Biochemical signatures of disease severity in multiple sulfatase deficiency

Consensus guidelines for the monitoring and management of metachromatic leukodystrophy in the United States

Metachromatic leukodystrophy (MLD) is a fatal, progressive neurodegenerative disorder caused by biallelic pathogenic mutations in the ARSA (Arylsulfatase A) gene. With the advent of presymptomatic diagnosis and the availability of therapies with a narrow window for intervention, it is critical to define a standardized approach to diagnosis, presymptomatic monitoring, and clinical care. To meet the needs of the MLD community, a panel of MLD experts was established to develop disease-specific guidelines based on healthcare resources in the United States. This group developed a consensus opinion for best-practice recommendations, as follows: (i) Diagnosis should include both genetic and biochemical testing; (ii) Early diagnosis and treatment for MLD is associated with improved clinical outcomes; (iii) The panel supported the development of newborn screening to accelerate the time to diagnosis and treatment; (iv) Clinical management of MLD should include specialists familiar with the disease who are able to follow patients longitudinally; (v) In early onset MLD, including late infantile and early juvenile subtypes, ex vivo gene therapy should be considered for presymptomatic patients where available; (vi) In late-onset MLD, including late juvenile and adult subtypes, hematopoietic cell transplant (HCT) should be considered for patients with no or minimal disease involvement. This document summarizes current guidance on the presymptomatic monitoring of children affected by MLD as well as the clinical management of symptomatic patients. Future data-driven evidence and evolution of these recommendations will be important to stratify clinical treatment options and improve clinical care.

Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry Analysis of Urinary Oligosaccharides and Glycoamino Acids for the Diagnosis of Mucopolysaccharidosis and Glycoproteinosis

BACKGROUND

Mucopolysaccharidosis (MPS) and glycoproteinosis are 2 groups of heterogenous lysosomal storage disorders (LSDs) caused by defective degradation of glycosaminoglycans (GAGs) and glycoproteins, respectively. Oligosaccharides and glycoamino acids have been recognized as biomarkers for MPS and glycoproteinosis. Given that both groups of LSDs have overlapping clinical features, a multiplexed assay capable of unambiguous subtyping is desired for accurate diagnosis, and potentially for severity stratification and treatment monitoring.

METHODS

Urinary oligosaccharides were derivatized with 3-methyl-1-phenyl-2-pyrazoline-5-one (PMP) and analyzed by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) together with the underivatized glycoamino acids. Novel biomarkers were identified with a semi-targeted approach with precursor mass scanning, the fragmentation pattern (if applicable), and the biochemical basis of the condition.

RESULTS

A UPLC-MS/MS analysis with improved chromatographic separation was developed. Novel biomarkers for MPS-IIIA, IIIB, IIIC, and VII were identified and validated. A total of 28 oligosaccharides, 2 glycoamino acids, and 2 ratios were selected as key diagnostic biomarkers. Validation studies including linearity, lower limit of quantitation (LLOQ), and precision were carried out with the assay performance meeting the required criteria. Age-specific reference ranges were collected. In the 76 untreated patients, unambiguous diagnosis was achieved with 100% sensitivity and specificity. Additionally, the levels of disease-specific biomarkers were substantially reduced in the treated patients.

CONCLUSIONS

A multiplexed UPLC-MS/MS assay for urinary oligosaccharides and glycoamino acids measurement was developed and validated. The assay is suitable for the accurate diagnosis and subtyping of MPS and glycoproteinosis, and potentially for severity stratification and monitoring response to treatment.

A novel iPSC model reveals selective vulnerability of neurons in multiple sulfatase deficiency

Multiple sulfatase deficiency (MSD) is an ultra-rare, inherited lysosomal storage disease caused by mutations in the gene sulfatase modifying factor 1 (SUMF1). MSD is characterized by the functional deficiency of all sulfatase enzymes, leading to the storage of sulfated substrates including glycosaminoglycans (GAGs), sulfolipids, and steroid sulfates. Patients with MSD experience severe neurological impairment, hearing loss, organomegaly, corneal clouding, cardiac valve disease, dysostosis multiplex, contractures, and ichthyosis. Here, we generated a novel human model of MSD by reprogramming patient peripheral blood mononuclear cells to establish an MSD induced pluripotent stem cell (iPSC) line (SUMF1 p.A279V). We also generated an isogenic control iPSC line by correcting the pathogenic variant with CRISPR/Cas9 gene editing. We successfully differentiated these iPSC lines into neural progenitor cells (NPCs) and NGN2-induced neurons (NGN2-iN) to model the neuropathology of MSD. Mature neuronal cells exhibited decreased SUMF1 gene expression, increased lysosomal stress, impaired neurite outgrowth and maturation, reduced sulfatase activities, and GAG accumulation. Interestingly, MSD iPSCs and NPCs did not exhibit as severe of phenotypes, suggesting that as neurons differentiate and mature, they become more vulnerable to loss of SUMF1. In summary, we demonstrate that this human iPSC-derived neuronal model recapitulates the cellular and biochemical features of MSD. These cell models can be used as tools to further elucidate the mechanisms of MSD pathology and for the development of therapeutics.