Metachromatic leukodystrophy: A single-center longitudinal study of 45 patients.

In this study, we characterize the natural course of metachromatic leukodystrophy (MLD), explore intra/inter group differences, and identify biomarkers to monitor disease progression. This is a longitudinal observational study. Genotype and characteristics at disease onset were recorded. Time-to-event analyses were performed to assess time to major disease-related milestones in different subgroups. Longitudinal trajectories of nerve conduction velocities (NCV), brain MRI score, and brainstem auditory evoked responses (BAERs) were described. We recruited 22 late-infantile, 14 early-juvenile, 5 late-juvenile, and 4 adult MLD patients. Thirty-four were prospectively evaluated (median FU time 43 months). In late-infantile patients, the attainment of independent walking was associated with a later age at dysphagia. In early-juvenile, the presence of isolated cognitive impairment at onset was not a favorable prognostic factor. Late-infantile and early-juvenile subjects showed similar rapid loss of ambulation and onset of seizures, but late-infantile displayed earlier loss of trunk control, dysphagia, and death. We found significant differences in all major disease-related milestones (except death) between early-juvenile and late-juvenile patients. Late-juvenile and adult patients both presented with a predominant cognitive impairment, mild/no peripheral neuropathy, lower brain MRI score at plateau compared to LI/EJ, and later cerebellar involvement. NCV and BAER were consistently severely abnormal in late-infantile but not in older subjects, in whom both NCV and BAER were variably affected, with no deterioration over time in some cases. This study clarifies intra/inter group differences between MLD subtypes and provides additional indications regarding reliable clinical and instrumental tools to monitor disease progression and to serve as areference to evaluate the efficacy of future therapeutic interventions inthe different MLD variants.

Metallothioneins are neuroprotective agents in lysosomal storage disorders.

OBJECTIVE: Lysosomal storage disorders (LSDs) are a broad class of inherited metabolic diseases caused by the defective activity of lysosomal enzymes. Central nervous system (CNS) manifestations are present in roughly 50% of LSD patients and represent an unmet medical need for them. We explored the therapeutic potential of metallothioneins (MTs), a newly identified family of proteins with reported neuroprotective roles, in the murine models of two LSDs with CNS involvement. METHODS: MT-1 overexpressing transgenic mice (MTtg) were crossed with the murine models of Batten and Krabbe diseases. Changes in the survival and manifestations of the disease in the MTtg setting were assessed. In addition, we analyzed the therapeutic effects of MT-1 CNS gene delivery in one of these LSD models. RESULTS: Constitutive expression of MT-1 exerted favorable phenotypic effects in both LSD models. MT-LSD mice showed a 5% to 10% increase in survival and slower disease progression as compared to not-transgenic LSD mice. Rescue of Purkinje cells from degeneration and apoptosis was also observed in the MT-LSD models. This phenotypic amelioration was accompanied by a modulation of the disease-associated activated inflammatory microglia phenotype, and by a reduction of oxidative stress. Importantly, for the clinical translation of our findings, the very same effects were obtained when MTs were delivered to brains by systemic AAV gene transfer. INTERPRETATION: MTs can be considered novel therapeutic agents (and targets) in LSDs and potentiate the effects of approaches aiming at correction of the disease-causing enzyme deficiency in the CNS. Ann Neurol 2018;83:418-432 Ann Neurol 2018;83:418-432.

Mutation Update of ARSA and PSAP Genes Causing Metachromatic Leukodystrophy.

Metachromatic leukodystrophy is a neurodegenerative disorder characterized by progressive demyelination. The disease is caused by variants in the ARSA gene, which codes for the lysosomal enzyme arylsulfatase A, or, more rarely, in the PSAP gene, which codes for the activator protein saposin B. In this Mutation Update, an extensive review of all the ARSA- and PSAP-causative variants published in the literature to date, accounting for a total of 200 ARSA and 10 PSAP allele types, is presented. The detailed ARSA and PSAP variant lists are freely available on the Leiden Online Variation Database (LOVD) platform at http://www.LOVD.nl/ARSA and http://www.LOVD.nl/PSAP, respectively.

Critical issues for the proper diagnosis of Metachromatic Leukodystrophy.

Metachromatic Leukodystrophy is a lysosomal storage disorder caused by Arylsulfatase A deficiency. Diagnosis is usually performed by measurement of enzymatic activity and/or characterization of the gene mutations. Here we describe a family case in which the determination of enzyme activity alone did not allow diagnosis of the pre-symptomatic sibling of the index case. Only combination of gene sequencing with thorough biochemical analysis allowed the correct diagnosis of the sibling, who was promptly directed to treatment.

Metallothioneins as dynamic markers for brain disease in lysosomal disorders.

OBJECTIVE: To facilitate development of novel disease-modifying therapies for lysosomal storage disorder (LSDs) characterized by nervous system involvement such as metachromatic leukodystrophy (MLD), molecular markers for monitoring disease progression and therapeutic response are needed. To this end, we sought to identify blood transcripts associated with the progression of MLD. METHODS: Genome-wide expression analysis was performed in primary T lymphocytes of 24 patients with MLD compared to 24 age- and sex-matched healthy controls. Genes associated with MLD were identified, confirmed on a quantitative polymerase chain reaction platform, and replicated in an independent patient cohort. mRNA and protein expression of the prioritized gene family of metallothioneins was evaluated in postmortem patient brains and in mouse models representing 6 other LSDs. Metallothionein expression during disease progression and in response to specific treatment was evaluated in 1 of the tested LSD mouse models. Finally, a set of in vitro studies was planned to dissect the biological functions exerted by this class of molecules. RESULTS: Metallothionein genes were significantly overexpressed in T lymphocytes and brain of patients with MLD and generally marked nervous tissue damage in the LSDs here evaluated. Overexpression of metallothioneins correlated with measures of disease progression in mice and patients, whereas their levels decreased in mice upon therapeutic treatment. In vitro studies indicated that metallothionein expression is regulated in response to oxidative stress and inflammation, which are biochemical hallmarks of lysosomal storage diseases. INTERPRETATION: Metallothioneins are potential markers of neurologic disease processes and treatment response in LSDs.

Lentiviral hematopoietic stem cell gene therapy benefits metachromatic leukodystrophy.

Metachromatic leukodystrophy (MLD) is an inherited lysosomal storage disease caused by arylsulfatase A (ARSA) deficiency. Patients with MLD exhibit progressive motor and cognitive impairment and die within a few years of symptom onset. We used a lentiviral vector to transfer a functional ARSA gene into hematopoietic stem cells (HSCs) from three presymptomatic patients who showed genetic, biochemical, and neurophysiological evidence of late infantile MLD. After reinfusion of the gene-corrected HSCs, the patients showed extensive and stable ARSA gene replacement, which led to high enzyme expression throughout hematopoietic lineages and in cerebrospinal fluid. Analyses of vector integrations revealed no evidence of aberrant clonal behavior. The disease did not manifest or progress in the three patients 7 to 21 months beyond the predicted age of symptom onset. These findings indicate that extensive genetic engineering of human hematopoiesis can be achieved with lentiviral vectors and that this approach may offer therapeutic benefit for MLD patients.

Lentiviral vector common integration sites in preclinical models and a clinical trial reflect a benign integration bias and not oncogenic selection.

A recent clinical trial for adrenoleukodystrophy (ALD) showed the efficacy and safety of lentiviral vector (LV) gene transfer in hematopoietic stem progenitor cells. However, several common insertion sites (CIS) were found in patients' cells, suggesting that LV integrations conferred a selective advantage. We performed high-throughput LV integration site analysis on human hematopoietic stem progenitor cells engrafted in immunodeficient mice and found the same CISs reported in patients with ALD. Strikingly, most CISs in our experimental model and in patients with ALD cluster in megabase-wide chromosomal regions of high LV integration density. Conversely, cancer-triggering integrations at CISs found in tumor cells from γ-retroviral vector-based clinical trials and oncogene-tagging screenings in mice always target a single gene and are contained in narrow genomic intervals. These findings imply that LV CISs are produced by an integration bias toward specific genomic regions rather than by oncogenic selection.

The galactocerebrosidase enzyme contributes to the maintenance of a functional hematopoietic stem cell niche.

The balance between survival and death in many cell types is regulated by small changes in the intracellular content of bioactive sphingolipids. Enzymes that either produce or degrade these sphingolipids control this equilibrium. The findings here described indicate that the lysosomal galactocerebrosidase (GALC) enzyme, defective in globoid cell leukodystrophy, is involved in the maintenance of a functional hematopoietic stem/progenitor cell (HSPC) niche by contributing to the control of the intracellular content of key sphingolipids. Indeed, we show that both insufficient and supraphysiologic GALC activity-by inherited genetic deficiency or forced gene expression in patients' cells and in the disease model-induce alterations of the intracellular content of the bioactive GALC downstream products ceramide and sphingosine, and thus affect HSPC survival and function and the functionality of the stem cell niche. Therefore, GALC and, possibly, other enzymes for the maintenance of niche functionality and health tightly control the concentration of these sphingolipids within HSPCs.

Characterization of new arylsulfatase A gene mutations reinforces genotype-phenotype correlation in metachromatic leukodystrophy.

Metachromatic Leukodystrophy (MLD) is a rare inherited lysosomal storage disorder caused by the deficiency of Arylsulfatase A (ARSA). The disease manifests itself with a broad spectrum of clinical variants, all characterized by progressive neurodegeneration in the central and peripheral nervous systems. The correlation between mutations in the ARSA gene, residual enzymatic activity associated with the mutated alleles and patients' phenotype, which has been extensively drawn for common ARSA mutations, has recently been expanded to rare ones. In this context, functional studies on the rare allelic variances acquire particular relevance for patients' prognostic evaluation. Here we have characterized eight newly identified ARSA mutations, through lentiviral vector-based expression studies on cell lines and ARSA defective murine fibroblasts. In each case, the residual activity associated with the new mutant allele correlates well with the patient's phenotype. Therefore, our results confirm the importance of functional characterization of mutant alleles for a precise genotype-based classification and definition of prognosis in MLD patients, which is particularly relevant for pre-symptomatic diagnosis.

Human hematopoietic stem cells in gene therapy: pre-clinical and clinical issues.

Hematopoietic stem and progenitor cells (HSC) have been widely used in allogeneic transplant procedures, therefore their intrinsic characteristics, the biology of their niche in the bone marrow, and the mobilization and homing processes have been extensively investigated. With the development of gene therapy strategies, new therapeutic options based on autologous HSC have become available which may reduce the morbidity and mortality associated to allogeneic transplantation, but require an ex vivo manipulation of the cells to be corrected before re-infusion. For the success of these approaches it is necessary to optimize culture conditions in order to achieve efficient cell transduction while preserving the biological properties of the stem cells. We review here the factors critical for achieving efficient HSC transduction and maintenance of HSC stemness and homing capacity upon ex vivo culture. When HSC gene therapy is used in genetic disorders, permanent integration of therapeutic genes into the chromosomes of affected cells is needed. Indeed, by use of integrating vectors, such as retroviruses, gene therapy has met significant success in immunodeficiency syndromes characterized by a selective advantage of the transduced cells. However, retroviral integration can take place in stem cells at a variety of chromosomal sites, and examples have been reported of integration of therapeutic vectors causing cancer in patients. The clinical benefit arising from the long-term correction of the genetic defect, due to vector integration into the HSC genome, and the adverse consequences of these events are also here discussed, together with the new and challenging perspectives of HSC gene therapy.