MPS VI associated ocular phenotypes in an MPS VI murine model and the therapeutic effects of odiparcil treatment

Maroteaux - Lamy syndrome (mucopolysaccharidosis type VI, MPS VI) is a lysosomal storage disease resulting from insufficient enzymatic activity for degradation of the specific glycosaminoglycans (GAG) chondroitin sulphate (CS) and dermatan sulphate (DS). Among the most pronounced MPS VI clinical manifestations caused by cellular accumulation of excess CS and DS are eye disorders, in particular those that affect the cornea. Ocular manifestations are not treated by the current standard of care, enzyme replacement therapy (ERT), leaving patients with a significant unmet need. Using in vitro and in vivo models, we previously demonstrated the potential of the β-D-xyloside, odiparcil, as an oral GAG clearance therapy for MPS VI. Here, we characterized the eye phenotypes in MPS VI arylsulfatase B deficient mice (Arsb^-) and studied the effects of odiparcil treatment in early and established disease models. Severe levels of opacification and GAG accumulation were detected in the eyes of MPS VI Arsb^- mice. Histological examination of MPS VI Arsb^- eyes showed an aggregate of corneal phenotypes, including reduction in the corneal epithelium thickness and number of epithelial cell layers, and morphological malformations in the stroma. In addition, colloidal iron staining showed specifically GAG accumulation in the cornea. Orally administered odiparcil markedly reduced GAG accumulation in the eyes of MPS VI Arsb^- mice in both disease models and restored the corneal morphology (epithelial layers and stromal structure). In the early disease model of MPS VI, odiparcil partially reduced corneal opacity area, but did not affect opacity area in the established model. Analysis of GAG types accumulating in the MPS VI Arsb^- eyes demonstrated major contribution of DS and CS, with some increase in heparan sulphate (HS) as well and all were reduced with odiparcil treatment. Taken together, we further reveal the potential of odiparcil to be an effective therapy for eye phenotypes associated with MPS VI disease.

Mucopolysaccharidosis Type VI, an Updated Overview of the Disease

Mucopolysaccharidosis type VI, or Maroteaux-Lamy syndrome, is a rare, autosomal recessive genetic disease, mainly affecting the pediatric age group. The disease is due to pathogenic variants of the ARSB gene, coding for the lysosomal hydrolase N-acetylgalactosamine 4-sulfatase (arylsulfatase B, ASB). The enzyme deficit causes a pathological accumulation of the undegraded glycosaminoglycans dermatan-sulphate and chondroitin-sulphate, natural substrates of ASB activity. Intracellular and extracellular deposits progressively take to a pathological scenario, often severe, involving most organ-systems and generally starting from the osteoarticular apparatus. Neurocognitive and behavioral abilities, commonly described as maintained, have been actually investigated by few studies. The disease, first described in 1963, has a reported prevalence between 0.36 and 1.3 per 100,000 live births across the continents. With this paper, we wish to contribute an updated overview of the disease from the clinical, diagnostic, and therapeutic sides. The numerous in vitro and in vivo preclinical studies conducted in the last 10-15 years to dissect the disease pathogenesis, the efficacy of the available therapeutic treatment (enzyme replacement therapy), as well as new therapies under study are here described. This review also highlights the need to identify new disease biomarkers, potentially speeding up the diagnostic process and the monitoring of therapeutic efficacy.

Long-term outcomes of patients with mucopolysaccharidosis VI treated with galsulfase enzyme replacement therapy since infancy

OBJECTIVE

Long-term outcomes of patients with mucopolysaccharidosis (MPS) VI treated with galsulfase enzyme replacement therapy (ERT) since infancy were evaluated.

METHODS

The study was a multicenter, prospective evaluation using data from infants with MPS VI generated during a phase 4 study (ASB-008; Clinicaltrials.govNCT00299000) and clinical data collected ≥5 years after completion of the study.

RESULTS

Parents of three subjects from ASB-008 (subjects 1, 2, and 4) provided written informed consent to participate in the follow-up study. One subject was excluded as consent was not provided. Subjects 1, 2, and 4 were aged 0.7, 0.3, and 1.1 years, respectively, at initiation of galsulfase and 10.5, 7.9, and 10.5 years, respectively, at follow-up. All subjects had classical MPS VI based on pre-treatment urinary glycosaminoglycans and the early onset of clinical manifestations. At follow-up, subject 4 had normal stature for age; subjects 1 and 2 had short stature, but height remained around the 90th percentile of growth curves for untreated classical MPS VI. Six-minute walk distance was normal for age/height in subjects 1 (550 m) and 4 (506 m), and reduced for subject 2 (340 m). Subject 2 preserved normal respiratory function, while percent predicted forced vital capacity and forced expiratory volume in 1 s decreased over time in the other subjects. Skeletal dysplasia was already apparent in all subjects at baseline and continued to progress. Cardiac valve disease showed mild progression in subject 1, mild improvement in subject 4, and remained trivial in subject 2. All subjects had considerably reduced pinch and grip strength at follow-up, but functional dexterity was relatively normal for age and there was limited impact on activities of daily living. Bruininks-Oseretsky Test of Motor Proficiency (BOT-2) results showed that subjects 2 and 4 had numerous fine and gross motor competencies. Corneal clouding progressed in all subjects, while progression of hearing impairment was variable. Liver size normalized from baseline in subjects 1 and 4, and remained normal in subject 2.

CONCLUSION

Very early and continuous ERT appears to slow down the clinical course of MPS VI, as shown by preservation of endurance, functional dexterity, and several fine and gross motor competencies after 7.7-9.8 years of treatment, and less growth impairment or progression of cardiac disease than could be expected based on the patients' classical phenotype. ERT does not seem to prevent progression of skeletal or eye disease in the long term.

Analysis of Mucopolysaccharidosis Type VI through Integrative Functional Metabolomics

Metabolic phenotyping is poised as a powerful and promising tool for biomarker discovery in inherited metabolic diseases. However, few studies applied this approach to mcopolysaccharidoses (MPS). Thus, this innovative functional approach may unveil comprehensive impairments in MPS biology. This study explores mcopolysaccharidosis VI (MPS VI) or Maroteaux–Lamy syndrome (OMIM #253200) which is an autosomal recessive lysosomal storage disease caused by the deficiency of arylsulfatase B enzyme. Urine samples were collected from 16 MPS VI patients and 66 healthy control individuals. Untargeted metabolomics analysis was applied using ultra-high-performance liquid chromatography combined with ion mobility and high-resolution mass spectrometry. Furthermore, dermatan sulfate, amino acids, carnitine, and acylcarnitine profiles were quantified using liquid chromatography coupled to tandem mass spectrometry. Univariate analysis and multivariate data modeling were used for integrative analysis and discriminant metabolites selection. Pathway analysis was done to unveil impaired metabolism. The study revealed significant differential biochemical patterns using multivariate data modeling. Pathway analysis revealed that several major amino acid pathways were dysregulated in MPS VI. Integrative analysis of targeted and untargeted metabolomics data with in silico results yielded arginine-proline, histidine, and glutathione metabolism being the most affected. This study is one of the first metabolic phenotyping studies of MPS VI. The findings might shed light on molecular understanding of MPS pathophysiology to develop further MPS studies to enhance diagnosis and treatments of this rare condition.

Another Novel Missense Mutation in ARSB Gene in Iran

Mucopolysaccharidosis VI (MPS-VI) is an infrequent autosomal recessive disorder caused by mutations in ARSB gene and deficiency in lysosomal enzyyme ARSB activities subsequently. This enzyme is essential for the breaking of glycosaminoglycans (GAGs) such as dermatan sulfate and chondroitin sulfate. ARSB dysfunction results in imperfect breakdown of GAGs and their accumulation in urine. Mutations in ARSB gene are the main players in MPS-VI disease and its clinical consequences. Most reported mutations are point mutations but there are some other examples in literature. Here we report a novel missense mutation in ARSB gene that is inherited as an autosomal recessive mode and probably explain the clinical status of the proband. This mutation replaces the threonine 92 by proline and alters ARSB structure. This is the most feasible scenario for clinical condition we described here. This novel mutation should be remarked for PND and PGD to improve the health and management of such families.

The constellation of skeletal deformities in a family with mixed types of mucopolysaccharidoses: Case report

INTRODUCTION

A 13-year-old child was clinically diagnosed with mucopolysaccharidosis type VI-Maroteaux-Lamy syndrome (MPS VI) at the age of 5 years, and the diagnosis was confirmed biochemically and genetically (homozygous mutation in ARSB gene). At that time, his older brother manifested with increasing severe mental retardation. His urinary glycosaminoglycan excretion in urine was elevated, but there was only 1 mutation in the ARSB gene defining him as a healthy carrier of MPS VI. The 15-year-old boy was born with dysmorphic facial features, cleft lip and palate, and multiple contractures associated with profound skeletal deformities manifested, severe mental retardation, and seizures, leading to the diagnosis of cerebral palsy from birth on.Clinical and radiographic phenotypic characterization was the baseline tool to document the older sibling, parents, and relatives, all of them examined at the Orthopaedic Hospital of Speising, Vienna, Austria. The family history (from maternal and paternal sides) showed >10 subjects with variable clinical histories of hyperactivity and attention deficit disorder, depression, and a diversity of skeletal abnormalities, such as dysplastic spondylolisthesis, discovertebral degeneration, osteopenia, osteophytosis, and progressive degeneration of the weight bearing zones (mostly developed at middle age).

METHODS

Eleven patients in a family with interrelated marriages (two male siblings of 15 and 13-year-old), parents and relatives over three generations were enrolled. One of the siblings was diagnosed with Maroteaux-Lamy syndrome at the age of five-years and mutation of the ARBS gene has been encountered. The older sibling manifested at birth craniofacial abnormalities associated with multiple contracture and seizures. Cerebral palsy was the suggested diagnosis. Clinical and radiographic phenotypes were the baseline tool to document the older sibling, parents and relatives at the orthopaedic Hospital of Speising, Vienna, Austria. These were followed by whole Exome sequencing in three family subjects.

RESULTS

A series of genetic studies in the older sibling showed homozygous mutation in GNS gene compatible with MPS IIID. Both parents are first related and were found to be heterozygous for N-acetylglucosamine-6-sulfatase GNS gene. Family history showed more than 10 subjects with variable clinical presentations such as dysplastic spondylolisthesis, disco-vertebral degeneration, osteopenia, osteophytosis, and progressive degeneration of the weight bearing zones (mostly developed at middle age).

CONCLUSION

Owing to the multiple systemic involvements, a genetic cause was suspected and a molecular genetic investigation by using whole-exome-sequencing method in 3 family subjects (trios) was performed: the 15-year-old boy and his parents. A homozygous splice-site-mutation in the GNS gene could be found, compatible with mucopolysaccharidosis-Sanfillipo syndrome (type IIID). Both parents are first related and were now found also to be heterozygous for the GNS gene mutation found in their older son. Therefore, both parents are heterozygous carriers for the ARSB gene mutation but also the GNS gene mutation. In the son with MPS VI, no mutation in the GNS gene was found, but the brother with MPS IIID was heterozygous for the ARSB gene mutation.We presume that the intrafamilial variability of clinical signs in different family members could be the result of various mutations in the ARSB/GNS genes in the carriers or potential modulating effects of other genes or differences in genetic backgrounds.

Long-term cognitive follow-up in children treated for Maroteaux-Lamy syndrome

BACKGROUND

It remains unclear to what extent the brain is affected by Maroteaux-Lamy syndrome (MPS VI), a progressive lysosomal storage disorder. While enzyme replacement therapy (ERT) elicits positive effects, the drug cannot cross the blood-brain barrier. We therefore studied cognitive development and brain abnormalities in the Dutch MPS VI patient population treated with ERT.

METHODS

In a series of 11 children with MPS VI (age 2 to 20 years), we assessed cognitive functioning and brain magnetic resonance imaging prospectively at the start of ERT and at regular times thereafter up to 4.8 years. We also assessed the children's clinical characteristics, their siblings' cognitive development, and their parents' educational levels.

RESULTS

The patients' intelligence scores ranged from normal to mentally delayed (range test scores 52-131). In 90%, their scores remained fairly stable during follow-up, generally lying in the same range as their siblings' test scores (median for patients = 104, median for siblings = 88) and comparing well with the parental educational levels. Native-speaking patients had higher intelligence test scores than non-native-speaking patients. Two patients, both with high baseline glycosaminoglycan levels in their urine and severe mutations in the arylsulfatase B gene, scored clearly lower than expected. Patients with pY210C performed best. Brain abnormalities were aspecific, occurring more in patients with severe symptoms.

CONCLUSION

Our study shows that cognitive development in MPS VI patients is determined not only by familial and social-background factors, but, in patients with a severe form of the disease, also by the disease itself. Therefore in patients with severe disease presentation cognition should be monitored carefully.

[Analysis of clinical features and arylsulfatase B gene mutation in thirteen Chinese children with mucopolysaccharidosis type VI]

OBJECTIVE

Mucopolysaccharidosis type VI (MPS VI) or Maroteaux-Lamy syndrome is an autosomal recessive lysosomal storage disease caused by a deficiency of arylsulfatase B(ARSB), which is required in the degradation of dermatan sulfate and chondroitin sulfate. The deficiency of ARSB leads to an accumulation of dermatan sulfate and chondroitin sulfate in lysosomes and gross excretion in the urine.Few articles about clinical study and ARSB gene mutation analysis of Chinese MPS VI patients were published. This study aimed to explore the clinical features and characteristics of ARSB gene in Chinese children with MPS VI.

METHOD

Thirteen children were diagnosed as MPS VI by ARSB enzyme activity determination during the period from 2009 to 2013. Their clinical features, radiological findings and urine glycosaminoglycan (GAG) levels were retrospectively reviewed. Direct sequencing was used to identify any mutation in the ARSB gene.

RESULT

Thirteen children were diagnosed at the average age of (3.9 ± 2.2) years with 6 male and 7 female. All of these children presented with severe form and onset at an early age of (1.5 ± 0.8) years.Other clinical features included coarse facies, short stature, skeleton deformity, corneal clouding, hepatosplenomegaly with normal intelligence. The radiological findings in all children were characteristic of dysostosis multiplex, like abnormal development of vertebral bodies of the spine, campylorrhachia and paddle-shaped widened ribs. The MRI in case 2 showed cervical cord compression and multiple cysts degeneration in the corona radiate, cella lateralis and callosum.High urine GAG levels were detected, (307.10 ± 112.14) mg/L (Normally below 70 mg/L) and (722.28 ± 245.68) µg/mg creatinine. The ARSB enzyme activity in leukocytes was low, (13.29 ± 6.22) nmol/(mg×h) [Normal range (47-169) nmol/(mg×h)] by fluorogenic assay and (0.24 ± 0.18) U/g [Normal range (1.01-11.47) U/g] by colorimetric assay. A total of 11 mutations were identified by molecular analysis, including seven previously reported mutations (p.L72R, p.G167R, p.G303E, p.F399L, p. T442M, p.Y255X and p.R327X) and four novel mutations (p.Y175D, p.S403X, p.S464X and large deletion including ex. 2, 3). The c.1197C>G (p.F399L) mutation was the most common mutation in this study (31%).

CONCLUSION

The severe form of MPS VI is characterized by early onset and rapid illness progression. Both the radiological findings and increased urine GAG are important clues to diagnose MPS VI.Large decrease or absence of ARSB activity is diagnostic for MPS VI.Four novel mutations of ARSB gene were identified. The reported mutation c.1197C>G (p.F399L) was the hot-spot mutation in this study.

Enzyme replacement therapy with galsulfase in 34 children younger than five years of age with MPS VI

BACKGROUND

Mucopolysaccharidosis type VI (MPS VI) is a progressive, chronic and multisystem lysosomal storage disease with a wide disease spectrum. Clinical and biochemical improvements have been reported for MPS VI patients on enzyme replacement therapy (ERT) with rhASB (recombinant human arylsulfatase B; galsulfase, Naglazyme®, BioMarin Pharmaceutical Inc.), making early diagnosis and intervention imperative for optimal patient outcomes. Few studies have included children younger than five years of age. This report describes 34 MPS VI patients that started treatment with galsulfase before five years of age.

METHODS

Data from patients who initiated treatment at <5 years of age were collected from patients' medical records. Baseline and follow-up assessments of common symptoms that led to diagnosis and that were used to evaluate disease progression and treatment efficacy were evaluated.

RESULTS

A significant negative correlation was seen with treatment with ERT and urinary GAG levels. Of those with baseline and follow-up growth data, 47% remained on their pre-treatment growth curve or moved to a higher percentile after treatment. Of the 9 patients with baseline and follow-up sleep studies, 5 remained unaffected and 1 patient initially with mild sleep apnea showed improvement. Data regarding cardiac, ophthalmic, central nervous system, hearing, surgical interventions and development are also reported. No patient discontinued treatment due to an adverse event and all that were treatment-emergent resolved.

CONCLUSIONS

The prescribed dosage of 1mg/kg IV weekly with galsulfase ERT is shown to be safe and effective in slowing and/or improving certain aspects of the disease, although patients should be closely monitored for complications associated with the natural history of the disease, especially cardiac valve involvement and spinal cord compression. A long-term follow-up investigation of this group of children will provide further information on the benefits of early treatment as well as disease progression and treatment efficacy and safety in this young patient population.

Up to five years experience with 11 mucopolysaccharidosis type VI patients

Maroteaux-Lamy syndrome (mucopolysaccharidosis type VI, MPS VI) is a rare progressive metabolic disorder characterized by coarse facial features, hepatosplenomegaly, restrictive pulmonary function, cardiac abnormalities and stiff joints. The disease is caused by a deficiency of the lysosomal enzyme N-acetyl galactosamine 4-sulfatase which leads to glycosaminoglycan (GAG) storage in various tissues. It presents as a clinical spectrum with varying disease progressions and severities. While the phases I/II/III studies proved the effectiveness of enzyme-replacement therapy (ERT) with recombinant human arylsulfatase B, long-term data are still scarce. Over treatment periods ranging from 1.3 to 5.4 years, this prospective open-label follow-up study in 11 Dutch mucopolysaccharidosis type VI patients (age 2-18 years) showed that ERT had significant positive effects on cardiac-wall diameters (IVSd and LVMI), left and right shoulder flexions (p<0.001), liver size and spleen size (p<0.001), urinary GAG excretion (p<0.001), and the scales of quality of life (motor functioning and body functioning). ERT did not affect cardiac valve regurgitation or hearing function; HRQoL decreased slightly in two domains ('anxiety' and 'negative emotions'), and patients with the rapid and slow progressive forms of the disease differed with regard to baseline GAG excretion and GAG decrease during treatment. In conclusion, ERT had an effect on several clinical parameters. This effect was established in an open cohort of young mucopolysaccharidosis type VI patients.

Pharmacological read-through of nonsense ARSB mutations as a potential therapeutic approach for mucopolysaccharidosis VI

Mucopolysaccharidosis type VI (MPS VI) is a severe lysosomal storage disorder without central nervous system involvement caused by arylsulfatase B (ARSB) deficiency. MPS VI is characterized by dysostosis multiplex, corneal clouding, heart valve defects and urinary excretion of glycosaminoglycans (GAGs). The current treatment for MPS VI is enzyme replacement therapy (ERT) which has limited efficacy on bone, joints and heart valve disease, as well as high costs. A potential therapeutic approach for the subgroup of MPS VI patients that carry nonsense mutations is to enhance stop-codon read-through, using small molecules, to restore production of the full-length ARSB protein. In this study we investigated whether two compounds known to induce stop codon read-through, the aminoglycoside gentamicin and PTC124, can promote read-through of four different ARSB nonsense mutations (p.R315X, p.R327X, p.Q456X and p.Q503X) associated with MPS VI and enable the synthesis of full-length functional ARSB protein in patients fibroblast cell lines. Our study demonstrates that PTC124 but not gentamicin, increases the level of ARSB activity in three MPS VI patient fibroblast cell lines. In two of them the levels of ARSB activity obtained were significantly higher than in untreated cells, reaching ≤2.5 % of those detected in wild-type fibroblasts and resulting in significant reduction of lysosomal size. Since even small increases in enzyme activity can dramatically influence the clinical phenotype of MPS VI, our study suggests that pharmacological read-through may be combined with ERT potentially increasing therapeutic efficacy in those patients bearing nonsense ARSB mutations.

Clinical characteristics of adults with slowly progressing mucopolysaccharidosis VI: a case series

OBJECTIVE

To assess clinical features and general health status of adult patients with mucopolysaccharidosis (MPS) VI.

METHODS

This report includes the clinical history of patients older than 18 years with slowly progressing MPS VI and the retrospective analysis of the outcomes of available data collected between September 2003 and October 2008 at the Center of Pediatric and Adolescent Medicine, University Medical Center, Johannes Gutenberg-University of Mainz, Germany. Variables included were urinary glycosaminoglycan (uGAG) level, mutation analysis, body height, forced vital capacity (FVC), 6-minute walk test, echocardiographic findings, the need for craniocervical decompression surgery, orthopaedic findings and ophthalmological assessments.

RESULTS

The analysis included nine patients with MPS VI aged 19-29 years. The median age at diagnosis was 12 (range 6-20) years. At the time of the assessment (median age 25 years), median uGAG was 29 (range 15-149) μg/mg creatinine and median height 152 (range 136-161) cm. All patients had a FVC below standard values, seven showed reduced endurance in the 6-minute-walk test, all had valve changes with valve replacement in three, two underwent craniocervical decompression surgery, two underwent carpal tunnel surgery, five had ear/nose/throat (ENT) interventions, seven had hip pain/dysplasia, seven had corneal clouding and two were visually impaired.

CONCLUSIONS

Although patients with slowly progressing MPS VI are a heterogeneous group showing disease manifestations in several organs, they seem to have some typical characteristics in common. Despite the attenuated clinical course, many of these patients show severe morbidity. Therefore, early diagnosis and proper follow-up and treatment are essential.

Molecular analysis of mucopolysaccharidosis type VI in Poland, Belarus, Lithuania and Estonia

Mucopolysaccharidosis VI (MPS VI) is a rare autosomal recessive disorder caused by a deficiency of N-acetylgalactosamine-4-sulfatase (ARSB). Over 130 ARSB gene mutations have been identified thus far and most mutations are unique to individual families. We aimed to analyze the spectrum of mutations in the ARSB gene responsible for the disorder in Poland, Belarus and Baltic States. Twenty one families with MPS VI patients, in whom diagnosis was confirmed biochemically and enzymatically, were studied. Direct sequencing of patient genomic DNA was used to identify ARSB mutations. In total, fourteen different disease-causing mutations were found. Three novel mutations included insertion c.375_376insT, a missense mutation c.499G>A (p.G167R) and deletion/insertion c.750_754delinsCCTGAAGTCAAG. We also report 11 previously described mutations (p.A33V, p.W57C, p.Q88X, p.T92K, p.Q97X, p.R152W, p.R160Q, p.R160X, p.Y210C, p.Y266S, p.G302R). The mutation p.R152W was present at a high prevalence of 50% (21/42) the mutated alleles in this group of patients. High prevalence of p.R152W mutation in Poland, Belarus and Baltic States indicates a possible founder effect and suggests that screening for this mutation may be appropriate in MPS VI patients from this region. Our study has also provided evidence to support genotype-phenotype correlation.

Mucopolysaccharidosis type VI (Maroteaux-Lamy syndrome) with a predominantly cardiac phenotype

We present here the first literature description of a predominantly cardiac phenotype in a patient homozygous for missense mutation p.R152W in the N-acetylogalactosamine-4-sulfatase (arylsulfatase B, ARSB) gene. An adult Caucasian woman, who displayed very few symptoms up to her late thirties, was diagnosed with mucopolysaccharidosis type VI (MPS VI) after her hospitalization due to acute heart failure originating mainly from valve disease. In addition to her cardiac phenotype some musculoskeletal involvement without other MPS characteristic features were found. Despite the common pharmacologic treatment and implementation of enzyme replacement therapy with galsulfase the patient died at the age of 38 years because of decompensation of chronic heart failure.

Attenuated mucopolysaccharidosis type VI (Maroteaux-Lamy syndrome) due to homozygosity for the p.Y210C mutation in the ARSB gene

We describe the case of a boy recently diagnosed with an attenuated form of mucopolysacchararidosis VI (MPS VI, Maroteaux-Lamy syndrome). The Y210C mutation has not been described previously in the homozygous state, although this is a common ARSB mutation. His phenotype is essentially musculoskeletal. Urine screening tests based on measuring total GAG may miss this presentation as total GAGs were not elevated in the patient (although the electrophoresis pattern was clearly abnormal). In this phenotype the benefit of ERT remains to be established.

Maroteaux-Lamy syndrome: functional characterization of pathogenic mutations and polymorphisms in the arylsulfatase B gene

Mucopolysaccharidosis VI (MPS VI; Maroteaux-Lamy syndrome) is an autosomal recessive lysosomal disorder caused by deficiency of N-acetylgalactosamine-4-sulfatase (ARSB), which is required for the degradation of dermatan sulfate. We recently reported mutational screening of 12 Spanish and 4 Argentinian MPS VI patients. In the present study, seven missense mutations (c.245T>G [p.L82R], c.413A>G [p.Y138C], c.719C>T [p.S240F], c.922G>A [p.G308R], c.937C>G [p.P313A], c.1340G>T [p.C447F] and c.1415T>C [p.L472P]) were transiently expressed in COS-7 cells and 4-sulfatase activity was measured in cell extracts. All mutations resulted in less than 6% of wild-type enzyme activity, in most cases undetectable. Mutations were expressed in their original haplotype context with respect to two non-synonymous polymorphisms present in the ARSB protein, p.V358M and p.S384N. The three less frequent haplotype combinations yielded an ARSB activity of 16%, 57% and 70%, when compared to the most frequent haplotype (p.358V and p.384S). Western blot analyses showed that the expressed mutations significantly reduced the amount of mature protein. Sub-cellular localization studies of mutant ARSB proteins in fibroblasts of MPS VI patients were performed. RNA analysis confirmed that nonsense-mediated RNA decay had taken place for all mutant alleles (c.1143-1G>C, c.1143-8T>G, p.W322X, c.427delG and c.1142+2T>A) which were candidates for causing RNA degradation by this mechanism. In summary, all the ARSB mutations studied had a significant effect on enzyme activity, protein processing and/or mRNA stability.

Structural and clinical implications of amino acid substitutions in N-acetylgalactosamine-4-sulfatase: insight into mucopolysaccharidosis type VI

To elucidate the basis of mucopolysaccharidosis type VI (MPS VI) from the point of view of enzyme structure, we built structural models of mutant N-acetylgalactosamine-4-sulfatase (4S) resulting from 34 missense mutations (17 severe and 17 attenuated), and analyzed the influence of each amino acid replacement on the structure by calculating the number of atoms affected. Then, we calculated the average of solvent-accessible surface area value of the residues for which a substitution was identified in the severe MPS VI group and compared it with that in the attenuated MPS VI group. In the severe MPS VI group, the number of atoms influenced by a mutation was generally larger than that in the attenuated MPS VI group in both the main chain and the side chain, and residues associated with the mutations found in the severe MPS VI group tended to be less solvent-accessible than those in the attenuated MPS VI group. Furthermore, we analyzed the structural changes in 4S caused by six amino acid substitutions, for which the expressed proteins have been characterized, by means of color imaging. The results revealed that R95Q, G144R, H393P, and C521Y cause large structural changes, and that they are associated with the severe phenotype. On the other hand, G137V and Y210C are thought to cause small structural changes in a limited region resulting in the attenuated phenotype. Structural study is useful for elucidating the basis of MPS VI and predicting the influence of amino acid substitutions on clinical outcome, although there are a couple of exceptional cases.

Molecular markers for the follow-up of enzyme-replacement therapy in mucopolysaccharidosis type VI disease

MPS VI (mucopolysaccharidosis type VI) is a lysosomal storage disease in which deficient activity of the enzyme N-acetylgalactosamine 4-sulfatase [ASB (arylsulfatase B)] impairs the stepwise degradation of the GAG (glycosaminoglycan) dermatan sulfate. Clinical studies of ERT (enzyme replacement therapy) by using rhASB (recombinant human ASB) have been reported with promising results. The release of GAG into the urine is currently used as a biomarker of disease, reflecting in some cases disease severity and in all cases therapeutic responsiveness. Using RNA studies in four Italian patients undergoing ERT, we observed that TNFalpha (tumour necrosis factor alpha) might be a biomarker for MPS VI responsive to therapy. In addition to its role as a potential biomarker, TNFalpha expression could provide insights into the possible pathophysiological mechanisms underlying the mucopolysaccharidoses.

Identification of the molecular defects in Spanish and Argentinian mucopolysaccharidosis VI (Maroteaux-Lamy syndrome) patients, including 9 novel mutations

Maroteaux-Lamy syndrome, or mucopolysaccharidosis VI (MPS VI), is an autosomal recessive lysosomal storage disorder caused by a deficiency of N-acetylgalactosamine-4-sulfatase or arylsulfatase B (ARSB). We aimed to analyze the spectrum of mutations responsible for the disorder in Spanish and Argentinian patients, not previously studied. We identified all the ARSB mutant alleles, nine of them novel, in 12 Spanish and 4 Argentinian patients. The new changes were as follows: six missense mutations: c.245T>G [p.L82R], c.413A>G [p.Y138C], c.719C>T [p.S240F], c.922G>A [p.G308R], c.1340G>T [p.C447F] and c.1415T>C [p.L472P]; one nonsense mutation: c.966G>A [p.W322X]; and two intronic changes involving splice sites: c.1142+2T>A, in the donor splice site of intron 5, which promotes skipping of exon 5, and c.1143-1G>C, which disrupts the acceptor site of intron 5, resulting in skipping of exon 6. We also report 10 previously described mutations as well as several non-pathogenic polymorphisms. Haplotype analysis indicated a common origin for most of the mutations found more than once. Most of the patients were compound heterozygotes, whereas only four of them were homozygous. These observations confirm the broad allelic heterogeneity of the disease, with 19 different mutations in 16 patients. However, the two most frequent mutations, c.1143-1G>C and c.1143-8T>G, present in both populations, accounted for one-third of the mutant alleles in this group of patients.

Mutational analysis of 105 mucopolysaccharidosis type VI patients

Mucopolysaccharidosis type VI (MPS VI; Maroteaux-Lamy syndrome) is a lysosomal storage disorder caused by mutations in the N-acetylgalactosamine-4-sulfatase (arylsulfatase B, ARSB) gene. ARSB is a lysosomal enzyme involved in the degradation of the glycosaminoglycans (GAG) dermatan and chondroitin sulfate. ARSB mutations reduce enzyme function and GAG degradation, causing lysosomal storage and urinary excretion of these partially degraded substrates. Disease onset and rate of progression is variable, producing a spectrum of clinical presentation. In this study, 105 MPS VI patients-representing about 10% of the world MPS VI population-were studied for molecular genetic and biochemical parameters. Direct sequencing of patient genomic DNA was used to identify ARSB mutations. In total, 83 different disease-causing mutations were found, 62 of which were previously unknown. The novel sequence changes included: 38 missense mutations, five nonsense mutations, 11 deletions, one insertion, seven splice-site mutations, and four polymorphisms. ARSB mutant protein and residual activity were determined on fibroblast extracts for each patient. The identification of many novel mutations unique to individuals/their families highlighted the genetic heterogeneity of the disorder and provided an appropriate cohort to study the MPS VI phenotypic spectrum. This mutation analysis has identified a clear correlation between genotype and urinary GAG that can be used to predict clinical outcome.

An index case for the attenuated end of the mucopolysaccharidosis type VI clinical spectrum

Mucopolysaccharidosis type VI (MPS VI, Maroteaux-Lamy syndrome, McKusick #253200) is a lysosomal storage disorder that is caused by a deficiency in the lysosomal exohydrolase N-acetylgalactosamine-4-sulphatase (4-sulphatase, EC 3.1.6.1). We report a patient with no obvious clinical signs of MPS VI that has 5% of normal 4-sulphatase catalytic capacity. This patient represents an index case for the attenuated end of the MPS VI clinical spectrum.

Mucopolysaccharidosis type VI: Identification of novel mutations on the arylsulphatase B gene in South American patients

Mucopolysaccharidosis type VI (Maroteaux-Lamy syndrome, MPS VI) is an autosomal recessive disorder caused by deficiency of N-acetylgalactosamine-4-sulphatase (ARSB),which leads to the lysosomal accumulation and excretion of dermatan sulphate (DS). In this study, 13 unrelated MPS VI patients (12 Brazilian and 1 Chilean) were investigated regarding the identification of the ARSB gene mutations using PCR, SSCP and sequencing. The exons with altered mobility on SSCP were sequenced, as well as all the exons of patients with no SSCP alteration. Seven novel mutations were identified: D59N, L72R, Q88H, P93S, R197X, 1279delA and c.1143-8T > G. The previously reported mutations 1533del23, R315Q and 427delG were found in six, three and two alleles respectively. The other mutations already reported, S384N and G144R, were found in only one allele. In addition, three polymorphisms previously described (V358M, V376M and P397P) were detected in the patients analysed. Our findings are in agreement with the literature confirming the great genetic heterogeneity associated with MPS VI.

Identification of a novel mutation in the ARSB gene that is frequent among Brazilian MPSVI patients

Mucopolysaccharidosis type VI, or Maroteaux-Lamy syndrome, is an autosomal recessive disease caused by the deficiency of arylsulfatase B (ARSB; N-acetyl-galactosamine-4-sulfatase, E.C.3.1.6.12), which is involved in the stepwise degradation of dermatan sulfate and chondroitin sulfate. The deficiency of this enzyme causes storage in the lysozomes and excretion in the urine of partially degraded dermatan sulfate. Twenty patients with MPSVI were analyzed, including 2 siblings. Genomic DNA from patients was extracted and amplified by PCR followed by analysis by single-strand conformation polymorphism (SSCP), which detects altered patterns in the single-stranded DNA. Amongst the patients analyzed for exon 8 of the ARSB gene, 5 patients presented an altered band pattern when compared to controls. After sequencing, we have detected a 23-bp deletion, extending from nucleotides 1,533 to 1,555, causing a frameshift and changing 2 amino acids before creating a premature stop codon at amino acid 514.

Aryplase (Biomarin)

BioMarin is developing Aryplase (BM-102), a recombinant form of the enzyme N-acetylgalactosamine 4-sulfatase, for the potential treatment of mucopolysaccharidosis type VI (Maroteaux-Lamy Syndrome). By November 2003 enrollment for a pivoltal phase III trial was complete.

Prevalence of mucopolysaccharidosis type VI mutations in Siamese cats

Mucopolysaccharidosis type VI (MPS VI), a lysosomal storage disease, is one of the more prevalent inherited diseases in cats and is commonly found in cats with Siamese ancestry. The prevalence of 2 known MPS VI mutations in cats was investigated in 101 clinically normal Siamese cats, in 2 cats with clinical signs of MPS VI, and in 202 cats from 4 research colonies. The mutation L476P which causes a severe clinical phenotype, was present on both alleles in the known MPS VI cats from Italy and North America and was present in all research colonies that originated from North America. However, LA76P was not detected in the Siamese population screened. In contrast, the mutation D520N, which causes a mild clinical phenotype, was identified in 23 of 202 (11.4%) alleles tested in Siamese cats from 3 continents, 2 of which were homozygous for D520N. Thus, the D520N mutation was widespread, and it is likely that cats inheriting both mutations (LA76P/D520N compound heterozygotes) would be in the general Siamese population, particularly in North America. Practitioners should note the high incidence of degenerative joint disease in these animals.

Mucopolysaccharidosis type VI (Maroteaux-Lamy syndrome): a Y210C mutation causes either altered protein handling or altered protein function of N-acetylgalactosamine 4-sulfatase at multiple points in the vacuolar network

The lysosomal hydrolase N-acetylgalactosamine 4-sulfatase (4-sulfatase) is required for the degradation of the glycosaminoglycan substrates dermatan and chondroitin sulfate. A 4-sulfatase deficiency results in the accumulation of undegraded substrate and causes the severe lysosomal storage disorder mucopolysaccharidosis type VI (MPS VI) or Maroteaux-Lamy syndrome. A wide variation in clinical severity is observed between MPS VI patients and reflects the number of different 4-sulfatase mutations that can cause the disorder. The most common 4-sulfatase mutation, Y210C, was detected in approximately 10% of MPS VI patients and has been associated with an attenuated clinical phenotype when compared to the archetypical form of MPS VI. To define the molecular defect caused by this mutation, Y210C 4-sulfatase was expressed in Chinese hamster ovary (CHO-K1) cells for protein and cell biological analysis. Biosynthetic studies revealed that Y210C 4-sulfatase was synthesized at a comparable molecular size and amount to wild-type 4-sulfatase, but there was evidence of delayed processing, traffic, and stability of the mutant protein. Thirty-three percent of the intracellular Y210C 4-sulfatase remained as a precursor form, for at least 8 h post labeling and was not processed to the mature lysosomal form. However, unlike other 4-sulfatase mutations causing MPS VI, a significant amount of Y210C 4-sulfatase escaped the endoplasmic reticulum and was either secreted from the expression cells or underwent delayed intracellular traffic. Sixty-seven percent of the intracellular Y210C 4-sulfatase was processed to the mature form (43, 8, and 7 kDa molecular mass forms) by a proteolytic processing step known to occur in endosomes-lysosomes. Treatment of Y210C CHO-K1 cells with the protein stabilizer glycerol resulted in increased amounts of Y210C 4-sulfatase in endosomes, which was eventually trafficked to the lysosome after a long, 24 h chase time. This demonstrated delayed traffic of Y210C 4-sulfatase to the lysosomal compartment. The endosomal Y210C 4-sulfatase had a low specific activity, suggesting that the mutant protein also had problems with stability. Treatment of Y210C CHO-K1 cells with the protease inhibitor ALLM resulted in an increased amount of mature Y210C 4-sulfatase localized in lysosomes, but this protein had a very low level of activity. This indicated that the mutant protein was being inactivated and degraded at an enhanced rate in the lysosomal compartment. Biochemical analysis of Y210C 4-sulfatase revealed a normal pH optimum for the mutant protein but demonstrated a reduced enzyme activity with time, also consistent with a protein stability problem. This study indicated that multiple subcellular and biochemical processes can contribute to the biogenesis of mutant protein and may in turn influence the clinical phenotype of a patient. In MPS VI patients with a Y210C allele, the composite effect of different stages of intracellular processing/handling and environment has been shown to cause a reduced level of Y210C 4-sulfatase protein and activity, resulting in an attenuated clinical phenotype.

Mucopolysaccharidosis type VI: Report of two Taiwanese patients and identification of one novel mutation

Mucopolysaccharidosis type VI (MPS VI) is an autosomal recessive lysosomal storage disease caused by a deficiency of N-acetylgalactosamine-4-sulphatase (arylsulfatase B, ASB). We report the clinical investigation and mutation analysis of two Taiwanese patients with severe (Case 1) and intermediate (Case 2) phenotypes of MPS VI. Three missense mutations and one polymorphism were identified. Case 1 was found to have a novel heteroallelic C-to-G transversion at nucleotide 1197 causing a phenylalanine to leucine substitution at residue 399 (Phe399Leu), and a heteroallelic Gln239Arg mutation. In Case 2, a heterozygous Cys192Arg mutation and a Val358Met polymorphism were identified. Among these three mutations, the Gln239Arg and Phe399Leu substitutions have so far been observed only in the Taiwanese population. The correlation between genotype and phenotype contributes to molecular pre- and post-natal diagnosis for MPS VI patients.

Mucopolysaccharidosis type VI: Structural and clinical implications of mutations in N-acetylgalactosamine-4-sulfatase

Mucopolysaccharidosis type VI (MPS-VI) is an autosomal recessive lysosomal storage disorder caused by the deficiency of N-acetylgalactosamine-4-sulfatase (4S; or ARSB). Mutations in the 4S gene are responsible for 4S deficiency, which leads to the intralysosomal storage of partially degraded glycosaminoglycans, dermatan sulfate, and chondroitin 4-sulfate. To date, a total of 45 clinically relevant mutations have been identified in the human 4S gene. Missense mutations are the largest group, with 31 identified mutations. Nonsense mutations and small insertions or deletions comprise the remainder, with seven mutations each. Six polymorphisms have also been reported: two amino acid substitutions and four silent transitions. Mapping of the missense mutations onto the 4S structure shows that they are distributed throughout the three subunits of the mature 4S polypeptide. Mutations have been identified in active site residues, in residues adjacent to the active site, in potential substrate binding residues, in residues exposed on the surface, and in residues buried within the protein core. Missense mutations have also been identified in disulfide crosslinks. Molecular modeling of MPS-VI mutations onto the 4S structure suggests that the majority cause 4S deficiency via destabilization and the consequent reduction of 4S protein concentration. The vast majority of MPS-VI mutant alleles are either unique to a patient or are present in a small number of patients. So far, no common mutations have been described. Therefore, screening of the general population for MPS-VI alleles will be difficult.

Two novel mutations of the arylsulfatase B gene in two Italian patients with severe form of mucopolysaccharidosis. Mutations in brief no. 127. Online

Mucopolysaccharidosis type VI (MPS VI) or Maroteaux-Lamy syndrome, is a autosomal recessive disorder, due to the deficiency of the lysosomal enzyme N-acetylgalactosamine-4-sulfatase (arylsufatase B, ASB: EC 3.1.6.12). Three classical forms of the disease have been differentiated: severe, intermediate, mild. Mutational analysis of the ASB gene resulted in the identification of 30 ASB mutant alleles, each of which was found to be unique among unrelated patients, demonstrating a broad molecular heterogeneity of the disease. In this communication we present two novel mutant alleles in two severely affected subjects. Both alterations, the missense mutation G302R and the nonsense Q456X, were found in homozygosity and were confirmed by amplification refractory mutation system (ARMS) or restriction analysis. The missense G302R mutation concerns an amino acid which may be of special importance to the polypeptide, since 302 position is completely conserved in all the eukaryotic sulfatases aligned so far; the nonsense mutation Q456X leads to the translation of a putative mutant ASB protein lacking the last 78 amino acids with a loss of the 8 kD mature polypeptide, one of the two peptides generated by intralysosomal proteolytic processing of the 64kD precursor.

[Identification of mutations in the arylsulfatase B gene in Russian mucopolysaccharidosis type VI patients]

Molecular genetic analysis of the gene for arylsulfatase B (ASB) was conducted in ten Russian patients with type VI mucopolysaccharidosis (MPS VI) of different severity. Eight exons from the translated region of the ASB gene of each patient were amplified and sequenced using the nonradioactive method. Fourteen mutant alleles were identified in the sample studied by means of DNA analysis; 13 of them had not been described before. All patients except for one, who was an offspring of a consanguineous marriage, were genetic compounds with respect to the mutations found. Polymorphic sites A/G 1072 and A/G 1126, which were earlier revealed in exon 5 of the ASB gene, were found in five out of ten patients studied. The spectrum of mutant alleles of the ASB gene was highly specific and agreed with the characteristics of the population genetic load.

Histomorphometric analysis of the tibial growth plate in a feline model of mucopolysaccharidosis type VI

Mucopolysaccharidosis type VI (MPS VI) is a genetically inherited lysosomal storage disorder. Severely affected children exhibit a range of skeletal abnormalities including short stature, facial dysmorphia, and dysostosis multiplex. Naturally occurring and transgenic animal models of MPS VI are also found which exhibit pathology similar to the human disorder. In this paper we have characterized the formation of trabecular bone from growth plate cartilage in a feline model of MPS VI. Tibial trabecular bone was shown to be osteopenic in MPS VI animals with a bone mineral volume (BV/TV) of 4.51% compared with a BV/TV of 15.64% in normal animals. In addition to osteopenia, a rearrangement of trabecular bone architecture was also observed in MPS VI tibiae, with fewer, thinner trabeculae noted; bone formation rate was also decreased. These observations support those previously made in the L5 vertebrae of MPS VI animals. When the sequential formation of growth plate cartilage structural elements, their transition into primary bone spongiosa, and remodeling into secondary bone spongiosa was characterized, no difference between normal and MPS VI could be detected in the number of cartilage septae and their arrangement in the proliferative and hypertrophic regions of the growth plate or trabecular elements in the primary spongiosa. However, a deviation from normal was observed in the resting zone of the growth plate and in the secondary spongiosa of bone. Thus, the osteopenia observed in MPS VI bone appears to arise primarily from a defect in bone production within the metaphysis and diaphysis rather than the creation of an abnormal template in the preceding growth plate cartilage.

Regulation of N-acetylgalactosamine 4-sulfatase expression in retrovirus-transduced feline mucopolysaccharidosis type VI muscle cells

As a preliminary step toward muscle-mediated gene therapy in the mucopolysaccharidosis (MPS) type VI cat, we have analyzed the transcriptional regulation of feline N-acetylgalactosamine 4-sulfatase (f4S) gene expression from various retroviral constructs in primary cultures of muscle cells. Two retroviral constructs were made containing the f4S cDNA under the transcriptional control of the human polypeptide chain-elongation factor 1alpha (EF1alpha) gene promoter or the cytomegalovirus (CMV) immediate-early promoter. Two further retroviral constructs were made with the murine muscle creatine kinase (mck) enhancer sequence upstream of the internal promoter. Virus made from each construct was used to transduce feline MPS VI myoblasts. The mck enhancer significantly upregulated f4S gene expression from both the EF1alpha promoter and the CMV promoter in transduced myoblasts and in differentiated myofibers. The highest level of 4S activity was observed in myoblasts and myofibers transduced with the retroviral construct Lmckcmv4S, in which the f4S gene is under the transcriptional regulation of the mck enhancer and CMV immediate-early promoter. Lmckcmv4S-transduced myofibers demonstrated correction of glycosaminoglycan storage and contained a 58-fold elevated level of 4S activity compared with normal myofibers. Recombinant f4S secreted from Lmckcmv4S-transduced myofibers was endocytosed by feline MPS VI myofibers, leading to correction of the biochemical storage phenotype.

Maroteaux-lamy syndrome: five novel mutations and their structural localization

Maroteaux-Lamy syndrome (mucopolysaccharidosis type VI, MPS VI) is an autosomal recessive disorder due to the deficiency of the lysosomal enzyme N-acetylgalactosamine-4-sulfatase (arylsulfatase B, ASB). Mutation analysis in Maroteaux-Lamy syndrome resulted in the identification of approximately 40 molecular defects underlying a great genetic heterogeneity. Here we report five novel mutations in Italian subjects: S65F, P116H, R315Q, Q503X, P531R; each defect was confirmed by restriction enzyme or amplification refractory mutation system (ARMS) analysis. We also performed a three-dimensional (3-D) structure analysis of the alterations identified by us, and of an additional 22 point mutations reported by other groups, in an attempt to draw helpful information about their possible effects on protein conformation.

Evaluation of fibroblast-mediated gene therapy in a feline model of mucopolysaccharidosis type VI

Fibroblast-mediated ex vivo gene therapy was evaluated in the N-acetylgalactosamine 4-sulfatase (4S) deficient mucopolysaccharidosis type VI (MPS VI) cat. Skin biopsies were obtained at birth from severely affected MPS VI kittens and used to initiate fibroblast outgrowths for retroviral transduction with the 4S cDNA. 4S gene expression in transduced cells was under the transcriptional control of the MoMLV long terminal repeat promoter or the cytomegalovirus (CMV) immediate-early promoter. Characterisation of gene-transduced fibroblasts demonstrated the cells to be over-expressing 4S activity. Twenty-four to forty million autologous, gene-corrected fibroblasts were implanted under the renal capsule of three MPS VI kittens at 8-16 weeks of age. Transient, low levels of 4S activity were detected in peripheral blood leukocytes shortly after implantation but were not detectable within 3-8 weeks' post-implantation. Long-term biochemical and clinical evaluation of these cats demonstrated identical disease progression to that previously described in untreated, clinically severe MPS VI cats.

Immune response to enzyme replacement therapy: clinical signs of hypersensitivity reactions and altered enzyme distribution in a high titre rat model

Immune responses to enzyme replacement therapy (ERT) have been reported and can result in a hypersensitivity/anaphylactic reaction during or immediately after enzyme infusion. We have investigated the infusion of the lysosomal enzyme N-acetylgalactosamine 4-sulphatase (4-sulphatase) into immunized, high titre rats as a model of immune response to ERT. To simulate ERT, high and low titre rats were infused with different doses of radiolabelled recombinant human 4-sulphatase (3H-rh4S). There was evidence of altered targeting, inactivation and degradation of 4-sulphatase in high titre (titre 1024000) compared to low titre (titre 64) rats. There was more 4-sulphatase enzyme activity detected in 5 mg/kg high titre rats when compared to 1 mg/kg high titre rats, suggesting that the antibodies could be saturable in vivo. However, the rats treated with 5 mg/kg 3H-rh4S all had clinical signs of hypersensitivity reactions to 4-sulphatase infusion. There were no apparent signs of adverse reactions in either the high titre 1 mg/kg rats or the low titre rats (1, 5 mg/kg). The high titre 5 mg/kg rats also had changes in 3H-rh4S distribution, with lower levels delivered to the liver and a marked increase in the level remaining in plasma, when compared to either 1 mg/kg high titre rats or low titre rats (1, 5 mg/kg).

Mild feline mucopolysaccharidosis type VI. Identification of an N-acetylgalactosamine-4-sulfatase mutation causing instability and increased specific activity

The missense mutation, L476P, in the N-acetylgalactosamine 4-sulfatase (4S) gene, has previously been shown to be associated with a severe feline mucopolysaccharidosis type VI (MPS VI) phenotype. The present study describes a second mutation, D520N, in the same MPS VI cat colony, which is inherited independently of L476P and is associated with a clinically mild MPS VI phenotype in D520N/L476P compound heterozygous cats. Biochemical and clinical assessment of L476P homozygous, D520N/L476P compound heterozygous, and D520N homozygous cats demonstrated that the entire range of clinical phenotypes, from severe MPS VI, to mild MPS VI, to normal are clustered within a narrow range of residual 4S activity from 0. 5% to 4.6% of normal levels. When overexpressed in CHO-KI cells, the secreted form of D520N 4S was inactivated in neutral pH conditions. In addition, intracellular D520N 4S protein was rapidly degraded and corresponded to 37%, 14.5%, and 0.67% of normal 4S protein levels in the microsomal, endosomal, and lysosomal compartments, respectively. However, the specific activity of lysosomal D520N 4S was elevated 22. 5-fold when compared with wild-type 4S. These results suggest that the D520N mutation causes a rapid degradation of 4S protein. The effect of this is partially ameliorated as a result of a significant elevation in the specific activity of mutant D520N 4S reaching the lysosomal compartment.

Two mutations within a feline mucopolysaccharidosis type VI colony cause three different clinical phenotypes

Mucopolysaccharidosis type VI (MPS VI) is a lysosomal storage disease caused by a deficiency of N-acetylgalactosamine-4-sulfatase (4S). A feline MPS VI model used to demonstrate efficacy of enzyme replacement therapy is due to the homozygous presence of an L476P mutation in 4-sulfatase. An additional mutation, D520N, inherited independently from L476P and recently identified in the same family of cats, has resulted in three clinical phenotypes. L476P homozygotes exhibit dwarfism and facial dysmorphia due to epiphyseal dysplasia, abnormally low leukocyte 4S/betahexosaminidase ratios, dermatan sulfaturia, lysosomal inclusions in most tissues including chondrocytes, corneal clouding, degenerative joint disease, and abnormal leukocyte inclusions. Similarly, D520N/D520N and L476P/D520N cats have abnormally low leukocyte 4S/betahexosaminidase ratios, mild dermatan sulfaturia, lysosomal inclusions in some chondrocytes, and abnormal leukocyte inclusions. However, both have normal growth and appearance. In addition, L476P/D520N cats have a high incidence of degenerative joint disease. We conclude that L476P/D520N cats have a very mild MPS VI phenotype not previously described in MPS VI humans. The study of L476P/D520N and D520N/ D520N genotypes will improve understanding of genotype to phenotype correlations and the pathogenesis of skeletal dysplasia and joint disease in MPS VI, and will assist in development of therapies to prevent lysosomal storage in chondrocytes.

Feline mucopolysaccharidosis type VI: correction of glycosaminoglycan storage in myoblasts by retrovirus-mediated transfer of the feline N-acetylgalactosamine 4-sulfatase gene

Mucopolysaccharidosis type VI (MPS VI) is an autosomal recessive lysosomal storage disorder characterised by the deficiency of N-acetylgalactosamine 4-sulfatase (4S). MPS VI has also been described in the cat. As an initial step toward muscle-mediated gene therapy in the MPS VI cat, we have made two retroviral constructs (pLf4S and pLf4SSN) that transduce the feline 4S gene. Both constructs were designed to express the feline 4S sequence from the viral long terminal repeat promoter. In addition pLf4SSN expressed the neomycin resistance gene from the SV40 early promoter. Amphotrophic virus was produced for each construct and used to transduce feline MPS VI myoblasts. Lf4S- and Lf4SSN-transduced MPS VI feline myoblasts demonstrated correction of glycosaminoglycan storage and contained 55-fold and 3.5-fold elevated levels of 4S activity when compared with normal feline myoblasts respectively. Recombinant feline 4S (rf4S) secreted by Lf4S-transduced MPS VI myoblasts was shown to be endocytosed by MPS VI feline cells via the mannose-6-phosphate receptor system, leading to metabolic correction. The results from this study demonstrate that muscle-mediated gene replacement therapy may be a viable method for achieving circulating levels of recombinant f4S (rf4S) in the MPS VI cat.

Structure of a human lysosomal sulfatase

BACKGROUND

. Sulfatases catalyze the hydrolysis of sulfuric acid esters from a wide variety of substrates including glycosaminoglycans, glycolipids and steroids. There is sufficient common sequence similarity within the class of sulfatase enzymes to indicate that they have a common structure. Deficiencies of specific lysosomal sulfatases that are involved in the degradation of glycosamino-glycans lead to rare inherited clinical disorders termed mucopolysaccharidoses. In sufferers of multiple sulfatase deficiency, all sulfatases are inactive because an essential post-translational modification of a specific active-site cysteine residue to oxo-alanine does not occur. Studies of this disorder have contributed to location and characterization of the sulfatase active site. To understand the catalytic mechanism of sulfatases, and ultimately the determinants of their substrate specificities, we have determined the structure of N-acetylgalactosamine-4-sulfatase.

RESULTS

. The crystal structure of the enzyme has been solved and refined at 2.5 resolution using data recorded at both 123K and 273K. The structure has two domains, the larger of which belongs to the alpha/beta class of proteins and contains the active site. The enzyme active site in the crystals contains several hitherto undescribed features. The active-site cysteine residue, Cys91, is found as the sulfate derivative of the aldehyde species, oxo-alanine. The sulfate is bound to a previously undetected metal ion, which we have identified as calcium. The structure of a vanadate-inhibited form of the enzyme has also been solved, and this structure shows that vanadate has replaced sulfate in the active site and that the vanadate is covalently linked to the protein. Preliminary data is presented for crystals soaked in the monosaccharide N-acetylgalactosamine, the structure of which forms a product complex of the enzyme.

CONCLUSIONS

. The structure of N-acetylgalactosamine-4-sulfatase reveals that residues conserved amongst the sulfatase family are involved in stabilizing the calcium ion and the sulfate ester in the active site. This suggests an archetypal fold for the family of sulfatases. A catalytic role is proposed for the post-translationally modified highly conserved cysteine residue. Despite a lack of any previously detectable sequence similarity to any protein of known structure, the large sulfatase domain that contains the active site closely resembles that of alkaline phosphatase: the calcium ion in sulfatase superposes on one of the zinc ions in alkaline phosphatase and the sulfate ester of Cys91 superposes on the phosphate ion found in the active site of alkaline phosphatase.

Feline mucopolysaccharidosis type VI. Characterization of recombinant N-acetylgalactosamine 4-sulfatase and identification of a mutation causing the disease

Mucopolysaccharidosis type VI (MPS VI) is an autosomal recessive disease caused by a deficiency of N-acetylgalactosamine 4-sulfatase (4S) leading to the lysosomal accumulation and urinary excretion of dermatan sulfate. MPS VI has also been described in the Siamese cat. As an initial step toward enzyme replacement therapy with recombinant feline 4S (rf4S) in MPS VI cats, the feline 4S cDNA was isolated and expressed in CHO-KI cells and rf4S was immunopurified from the culture medium. SDS-polyacrylamide gel electrophoresis analysis showed that the precursor form of immunopurified rf4S was a 66-kDa polypeptide that underwent maturation to a 43-44-kDa polypeptide. Endocytosis of rf4S by cultured feline MPS VI myoblasts was predominantly mediated by a mannose 6-phosphate receptor and resulted in the correction of dermatan sulfate storage. The mutation causing feline MPS VI was identified as a base substitution at codon 476, altering a leucine codon to a proline (L476P). The L476P allele displayed no detectable 4S activity when expressed in CHO-KI cells and was observed only as a "precursor" polypeptide that was not secreted into the medium. Identification of the mutation has allowed the development of a rapid PCR-based screening method to genotype individuals within the cat colony.

Targeted disruption of the arylsulfatase B gene results in mice resembling the phenotype of mucopolysaccharidosis VI

Mucopolysaccharidosis VI (MPS VI) is a lysosomal storage disease with autosomal recessive inheritance caused by a deficiency of the enzyme arylsulfatase B (ASB), which is involved in degradation of dermatan sulfate and chondroitin 4-sulfate. A MPS VI mouse model was generated by targeted disruption of the ASB gene. Homozygous mutant animals exhibit ASB enzyme deficiency and elevated urinary secretion of dermatan sulfate. They develop progressive symptoms resembling those of MPS VI in humans. Around 4 weeks of age facial dysmorphia becomes overt, long bones are shortened, and pelvic and costal abnormalities are observed. Major alterations in bone formation with perturbed cartilaginous tissues in newborns and widened, perturbed, and persisting growth plates in adult animals are seen. All major parenchymal organs show storage of glycosaminoglycans preferentially in interstitial cells and macrophages. Affected mice are fertile and mortality is not elevated up to 15 months of age. This mouse model will be a valuable tool for studying pathogenesis of MPS VI and may help to evaluate therapeutical approaches for lysosomal storage diseases.

Identification, expression, and biochemical characterization of N-acetylgalactosamine-4-sulfatase mutations and relationship with clinical phenotype in MPS-VI patients

Maroteaux-Lamy syndrome, or mucopolysaccharidosis type VI (MPS-VI), is a lysosomal storage disorder characterized by the defective degradation of dermatan sulfate due to the deficiency of N-acetylgalactosamine-4-sulfatase (4S). The clinical severity of MPS-VI ranges in a continuum from mildly affected to severely affected patients. Mutations in MPS-VI patient samples were identified by chemical cleavage and direct DNA sequencing of PCR products derived from patient cDNA. Five amino acid substitutions were identified (T92M, R95Q, Y210C, H393P, and L498P), individually introduced into the wild-type 4S cDNA by site-directed in vitro mutagenesis, and transfected into Chinese hamster ovary cells. Three of the five mutations (R95Q, Y210C, and H393P) were observed in >1 of 25 unrelated MPS-VI patients; however, the mutations were not found in 20 control individuals. The residual 4S activity and protein (biochemical phenotype) were determined for each mutant in order to confirm their identity as mutations and to dissect the contribution of each mutant allele to the overall clinical phenotype of the patient. For each patient, the combined biochemical phenotypes of the two 4S mutant alleles demonstrated a good correspondence with the observed clinical phenotype (with the possible exception of a patient who was a compound heterozygote for T92M and L498P). This preliminary correspondence between genotype and the phenotype in MPS-VI may, with further refinement, contribute to the assessment of therapeutic approaches for MPS-VI patients.

[A novel nonsense point mutation in the arylsulfatase B gene with a severe type Maroteaux-Lamy syndrome]

Maroteaux-Lamy syndrome (MLS, also known as Mucopolysaccharidosis VI) is an inherited lysosomal disease due to a deficiency of the enzyme arylsulfatase B (ASB). Clinically, severe, intermediate and mild types are classified according to the symptoms and the age of onset. In recent years, several cases have been reported in which various mutations have been found by sequence analysis of ASB cDNA or genomic DNA. All of these mutations were reported occurred in single patients. Here I report a severe type MLS patient. A new point mutation was found on ASB gene which resulted in a stop codon at ASB peptide 421 (Glu). Due to this point mutation, a peptide fragment composed of 112 amino acids should have been deleted out. This point mutation was confirmed as a homoallele by direct sequence analysis of genomic DNA. Expression experiment on this point mutation revealed that the mutant produced neither mature ASB protein nor enzyme activity.

N-acetylgalactosamine-4-sulfatase: identification of four new mutations within the conserved sulfatase region causing mucopolysaccharidosis type VI

Mucopolysaccharidosis type VI (MPS VI; Maroteaux-Lamy syndrome) is the lysosomal storage disorder resulting from the deficient activity of N-acetylgalactosamine-4-sulfatase (arylsulfatase B; ASB). MPS VI has been described in man, cats and rats, and several mutations in the ASB gene have been identified in human patients and the animal models. Notably, ASB belongs to a family of sulfatases which are highly conserved, suggesting that they are related evolutionarily and functionally. In this manuscript, four new mutations causing MPS VI are described within the human ASB gene. Each of these mutations occurred in or near the hexapeptide 144GKWHLG149, one of the most highly conserved 'sulfatase' regions. In fact, three of the mutations occurred within the same codon, W146. Thus, these results provide new insights into the molecular lesions causing MPS VI and highlight the importance of this conserved sulfatase region.

The gene for pycnodysostosis maps to human chromosome 1cen-q21

Pycnodysostosis (OMIM 265800) is an autosomal recessive skeletal disorder first described by Maroteaux and Lamy that is characterized by short stature, increased bone density, delayed closure of cranial sutures, loss of the mandibular angle, dysplastic clavicles, dissolution of the terminal phalanges of the hands and feet, dental abnormalities and increased bone fragility. Patients have a typical appearance secondary to prominence of the calvarium, smallness of the facial features, prominent nose and micrognathia. The French painter, Henri de Toulouse Lautrec (1864-1901), is believed to have had the disorder. Although more than 100 cases have been reported, we are aware of only two large consanguinous pedigrees in which the pycnodysostosis disorder segregates. We have studied the segregation of the pycnodysostosis phenotype in a large consanguinous Mexican pedigree, the clinical features of which are very similar to those described in the Arab pedigree studied by Edelson et al. Here, we report linkage for the pycnodysostosis phenotype in the 1cen-q21 region of human chromosome 1, and discuss candidate genes for this skeletal disorder.

Juvenile form of mucopolysaccharidosis VI (Maroteaux-Lamy syndrome). A C-terminal extension causes instability but increases catalytic efficiency of arylsulfatase B

A deficiency of the enzyme arylsulfatase B results in the lysosomal storage disorder Maroteaux-Lamy syndrome or mucopolysaccharidosis type VI. Severe, intermediate and mild forms of this autosomal recessively inherited disease can be clinically differentiated. To determine the molecular defect in a patient with the intermediate form of the disorder, DNA fragments generated from the patient's mRNA by reverse transcription and subsequent amplification by the polymerase chain reaction were subcloned and sequenced. The mRNA transcribed from one allele contains a 244-base pair deletion causing a frameshift and a truncation of the open reading frame. The C-terminal third of the encoded mutant polypeptide has a nonsense sequence. This mutation is due to a deletion of exon 5 in this allele. A silent A to G transition at nucleotide 1191 was present in the same allele, and the second allele was characterized by a T to C transition at nucleotide 1600 causing a mutation of the translational stop codon to a glutamine codon (*534Q) and extending the encoded polypeptide by 50 amino acids. Stable expression of the *534Q allele in LTK- cells resulted in a mutant precursor 4 kDa larger than the wild-type precursor. The majority of the mutant precursor appears to be degraded before reaching the trans Golgi. This is consistent with an altered polypeptide structure, where a number of missing or masked epitopes were observed in an enzyme immunobinding assay using a panel of monoclonal antibodies. Immunoquantification analysis showed that epitopes were most likely masked, as missing epitopes could be reformed by binding the mutant protein to a polyclonal antibody of arylsulfatase B. It is suggested that the additional amino acids at the C terminus of the arylsulfatase B polypeptide induce a protein conformational change. *534Q mutant polypeptide escaping degradation is sorted to dense lysosomes. The mutant polypeptide has an approximately 9-fold higher catalytic efficiency than wild-type arylsulfatase B.