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.

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.

Comprehensive clinical, biochemical, radiological and genetic analysis of 28 Turkish cases with suspected metachromatic leukodystrophy and their relatives

Metachromatic leukodystrophy (MLD) is a glycosphingolipid storage disease caused by deficiency of the lysosomal enzyme arylsulfatase A (ASA) or its activator protein saposin B. MLD can affect all age groups in severity varying from a severe fatal form to milder adult onset forms. Diagnosis is usually made by measuring leukocyte ASA activity. However, this test can give false negative or false positive laboratory results due to pseudodeficiency of ASA and saposin B deficiency, respectively. Therefore, we aimed to evaluate patients with suspected MLD in a Turkish population by comprehensive clinical, biochemical, radiological, and genetic analyses for molecular and phenotypic characterization. We analyzed 28 suspected MLD patients and 41 relatives from 24 families. ASA activity was found to be decreased in 21 of 28 patients. Sixteen patients were diagnosed as MLD (11 late infantile, 2 juvenile and 3 adult types), 2 MSD, 2 pseudodeficiency (PD) and the remaining 8 patients were diagnosed as having other leukodystrophies. Enzyme analysis showed that the age of onset of MLD did not correlate with residual ASA activity. Sequence analysis showed 11 mutations in ARSA, of which 4 were novel (p.Trp195GlyfsTer5, p.Gly298Asp, p.Arg301Leu, and p.Gly311Asp), and 2 mutations in SUMF1 causing multiple sulfatase deficiency, and confirmed the diagnosis of MLD in 2 presymptomatic relatives. All individuals with confirmed mutations had low ASA activity and urinary sulfatide excretion. Intra- and inter-familial variability was high for the same ARSA missense genotypes, indicating the contribution of other factors to disease expression. Imaging findings were evaluated through a modified brain MRI scoring system which indicated patients with protein-truncating mutations had more severe MRI findings and late-infantile disease onset. MRI findings were not specific for the diagnosis. Anti-sulfatide IgM was similar to control subjects, and IgG, elevated in multiple sulfatase deficiency. In conclusion, the knowledge on the biochemical, clinical and genetic basis of MLD was expanded, a modified diagnostic laboratory algorithm for MLD based on integrated evaluation of ASA activity, urinary sulfatide excretion and genetic tests was devised.

Clinical, Biochemical, and Molecular Characterization of Metachromatic Leukodystrophy Among Egyptian Pediatric Patients: Expansion of the ARSA Mutational Spectrum

Metachromatic leukodystrophy (MLD) is a neurodegenerative disorder characterized by progressive demyelination due to deficiency of the enzyme arylsulfatase A (ARSA) in leukocytes, and consequently leads to impaired degradation and accumulation of cerebroside-3-sulfate (sulfatide). This study aimed to sequence the ARSA gene in a total of 43 patients with metachromatic leukodystrophy descendant from 40 Egyptian families. In addition, four carrier parents from two families with children who had died from MLD came to the clinic for genetic analysis. Prenatal diagnosis was performed for four families with molecularly diagnosed MLD sibs. Different mutations were characterized in our cohort, including missense, nonsense, splice, and deletion. Overall, 21 different mutations in the ARSA gene were detected, with 12 novel mutations, i.e. p.Arg60Pro, p.Tyr65*, p.Val112Asp, p.Arg116*, p.Gly124Asp, p.Pro193Ser, p.Gln238*, p.Gln456*, p.Thr276Lys, and p.Gly311Arg, in addition to two new acceptor splice-site mutations 685-1G > A and c.954_956 delCTT. The amniotic fluid samples revealed two carrier fetuses with heterozygous monoallelic mutations, and two affected fetuses had the homozygous biallelic mutations. In conclusion, the current study sheds light on the underlying ARSA gene defect, with an expansion of the mutation spectrum. To our knowledge, this is the first molecular study of MLD among the Egyptian population.

Arylsulfatase A (ASA) in Parkinson's Disease: From Pathogenesis to Biomarker Potential

Parkinson's disease (PD), the second most common neurodegenerative disorder after Alzheimer's disease, is a clinically heterogeneous disorder, with obscure etiology and no disease-modifying therapy to date. Currently, there is no available biomarker for PD endophenotypes or disease progression. Accumulating evidence suggests that mutations in genes related to lysosomal function or lysosomal storage disorders may affect the risk of PD development, such as GBA1 gene mutations. In this context, recent studies have revealed the emerging role of arylsulfatase A (ASA), a lysosomal hydrolase encoded by the ARSA gene causing metachromatic leukodystrophy (MLD) in PD pathogenesis. In particular, altered ASA levels have been detected during disease progression, and reduced enzymatic activity of ASA has been associated with an atypical PD clinical phenotype, including early cognitive impairment and essential-like tremor. Clinical evidence further reveals that specific ARSA gene variants may act as genetic modifiers in PD. Recent in vitro and in vivo studies indicate that ASA may function as a molecular chaperone interacting with α-synuclein (SNCA) in the cytoplasm, preventing its aggregation, secretion and cell-to-cell propagation. In this review, we summarize the results of recent preclinical and clinical studies on the role of ASA in PD, aiming to shed more light on the potential implication of ASA in PD pathogenesis and highlight its biomarker potential.

Safety of intrathecal delivery of recombinant human arylsulfatase A in children with metachromatic leukodystrophy: Results from a phase 1/2 clinical trial

BACKGROUND

Metachromatic leukodystrophy (MLD) is an autosomal recessive disorder caused by deficient arylsulfatase A (ASA) activity and characterized by neurological involvement that results in severe disability and premature death. We examined the safety and tolerability of intrathecally delivered recombinant human ASA (rhASA; SHP611, now TAK-611) in children with MLD (NCT01510028). Secondary endpoints included change in cerebrospinal fluid (CSF) sulfatide and lysosulfatide levels, and motor function (assessed by Gross Motor Function Measure-88 total score).

METHODS

Twenty-four children with MLD who experienced symptom onset aged ≤ 30 months were enrolled. Patients received rhASA every other week (EOW) for 38 weeks at 10, 30, or 100 mg (cohorts 1-3; n = 6 per cohort), or 100 mg manufactured using a revised process (cohort 4; n = 6).

RESULTS

No rhASA-related serious adverse events (SAEs) were observed; 25% of patients experienced an SAE related to the intrathecal device or drug delivery method. Mean CSF sulfatide and lysosulfatide levels fell to within normal ranges in both 100 mg cohorts following treatment. Although there was a general decline in motor function over time, there was a tendency towards a less pronounced decline in patients receiving 100 mg.

CONCLUSION

Intrathecal rhASA was generally well tolerated at doses up to 100 mg EOW. These preliminary data support further development of rhASA as a therapy for patients with MLD.

Metachromatic leukodystrophy genotypes in The Netherlands reveal novel pathogenic ARSA variants in non-Caucasian patients

Metachromatic leukodystrophy (MLD) is an autosomal recessively inherited sulfatide storage disease caused by deficient activity of the lysosomal enzyme arylsulfatase A (ASA). Genetic analysis of the ARSA gene is important in MLD diagnosis and screening of family members. In addition, more information on genotype prevalence will help interpreting MLD population differences between countries. In this study, we identified 31 different ARSA variants in the patient cohort (n = 67) of the Dutch expertise center for MLD. The most frequently found variant, c.1283C > T, p.(Pro428Leu), was present in 43 (64%) patients and resulted in a high prevalence of the juvenile MLD type (58%) in The Netherlands. Furthermore, we observed in five out of six patients with a non-Caucasian ethnic background previously unreported pathogenic ARSA variants. In total, we report ten novel variants including four missense, two nonsense, and two frameshift variants and one in-frame indel, which were all predicted to be disease causing in silico. In addition, one silent variant was found, c.1200C > T, that most likely resulted in erroneous exonic splicing, including partial skipping of exon 7. The c.1200C > T variant was inherited in cis with the pseudodeficiency allele c.1055A > G, p.(Asn352Ser) + ∗96A > G. With this study we provide a genetic base of the unique MLD phenotype distribution in The Netherlands. In addition, our study demonstrated the importance of genetic analysis in MLD diagnosis and the increased likelihood of unreported, pathogenic ARSA variants in patients with non-Caucasian ethnic backgrounds.

Arylsulfatase A pseudodeficiency in Mexico: Enzymatic activity and haplotype analysis

Background

Metachromatic Leukodystrophy (MLD, OMIM 250100) is a neurodegenerative disease caused by mutations in the ARSA gene (OMIM 607574) that lead to deficiency in Arylsulfatase A (ASA). ASA pseudodeficiency (PD‐ASA) is a biochemical condition that substantially diminishes ASA activity but is not associated with clinical manifestations. PD‐ASA is associated with the c.1055A>G (p.Asn352Ser) (rs2071421) and c.*96A>G (rs6151429) variants, which have an estimated frequency of 2% in the population.

Objective

To determine the activity of Arylsulfatase A and to identify variants and haplotypes in the ARSA gene in Mexican individuals with pseudodeficiency.

Methods

Two‐hundred apparently healthy individuals were included to determine the enzymatic activity of ASA in leukocytes by spectrophotometric analysis, and identification of the PD‐ASA alleles was performed by PCR‐RFLP assays. Genotypes were confirmed by semi‐automated Sanger sequencing. Haplotypes were constructed using Arlequin v.10.04, and linkage disequilibrium analysis was performed with Cube X.

Results

The enzymatic activity of ASA was determined to be 1.74–2.09 nmol/mg protein/min and later correlated with genotypes and haplotypes. For the (p.Asn352Ser) variant, we found 126 (0.63) individuals with the AA genotype, 62 with AG (0.31) and 12 with GG (0.06); the frequency of the polymorphic allele was 0.215 (86 alleles, 21.5%), and the variant was in HWE (p = .2484). The variant c.*96A>G was also in HWE (p = .2105): 185 individuals (0.925) with the AA genotype, 14 (0.07) with AG, and 1 (0.005) with (GG), with a frequency of 0.04 (4%) for the polymorphic allele. The inference of haplotypes resulted in 312 (0.78) AA, 72 (0.18) GA, and 16 (0.04) GG haplotypes. The AG haplotype was not found. The variants were found to be in linkage disequilibrium (D' = 1). Of the nine possible diplotypes, AA/AG, AA/GG, and AG/GG were not found, in concordance with the hypothesis that the G allele of c.*96A>G does not occur in the absence of the G allele of c.1055A>G. We found a slight correlation between ASA biochemical activity and variants, mainly due to the G allele of c.*96A>G in either genotypes or haplotypes.

Conclusions

In Northwestern Mexico, the presence of PD‐ASA alleles was biochemically and molecularly determined, and the frequencies were found to be in HWE. The frequency of PD‐ASA for the North Western Mexican mestizo is 8%.

Reciprocal surface expression of arylsulfatase A and ubiquitin in normal and defective mammalian spermatozoa

Defective mammalian spermatozoa are marked on their surface by proteolytic chaperone ubiquitin. To identify potential ubiquitinated substrates in the defective spermatozoa, we resolved bull sperm protein extracts on a two-dimensional gel and isolated a 64-65-kDa spot (p64) corresponding to one of the major ubiquitin-immunoreactive bands observed in the one-dimensional Western blots. Immune serum raised against this protein recognized a prominent, possibly glycosylated band/spot in the range of 55-68 kDa, consistent with the original spot used for immunization. Internal sequences obtained by Edman degradation of this spot matched the sequence of arylsulfatase A (ARSA), the sperm acrosomal enzyme thought to be important for fertility. By immunofluorescence, a prominent signal was detected on the acrosomal surface (boar and bull) and on the sperm tail principal piece (bull). A second immune serum raised against a synthetic peptide corresponding to an immunogenic internal sequence (GTGKSPRRTL) of the porcine ARSA also labeled sperm acrosome and principal piece. Both sera showed diminished immunoreactivity in the defective bull spermatozoa co-labeled with an anti-ubiquitin antibody. Western blotting and image-based flow cytometry (IBFC) confirmed a reduced ARSA immunoreactivity in the immotile sperm fraction rich in ubiquitinated spermatozoa. Larger than expected ARSA-immunoreactive bands were found in sperm protein extracts immunoprecipitated with anti-ubiquitin antibodies and affinity purified with matrix-bound, recombinant ubiquitin-binding UBA domain. These bands did not show the typical pattern of ARSA glycosylation but overlapped with bands preferentially binding the Lens culinaris agglutinin (LCA) lectin. By both epifluorescence microscopy and IBFC, the LCA binding was increased in the ubiquitinated spermatozoa with diminished ARSA immunoreactivity. ARSA was also found in the epididymal fluid suggesting that in addition to intrinsic ARSA expression in the testis, epididymal spermatozoa take up ARSA on their surface during the epididymal passage. We conclude that sperm surface ARSA is one of the ubiquitinated sperm surface glycoproteins in defective bull spermatozoa. Defective sperm surface thus differs from normal sperm surface by increased ubiquitination, reduced ARSA binding, and altered glycosylation.

Arylsulfatases A and B: From normal tissues to malignant tumors

Arylsulfatases are lysosomal enzymes with important roles in the cell metabolism. Several subtypes of arylsulfatase are known, from A to K. Congenital deficiencies of arylsulfatases, especially A (ARSA) and B (ARSB), can induce metabolic disorders such as metachromatic leucodystrophy (ARSA deficiency) and Maroteaux-Lamy syndrome (ARSB deficiency). ARSA and ARSB pseudodeficiencies were recently described but their exact roles are far to be known. The aim of this review was to synthesize the literature data, combined with personal results, regarding the roles of ARSA and ARSB in non-tumor disorders but also carcinogenesis. Few than 50 published papers regard ARSA and ARSB expression in cancer. They suggest decreased activity of these arylsulfatases in most of carcinomas, compared with normal tissues. However, the clinical impact is still unknown. Further complex studies are necessary to be done, to understand the role of ARSA and ARSB expression in cancer.

A closer look at ARSA activity in a patient with metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is an autosomal recessive lysosomal storage disease mainly caused by a deficiency of arylsulfatase A activity. The typical clinical course of patients with the late infantile form includes a regression in motor skills with progression to dysphagia, seizures, hypotonia and death. We present a case of a 4-year-old female with rapidly progressive developmental regression with loss of motor milestones, spasticity and dysphagia. MRI showed volume loss and markedly abnormal deep white matter. Enzymatic testing in one laboratory showed arylsulfatase A activity in their normal range. However, extraction of urine showed a large increase in sulfatide excretion in a second laboratory. Measurement of arylsulfatase A in that laboratory showed a partial decrease in arylsulfatase A activity measured under typical conditions (about 37% of the normal mean). When the concentration of substrate in the assay was lowered to one quarter of that normally used, this individual had activity <10% of controls. The patient was found to be homozygous for an unusual missense mutation in the arylsulfatase A gene confirming the diagnosis of MLD. This case illustrates the importance of careful biochemical and molecular testing for MLD if there is suspicion of this diagnosis.

[Late infantile metachromatic leukodystrophy: case report]

Metachromatic leukodystrophy is an uncommon autosomal recessive disease caused by the deficiency of the arylsulfatase A lysosomal enzyme, which causes a progressive demyelin-ation with subsequent neurological manifestations. Between its manifestation forms, the one presenting in late childhood has the worst prognosis. Magnetic resonance plays an important role in the characterization of underlying abnormalities, which makes it possible to rule out other clinical conditions and approximate a diagnosis that is later confirmed by the appropriate molecular studies. Given the limited knowledge of the condition, coupled with a generally fatal clinical course, an early and accurate identification is fundamental in order to start palliative management and genetic counseling. A 24 months old female patient with psychomotor retardation history and imaging findings compatible with leukodystrophy is presented. Enzymatic and molecular studies confirmed a diagnosis of late childhood metachromatic leukodystrophy.

Late-Onset Metachromatic Leukodystrophy with Early Onset Dementia Associated with a Novel Missense Mutation in the Arylsulfatase A Gene

A 48-year-old male patient presented with personality changes and progressive memory loss over 2 years with initially suspected Hashimoto's encephalopathy. Strategy of diagnostic workup of early onset dementia included dementia from neurodegenerative, neuroinflammatory, metabolic/toxic, and psychiatric origin. The patient's neurological exam was normal. MRI revealed a leukencephalopathy, predominantly in the frontal periventricular white matter, without notable changes over 2 years. On neurophysiological examination, prolonged central conduction times and a sensorimotor polyneuropathy were noted. Neuropsychological impairment included disorientation in place and a reduced short time memory. Behavioral alterations were predominated by sudden mood changes and disinhibition. Cerebrospinal fluid was normal. Despite presence of thyroid autoantibodies, glucocorticosteroid treatment did not improve the dementia. A metachromatic leukodystrophy was diagnosed by decreased arylsulfatase-A activity in leucocytes/fibroblasts and identification of a compound heterozygous mutation in the ARSA gene: c.542T>G (exon 3) and the novel mutation c.1013T>C (exon 6). Pathogenic function was suggested by bioinformatic mutation search. In a patient with early onset dementia, strategic diagnostic workup including genetic assessment revealed an adult-onset metachromatic leukodystrophy with a novel mutation in the arylsulfatase A gene.

Whole-exome sequencing identifies compound heterozygous mutations in ARSA of two siblings presented with atypical onset of metachromatic leukodystrophy from a Chinese pedigree

BACKGROUND

Metachromatic leukodystrophy (MLD) is a rare inherited lysosomal storage disorder caused mainly by variants in arylsulfatase A (ARSA) gene. MLD can be divided into three major clinical forms according to the age of onset: late infantile, juvenile, and adult. We report two siblings of late infantile MLD presenting with cerebellar ataxia as the only first clinical symptom.

METHODS

Because of the unspecific neurological manifestation, whole-exome sequencing (WES) was performed to find disease-causing mutations for molecular diagnosis. Then successive MRI and ARSA activity determination were performed to further confirm the diagnosis. Moreover, the prenatal diagnosis was carried out on the basis of molecular diagnosis.

RESULTS

The siblings exhibited compound heterozygous variants {[c.302G>T]+[c.1344dupC]} in the ARSA gene, and both of the variants have been reported as disease-causing mutations previously. The results of MRI and low ARSA activity confirmed the diagnosis of MLD. Prenatal diagnosis showed that the fetus was a heterozygous carrier.

CONCLUSIONS

It is recommended that WES be considered as a first line diagnostic procedure to discover potential disease-causing genetic variants in affected individuals with hereditary traits but without definite clinical diagnosis. However, the final diagnosis should be confirmed by comprehensive evaluations including biochemical, enzymatic or imaging investigations.

Biochemical and Genetic Analysis of Seven Korean Individuals With Suspected Metachromatic Leukodystrophy

Metachromatic leukodystrophy (MLD) is an autosomal recessive disease caused by a deficiency in arylsulfatase A (ARSA). However, decreased ARSA activity is also observed in pseudodeficiency (PD). To distinguish between MLD and PD, we performed gene mutation and sulfatide analyses by using dried blood spots (DBSs) from seven Korean individuals who underwent an analysis of ARSA activity. DNA was extracted from DBSs, and PCR-direct sequencing of ARSA was performed. The cDNA obtained was analyzed to confirm a novel mutation. Of the seven subjects, three were confirmed as having MLD, one was confirmed as having MLD-PD, one was confirmed as having PD, and the remaining two were obligate heterozygotes. We verified the novel pathogenic variant c.1107+1delG by performing familial and cDNA analyses. Sulfatide concentrations in DBSs were analyzed and were quantified by using ultra-performance liquid chromatography and tandem mass spectrometry, respectively. Total sulfatide concentration was inversely correlated with ARSA activity (Spearman's coefficient of rank correlation, P=0.929, P=0.0025). The results of this mutational and biochemical study on MLD will increase our understanding of the genetic characteristics of MLD in Koreans.

Dysfunction of platelet-derived growth factor receptor α (PDGFRα) represses the production of oligodendrocytes from arylsulfatase A-deficient multipotential neural precursor cells

The membrane-bound receptor for platelet-derived growth factor A (PDGFRα) is crucial for controlling the production of oligodendrocytes (OLs) for myelination, but regulation of its activity during OL differentiation is largely unknown. We have examined the effect of increased sulfated content of galactosylceramides (sulfatides) on the regulation of PDGFRα in multipotential neural precursors (NPs) that are deficient in arylsulfatase A (ASA) activity. This enzyme is responsible for the lysosomal hydrolysis of sulfatides. We show that sulfatide accumulation significantly impacts the formation of OLs via deregulation of PDGFRα function. PDGFRα is less associated with detergent-resistant membranes in ASA-deficient cells and showed a significant decrease in AKT phosphorylation. Rescue experiments with ASA showed a normalization of the ratio of long versus short sulfatides, restored PDGFRα levels, corrected its localization to detergent-resistant membranes, increased AKT phosphorylation, and normalized the production of OLs in ASA-deficient NPs. Moreover, our studies identified a novel mechanism that regulates the secretion of PDGFRα in NPs, in glial cells, and in the brain cortex via exosomal shedding. Our study provides a first step in understanding the role of sulfatides in regulating PDGFRα levels in OLs and its impact in myelination.

A homozygote for the c.459+1G>A mutation in the ARSA gene presents with cerebellar ataxia as the only first clinical sign of metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is a rare lysosomal disorder caused by deficient activity of arylsulfatase A or the lack of saposin B, which results in the accumulation of sulfatide in the oligodendrocytes and in the Schwann cells. Three main clinical types of MLD can be distinguished according to the age of onset and the dynamics of clinical outcome: late infantile, juvenile, and adult. We report on a case of late infantile MLD presenting with cerebellar ataxia as the only first clinical sign preceding even changes in white matter visible in MR imaging. The diagnosis was made on the basis of successive MRI, characteristic of demyelination, which developed in the course of the disease, and on the results of the following biochemical and molecular analyses. Very low residual activity of arylsulfatase A was demonstrated in blood leukocytes and the patient was a homozygote for a common mutation c.459+1G>A in the ARSA gene. Since cerebellar ataxia is a relatively common but unspecific neurological symptom in toddlers, it is recommended that MLD be considered as part of the differential diagnosis even if the initial neuroimaging studies are normal and ataxia is the only clinical symptom of the disease.

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.

Sixteen novel mutations in the arylsulfatase A gene causing metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is a lysosomal storage disorder caused mainly by mutations in the arylsulfatase A (ARSA) gene. In this manuscript we report sixteen novel mutations identified in the ARSA gene of fifteen unrelated patients affected with MLD. Of these 16 mutations nine were missense mutations (p.L11Q, p.S44P, p.L81P, p.R84L, p.V177D, p.P284S, p.R288S, p.G301R, p.P425S), three were nonsense mutations (p.Q51X, p.Y149X, p.C156X), three were frame shift mutations (c.28delG, c.105C>A+106_124dup, c.189delC) and one was a splice-site mutation (c.1102-2A>G). In addition, three previously reported mutations were identified on an allelic background different from the one in the original reports. Two mutations, p.G309S and p.E312D, were identified on the background of the so-called pseudodeficiency (Pd) allele while previously they were reported alone. On the other hand, mutation p.R311X was identified in two unrelated patients not in cis with the Pd mutations, as previously reported.