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

Predicting disease severity in metachromatic leukodystrophy using protein activity and a patient phenotype matrix

BACKGROUND

Metachromatic leukodystrophy (MLD) is a lysosomal storage disorder caused by mutations in the arylsulfatase A gene (ARSA) and categorized into three subtypes according to age of onset. The functional effect of most ARSA mutants remains unknown; better understanding of the genotype-phenotype relationship is required to support newborn screening (NBS) and guide treatment.

RESULTS

We collected a patient data set from the literature that relates disease severity to ARSA genotype in 489 individuals with MLD. Patient-based data were used to develop a phenotype matrix that predicts MLD phenotype given ARSA alleles in a patient's genotype with 76% accuracy. We then employed a high-throughput enzyme activity assay using mass spectrometry to explore the function of ARSA variants from the curated patient data set and the Genome Aggregation Database (gnomAD). We observed evidence that 36% of variants of unknown significance (VUS) in ARSA may be pathogenic. By classifying functional effects for 251 VUS from gnomAD, we reduced the incidence of genotypes of unknown significance (GUS) by over 98.5% in the overall population.

CONCLUSIONS

These results provide an additional tool for clinicians to anticipate the disease course in MLD patients, identifying individuals at high risk of severe disease to support treatment access. Our results suggest that more than 1 in 3 VUS in ARSA may be pathogenic. We show that combining genetic and biochemical information increases diagnostic yield. Our strategy may apply to other recessive diseases, providing a tool to address the challenge of interpreting VUS within genotype-phenotype relationships and NBS.

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.

Diagnosis of Attenuated Mucopolysaccharidosis VI: Clinical, Biochemical, and Genetic Pitfalls

Mucopolysaccharidosis type VI (MPS VI) is a clinically heterogeneous lysosomal disease, which can be divided into 2 main categories on the basis of age of onset and severity of symptoms. The diagnosis of the attenuated form is often delayed given subtle facial features rather than the typical coarse facial features of the classic form. Here, we discuss the difficulties in establishing the diagnosis of MPS VI on the basis of the report of 4 individuals. The most common signs and symptoms in our series were bone abnormalities and hip pain as initial manifestations and cardiac changes detected after follow-up studies. On the basis of our cohort and others worldwide, awareness of attenuated forms of MPS VI should be increased particularly among general practitioners, pediatricians, rheumatologists, orthopedists, ophthalmologists, and cardiologists. Moreover, these health care providers should be aware of the technical aspects involved in the molecular and biochemical diagnosis process so that they are aware how diagnostic errors may occur.

Mucopolysaccharidosis type VI (MPS VI) and molecular analysis: Review and classification of published variants in the ARSB gene

Maroteaux–Lamy syndrome (MPS VI) is an autosomal recessive lysosomal storage disorder caused by pathogenic ARSB gene variants, commonly diagnosed through clinical findings and deficiency of the arylsulfatase B (ASB) enzyme. Detection of ARSB pathogenic variants can independently confirm diagnosis and render genetic counseling possible. In this review, we collect and summarize 908 alleles (201 distinct variants, including 3 polymorphisms previously considered as disease‐causing variants) from 478 individuals diagnosed with MPS VI, identified from literature and public databases. Each variant is further analyzed for clinical classification according to American College of Medical Genetics and Genomics (ACMG) guidelines. Results highlight the heterogeneity of ARSB alleles, with most unique variants (59.5%) identified as missense and 31.7% of unique alleles appearing once. Only 18% of distinct variants were previously recorded in public databases with supporting evidence and clinical significance. ACMG recommends publishing clinical and biochemical data that accurately characterize pathogenicity of new variants in association with reporting specific alleles. Variants analyzed were sent to ClinVar (https://www.ncbi.nlm.nih.gov/clinvar/), and MPS VI locus‐specific database (http://mps6-database.org) where they will be available. High clinical suspicion coupled with diagnostic testing for deficient ASB activity and timely submission and classification of ARSB variants with biochemical and clinical data in public databases is essential for timely diagnosis of MPS VI.

Genotypic-phenotypic features and enzyme replacement therapy outcome in patients with mucopolysaccharidosis VI from Turkey

Mucopolysaccharidosis type VI (MPS VI) is a lysosomal storage disorder (LSD) characterized by a chronic, progressive course with multiorgan involvement. In our study, clinical, biochemical, molecular findings, and response to enzyme replacement therapy (ERT) for at least 6 months were evaluated in 20 patients with MPS VI. Treatment effects on clinical findings such as liver and spleen sizes, cardiac and respiratory parameters, visual and auditory changes, joints' range of motions, endurance tests and changes in urinary glycosaminoglycan excretions, before and after ERT were analyzed. ERT caused increased physical endurance and decreased urinary dermatan sulfate/chondroitin sulfate ratios. Changes in growth parameters, cardiac, respiratory, visual, auditory findings, and joint mobility were not significant. All patients and parents reported out an increased quality of life, which were not correlated with clinical results. The most prevalent mutation was p.L321P, accounting for 58.8% of the mutant alleles and two novel mutations (p.G79E and p.E390 K) were found. ERT was a safe but expensive treatment for MPS VI, with mild benefits in severely affected patients. Early treatment with ERT is mandatory before many organs and systems are involved.

A long term follow-up study of the development of hip disease in Mucopolysaccharidosis type VI

Hip problems in Mucopolysaccharidosis type VI (MPS VI) lead to severe disability. Lack of data on the course of hip disease in MPS VI make decisions regarding necessity, timing and type of surgical intervention difficult. We therefore studied the development of hip pathology in MPS VI patients over time. Data were collected as part of a prospective follow-up study. Standardized supine AP pelvis and frog leg lateral radiographs of both hips were performed yearly or every 2years. Image assessment was performed quantitatively (angle measurements) and qualitatively (hip morphology). Clinical burden of hip disease was evaluated by physical examination, six minute walking test (6MWT) and a questionnaire assessing pain, wheelchair-dependency and walking distance. A total of 157 pelvic radiographs of 14 ERT treated MPS VI patients were evaluated. Age at first image ranged from 2.0 to 21.1years. Median follow up duration was 6.8years. In all patients, even in the youngest, the acetabulum and os ilium were dysplastic. Coverage of the femoral head by the acetabulum improved over time, but remained insufficient. While the femoral head appeared normal in the radiographs at young age, the ossification pattern became abnormal in all patients over time. In all patients the distance covered in the 6MWT was reduced (median Z scores -3.3). Twelve patients had a waddling gait. Four patients were partially wheelchair-dependent and ten patients had limitations in their maximum walking distance. In conclusion, clinically significant hip abnormalities develop in all MPS VI patients from very early in life, starting with deformities of the os ilium and acetabulum. Femoral head abnormalities occur later, most likely due to altered mechanical forces in combination with epiphyseal abnormalities due to glycosaminoglycan storage. The final shape and angle of the femoral head differs significantly between individual MPS VI patients and is difficult to predict.

Mucopolysaccharidosis IVA (Morquio A syndrome) and VI (Maroteaux-Lamy syndrome): under-recognized and challenging to diagnose

OBJECTIVE

Mucopolysaccharidosis IVA (MPS IVA, or Morquio A syndrome) and VI (MPS VI, or Maroteaux-Lamy syndrome) are autosomal recessive lysosomal storage disorders. Skeletal abnormalities are common initial presenting symptoms and, when recognized early, may facilitate timely diagnosis and intervention, leading to improved patient outcomes. Patients with slowly progressing disease and nonclassic phenotypes can be particularly challenging to diagnose. The objective was to describe the radiographic features of patients with a delayed diagnosis of MPS IVA or VI.

MATERIALS AND METHODS

This was a retrospective study. The records of 5 MPS IVA and 3 MPS VI patients with delayed diagnosis were reviewed. Radiographs were evaluated by a radiologist with special expertise in skeletal dysplasias.

RESULTS

An important common theme in these cases was the appearance of multiple epiphyseal dysplasia (MED) with epiphyseal changes seemingly confined to the capital (proximal) femoral epiphyses. Very few patients had the skeletal features of classical dysostosis multiplex.

CONCLUSIONS

Radiologists should appreciate the wide phenotypic variability of MPS IVA and VI. The cases presented here illustrate the importance of considering MPS in the differential diagnosis of certain skeletal dysplasias/disorders, including MED, some forms of spondylo-epiphyseal dysplasia (SED), and bilateral Perthes-like disease. It is important to combine radiographic findings with clinical information to facilitate early testing and accurate diagnosis.

Attenuated osteoarticular phenotype of type VI mucopolysaccharidosis: a report of four patients and a review of the literature

Mucopolysaccharidosis type VI (Maroteaux–Lamy syndrome, MPS VI, OMIM 253200) is caused by mutations in the gene coding for N-acetylgalactosamine-4-sulfatase (4-sulfatase, arylsulfatase B, ARSB, EC 3.1.6.12), a lysosomal enzyme involved in the degradation of dermatan sulfate (DS). The clinical presentation of MPS VI varies greatly with respect to age of onset and rate of disease progression. This report focuses on the attenuated form of MPS VI, which can go unrecognized for years and often presents with atypical signs or symptoms. We described a cohort of MPS VI patients (n = 4) heterozygous for the p.Y210C mutation who had a significant osteoarticular involvement at the onset of their disease and who were diagnosed years or even decades later. We have also reviewed the literature (n = 36). Two types of attenuated MPS VI phenotypes could be distinguished: osteoarticular and cardiac. The majority of MPS VI patients reported so far as relatively attenuated presented with an essentially osteoarticular phenotype associated with the p.Y210C mutation. Patients homozygous for the p.R152W mutation presented with a cardiac phenotype, which, despite fulfilling the generally used criteria for attenuated phenotype, may lead to fast disease progression and abrupt death. The knowledge of natural history and genotype–phenotype correlation may help in developing a tailored therapy potentially using enzyme replacement therapy with substrate reduction therapy or chaperones.

Spondyloepiphyseal dysplasias and bilateral legg-calvé-perthes disease: diagnostic considerations for mucopolysaccharidoses

Mucopolysaccharidosis type VI (MPS VI, Maroteaux-Lamy syndrome, MIM 253200 ) is an autosomal recessive lysosomal storage disease (LSD) caused by decreased activity of arylsulfatase B (N-acetylgalactosamine 4-sulfatase) enzyme resulting in dermatan sulfate accumulation; mucopolysaccharidosis type IVA (MPS IVA, Morquio syndrome A, MIM 253000 ) by decreased activity of N-acetylgalactosamine 6-sulfatase enzyme resulting in accumulation of keratan sulfate. Clinical symptoms include coarse facial features, joint stiffness, hepatosplenomegaly, hip osteonecrosis, and dysostosis multiplex. MPS IVA symptoms are similar but with joint hypermobility.With suspicion of MPS disease, clinicians request urine studies for quantitative and qualitative glycosaminoglycans (GAGs). Diagnosis is confirmed by decreased enzyme activity in leukocytes or cultured skin fibroblasts. Further confirmation is obtained with identification of two mutations in the ARSB gene for MPS VI or mutations in the GALNS gene for MPS IVA.We report slowly progressing patients, one with MPS VI and two with MPS IVA, who presented with skeletal changes and hip findings resembling Legg-Calvé-Perthes disease or spondyloepiphyseal dysplasia and normal/near normal urine GAG levels. The urine analysis data presented suggest that present screening techniques for MPS are inadequate in milder patients and result in delayed or missed diagnoses. The patients presented in this paper emphasize the importance of enzymatic and molecular testing.

Mucopolysaccharidosis type VI phenotypes-genotypes and antibody response to galsulfase

Background

Mucopolysaccharidosis type VI (Maroteaux-Lamy syndrome; MPS VI) is an autosomal recessive lysosomal storage disorder in which deficiency of N-acetylgalactosamine 4-sulfatase (arylsulfatase B; ARSB) leads to the storage of glycosaminoglycans (GAGs) in connective tissue. The genotype-phenotype correlation has been addressed in several publications but the picture is not complete. Since 2007, enzyme-replacement therapy (ERT) has been available for patients with MPS VI in the Netherlands. The purpose of our study was to learn more about the genotype-phenotype correlations in MPS VI and the antibody response to ERT with galsulfase (recombinant human arylsulfatase B).

Methods

We identified ARSB mutations in 12 patients and used site-directed mutagenesis to study their effect. Antibody levels to galsulfase were measured using ELISA and a semi-quantitative immunoprecipitation method. We assessed the in vitro inhibitory effect of antibodies on galsulfase uptake and their effect on clinical outcome.

Results

Five patients had a rapidly progressive phenotype and seven a slowly progressive phenotype. In total 9 pathogenic mutations were identified including 4 novel mutations (N301K, V332G, A237D, and c.1142 + 2 T > C) together composing 8 pathogenic genotypes. Most mutations appeared not to affect the synthesis of ARSB (66 kD precursor), but to hamper its maturation (43 kD ARSB). Disease severity was correlated with urinary GAG excretion. All patients developed antibodies to galsulfase within 26 weeks of treatment. It was demonstrated that these antibodies can inhibit the uptake of galsulfase in vitro.

Conclusions

The clinical phenotypes and the observed defects in the biosynthesis of ARSB show that some of the mutations that we identified are clearly more severe than others. Patients receiving galsulfase as enzyme-replacement therapy can develop antibodies towards the therapeutic protein. Though most titers are modest, they can exceed a level at which they potentially affect the clinical outcome of enzyme-replacement therapy.

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.

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.

Expert recommendations for the laboratory diagnosis of MPS VI

Mucopolysaccharidosis VI (MPS VI) is a lysosomal storage disease caused by a deficiency of N-acetylgalactosamine 4-sulfatase (arylsulfatase B, ASB). This enzyme is required for the degradation of dermatan sulfate. In its absence, dermatan sulfate accumulates in cells and is excreted in large quantities in urine. Specific therapeutic intervention is available; however, accurate and timely diagnosis is crucial for maximal benefit. To better understand the current practices for diagnosis and to establish diagnostic guidelines, an international MPS VI laboratory diagnostics scientific summit was held in February of 2011 in Miami, Florida. The various steps in the diagnosis of MPS VI were discussed including urinary glycosaminoglycan (uGAG) analysis, enzyme activity analysis, and molecular analysis. The following conclusions were reached. Dilute urine samples pose a significant problem for uGAG analysis and MPS VI patients can be missed by quantitative uGAG testing alone as dermatan sulfate may not always be excreted in large quantities. Enzyme activity analysis is universally acknowledged as a key component of diagnosis; however, several caveats must be considered and the appropriate use of reference enzymes is essential. Molecular analysis supports enzyme activity test results and is essential for carrier testing, subsequent genetic counseling, and prenatal testing. Overall the expert panel recommends caution in the use of uGAG screening alone to rule out or confirm the diagnosis of MPS VI and acknowledges enzyme activity analysis as a critical component of diagnosis. Measurement of another sulfatase enzyme to exclude multiple sulfatase deficiency was recommended prior to the initiation of therapy. When feasible, the use of molecular testing as part of the diagnosis is encouraged. A diagnostic algorithm for MPS VI is provided.

Diagnosis of the mucopolysaccharidoses

The mucopolysaccharidoses (MPSs) often present a diagnostic challenge, particularly for patients who have more slowly progressive disease phenotypes, as early disease manifestations can be subtle or non-specific. However, certain types of bone and joint involvement should always prompt consideration of an MPS diagnosis, such as early joint involvement without classic inflammatory features or erosive bone lesions, claw hand, spinal deformities or dysostosis multiplex. All such patients should be referred to a geneticist or metabolic specialist for diagnostic evaluation. The earlier the diagnosis is made, the better the potential outcome of treatment. Each type of MPS is associated both with deficient activity of a specific lysosomal enzyme that degrades specific glycosaminoglycans (GAGs) and with abnormalities in urinary GAG excretion. MPS patients usually excrete excess GAG in urine and/or have different relative proportions of types of GAG in urine as compared with age-matched normal subjects. Although urinary GAG analyses (both quantitative and qualitative) can suggest the most likely type of MPS, diagnosis must be confirmed by enzyme assay. Multiple assays may be necessary to identify the disease subtype. Correct identification of the MPS type is essential to guide treatment and management decisions.

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.