Comprehensive Preventive and Therapeutic Oral Health Care: A Case Report of Mucopolysaccharidosis Type IV A in a Pediatric Patient

Mucopolysaccharidosis (MPS) is a metabolic disorder resulting from a deficiency of lysosomal enzymes. It is an autosomal recessive disorder with similar incidences in men and women. Mucopolysaccharidosis type IV A is caused by a deficiency of N-acetylgalactosamine-6-sulfatase, which deficiency is, in turn, caused by alterations in the GALNS gene. It is marked by a short stature, a pigeon chest, frontal bossing, kyphosis, and a flat nasal bridge. Intraorally, macroglossia, hypodontia, dentinogenesis imperfecta, a broad mouth, and an anterior open bite are some of the common features. The present paper reports on a case of MPS in a 5-year-old male patient, along with providing a review of the literature and insight into the oral manifestations related to MPS IV A, also called Morquio A syndrome, and its dental treatment. It aims to highlight the clinical recommendations for oral health care in such cases during different phases of MPS IV A treatment.

Mucopolysaccharidosis IVA: Current Disease Models and Drawbacks

Mucopolysaccharidosis IVA (MPS IVA) is a rare disorder caused by mutations in the N-acetylgalactosamine-6-sulfate-sulfatase (GALNS) encoding gene. GALNS leads to the lysosomal degradation of the glycosaminoglyccreasans keratan sulfate and chondroitin 6-sulfate. Impaired GALNS enzymes result in skeletal and non-skeletal complications in patients. For years, the MPS IVA pathogenesis and the assessment of promising drugs have been evaluated using in vitro (primarily fibroblasts) and in vivo (mainly mouse) models. Even though value information has been raised from those studies, these models have several limitations. For instance, chondrocytes have been well recognized as primary cells affected in MPS IVA and responsible for displaying bone development impairment in MPS IVA patients; nonetheless, only a few investigations have used those cells to evaluate basic and applied concepts. Likewise, current animal models are extensively represented by mice lacking GALNS expression; however, it is well known that MPS IVA mice do not recapitulate the skeletal dysplasia observed in humans, making some comparisons difficult. This manuscript reviews the current in vitro and in vivo MPS IVA models and their drawbacks.

Enhanced Efficiency of the Basal and Induced Apoptosis Process in Mucopolysaccharidosis IVA and IVB Human Fibroblasts

Morquio disease, also called mucopolysaccharidosis IV (MPS IV), belongs to the group of lysosomal storage diseases (LSD). Due to deficiencies in the activities of galactose-6-sulfate sulfatase (in type A) or β-galactosidase (in type B), arising from mutations in GALNS or GLB1, respectively, keratan sulfate (one of glycosaminoglycans, GAGs) cannot be degraded efficiently and accumulates in lysosomes. This primary defect leads to many cellular dysfunctions which then cause specific disease symptoms. Recent works have indicated that different secondary effects of GAG accumulation might significantly contribute to the pathomechanisms of MPS. Apoptosis is among the cellular processes that were discovered to be affected in MPS cells on the basis of transcriptomic studies and some cell biology experiments. However, Morquio disease is the MPS type which is the least studied in light of apoptosis dysregulation, while RNA-seq analyses suggested considerable changes in the expression of genes involved in apoptosis in MPS IVA and IVB fibroblasts. Here we demonstrate that cytochrome c release from mitochondria is more efficient in MPS IVA and IVB fibroblasts relative to control cells, both under the standard cultivation conditions and after treatment with staurosporine, an apoptosis inducer. This indication of apoptosis stimulation was corroborated by measurements of the levels of caspases 9, 3, 6, and 7, as well as PARP, cleaved at specific sites, in Morquio disease and control fibroblasts. The more detailed analyses of the transcriptomic data revealed which genes related to apoptosis are down- and up-regulated in MPS IVA and IVB fibroblasts. We conclude that apoptosis is stimulated in Morquio disease under both standard cell culture conditions and after induction with staurosporine which may contribute to the pathomechanism of this disorder. Dysregulation of apoptosis in other MPS types is discussed.

Inflammatory process and oxidative/nitrative stress: in vivo study in mucopolysaccharidosis type IV A patients under long-term enzyme replacement therapy

Mucopolysaccharidosis type IV A (MPS IVA) is an inborn error of the metabolism (IEM) caused by a deficiency of the enzyme N-acetylgalactosamine 6-sulfate sulfatase (GALNS). Since 2014, enzyme replacement therapy (ERT) is the recommended treatment for these patients. It is known that the inflammatory response is closely related to antioxidant defenses and oxidative stress, and literature shows involvement of oxidative stress in the pathogenesis of IEM. The aim of this study is to investigate the mechanisms of oxidative/nitrative stress and inflammation in patients with MPS IVA under long-term ERT. In the present work we investigate parameters of oxidative/nitrative stress in plasma and urine of MPS IVA patients under long-term ERT and controls, such as plasmatic nitrate/nitrite levels using the LDH Method, urinary di-tyrosine levels by fluorometric method, plasmatic content of sulfhydryl groups, urinary oxidized guanine species by ELISA kit and the plasmatic total antioxidant status. We next evaluated the plasmatic pro and anti-inflammatory cytokines concentration (IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, TNF-α) and the expression of factors and enzymes Nrf-2, NF-κβ and HO-1, main mediators between inflammation and oxidative stress. In concern to the oxidative/nitrative stress parameters, there was no significant difference between the groups MPS IVA patients under long-term ERT and controls, showing that there is no overproducing of RNS, no protein damage, no DNA/RNA oxidative damage and no modification in the non-enzymatic antioxidant capacity of a tissue to prevent the damage associated to free radical processes in these patients. It was also verified no significant difference between the MPS IVA patients under long-term ERT and controls groups regarding the production of proinflammatory cytokines. About anti-inflammatory cytokines, IL 10 was shown to be elevated in MPS IVA patients under long-term ERT in comparison to the control group. We next evaluated the genic expression of Nrf-2, NF-κβ and HO-1and there was no significant difference between the MPS IVA patients under long-term ERT and control groups. In conclusion, MPS IVA patients under long term ERT are not in an inflammatory state and there is no alteration in genic expression in the genes analyzed which are involved in oxidative stress and inflammatory pathways. It is,however, important to consider that absence of imbalance of antioxidant defenses in MPS IVA patients under long term ERT is so far preliminary it is supported by methodologies that are not highly sensitive nor very accurate. Further experiments in future using state-of-the-art methodologies will corroborate these findings. Nevertheless, our results demonstrated the protective effect of the treatment in relation to the parameters studied and the importance of starting treatment in the early stages of the disease.

Sex Difference Leads to Differential Gene Expression Patterns and Therapeutic Efficacy in Mucopolysaccharidosis IVA Murine Model Receiving AAV8 Gene Therapy

Adeno-associated virus (AAV) vector-based therapies can effectively correct some disease pathology in murine models with mucopolysaccharidoses. However, immunogenicity can limit therapeutic effect as immune responses target capsid proteins, transduced cells, and gene therapy products, ultimately resulting in loss of enzyme activity. Inherent differences in male versus female immune response can significantly impact AAV gene transfer. We aim to investigate sex differences in the immune response to AAV gene therapies in mice with mucopolysaccharidosis IVA (MPS IVA). MPS IVA mice, treated with different AAV vectors expressing human N-acetylgalactosamine 6-sulfate sulfatase (GALNS), demonstrated a more robust antibody response in female mice resulting in subsequent decreased GALNS enzyme activity and less therapeutic efficacy in tissue pathology relative to male mice. Under thyroxine-binding globulin promoter, neutralizing antibody titers in female mice were approximately 4.6-fold higher than in male mice, with GALNS enzyme activity levels approximately 6.8-fold lower. Overall, male mice treated with AAV-based gene therapy showed pathological improvement in the femur and tibial growth plates, ligaments, and articular cartilage as determined by contrasting differences in pathology scores compared to females. Cardiac histology revealed a failure to normalize vacuolation in females, in contrast, to complete correction in male mice. These findings promote the need for further determination of sex-based differences in response to AAV-mediated gene therapy related to developing treatments for MPS IVA.

Exome Sequencing Identifies a Biallelic GALNS Variant (p.Asp233Asn) Causing Mucopolysaccharidosis Type IVA in a Pakistani Consanguineous Family

Mucopolysaccharidoses (MPS) type IVA is a lysosomal storage disease that mainly affects the skeletal system and is caused by a deficiency of the enzyme N-acetylgalactosamine-6-sulfatase (GALNS). The condition can mistakenly be diagnosed as a primary skeletal dysplasia such as spondylo-epiphyseal dysplasia, which shares many similar phenotypic features. Here, we utilised whole exome sequencing to make the diagnosis of MPS IVA in a resource poor country. We report for the first time the identification of a biallelic GALNS missense variant (c.697G>A, p.Asp233Asn) in the Pakistani population and highlight the potential contribution that academic institutions can make in rare disease diagnosis in the absence of a developed clinical genetic service.

Investigation of GALNS variants and genotype-phenotype correlations in a large cohort of patients with mucopolysaccharidosis type IVA

Mucopolysaccharidosis type IVA (MPS IVA) is a rare autosomal recessive disorder resulting from the deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS) caused by pathogenic variants in the GALNS gene. A systematic analysis for genotype-phenotype correlation is essential due to hundreds of variants generating different levels of residual GALNS activity and causing a wide degree of clinical manifestation effects. Here, we retrospectively analyzed clinical and genetic data of 108 unrelated patients with MPS IVA to investigate the variants spectrum of GALNS and assess their clinical effects. In this cohort, 82 patients were classified as severe, 14 as intermediate, and 12 as mild. One hundred and one GALNS variants were identified, of which 47 were novel. Most patients with at least one GALNS null variant were classified as severe phenotype (92%, 33/36). Missense variants mapped to different residues of GALNS protein resulted in different phenotypes in patients with MPS IVA. Ninety-two percent of patients with two missense variants mapped to buried residues were classified as severe (92%, 24/26), while at least one missense variant mapped to surface residues was identified in patients with biallelic missense variants presenting intermediate MPS IVA (78%, 7/9) and presenting mild MPS IVA (86%, 6/7). Our study contributes to a better understanding of the molecular spectrum of GALNS variants and their clinical implications. Based on the data herein reported, we generated a systematic flowchart correlating the GALNS variants to assist in phenotype prediction and classification of patients with MPS IVA.

Treatment of skeletal and non-skeletal alterations of Mucopolysaccharidosis type IVA by AAV-mediated gene therapy

Mucopolysaccharidosis type IVA (MPSIVA) or Morquio A disease, a lysosomal storage disorder, is caused by N-acetylgalactosamine-6-sulfate sulfatase (GALNS) deficiency, resulting in keratan sulfate (KS) and chondroitin-6-sulfate accumulation. Patients develop severe skeletal dysplasia, early cartilage deterioration and life-threatening heart and tracheal complications. There is no cure and enzyme replacement therapy cannot correct skeletal abnormalities. Here, using CRISPR/Cas9 technology, we generate the first MPSIVA rat model recapitulating all skeletal and non-skeletal alterations experienced by patients. Treatment of MPSIVA rats with adeno-associated viral vector serotype 9 encoding Galns (AAV9-Galns) results in widespread transduction of bones, cartilage and peripheral tissues. This led to long-term (1 year) increase of GALNS activity and whole-body correction of KS levels, thus preventing body size reduction and severe alterations of bones, teeth, joints, trachea and heart. This study demonstrates the potential of AAV9-Galns gene therapy to correct the disabling MPSIVA pathology, providing strong rationale for future clinical translation to MPSIVA patients.

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.

Clinical, biochemical and genetic profiles of patients with mucopolysaccharidosis type IVA (Morquio A syndrome) in Malaysia: the first national natural history cohort study

BACKGROUND

Mucopolysaccharidosis IVA (MPS IVA) is an autosomal recessive lysosomal storage disease due to N-acetylgalactosamine-6-sulfatase (GALNS) deficiency. It results in accumulation of the glycosaminoglycans, keratan sulfate and chondroitin-6-sulfate, leading to skeletal and other systemic impairments. Data on MPS IVA in Asian populations are scarce.

METHODS

This is a multicentre descriptive case series of 21 patients comprising all MPS IVA patients in Malaysia. Mutational analysis was performed by PCR and Sanger sequencing of the GALNS gene in 17 patients.

RESULTS

The patients (15 females and 6 males) had a mean age (± SD) of 15.5 (± 8.1) years. Mean age at symptom onset was 2.6 (± 2.1) years and at confirmed diagnosis was 6.9 (± 4.5) years. The study cohort included patients from all the main ethnic groups in Malaysia - 57% Malay, 29% Chinese and 14% Indian. Common presenting symptoms included pectus carinatum (57%) and genu valgum (43%). Eight patients (38%) had undergone surgery, most commonly knee surgeries (29%) and cervical spine decompression (24%). Patients had limited endurance with lower mean walking distances with increasing age. GALNS gene analysis identified 18 distinct mutations comprising 13 missense, three nonsense, one small deletion and one splice site mutation. Of these, eight were novel mutations (Tyr133Ser, Glu158Valfs*12, Gly168*, Gly168Val, Trp184*, Leu271Pro, Glu320Lys, Leu508Pro). Mutations in exons 1, 5 and 9 accounted for 51% of the mutant alleles identified.

CONCLUSIONS

All the MPS IVA patients in this study had clinical impairments. A better understanding of the natural history and the clinical and genetic spectrum of MPS IVA in this population may assist early diagnosis, improve management and permit timely genetic counselling and prenatal diagnosis.

Recommendations for the management of MPS IVA: systematic evidence- and consensus-based guidance

INTRODUCTION

Mucopolysaccharidosis (MPS) IVA or Morquio A syndrome is an autosomal recessive lysosomal storage disorder (LSD) caused by deficiency of the N-acetylgalactosamine-6-sulfatase (GALNS) enzyme, which impairs lysosomal degradation of keratan sulphate and chondroitin-6-sulphate. The multiple clinical manifestations of MPS IVA present numerous challenges for management and necessitate the need for individualised treatment. Although treatment guidelines are available, the methodology used to develop this guidance has come under increased scrutiny. This programme was conducted to provide evidence-based, expert-agreed recommendations to optimise management of MPS IVA.

METHODS

Twenty six international healthcare professionals across multiple disciplines, with expertise in managing MPS IVA, and three patient advocates formed the Steering Committee (SC) and contributed to the development of this guidance. Representatives from six Patient Advocacy Groups (PAGs) were interviewed to gain insights on patient perspectives. A modified-Delphi methodology was used to demonstrate consensus among a wider group of healthcare professionals with experience managing patients with MPS IVA and the manuscript was evaluated against the validated Appraisal of Guidelines for Research and Evaluation (AGREE II) instrument by three independent reviewers.

RESULTS

A total of 87 guidance statements were developed covering five domains: (1) general management principles; (2) recommended routine monitoring and assessments; (3) disease-modifying interventions (enzyme replacement therapy [ERT] and haematopoietic stem cell transplantation [HSCT]); (4) interventions to support respiratory and sleep disorders; (5) anaesthetics and surgical interventions (including spinal, limb, ophthalmic, cardio-thoracic and ear-nose-throat [ENT] surgeries). Consensus was reached on all statements after two rounds of voting. The overall guideline AGREE II assessment score obtained for the development of the guidance was 5.3/7 (where 1 represents the lowest quality and 7 represents the highest quality of guidance).

CONCLUSION

This manuscript provides evidence- and consensus-based recommendations for the management of patients with MPS IVA and is for use by healthcare professionals that manage the holistic care of patients with the intention to improve clinical- and patient-reported outcomes and enhance patient quality of life. It is recognised that the guidance provided represents a point in time and further research is required to address current knowledge and evidence gaps.

Mutation analysis and pathogenicity identification of Mucopolysaccharidosis type IVA in 8 south China families

BACKGROUND

Mucopolysaccharidosis type IVA (MPS IVA) is a rare autosomal recessive lysosomal storage disorder caused by GALNS gene mutation. The aim of our study is to detect pathogenic variants for patients suspected of MPS IVA and set the base for subsequent prenatal diagnosis and preimplantation genetic diagnosis.

METHODS

In our study, 9 MPS IVA patients from south China families were investigated. Urine glycosaminoglycans (GAG_S) screening was used as an initial method. For patients with abnormal result, all 14 exons and intron-exon junctions of the GALNS gene were sequenced after amplification from genomic DNA. The pathogenicity of novel mutations were analyzed with molecular genetics, bioinformatics and structure modeling in light of clinical manifestations and biochemical results.

RESULTS

Among 12 mutations detected, direct sequencing found 3 novel mutations (c.686A>C, p.Y229S; c.1498G>T, p.G500C; c.278T>C, p.I93T). The pathogenicity of these novel mutations was illustrated by correlating clinical symptoms with pedigree analysis and bioinformatics analysis.

CONCLUSION

The detection and variant analysis are essential for accurate diagnosis of MPS IVA patients. Our results enrich GALNS gene mutation spectrum of Chinese population. This information has important clinical value for molecular diagnosis and genetic counseling of patients with this disease.

Analysis of endocrine hormone metabolism level in a Chinese patient with mucopolysaccharidosis IVA: A case report

RATIONALE

Mucopolysaccharidosis IVA (Morquio A) is a catabolic mucopolysaccharide disorder caused by galactose-6-sulfate sulfatase deficiency. It is an autosomal recessive inherited disease. Previous reports on clinical characteristics of Morquio A mainly focused on growth retardation, skeletal deformities, and organ damage in children and adolescents, while the effects of mucopolysaccharide metabolism disorders on endocrine hormone metabolism level have not been reported. Herein, we reported the endocrine hormone metabolism in a case diagnosed as Morquio A.

PATIENT CONCERNS

The patient was a 17-year-old girl with growth retardation, hearing loss, and severe skeletal dysplasia(scoliosis and chicken breast), and was evaluated to have normal nervous system function and intelligence by physicians.

DIAGNOSES

She was diagnosed as Morquio A based on gene analysis, mucopolysaccharide-related enzymes and her clinical features.

INTERVENTIONS

The patient didn't accepted the enzyme replacement therapy.

OUTCOMES

She had a homozygous mutation of the GALNS gene. The b-glucuronidase content in the blood was reduced. The serum sodium, serum adrenocorticotropic hormone, and cortisol rhythms (8 AM) were decreased. The levels of PRA(plasma renin activity) , PAII(plasma angiotensin II), and PALD(plasma aldosterone) were elevated. Bone mineral density suggests osteoporosis. There were no abnormalities in bone metabolism indicators, growth hormone, thyroid hormone, and sex hormones. In summary, the level of endocrine hormones in patients with mucopolysaccharidosis IV changes.

LESSONS

This is the report on endocrine hormone level in a patient with mucopolysaccharidosis IV in China. Due to the disease may have relatively incomplete adrenal function, which provides a basis for future understanding and diagnosis of this disease.

Molecular genetics and metabolism, special edition: Diagnosis, diagnosis and prognosis of Mucopolysaccharidosis IVA

Mucopolysaccharidosis IVA (MPS IVA, Morquio A syndrome) is an autosomal recessive disorder caused by the deficiency of N-acetylgalactosamine-6-sulfate sulfatase. Deficiency of this enzyme leads to the accumulation of specific glycosaminoglycans (GAGs), chondroitin-6-sulfate (C6S) and keratan sulfate (KS), which are mainly synthesized in the cartilage. Therefore, the substrates are stored primarily in the cartilage and its extracellular matrix (ECM), leading to a direct impact on bone development and successive systemic skeletal spondylepiphyseal dysplasia. The skeletal-related symptoms for MPS IVA include short stature with short neck and trunk, odontoid hypoplasia, spinal cord compression, tracheal obstruction, obstructive airway, pectus carinatum, restrictive lung, kyphoscoliosis, platyspondyly, coxa valga, genu valgum, waddling gait, and laxity of joints. The degree of imbalance of growth in bone and other organs and tissues largely contributes to unique skeletal dysplasia and clinical severity. Diagnosis of MPS IVA needs clinical, radiographic, and laboratory testing to make a complete conclusion. To diagnose MPS IVA, total urinary GAG analysis which has been used is problematic since the values overlap with those in age-matched controls. Currently, urinary and blood KS and C6S, the enzyme activity of GALNS, and GALNS molecular analysis are used for diagnosis and prognosis of clinical phenotype in MPS IVA. MPS IVA can be diagnosed with unique characters although this disorder relates closely to other disorders in some characteristics. In this review article, we comprehensively describe clinical, radiographic, biochemical, and molecular diagnosis and clinical assessment tests for MPS IVA. We also compare MPS IVA to other closely related disorders to differentiate MPS IVA. Overall, imbalance of growth in MPS IVA patients underlies unique skeletal manifestations leading to a critical indicator for diagnosis.

[Analysis of clinical features and GALNS gene mutation in a patient with mucopolysaccharidosis type IV A]

OBJECTIVE

To detect potential mutation of galactosamine-6-sulfate (GALNS) gene in a Chinese girl affected with mucopolysaccharidosis type IV A (Morquio A syndrome).

METHODS

The patient was diagnosed by assaying the activities of mucopolysaccharidosis-related enzymes in leukocytes. Potential mutation in the GALNS gene was detected with PCR and Sanger sequencing.

RESULTS

The patient was characterized by short stature, skeletal deformities, normal intelligence, and auditory dysfunction. The activities of GALNS enzymes were low. A compound heterozygous missense mutation, c.1094G>T (p.Gly365Val)/c.938C>T (p.Thr313Met), was detected in the GALNS gene. The mutations were respectively inherited from her father and mother. Among them, the c.1094G>T (p.Gly365Val) mutation was not reported previously.

CONCLUSION

The mutations c.1094G>T (p.Gly365Val)/c.938C>T (p.Thr313Met) probably underlie the pathogenesis of the disease in our patient.

Long-term endurance and safety of elosulfase alfa enzyme replacement therapy in patients with Morquio A syndrome

Long-term efficacy and safety of elosulfase alfa enzyme replacement therapy were evaluated in Morquio A patients over 96weeks (reaching 120weeks in total from pre-treatment baseline) in an open-label, multi-center, phase III extension study. During this extension of a 24-week placebo-controlled phase III study, all patients initially received 2.0mg/kg elosulfase alfa either weekly or every other week, prior to establishment of 2.0mg/kg/week as the recommended dose, at which point all patients received weekly treatment. Efficacy measures were compared to baseline of the initial 24-week study, enabling analyses of changes over 120weeks. In addition to performing analyses for the entire intent-to-treat (ITT) population (N=173), analyses were also performed for a modified per-protocol (MPP) population (N=124), which excluded patients who had orthopedic surgery during the extension study or were non-compliant with the study protocol (as determined by ≥20% missed infusions). Six-minute walk test (6MWT) was the primary efficacy measure; three-minute stair climb test (3MSCT) and normalized urine keratan sulfate (uKS) were secondary efficacy measures. Mean (SE) change from baseline to Week 120 in 6MWT distance was 32.0 (11.3)m and 39.9 (10.1)m for patients receiving elosulfase alfa at 2.0mg/kg/week throughout the study (N=56) and 15.1 (7.1)m and 31.7 (6.8)m in all patients combined, regardless of dosing regimen, for the ITT and MPP populations, respectively. Further analyses revealed that durability of 6MWT improvements was not impacted by baseline 6MWT distance, use of a walking aid, or age. Mean (SE) change at Week 120 in the 3MSCT was 5.5 (1.9) and 6.7 (2.0)stairs/min for patients receiving elosulfase alfa at 2.0mg/kg/week throughout the study and 4.3 (1.2) and 6.8 (1.3)stairs/min in all patients combined, regardless of dosing regimen, for the ITT and MPP populations, respectively Across all patients, mean (SE) change at Week 120 in normalized uKS was -59.4 (1.8)% and -62.3 (1.8)% in the ITT and MPP populations, respectively. In the absence of a placebo group, significance of the sustained improvements could not be evaluated directly. However, to provide context for interpretation of results, comparisons were performed with untreated patients from a Morquio A natural history study. In contrast to the results of the extension study, the untreated patients experienced constant uKS levels and a gradual decline in endurance test results over a similar period of time. Differences from the untreated natural history study patients were significant for 6MWT, 3MSCT, and uKS outcomes for the cohort of patients receiving optimal dosing throughout the study and for all cohorts pooled together, for both ITT and MPP populations (P<0.05). Safety findings were consistent with those of the initial 24-week study, with no new safety signals identified.

Recombinant human N-acetylgalactosamine-6-sulfate sulfatase (GALNS) produced in the methylotrophic yeast Pichia pastoris

Mucopolysaccharidosis IV A (MPS IV A, Morquio A disease) is a lysosomal storage disease (LSD) produced by mutations on N-acetylgalactosamine-6-sulfate sulfatase (GALNS). Recently an enzyme replacement therapy (ERT) for this disease was approved using a recombinant enzyme produced in CHO cells. Previously, we reported the production of an active GALNS enzyme in Escherichia coli that showed similar stability properties to that of a recombinant mammalian enzyme though it was not taken-up by culture cells. In this study, we showed the production of the human recombinant GALNS in the methylotrophic yeast Pichia pastoris GS115 (prGALNS). We observed that removal of native signal peptide and co-expression with human formylglycine-generating enzyme (SUMF1) allowed an improvement of 4.5-fold in the specific GALNS activity. prGALNS enzyme showed a high stability at 4 °C, while the activity was markedly reduced at 37 and 45 °C. It was noteworthy that prGALNS was taken-up by HEK293 cells and human skin fibroblasts in a dose-dependent manner through a process potentially mediated by an endocytic pathway, without any additional protein or host modification. The results show the potential of P. pastoris in the production of a human recombinant GALNS for the development of an ERT for Morquio A.

Enzyme replacement therapy in newborn mucopolysaccharidosis IVA mice: early treatment rescues bone lesions?

We treated mucopolysaccharidosis IVA (MPS IVA) mice to assess the effects of long-term enzyme replacement therapy (ERT) initiated at birth, since adult mice treated by ERT showed little improvement in bone pathology [1]. To conduct ERT in newborn mice, we used recombinant human N-acetylgalactosamine-6-sulfate sulfatase (GALNS) produced in a CHO cell line. First, to observe the tissue distribution pattern, a dose of 250units/g body weight was administered intravenously in MPS IVA mice at day 2 or 3. The infused enzyme was primarily recovered in the liver and spleen, with detectable activity in the bone and brain. Second, newborn ERT was conducted after a tissue distribution study. The first injection of newborn ERT was performed intravenously, the second to fourth weekly injections were intraperitoneal, and the remaining injections from 5th to 14th weeks were intravenous into the tail vein. MPS IVA mice treated with GALNS showed clearance of lysosomal storage in the liver and spleen, and sinus lining cells in bone marrow. The column structure of the growth plate was organized better than that in adult mice treated with ERT; however, hyaline and fibrous cartilage cells in the femur, spine, ligaments, discs, synovium, and periosteum still had storage materials to some extent. Heart valves were refractory to the treatment. Levels of serum keratan sulfate were kept normal in newborn ERT mice. In conclusion, the enzyme, which enters the cartilage before the cartilage cell layer becomes mature, prevents disorganization of column structure. Early treatment from birth leads to partial remission of bone pathology in MPS IVA mice.

Molecular testing of 163 patients with Morquio A (Mucopolysaccharidosis IVA) identifies 39 novel GALNS mutations

Morquio A (Mucopolysaccharidosis IVA; MPS IVA) is an autosomal recessive lysosomal storage disorder caused by partial or total deficiency of the enzyme galactosamine-6-sulfate sulfatase (GALNS; also known as N-acetylgalactosamine-6-sulfate sulfatase) encoded by the GALNS gene. Patients who inherit two mutated GALNS gene alleles have a decreased ability to degrade the glycosaminoglycans (GAGs) keratan sulfate and chondroitin 6-sulfate, thereby causing GAG accumulation within lysosomes and consequently pleiotropic disease. GALNS mutations occur throughout the gene and many mutations are identified only in single patients or families, causing difficulties both in mutation detection and interpretation. In this study, molecular analysis of 163 patients with Morquio A identified 99 unique mutations in the GALNS gene believed to negatively impact GALNS protein function, of which 39 are previously unpublished, together with 26 single-nucleotide polymorphisms. Recommendations for the molecular testing of patients, clear reporting of sequence findings, and interpretation of sequencing data are provided.

Mucopolysaccharidosis IVA: correlation between genotype, phenotype and keratan sulfate levels

Mucopolysaccharidosis IVA (MPS IVA) is caused by deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS), leading to systemic skeletal dysplasia because of excessive storage of keratan sulfate (KS) in chondrocytes. In an effort to determine a precise prognosis and personalized treatment, we aim to characterize clinical, biochemical, and molecular findings in MPS IVA patients, and to seek correlations between genotype, phenotype, and blood and urine KS levels. Mutation screening of GALNS gene was performed in 55 MPS IVA patients (severe: 36, attenuated: 13, undefined: 6) by genomic PCR followed by direct sequence analysis. Plasma and urine KS levels were measured by ELISA method. Genotype/phenotype/KS correlations were assessed when data were available. Fifty-three different mutations including 19 novel ones (41 missense, 2 nonsense, 4 small deletions, 1 insertion, and 5 splice-site) were identified in 55 patients and accounted for 93.6% of the analyzed mutant alleles. Thirty-nine mutations were associated with a severe phenotype and ten mutations with an attenuated one. Blood and urine KS concentrations in MPS IVA patients were age-dependent and markedly higher than those in age-matched normal controls. Plasma and urine KS levels in MPS IVA patients with the severe phenotype were higher than in those with an attenuated form. This study provides evidence for extensive allelic heterogeneity of MPS IVA. Accumulation of mutations as well as clinical descriptions and KS levels allows us to predict clinical severity more precisely and should be used for evaluation of responses to potential treatment options.

Review of clinical presentation and diagnosis of mucopolysaccharidosis IVA

Mucopolysaccharidosis type IVA (MPS IVA) was described in 1929 by Luis Morquio from Uruguay and James Brailsford from England, and was later found as an autosomal recessive lysosomal storage disease. MPS IVA is caused by mutations in the gene encoding the enzyme, N-acetylgalactosamine-6-sulfate sulfatase (GALNS). Reduced GALNS activity results in impaired catabolism of two glycosaminoglycans (GAGs), chondroitin-6-sulfate (C6S) and keratan sulfate (KS). Clinical presentations of MPS IVA reflect a spectrum of progression from a severe "classical" phenotype to a mild "attenuated" phenotype. More than 180 different mutations have been identified in the GALNS gene, which likely explains the phenotypic heterogeneity of the disorder. Accumulation of C6S and KS manifests predominantly as short stature and skeletal dysplasia (dysostosis multiplex), including atlantoaxial instability and cervical cord compression. However, abnormalities in the visual, auditory, cardiovascular, and respiratory systems can also affect individuals with MPS IVA. Diagnosis is typically based on clinical examination, skeletal radiographs, urinary GAG, and enzymatic activity of GALNS in blood cells or fibroblasts. Deficiency of GALNS activity is a common assessment for the laboratory diagnosis of MPS IVA; however, with recently increased availability, gene sequencing for MPS IVA is often used to confirm enzyme results. As multiple clinical presentations are observed, diagnosis of MPS IVA may require multi-system considerations. This review provides a history of defining MPS IVA and how the understanding of the disease manifestations has changed over time. A summary of the accumulated knowledge is presented, including information from the International Morquio Registry. The classical phenotype is contrasted with attenuated cases, which are now being recognized and diagnosed more frequently. Laboratory based diagnoses of MPS IVA are also discussed.

[Analysis of GALNS gene mutation in thirty-eight Chinese patients with mucopolysaccharidosis type IVA]

OBJECTIVE

Mucopolysaccharidosis (MPS) type IVA (MPS IVA) is an autosomal recessive lysosomal storage disease caused by deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS) needed to degrade glycosaminoglycanes (GAGs), accumulation of GAGs in the tissue resulting in disorder of function. So far, the small number of articles about clinical study of Chinese MPS IVA were published and only one paper about gene mutation analysis was published. This study aimed to investigate the mutation spectrum and characteristic of GALNS gene in Chinese patients with MPS IVA who were diagnosed in our hospital.

METHOD

Thirty-eight patients from 36 families (male 17, female 21) were diagnosed as MPS IVA by GALNS activity determination [(0.85 ± 1.33) nmol/(17 h·mg)] and clinical symptoms during 2006-2012. The average age of diagnosis was (5.7 ± 3.6) years. Mutation analysis of GALNS gene performed performed by PCR-direct DNA sequencing for 38 patients. PCR-restriction fragment length polymorphism analysis was used for validating novel mutation, and also to assess amino acid conservation for novel missense variants in five different species. PolyPhen-2 tool was used to predict the possible impact of missense mutations on the structure and function of the human GALNS protein, etc. Analysis of GALNS activity and gene mutation in amniotic fluid were performed to provide the prenatal diagnosis for some families with MPS type IVA.

RESULT

(1) Thirty-eight kinds of mutation in GALNS gene were identified in 38 patients of them, 71% were missense mutations. p. M318R was a hot-spot mutation (21%) tested. Five kinds of mutation i.e., p. P163H, p.G168L, p. A324E, p. L366P and p. F452L were only found in Chinese patients with MPS IVA. Eighteen kinds of novel mutation were detected including p. E315K, p.G304D, p.R251Q, p.Y240C, p.G161E, p.N32D, p.L390P, p. D60E, p. P420S, W403C/T404S, p.L454P, for p.W405X, p. M1I, c.409_ c.420del12, c.1176_1178del3, c.1046delG, c.1188delG and IVS9-2A>C. (2) The polymorphism of novel missense variants were ruled out by the PCR-restriction fragment length polymorphism analysis and no related mutations were found in 50 normal controls. A splice site mutation IVS9-2A>C had been validated by reverse transcription PCR direct sequencing. The amino acid of mutant position of 10 kinds of missense variants are highly conserved and only p. L454 is moderately conserved position. These missense variants were predicted to cause damage to the structure and function of human GALNS protein possibly according to the PolyPhen-2 tool, so these novel missense variants may be disease-causing mutations. (3) Prenatal diagnosis was provided for 7 families and three fetuses were diagnosed as MPS IVA.

CONCLUSION

The GALNS gene mutation spectrum in Chinese patients with MPS IVA is really different from that in other countries, five kinds of mutation were only found in Chinese patients with MPS IVA. The reports of hot-spot mutation in Chinese patients were also different, and should be analyzed by more data of gene mutation analysis and epidemiological study.

Molecular characterization of 355 mucopolysaccharidosis patients reveals 104 novel mutations

Mucopolysaccharidosis (MPS) disorders are heterogeneous and caused by deficient lysosomal degradation of glycosaminoglycans, resulting in distinct but sometimes overlapping phenotypes. Molecular analysis was performed for a total of 355 MPS patients with MPSI (n = 15), MPSII (n = 218), MPSIIIA (n = 86), MPSIIIB (n = 20), MPSIVA (n = 6) or MPSVI (n = 10). This analysis revealed 104 previously unreported mutations: seven in IDUA (MPSI), 61 in IDS (MPSII), 19 in SGSH (MPSIIIA), 11 in NAGLU (MPSIIIB), two in GALNS (MPSIVA) and four in ARSB (MPSVI). The intergenic comparison of the mutation data for these disorders has revealed interesting differences. Whereas IDUA, IDS, NAGLU and ARSB demonstrate similar levels of mutation heterogeneity (0.6-0.675 different mutations per total alleles), SGSH and GALNS have lower levels of mutation heterogeneity (0.282 and 0.455, respectively), due to more recurrent mutations. The type of mutation also varies significantly by gene. SGSH, GALNS and ARSB mutations are usually missense (76.5 %, 81.8 % and 85 %), while IDUA has many more nonsense mutations (56 %) than the other genes (≤20%). The mutation spectrum is most diverse for IDS, including intergenic inversions and multi-exon deletions. By testing 102 mothers of MPSII patients, we determined that 22.5 % of IDS mutations are de novo. We report the allele frequency of common mutations for each gene in our patient cohort and the exonic distribution of coding sequence alterations in the IDS, SGSH and NAGLU genes, which reveals several potential "hot-spots". This further molecular characterization of these MPS disorders is expected to assist in the diagnosis and counseling of future patients.

[GLB1 gene mutation and clinical characteristics of a patient with mucopolysaccharidosis type IVB]

OBJECTIVE

To report the results of clinical characteristics, enzyme activity determination and mutation analysis of GLB1 gene in a Chinese patient with mucopolysaccharidosis (MPS) type IVB (Morquio B disease).

METHOD

A 14-year-old Chinese boy with MPS type IVB was firstly diagnosed by blood leucocytes galactosamine-6-sulfate sulfatase (GALNS) and β-galactosidase (GLB1) determination, who was characterized by short stature, multiplex skeletal abnormalities, difficulty in walking. PCR-sequencing analysis was applied to detect the mutations in GLB1 of the patient.

RESULT

The patient was characterized by dwarfism, pectus carinatum, kyphosis, normal intelligence, and no neurologic damage of spasms, linguistic capacity and so on. The patient had normal GALNS enzyme activity and very low GLB1 enzyme activity [5.03 nmol/(h·mg) vs. normal value 118 - 413 nmol/(h·mg) ] in leukocytes. A compound heterozygous missense mutations c.442C > T(p.R148C)/c.1454A > G(p.Y485C) in GLB1 gene were detected in this patient. The mutation p.Y485C is a novel variant. With the method of gene analysis of new variant, the mutation p.Y485C was considered to be a pathogenic mutation.

CONCLUSION

The MPS IVB patient showed severe multiple skeletal deformities, normal intelligence, no neurologic damage and very low GLB1 enzyme activity, who carries compound heterozygous mutations p.R148C/p.Y485C. The mutation p.Y485C in GLB1 gene may be a novel pathologic mutation of MPS type IVB.

Molecular analysis of mucopolysaccharidosis IVA (Morquio A) in Spain

Mucopolysaccharidosis type IVA (Morquio A) is an inherited metabolic disease with autosomal recessive inheritance. The pathology is due to a deficient activity of N-acetylgalactosamine-6-sulfate-sulfatase, which is involved in the degradation of keratan sulfate and chondroitin-6-sulfate. To date more than 150 mutations have been described in the GALNS gene in different populations. The aim of this study was to analyze the mutations and polymorphisms in Spain in order to know the epidemiology of our population and also to offer genetic counseling to affected families. We found 30 mutant alleles in the 15 families analyzed completing all the genotypes. Most of the mutations that we found were missense mutations, six of which were novel: p.S74F, p.E121D, p.Y254C, p.E260K, p.T394P and p.N495Y; we also found a small deletion (c.1142delC) and a probable deep intronic mutation that causes the loss of exon 5 (c.423_566del) found in cDNA. Both mutations are described in this study for the first time. We also identified 20 polymorphisms previously reported and 2 novel ones: (c.633+222T/C and c.898+25C>G). In conclusion, we have identified the mutations responsible for Mucopolysaccharidosis IV A in Spain. We found great allelic heterogeneity, as occurs in other populations, which hinders the establishment of genotype-phenotype correlations in Spain. This study has been very useful for genetic counseling to the affected families.

Morquio A syndrome due to maternal uniparental isodisomy of the telomeric end of chromosome 16

Morquio A syndrome (MPS IVA) is a recessive lysosomal storage disorder (LSD) caused by mutations in the GALNS gene leading to the deficiency of lysosomal enzyme N-acetylgalactosamine-6-sulfate sulfatase (GALNS). Patients show a broad spectrum of phenotypes ranging from classical severe type to mild forms. Classical forms are characterized by severe bone dysplasia and usually normal intelligence. So far, more than 170 unique mutations have been identified in the GALNS gene of MPS IVA patients. We report on a Morquio A patient with a classical phenotype who was found to be homozygous for a missense mutation (c.236 G>A; p.Cys79Tyr) in the GALNS gene. This alteration affects the highly conserved p.Cys79 that is transformed into formylglycine, the catalytic residue of the active site. The mutation was present in the proband's mother, but not in the father, whose paternity was confirmed by microsatellite analysis. In order to test the hypothesis of maternal uniparental disomy (UPD), we investigated the segregation of sixteen microsatellite markers from chromosome 16. The results showed a condition of maternal UPD due to an error in meiosis I. Maternal isodisomy of the 16q24 region led to homozygosity for the GALNS mutant allele, causing the patient's disease. These findings allow to add for the first time the LSD Morquio A syndrome to the list of conditions that can be caused by UPD. The possibility of UPD is relevant when giving genetic counseling to couples since the recurrent risk in future pregnancies is dramatically reduced.

Effect of elongation factor 1alpha promoter and SUMF1 over in vitro expression of N-acetylgalactosamine-6-sulfate sulfatase

Morquio A is an autosomal recessive disease caused by the deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS), leading to the lysosomal accumulation of keratan-sulfate and chondroitin-6-sulfate. We evaluated in HEK293 cells the effect of the cytomegalovirus immediate early enhancer/promoter (CMV) or the elongation factor 1alpha (EF1alpha) promoters, and the coexpression with the sulfatase modifying factor 1 (SUMF1) on GALNS activity. Four days postransfection GALNS activity in transfected cells with CMV-pIRES-GALNS reached a plateau, whereas in cells transfected with EF1alpha-pIRES-GALNS continued to increase until day 8. Co-transfection with pCXN-SUMF1 showed an increment up to 2.6-fold in GALNS activity. Finally, computational analysis of transcription factor binding-sites and CpG islands showed that EF1alpha promoter has long CpG islands and high-density binding-sites for Sp1 compared to CMV. These results show the advantage of the SUMF1 coexpression on GALNS activity and indicate a considerable effect on the expression stability using EF1alpha promoter compared to CMV.

[Construction of an adenoassociated, viral derived, expression vector to correct the genetic defect in Morquio A disease]

INTRODUCTION

Mucopolysaccharidosis IVA (Morquio A) is caused by a deficiency of N-acetylgalactosamine-6-sulphate-sulphatase, a lysosomal enzyme required for the stepwise degradation of keratan-sulfate and chondroitin-6-sulfate. A deficiency in this enzyme results in an accumulation of glycosaminoglycans in several tissues. Currently, no effective therapies exist and only supportive measures are used to treat some manifestations of the disease. An ideal therapy is one that can be administrated early in life, has low mortality, and leads to long-term expression of the enzyme. Gene therapy emerges as a potential alternative to correct the genetic defect in MPS IVA.

OBJECTIVE

Adenoassociated virus-derived expression vectors (AAV) were constructed to correct in vitro the enzyme deficiency in mucopolysaccharidosis IVA.

MATERIALS AND METHODS

Adenoasociated virus-derived vectors containing the human GALNS gene and driven by the citomegalivirus immedited-early promoter were constructed using a free-adenoviral protocol. HEK293 cells and human skin Morquio A fibroblasts were transfected with the recombinat vectors. Enzyme activity was measured in cells 24 and 48 hours post-transfection.

RESULTS

Free-adenovirus recombinant AAV vectors were obtained with titres up to 2.08x1010 capsids/mL. HEK293 cells and Morquio A fibroblasts transfected with vectors showed GALNS activity up to 3.05 nmoles/mg/h 48 hours post-transfection.

CONCLUSION

The AAV mediated the in vitro expression of GALNS enzyme in the transfected cells. These results are the first step towards a gene therapy alternative to Morquio A disease using adenoassociated virus-derived vectors.

Effect of 'attenuated' mutations in mucopolysaccharidosis IVA on molecular phenotypes of N-acetylgalactosamine-6-sulfate sulfatase

Mucopolysaccharidosis IVA is an autosomal recessive disease caused by the deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS). Mutation screening of the GALNS gene was performed for seven MPS IVA patients with attenuated phenotypes from three unrelated families. Four of 5 missense mutations identified in this study (p.F167V, p.R253W, p.R380S, p.P484S) and two reported (p.F97V, p.N204K), associated with attenuated phenotypes, were characterized using in vitro stable expression experiments, enzyme kinetic study, protein processing and structural analysis. The stably expressed mutant enzymes defining the attenuated phenotype exhibited a considerable residual activity (1.2-36.7% of the wild-type GALNS activity) except for p.R380S. Enzyme kinetic studies showed that p.F97V, p.F167V and p.N204K have lower affinity to the substrate compared with other mutants. The p.F97V enzyme was the most thermolabile at 55 degrees C. Immunoblot analyses indicated a rapid degradation and/or an insufficiency in processing in the mutant proteins. Tertiary structure analysis revealed that although there was a tendency for 'attenuated' mutant residues to be located on the surface of GALNS, they have a different effect on the protein including modification of the hydrophobic core and salt-bridge formation and different potential energy. This study demonstrates that 'attenuated' mutant enzymes are heterogeneous in molecular phenotypes, including biochemical properties and tertiary structure.

Murine model (Galns(tm(C76S)slu)) of MPS IVA with missense mutation at the active site cysteine conserved among sulfatase proteins

Mucopolysaccharidosis IVA (MPS IVA) is an autosomal recessive disorder caused by deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS), required for degradation of keratan sulfate and chondroitin-6-sulfate. In order to study the effects of a missense mutation in the active site cysteine in the GALNS gene that is conserved in all mammalian sulfatases, we produced a p.C76S (an active site replacement) knock-in mouse by replacing the Cys76 with Ser in the endogenous murine Galns by targeted mutagenesis. Homozygous Galns(tm(C76S)slu) mice had no detectable GALNS enzyme activity. At age of 2-4 months, lysosomal storage was present primarily within reticuloendothelial cells such as Kupffer cells and spleen sinusoidal lining cells. Vacuolar change was present in glomerular visceral epithelial cells and was not present in hepatocytes or renal tubular cells. In the brain, hippocampal and neocortical neurons and meningeal cells showed lysosomal storage. Radiographs revealed no change in the skeletal bones of mice up to 12 months old. Thus, the Galns(tm(C76S)slu) mice had visceral storage of GAGs in organs but lacked the skeletal features of human MPS IVA. In contrast to a previously reported transgenic model (Galns(tm(hC79S.mC76S)slu)), in which the inactive human GALNS transgene was overexpressed, no reduction in other sulfatases was observed. In addition, the Galns(tm(C76S)slu) mice displayed milder storage. We conclude that the milder phenotype is characteristic of isolated GALNS deficiency while the more severe phenotype reflected in the Galns(tm(hC79S.mC76S)slu) mice was due to deficiency of other sulfatases caused by oversaturation of the sulfate modifying enzyme by the inactive human gene product.

Characterization and pharmacokinetic study of recombinant human N-acetylgalactosamine-6-sulfate sulfatase

Mucopolysaccharidosis IVA (MPS IVA) is an autosomal recessive disorder caused by a deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS). The aims of this study were to establish Chinese hamster ovary (CHO) cells overexpressing recombinant human GALNS (rhGALNS) and to assess pharmacokinetics and tissue distribution of purified enzymes by using MPS IVA knock-out mouse (Galns(-/-)). The CHO-cell derived rhGALNS was purified from the media by a two-step affinity chromatography procedure. The rhGALNS was administered intravenously to 3-month-old Galns(-/-) mice at a single dose of 250U/g of body weight. The treated mice were examined by assaying the GALNS activity at baseline and up to 240min to assess clearance of the enzyme from blood circulation. The mice were sacrificed 4h after infusion of the enzyme to study the enzyme distribution in tissues. The rhGALNS was purified 1317-fold with 71% yield. The enzyme was taken up by Galns(-/-) chondrocytes (150U/mg/15h). The uptake was inhibited by mannose-6-phosphate. The enzyme activity disappeared from circulation with a half-life of 2.9min. After enzyme infusion, the enzyme was taken up and detected in multiple tissues (40.7% of total infused enzymes in liver). Twenty-four hours after a single infusion of the fluorescence-labeled enzymes into MPS IVA mice, biodistribution pattern showed the amount of tagged enzyme retained in bone, bone marrow, liver, spleen, kidney, and heart. In conclusion, we have shown that the phosphorylated rhGALNS is delivered to multiple tissues, including bone, and that it functions bioactively in Galns(-/-) chondrocytes implying a potential enzyme replacement treatment.

[Mucopolysaccharidosis IVA (Morquio A syndrome): clinical, biological and therapeutic aspects]

Mucopolysaccharidosis IVA (MPS IVA; Morquio A disease) is an autosomal recessive lysosomal storage disorder caused by a genetic deficiency of the N-acetylgalactosamine-6-sulfate sulfatase (GALNS; E.C.3.1.6.4). GALNS is required to degrade keratan sulfate (KS) and chondroitine-6-sulfate (C6S). The accumulation of undegraded substrates in lysosomes of the affected tissues leads to a systemic bone dysplasia. Total urine glycosaminoglycans (GAG) in patients with MPS IVA are close to the normal range so it is difficult to distinguish this disease based on urine GAG excretion. Another potential disease marker could be KS levels in urine and plasma. Although the enzymatic diagnosis of affected patients with MPS IVA can be made, the detection of obligate heterozygotes by enzymatic measurement is less reliable because of a marked overlap of GALNS in fibroblasts or leucocytes from affected phenotype and normal controls. The genetic heterozygoty of MPS IVA has been facilitated by the isolation and characterization of the full lengh cDNA encoding human GALNS. Conventional therapy is symptomatic and limited to palliative procedures, which have virtually no impact upon mortality. To date, there is still no general consensus about the effectiveness of bone marrow transplantation. In the future, gene therapy could represent a great therapeutic improvement.

[Clinical, biologic and molecular characteristics of two Tunisian MPS IV A patients]

Mucopolysaccharidosis type IV A (MPS IV A) is an autosomal recessive disorder resulting from the deficient activity of the lysosomal enzyme, N-acetylgalactosamine-6-sulfate sulfatase (GALNS) and the progressive lysosomal accumulation of keratane sulfate. Clinically, the MPS IV A differs from the other MPS by the localisation of the keratane sulfate in skelet and in eyes associated to the conservation of a normal intelligence. To date, the characterization and purification of the GALNS gene made a research for pathogenic mutations in patients with MPS IV A easier. These mutations are responsible of severe, intermediate or mild phenotype. The aim for this work was the research of clinical, biologic and molecular characteristics of two Tunisian MPS IV A patients who were offsprings of consanguineous mating. Enzymatic and urinary diagnostics suggested a MPS IV A phenotype. A novel homozygous mutation IVS1+1G-A was identified by direct sequencing in the GALNS gene of the two patients. Identification of GALNS mutations provide genotype/phenotype correlations and permit the precision of anomalies responsible of Morquio A phenotype in concerned families.

Mutation and polymorphism spectrum of the GALNS gene in mucopolysaccharidosis IVA (Morquio A)

Mucopolysaccharidosis IVA (MPS IVA; Morquio A disease) is an autosomal-recessive disorder caused by a deficiency of lysosomal N-acetylgalactosamine-6-sulfate sulfatase (GALNS; E.C.3.1.6.4). GALNS is required to degrade glycosaminoglycans, keratan sulfate (KS), and chondroitin-6-sulfate. Accumulation of undegraded substrates in lysosomes of the affected tissues leads to a systemic bone dysplasia. We summarize information on 148 unique mutations determined to date in the GALNS gene, including 26 novel mutations (19 missense, four small deletions, one splice-site, and two insertions). This heterogeneity in GALNS gene mutations accounts for an extensive clinical variability within MPS IVA. Seven polymorphisms that cause an amino acid change, and nine silent variants in the coding region are also described. Of the analyzed mutant alleles, missense mutations accounted for 78.4%; small deletions, 9.2%; nonsense mutation, 5.0%; large deletion, 2.4%; and insertions, 1.6%. Transitional mutations at CpG dinucleotides accounted for 26.4% of all the described mutations. The importance of the relationship between methylation status and distribution of transitional mutations at CpG sites at the GALNS gene locus was elucidated. The three most frequent mutations (over 5% of all mutations) were represented by missense mutations (p.R386C, p.G301C, and p.I113F). A genotype/phenotype correlation was defined in some mutations. Missense mutations associated with a certain phenotype were studied for their effects on enzyme activity and stability, the levels of blood and urine KS, the location of mutations with regard to the tertiary structure, and the loci of the altered amino acid residues among sulfatase proteins.

Mucopolysaccharidosis type IV: N-acetylgalactosamine-6-sulfatase mutations in Tunisian patients

Mucopolysaccharidosis type IVA (MPS IVA; OMIM #253000) or Morquio A syndrome is an autosomal recessive inborn error resulting from the deficient activity of the lysosomal enzyme, N-acetylgalactosamine-6-sulfatase (GALNS), and the progressive lysosomal accumulation of sulfated glycosaminoglycans. Clinically, the severe form of this lysosomal storage disease is characterized by a characteristic severe bone dysplasia and normal intelligence. To date, a variety of mutations have been associated with the severe MPS IVA phenotype. Here, we report the GALNS mutations in six severe MPS IVA patients from four unrelated Tunisian families. For mutation detection, each of the 14 exons and adjacent intron-exon junctions of the GALNS gene were sequenced after PCR-amplification from genomic DNA. Two novel mutations were identified: a G to A transition in the conserved 5' donor splice site of intron 1 (GACgt-->GACat: designated IVS1(+1g-->a)) and a G to C transversion in codon 66 of exon 2 predicting a glycine to arginine substitution (G66R). The IVS1(+1g-->a) mutation was homozygous in five similarly affected patients from three presumably unrelated families, but haplotype analysis suggested a common ancestor. The affected patient in the fourth family was homozygous for the G66R mutation. These are the first GALNS mutations causing severe MPS IVA disease identified in Tunisia. These molecular findings provide genotype/phenotype correlations, and permit accurate carrier detection, prenatal diagnosis, and counseling for MPS IVA disease in Tunisia where first cousin consanguineous mating remains frequent.

Development of MPS IVA mouse (Galnstm(hC79S.mC76S)slu) tolerant to human N-acetylgalactosamine-6-sulfate sulfatase

Mucopolysaccharidosis IVA (MPS IVA) is an autosomal recessive disease caused by N-acetylgalactosamine-6-sulfate sulfatase (GALNS) deficiency. In recent studies of enzyme replacement therapy for animal models with lysosomal storage diseases, cellular and humoral immune responses to the injected enzymes have been recognized as major impediments to effective treatment. To study the long-term effectiveness and side effects of therapies in the absence of immune responses, we have developed an MPS IVA mouse model, which has many similarities to human MPS IVA and is tolerant to human GALNS protein. We used a construct containing both a transgene (cDNA) expressing inactive human GALNS in intron 1 and an active site mutation (C76S) in adjacent exon 2 and thereby introduced both the inactive cDNA and the C76S mutation into the murine Galns by targeted mutagenesis. Affected homozygous mice have no detectable GALNS enzyme activity and accumulate glycosaminoglycans in multiple tissues including visceral organs, brain, cornea, bone, ligament and bone marrow. At 3 months, lysosomal storage is marked within hepatocytes, reticuloendothelial Kupffer cells, and cells of the sinusoidal lining of the spleen, neurons and meningeal cells. The bone storage is also obvious, with lysosomal distention in osteoblasts and osteocytes lining the cortical bone, in chondrocytes and in the sinus lining cells in bone marrow. Ubiquitous expression of the inactive human GALNS was also confirmed by western blot using the anti-GALNS monoclonal antibodies newly produced, which resulted in tolerance to immune challenge with human enzyme. The newly generated MPS IVA mouse model should provide a good model to evaluate long-term administration of enzyme replacement.

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 common mutation in mucopolysaccharidosis IVA: correlation among genotype, phenotype, and keratan sulfate

Mucopolysaccharidosis IVA (MPS IVA) is a lysosomal storage disorder caused by the deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS). Mutation screening of the GALNS was performed by genomic PCR and direct sequence analyses in 20 MPS IVA patients from Latin America. In this study, 12 different gene mutations including nine unreported ones were identified in 16 severe and four attenuated patients and accounted for 90.0% of the unrelated mutant alleles. The gene alterations were missense mutations except one insertion. Six recurrent mutations, p.A75G, p.G116S, p.G139S, p.N164T, p.R380S, and p.R386C, accounted for 5.0, 10.0, 5.0, 7.5, 5.0, and 32.5% of the unrelated mutant alleles, respectively. The p.R386C mutation was identified in all Latin American populations studied. Eleven mutations correlated with a severe form, while one mutation, p.R380S, was associated with an attenuated form. MPS IVA patients had an elevation of urine and plasma keratan sulfate (KS) concentrations compared with those of the age-matched control. KS concentrations in severe patients were higher than those in attenuated patients. These data provide evidence for extensive allelic heterogeneity and presence of a common mutation in Latin American patients. Accumulation of mutations with clinical description and KS concentration will lead us to predict clinical severity of the patient more precisely.

Mucopolysaccharidosis IVA (Morquio A): Identification of novel common mutations in the N-acetylgalactosamine-6-sulfate sulfatase (GALNS) gene in Italian patients

Mucopolysaccharidosis IVA (MPS IVA) is a lysosomal storage disorder caused by the deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS). Mutation screening of the GALNS gene was performed by RT-PCR with one amplicon and direct sequence analyses using cDNA samples from 15 Italian MPS IVA patients. Each mutation was confirmed at the genomic level. In this study, 13 different gene mutations with four common mutations (over 10% of mutant alleles) were identified in 12 severe and three milder (attenuated) MPS IVA patients. The gene alterations in 12 out of 13 were found to be point mutations and only one mutation was deletion. Ten of 13 mutations were novel. The c.1070C>T (p.Pro357Leu) mutation coexisted with c.1156C>T (p.Arg386Cys) mutation on the same allele. Together they accounted for 100% of the 30 disease alleles of the patients investigated. Four common mutations accounted for 70% of mutant alleles investigated. Urine keratan sulfate (KS) concentrations were elevated in all patients investigated. These data provide further evidence for extensive allelic heterogeneity and importance of relation among genotype, phenotype, and urine KS excretion as a biomarker in MPS IVA.

Lysosomal high molecular weight multienzyme complex

Three acidic glycosidases: beta-galactosidase (beta-GAL, EC 3.2.1.23), alpha-neuraminidase (NEUR, sialidase, EC 3.2.1.18), N-acetylaminogalacto-6-sulfate sulfatase (GALNS, EC 3.1.6.4) and serine carboxypepidase cathepsin A (EC 3.4.16.1) form a functional high molecular weight complex in the lysosomes. The major constituent of this complex is cathepsin A, the so-called "lysosomal protective protein" (PPCA). By forming a multienzyme complex, it protects the glycosidases from rapid intralysosomal proteolysis, and it is also required for the intracellular sorting and proteolytic processing of their precursors. In man, a deficiency of cathepsin A leads to a combined deficiency of beta-GAL and NEUR activities, called "galactosialidosis". Multiple mutations identified in the cathepsin A gene are the molecular basis of this lysosomal storage disease. This review describes the structural organization of the lysosomal high molecular weight multienzyme complex and the importance of the protective protein/cathepsin A in physiology and pathology.

Mouse model of N-acetylgalactosamine-6-sulfate sulfatase deficiency (Galns-/-) produced by targeted disruption of the gene defective in Morquio A disease

Mucopolysaccharidosis IVA is an autosomal recessive disorder caused by a deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS), a lysosomal enzyme required for the stepwise degradation of keratan sulfate (KS) and chondroitin-6-sulfate (C6S). To generate a model for studies of the pathophysiology and of potential therapies, we disrupted exon 2 of Galns, the homologous murine gene. Homozygous Galns-/- mice have no detectable GALNS enzyme activity and show increased urinary glycosaminoglycan (GAGs) levels. These mice accumulate GAGs in multiple tissues including liver, kidney, spleen, heart, brain and bone marrow. At 2 months old, lysosomal storage is present primarily within reticuloendothelial cells such as Kupffer cells and cells of the sinusoidal lining of the spleen. Additionally, by 12 months old, vacuolar change is observed in the visceral epithelial cells of glomeruli and cells at the base of heart valves but it is not present in parenchymal cells such as hepatocytes and renal tubular epithelial cells. In the brain, hippocampal and neocortical neurons and meningeal cells had lysosomal storage. KS and C6S were more abundant in the cytoplasm of corneal epithelial cells of Galns-/- mice compared with wild-type mice by immunohistochemistry. Radiographs revealed no change in the skeletal bones of mice up to 12 months old. Thus, targeted disruption of the murine Galns gene has produced a murine model, which shows visceral storage of GAGs but lacks the skeletal features. The complete absence of GALNS in mutant mice makes them useful for studies of pharmacokinetics and tissue targeting of recombinant GALNS designed for enzyme replacement.

Mucopolysaccharidosis IVA: characterization of a common mutation found in Finnish patients with attenuated phenotype

Mucopolysaccharidosis IVA (MPS IVA) is caused by the deficiency of the lysosomal enzyme N-acetylgalactosamine-6-sulfate sulfatase encoded by the GALNS gene on chromosome 16. We describe, in detail, the clinical phenotype of five patients from three unrelated Finnish families and have characterized the disease-causing mutations in GALNS. Genotypes of the patients are D60N/A291T, D60N/W230X, and D60N/1374delT. Mutation 1374delT introduces premature termination of GALNS. Cells over-expressing the novel mutation W230X and A291T had no residual GALNS activity, whereas D60N gave 12.2% residual activity compared with the wild type. Co-transfection of D60N/A291T and D60N/W230X showed 5.5% and 6.7% of wild type activity, respectively. The precursor proteins of D60N and A291T were observed at 55 kDa and 57 kDa, respectively, whereas there was no detectable band in cells over-expressing W230X. At 55 degrees C, the mutant protein showed lower thermostability than the wild type protein at pH 3.8 and 7.0. The tertiary structural model of the GALNS protein revealed that aspartic acid at position 60 is located on the surface of the molecule, away from the active site. This makes it unlikely that the enzymatic function of the protein with D60N is severely impaired. On the other hand, A291 and W230 are localized near the active site. The molecular characteristics of the D60N mutation explain the attenuated clinical phenotype of the patients.

Porcine N-acetylgalactosamine 6-sulfatase (GALNS) cDNA sequence and expression in developing teeth

Mucopolysaccharidosis type IVA (Morquio A syndrome, MPS IVA) is a rare, autosomal recessive disorder with a prevalence of 1 in 170,000 live births. It is caused by a deficiency of N-acetylgalactosamine 6-sulfatase (GALNS), a lysosomal hydrolase encoded by a gene on human chromosome 16q24.3. Mucopolysaccharidosis type IVA is the only known MPS that is associated with structural defects in dental enamel. GALNS cleaves the sulfate group from N-acetylgalactosamine 6-sulfate and galactose 6-sulfate, which are specifically found in keratan sulfate and chondroitin 6-sulfate. A pathologic absence of GALNS activity results in the accumulation of these glycosaminoaglycans in the urine and in the lysosomes of tissues that turn them over. There is currently no animal model for MPS IVA. To learn more about how a GALNS deficit could lead to enamel defects, we have cloned and characterized a full-length pig GALNS cDNA. GALNS mRNA was localized in developing teeth by in situ hybridization, Northern blot, and reverse-transcription polymerase chain reaction analyses, while GALNS substrates were localized using immunohistochemistry. We report that secretory ameloblasts were positive for GALNS mRNA, as well as for keratan sulfate and chondroitin 6-sulfate. We conclude that enamel defects associated with the loss of GALNS activity in persons with MPS IVA are likely to result from the pathological accumulation of keratan sulfate and chondroitin 6-sulfate in the lysosomes of secretory stage ameloblasts.

Molecular analysis of Turkish mucopolysaccharidosis IVA (Morquio A) patients: identification of novel mutations in the N-acetylgalactosamine-6-sulfate sulfatase (GALNS) gene

Mucopolysaccharidosis IVA (MPS IVA) is a lysosomal storage disorder caused by the deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS; EC 3.1.6.4). The deficiency of N-acetylgalactosamine-6-sulfate sulfatase leads to lysosomal accumulation of undegraded glycosaminoglycans, keratan sulfate and chondroitin-6-sulfate. Mutation screening of the GALNS gene was performed by SSCP and direct sequence analyses using genomic DNA samples from 10 Morquio A patients. By nonradioactive SSCP screening, 6 different gene mutations and 2 polymorphisms were identified in 10 severely affected MPS IVA patients. Five of the mutations and one of the polymorphisms are novel. The vast majority of the gene alterations were found to be single nucleotide deletions (389delG, 929delG, and 763delT) or insertions (1232-1233insT). The other two mutations were one previously identified missense mutation (Q473X) and one novel nonsense (P179S) mutation. Together they account for 95% of the disease alleles of the patients investigated. Beside mutations, one previously identified E477 polymorphism and one novel W520 polymorphism were found among Turkish MPS IVA patients.

Various cells retrovirally transduced with N-acetylgalactosoamine-6-sulfate sulfatase correct Morquio skin fibroblasts in vitro

Gene therapy may provide a long-term approach to the treatment of mucopolysaccharidoses. As a first step toward the development of an effective gene therapy for mucopolysaccharidosis type IVA (Morquio syndrome), a recombinant retroviral vector, LGSN, derived from the LXSN vector, containing a full-length human wildtype N-acetylgalactosamine-6-sulfate sulfatase (GALNS) cDNA, was produced. Severe Morquio and normal donor fibroblasts were transduced by LGSN. GALNS activity in both Morquio and normal transduced cells was several fold higher than normal values. To measure the variability of GALNS expression among different transduced cells, we transduced normal and Morquio lymphoblastoid B cells and PBLs, human keratinocytes, murine myoblasts C2C12, and rabbit synoviocytes HIG-82 with LGSN. In all cases, an increase of GALNS activity after transduction was measured. In Morquio cells co-cultivated with enzyme-deficient transduced cells, we demonstrated enzyme uptake and persistence of GALNS activity above normal levels for up to 6 days. The uptake was mannose-6-phosphate dependent. Furthermore, we achieved clear evidence that LGSN transduction of Morquio fibroblasts led to correction of the metabolic defect. These results provide the first evidence that GALNS may be delivered either locally or systematically by various cells in an ex vivo gene therapy of MPS IVA.

Lysosomal multienzyme complex: biochemistry, genetics, and molecular pathophysiology

Lysosomal enzymes sialidase (alpha-neuraminidase), beta-galactosidase, and N-acetylaminogalacto-6-sulfate sulfatase are involved in the catabolism of glycolipids, glycoproteins, and oligosaccharides. Their functional activity in the cell depends on their association in a multienzyme complex with lysosomal carboxypeptidase, cathepsin A. We review the data suggesting that the integrity of the complex plays a crucial role at different stages of biogenesis of lysosomal enzymes, including intracellular sorting and proteolytic processing of their precursors. The complex plays a protective role for all components, extending their half-life in the lysosome from several hours to several days; and for sialidase, the association with cathepsin A is also necessary for the expression of enzymatic activity. The disintegration of the complex due to genetic mutations in its components results in their functional deficiency and causes severe metabolic disorders: sialidosis (mutations in sialidase), GM1-gangliosidosis and Morquio disease type B (mutations in beta-galactosidase), galactosialidosis (mutations in cathepsin A), and Morquio disease type A (mutations in N-acetylaminogalacto-6-sulfate sulfatase). The genetic, biochemical, and direct structural studies described here clarify the molecular pathogenic mechanisms of these disorders and suggest new diagnostic tools.