, in addition to occurring as part of many diseases, pediatric ataxia is a common symptom in neurometabolic diseases. To date, there are more than 150 inherited metabolic disorders that can manifest as ataxia in children. Neuroimaging studies (magnetic resonance imaging of the head and spinal cord) are essential in the diagnosis of ataxia, and genetic studies are performed when metabolic diseases are suspected. It is important to remember that most of these disorders are progressive if left untreated. Therefore, it is crucial to include neurometabolic disorders in the differential diagnosis of ataxia, so that an early diagnosis can be made. Initiating prompt treatment influences positive neurodevelopmental outcomes.

Towards sustainability and affordability of expensive cell and gene therapies? Applying a cost-based pricing model to estimate prices for Libmeldy and Zolgensma

BACKGROUND AIMS

Drug prices are regarded as one of the most influential factors in determining accessibility and affordability to novel therapies. Cell and gene therapies such as OTL-200 (brand name: Libmeldy) and AVXS-101 (brand name: Zolgensma) with (expected) list prices of 3.0 million EUR and 1.9 million EUR per treatment, respectively, spark a global debate on the affordability of such therapies. The aim of this study was to use a recently published cost-based pricing model to calculate prices for cell and gene therapies, with OTL-200 and AVXS-101 as case study examples.

METHODS

Using the pricing model proposed by Uyl-de Groot and Löwenberg, we estimated a price for both therapies. We searched the literature and online public sources to estimate (i) research and development (R&D) expenses adjusted for risk of failure and cost of capital, (ii) the eligible patient population and (iii) costs of drug manufacturing to calculate a base-case price for OTL-200 and AVXS-101. All model input parameters were varied in a stepwise, deterministic sensitivity analysis and scenario analyses to assess their impact on the calculated prices.

RESULTS

Prices for OTL-200 and AVXS-101 were estimated at 1 048 138 EUR and 380 444 EUR per treatment, respectively. In deterministic sensitivity analyses, varying R&D estimates had the greatest impact on the price for OTL-200, whereas for AVXS-101, changes in the profit margin changed the calculated price substantially. Highest prices in scenario analyses were achieved when assuming the lowest number of patients for OTL-200 and highest R&D expenses for AVXS-101. The lowest R&D expenses scenario resulted in lowest prices for either therapy.

CONCLUSIONS

Our results show that, using the proposed model, prices for both OTL-200 and AVXS-101 lie substantially below the currently (proposed) list prices for both therapies. Nevertheless, the uncertainty of the used model input parameters is considerable, which translates in a wide range of estimated prices. This is mainly because of a lack of transparency from pharmaceutical companies regarding R&D expenses and the costs of drug manufacturing. Simultaneously, the disease indications for both therapies remain heavily understudied in terms of their epidemiological profile. Despite the considerable variation in the estimated prices, our results may support the public debate on value-based and cost-based pricing models, and on "fair" drug prices in general.

Pearls & Oy-sters: Tumefactive Demyelinating Lesions With MOG Antibodies Preceding Late Infantile Metachromatic Leukodystrophy

The development of acute neurologic dysfunction associated with tumefactive demyelinating lesions and mild diffuse involvement of the corpus callosum has been described in children as a sentinel event that may allow diagnosis of juvenile metachromatic leukodystrophy (MLD) at an early and potentially treatable stage. We report a child who developed this clinico-radiologic pattern associated with myelin oligodendrocyte glycoprotein antibodies several months before the onset of progressive symptoms of late infantile MLD.

Recognizing early MRI signs (or their absence) is crucial in diagnosing metachromatic leukodystrophy

OBJECTIVES

Metachromatic leukodystrophy (MLD) has characteristic white matter (WM) changes on brain MRI, which often trigger biochemical and genetic confirmation of the diagnosis. In early or pre-symptomatic disease stages, these typical MRI changes might be absent, hampering early diagnosis. This study aims to describe the characteristics of MRI WM abnormalities at diagnosis, related to clinical presentation.

METHODS

We retrospectively reviewed brain MRIs of MLD patients followed in 2 centers at the time of diagnosis regarding MLD MRI score and presence of tigroid pattern. In addition, MLD subtype, symptom status, CNS/PNS phenotype, motor/cognitive/mixed phenotype, and the presence of CNS symptoms were evaluated.

RESULTS

We included 104 brain MRIs from patients with late-infantile (n = 43), early-juvenile (n = 24), late-juvenile (n = 20) and adult (n = 17) onset. Involvement of the corpus callosum was a characteristic early MRI sign and was present in 71% of the symptomatic late-infantile patients, 94% of the symptomatic early-juvenile patients and 100% of the symptomatic late-juvenile and adult patients. Symptomatic early-juvenile, late-juvenile and adult patients generally had WM abnormalities on MRI suggestive of MLD. By contrast, 47% of the early-symptomatic late-infantile patients had no or only mild WM abnormalities on MRI, even in the presence of CNS symptoms including pyramidal signs.

INTERPRETATION

Patients with late-infantile MLD may have no or only mild, nonspecific abnormalities at brain MRI, partly suggestive of 'delayed myelination', even with clear clinical symptoms. This may lead to significant diagnostic delay. Knowledge of these early MRI signs (or their absence) is important for fast diagnosis.

The importance of early diagnosis and views on newborn screening in metachromatic leukodystrophy: results of a Caregiver Survey in the UK and Republic of Ireland

Metachromatic Leukodystrophy (MLD) is a rare, autosomal recessive lysosomal storage disorder caused by a deficiency of the enzyme arylsulfatase A (ARSA). MLD causes progressive loss of motor function and severe decline in cognitive function, leading to premature death. Early diagnosis of MLD provides the opportunity to begin treatment before the disease progresses and causes severe disability. MLD is not currently included in newborn screening (NBS) in the UK.

This study consisted of an online survey, and follow-up semi-structured interviews open to MLD patients or caregivers, aged 18 years and over. The aims of the study were to understand the importance of early diagnosis and to establish the views of families and caregivers of patients with MLD on NBS.

A total of 24 patients took part in the survey, representing 20 families (two families had two children with MLD, one family had three children with MLD). Following on from the survey, six parents participated in the interviews. Our data showed diagnostic delay from first symptoms was between 0 and 3 years, with a median of 1 year (n = 18); during this time deterioration was rapid, especially in earlier onset MLD. In patients with late infantile MLD (n = 10), 50% were wheelchair dependent, 30% were unable to speak, and 50% were tube fed when a diagnosis of MLD was confirmed. In patients with early juvenile MLD (n = 5), over half used a wheelchair some of the time, had uncontrollable crying, and difficulty speaking (all 60%) before or at the time of diagnosis. A high degree of support was expressed for NBS among caregivers, 95% described it as very or extremely important and 86% believed detection of MLD at birth would have changed their child’s future. One parent expressed their gratitude for an early diagnosis as a result of familial MLD screening offered at birth and how it had changed their child’s future: “It did and it absolutely has I will be forever grateful for his early diagnosis thanks to his older sister.”

The rapid rate of deterioration in MLD makes it an essential candidate for NBS, particularly now the first gene therapy (Libmeldy™) has been approved by the European Medicines Agency. Libmeldy™ has also been recommended as a treatment option in England and Wales by the National Institute for Health and Care Excellence (NICE) and is being made available to patients in Scotland via the Scottish Medicines Consortium’s ultra-orphan pathway.

Case report: A compound heterozygous mutations in ARSA associated with adult-onset metachromatic leukodystrophy

Metachromatic Leukodystrophy (MLD) is a rare autosomal recessive disease, which is caused by mutations in the arylsulfatase A (ARSA) gene. The ARSA gene is located on chromosome 22q13, containing eight exons. According to the age of onset, MLD can be divided into late infantile type, juvenile type, and adult type. Adult MLD has an insidious onset after the age of 16 years. Additionally, intellectual as well as behavioral changes, such as memory deficits or emotional instability, are commonly the first presenting symptoms. There is a study that reported an adult-onset MLD manifested cognitive impairment progressively due to compound heterozygous mutations of NM_000487: c.[185_186dupCA], p.(Asp63GlnfsTer18), and NM_000487: c.[154G>T], p.(Gly172Cys), rs74315271 in the ARSA gene, finding that the c.[154G>T], p.(Gly172Cys) is a novel missense mutation. Brain magnetic resonance imaging (MRI) revealed symmetrical demyelination of white matter. The activity of ARSA enzymatic in leukocytes decreased. Nerve conduction studies displayed that evidence of polyneuropathy was superimposed upon diffuse, uniform demyelinating, and sensorimotor polyneuropathy. Family genes revealed that each family member carried one of two heterozygous mutant genes. She has been discharged and is currently being followed up. This study found a compound heterozygous mutation in the ARSA gene associated with MLD and identified a novel missense mutation NM_000487: c.[154G>T], p.(Gly172Cys), rs74315271. This will provide a critical clue for prenatal diagnosis of the offspring in this family, and expand the mutation spectrum of MLD-related ARSA.

Understanding caregiver descriptions of initial signs and symptoms to improve diagnosis of metachromatic leukodystrophy

BACKGROUND

Metachromatic leukodystrophy (MLD), a relentlessly progressive and ultimately fatal condition, is a rare autosomal recessive lysosomal storage disorder caused by a deficiency of the enzyme arylsulfatase A (ARSA). Historically management has been palliative or supportive care. Hematopoietic stem cell transplantation is poorly effective in early-onset MLD and benefit in late-onset MLD remains controversial. Hematopoietic stem cell gene therapy, Libmeldy (atidarsagene autotemcel), was recently approved by the European Medicines Agency for early-onset MLD. Treatment benefit is mainly observed at an early disease stage, indicating the need for early diagnosis and intervention. This study contributes insights into the caregiver language used to describe initial MLD symptomatology, and thereby aims to improve communication between clinicians and families impacted by this condition and promote a faster path to diagnosis.

RESULTS

Data was collected through a moderator-assisted online 60-min survey and 30-min semi-structured follow-up telephone interview with 31 MLD caregivers in the United States (n = 10), France (n = 10), the United Kingdom (n = 5), and Germany (n = 6). All respondents were primary caregivers of a person with late infantile (n = 20), juvenile (n = 11) or borderline late infantile/juvenile (n = 1) MLD (one caregiver reported for 2 children leading to a sample of 32 individuals with MLD). Caregivers were asked questions related to their child's initial signs and symptoms, time to diagnosis and interactions with healthcare providers. These results highlight the caregiver language used to describe the most common initial symptoms of MLD and provide added context to help elevate the index of suspicion of disease. Distinctions between caregiver descriptions of late infantile and juvenile MLD in symptom onset and disease course were also identified.

CONCLUSIONS

This study captures the caregiver description of the physical, behavioral, and cognitive signs of MLD prior to diagnosis. The understanding of the caregiver language at symptom onset sheds light on a critical window of often missed opportunity for earlier diagnosis and therapeutic intervention in MLD.

Hematopoietic Stem Cell Transplantation for Neurological Disorders: A Focus on Inborn Errors of Metabolism

Hematopoietic stem cells have been investigated and applied for the treatment of certain neurological disorders for a long time. Currently, their therapeutic potential is harnessed in autologous and allogeneic hematopoietic stem cell transplantation (HSCT). Autologous HSCT is helpful in immune-mediated neurological diseases such as Multiple Sclerosis. However, clinical benefits derive more from the immunosuppressive conditioning regimen than the interaction between stem cells and the nervous system. Mainly used for hematologic malignancies, allogeneic HSCT explores the therapeutic potential of donor-derived hematopoietic stem cells. In the neurological setting, it has proven to be most valuable in Inborn Errors of Metabolism, a large spectrum of multisystem disorders characterized by congenital deficiencies in enzymes involved in metabolic pathways. Inborn Errors of Metabolism such as X-linked Adrenoleukodystrophy present with brain accumulation of enzymatic substrates that result in progressive inflammatory demyelination. Allogeneic HSCT can halt ongoing inflammatory neural destruction by replacing hematopoietic-originated microglia with donor-derived myeloid precursors. Microglia, the only neural cells successfully transplanted thus far, are the most valuable source of central nervous system metabolic correction and play a significant role in the crosstalk between the brain and hematopoietic stem cells. After transplantation, engrafted donor-derived myeloid cells modulate the neural microenvironment by recapitulating microglial functions and enhancing repair mechanisms such as remyelination. In some disorders, additional benefits result from the donor hematopoietic stem cell secretome that cross-corrects neighboring neural cells via mannose-6-phosphatase paracrine pathways. The limitations of allogeneic HSCT in this setting relate to the slow turnover of microglia and complications such as graft-vs.-host disease. These restraints have accelerated the development of hematopoietic stem cell gene therapy, where autologous hematopoietic stem cells are collected, manipulated ex vivo to overexpress the missing enzyme, and infused back into the patient. With this cellular drug vehicle strategy, the brain is populated by improved cells and exposed to supraphysiological levels of the flawed protein, resulting in metabolic correction. This review focuses on the mechanisms of brain repair resulting from HSCT and gene therapy in Inborn Errors of Metabolism. A brief mention will also be made on immune-mediated nervous system diseases that are treated with this approach.

Haematopoietic stem cell gene therapy in inborn errors of metabolism

Over the last 30 years, allogeneic haematopoietic stem cell transplantation (allo-HSCT) has been adopted as a therapeutic strategy for many inborn errors of metabolism (IEM), due to the ability of donor-derived cells to provide life-long enzyme delivery to deficient tissues and organs. However, (a) the clinical benefit of allo-HSCT is limited to a small number of IEM, (b) patients are left with a substantial residual disease burden and (c) allo-HSCT is still associated with significant short- and long-term toxicities and transplant-related mortality. Haematopoietic stem/progenitor cell gene therapy (HSPC-GT) was established in the 1990s for the treatment of selected monogenic primary immunodeficiencies and over the past few years, its use has been extended to a number of IEM. HSPC-GT is particularly attractive in neurodegenerative IEM, as gene corrected haematopoietic progenitors can deliver supra-physiological enzyme levels to difficult-to-reach areas, such as the brain and the skeleton, with potential increased clinical benefit. Moreover, HSPC-GT is associated with reduced morbidity and mortality compared to allo-HSCT, although this needs to be balanced against the potential risk of insertional mutagenesis. The number of clinical trials in the IEM field is rapidly increasing and some HSPC-GT products recently received market approval. This review describes the development of ex vivo HSPC-GT in a number of IEM, with a focus on recent results from GT clinical trials and risks versus benefits considerations, when compared to established therapeutic strategies, such as allo-HSCT.

Adult Hereditary White Matter Diseases With Psychiatric Presentation: Clinical Pointers and MRI Algorithm to Guide the Diagnostic Process

OBJECTIVE

The investigators aimed to provide clinical and MRI guidelines for determining when genetic workup should be considered in order to exclude hereditary leukoencephalopathies in affected patients with a psychiatric presentation.

METHODS

A systematic literature review was conducted, and clinical cases are provided. Given the central role of MRI pattern recognition in the diagnosis of white matter disorders, the investigators adapted an MRI algorithm that guides the interpretation of MRI findings and thus directs further investigations, such as genetic testing.

RESULTS

Twelve genetic leukoencephalopathies that can present with psychiatric symptoms were identified. As examples of presentations that can occur in clinical practice, five clinical vignettes from patients assessed at a referral center for adult genetic leukoencephalopathies are provided.

CONCLUSIONS

Features such as drug-resistant symptoms, presence of long-standing somatic features, trigger events, consanguinity, and positive family history should orient the clinician toward diagnostic workup to exclude the presence of a genetic white matter disorder. The identification of MRI white matter abnormalities, especially when presenting a specific pattern of involvement, should prompt genetic testing for known forms of genetic leukoencephalopathies.

Hematopoietic stem cell transplantation with mesenchymal stromal cells in children with metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is a lysosomal storage disorder primarily affecting the white matter of the nervous system that results from a deficiency of the arylsulfatase A (ARSA). Mesenchymal stem cells (MSCs) are able to secrete ARSA and have shown beneficial effects in MLD patients. In this retrospective analysis, 10 pediatric MLD patients (MSCG) underwent allogeneic hematopoietic stem cell transplantation (HSCT) and received two applications of 2 x 106 MSCs/kg bodyweight at day +30 and +60 after HSCT between 2007 and 2018. MSC safety, occurrence of graft-versus-host disease (GvHD), blood ARSA levels, chimerism, cell regeneration and engraftment, MRI changes, and the gross motor function were assessed within the first year of HSCT. The long-term data included clinical outcomes and safety aspects of MSCs. Data were compared to a control cohort of seven pediatric MLD patients (CG) who underwent HSCT only. The application of MSC in pediatric MLD patients after allogeneic HSCT was safe and well tolerated and long-term potentially MSC-related adverse effects up to 13.5 years after HSCT were not observed. Patients achieved significantly higher ARSA levels (CG: median 1.03 nmol∙10-6, range 0.41-1.73 | MSCG: median 1.58 nmol∙10-6, range 0.44-2.6; p<0.05), as well as significantly higher leukocyte (p<0.05) and thrombocyte (p<0.001) levels within 365 days of MSC application compared to CG patients. Statistically significant effects on acute GvHD, regeneration of immune cells, engraftment, MRI changes, gross motor function, and clinical outcomes were not detected. In conclusion, the application of MSCs in pediatric MLD patients after allogeneic HSCT was safe and well tolerated. The two applications of 2 x 106/kg allogeneic MSCs were followed by improved engraftment and hematopoiesis within the first year after HSCT. Larger, prospective trials are necessary to evaluate the impact of MSC application on engraftment and hematopoietic recovery.