A systematic cross-sectional survey of multiple sulfatase deficiency

A novel iPSC model reveals selective vulnerability of neurons in multiple sulfatase deficiency

Multiple sulfatase deficiency (MSD) is an ultra-rare, inherited lysosomal storage disease caused by mutations in the gene sulfatase modifying factor 1 (SUMF1). MSD is characterized by the functional deficiency of all sulfatase enzymes, leading to the storage of sulfated substrates including glycosaminoglycans (GAGs), sulfolipids, and steroid sulfates. Patients with MSD experience severe neurological impairment, hearing loss, organomegaly, corneal clouding, cardiac valve disease, dysostosis multiplex, contractures, and ichthyosis. Here, we generated a novel human model of MSD by reprogramming patient peripheral blood mononuclear cells to establish an MSD induced pluripotent stem cell (iPSC) line (SUMF1 p.A279V). We also generated an isogenic control iPSC line by correcting the pathogenic variant with CRISPR/Cas9 gene editing. We successfully differentiated these iPSC lines into neural progenitor cells (NPCs) and NGN2-induced neurons (NGN2-iN) to model the neuropathology of MSD. Mature neuronal cells exhibited decreased SUMF1 gene expression, increased lysosomal stress, impaired neurite outgrowth and maturation, reduced sulfatase activities, and GAG accumulation. Interestingly, MSD iPSCs and NPCs did not exhibit as severe of phenotypes, suggesting that as neurons differentiate and mature, they become more vulnerable to loss of SUMF1. In summary, we demonstrate that this human iPSC-derived neuronal model recapitulates the cellular and biochemical features of MSD. These cell models can be used as tools to further elucidate the mechanisms of MSD pathology and for the development of therapeutics.

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.

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.

Unexpected Phenotype Reversion and Survival in a Zebrafish Model of Multiple Sulfatase Deficiency

Multiple sulfatase deficiency (MSD) is a rare recessively inherited Mendelian disorder that manifests with developmental delay, neurodegeneration, skeletal deformities, facial dysmorphism, congenital growth retardation, and other clinical signs. The disorder is caused by mutations in the SUMF1 gene, which encodes the formylglycine-generating enzyme (FGE), and responsible for the activation of sulfatases. Mutations in SUMF1 result in reduced or absent FGE function with consequent compromised activities of its client sulfatases. This leads to an accumulation of enzyme substrates, such as glycosaminoglycans and sulfolipids, within lysosomes and subsequently impaired lysosome function and cellular pathology. Currently, there are no disease modifying therapeutic options for MSD patients, hence the need for more suitable animal models to investigate the disorder. Here, we describe the characterisation of a sumf1 null zebrafish model, which has negligible sulfatase activity. Our sumf1 ^-/- zebrafish model successfully recapitulates the pathology of MSD such as cranial malformation, altered bone development, an enlarged population of microglia, and growth retardation during early development but lacks early lethality of mouse Sumf1 ^-/- models. Notably, we provide evidence of recovery in MSD pathology during later developmental stages, resulting in homozygous mutants that are viable. Hence, our data suggest the possibility of a unique compensatory mechanism that allows the sumf1 ^-/- null zebrafish to survive better than human MSD patients and mouse Sumf1 ^-/- models.

Acute-onset paralytic strabismus in toddlers is important to consider as a potential early sign of late-infantile Metachromatic Leukodystrophy

OBJECTIVES

Metachromatic leukodystrophy (MLD) is a fatal lysosomal storage disease characterized by progressive demyelination within the central and peripheral nervous system. Rapid diagnosis is crucial in view of evolving therapeutic options. Strabismus has anecdotally been described as a feature in children with MLD. Our first aim was to examine the prevalence of strabismus as an early or even presenting sign of MLD in two nationwide cohorts. Second, we aimed to investigate the temporal relation between the onset of strabismus and gross motor deterioration, other early onset eye movement disorders and brain white matter abnormalities.

METHODS

Clinical records of 204 MLD patients at the University Children's Hospital Tubingen and Amsterdam University Medical Center were reviewed on the presence of strabismus and other eye movement disorders. Gross motor deterioration and white matter abnormalities on brain MRI were evaluated by using the Gross Motor Function Classification in MLD and MLD LOES score, respectively.

RESULTS

We identified strabismus as an early sign in MLD patients with the late-infantile form, with a prevalence of 27% (N = 17). The onset of strabismus preceded gross motor symptoms and brain white matter abnormalities in 71% and 46% respectively of the cases. Important characteristics were an acute-onset paralytic esotropia, partly accompanied by other eye movement abnormalities, and gadolinium enhancement of the cranial nerves.

CONCLUSIONS

Acute-onset paralytic strabismus in toddlers should be considered a potential early sign of late-infantile MLD and might result from early cranial nerve involvement. Brain MRI with gadolinium contrast may facilitate early diagnosis.

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.