Molecular and functional analysis of SUMF1 mutations in multiple sulfatase deficiency

The Effects of N-Acetyl-L-Leucine on the Improvement of Symptoms in a Patient with Multiple Sulfatase Deficiency

Multiple Sulfatase Deficiency (MSD) is a rare autosomal recessive disease with specific clinical findings such as psychomotor retardation and neurological deterioration. No therapy is available for this genetic disorder. Previous studies have shown that N-acetyl-L-leucine (NALL) can improve the neurological inflammation in the cerebellum.In the current study, the effects of NALL on ataxia symptoms and quality of life were explored in a patient with MSD.This study was a crossover case study. The subject, a girl aged 12 years old, received NALL at a dose of 3 g/day (1 g in the morning, 1 g in the afternoon, and 1 g in the evening). A fasting blood sample was taken from the subject to evaluate side effects before the intervention and 4 weeks after taking supplement/placebo in every study stage. The ataxia moving symptoms were evaluated using the Scale for the Assessment and Rating of Ataxia (SARA) score in every study stage. Dietary intake was measured using 24-h dietary recall before and after the intervention. The diet compositions were assessed by Nutritionist IV software. Serum IL-6 level was measured using an ELISA kit.There was no significant change in complete blood count (CBC) and serum biochemical factors in the patient with MSD after receiving NALL (3 g/day) over 4 weeks. The SARA score was reduced by 25%. The gait whose maximum score accounts for approximately one-fifth of the maximum total SARA score (8/40) was decreased. The heel-to-shin slide, the only SARA item performed without visual control, was also improved after therapy. Furthermore, there was a downward trend in the 8MWT (8.71 to 7.93 s). Regarding quality of life assessments, the parent and child reported improved quality of life index, physical health, and emotional function after taking NALL. Moreover, total energy intake was increased with NALL treatment through the study period.Supplementation with NALL at a dose of 3 g/day over 4 weeks was well tolerated and improved ataxia symptoms, quality of life measure, and serum IL-6 levels in the patient with MSD. Further proof-of-concept trials are warranted to confirm the present findings.

Late infantile form of multiple sulfatase deficiency with a novel missense variant in the SUMF1 gene: case report and review

BACKGROUND

Multiple sulfatase deficiency (MSD) is a rare lysosomal storage disorder caused due to pathogenic variants in the SUMF1 gene. The SUMF1 gene encodes for formylglycine generating enzyme (FGE) that is involved in the catalytic activation of the family of sulfatases. The affected patients present with a wide spectrum of clinical features including multi-organ involvement. To date, almost 140 cases of MSD have been reported worldwide, with only four cases reported from India. The present study describes two cases of late infantile form of MSD from India and the identification of a novel missense variant in the SUMF1 gene.

CASE PRESENTATION

In case 1, a male child presented to us at the age of 6 years. The remarkable presenting features included ichthyosis, presence of irritability, poor social response, thinning of corpus callosum on MRI and, speech regression. Clinical suspicion of MSD was confirmed by enzyme analysis of two sulfatase enzymes followed by gene sequencing. We identified a novel missense variant c.860A > T (p.Asn287Ile) in exon 7 of the SUMF1 gene. In case 2, a two and a half years male child presented with ichthyosis, leukodystrophy and facial dysmorphism. We performed an enzyme assay for two sulfatases, which showed significantly reduced activities thereby confirming MSD diagnosis.

CONCLUSION

Overall, present study has added to the existing data on MSD from India. Based on the computational analysis, the novel variant c.860A > T identified in this study is likely to be associated with a milder phenotype and prolonged survival.

New mouse models with hypomorphic SUMF1 variants mimic attenuated forms of multiple sulfatase deficiency

Multiple sulfatase deficiency (MSD) is an ultrarare lysosomal storage disorder due to deficiency of all known sulfatases. MSD is caused by mutations in the Sulfatase Modifying Factor 1 (SUMF1) gene encoding the enzyme responsible for the post-translational modification and activation of all sulfatases. Most MSD patients carry hypomorph SUMF1 variants resulting in variable degrees of residual sulfatase activities. In contrast, Sumf1 null mice with complete deficiency in all sulfatase enzyme activities, have very short lifespan with significant pre-wean lethality, owing to a challenging preclinical model. To overcome this limitation, we genetically engineered and characterized in mice two commonly identified patient-based SUMF1 pathogenic variants, namely p.Ser153Pro and p.Ala277Val. These pathogenic missense variants correspond to variants detected in patients with attenuated MSD presenting with partial-enzyme deficiency and relatively less severe disease. These novel MSD mouse models have a longer lifespan and show biochemical and pathological abnormalities observed in humans. In conclusion, mice harboring the p.Ser153Pro or the p.Ala277Val variant mimic the attenuated MSD and are attractive preclinical models for investigation of pathogenesis and treatments for MSD.

Genetic analysis of a novel SUMF1 variation associated with a late infantile form of multiple sulfatase deficiency

BACKGROUND

Multiple sulfatase deficiency (MSD) (MIM#272200) is an ultra-rare autosomal recessive lysosomal storage disorder caused by mutation of the Sulfatase Modifying Factor 1 (SUMF1) gene.

METHODS

Herein, we report an eight-year-old boy with a late infantile form of multiple sulfatase deficiency. A combination of copy-number variation sequencing (CNV-seq) and whole-exome sequencing (WES) were used to analyze the genetic cause for the MSD patient.

RESULTS

Our results, previously not seen in China, show a novel compound heterozygous mutation with one allele containing a 240.55 kb microdeletion on 3p26.1 encompassing the SETMAR gene and exons 4-9 of the SUMF1 gene, and the other allele containing a novel missense mutation of c.671G>A (p.Arg224Gln) in the SUMF1 gene. Both were inherited from the proband's unaffected parents, one from each. Bioinformatics analyses show the novel variation to be "likely pathogenic." SWISS-MODEL analysis shows that the missense mutation may alter the three-dimensional (3D) structure.

CONCLUSIONS

In summary, this study reported a novel compound heterozygous with microdeletion in SUMF1 gene, which has not been reported in China. The complex clinical manifestations of MSD may delay diagnosis; however, molecular genetic analysis of the SUMF1 gene can be performed to help obtain an early diagnosis.

Porokeratotic eccrine ostial and dermal duct nevus associated with an 11 megabase 3p deletion

Porokeratotic eccrine ostial and dermal duct nevus (PEODDN) is a rare eccrine hamartoma; the etiology is incompletely understood. A patient presented with congenital, widespread PEODDN. Clinical assessment, histopathologic, cytogenetic, and molecular genetic investigations on affected cells were pursued. Histopathology confirmed PEODDN, and chromosomal microarray on affected tissues identified a mosaic 3p26.3p25.3 deletion in affected tissues. This 11Mb deletion encompasses 47 OMIM genes. We propose that this and other chromosomal deletions may be implicated in some cases of PEODDN, suggesting locus heterogeneity and underscoring the importance of incorporating cytogenetic and molecular investigations into the multidisciplinary care of individuals with suspected mosaic genetic skin disorders.

Long-term disease course of two patients with multiple sulfatase deficiency differs from metachromatic leukodystrophy in a broad cohort

Multiple sulfatase deficiency (MSD) is a lysosomal storage disease caused by a deficiency of formylglycine-generating enzyme due to SUMF1 defects. MSD may be misdiagnosed as metachromatic leukodystrophy (MLD), as neurological and neuroimaging findings are similar, and arylsulfatase A (ARSA) deficiency and enhanced urinary sulfatide excretion may also occur. While ARSA deficiency seems a cause for neurological symptoms and later neurodegenerative disease course, deficiency of other sulfatases results in clinical features such as dysmorphism, dysostosis, or ichthyosis. We report on a girl and a boy of the same origin presenting with severe ARSA deficiency and neurological and neuroimaging features compatible with MLD. However, exome sequencing revealed not yet described homozygosity of the missense variant c.529G > C, p.Ala177Pro in SUMF1. We asked whether dynamics of disease course differs between MSD and MLD. Comparison to a cohort of 59 MLD patients revealed different disease course concerning onset and disease progression in both MSD patients. The MSD patients showed first gross motor symptoms earlier than most patients with juvenile MLD (<10th percentile of Gross-Motor-Function in MLD [GMFC-MLD] 1). However, subsequent motor decline was more protracted (75th and 90th percentile of GMFC-MLD 2 (loss of independent walking) and 75th percentile of GMFC-MLD 5 (loss of any locomotion)). Language decline started clearly after 50th percentile of juvenile MLD and progressed rapidly. Thus, dynamics of disease course may be a further clue for the characterization of MSD. These data may contribute to knowledge of natural course of ultra-rare MSD and be relevant for counseling and therapy.

A systematic review and meta-analysis of published cases reveals the natural disease history in multiple sulfatase deficiency

Multiple Sulfatase Deficiency (MSD, MIM#272200) is an ultra-rare lysosomal storage disorder arising from mutations in the SUMF1 gene, which encodes the formylglycine-generating enzyme (FGE). FGE is necessary for the activation of sulfatases, a family of enzymes that are involved in the degradation of sulfated substrates such as glycosaminoglycans and sulfolipids. SUMF1 mutations lead to functionally impaired FGE and individuals with MSD demonstrate clinical signs of single sulfatase deficiencies, including metachromatic leukodystrophy (MLD) and several mucopolysaccharidosis (MPS) subtypes. Comprehensive information related to the natural history of MSD is missing. We completed a systematic literature review and a meta-analysis on data from published cases reporting on MSD. As available from these reports, we extracted clinical, genetic, biochemical, and brain imaging information. We identified 75 publications with data on 143 MSD patients with a total of 53 unique SUMF1 mutations. The mean survival was 13 years (95% CI 9.8-16.2 years). Seventy-five clinical signs and 11 key clusters of signs were identified. The most frequently affected organs systems were the nervous, skeletal, and integumentary systems. The most frequent MRI features were abnormal myelination and cerebral atrophy. Individuals with later onset MSD signs and survived longer than those with signs at birth. Less severe mutations, low disease burden and achievement of independent walking positively correlated with longer survival. Despite the limitations of our approach, we were able to define clinical characteristics and disease outcomes in MSD. This work will provide the foundation of natural disease history data needed for future clinical trial design.

A systematic cross-sectional survey of multiple sulfatase deficiency

Multiple Sulfatase Deficiency (MSD) is an inborn error of metabolism caused by pathogenic variants in the SUMF1 gene encoding the formylglycine-generating enzyme (FGE) that activates all known sulfatases. FGE deficiency results in widespread tissue accumulation of multiple sulphated substrates. Through a systematic analysis of published cases, we retrieved 80 MSD cases and reviewed the disease clinical, biochemical, and genetic findings. Leukodystrophy, neurosensorial hearing loss, and ichthyosis were the most frequent findings at diagnosis. Of 51 reported pathogenic variants, 20 were likely gene disruptive and the remaining were missense variants. No correlations between class of variants and clinical severity or degree of enzyme deficiency were detected. However, cases harboring variants located at N-terminal always had severe neonatal presentations. Moreover, cases with neonatal onset showed the lowest overall survival rate compared to late-infantile and juvenile onsets. Using GnomAD, carrier frequency for pathogenic SUMF1 variants was estimated to be ~1/700 and the disease prevalence was approximately 1/2,000,000. In summary, MSD is an ultra-rare multisystem disorder with mainly neurologic, hearing and skin involvements. Although the collected data were retrospective and heterogenous, the quantitative data inform the disease natural history and are important for both counseling and design of future interventional studies.

Multiple Sulfatase Deficiency: A Disease Comprising Mucopolysaccharidosis, Sphingolipidosis, and More Caused by a Defect in Posttranslational Modification

Multiple sulfatase deficiency (MSD, MIM #272200) is an ultra-rare disease comprising pathophysiology and clinical features of mucopolysaccharidosis, sphingolipidosis and other sulfatase deficiencies. MSD is caused by impaired posttranslational activation of sulfatases through the formylglycine generating enzyme (FGE) encoded by the sulfatase modifying factor 1 (SUMF1) gene, which is mutated in MSD. FGE is a highly conserved, non-redundant ER protein that activates all cellular sulfatases by oxidizing a conserved cysteine in the active site of sulfatases that is necessary for full catalytic activity. SUMF1 mutations result in unstable, degradation-prone FGE that demonstrates reduced or absent catalytic activity, leading to decreased activity of all sulfatases. As the majority of sulfatases are localized to the lysosome, loss of sulfatase activity induces lysosomal storage of glycosaminoglycans and sulfatides and subsequent cellular pathology. MSD patients combine clinical features of all single sulfatase deficiencies in a systemic disease. Disease severity classifications distinguish cases based on age of onset and disease progression. A genotype- phenotype correlation has been proposed, biomarkers like excreted storage material and residual sulfatase activities do not correlate well with disease severity. The diagnosis of MSD is based on reduced sulfatase activities and detection of mutations in SUMF1. No therapy exists for MSD yet. This review summarizes the unique FGE/ sulfatase physiology, pathophysiology and clinical aspects in patients and their care and outlines future perspectives in MSD.

Identification of arylsulfatase B gene mutations and clinical presentations of Iranian patients with Mucopolysaccharidosis VI

BACKGROUND

Mucopolysaccharidosis (MPS) type VI, also known as Maroteaux-Lamy syndrome, is an autosomal recessive lysosomal storage disorder caused by a deficiency in arylsulfatase B (ARSB) enzyme. Our objectives were to investigate clinical phenotypes and performed molecular studies in Iranian patients with MPS VI, for the first time, in the southwestern Iran.

METHODS

We studied 14 cases from 10 unrelated kindreds with MPS VI that were enrolled during 8 years. The mutational analysis of coding and flanking regions of ARSB gene was performed for the patients and their families using genomic DNA from whole blood by direct sequencing.

RESULTS

All cases had parental consanguinity. Except one who had Fars ethnicity and presented with a very mild degree of coarse face, but normal otherwise, even near normal height, all were from Arab ethnicity with characteristic phenotypes including severe facial changes, cardiac involvement and dysostosis multiplex. Sequencing analysis of ARSB gene revealed four pathogenic homozygote mutations, including a novel nonsense mutation c.281C>A (p.Ser94X) in 9 patients, as well as, a known nonsense mutation c.753C>G (p.Try251X) in 3 cases, and two missense mutations c.904G>A (p.Gly302Arg) and c.454C>T (p.Arg152Trp) in two cases. The type of mutations affected the severity patient's phenotypes.

CONCLUSIONS

These findings increased the genetic databases of Iranian patients with MPS VI and would be so much helpful for the high-risk families to speed the detection of carriers with accuracy and perform the prenatal test of disorder with cost-effective in this population.

Clinical implementation of gene panel testing for lysosomal storage diseases

Background

The diagnostic workup in patients with a clinical suspicion of lysosomal storage diseases (LSD) is often difficult due to the variability in the clinical phenotype. The gold standard for diagnosis of LSDs consists of enzymatic testing. However, due to the sequential nature of this methodology and inconsistent genotype–phenotype correlations of certain LSDs, finding a diagnosis can be challenging.

Method

We developed and clinically implemented a gene panel covering 50 genes known to cause LSDs when mutated. Over a period of 18 months, we analyzed 150 patients who were referred for LSD testing and compared these results with the data of patients who were previously enrolled in a scheme of classical biochemical testing.

Results

Our panel was able to determine the molecular cause of the disease in 22 cases (15%), representing an increase in diagnostic yield compared to biochemical tests developed for 21 LSDs (4.6%). We were furthermore able to redirect the diagnosis of a mucolipidosis patient who was initially suspected to be affected with galactosialidosis. Several patients were identified as being affected with neuronal ceroid lipofuscinosis, which cannot readily be detected by enzyme testing. Finally, several carriers of pathogenic mutations in LSD genes related to the disease phenotype were identified as well, thus potentially increasing the diagnostic yield of the panel as heterozygous deletions cannot be detected.

Conclusion

We show that the implementation of a gene panel for LSD diagnostics results in an increased yield in comparison to classical biochemical testing. As the panel is able to cover a wider range of diseases, we propose to implement this methodology as a first‐tier test in cases of an aspecific LSD presentation, while enzymatic testing remains the first choice in patients with a more distinctive clinical presentation. Positive panel results should however still be enzymatically confirmed whenever possible.

Structure and expression of sulfatase and sulfatase modifying factor genes in the diamondback moth, Plutella xylostella

The diamondback moth, Plutella xylostella (L.), uses sulfatases (SULF) to counteract the glucosinolate-myrosinase defensive system that cruciferous plants have evolved to deter insect feeding. Sulfatase activity is regulated by post-translational modification of a cysteine residue by sulfatase modifying factor 1 (SUMF1). We identified 12 SULF genes (PxylSulfs) and two SUMF1 genes (PxylSumf1s) in the P. xylostella genome. Phylogenetic analysis of SULFs and SUMFs from P. xylostella, Bombyx mori, Manduca sexta, Heliconius melpomene, Danaus plexippus, Drosophila melanogaster, Tetranychus urticae and Homo sapiens showed that the SULFs were clustered into five groups, and the SUMFs could be divided into two groups. Profiling of the expression of PxylSulfs and PxylSumfs by RNA-seq and by quantitative real-time polymerase chain reaction showed that two glucosinolate sulfatase genes (GSS), PxylSulf2 and PxylSulf3, were primarily expressed in the midgut of 3rd- and 4th-instar larvae. Moreover, expression of sulfatases PxylSulf2, PxylSulf3 and PxylSulf4 were correlated with expression of the sulfatases modifying factor PxylSumf1a. The findings from this study provide new insights into the structure and expression of SUMF1 and PxylSulf genes that are considered to be key factors for the evolutionary success of P. xylostella as a specialist herbivore of cruciferous plants.

Multiple Sulfatase Deficiency: A Case Series With a Novel Mutation

Multiple sulfatase deficiency is an autosomal recessive lysosomal storage disorder due to a deficiency in formylglycine-generating enzyme, which is encoded by the Sulfatase Modifying Factor 1 ( SUMF1) gene. Clinically, the disorder is variable. The most common characteristics are developmental regression, intellectual disability, ichthyosis, and periventricular white matter disease. Herein, we report 6 Saudi patients with multiple sulfatase deficiency caused by a novel homozygous missense mutation in the SUMF1 gene (NM_182760.3; c.785A>G [p.Gln262Arg]). The patients are 2 females and 4 males between 5 and 13 years of age, with an age of onset of 1 to 3 years. All patients are consanguineous and suffer from developmental regression, intellectual disability, ichthyosis, and periventricular white matter disease. This cohort differs from previous cohorts because of the absence of organomegaly and skeletal abnormalities.

Congenital methemoglobinemia type II in a 5-year-old boy

Congenital Methemoglobinemia is a rare neurologic condition which can mimic other diseases such as epilepsy syndromes and leukodystrophies. The responsible gene, CYB5R3, is not typically included on commonly order neurologic and epilepsy panels. We recommend that laboratories include this gene on these tests which often precede larger-scale genetic studies.

Structural distortions due to missense mutations in human formylglycine-generating enzyme leading to multiple sulfatase deficiency

The major candidate for multiple sulfatase deficiency is a defective formylglycine-generating enzyme (FGE). Though adequately produced, mutations in FGE stall the activation of sulfatases and prevent their activity. Missense mutations, viz. E130D, S155P, A177P, W179S, C218Y, R224W, N259I, P266L, A279V, C336R, R345C, A348P, R349Q and R349W associated with multiple sulfatase deficiency are yet to be computationally studied. Aforementioned mutants were initially screened through ws-SNPs&GO^3D program. Mutant R345C acquired the highest score, and hence was studied in detail. Discrete molecular dynamics explored structural distortions due to amino acid substitution. Therein, comparative analyses of wild type and mutant were carried out. Changes in structural contours were observed between wild type and mutant. Mutant had low conformational fluctuation, high atomic mobility and more compactness than wild type. Moreover, free energy landscape showed mutant to vary in terms of its conformational space as compared to wild type. Subsequently, wild type and mutant were subjected to single-model analyses. Mutant had lesser intra molecular interactions than wild type suggesting variations pertaining to its secondary structure. Furthermore, simulated thermal denaturation showed dissimilar pattern of hydrogen bond dilution. Effects of these variations were observed as changes in elements of secondary structure. Docking studies of mutant revealed less favourable binding energy towards its substrate as compared to wild type. Therefore, theoretical explanations for structural distortions of mutant R345C leading to multiple sulfatase deficiency were revealed. The protocol of the study could be useful to examine the effectiveness of pharmacological chaperones prior to experimental studies.

Lysosomal enzyme replacement therapies: Historical development, clinical outcomes, and future perspectives

Lysosomes and lysosomal enzymes play a central role in numerous cellular processes, including cellular nutrition, recycling, signaling, defense, and cell death. Genetic deficiencies of lysosomal components, most commonly enzymes, are known as "lysosomal storage disorders" or "lysosomal diseases" (LDs) and lead to lysosomal dysfunction. LDs broadly affect peripheral organs and the central nervous system (CNS), debilitating patients and frequently causing fatality. Among other approaches, enzyme replacement therapy (ERT) has advanced to the clinic and represents a beneficial strategy for 8 out of the 50-60 known LDs. However, despite its value, current ERT suffers from several shortcomings, including various side effects, development of "resistance", and suboptimal delivery throughout the body, particularly to the CNS, lowering the therapeutic outcome and precluding the use of this strategy for a majority of LDs. This review offers an overview of the biomedical causes of LDs, their socio-medical relevance, treatment modalities and caveats, experimental alternatives, and future treatment perspectives.

Heparan sulfate proteoglycans as key regulators of the mesenchymal niche of hematopoietic stem cells

The complex microenvironment that surrounds hematopoietic stem cells (HSCs) in the bone marrow niche involves different coordinated signaling pathways. The stem cells establish permanent interactions with distinct cell types such as mesenchymal stromal cells, osteoblasts, osteoclasts or endothelial cells and with secreted regulators such as growth factors, cytokines, chemokines and their receptors. These interactions are mediated through adhesion to extracellular matrix compounds also. All these signaling pathways are important for stem cell fates such as self-renewal, proliferation or differentiation, homing and mobilization, as well as for remodeling of the niche. Among these complex molecular cues, this review focuses on heparan sulfate (HS) structures and functions and on the role of enzymes involved in their biosynthesis and turnover. HS associated to core protein, constitute the superfamily of heparan sulfate proteoglycans (HSPGs) present on the cell surface and in the extracellular matrix of all tissues. The key regulatory effects of major medullar HSPGs are described, focusing on their roles in the interactions between hematopoietic stem cells and their endosteal niche, and on their ability to interact with Heparin Binding Proteins (HBPs). Finally, according to the relevance of HS moieties effects on this complex medullar niche, we describe recent data that identify HS mimetics or sulfated HS signatures as new glycanic tools and targets, respectively, for hematopoietic and mesenchymal stem cell based therapeutic applications.

Sulfatase modifying factor 1 (SUMF1) is associated with Chronic Obstructive Pulmonary Disease

Background

It has been observed that mice lacking the sulfatase modifying factor (Sumf1) developed an emphysema-like phenotype. However, it is unknown if SUMF1 may play a role in Chronic Obstructive Pulmonary Disease (COPD) in humans. The aim was to investigate if the expression and genetic regulation of SUMF1 differs between smokers with and without COPD.

Methods

SUMF1 mRNA was investigated in sputum cells and whole blood from controls and COPD patients (all current or former smokers). Expression quantitative trait loci (eQTL) analysis was used to investigate if single nucleotide polymorphisms (SNPs) in SUMF1 were significantly associated with SUMF1 expression. The association of SUMF1 SNPs with COPD was examined in a population based cohort, Lifelines. SUMF1 mRNA from sputum cells, lung tissue, and lung fibroblasts, as well as lung function parameters, were investigated in relation to genotype.

Results

Certain splice variants of SUMF1 showed a relatively high expression in lung tissue compared to many other tissues. SUMF1 Splice variant 2 and 3 showed lower levels in sputum cells from COPD patients as compared to controls. Twelve SNPs were found significant by eQTL analysis and overlapped with the array used for genotyping of Lifelines. We found alterations in mRNA expression in sputum cells and lung fibroblasts associated with SNP rs11915920 (top hit in eQTL), which validated the results of the lung tissue eQTL analysis. Of the twelve SNPs, two SNPs, rs793391 and rs308739, were found to be associated with COPD in Lifelines. The SNP rs793391 was also confirmed to be associated with lung function changes.

Conclusions

We show that SUMF1 expression is affected in COPD patients compared to controls, and that SNPs in SUMF1 are associated with an increased risk of COPD. Certain COPD-associated SNPs have effects on either SUMF1 gene expression or on lung function. Collectively, this study shows that SUMF1 is associated with an increased risk of developing COPD.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-017-0562-5) contains supplementary material, which is available to authorized users.

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.

Multiple sulfatase deficiency with neonatal manifestation

Multiple Sulfatase Deficiency (MSD; OMIM 272200) is a rare autosomal recessive inborn error of metabolism caused by mutations in the sulfatase modifying factor 1 gene, encoding the formylglycine-generating enzyme (FGE), and resulting in tissue accumulation of sulfatides, sulphated glycosaminoglycans, sphingolipids and steroid sulfates. Less than 50 cases have been published so far. We report a new case of MSD presenting in the newborn period with hypotonia, apnoea, cyanosis and rolling eyes, hepato-splenomegaly and deafness. This patient was compound heterozygous for two so far undescribed SUMF1 mutations (c.191C > A; p.S64X and c.818A > G; p.D273G).

Proprotein convertases process and thereby inactivate formylglycine-generating enzyme

Formylglycine-generating enzyme (FGE) post-translationally converts a specific cysteine in newly synthesized sulfatases to formylglycine (FGly). FGly is the key catalytic residue of the sulfatase family, comprising 17 nonredundant enzymes in human that play essential roles in development and homeostasis. FGE, a resident protein of the endoplasmic reticulum, is also secreted. A major fraction of secreted FGE is N-terminally truncated, lacking residues 34-72. Here we demonstrate that this truncated form is generated intracellularly by limited proteolysis mediated by proprotein convertase(s) (PCs) along the secretory pathway. The cleavage site is represented by the sequence RYSR(72)↓, a motif that is conserved in higher eukaryotic FGEs, implying important functionality. Residues Arg-69 and Arg-72 are critical because their mutation abolishes FGE processing. Furthermore, residues Tyr-70 and Ser-71 confer an unusual property to the cleavage motif such that endogenous as well as overexpressed FGE is only partially processed. FGE is cleaved by furin, PACE4, and PC5a. Processing is disabled in furin-deficient cells but fully restored upon transient furin expression, indicating that furin is the major protease cleaving FGE. Processing by endogenous furin occurs mostly intracellularly, although also extracellular processing is observed in HEK293 cells. Interestingly, the truncated form of secreted FGE no longer possesses FGly-generating activity, whereas the unprocessed form of secreted FGE is active. As always both forms are secreted, we postulate that furin-mediated processing of FGE during secretion is a physiological means of higher eukaryotic cells to regulate FGE activity upon exit from the endoplasmic reticulum.

Efficacy of a combined intracerebral and systemic gene delivery approach for the treatment of a severe lysosomal storage disorder

Multiple sulfatase deficiency (MSD), a severe autosomal recessive disease is caused by mutations in the sulfatase modifying factor 1 gene (Sumf1). We have previously shown that in the Sumf1 knockout mouse model (Sumf1(-/-)) sulfatase activities are completely absent and, similarly to MSD patients, this mouse model displays growth retardation and early mortality. The severity of the phenotype makes MSD unsuitable to be treated by enzyme replacement or bone marrow transplantation, hence the importance of testing the efficacy of novel treatment strategies. Here we show that recombinant adeno-associated virus serotype 9 (rAAV9) vector injected into the cerebral ventricles of neonatal mice resulted in efficient and widespread transduction of the brain parenchyma. In addition, we compared a combined, intracerebral ventricles and systemic, administration of an rAAV9 vector encoding SUMF1 gene to the single administrations-either directly in brain, or systemic alone -in MSD mice. The combined treatment resulted in the global activation of sulfatases, near-complete clearance of glycosaminoglycans (GAGs) and decrease of inflammation in both the central nervous system (CNS) and visceral organs. Furthermore, behavioral abilities were improved by the combined treatment. These results underscore that the "combined" mode of rAAV9 vector administration is an efficient option for the treatment of severe whole-body disorders.

SUMF1 mutations affecting stability and activity of formylglycine generating enzyme predict clinical outcome in multiple sulfatase deficiency

Multiple Sulfatase Deficiency (MSD) is caused by mutations in the sulfatase-modifying factor 1 gene encoding the formylglycine-generating enzyme (FGE). FGE post translationally activates all newly synthesized sulfatases by generating the catalytic residue formylglycine. Impaired FGE function leads to reduced sulfatase activities. Patients display combined clinical symptoms of single sulfatase deficiencies. For ten MSD patients, we determined the clinical phenotype, FGE expression, localization and stability, as well as residual FGE and sulfatase activities. A neonatal, very severe clinical phenotype resulted from a combination of two nonsense mutations leading to almost fully abrogated FGE activity, highly unstable FGE protein and nearly undetectable sulfatase activities. A late infantile mild phenotype resulted from FGE G263V leading to unstable protein but high residual FGE activity. Other missense mutations resulted in a late infantile severe phenotype because of unstable protein with low residual FGE activity. Patients with identical mutations displayed comparable clinical phenotypes. These data confirm the hypothesis that the phenotypic outcome in MSD depends on both residual FGE activity as well as protein stability. Predicting the clinical course in case of molecularly characterized mutations seems feasible, which will be helpful for genetic counseling and developing therapeutic strategies aiming at enhancement of FGE.

Pathology and current treatment of neurodegenerative sphingolipidoses

Sphingolipidoses constitute a large subgroup of lysosomal storage disorders (LSDs). Many of them are associated with a progressive neurodegeneration. As is the case for LSDs in general, most sphingolipidoses are caused by deficiencies in lysosomal hydrolases. However, accumulation of sphingolipids can also result from deficiencies in proteins involved in the transport or posttranslational modification of lysosomal enzymes, transport of lipids, or lysosomal membrane proteins required for transport of lysosomal degradation end products. The accumulation of sphingolipids in the lysosome together with secondary changes in the concentration and localization of other lipids may cause trafficking defects of membrane lipids and proteins, affect calcium homeostasis, induce the unfolded protein response, activate apoptotic cascades, and affect various signal transduction pathways. To what extent, however, these changes contribute to the pathogenesis of the diseases is not fully understood. Currently, there is no cure for sphingolipidoses. Therapies like enzyme replacement, pharmacological chaperone, and substrate reduction therapy, which have been shown to be efficient in non-neuronopathic LSDs, are currently evaluated in clinical trials of neuronopathic sphingolipidoses. In the future, neural stem cell therapy and gene therapy may become an option for these disorders.

Sulfatase modifying factor 1-mediated fibroblast growth factor signaling primes hematopoietic multilineage development

Self-renewal and differentiation of hematopoietic stem cells (HSCs) are balanced by the concerted activities of the fibroblast growth factor (FGF), Wnt, and Notch pathways, which are tuned by enzyme-mediated remodeling of heparan sulfate proteoglycans (HSPGs). Sulfatase modifying factor 1 (SUMF1) activates the Sulf1 and Sulf2 sulfatases that remodel the HSPGs, and is mutated in patients with multiple sulfatase deficiency. Here, we show that the FGF signaling pathway is constitutively activated in Sumf1(-/-) HSCs and hematopoietic stem progenitor cells (HSPCs). These cells show increased p-extracellular signal-regulated kinase levels, which in turn promote beta-catenin accumulation. Constitutive activation of FGF signaling results in a block in erythroid differentiation at the chromatophilic erythroblast stage, and of B lymphocyte differentiation at the pro-B cell stage. A reduction in mature myeloid cells and an aberrant development of T lymphocytes are also seen. These defects are rescued in vivo by blocking the FGF pathway in Sumf1(-/-) mice. Transplantation of Sumf1(-/-) HSPCs into wild-type mice reconstituted the phenotype of the donors, suggesting a cell autonomous defect. These data indicate that Sumf1 controls HSPC differentiation and hematopoietic lineage development through FGF and Wnt signaling.

A potentially dynamic lysosomal role for the endogenous TRPML proteins

Lysosomal storage disorders (LSDs) constitute a diverse group of inherited diseases that result from lysosomal storage of compounds occurring in direct consequence to deficiencies of proteins implicated in proper lysosomal function. Pathology in the LSD mucolipidosis type IV (MLIV), is characterized by lysosomal storage of lipids together with water-soluble materials in cells from every tissue and organ of affected patients. Mutations in the mucolipin 1 (TRPML1) protein cause MLIV and TRPML1 has also been shown to interact with two of its paralogous proteins, mucolipin 2 (TRPML2) and mucolipin 3 (TRPML3), in heterologous expression systems. Heterogeneous lysosomal storage is readily identified in electron micrographs of MLIV patient cells, suggesting that proper TRPML1 function is essential for the maintenance of lysosomal integrity. In order to investigate whether TRPML2 and TRPML3 also play a role in the maintenance of lysosomal integrity, we conducted gene-specific knockdown assays against these protein targets. Ultrastructural analysis revealed lysosomal inclusions in both TRPML2 and TRPML3 knockdown cells, suggestive of a common mechanism for these proteins, in parallel with TRPML1, in the regulation of lysosomal integrity. However, co-immunoprecipitation assays revealed that physical interactions between each of the endogenous TRPML proteins are quite limited. In addition, we found that all three endogenous proteins only partially co-localize with each other in lysosomal as well as extra-lysosomal compartments. This suggests that native TRPML2 and TRPML3 might participate with native TRPML1 in a dynamic form of lysosomal regulation. Given that depletion of TRPML2/3 led to lysosomal storage typical to an LSD, we propose that depletion of these proteins might also underlie novel LSD pathologies not described hitherto.

Multiple sulfatase deficiency: clinical report and description of two novel mutations in a Brazilian patient

Multiple Sulfatase Deficiency (MSD) is a rare autosomal recessive disease in which the activities of all sulfatases are reduced; its estimated prevalence is 1:1.4 million births. The disease is caused by mutations in SUMF1, which encodes an enzyme involved in the post-translational modification of sulfatases. The MSD phenotype is a combination of the clinical features found in diseases resulting from a deficiency of the individual sulfatases; i.e., mucopolysaccharidosis II, IIIA, IIID, IVA and VI, metachromatic leukodystrophy, X-linked ichthyosis, and the X-linked recessive form of chondrodysplasia punctata. We describe herein the first case of a Brazilian patient with MSD. The case was initially diagnosed as having mucopolysaccharidosis (MPS), due to skeletal alterations, coarse facial features, and urinary excretion of dermatan sulfate and heparan sulfate. Later, after a detailed biochemical investigation, the diagnosis of MSD was established. The analysis of the SUMF1 showed the patient was a compound heterozygote for two novel mutations (p.R349G and p.F244S). This case illustrates the challenges in the diagnosis of a disease considered rare, such as MSD. We point out that the availability of therapy for certain MPS disorders necessitates correct disease assignment, and the need to exclude the likelihood of MSD.

Neonatal manifestation of multiple sulfatase deficiency

INTRODUCTION

Multiple sulfatase deficiency is biochemically characterized by the accumulation of sulfated lipids and acid mucopolysaccharides.

CASE REPORT

We report clinical, biochemical, and molecular findings in a female newborn affected with a severe form of multiple sulfatase deficiency (Mendelian Inheritance in Man (MIM) # 272200). She presented with primary microcephaly, facial anomalies including depressed nasal bridge, nasal hypoplasia, anteverted nostrils, smooth philtrum, limited mobility of hip and knee joints, mild ichthyosis, as well as muscular hypotonia. The diagnosis is based on detection of excessive mucopolysacchariduria and enzymatic assays performed in leucocytes which showed complete deficiency of all of the measured sulfatases. Sequencing of the coding region of the underlying gene, SUMF1, could not identify any mutation. However, failure to detect the corresponding mRNA by reverse transcription polymerase chain reaction proves defective SUMF1 expression.

CONCLUSION

The diagnosis of neonatal MSD should be considered when dealing with the association of distinct facial anomalies, limited joint mobility, ichthyosis, and muscular hypotonia.

Multiple sulfatase deficiency in a Turkish family resulting from a novel mutation

Multiple sulfatase deficiency (MSD) is an inherited lysosomal storage disease that affects post-translational activation of all of the sulfatases. Since biochemical and clinical findings are variable, the diagnosis is difficult in most of the cases. Missense, nonsense, microdeletion and splicing mutations in SUMF1 gene were found in all of the MSD patients analyzed. Here, we present clinical findings of two consanguineous patients with multiple sulfatase deficiency. They were found to be homozygous for a novel missense mutation c.739G > C causing a p.G247R amino acid substitution in the SUMF1 protein.

Serial magnetic resonance imaging and neurophysiological studies in multiple sulphatase deficiency

We present serial clinical, magnetic resonance imaging (MRI) and neurophysiological findings of a patient with multiple sulphatase deficiency (MSD), who was first admitted at the age of 9 months, because of psychomotor retardation. MRI demonstrated extensive diffuse symmetrical high signal in the deep white matter of both cerebral hemispheres, as well as of the subcortical white matter and the brainstem, while there was additional enlargement of sulci and subdural spaces and mild atrophy. Assay of arylsulphatase A activity in white blood cell homogenates at the age of 29 months disclosed a marked deficiency of the enzyme, compatible with the diagnosis of early-infantile metachromatic leukodystrophy. During the course of a later admission, the presence of ichthyosis pointed out to the possible diagnosis of MSD; further assays of sulphatases in plasma, leukocytes as well as in cultured fibroblasts, combined with an abnormal excretion of mucopolysaccharides and sulphatides in urine confirmed the diagnosis. Molecular analysis identified a homozygous disease-causing mutation (R349W) of the SUMF1 gene. Serial neurophysiological and MRI studies demonstrated the progressive nature of the disorder (regarding both central and peripheral nervous system), correlating with the clinical deterioration (spastic quadriplegia, optic atrophy and epilepsy) with subsequent death at the age of 4 years.

Gene identification for the cblD defect of vitamin B12 metabolism

BACKGROUND

Vitamin B12 (cobalamin) is an essential cofactor in several metabolic pathways. Intracellular conversion of cobalamin to its two coenzymes, adenosylcobalamin in mitochondria and methylcobalamin in the cytoplasm, is necessary for the homeostasis of methylmalonic acid and homocysteine. Nine defects of intracellular cobalamin metabolism have been defined by means of somatic complementation analysis. One of these defects, the cblD defect, can cause isolated methylmalonic aciduria, isolated homocystinuria, or both. Affected persons present with multisystem clinical abnormalities, including developmental, hematologic, neurologic, and metabolic findings. The gene responsible for the cblD defect has not been identified.

METHODS

We studied seven patients with the cblD defect, and skin fibroblasts from each were investigated in cell culture. Microcell-mediated chromosome transfer and refined genetic mapping were used to localize the responsible gene. This gene was transfected into cblD fibroblasts to test for the rescue of adenosylcobalamin and methylcobalamin synthesis.

RESULTS

The cblD gene was localized to human chromosome 2q23.2, and a candidate gene, designated MMADHC (methylmalonic aciduria, cblD type, and homocystinuria), was identified in this region. Transfection of wild-type MMADHC rescued the cellular phenotype, and the functional importance of mutant alleles was shown by means of transfection with mutant constructs. The predicted MMADHC protein has sequence homology with a bacterial ATP-binding cassette transporter and contains a putative cobalamin binding motif and a putative mitochondrial targeting sequence.

CONCLUSIONS

Mutations in a gene we designated MMADHC are responsible for the cblD defect in vitamin B12 metabolism. Various mutations are associated with each of the three biochemical phenotypes of the disorder.

The non-catalytic N-terminal extension of formylglycine-generating enzyme is required for its biological activity and retention in the endoplasmic reticulum

Formylglycine-generating enzyme (FGE) catalyzes the oxidation of a specific cysteine residue in nascent sulfatase polypeptides to formylglycine (FGly). This FGly is part of the active site of all sulfatases and is required for their catalytic activity. Here we demonstrate that residues 34-68 constitute an N-terminal extension of the FGE catalytic core that is dispensable for in vitro enzymatic activity of FGE but is required for its in vivo activity in the endoplasmic reticulum (ER), i.e. for generation of FGly residues in nascent sulfatases. In addition, this extension is needed for the retention of FGE in the ER. Fusing a KDEL retention signal to the C terminus of FGE is sufficient to mediate retention of an N-terminally truncated FGE but not sufficient to restore its biological activity. Fusion of FGE residues 1-88 to secretory proteins resulted in ER retention of the fusion protein. Moreover, when fused to the paralog of FGE (pFGE), which itself lacks FGly-generating activity, the FGE extension (residues 34-88) of this hybrid construct led to partial restoration of the biological activity of co-expressed N-terminally truncated FGE. Within the FGE N-terminal extension cysteine 52 is critical for the biological activity. We postulate that this N-terminal region of FGE mediates the interaction with an ER component to be identified and that this interaction is required for both the generation of FGly residues in nascent sulfatase polypeptides and for retention of FGE in the ER.

Paralog of the formylglycine-generating enzyme--retention in the endoplasmic reticulum by canonical and noncanonical signals

Formylglycine-generating enzyme (FGE) catalyzes in newly synthesized sulfatases the oxidation of a specific cysteine residue to formylglycine, which is the catalytic residue required for sulfate ester hydrolysis. This post-translational modification occurs in the endoplasmic reticulum (ER), and is an essential step in the biogenesis of this enzyme family. A paralog of FGE (pFGE) also localizes to the ER. It shares many properties with FGE, but lacks formylglycine-generating activity. There is evidence that FGE and pFGE act in concert, possibly by forming complexes with sulfatases and one another. Here we show that human pFGE, but not FGE, is retained in the ER through its C-terminal tetrapeptide PGEL, a noncanonical variant of the classic KDEL ER-retention signal. Surprisingly, PGEL, although having two nonconsensus residues (PG), confers efficient ER retention when fused to a secretory protein. Inducible coexpression of pFGE at different levels in FGE-expressing cells did not significantly influence the kinetics of FGE secretion, suggesting that pFGE is not a retention factor for FGE in vivo. PGEL is accessible at the surface of the pFGE structure. It is found in 21 mammalian species with available pFGE sequences. Other species carry either canonical signals (eight mammals and 26 nonmammals) or different noncanonical variants (six mammals and six nonmammals). Among the latter, SGEL was tested and found to also confer ER retention. Although evolutionarily conserved for mammalian pFGE, the PGEL signal is found only in one further human protein entering the ER. Its consequences for KDEL receptor-mediated ER retrieval and benefit for pFGE functionality remain to be fully resolved.

Deletion at ITPR1 underlies ataxia in mice and spinocerebellar ataxia 15 in humans

We observed a severe autosomal recessive movement disorder in mice used within our laboratory. We pursued a series of experiments to define the genetic lesion underlying this disorder and to identify a cognate disease in humans with mutation at the same locus. Through linkage and sequence analysis we show here that this disorder is caused by a homozygous in-frame 18-bp deletion in Itpr1 (Itpr1^Δ18/Δ18), encoding inositol 1,4,5-triphosphate receptor 1. A previously reported spontaneous Itpr1 mutation in mice causes a phenotype identical to that observed here. In both models in-frame deletion within Itpr1 leads to a decrease in the normally high level of Itpr1 expression in cerebellar Purkinje cells. Spinocerebellar ataxia 15 (SCA15), a human autosomal dominant disorder, maps to the genomic region containing ITPR1; however, to date no causal mutations had been identified. Because ataxia is a prominent feature in Itpr1 mutant mice, we performed a series of experiments to test the hypothesis that mutation at ITPR1 may be the cause of SCA15. We show here that heterozygous deletion of the 5′ part of the ITPR1 gene, encompassing exons 1–10, 1–40, and 1–44 in three studied families, underlies SCA15 in humans.

We have identified a spontaneous in-frame deletion mutation in the gene Itpr1 that causes a recessive movement disorder in mice. In an attempt to define whether any similar disease occurs in humans we performed a literature search for diseases linked to the human chromosomal region containing ITPR1. We identified the disease spinocerebellar ataxia 15 as linked to this region. High-density genomic analysis of affected members from three families revealed that disease in these patients was caused by deletion of a large portion of the region containing ITPR1. We show here that this mutation results in a dramatic reduction in ITPR1 in cells from these patients. These data show convincingly that ITPR1 deletion underlies spinocerebellar ataxia 15 in humans.

Sulfatase modifying factor 1 trafficking through the cells: from endoplasmic reticulum to the endoplasmic reticulum

Sulfatase modifying factor 1 (SUMF1) is the gene mutated in multiple sulfatase deficiency (MSD) that encodes the formylglycine-generating enzyme, an essential activator of all the sulfatases. SUMF1 is a glycosylated enzyme that is resident in the endoplasmic reticulum (ER), although it is also secreted. Here, we demonstrate that upon secretion, SUMF1 can be taken up from the medium by several cell lines. Furthermore, the in vivo engineering of mice liver to produce SUMF1 shows its secretion into the blood serum and its uptake into different tissues. Additionally, we show that non-glycosylated forms of SUMF1 can still be secreted, while only the glycosylated SUMF1 enters cells, via a receptor-mediated mechanism. Surprisingly, following its uptake, SUMF1 shuttles from the plasma membrane to the ER, a route that has to date only been well characterized for some of the toxins. Remarkably, once taken up and relocalized into the ER, SUMF1 is still active, enhancing the sulfatase activities in both cultured cells and mice tissues.

SUMF1 enhances sulfatase activities in vivo in five sulfatase deficiencies

Sulfatases are enzymes that hydrolyse a diverse range of sulfate esters. Deficiency of lysosomal sulfatases leads to human diseases characterized by the accumulation of either GAGs (glycosaminoglycans) or sulfolipids. The catalytic activity of sulfatases resides in a unique formylglycine residue in their active site generated by the post-translational modification of a highly conserved cysteine residue. This modification is performed by SUMF1 (sulfatase-modifying factor 1), which is an essential factor for sulfatase activities. Mutations in the SUMF1 gene cause MSD (multiple sulfatase deficiency), an autosomal recessive disease in which the activities of all sulfatases are profoundly reduced. In previous studies, we have shown that SUMF1 has an enhancing effect on sulfatase activity when co-expressed with sulfatase genes in COS-7 cells. In the present study, we demonstrate that SUMF1 displays an enhancing effect on sulfatases activity when co-delivered with a sulfatase cDNA via AAV (adeno-associated virus) and LV (lentivirus) vectors in cells from individuals affected by five different diseases owing to sulfatase deficiencies or from murine models of the same diseases [i.e. MLD (metachromatic leukodystrophy), CDPX (X-linked dominant chondrodysplasia punctata) and MPS (mucopolysaccharidosis) II, IIIA and VI]. The SUMF1-enhancing effect on sulfatase activity resulted in an improved clearance of the intracellular GAG or sulfolipid accumulation. Moreover, we demonstrate that the SUMF1-enhancing effect is also present in vivo after AAV-mediated delivery of the sulfamidase gene to the muscle of MPSIIIA mice, resulting in a more efficient rescue of the phenotype. These results indicate that co-delivery of SUMF1 may enhance the efficacy of gene therapy in several sulfatase deficiencies.

Retinoid-mediated stimulation of steroid sulfatase activity in myeloid leukemic cell lines requires RARalpha and RXR and involves the phosphoinositide 3-kinase and ERK-MAP kinase pathways

All-trans retinoic acid and 9-cis-retinoic acid stimulate the activity of steroid sulfatase in HL60 acute myeloid leukemia cells in a concentration- and time-dependent manner. Neither of these 'natural retinoids' augmented steroid sulfatase activity in a HL60 sub-line that expresses a dominant-negative retinoic acid receptor alpha (RARalpha). Experiments with synthetic RAR and RXR agonists and antagonists suggest that RARalpha/RXR heterodimers play a role in the retinoid-stimulated increase in steroid sulfatase activity. The retinoid-driven increase in steroid sulfatase activity was attenuated by inhibition of phospholipase D (PLD), but not by inhibitors of phospholipase C. Experiments with inhibitors of protein kinase C (PKC) show that PKCalpha and PKCdelta play an important role in modulating the retinoid-stimulation of steroid sulfatase activity in HL60 cells. Furthermore, we show that pharmacological inhibition of the RAF-1 and ERK MAP kinases blocked the retinoid-stimulated increase in steroid sulfatase activity in HL60 cells and, by contrast, inhibition of the p38-MAP kinase or JNK-MAP kinase had no effect. Pharmacological inhibitors of the phosphatidylinositol 3-kinase, Akt, and PDK-1 also abrogated the retinoid-stimulated increase in steroid sulfatase activity in HL60 cells. These results show that crosstalk between the retinoid-stimulated genomic and non-genomic pathways is necessary to increase steroid sulfatase activity in HL60 cells.

A general binding mechanism for all human sulfatases by the formylglycine-generating enzyme

The formylglycine (FGly)-generating enzyme (FGE) uses molecular oxygen to oxidize a conserved cysteine residue in all eukaryotic sulfatases to the catalytically active FGly. Sulfatases degrade and remodel sulfate esters, and inactivity of FGE results in multiple sulfatase deficiency, a fatal disease. The previously determined FGE crystal structure revealed two crucial cysteine residues in the active site, one of which was thought to be implicated in substrate binding. The other cysteine residue partakes in a novel oxygenase mechanism that does not rely on any cofactors. Here, we present crystal structures of the individual FGE cysteine mutants and employ chemical probing of wild-type FGE, which defined the cysteines to differ strongly in their reactivity. This striking difference in reactivity is explained by the distinct roles of these cysteine residues in the catalytic mechanism. Hitherto, an enzyme-substrate complex as an essential cornerstone for the structural evaluation of the FGly formation mechanism has remained elusive. We also present two FGE-substrate complexes with pentamer and heptamer peptides that mimic sulfatases. The peptides isolate a small cavity that is a likely binding site for molecular oxygen and could host reactive oxygen intermediates during cysteine oxidation. Importantly, these FGE-peptide complexes directly unveil the molecular bases of FGE substrate binding and specificity. Because of the conserved nature of FGE sequences in other organisms, this binding mechanism is of general validity. Furthermore, several disease-causing mutations in both FGE and sulfatases are explained by this binding mechanism.

Sulfatases and human disease

Sulfatases are a highly conserved family of proteins that cleave sulfate esters from a wide range of substrates. The importance of sulfatases in human metabolism is underscored by the presence of at least eight human monogenic diseases caused by the deficiency of individual sulfatases. Sulfatase activity requires a unique posttranslational modification, which is impaired in patients with multiple sulfatase deficiency (MSD) due to a mutation of the sulfatase modifying factor 1 (SUMF1). Here we review current knowledge and future perspectives on the evolution of the sulfatase gene family, on the role of these enzymes in human metabolism, and on new developments in the therapy of sulfatase deficiencies.

Application of a comprehensive subtelomere array in clinical diagnosis of mental retardation

In 2-8% of patients with mental retardation, small copy number changes in the subtelomeric region are thought to be the underlying cause. As detection of these genomic rearrangements is labour intensive using FISH, we constructed and validated a high-density BAC/PAC array covering the first 5 Mb of all subtelomeric regions and applied it in our routine screening of patients with idiopathic mental retardation for submicroscopic telomeric rearrangements. The present study shows the efficiency of this comprehensive subtelomere array in detecting terminal deletions and duplications but also small interstitial subtelomeric rearrangements, starting from small amounts of DNA. With our array, the size of the affected segments, at least those smaller than 5 Mb, can be determined simultaneously in the same experiment. In the first 100 patient samples analysed in our diagnostic practice by the use of this comprehensive telomere array, we found three patients with deletions in 3p, 10q and 15q, respectively, four patients with duplications in 9p, 12p, 21q and Xp, respectively, and one patient with a del 6q/dup 16q. The patients with del 3p and 10q and dup 12p had interstitial rearrangements that would have been missed with techniques using one probe per subtelomeric region chosen close to the telomere.

Sulphatase activities are regulated by the interaction of sulphatase-modifying factor 1 with SUMF2

Sulphatases undergo a unique post-translational modification that converts a highly conserved cysteine located within their active site into formylglycine. This modification is necessary for the catalytic activities of the sulphatases, and it is generated by the protein product of sulphatase-modifying factor 1 (SUMF1), the gene mutated in multiple sulphatase deficiency (MSD). A paralogous gene, SUMF2, was discovered through its sequence similarity to SUMF1. We present evidence that SUMF2 colocalizes with SUMF1 within the endoplasmic reticulum and that the two proteins form heterodimers. SUMF1 and SUMF2 also form homodimers. In addition, SUMF2 is able to associate with the sulphatases with and without SUMF1. We have previously shown that co-transfection of SUMF1 with the sulphatase complementary DNAs greatly enhances the activities of the overexpressed sulphatases. Here, we show that SUMF2 inhibits the enhancing effects of SUMF1 on sulphatases, suggesting that the SUMF1-SUMF2 interaction represents a further level of control of these sulphatase activities.

Molecular basis for multiple sulfatase deficiency and mechanism for formylglycine generation of the human formylglycine-generating enzyme

Sulfatases are enzymes essential for degradation and remodeling of sulfate esters. Formylglycine (FGly), the key catalytic residue in the active site, is unique to sulfatases. In higher eukaryotes, FGly is generated from a cysteine precursor by the FGly-generating enzyme (FGE). Inactivity of FGE results in multiple sulfatase deficiency (MSD), a fatal autosomal recessive syndrome. Based on the crystal structure, we report that FGE is a single-domain monomer with a surprising paucity of secondary structure and adopts a unique fold. The effect of all 18 missense mutations found in MSD patients is explained by the FGE structure, providing a molecular basis of MSD. The catalytic mechanism of FGly generation was elucidated by six high-resolution structures of FGE in different redox environments. The structures allow formulation of a novel oxygenase mechanism whereby FGE utilizes molecular oxygen to generate FGly via a cysteine sulfenic acid intermediate.

Expression, localization, structural, and functional characterization of pFGE, the paralog of the Calpha-formylglycine-generating enzyme

pFGE is the paralog of the formylglycine-generating enzyme (FGE), which catalyzes the oxidation of a specific cysteine to Calpha-formylglycine, the catalytic residue in the active site of sulfatases. The enzymatic activity of sulfatases depends on this posttranslational modification, and the genetic defect of FGE causes multiple sulfatase deficiency. The structural and functional properties of pFGE were analyzed. The comparison with FGE demonstrates that both share a tissue-specific expression pattern and the localization in the lumen of the endoplasmic reticulum. Both are retained in the endoplasmic reticulum by a saturable mechanism. Limited proteolytic cleavage at similar sites indicates that both also share a similar three-dimensional structure. pFGE, however, is lacking the formylglycine-generating activity of FGE. Although overexpression of FGE stimulates the generation of catalytically active sulfatases, overexpression of pFGE has an inhibitory effect. In vitro pFGE interacts with sulfatase-derived peptides but not with FGE. The inhibitory effect of pFGE on the generation of active sulfatases may therefore be caused by a competition of pFGE and FGE for newly synthesized sulfatase polypeptides.

Molecular characterization of the human Calpha-formylglycine-generating enzyme

Calpha-formylglycine (FGly) is the catalytic residue in the active site of sulfatases. In eukaryotes, it is generated in the endoplasmic reticulum by post-translational modification of a conserved cysteine residue. The FGly-generating enzyme (FGE), performing this modification, is an endoplasmic reticulum-resident enzyme that upon overexpression is secreted. Recombinant FGE was purified from cells and secretions to homogeneity. Intracellular FGE contains a high mannose type N-glycan, which is processed to the complex type in secreted FGE. Secreted FGE shows partial N-terminal trimming up to residue 73 without loosing catalytic activity. FGE is a calcium-binding protein containing an N-terminal (residues 86-168) and a C-terminal (residues 178-374) protease-resistant domain. The latter is stabilized by three disulfide bridges arranged in a clamp-like manner, which links the third to the eighth, the fourth to the seventh, and the fifth to the sixth cysteine residue. The innermost cysteine pair is partially reduced. The first two cysteine residues are located in the sequence preceding the N-terminal protease-resistant domain. They can form intramolecular or intermolecular disulfide bonds, the latter stabilizing homodimers. The C-terminal domain comprises the substrate binding site, as evidenced by yeast two-hybrid interaction assays and photocross-linking of a substrate peptide to proline 182. Peptides derived from all known human sulfatases served as substrates for purified FGE indicating that FGE is sufficient to modify all sulfatases of the same species.