Genotypic characterization of Brazilian patients with infantile and juvenile forms of metachromatic leukodystrophy

Improving newborn screening test performance for metachromatic leukodystrophy: Recommendation from a pre-pilot study that identified a late-infantile case for treatment

Metachromatic leukodystrophy (MLD) is a devastating rare neurodegenerative disease. Typically, loss of motor and cognitive skills precedes early death. The disease is characterised by deficient lysosomal arylsulphatase A (ARSA) activity and an accumulation of undegraded sulphatide due to pathogenic variants in the ARSA gene. Atidarsagene autotemcel (arsa-cel), an ex vivo haematopoietic stem cell gene therapy was approved for use in the UK in 2021 to treat early-onset forms of pre- or early-symptomatic MLD. Optimal outcomes require early diagnosis, but in the absence of family history this is difficult to achieve without newborn screening (NBS). A pre-pilot MLD NBS study was conducted as a feasibility study in Manchester UK using a two-tiered screening test algorithm. Pre-established cutoff values (COV) for the first-tier C16:0 sulphatide (C16:0-S) and the second-tier ARSA tests were evaluated. Before the pre-pilot study, initial test validation using non‑neonatal diagnostic bloodspots demonstrated ARSA pseudodeficiency status was associated with normal C16:0-S results for age (n = 43) and hence not expected to cause false positive results in this first-tier test. Instability of ARSA in bloodspot required transfer of NBS bloodspots from ambient temperature to -20°C storage within 7-8 days after heel prick, the earliest possible in this UK pre-pilot study. Eleven of 3687 de-identified NBS samples in the pre-pilot were positive for C16:0-S based on the pre-established COV of ≥170 nmol/l or ≥ 1.8 multiples of median (MoM). All 11 samples were subsequently tested negative determined by the ARSA COV of <20% mean of negative controls. However, two of 20 NBS samples from MLD patients would be missed by this C16:0-S COV. A further suspected false negative case that displayed 4% mean ARSA activity by single ARSA analysis for the initial test validation was confirmed by genotyping of this NBS bloodspot, a severe late infantile MLD phenotype was predicted. This led to urgent assessment of this child by authority approval and timely commencement of arsa-cel gene therapy at 11 months old. Secondary C16:0-S analysis of this NBS bloodspot was 150 nmol/l or 1.67 MoM. This was the lowest result reported thus far, a new COV of 1.65 MoM is recommended for future pilot studies. Furthermore, preliminary data of this study showed C16:1-OH sulphatide is more specific for MLD than C16:0-S. In conclusion, this pre-pilot study adds to the international evidence that recommends newborn screening for MLD, making it possible for patients to benefit fully from treatment through early diagnosis.

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.

Metachromatic Leukodystrophy: Diagnosis and Treatment Challenges

Metachromatic leukodystrophy is a neurological disease of the lysosomal deposit that has a significant impact given the implications for the neurodegenerative deterioration of the patient. Currently, there is no treatment available that reverses the development of characteristic neurological and systemic symptoms. Objective. Carry out an updated bibliographic search on the most critical advances in the treatment and diagnosis for LDM. A retrospective topic review published in English and Spanish in the Orphanet and Pubmed databases. Current treatment options, such as enzyme replacement therapy and hematopoietic stem cell transplantation aimed at decreasing the rapid progression of the disease, improving patient survival; however, these are costly. The pathophysiological events of intracellular signaling related to the deficiency of the enzyme Arylsulfatase A and subsequent accumulation of sulphatides and glycosylated ceramides have not yet been established. Recently, the accumulation of C16 sulphatides has been shown to inhibit glycolysis and insulin secretion in pancreatic cells. The significant advance in technology has allowed timely diagnosis in patients suffering from LDM; however, they still do not have an effective treatment.

Identification of a novel mutation in ARSA gene in three patients of an Iranian family with metachromatic leukodystrophy disorder

Metachromatic leukodystrophy disorder (MLD) is an autosomal recessive and lysosomal storage disease. The disease is caused by the deficiency of the enzyme arylsulfatase A (ARSA) which is encoded by the ARSA gene. Different mutations have been reported in different populations. The present study was aimed to detect the mutation type of the ARSA gene in three relative Iranian patients. We found a novel homozygous missense mutation c.1070 G > T (p.Gly357Val) in exon 6 of these patients. The mutation was found to be reported for the first time in MLD patients. The data can update the mutation profile and contribute toward improved clinical management and counseling of MLD patients.

Mutation Frequency of Three Neurodegenerative Lysosomal Storage Diseases: From Screening to Treatment?

BACKGROUND

The ascertainment of mutation frequencies in the general population may have impact on the population's wellbeing and respective healthcare services. Furthermore, it may help define which approaches will be more effective for certain patients based on the genetic cause of disease.

AIM OF THE STUDY

Determine the frequency of three mutations, known to be a major cause of three distinct Lysosomal Storage Diseases (LSDs).

METHODS

The following pre-requisites were met: each mutation accounted for over 55% of the disease alleles among previously reported unrelated patients, all three diseases were among the most prevalent LSDs in the population under study, they all involved devastating deterioration of the nervous system, lacked curative treatment and may be fatal in childhood or adolescence. The anonymous samples used in this study were representative of the whole population; mutations were tested by PCR based methods, positive results were further confirmed. The diseases studied were Mucopolysaccharidosis type I (Hurler, MIM 607014), Tay Sachs disease variant B1 (TS, MIM 272800) and Metachromatic Leukodystrophy (MLD, MIM 250100); the mutations were, respectively, p.W402X, p.R178C and c.465+1G>A.

RESULTS AND CONCLUSION

Increased carrier frequencies were found for Tay Sachs disease variant B1 HEXA p.R178C mutation (1:340) and for the infantile MLD ARSA c.465+1G> A mutation (1:350) denoting higher risk for these sub-types of disease in Portugal and possibly in individuals of Iberian ancestry. Carrier screening in target populations may provide the foundations for more effective approaches to precision medicine.

Neurological outcomes after hematopoietic stem cell transplantation for cerebral X-linked adrenoleukodystrophy, late onset metachromatic leukodystrophy and Hurler syndrome

Objective

To describe survival and neurological outcomes after HSCT for these disorders.

Methods

Seven CALD, 2 MLD and 2 MPS-IH patients underwent HSCT between 2007 and 2014. Neurological examinations, magnetic resonance imaging, molecular and biochemical studies were obtained at baseline and repeated when appropriated.

Results

Favorable outcomes were obtained with 4/5 related and 3/6 unrelated donors. Two patients died from procedure-related complications. Nine transplanted patients were alive after a median of 3.7 years: neurological stabilization was obtained in 5/6 CALD, 1/2 MLD, and one MPS-IH patient. Brain lesions of the MPS-IH patient were reduced four years after HSCT.

Conclusion

Good outcomes were obtained when HSCT was performed before adulthood, early in the clinical course, and/or from a related donor.

Determination of frequencies of alleles, associated with the pseudodeficiency of lysosomal hydrolases, in population of Ukraine

The pseudodeficiency of lysosomal hydrolases described as a significant reduction in enzyme activi­ty in vitro in clinically healthy individuals, can lead to diagnostic errors in the process of biochemical analysis of lysosomal storage disease in case of its combination with pathology of another origin. Pseudodeficiency is mostly caused by some non-pathogenic changes in the corresponding gene. These changes lead to the in vitro lability of the enzyme molecule, whereas in vivo the enzyme retains its functional activity. To assess the prevalence of the most common lysosomal hydrolases pseudodeficiency alleles in Ukraine, we have determined the frequency of alleles c.1055A>G and c.* 96A>G in the ARSA gene, substitutions c.739C>T (R247W) and c.745C>T (R249W) in the HEXA gene, c.1726G>A (G576S) and c.2065G>A (E689K) in the GAA gene, c.937G>T (D313Y) in the GLA1 gene and c.898G>A (A300T) in the IDUA gene in a group of 117 healthy individuals from different regions of the country and 14 heterozygous carriers of pathogenic mutations in the HEXA gene (parents of children with confirmed diagnosis of Tay-Sachs disease). The total frequency of haplotypes, associated with arylsulfatase A pseudodeficiency, in healthy people in Ukraine (c.1055G/c.*96G and c.1055G/c.*96A haplotypes) was 10.3%. The frequency of c.739C>T (R247W) allele, associated with hexo­saminidase A pseudodeficiency, among Tay-Sachs carriers from Ukraine was 7.1%. The total frequency of α-glucosidase pseudodeficiency haplotypes in healthy individuals in Ukraine (c.1726A/c.2065A and c.1726G/c.2065A haplotypes) was 2.6%. No person among examined individuals with the substitution c.937G>T (D313Y) in the GLA1 gene and c.898G>A (A300T) in the IDUA gene was found. The differential diagnostics of lysosomal storage diseases requires obligatory determination of the presence of the pseudodeficiency alleles, particularly the ones with high incidence in the total population. Ignoring phenomenon of pseudodeficiency may lead to serious diagnostic errors.