Severe Central Nervous System Demyelination in Sanfilippo Disease

Neurodegeneration and chronic progressive neuroinflammation are well-documented in neurological lysosomal storage diseases, including Sanfilippo disease or mucopolysaccharidosis III (MPS III). Since chronic neuroinflammation has been linked to white matter tract pathology and defects in axonal transmission, we analysed axonal myelination and white matter density in the mouse model of MPS IIIC and human post-mortem brain samples from MPS IIIA, C, and D patients. Analyses of corpus callosum (CC) and spinal cord tissues by immunohistochemistry revealed substantially reduced levels of myelin-associated proteins including Myelin Basic Protein, Myelin Associated Glycoprotein, and Myelin Oligodendrocyte Glycoprotein. Furthermore, ultrastructural analyses revealed disruption of myelin sheath organization and reduced myelin thickness in the brains of MPS IIIC mice and human MPS IIIC patients compared to healthy controls. Oligodendrocytes (OLs) in the CC of MPS IIIC mice were scarce, while examination of the remaining cells revealed numerous enlarged lysosomes containing heparan sulfate, GM3 ganglioside or “zebra bodies” consistent with accumulation of lipids and myelin fragments. In addition, OLs contained swollen mitochondria with largely dissolved cristae, resembling those previously identified in the dysfunctional neurons of MPS IIIC mice. When brains of 7-month-old MPS IIIC mice were analysed by ex-vivo Diffusion Basis Spectrum Imaging to assess microarchitectural changes in the corpus callosum, we found compelling signs of demyelination (26% increase in radial diffusivity) and tissue loss (76% increase in hindered diffusivity). Our findings demonstrate an import role for white matter injury in the pathophysiology of MPS III. Moreover, this study reveals specific parameters and brain regions for MRI analysis, a crucial non-invasive method to evaluate disease progression and therapeutic response in neurological lysosomal storage diseases. ### Competing Interest Statement Alexey V. Pshezhetsky has received research funding and honoraria from Phoenix Nest Inc. * APC(CC-1) : Adenomatous polyposis coli (APC) clone CC1 ARSA : Arylsulfatase A BSA : Bovine serum albumin CC : Corpus callosum CCAC : Canadian Council on Animal Care CNS : Central Nervous System CT-scan : Computed tomography-scan DBSI : Diffusion Basis Spectrum Imaging DTI : Diffuse tension imaging EGFP : Enhanced green fluorescent protein EM : Electron microscopy GAG : Glycosaminoglycan GALC : β-galactocerebrosidase GNS : N-acetylglucosamine-6-sulfate sulfatase HGSNAT : Heparan sulphate acetyl-CoA: α-glucosaminide N-acetyltransferase HS : Heparan sulphate IHC : Immunohistochemistry KI : Knock-in LAMP : Lysosomal associated membrane protein LSD : Lysosomal storage disorder MAG : Myelin-associated glycoprotein MBP : Myelin basic protein MLD : Metachromatic leukodystrophy MOG : Myelin oligodendrocyte glycoprotein MPS : Mucopolysaccharidosis MRI : Magnetic resonance imaging NAGLU : N-acetyl-α-D-glucosaminidase NF-M : Neurofilament medium chain NPC : Niemann-Pick disease type C OCT : Optimum cutting temperature OL : Oligodendrocyte Oligo2 : Oligodendrocyte transcription factor2 PFA : Paraformaldehyde SC : Spinal cord SGSH : N-sulfoglucosamine sulfohydrolase SSC : Somatosensory cortices TEM : Transmission electron microscopy WT : Wild type