Lysosomal storage diseases are caused by defective lysosomal function, such as impaired lysosomal enzyme activities, which include more than 70 different diseases. Although biomarkers and therapies have been developed to date for some of them, many others remain challenging to diagnose and treat. In this study, an elevated level of Globotriaosylsphingosine (Lyso-Gb3), an already known biomarker for Fabry disease, was confirmed in the knock-out cells of the GLA, GNPTAB, and PSAP genes and models for Fabry, mucolipidosis II/III (ML II/III), and combined saposin deficiency, respectively. Lyso-Gb3 was high in ML II/III patient skin fibroblasts compared with normal cells and was decreased after total lysosomal enzyme supplementation. There have been no useful biomarkers reported in ML II/III until now. This study shows that Lyso-Gb3 is elevated in ML II/III patient cells and is decreased by treatment, indicating that Lyso-Gb3 is a potential biomarker for ML II/III.

Prosaposin is a precursor of lysosomal hydrolases activator proteins, saposins, and also acts as a secretory protein that is not processed into saposins. Prosaposin elicits neurotrophic function via G protein-coupled receptor (GPR) 37, and prosaposin deficiency causes abnormal vestibuloauditory end-organ development. In this study, immunohistochemistry was used to examine prosaposin and GPR37 expression patterns in the mouse cochlear and vestibular nuclei. Prosaposin immunoreactivity was observed in neurons and glial cells in both nuclei. GPR37 immunoreactivity was observed in only some neurons, and its immunoreactivity in the vestibular nucleus was weaker than that in the cochlear nucleus. This study suggests a possibility that prosaposin deficiency affects not only the end-organs but also the first center of the vestibuloauditory system.

Sphingolipidoses are a subcategory of lysosomal storage diseases (LSDs) caused by mutations in enzymes of the sphingolipid catabolic pathway. Like many LSDs, neurological involvement in sphingolipidoses leads to early mortality with limited treatment options. Given the role of myelin loss as a major contributor toward LSD-associated neurodegeneration, we investigated the pathways contributing to demyelination in a CRISPR-Cas9-generated zebrafish model of combined saposin (psap) deficiency. psap knockout (KO) zebrafish recapitulated major LSD pathologies, including reduced lifespan, reduced lipid storage, impaired locomotion and severe myelin loss; loss of myelin basic protein a (mbpa) mRNA was progressive, with no changes in additional markers of oligodendrocyte differentiation. Brain transcriptomics revealed dysregulated mTORC1 signaling and elevated neuroinflammation, where increased proinflammatory cytokine expression preceded and mTORC1 signaling changes followed mbpa loss. We examined pharmacological and genetic rescue strategies via water tank administration of the multiple sclerosis drug monomethylfumarate (MMF), and crossing the psap KO line into an acid sphingomyelinase (smpd1) deficiency model. smpd1 mutagenesis, but not MMF treatment, prolonged lifespan in psap KO zebrafish, highlighting the modulation of acid sphingomyelinase activity as a potential path toward sphingolipidosis treatment.

Hematopoietic cell transplantation after myeloablative conditioning has been used to treat various genetic metabolic syndromes but is largely ineffective in diseases affecting the brain presumably due to poor and variable myeloid cell incorporation into the central nervous system. Here, we developed and characterized a near-complete and homogeneous replacement of microglia with bone marrow cells in mice without the need for genetic manipulation of donor or host. The high chimerism resulted from a competitive advantage of scarce donor cells during microglia repopulation rather than enhanced recruitment from the periphery. Hematopoietic stem cells, but not immediate myeloid or monocyte progenitor cells, contained full microglia replacement potency equivalent to whole bone marrow. To explore its therapeutic potential, we applied microglia replacement to a mouse model for Prosaposin deficiency, which is characterized by a progressive neurodegeneration phenotype. We found a reduction of cerebellar neurodegeneration and gliosis in treated brains, improvement of motor and balance impairment, and life span extension even with treatment started in young adulthood. This proof-of-concept study suggests that efficient microglia replacement may have therapeutic efficacy for a variety of neurological diseases.

Diagnosis of rare disorders requires heightened clinical acumen. When such disorders present with atypical or novel features, it adds to the diagnostic challenge. A 9-month-old female infant who had received a diagnosis of neonatal hepatitis due to cytomegalovirus infection at 2 months of age presented to our institute with developmental delay, fever, vomiting, feeding difficulty, breathlessness and features of elevated intracranial pressure due to hydrocephalus. Key examination findings with cholestatic jaundice as an early manifestation led to suspicion of type 4 Farber disease. Observation of hydrocephalus, hypertension, bilateral pinguecula and Erlenmeyer flask deformity of the femur were unusual findings for Farber disease. The child had few features (pinguecula, Erlenmeyer flask deformity and hydrocephalus) overlapping with Gaucher disease. Alternatively, prosaposin deficiency (Farber disease type 7) was another differential diagnosis. Diagnosis of Farber disease was confirmed by detection of foamy macrophages on skin biopsy and two homozygous missense variants in ASAH1 gene.