Complex care of individuals with multiple sulfatase deficiency: Clinical cases and consensus statement

Preclinical use of a clinically-relevant scAAV9/SUMF1 vector for the treatment of multiple sulfatase deficiency

BACKGROUND

Multiple Sulfatase Deficiency (MSD) is a rare inherited lysosomal storage disorder characterized by loss of function mutations in the SUMF1 gene that manifests as a severe pediatric neurological disease. There are no available targeted therapies for MSD.

METHODS

We engineered a viral vector (AAV9/SUMF1) to deliver working copies of the SUMF1 gene and tested the vector in Sumf1 knock out mice that generally display a median lifespan of 10 days. Mice were injected as pre-symptomatic neonates via intracerebroventricular administration, or as post-symptomatic juveniles via intrathecal alone or combination intrathecal and intravenous delivery. Cohorts were assessed for survival, behavioral outcomes, and post-mortem for sulfatase activity.

RESULTS

We show that treatment of neonates extends survival up to 1-year post-injection. Importantly, delivery of SUMF1 through cerebral spinal fluid at 7 days of age alleviates MSD symptoms. The treated mice show wide distribution of the SUMF1 gene, no signs of toxicity or neuropathy, improved vision and cardiac function, and no behavioral deficits. One-year post treatment, tissues show increased sulfatase activity, indicating functional SUMF1. Further, a GLP toxicology study conducted in rats demonstrates favorable overall safety of this approach.

CONCLUSIONS

These preclinical studies highlight the potential of our AAV9/SUMF1 vector, the design of which is directly translatable for clinical use, as a gene replacement therapy for MSD patients.

Bone marrow transplantation reverses metabolic alterations in multiple sulfatase deficiency: a case series

BACKGROUND

Multiple sulfatase deficiency (MSD) is an exceptionally rare neurodegenerative disorder due to the absence or deficiency of 17 known cellular sulfatases. The activation of all these cellular sulfatases is dependent on the presence of the formylglycine-generating enzyme, which is encoded by the SUMF1 gene. Disease-causing homozygous or compound heterozygous variants in SUMF1 result in MSD. Other than symptomatic treatment, no curative therapy exists as of yet for MSD. Eight out of these 17 sulfatases are primarily localized in the lysosome.

METHODS

Two siblings with attenuated MSD underwent hematopoietic cell transplantation (HCT), evaluating the possibility of lysosomal enzymatic cross-correction from the donor cells.

RESULTS

There is evidence of correction of currently available biomarkers within 3 months post-HCT. Untargeted metabolomics also shows continued correction of multiple biochemical abnormalities in the post-HCT period. Furthermore, this article also presents the neuropsychological outcomes of these children as well as the results of untargeted metabolomics analysis in this condition.

CONCLUSIONS

These data suggest biochemical benefits post-transplant along with slowing of disease progression. Long-term follow-up is necessary to fully evaluate the therapeutic benefit of HCT in MSD.

Hematopoietic stem cell gene therapy improves outcomes in a clinically relevant mouse model of multiple sulfatase deficiency

Multiple sulfatase deficiency (MSD) is a severe, lysosomal storage disorder caused by pathogenic variants in the gene SUMF1, encoding the sulfatase modifying factor formylglycine-generating enzyme. Patients with MSD exhibit functional deficiencies in all cellular sulfatases. The inability of sulfatases to break down their substrates leads to progressive and multi-systemic complications in patients, similar to those seen in single-sulfatase disorders such as metachromatic leukodystrophy and mucopolysaccharidoses IIIA. Here, we aimed to determine if hematopoietic stem cell transplantation with ex vivo SUMF1 lentiviral gene therapy could improve outcomes in a clinically relevant mouse model of MSD. We first tested our approach in MSD patient-derived cells and found that our SUMF1 lentiviral vector improved protein expression, sulfatase activities, and glycosaminoglycan accumulation. In vivo, we found that our gene therapy approach rescued biochemical deficits, including sulfatase activity and glycosaminoglycan accumulation, in affected organs of MSD mice treated post-symptom onset. In addition, treated mice demonstrated improved neuroinflammation and neurocognitive function. Together, these findings suggest that SUMF1 HSCT-GT can improve both biochemical and functional disease markers in the MSD mouse.

Bone marrow transplantation increases sulfatase activity in somatic tissues in a multiple sulfatase deficiency mouse model

BACKGROUND

Multiple Sulfatase Deficiency (MSD) is an ultra-rare autosomal recessive disorder characterized by deficient enzymatic activity of all known sulfatases. MSD patients frequently carry two loss of function mutations in the SUMF1 gene, encoding a formylglycine-generating enzyme (FGE) that activates 17 different sulfatases. MSD patients show common features of other lysosomal diseases like mucopolysaccharidosis and metachromatic leukodystrophy, including neurologic impairments, developmental delay, and visceromegaly. There are currently no approved therapies for MSD patients. Hematopoietic stem cell transplant (HSCT) has been applied with success in the treatment of certain lysosomal diseases. In HSCT, donor-derived myeloid cells are a continuous source of active sulfatase enzymes that can be taken up by sulfatase-deficient host cells. Thus, HSCT could be a potential approach for the treatment of MSD.

METHODS

To test this hypothesis, we used a clinically relevant mouse model for MSD, B6-Sumf1(S153P/S153P) mice, engrafted with bone marrow cells, Sumf1+/+, from B6-PtprcK302E mice (CD45.1 immunoreactive).

RESULTS

After 10 months post-transplant, flow cytometric analysis shows an average of 90% of circulating leukocytes of donor origin (Sumf1(+/+)). Enzymatic activity for ARSA, ARSB, and SGSH is significantly increased in spleen of B6-Sumf1(S153P/S153P) recipient mice. In non-lymphoid organs, only liver and heart show a significant correction of sulfatase activity and GAG accumulation. Frequency of inflammatory cells and lysosomal pathology is significantly reduced in liver and heart, while no significant improvement is detected in brain.

CONCLUSIONS

Our results indicate that HSCT could be a suitable approach to treat MSD-pathology affecting peripheral organs, however that benefit to CNS pathology might be limited.

Boolean Modeling of Biological Network Applied to Protein-Protein Interaction Network of Autism Patients

Cellular molecules interact with one another in a structured manner, defining a regulatory network topology that describes cellular mechanisms. Genetic mutations alter these networks' pathways, generating complex disorders such as autism spectrum disorder (ASD). Boolean models have assisted in understanding biological system dynamics since Kauffman's 1969 discovery, and various analytical tools for regulatory networks have been developed. This study examined the protein-protein interaction network created in our previous publication of four ASD patients using the SPIDDOR R package, a Boolean model-based method. The aim is to examine how patients' genetic variations in INTS6L, USP9X, RSK4, FGF5, FLNA, SUMF1, and IDS affect mTOR and Wnt cell signaling convergence. The Boolean network analysis revealed abnormal activation levels of essential proteins such as β-catenin, MTORC1, RPS6, eIF4E, Cadherin, and SMAD. These proteins affect gene expression, translation, cell adhesion, shape, and migration. Patients 1 and 2 showed consistent patterns of increased β-catenin activity and decreased MTORC1, RPS6, and eIF4E activity. However, patient 2 had an independent decrease in Cadherin and SMAD activity due to the FLNA mutation. Patients 3 and 4 have an abnormal activation of the mTOR pathway, which includes the MTORC1, RPS6, and eIF4E genes. The shared mTOR pathway behavior in these patients is explained by a shared mutation in two closely related proteins (SUMF1 and IDS). Diverse activities in β-catenin, MTORC1, RPS6, eIF4E, Cadherin, and SMAD contributed to the reported phenotype in these individuals. Furthermore, it unveiled the potential therapeutic options that could be suggested to these individuals.

Biochemical signatures of disease severity in multiple sulfatase deficiency

Sulfatases catalyze essential cellular reactions, including degradation of glycosaminoglycans (GAGs). All sulfatases are post-translationally activated by the formylglycine generating enzyme (FGE) which is deficient in multiple sulfatase deficiency (MSD), a neurodegenerative lysosomal storage disease. Historically, patients were presumed to be deficient of all sulfatase activities; however, a more nuanced relationship is emerging. Each sulfatase may differ in their degree of post-translational modification by FGE, which may influence the phenotypic spectrum of MSD. Here, we evaluate if residual sulfatase activity and accumulating GAG patterns distinguish cases from controls and stratify clinical severity groups in MSD. We quantify sulfatase activities and GAG accumulation using three complementary methods in MSD participants. Sulfatases differed greatly in their tolerance of reduction in FGE-mediated activation. Enzymes that degrade heparan sulfate (HS) demonstrated lower residual activities than those that act on other GAGs. Similarly, HS-derived urinary GAG subspecies preferentially accumulated, distinguished cases from controls, and correlated with disease severity. Accumulation patterns of specific sulfatase substrates in MSD provide fundamental insights into sulfatase regulation and will serve as much-needed biomakers for upcoming clinical trials. This work highlights that biomarker investigation of an ultra-rare disease can simultaneously inform our understanding of fundamental biology and advance clinical trial readiness efforts.

Lysosomal storage diseases

Lysosomal storage disorders (LSDs) are a group of inherited metabolic diseases caused by dysfunction of the lysosomal system, with subsequent progressive accumulation of macromolecules, activation of inflammatory response, and cell death. Neurologic damage is almost always present, and it is usually degenerative. White matter (WM) involvement may be primary or secondary. Diseases with primary WM involvement are leukodystrophies, demyelinating (Krabbe disease and metachromatic leukodystrophy), and hypomyelinating leukodystrophies (free sialic acid storage disease, fucosidosis, and mucolipidosis type IV). LSDs with secondary WM involvement are classified as leukoencephalopathies and include gangliosidosis, mucopolysaccharidosis (MPS), ceroid neuronal lipofuscinosis, multiple sulfatase deficiency, alpha-mannosidosis, Pompe disease, and Fabry disease. Neurologic manifestations may overlap among LSDs and include developmental delays, motor, cognitive and speech impairments, seizures, visual failure, ataxia, and extrapyramidal signs. Most of LSDs are typically present in early or late infancy, but juvenile and adult forms also exist and are associated with predominantly neuropsychiatric and behavioral symptoms. The outcome of these disorders is generally poor and specific treatments (enzyme replacement therapy, hematopoietic stem cell transplantation, or gene therapy) are only available in a small number of them.

Association between SUMF1 polymorphisms and COVID-19 severity

BACKGROUND

Evidence shows that genetic factors play important roles in the severity of coronavirus disease 2019 (COVID-19). Sulfatase modifying factor 1 (SUMF1) gene is involved in alveolar damage and systemic inflammatory response. Therefore, we speculate that it may play a key role in COVID-19.

RESULTS

We found that rs794185 was significantly associated with COVID-19 severity in Chinese population, under the additive model after adjusting for gender and age (for C allele = 0.62, 95% CI = 0.44-0.88, P = 0.0073, logistic regression). And this association was consistent with this in European population Genetics Of Mortality In Critical Care (GenOMICC: OR for C allele = 0.94, 95% CI = 0.90-0.98, P = 0.0037). Additionally, we also revealed a remarkable association between rs794185 and the prothrombin activity (PTA) in subjects (P = 0.015, Generalized Linear Model).

CONCLUSIONS

In conclusion, our study for the first time identified that rs794185 in SUMF1 gene was associated with the severity of COVID-19.

Novel Therapeutic Approaches in Inherited Neuropathies: A Systematic Review

The management of inherited neuropathies relies mostly on the treatment of symptoms. In recent years, a better understanding of the pathogenic mechanisms that underlie neuropathies has allowed for the development of disease-modifying therapies. Here, we systematically review the therapies that have emerged in this field over the last five years. An updated list of diseases with peripheral neuropathy as a clinical feature was created based on panels of genes used clinically to diagnose inherited neuropathy. This list was extended by an analysis of published data by the authors and verified by two experts. A comprehensive search for studies of human patients suffering from one of the diseases in our list yielded 28 studies that assessed neuropathy as a primary or secondary outcome. Although the use of various scales and scoring systems made comparisons difficult, this analysis identified diseases associated with neuropathy for which approved therapies exist. An important finding is that the symptoms and/or biomarkers of neuropathies were assessed only in a minority of cases. Therefore, further investigation of treatment efficacy on neuropathies in future trials must employ objective, consistent methods such as wearable technologies, motor unit indexes, MRI or sonography imaging, or the use of blood biomarkers associated with consistent nerve conduction studies.

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.

Drug screening identifies tazarotene and bexarotene as therapeutic agents in multiple sulfatase deficiency

Multiple sulfatase deficiency (MSD, MIM #272200) results from pathogenic variants in the SUMF1 gene that impair proper function of the formylglycine-generating enzyme (FGE). FGE is essential for the posttranslational activation of cellular sulfatases. MSD patients display reduced or absent sulfatase activities and, as a result, clinical signs of single sulfatase disorders in a unique combination. Up to date therapeutic options for MSD are limited and mostly palliative. We performed a screen of FDA-approved drugs using immortalized MSD patient fibroblasts. Recovery of arylsulfatase A activity served as the primary readout. Subsequent analysis confirmed that treatment of primary MSD fibroblasts with tazarotene and bexarotene, two retinoids, led to a correction of MSD pathophysiology. Upon treatment, sulfatase activities increased in a dose- and time-dependent manner, reduced glycosaminoglycan content decreased and lysosomal position and size normalized. Treatment of MSD patient derived induced pluripotent stem cells (iPSC) differentiated into neuronal progenitor cells (NPC) resulted in a positive treatment response. Tazarotene and bexarotene act to ultimately increase the stability of FGE variants. The results lay the basis for future research on the development of a first therapeutic option for MSD patients.

The effect of intravenous trehalose administration in a patient with multiple sulfatase deficiency

Introduction

We describe the case of a female child with multiple sulfatase deficiency (MSD) who received intravenous (IV) trehalose (15 g/week) for 3 months.

Methods

The efficacy of trehalose was evaluated by comparing serum biomarkers, a quality-of-life questionnaire (HRQoL), and imaging (brain MRI and ultrasonography of liver and spleen) at weeks 0 (W0) and 12 (W12).

Results

The improvement in quality of life assessments along with a slight decrease in the spleen dimensions were observed after 3-month intervention.

Conclusions

Future research with a larger MSD population and a longer-term follow-up is warranted to determine whether trehalose can improve MSD patient health and clinical outcomes.

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.

Myelin oligodendrocyte glycoprotein antibodies in genetic leukodystrophies

Accumulation of intermediate metabolites due to enzyme deficiencies and demyelination can provoke inflammation in genetic leukodystrophies. Thirty patients with genetic leukodystrophy and 48 healthy control sera were tested for anti-myelin oligodendrocyte glycoprotein (MOG) antibodies by fixed and/or live cell-based assays. MOG-IgG was detected in two late infantile metachromatic leukodystrophy (MLD) cases, both of which were also weakly positive for IgG1, and one with IgG3 as the dominant anti-MOG IgG subclass. MOG-IgG was borderline positive in a vanishing white matter (VWM) disease patient. These results suggest that inherited metabolic or degenerative processes can have an autoimmune component, possibly as an epiphenomenon.

Pitfalls in Genetic Testing for Consanguineous Pediatric Populations

We describe the diagnostic odyssey of an eight-year-old female born to consanguineous parents. Our patient presented with global developmental delay, regression, microcephaly, spastic diplegia, and leukodystrophy confirmed on brain magnetic resonance imaging (MRI). She was found on whole exome sequencing (WES) to have dual genetic diagnoses. The first was a homozygous pathogenic HERC2 gene partial deletion of exons 43–45 that causes HERC2-related disorder. The second was a homozygous pathogenic variant (c.836 C > T, p.A279 V) in the SUMF1 gene responsible for multiple sulfatase deficiency. This case highlights some of the challenges in diagnosing consanguineous pediatric populations where standard genetic and metabolic testing may not provide answers. Our case further supports the recent American College of Medical Genetics and Genomics (ACMG) recommendation of WES as a first or second-tier test for patients with developmental delay, particularly in a population where the chances of dual diagnosis is high.

Reliability of the Telemedicine Application of the Gross Motor Function Measure-88 in Patients With Leukodystrophy

BACKGROUND

Leukodystrophies are a rare class of disorders characterized by severe neuromotor disability. There is a strong need for research regarding the functional status of people with leukodystrophy which is limited by the need for in-person assessments of mobility. The purpose of this study is to assess the reliability of the Gross Motor Function Measure-88 (GMFM-88) using telemedicine compared with standard in-person assessments in patients with leukodystrophy.

METHODS

A total of 21 subjects with a diagnosis of leukodystrophy (age range = 1.79-52.82 years) were evaluated by in-person and by telemedicine evaluations with the GMFM-88 by physical therapists. Inter-rater reliability was assessed through evaluation of the same subject by two independent raters within a three-week period (n = 10 encounters), and intrarater reliability was assessed through blinded rescoring of video-recorded assessments after a one-week time interval (n = 6 encounters).

RESULTS

Remote assessments were performed by caregivers in all 21 subjects using resources found in the home with remote guidance. There was agreement between all paired in-person and remote measurements (Lin's concordance correlation ≥0.995). The Bland-Altman analysis indicated that the paired differences were within ±5%. Intrarater and inter-rater reliability demonstrated an intraclass correlation coefficient of >0.90.

CONCLUSIONS

These results support that remote application of the GMFM-88 is a feasible and reliable approach to assess individuals with leukodystrophy. Telemedicine application of outcome measures may be of particular value in rare diseases and those with severe neurologic disability that impacts the ability to travel.

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.

Natural history of multiple sulfatase deficiency: Retrospective phenotyping and functional variant analysis to characterize an ultra-rare disease

Multiple sulfatase deficiency (MSD) is an ultra-rare neurodegenerative disorder caused by pathogenic variants in SUMF1. This gene encodes formylglycine-generating enzyme (FGE), a protein required for sulfatase activation. The clinical course of MSD results from additive effect of each sulfatase deficiency, including metachromatic leukodystrophy (MLD), several mucopolysaccharidoses (MPS II, IIIA, IIID, IIIE, IVA, VI), chondrodysplasia punctata, and X-linked ichthyosis. While it is known that affected individuals demonstrate a complex and severe phenotype, the genotype-phenotype relationship and detailed clinical course is unknown. We report on 35 cases enrolled in our retrospective natural history study, n = 32 with detailed histories. Neurologic function was longitudinally assessed with retrospective scales. Biochemical and computational modeling of novel SUMF1 variants was performed. Genotypes were classified based on predicted functional change, and each individual was assigned a genotype severity score. The median age at symptom onset was 0.25 years; median age at diagnosis was 2.7 years; and median age at death was 13 years. All individuals demonstrated developmental delay, and only a subset of individuals attained ambulation and verbal communication. All subjects experienced an accumulating systemic symptom burden. Earlier age at symptom onset and severe variant pathogenicity correlated with poor neurologic outcomes. Using retrospective deep phenotyping and detailed variant analysis, we defined the natural history of MSD. We found that attenuated cases can be distinguished from severe cases by age of onset, attainment of ambulation, and genotype. Results from this study can help inform prognosis and facilitate future study 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.

A homozygous missense variant of SUMF1 in the Bedouin population extends the clinical spectrum in ultrarare neonatal multiple sulfatase deficiency

BACKGROUND

Multiple sulfatase deficiency (MSD, MIM #272200) is an ultrarare congenital disorder caused by SUMF1 mutation and often misdiagnosed due to its complex clinical presentation. Impeded by a lack of natural history, knowledge gained from individual case studies forms the source for a reliable diagnosis and consultation of patients and parents.

METHODS

We collected clinical records as well as genetic and metabolic test results from two MSD patients. The functional properties of a novel SUMF1 variant were analyzed after expression in a cell culture model.

RESULTS

We report on two MSD patients-the first neonatal type reported in Israel-both presenting with this most severe manifestation of MSD. Our patients showed uniform clinical symptoms with persistent pulmonary hypertension, hypotonia, and dysmorphism at birth. Both patients were homozygous for the same novel SUMF1 mutation (c.1043C>T, p.A348V). Functional analysis revealed that the SUMF1-encoded variant of formylglycine-generating enzyme is highly instable and lacks catalytic function.

CONCLUSION

The obtained results confirm genotype-phenotype correlation in MSD, expand the spectrum of clinical presentation and are relevant for diagnosis including the extremely rare neonatal severe type of MSD.

Multiplex testing for the screening of lysosomal storage disease in urine: Sulfatides and glycosaminoglycan profiles in 40 cases of sulfatiduria

PURPOSE

To describe an efficient and effective multiplex screening strategy for sulfatide degradation disorders and mucolipidosis type II/III (MLII/III) using 3 mL of urine.

METHODS

Glycosaminoglycans were analyzed by liquid chromatography-tandem mass spectrometry. Matrix assisted laser desorption/ionization-time of flight tandem mass spectrometry was used to identify free oligosaccharides and identify 22 ceramide trihexosides and 23 sulfatides, which are integrated by 670 calculated ratios. Collaborative Laboratory Integrated Reports (CLIR; https://clir.mayo.edu) was used for post-analytical interpretation of the complex metabolite profile and to aid in the differential diagnosis of abnormal results.

RESULTS

Multiplex analysis was performed on 25 sulfatiduria case samples and compiled with retrospective data from an additional 15 cases revealing unique patterns of biomarkers for each disorder of sulfatide degradation (MLD, MSD, and Saposin B deficiency) and for MLII/III, thus allowing the formulation of a novel algorithm for the biochemical diagnosis of these disorders.

CONCLUSIONS

Comprehensive and integrated urine screening could be very effective in the initial workup of patients suspected of having a lysosomal disorder as it covers disorders of sulfatide degradation and narrows down the differential diagnosis in patients with elevated glycosaminoglycans.

Severe neonatal multiple sulfatase deficiency presenting with hydrops fetalis in a preterm birth patient

Multiple sulfatase deficiency (MSD) is an ultra-rare lysosomal storage disorder (LSD). Mutations in the SUMF1 gene encoding the formylglycine generating enzyme (FGE) result in an unstable FGE protein with reduced enzymatic activity, thereby affecting the posttranslational activation of newly synthesized sulfatases. Complete absence of FGE function results in the most severe clinical form of MSD with neonatal onset and rapid deterioration. We report on a preterm infant presenting with hydrops fetalis, lung hypoplasia, and dysmorphism as major clinical signs. The patient died after 6 days from an intraventricular hemorrhage followed by multi-organ failure. MSD was caused by a homozygous SUMF1 stop mutation (c.191C>A, p.Ser64Ter). FGE protein and sulfatase activities were absent in patient fibroblasts. Hydrops fetalis is a rare symptom of LSDs and should be considered in the differential diagnosis in combination with dysmorphism. The diagnostic set up should include measurements of glycosaminoglycan excretion and lysosomal enzyme activities, among them at least two sulfatases, and molecular confirmation.

Site-Specific Labeling of Proteins Using the Formylglycine-Generating Enzyme (FGE)

Use of the formylglycine generating enzyme (FGE)-a copper-dependent posttranslational protein modifier-represents a particularly elegant method taken directly from nature of introducing a unique amino acid into the larger context of a protein. Formylglycine (fGly) is a crucial component of the active site of sulfatases, where it directly participates in the breakdown of sulfate ester substrates. In the context of bioconjugation this aldehyde containing amino acid can be an invaluable reactive handle for the chemical conjugation of molecules. Here we describe a detailed method for generating formylglycine-containing proteins in a mammalian system developed specifically for the production of antibody-drug conjugates (ADCs) but applicable to a wide range of proteins.

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.