Mental retardation in mucopolysaccharidoses correlates with high molecular weight urinary heparan sulphate derived glucosamine

Open-label, single-center, clinical study evaluating the safety, tolerability and clinical effects of pentosan polysulfate sodium in subjects with mucopolysaccharidosis I

Lysosomal enzyme deficiency in mucopolysaccharidosis (MPS) I results in glycosaminoglycan (GAG) accumulation leading to pain and limited physical function. Disease-modifying treatments for MPS I, enzyme replacement, and hematopoietic stem cell therapy (HSCT), do not completely resolve MPS I symptoms, particularly skeletal manifestations. The GAG reduction, anti-inflammatory, analgesic, and tissue remodeling properties of pentosan polysulfate sodium (PPS) may provide disease-modifying treatment for musculoskeletal symptoms and joint inflammation in MPS I following ERT and/or HSCT. The safety and efficacy of PPS were evaluated in four subjects with MPS I aged 14-19 years, previously treated with ERT and/or HSCT. Subjects received doses of 0.75 mg/kg or 1.5 mg/kg PPS via subcutaneous injections weekly for 12 weeks, then every 2 weeks for up to 72 weeks. PPS was well tolerated at both doses with no serious adverse events. MPS I GAG fragment (UA-HNAc [1S]) levels decreased at 73 weeks. Cartilage degradation biomarkers serum C-telopeptide of crosslinked collagen (CTX) type I (CTX-I) and type II (CTX-II) and urine CTX-II decreased in all subjects through 73 weeks. PROMIS scores for pain interference, pain behavior, and fatigue decreased in all subjects through 73 weeks. Physical function, measured by walking distance and dominant hand function, improved at 49 and 73 weeks. Decreased GAG fragments and cartilage degradation biomarkers, and positive PROMIS outcomes support continued study of PPS as a potential disease-modifying treatment for MPS I with improved pain and function outcomes.

Impaired neural differentiation of MPS IIIA patient induced pluripotent stem cell-derived neural progenitor cells

Mucopolysaccharidosis type IIIA (MPS IIIA) is characterised by a progressive neurological decline leading to early death. It is caused by bi-allelic loss-of-function mutations in SGSH encoding sulphamidase, a lysosomal enzyme required for heparan sulphate glycosaminoglycan (HS GAG) degradation, that results in the progressive build-up of HS GAGs in multiple tissues most notably the central nervous system (CNS). Skin fibroblasts from two MPS IIIA patients who presented with an intermediate and a severe clinical phenotype, respectively, were reprogrammed into induced pluripotent stem cells (iPSCs). The intermediate MPS IIIA iPSCs were then differentiated into neural progenitor cells (NPCs) and subsequently neurons. The patient derived fibroblasts, iPSCs, NPCs and neurons all displayed hallmark biochemical characteristics of MPS IIIA including reduced sulphamidase activity and increased accumulation of an MPS IIIA HS GAG biomarker. Proliferation of MPS IIIA iPSC-derived NPCs was reduced compared to control, but could be partially rescued by reintroducing functional sulphamidase enzyme, or by doubling the concentration of the mitogen fibroblast growth factor 2 (FGF2). Whilst both control heparin, and MPS IIIA HS GAGs had a similar binding affinity for FGF2, only the latter inhibited FGF signalling, suggesting accumulated MPS IIIA HS GAGs disrupt the FGF2:FGF2 receptor:HS signalling complex. Neuronal differentiation of MPS IIIA iPSC-derived NPCs was associated with a reduction in the expression of neuronal cell marker genes βIII-TUBULIN, NF-H and NSE, revealing reduced neurogenesis compared to control. A similar result was achieved by adding MPS IIIA HS GAGs to the culture medium during neuronal differentiation of control iPSC-derived NPCs. This study demonstrates the generation of MPS IIIA iPSCs, and NPCs, the latter of which display reduced proliferation and neurogenic capacity. Reduced NPC proliferation can be explained by a model in which soluble MPS IIIA HS GAGs compete with cell surface HS for FGF2 binding. The mechanism driving reduced neurogenesis remains to be determined but appears downstream of MPS IIIA HS GAG accumulation.

Differences in MPS I and MPS II Disease Manifestations

Mucopolysaccharidosis (MPS) type I and II are two closely related lysosomal storage diseases associated with disrupted glycosaminoglycan catabolism. In MPS II, the first step of degradation of heparan sulfate (HS) and dermatan sulfate (DS) is blocked by a deficiency in the lysosomal enzyme iduronate 2-sulfatase (IDS), while, in MPS I, blockage of the second step is caused by a deficiency in iduronidase (IDUA). The subsequent accumulation of HS and DS causes lysosomal hypertrophy and an increase in the number of lysosomes in cells, and impacts cellular functions, like cell adhesion, endocytosis, intracellular trafficking of different molecules, intracellular ionic balance, and inflammation. Characteristic phenotypical manifestations of both MPS I and II include skeletal disease, reflected in short stature, inguinal and umbilical hernias, hydrocephalus, hearing loss, coarse facial features, protruded abdomen with hepatosplenomegaly, and neurological involvement with varying functional concerns. However, a few manifestations are disease-specific, including corneal clouding in MPS I, epidermal manifestations in MPS II, and differences in the severity and nature of behavioral concerns. These phenotypic differences appear to be related to different ratios between DS and HS, and their sulfation levels. MPS I is characterized by higher DS/HS levels and lower sulfation levels, while HS levels dominate over DS levels in MPS II and sulfation levels are higher. The high presence of DS in the cornea and its involvement in the arrangement of collagen fibrils potentially causes corneal clouding to be prevalent in MPS I, but not in MPS II. The differences in neurological involvement may be due to the increased HS levels in MPS II, because of the involvement of HS in neuronal development. Current treatment options for patients with MPS II are often restricted to enzyme replacement therapy (ERT). While ERT has beneficial effects on respiratory and cardiopulmonary function and extends the lifespan of the patients, it does not significantly affect CNS manifestations, probably because the enzyme cannot pass the blood-brain barrier at sufficient levels. Many experimental therapies, therefore, aim at delivery of IDS to the CNS in an attempt to prevent neurocognitive decline in the patients.

Posterior fossa horns; a new calvarial finding of mucopolysaccharidoses with well-known cranial MRI features

Background/aim

Mucopolysaccharidoses (MPS) are a group of hereditary metabolic diseases. The aim of this study was to share the previously unreported calvarial finding of internal hypertrophy of the occipitomastoid sutures (IHOMS) together with some other well-known cranial MRI findings in this patient series.

Materials and methods

A retrospective evaluation was conducted of 80 cranial MRIs of patients who had been diagnosed and followed up with MPS from 2008 to 2019 in our center. Of these patients, 11 had Hurler, 14 had Hunter, 24 had Sanfilippo, 15 had Morquio, 14 had Maroteaux–Lamy, and 2 had Sly disease. The cranial MRIs were assessed in two main groups as parenchymal intradural cranial MRI findings and extradural calvarial findings.

Results

The most common parenchymal intradural cranial MRI findings were white matter signal alterations (n = 51, 63%) and perivascular space enlargements (n = 39, 48%). The most common extradural calvarial findings were J-shaped sella (n = 45, 56%) and tympanic effusion (n = 44, 55%). Although IHOMS was defined in a relatively small number of the patients (n = 12, 15%), the prevalence rate was high in MPS type I (n = 6, 54%).

Conclusion

The abnormal cranial MRI findings of the MPS patients, including the newly identified IHOMS, may provide diagnostic clues to differentiate the type of the disease in radiological imaging.

Anatomical changes and pathophysiology of the brain in mucopolysaccharidosis disorders

Mucopolysaccharidosis (MPS) disorders are caused by deficiencies in lysosomal enzymes, leading to impaired glycosaminoglycan (GAG) degradation. The resulting GAG accumulation in cells and connective tissues ultimately results in widespread tissue and organ dysfunction. The seven MPS types currently described are heterogeneous and progressive disorders, with somatic and neurological manifestations depending on the type of accumulating GAG. Heparan sulfate (HS) is one of the GAGs stored in patients with MPS I, II, and VII and the main GAG stored in patients with MPS III. These disorders are associated with significant central nervous system (CNS) abnormalities that can manifest as impaired cognition, hyperactive and/or aggressive behavior, epilepsy, hydrocephalus, and sleeping problems. This review discusses the anatomical and pathophysiological CNS changes accompanying HS accumulation as well as the mechanisms believed to cause CNS abnormalities in MPS patients. The content of this review is based on presentations and discussions on these topics during a meeting on the brain in MPS attended by an international group of MPS experts.

The efficacy of intracerebroventricular idursulfase-beta enzyme replacement therapy in mucopolysaccharidosis II murine model: heparan sulfate in cerebrospinal fluid as a clinical biomarker of neuropathology

Mucopolysaccharidosis II (MPS II) is caused by a deficiency of iduronate-2-sulfatase that results in accumulation of glycosaminoglycans (GAG), including heparan sulfate (HS), which is considered to contribute to neuropathology. We examined the efficacy of intracerebroventricular (ICV) enzyme replacement therapy (ERT) of idursulfase-beta (IDS-β) and evaluated the usefulness of HS as a biomarker for neuropathology in MPS II mice. We first examined the efficacy of three different doses (3, 10, and 30 μg) of single ICV injections of IDS-β in MPS II mice. After the single-injection study, its long-term efficacy was elucidated with 30 μg of IDS-β ICV injections repeated every 4 weeks for 24 weeks. The efficacy was assessed by the HS content in the cerebrospinal fluid (CSF) and the brain of the animals along with histologic examinations and behavioral tests. In the single-injection study, the 30 μg of IDS-β ICV injection showed significant reductions of HS content in brain and CSF that were maintained for 28 days. Furthermore, HS content in CSF was significantly correlated with HS content in brain. In the long-term repeated-injection study, the HS content in the brain and CSF was also significantly reduced and correlated. The histologic examinations showed a reduction in lysosomal storage. A significant improvement in memory/learning function was observed in open-field and fear-conditioning tests. ICV ERT with 30 μg of IDS-β produced significant improvements in biochemical, histological, and functional parameters in MPS II mice. Furthermore, we demonstrate for the first time that the HS in the CSF had significant positive correlation with brain tissue HS and GAG levels, suggesting HS in CSF as a useful clinical biomarker for neuropathology.