Metachromatic Leukodystrophy Patients Research Articles

Clinical and Radiological Profile of Nine Patients with Metachromatic Leukodystrophy

Introduction: Metachromatic leukodystrophy (MLD) is a rare, demyelinating, autosomal recessive lysosomal storage disease caused by a deficiency in the arylsulfatase A enzyme (ASA), which is encoded by ARSA gene. A lack of ASA activity results in an accumulation of sulfatides in the myelin sheaths of both the central and peripheral nervous systems, leading to developmental and neurocognitive progressive deterioration that can be observed in all age groups. Methods: We present a total of 9 patients with MLD with an average age of 61 months, whose clinical, laboratory and cranial magnetic resonance imaging findings were evaluated, and who underwent an ARSA gene molecular analysis. Results: Of the 9 patients, 7 had the late infantile form of the condition, 2 had the juvenile form, and 3 were identified through family screening. The median age at diagnosis was 30 months (min 3–max 73 months), the mean ASA activity value was 2 nmol/h/mgprt and the median cranial MR imaging severity score was 10 (min 5–max 18). The grey and white matter volumes of all patients, evaluated using volBrain software, were within the normal range. At an average age of 48 months, the late-infantile MLD patients were unable to control any body part. Conclusions: Hematopoietic stem cell transplantation (HSCT), a treatment option for both the juvenile and adult forms of MLD in asymptomatic or early symptomatic patients, was performed on two of the asymptomatic and early symptomatic patients, and post-HSCT ASA activity settled within the normal range and their developmental milestones stabilized. It is important to diagnose MLD in the asymptomatic period and newborn screening can support early diagnosis.

Association between Neuroimaging Scores and Clinical Status in Pediatric Patients Diagnosed with Metachromatic Leukodystrophy

Purpose: Metachromatic leukodystrophy (MLD) is a lysosomal storage disease caused by arylsulfatase A deficiency, which leads to progressive demyelination in both the central and peripheral nervous systems, resulting in significant gross motor deterioration. This study aimed to analyze data concerning neuroimaging and clinical phenotypes of MLD patients, categorized by disease subtype.Methods: Patients diagnosed with MLD based on arylsulfatase A enzymatic activity, demyelination observed in brain magnetic resonance images, and/or pathogenic mutations were included in this study. The medical charts of 10 patients with confirmed MLD were retrospectively reviewed. We used a simplified magnetic resonance imaging (MRI) scoring system and clinical status, including survival. We analyzed the correlations between the scores of specific neuroimaging lesions and clinical status in two groups, categorized as late-infantile and juvenile types based on the age at symptom onset.Results: We detected a positive relationship between clinical function deterioration and MRI score (rho=0.59, P=0.002) in patients with MLD. This correlation was stronger in the late-infantile type (rho=0.700, P=0.003) than in the juvenile type (rho=0.513, P=0.029). A strong relationship was also noted in patients with high signal intensities in the pons and basal ganglia, and cerebellar atrophy, but not in those with lesions in the midbrain. MLD with a high MRI score was associated with poor clinical function. Conclusion: The identified correlations between modified MRI scores and clinical function scales may help predict the prognosis of patients with MLD, thereby aiding in the identification of treatment options and enhancing the quality of life for these 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.

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.

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.

Higher precision, first tier newborn screening for metachromatic leukodystrophy using 16:1-OH-sulfatide

Newborn screening (NBS) for metachromatic leukodystrophy (MLD) is based on first-tier measurement of sulfatides in dried blood spots (DBS) followed by second-tier measurement of arylsulfatase A in the same DBS. This approach is very precise with 0–1 false positives per ∼30,000 newborns tested. Recent data reported here shows that the sulfatide molecular species with an α-hydroxyl, 16‑carbon, mono-unsaturated fatty acyl group (16:1-OH-sulfatide) is superior to the original biomarker 16:0-sulfatide in reducing the number of first-tier false positives. This result is consistent across 4 MLD NBS centers. By measuring 16:1-OH-sulfatide alone or together with 16:0-sulfatide, the estimated false positive rate is 0.048% and is reduced essentially to zero with second-tier arylsulfatase A activity assay. The false negative rate is predicted to be extremely low based on the demonstration that 40 out of 40 newborn DBS from clinically-confirmed MLD patients are detected with these methods. The work shows that NBS for MLD is extremely precise and ready for deployment. Furthermore, it can be multiplexed with several other inborn errors of metabolism already tested in NBS centers worldwide.

Longitudinal volumetric analysis of gray matter atrophy in metachromatic leukodystrophy.

Metachromatic leukodystrophy (MLD) is an inherited lysosomal storage disorder characterized by arylsulfatase A (ASA) deficiency, leading to sulfatide accumulation and myelin degeneration in the central nervous system. While primarily considered a white matter (WM) disease, gray matter (GM) is also affected in MLD, and hematopoietic stem cell transplantation (HSCT) may have limited effect on GM atrophy. We cross-sectionally and longitudinally studied GM volumes using volumetric MRI in a cohort of 36 (late-infantile, juvenile and adult type) MLD patients containing untreated and HSCT treated subjects. Cerebrum, cortical GM, (total) CSF, cerebellum, deep gray matter (DGM) (excluding thalamus) and thalamus volumes were analyzed. Longitudinal correlations with measures of cognitive and motor functioning were assessed. Cross-sectionally, juvenile and adult type patients (infantiles excluded based on limited numbers) were compared with controls at earliest scan, before possible treatment. Patients had lower cerebrum, cortical GM, DGM and thalamus volumes. Differences were most pronounced for adult type patients. Longitudinal analyses showed substantial and progressive atrophy of all regions and increase of CSF in untreated patients. Similar, albeit less pronounced, effects were seen in treated patients for cerebrum, cortical GM, CSF and thalamus volumes. Deterioration in motor performance (all patients) was related to atrophy, and increase of CSF, in all regions. Cognitive functioning (data available for treated patients) was related to cerebral, cortical GM and thalamus atrophy; and to CSF increase. Our findings illustrate the importance of recognizing GM pathology as a potentially substantial, clinically relevant part of MLD, apparently less amenable to treatment.

The burden of disease 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 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]). 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. 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.

Allogeneic hematopoietic cell transplantation for adult metachromatic leukodystrophy: a case series

AbstractMetachromatic leukodystrophy (MLD) is a rare genetic disorder caused by pathogenic variants of the ARSA gene, leading to a deficiency of the arylsulfatase A enzyme (ARSA) and consecutive accumulation of galactosylceramide-3-0-sulfate in the nervous system. The condition leads to severe neurological deficits and subsequently results in profound intellectual and motoric disability. Especially, the adult form of MLD, which occurs in individuals aged >16 years, poses significant challenges for treating physicians because of the rarity of cases, limited therapeutic options, and different allogeneic hematopoietic cell transplantation (allo-HCT) protocols worldwide. Here, we report the results of allo-HCT treatment in 4 patients with a confirmed adult MLD diagnosis. Bone marrow or mobilized peripheral progenitor cells were infused after a reduced intensity conditioning regime consisting of fludarabine and treosulfan. In 3 patients, allo-HCT was followed by an infusion of mesenchymal cells to further consolidate ARSA production. We observed a good tolerability and an increase in ARSA levels up to normal range values in all patients. A full donor chimerism was detected in 3 patients within the first 12 months. In a 1-year follow-up, patients with complete donor chimerism showed a neurological stable condition. Only 1 patient with an increasing autologous chimerism showed neurological deterioration and a decline in ARSA levels in the first year. In summary, allo-HCT offers a therapeutic option for reconstituting ARSA enzyme levels in adult patients with MLD, with tolerable side effects.

Inventory of current practices regarding hematopoietic stem cell transplantation in metachromatic leukodystrophy in Europe and neighboring countries

BackgroundFor decades, early allogeneic stem cell transplantation (HSCT) has been used to slow neurological decline in metachromatic leukodystrophy (MLD). There is lack of consensus regarding who may benefit, and guidelines are lacking. Clinical practice relies on limited literature and expert opinions. The European Reference Network for Rare Neurological Diseases (ERN-RND) and the MLD initiative facilitate expert panels for treatment advice, but some countries are underrepresented. This study explores organizational and clinical HSCT practices for MLD in Europe and neighboring countries to enhance optimization and harmonization of cross-border MLD care.MethodsA web-based EUSurvey was distributed through the ERN-RND and the European Society for Blood and Marrow Transplantation Inborn Errors Working Party. Personal invitations were sent to 89 physicians (43 countries) with neurological/metabolic/hematological expertise. The results were analyzed and visualized using Microsoft Excel and IBM SPSS statistics.ResultsOf the 30 countries represented by 42 respondents, 23 countries offer HSCT for MLD. The treatment is usually available in 1–3 centers per country (18/23, 78%). Most countries have no or very few MLD patients transplanted during the past 1–5 years. The eligibility criteria regarding MLD subtype, motor function, IQ, and MRI largely differ across countries.ConclusionHSCT for MLD is available in most European countries, but uncertainties exist in Eastern and South-Eastern Europe. Applied eligibility criteria and management vary and may not align with the latest scientific insights, indicating physicians’ struggle in providing evidence-based care. Interaction between local physicians and international experts is crucial for adequate treatment decision-making and cross-border care in the rapidly changing MLD field.

Exploring the effect of disease causing mutations in metal binding sites of human ARSA in metachromatic leukodystrophy.

The arylsulfatase A (ARSA) gene is observed to be deficient in patients with metachromatic leukodystrophy (MLD), a type of lysosomal storage disease. MLD is a severe neurodegenerative disorder characterized by an autosomal recessive inheritance pattern. This study aimed to map the most deleterious mutations at the metal binding sites of ARSA and the amino acids in proximity to the mutated positions. We utilized an array of computational tools, including PredictSNP, MAPP, PhD-SNP, PolyPhen-1, PolyPhen-2, SIFT, SNAP, and ConSurf, to identify the most detrimental mutations potentially implicated in MLD collected from UniProt, ClinVar, and HGMD. Two mutations, D29N and D30H, as being extremely deleterious based on assessments of pathogenicity, conservation, biophysical characteristics, and stability analysis. The D29 and D30 are located at the metal-interacting regions of ARSA and found to undergo post-translational modification, specifically phosphorylation. Henceforth, the in-depth effect of metal binding upon mutation was examined using molecular dynamics simulations (MDS) before and after phosphorylation. The MDS results exhibited high deviation for the D29N and D30H mutations in comparison to the native, and the same was confirmed by significant residue fluctuation and reduced compactness. These structural alterations suggest that such mutations may influence protein functionality, offering potential avenues for personalized therapeutic and providing a basis for potential mutation-specific treatments for severe MLD patients.

Complex genotypes in family with metachromatic leukodystrophy: Effect of trans and cis mutations distribution on the phenotype variability.

Metachromatic leukodystrophy (MLD) is a severe metabolic disorder caused by the deficient activity of arylsulfatase A due to ARSA gene mutations. According to the age of onset, MLD is classified into three forms: infantile, juvenile, and adult. In our study, we aimed to perform a genetic analysis for two siblings with juvenile MLD for a better characterization of the molecular mechanisms behind the disease. A consanguineous family including two MLD patients (PII.1 and PII.2) was enrolled in our study. The diagnosis was made based on the clinical and neuroimaging investigations. The sequencing of ARSA gene was performed followed by in silico analysis. Besides, the cis/trans distribution of the variants was verified through a PCR-RFLP. The ARSA gene sequencing revealed three known variants, two exonic c.1055A > G and c.1178C > G and an intronic one (c.1524 + 95A > G) in the 3'UTR region. All variants were present at heterozygous state in the two siblings and their mother. The assessment of the cis/trans distribution showed the presence of these variants in cis within the mother, while PII.2 and PII.2 present the c.1055A > G/c.1524 + 95A > G and the c.1178C > G in trans. Additionally, PII.1 harbored a de novo novel missense variant c.1119G > T, whose pathogenicity was supported by our predictive results. Our genetic findings, supported by a clinical examination, confirmed the affection of the mother by the adult MLD. Our results proved the implication of the variable distribution of the found variants in the age of MLD onset. Besides, we described a variable severity between the two siblings due to the de novo pathogenic variant. In conclusion, we identified a complex genotype of ARSA variants within two MLD siblings with a variable severity due to a de novo variant present in one of them. Our results allowed the establishment of an adult MLD diagnosis and highlighted the importance of an assessment of the trans/cis distribution in the cases of complex genotypes.

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.

PCR176 Estimating Utility Values for Health States in Metachromatic Leukodystrophy (MLD)

Metachromatic leukodystrophy (MLD) is a rare lysosomal storage disease caused by deficient arylsulfatase A activity, leading to progressive cognitive and motor dysfunction and death. We estimated late-infantile MLD (LI-MLD) patient and caregiver health state utilities to inform cost–utility evaluations of MLD treatments. Utilities range from 1 (full health) to 0 (dead); values <0 reflect states considered worse than dead.

Neurodegenerative disease after hematopoietic stem cell transplantation in metachromatic leukodystrophy.

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. 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. 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. 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.

Clinical Significance of Diffusion Tensor Imaging in Metachromatic Leukodystrophy.

Metachromatic leukodystrophy (MLD) is a lysosomal enzyme deficiency disorder leading to progressive demyelination and, consecutively, to cognitive and motor decline. Brain magnetic resonance imaging (MRI) can detect affected white matter as T2 hyperintense areas but cannot quantify the gradual microstructural process of demyelination more accurately. Our study aimed to investigate the value of routine MR diffusion tensor imaging in assessing disease progression. MR diffusion parameters (apparent diffusion coefficient [ADC] and fractional anisotropy [FA]) were in the frontal white matter, central region (CR), and posterior limb of the internal capsule in 111 MR datasets from a natural history study of 83 patients (age: 0.5-39.9 years; 35 late-infantile, 45 juvenile, 3 adult, with clinical diffusion sequences of different scanner manufacturers) as well as 120 controls. Results were correlated with clinical parameters reflecting motor and cognitive function. ADC values increase and FA values decrease depending on disease stage/severity. They show region-specific correlations with clinical parameters of motor and cognitive symptoms, respectively. Higher ADC levels in CR at diagnosis predicted a disease course with more rapid motor deterioration in juvenile MLD patients. In highly organized tissues such as the corticospinal tract, in particular, diffusion MR parameters were highly sensitive to MLD-associated changes and did not correlate with the visual quantification of T2 hyperintensities. Our results show that diffusion MRI can deliver valuable, robust, clinically meaningful, and easily obtainable/accessible/available parameters in the assessment of prognosis and progression of MLD. Therefore, it provides additional quantifiable information to established methods such as T2 hyperintensity.

Adaptive Routes of Hematopoietic Stem Cell Differentiation to Disease Conditions and Age in Gene Therapy Patients

In lentiviral vector-based Hematopoietic Stem Progenitor Cell (HSPC) gene therapy (GT), transplantation of genetically modified HSPCs can result in the full reconstitution of the patients' hematopoietic system and provide a therapeutic benefit in a variety of genetic diseases. However, it is still unclear how the underlying genetic disease and other factors may impact the reconstitution process, lineage specification, and patients' safety. Here we analyzed the clonal repertoire and dynamics of hematopoietic reconstitution by studying >4 million vector integration sites (IS), a surrogate of clonal identity, from purified myeloid, lymphoid, erythroid cell lineages and HSPCs from 53 patients treated by lentiviral-based HSPC-GT up to 8 years of follow-up, 29 patients for metachromatic leukodystrophy (MLD) - a neurodegenerative lysosomal storage disorder, 15 patients for Wiskott-Aldrich syndrome (WAS) - an immunodeficiency with thrombocytopenia, and 9 patients for β-thalassemia (β-Thal) - a hemoglobinopathy. This analysis showed that patients had a polyclonal repertoire without signs of insertional mutagenesis. We next dissected the hematopoietic reconstitution over time in terms of HSPC numbers, output and commitment of HSPCs toward the different lineages. We estimated that the number of engrafted and active HSPCs in patients over time ranged from 770 to 35,000 cells, remaining stable long-term. The estimates were based on the Chao1 model, a well-established capture-recapture statistics developed in ecology. A large fraction of clones estimated in the early phase were exhausted within 12 months and were replaced by a smaller, yet substantial, number of long-term IS in stable and sustained steady-state hematopoiesis. We did not observe any statistical difference of the fraction of HSPCs actively contributing to hematopoiesis at steady state across the 3 trials, ranging from 0.0007% to 0.0274%. Unsupervised clustering analysis revealed a positive correlation between the clonal diversity and the total dose (CD34+ cells 10e6/kg) of infused HSPCs, and between in vivo HSPC size and the patient's age. About 50% of hematopoietic clones had multilineage potential in all disease conditions, while the remaining clones showed a preferential lineage output and long-term linage commitment which was specific to the disease condition: MLD patients showed a long-term commitment towards myeloid lineages, while patients treated for WAS had a preferential output and commitment towards lymphoid lineages and β-Thal for erythroid lineages, especially in adult patients. Our results showed for the first time that the long-term output, as well as the lineage commitment of HSPCs, is strongly modulated by the patients' genetic background to better compensate for the demands posed by the specific clinical condition

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

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. 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. 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. 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.

Extremely low arylsulfatase A enzyme activity does not necessarily cause symptoms: A long-term follow-up and review of the literature.

Metachromatic leukodystrophy (MLD) is an autosomal recessive lysosomal storage disease caused by deficiency of arylsulfatase A (ARSA). Heterozygous carriers of disease‐causing variants and individuals harbouring pseudodeficiency alleles in the ARSA gene exhibit reduced ARSA activity. In the context of these genotypes, low ARSA activity has been suggested to lead to an atypical form of MLD or other neurological abnormalities, but data are limited. The aim of our study was to analyse the impact of low ARSA activity in two subjects who are heterozygous for the ARSA pseudodeficiency allele and a disease‐causing variant. Biochemical testing included ARSA activity measurements and urinary sulfatide analysis. Biochemical data of a large cohort of MLD patients, heterozygotes, pseudodeficient individuals and healthy controls were analysed. MRI was performed at 3T using T1‐ and T2‐weighted sequences and MR spectroscopy. We present two long‐term follow‐ups who are heterozygous for the ARSA pseudodeficiency allele and a disease‐causing variant in the ARSA gene in cis. The two related index cases exhibit markedly reduced ARSA activity compared to controls and heterozygous carriers. The neurological evaluation and MRI do not reveal any abnormalities. Our data underline that extremely low enzyme activity due to a pseudodeficiency allele and a disease‐causing variant in the ARSA gene even in cis does not lead to clinical symptoms or pre‐symptomatic MRI changes suspicious for MLD. The review of literature corroborates that any association of low ARSA activity with disease features remains questionable. It seems important to combine the measurement of ARSA activity with elevated sulfatide as well as genetic testing, as done in current newborn screening approaches. Heterozygosity for metachromatic leukodystrophy and an arylsulfatase A pseudodeficiency allele does not cause neurological or neuropsychiatric features.