Natural disease history and characterisation of SUMF1 molecular defects in ten unrelated patients with multiple sulfatase deficiency.

BACKGROUND: Multiple sulfatase deficiency is a rare inherited metabolic disorder caused by mutations in the SUMF1 gene. The disease remains poorly known, often leading to a late diagnosis. This study aimed to provide improved knowledge of the disease, through complete clinical, biochemical, and molecular descriptions of a cohort of unrelated patients. The main objective was to identify prognostic markers, both phenotypic and genotypic, to accelerate the diagnosis and improve patient care. METHODS: The phenotypes of ten unrelated patients were fully documented at the clinical and biochemical levels. The long-term follow-up of each patient allowed correlations of the phenotypes to the disease outcomes. Each patient's molecular defects were also identified. Site-directed mutagenesis was used to individually express the mutants and assess their stability. Characterisation of the protein mutants was completed by in silico analyses based on sequence comparisons and structural models. RESULTS: The most severe cases were characterised by the presence of non-neurological symptoms as well as the occurrence of psychomotor regression before 2 years of age. Nine novel SUMF1 mutations were identified. Clinically severe forms were often associated with SUMF1 mutations that strongly affected the protein stability and/or catalytic function as predicted from in silico and western blot analyses. CONCLUSIONS: This detailed clinical description and follow-up of a cohort of patients, together with the molecular characterisation of their underlying defects, contribute to improved knowledge of multiple sulfatase deficiency. Predictors of a bad prognosis were the presence of several non-neurological symptoms and the onset of psychomotor regression before 2 years of age. No strict correlation existed between in vitro residual sulfatase activity and disease severity. Genotype-phenotype correlations related to previously reported mutants were strengthened. These and previous observations allow not only improved prediction of the disease outcome but also provision of appropriate care for patients, in the expectation of specific treatment development.

A non-conserved miRNA regulates lysosomal function and impacts on a human lysosomal storage disorder.

Sulfatases are key enzymatic regulators of sulfate homeostasis with several biological functions including degradation of glycosaminoglycans (GAGs) and other macromolecules in lysosomes. In a severe lysosomal storage disorder, multiple sulfatase deficiency (MSD), global sulfatase activity is deficient due to mutations in the sulfatase-modifying factor 1 (SUMF1) gene, encoding the essential activator of all sulfatases. We identify a novel regulatory layer of sulfate metabolism mediated by a microRNA. miR-95 depletes SUMF1 protein levels and suppresses sulfatase activity, causing the disruption of proteoglycan catabolism and lysosomal function. This blocks autophagy-mediated degradation, causing cytoplasmic accumulation of autophagosomes and autophagic substrates. By targeting miR-95 in cells from MSD patients, we can effectively increase residual SUMF1 expression, allowing for reactivation of sulfatase activity and increased clearance of sulfated GAGs. The identification of this regulatory mechanism opens the opportunity for a unique therapeutic approach in MSD patients where the need for exogenous enzyme replacement is circumvented.

Neonatal multiple sulfatase deficiency with a novel mutation and review of the literature.

Multiple sulfatase deficiency is a rare autosomal recessive disorder in which affected individuals present a complex phenotype due to the impaired activity of all sulfatases. There are different types of multiple sulfatase deficiency; among them, the neonatal form is the most severe, with a broad range of mucopolysaccharidosis-like symptoms and death within the first year of life. The disorder is caused by homozygous or compound heterozygous mutations in the sulfatase-modifying factor-1 (SUMF1) gene. In this article, we describe a non-ichthyotic neonatal multiple sulfatase deficiency patient with a novel mutation in the SUMF1 gene. The missense mutation c.777C>G, for which the patient was homozygous, had been caused by a p.N259K amino acid substitution. We evaluated the patient using clinical findings, neuroimaging studies and molecular analysis via the literature; we also wanted to note the difficulties in the diagnosis of this rare disease.

[Clinical characterization and mutation identification for multiple sulfatase deficiency patients in China].

OBJECTIVE: Multiple sulfatase deficiency is a rare autosomal recessively inherited lysosomal storage disorder characterized by the accumulation of sulfated lipids and acid mucopolysaccharides. The aim of this study was to explore the clinical manifestations, enzyme activities and SUMF1 gene mutations in two Chinese patients with multiple sulfatase deficiency. METHOD: One boy and one girl from two families were studied. Both patients presented with mental retardation, mild coarse facial features, a neurodegenerative course of disease with loss of sensory and motor function after 2 years of age, ichthyosis and skeletal abnormalities (kyphosis or/and scoliosis). Clinical characteristics indicate multiple sulfatase deficiency.Sulfatases activities in blood leucocytes, plasma or cultured fibroblast of the patients were measured.Genomic DNAs were extracted from peripheral blood leukocytes from the patients and their parents. All SUMF1 gene exons and intron-exon boundaries were amplified by PCR and subjected for direct sequencing. RESULT: In case 1, five sulfatases activities of blood leucocytes and four sulfatases of cultured skin-fibroblasts were analyzed.In case 2, three sulfatases activities of blood leucocytes were tested.Significantly decreased sulfatases activities confirmed the diagnosis of multiple sulfatase deficiency.On SUMF1 gene, c.793_794 insATG (p. P265X)/ c.1045C>T (p.R349W) in case 1 and c.451A>G (p.K151E)/ c.1046G>C (p.R349Q) in case 2 were detected, respectively. Three novel mutations c.793_794insAGT, c.1046G>C and c.451A>G were identified. CONCLUSIONS: Multiple sulfatase deficiency usually results in multi-organ damage, especially neurologic, skeletal and skin.Sulfatases assay and SUMF1 gene analysis are necessary for the diagnosis. Two Chinese cases with multiple sulfatase deficiency were firstly reported. Three novel mutations were found.It should be considered that the mutation profile of SUMF1 gene in Chinese patients is different from other populations.

Impaired parkin-mediated mitochondrial targeting to autophagosomes differentially contributes to tissue pathology in lysosomal storage diseases.

Dysfunctional mitochondria are a well-known disease hallmark. The accumulation of aberrant mitochondria can alter cell homeostasis, thus resulting in tissue degeneration. Lysosomal storage disorders (LSDs) are a group of inherited diseases characterized by the buildup of undegraded material inside the lysosomes that leads to autophagic-lysosomal dysfunction. In LSDs, autophagic stress has been associated to mitochondrial accumulation and dysfunction. However, the mechanisms underlying mitochondrial aberrations and how these are involved in tissue pathogenesis remain largely unexplored. In normal conditions, mitochondrial clearance occurs by mitophagy, a selective form of autophagy, which relies on a parkin-mediated mitochondrial priming and subsequent sequestration by autophagosomes. Here, we performed a detailed analysis of key steps of mitophagy in a mouse model of multiple sulfatase deficiency (MSD), a severe type of LSD characterized by both neurological and systemic involvement. We demonstrated that in MSD liver reduced parkin levels resulted in inefficient mitochondrial priming, thus contributing to the accumulation of giant mitochondria that are located outside autophagic vesicles ultimately leading to cytochrome c release and apoptotic cell death. Morphological and functional changes were also observed in mitochondria from MSD brain but these were not directly associated with neuronal cell loss, suggesting a secondary contribution of mitochondria to neurodegeneration. Together, these data shed new light on the mechanisms underlying mitochondrial dysfunction in LSDs and on their tissue-specific differential contribution to the pathogenesis of this group of metabolic disorders.

Transcriptional activation of lysosomal exocytosis promotes cellular clearance.

Lysosomes are cellular organelles primarily involved in degradation and recycling processes. During lysosomal exocytosis, a Ca²âº-regulated process, lysosomes are docked to the cell surface and fuse with the plasma membrane (PM), emptying their content outside the cell. This process has an important role in secretion and PM repair. Here we show that the transcription factor EB (TFEB) regulates lysosomal exocytosis. TFEB increases the pool of lysosomes in the proximity of the PM and promotes their fusion with PM by raising intracellular Ca²âº levels through the activation of the lysosomal Ca²âº channel MCOLN1. Induction of lysosomal exocytosis by TFEB overexpression rescued pathologic storage and restored normal cellular morphology both in vitro and in vivo in lysosomal storage diseases (LSDs). Our data indicate that lysosomal exocytosis may directly modulate cellular clearance and suggest an alternative therapeutic strategy for disorders associated with intracellular storage.

Disease pathogenesis explained by basic science: lysosomal storage diseases as autophagocytic disorders.

Lysosomal storage diseases (LSDs) are characterized by intra-lysosomal accumulation of undegraded metabolites due to the defective activity of lysosomal enzymes. There is a paucity of data, however, relating to the mechanisms that link this accumulation with disease pathology. Several LSDs can be attributed to deficiencies in the activity of sulfatase enzymes. The gene responsible for the post-translational modification that activates sulfatases, sulfatase modifying factor 1 (SUMF1), is defective in the rare autosomal recessive disorder multiple sulfatase deficiency (MSD). A mouse model of MSD (Sumf1 knockout mouse) exhibits a similar phenotype to patients with MSD, with marked lysosomal storage of undegraded metabolites, and increased expression of inflammatory markers and apoptotic markers. Investigation of disease pathology in mouse models of two LSDs (MSD and mucopolysaccharidosis (MPS) Type IIIA) has revealed an increased number of autophagosomes in these animals compared with wild-type mice. This appears to result from impaired autophagosome-lysosome fusion, which may in turn lead to an absence of autophagy. The suggestion that LSDs can be defined as disorders of autophagy implies that there may be some overlap between pathological mechanisms of LSDs and more common neurodegenerative diseases, and this may help provide direction for future therapeutic strategies.