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.

Morquio B disease: From pathophysiology towards diagnosis

Morquio B disease is an attenuated phenotype within the spectrum of beta galactosidase (GLB1) deficiencies. It is characterised by dysostosis multiplex, ligament laxity, mildly coarse facies and heart valve defects due to keratan sulphate accumulation, predominantly in the cartilage. Morquio B patients have normal neurological development, setting them apart from those with the more severe GM1 gangliosidosis. Morquio B disease, with an incidence of 1:250.000 to 1:1.000.000 live births, is very rare. Here we report the clinical-biochemical data of nine patients. High amounts of keratan sulfate were detected using LC-MS/MS in the patients' urinary samples, while electrophoresis, the standard procedure of qualitative glycosaminoglycans analysis, failed to identify this metabolite in any of the patients' samples. We performed molecular analyses at gene, gene expression and protein expression levels, for both isoforms of the GLB1 gene, lysosomal GLB1, and the cell-surface expressed Elastin Binding Protein. We characterised three novel GLB1 mutations [c.75 + 2 T > G, c.575A > G (p.Tyr192Cys) and c.2030 T > G (p.Val677Gly)] identified in three heterozygous patients. We also set up a copy number variation assay by quantitative PCR to evaluate the presence of deletions/ insertions in the GLB1 gene. We propose a diagnostic plan, setting out the specific clinical- biochemical and molecular features of Morquio B, in order to avoid misdiagnoses and improve patients' management.

Morquio B Disease. Disease Characteristics and Treatment Options of a Distinct GLB1-Related Dysostosis Multiplex

Morquio B disease (MBD) is an autosomal recessive GLB1-gene-related lysosomal storage disease, presenting with a peculiar type of dysostosis multiplex which is also observed in GALNS-related Morquio A disease. MBD may present as pure skeletal phenotype (pure MBD) or in combination with the neuronopathic manifestations seen in type 2 (juvenile) or type 3 (late onset) GM1 gangliosidosis (MBD plus). The main skeletal features are progressive growth impairment, kyphoscoliosis, coxa/genua valga, joint laxity, platyspondyly and odontoid hypoplasia. The main neuronopathic features are dystonia, ataxia, and intellectual/developmental/speech delay. Spinal cord compression occurs as a complication of spinal dysostosis. Chronic pain is reported, along with mobility issues and challenges with daily living and self-care activities, as the most common health concern. The most commonly reported orthopedic surgeries are hip and knee replacements. Keratan sulphate-derived oligosaccharides are characteristic biomarkers. Residual β-galactosidase activities measured against synthetic substrates do not correlate with the phenotype. W273 L and T500A are the most frequently observed GLB1 variants in MBD, W273L being invariably associated with pure MBD. Cytokines play a role in joint destruction and pain, providing a promising treatment target. In the future, patients may benefit from small molecule therapies, and gene and enzyme replacement therapies, which are currently being developed for GM1 gangliosidosis.

Mucopolysaccharidosis IVA: Diagnosis, Treatment, and Management

Mucopolysaccharidosis type IVA (MPS IVA, or Morquio syndrome type A) is an inherited metabolic lysosomal disease caused by the deficiency of the N-acetylglucosamine-6-sulfate sulfatase enzyme. The deficiency of this enzyme accumulates the specific glycosaminoglycans (GAG), keratan sulfate, and chondroitin-6-sulfate mainly in bone, cartilage, and its extracellular matrix. GAG accumulation in these lesions leads to unique skeletal dysplasia in MPS IVA patients. Clinical, radiographic, and biochemical tests are needed to complete the diagnosis of MPS IVA since some clinical characteristics in MPS IVA are overlapped with other disorders. Early and accurate diagnosis is vital to optimizing patient management, which provides a better quality of life and prolonged life-time in MPS IVA patients. Currently, enzyme replacement therapy (ERT) and hematopoietic stem cell transplantation (HSCT) are available for patients with MPS IVA. However, ERT and HSCT do not have enough impact on bone and cartilage lesions in patients with MPS IVA. Penetrating the deficient enzyme into an avascular lesion remains an unmet challenge, and several innovative therapies are under development in a preclinical study. In this review article, we comprehensively describe the current diagnosis, treatment, and management for MPS IVA. We also illustrate developing future therapies focused on the improvement of skeletal dysplasia in MPS IVA.

Newborn screening for Morquio disease and other lysosomal storage diseases: results from the 8-plex assay for 70,000 newborns

BACKGROUND

The necessity of early treatment for lysosomal storage diseases (LSDs) has triggered the development of newborn screening for LSDs in recent years. Here we report the first 70,000 newborns screened for Mucopolysaccharidosis (MPS) type 4A (Morquio syndrome) and other LSDs by an 8-plex assay including the original 4-plex LSD screening tandem mass spectrometry (MS/MS) assay for Pompe disease, Fabry disease, Gaucher disease, and MPS I disease.

METHODS

The additional reaction for MPS II, MPS 3B, MPS 4A, and MPS 6 enzymes was performed separately from the 4-plex reaction. The two reactions were quenched and extracted, then combined before carrying out a single 2-min UPLC-MS/MS analysis.

RESULTS

From Mar. 2018 to Apr. 2019, 73,743 newborns were screened with the 8-plex LSD screening assay. The 8-plex assay revealed a better analytical precision than the previous 4-plex assay possibly because the 8-plex was carried out using UPLC-MS/MS. Six newborns were found to have low MPS-4A enzyme (N-acetylgalactosamine-6-sulfatase) activity and biallelic GALNS pathogenic mutations in trans; these patients are presumably affected with MPS4A, making an incidence of one in 12,291 (95% confident interval (CI): 5633-26,817). One mutation, c.857C > T (p.T286 M) of the GALNS gene, accounted 5 of the 12 mutated alleles. These newborns had immature vertebral bodies at 1 month of age, and one case was treated with elosulfase alfa 2 mg/kg/week starting from 4 months of age. Among other MPSs screened, one case of MPS I, 3 cases of MPS II, and 3 cases of MPS 3B were detected. One case of mucolipidosis type III was also diagnosed. In conjunction with another 9 patients of Pompe disease, Gaucher disease, and classical Fabry disease, making an incidence of LSDs as one in 3206 newborns (95% CI: 2137 - 4811). The one with infantile-onset Pompe disease and the one with Gaucher disease were treated since the age of 8 days and 41 days respectively.

CONCLUSIONS

Routine newborn screening of MPS 4A and other LSDs were made possible by the 8-plex LSD screening assay. However, detailed phenotype prediction and the time to start treatment will need further elucidation.

Taiwan National Newborn Screening Program by Tandem Mass Spectrometry for Mucopolysaccharidoses Types I, II, and VI

OBJECTIVE

To evaluate the initial cutoff values, rates of screen positives, and genotypes for the large-scale newborn screening program for multiple mucopolysaccharidoses (MPS) in Taiwan.

STUDY DESIGN

More than 100 000 dried blood spots were collected consecutively as part of the national Taiwan newborn screening programs. Enzyme activities were measured by tandem mass spectrometry from dried blood spot punches. Genotypes were obtained when a second newborn screening specimen again had a decreased enzyme activity. Additional clinical evaluation was then initiated based on enzyme activity and/or genotype.

RESULTS

Molecular genetic analysis for cases with low enzyme activity revealed 5 newborns with pathogenic alpha-L-iduronidase mutations, 3 newborns with pathogenic iduronate-2-sulfatase mutations, and 1 newborn was a carrier of an arylsulfatase B mutation. Several variants of unknown pathogenic significance were also identified, most likely causing pseudodeficiency.

CONCLUSIONS

The highly robust tandem mass spectrometry-based enzyme assays for MPS-I, MPS-II, and MPS-VI allow for high-throughput newborn screening for these lysosomal storage disorders. Optimized cutoff values combined with second tier testing could largely eliminate false-positive results. Accordingly, newborn screening for these lysosomal storage disorders is possible.

Association of Mucopolysaccharidosis Type 4A and Bartter Syndrome

A 6-year-old Syrian boy presented with complaints of facial dysmorphism and difficulty of walking. He had coarse face, macrocephaly, pectus carinatum, x-bain deformity, kyphosis, corneal clouding, and claw hand deformity. Galactose-6 sulphatase enzyme level was 0.1 nmol/mg.17 h (reference range, > 68 nmol/mg.17 h), compatible with Morquio syndrome. On laboratory examinations, potassium level was 2.9 mmol/L (reference range, 3.5 mmol/L to 5.1 mmol/L), sodium level was 130 mmol/L (reference range, 135 mmol/L to 148 mmol/L), and chloride level was 92 mmol/L (reference range, 101 mmol/L to 109 mmol/L). Blood pH was 7.5 and bicarbonate level was 31 mEq/L. Urine sodium and chloride levels were high. Arterial blood pressure was normal and these findings were consistent with Bartter syndrome. This is the first report of a patient with the association of Bartter syndrome and mucopolysaccharidosis type 4A, which was thought to be coincidental.

Widespread Vasculopathy in a Patient with Morquio A Syndrome

Morquio A syndrome (mucopolysaccharidosis IV type A), an autosomal recessive lysosomal storage disorder caused by a defective N-acetylgalactosamine 6-sulfatase gene, leads to lysosomal accumulation of keratan sulfate and chondroitin 6-sulfate. This accumulation affects multiple systems and causes notable cardiovascular manifestations, such as thickening of the left-sided valves, ventricular hypertrophy, and intimal stenosis of the coronary arteries. There have been few reports of vasculopathy in this population. We present the case of a 58-year-old woman with Morquio A syndrome who was found to have aortic dilation on a routine screening echocardiogram. Magnetic resonance images revealed multiple tortuous, dilated arteries in her head, neck, and abdomen. The diffuse vasculopathy seen in this patient should prompt further study to determine whether this is an underreported phenomenon of clinical significance or an unusual finding in this rare disorder.

Bio-Plex immunoassay measuring the quantity of lysosomal N-acetylgalactosamine-6-sulfatase protein in dried blood spots for the screening of mucopolysaccharidosis IVA in newborn: a pilot study

OBJECTIVE

Mucopolysaccharidosis (MPS) IVA (Morquio syndrome A) is an autosomal-recessive lysosomal storage disorder caused by the deficiency of N-acetylgalactosamine-6-sulfatase (GALNS) resulting in excessive lysosomal storage of keratan sulfate. Treatments for MPS IVA have recently become available with optimal outcomes associated with early diagnosis and treatment which can be achieved by newborn screening.

DESIGN

Newborn screening programme for MPS IVA pilot study.

SETTING

MacKay Memorial Hospital (MMH), Taipei and another three branch hospitals in Taiwan.

PARTICIPANTS

A total of 7415 newborns were born in four branch hospitals of MMH and had joined the MPS IVA newborn screening programme. Written informed consents were obtained from parents prior to the screening process (12MMHIS188 approved by MacKay Memorial Hospital Institutional Review Board).

OUTCOME MEASURES

An alternative newborn screening method for MPS IVA has been performed. Screening involved measuring the quantity of GALNS in dried blood spot (DBS) from newborn infants using the Bio-Plex immunoassay. The amount of fluorescence sorting detected by yttrium aluminium garnet laser was proportional to the quantity of GALNS protein.

RESULTS

Of the 7415 neonates analysed, eight infants whose GALNS levels were below the cut-off value of 8.30 µg/L had been recalled for a second DBS collection. The reference values were 8.30-27.43 µg/L. In patients with confirmed MPS IVA (n=11), the GALNS quantities were far below 5% of the normal population.

CONCLUSION

The Bio-Plex immunoassay is a validated method used for measuring GALNS protein in DBS and has the potential to be adopted for MPS IVA newborn screening study design.

Mucopolysaccharidosis IVA and glycosaminoglycans

Mucopolysaccharidosis IVA (MPS IVA; Morquio A: OMIM 253000) is a lysosomal storage disease with an autosomal recessive trait caused by the deficiency of N-acetylgalactosamine-6-sulfate sulfatase. Deficiency of this enzyme leads to accumulation of specific glycosaminoglycans (GAGs): chondroitin-6-sulfate (C6S) and keratan sulfate (KS). C6S and KS are mainly produced in the cartilage. Therefore, the undegraded substrates are stored primarily in cartilage and in its extracellular matrix (ECM), leading to a direct impact on cartilage and bone development, and successive systemic skeletal dysplasia. Chondrogenesis, the earliest phase of skeletal formation, is maintained by cellular interactions with the ECM, growth and differentiation factors, signaling pathways, and transcription factors in a temporal-spatial manner. In patients with MPS IVA, the cartilage is disrupted at birth as a consequence of abnormal chondrogenesis and/or endochondral ossification. The unique skeletal features are distinguished by a disproportional short stature, odontoid hypoplasia, spinal cord compression, tracheal obstruction, pectus carinatum, kyphoscoliosis, platyspondyly, coxa valga, genu valgum, waddling gait, and laxity of joints. In spite of many descriptions of these unique clinical features, delay of diagnosis still happens. The pathogenesis and treatment of systemic skeletal dysplasia in MPS IVA remains an unmet challenge. In this review article, we comprehensively describe historical aspect, property of GAGs, diagnosis, screening, pathogenesis, and current and future therapies of MPS IVA.

Diagnosis of Morquio Syndrome in Dried Blood Spots Based on a New MRM-MS Assay

Background

Mucopolysaccharidosis IVA (MPS IVA; Morquio A disease) is an autosomal recessive disease caused and characterized by a decreased activity of N-acetylgalactosamine-6-sulfate sulfatase (GALNS), resulting in accumulation of keratan sulfate and chondroitin-6-sulfate in tissues and secondary organ damage. Recently approved enzyme replacement therapy renders the easy and early identification of MPS IVA of out-most importance.

Methodology

We propose a completely new assay for the stable and reproducible detection of GALNS deficiency in dry blood spots (DBS). For the validation blood samples were taken from 59 healthy individuals and 24 randomly selected genetically confirmed MPS IVA patients. The material extracted from DBS was incubated with a 4-methylumbelliferyl-β-D-galactopyranoside-6-sulfate as a specific substrate. Final enzymatic product, 4-methylumbelliferone, obtained after adding exogenous beta-galactosidase, was quantified by LC/MRM-MS (liquid-chromatography/multiple-reaction-monitoring mass-spectrometry). 4-propyl-5-hydroxy-7-methyl-2h-chromen-2-one was used as internal standard, a compound with a similar molecular structure and fragmentation pattern in negative ion mode as 4-methylumbelliferone.

Findings

The enzymatic assay yielded a positive and negative predictive value of 1.0 for genetically confirmed MPS IVA patients (GALNS activity of 0.35 ± 0.21 μmol/L/h) and for controls with normal GALNS activity (23.1 ± 5.3 μmol/L /h). With present enzymatic conditions, the reaction yield in dried blood spots is at least 20 fold higher than any previously reported data with other assays.

Interpretation

The present LC/MRM-MS based assay for MPS IVA diagnosis provides an easy, highly-standardized, accurate and innovative quantification of the enzymatic product in vitro and distinguishes perfectly between MPS IVA affected patients and normal controls. This technique will significantly simplify the early detection of MPS IVA patients.

Morquio A syndrome: diagnosis and current and future therapies

Morquio A syndrome is an autosomal recessive disorder, one of 50 lysosomal storage diseases (LSDs), and is caused by the deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS). Deficiency of this enzyme causes specific glycosaminoglycan (GAG) accumulation: keratan sulfate (KS) and chondroitin-6-sulfate (C6S). The majority of KS is produced in the cartilage, therefore, the undegraded substrates accumulate mainly in cartilage and in its extracelluar matrix (ECM), causing direct leads to direct impact on cartilage and bone development and leading to the resultant systemic skeletal spondyloepiphyseal dysplasia. Chondrogenesis ,the earliest phase of skeletal formation that leads to cartilage and bone formation is controlled by cellular interactions with the ECM, growth and differentiation factors and other molecules that affect signaling pathways and transcription factors in a temporal-spatial manner. In Morquio A patients, in early childhood or even at birth, the cartilage is disrupted presumably as a result of abnormal chondrogenesis and/ or endochondral ossification. The unique clinical features are characterized by a marked short stature, odontoid hypoplasia, protrusion of the chest, kyphoscoliosis, platyspondyly, coxa valga, abnormal gait, and laxity of joints. In spite of many descriptions of the unique clinical manifestations, diagnosis delay still occurs. The pathogenesis of systemic skeletal dysplasia in Morquio A syndrome remains an enigmatic challenge. In this review article, screening, diagnosis, pathogenesis and current and future therapies of Morquio A are discussed.

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.

Radiological and clinical characterization of the lysosomal storage disorders: non-lipid disorders

Lysosomal storage diseases (LSDs) are a large group of genetic metabolic disorders that result in the accumulation of abnormal material, such as mucopolysaccharides, glycoproteins, amino acids and lipids, within cells. Since many LSDs manifest during infancy or early childhood, with potentially devastating consequences if left untreated, timely identification is imperative to prevent irreversible damage and early death. In this review, the key imaging features of the non-lipid or extralipid LSDs are examined and correlated with salient clinical manifestations and genetic information. Disorders are stratified based on the type of excess material causing tissue or organ dysfunction, with descriptions of the mucopolysaccharidoses, mucolipidoses, alpha-mannosidosis, glycogen storage disorder II and cystinosis. In addition, similarities and differences in radiological findings between each of these LSDs are highlighted to facilitate further recognition. Given the rare and extensive nature of the LSDs, mastery of their multiple clinical and radiological traits may seem challenging. However, an understanding of the distinguishing imaging characteristics of LSDs and their clinical correlates may allow radiologists to play a key role in the early diagnosis of these progressive and potentially fatal disorders.

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.

Pathogenesis of Morquio A syndrome: an autopsied case reveals systemic storage disorder

Mucopolysaccharidosis IVA (MPS IVA; Morquio A syndrome) is a lysosomal storage disorder caused by deficiency of N-acetylgalactosamine-6-sulfate sulfatase, which results in systemic accumulation of glycosaminoglycans (GAGs), keratan sulfate and chondroitin-6-sulfate. Accumulation of these GAGs causes characteristic features as disproportionate dwarfism associated with skeletal deformities, genu valgum, pigeon chest, joint laxity, and kyphoscoliosis. However, the pathological mechanism of systemic skeletal dysplasia and involvement of other tissues remain unanswered in the paucity of availability of an autopsied case and successive systemic analyses of multiple tissues. We report here a 20-year-old male autopsied case with MPS IVA, who developed characteristic skeletal features by the age of 1.5 years and died of acute respiratory distress syndrome five days later after occipito-C1-C2 cervical fusion. We pathohistologically analyzed postmortem tissues including trachea, lung, thyroid, humerus, aorta, heart, liver, spleen, kidney, testes, bone marrow, and lumbar vertebrae. The postmortem tissues relevant with clinical findings demonstrated 1) systemic storage materials in multiple tissues beyond cartilage, 2) severely vacuolated and ballooned chondrocytes in trachea, humerus, vertebrae, and thyroid cartilage with disorganized extracellular matrix and poor ossification, 3) appearance of foam cells and macrophages in lung, aorta, heart valves, heart muscle, trachea, visceral organs, and bone marrow, and 4) storage of chondrotin-6-sulfate in aorta. This is the first autopsied case with MPS IVA whose multiple tissues have been analyzed pathohistologically and these pathological findings should provide a new insight into pathogenesis of MPS IVA.

The Morquio A Clinical Assessment Program: baseline results illustrating progressive, multisystemic clinical impairments in Morquio A subjects

OBJECTIVES

The objectives of this study are to quantify endurance and respiratory function and better characterize spectrum of symptoms and biochemical abnormalities in mucopolysaccharidosis IVA subjects.

METHODS

MorCAP was a multicenter, multinational, cross sectional study amended to be longitudinal in 2011. Each study visit required collection of medical history, clinical assessments, and keratan sulfate (KS) levels.

RESULTS

Data from the first visit of 325 subjects (53% female) were available. Mean age was 14.5 years. Mean ± SD height z-scores were -5.6 ± 3.1 as determined by the CDC growth charts. Mean ± SD from the 6-minute-walk-test was 212.6 ± 152.2m, revealing limitations in functional endurance testing, and 30.0 ± 24.0 stairs/min for the 3-minute-stair-climb test. Respiratory function showed limitations comparable to MPS VI patients; mean ± SD was 1.2 ± 0.9l based on forced vital capacity and 34.8 ± 25.5l/min based on maximum voluntary ventilation. Mean urinary keratan sulfate (uKS) was elevated for all ages, and negatively correlated with age. Higher uKS correlated with greater clinical impairment based on height z-scores, endurance and respiratory function tests. The MPS Health Assessment Questionnaire reveals impairments in mobility and activities of daily living in comparison to an age-matched control population.

CONCLUSIONS

MPS IVA is a multisystem disorder with a continuum of clinical presentation. All affected individuals experience significant functional limitations and reduced quality of life. Older patients have more severe exercise and respiratory capacity limitations, and more frequent cardiac pathology illustrating the progressive nature of disease.

Diagnosing mucopolysaccharidosis IVA

Mucopolysaccharidosis IVA (MPS IVA; Morquio A syndrome) is an autosomal recessive lysosomal storage disorder resulting from a deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS) activity. Diagnosis can be challenging and requires agreement of clinical, radiographic, and laboratory findings. A group of biochemical genetics laboratory directors and clinicians involved in the diagnosis of MPS IVA, convened by BioMarin Pharmaceutical Inc., met to develop recommendations for diagnosis. The following conclusions were reached. Due to the wide variation and subtleties of radiographic findings, imaging of multiple body regions is recommended. Urinary glycosaminoglycan analysis is particularly problematic for MPS IVA and it is strongly recommended to proceed to enzyme activity testing even if urine appears normal when there is clinical suspicion of MPS IVA. Enzyme activity testing of GALNS is essential in diagnosing MPS IVA. Additional analyses to confirm sample integrity and rule out MPS IVB, multiple sulfatase deficiency, and mucolipidoses types II/III are critical as part of enzyme activity testing. Leukocytes or cultured dermal fibroblasts are strongly recommended for enzyme activity testing to confirm screening results. Molecular testing may also be used to confirm the diagnosis in many patients. However, two known or probable causative mutations may not be identified in all cases of MPS IVA. A diagnostic testing algorithm is presented which attempts to streamline this complex testing process.

Spinal involvement in mucopolysaccharidosis IVA (Morquio-Brailsford or Morquio A syndrome): presentation, diagnosis and management

Mucopolysaccharidosis IVA (MPS IVA), also known as Morquio-Brailsford or Morquio A syndrome, is a lysosomal storage disorder caused by a deficiency of the enzyme N-acetyl-galactosamine-6-sulphate sulphatase (GALNS). MPS IVA is multisystemic but manifests primarily as a progressive skeletal dysplasia. Spinal involvement is a major cause of morbidity and mortality in MPS IVA. Early diagnosis and timely treatment of problems involving the spine are critical in preventing or arresting neurological deterioration and loss of function. This review details the spinal manifestations of MPS IVA and describes the tools used to diagnose and monitor spinal involvement. The relative utility of radiography, computed tomography (CT) and magnetic resonance imaging (MRI) for the evaluation of cervical spine instability, stenosis, and cord compression is discussed. Surgical interventions, anaesthetic considerations, and the use of neurophysiological monitoring during procedures performed under general anaesthesia are reviewed. Recommendations for regular radiological imaging and neurologic assessments are presented, and the need for a more standardized approach for evaluating and managing spinal involvement in MPS IVA is addressed.

Intellectual and neurological functioning in Morquio syndrome (MPS IVa)

Mucopolysaccharidosis type IVa (MPS IVa, Morquio syndrome OMIM #253000) is a lysosomal storage disease caused by deficiency in N-acetylgalactosamine-6-sulfatase (GALNS, EC 3.1.6.4; encoded by GALNS gene at 16q24.3). Unlike other MPS disorders involving excessive heparan and dermatan sulfate, Morquio syndrome has not been associated with neurological involvement nor with intellectual impairment as this disorder of keratan sulfate has been described as a purely visceral and skeletal disorder. Neurocognitive assessment was undertaken of MPS IVa patients with age appropriate intellectual tests as well as a Child Behaviour Checklist as part of clinical follow up. Available neuroimaging studies (MRI and MR spectroscopy) were reviewed. Whilst more than half of the overall IQ scores fell in the average range, scores for 3/8 children fell below average. A number of behavioural problems were highlighted, including anxiety/depression, attention and somatic complaints. Subtle neuroimaging abnormalities were demonstrated in over half of the children. These findings present a challenge to existing assumptions about the nature of Morquio A syndrome. A hypothesis regarding the potential role of calcium signalling is explored.

Enzyme replacement therapy attenuates disease progression in two Japanese siblings with mucopolysaccharidosis type VI

Mucopolysaccharidosis type VI (MPS VI) is a progressive, multisystem autosomal recessive lysosomal disorder resulting from deficient N-acetylgalactosamine-4-sulphatase (ASB) and the consequent accumulation of glycosaminoglycan (GAG). Preclinical and clinical studies had demonstrated clinical benefits of early initiation of systemic therapies in patients with MPS. In this case report, two siblings with MPS VI started enzyme replacement therapy (ERT) with weekly infusions of recombinant human ASB (Galsulfase) at 1mg/kg. Sibling 1 started ERT 5.6 years of age and Sibling 2 was 6 weeks old. The disease status in these two siblings prior to and for no less than 36 months of ERT was followed up and compared. The treatment was well tolerated by both siblings. During 36 months of ERT, symptoms typical of MPS VI including short stature, progressive dysmorphic facial features, hepatosplenomegaly, hearing impairment, corneal clouding, and dysostosis multiplex were largely absent in the younger sibling. Her cardiac functions and joint mobility were well preserved. On the other hand, her affected brother had typical MPS VI phenotypic features described above before commencing ERT at the equivalent age, of 3 years. There was significant improvement in the shoulder range of motion and hearing loss after 36 months of treatment and cardiac function was largely preserved. His skeletal deformity and short stature remained unchanged. The results showed that early ERT initiated at newborn is safe and effective in preventing or slowing down disease progression of MPS VI including bone deformities. These observations indicate that early diagnosis and treatment of MPS VI before development of an irreversible disease is critical for optimal clinical outcome.

Placenta analysis of prenatally diagnosed patients reveals early GAG storage in mucopolysaccharidoses II and VI

We analyzed placental tissue in one fetus with MPS II (iduronate sulphatase deficiency) and another with MPS VI (arylsulfatase B deficiency). Both were diagnosed prenatally, but families decided to continue pregnancies and placentas were collected at birth. We were able to demonstrate early storage of GAGs in both diseases by GAG measurement and microscopy analysis. Our results suggest that some alterations related to MPS storage, although not pronounced, may be observed in placental tissue of patients affected by MPS II and MPS VI.

Enzyme replacement therapy for mucopolysaccharidosis VI--experience in Taiwan

Information regarding the clinical outcome of enzyme replacement therapy (ERT) with recombinant human N-acetylgalactosamine 4-sulfatase (rhASB) for mucopolysaccharidosis (MPS) VI in Asian patients is limited. We reviewed nine Taiwanese patients with MPS VI (four males and five females; age range 1.4-21.1 years) treated with weekly intravenous infusions of rhASB (1.0 mg/kg) for at least 2 years. We assessed the biochemical and clinical response every 3 months. After 2 years of treatment, seven patients experienced improvement over baseline in the 6-min walk by a mean of 69.3 m (27.3%), and seven also increased the 3-min stair climb by a mean of 47 steps (35.7%). Shoulder range of motion in all patients improved, and Joint Pain and Stiffness Questionnaire scores improved by 0.597 points (30.5%). Four patients had improved pulmonary function [forced expiratory volume in 1 s increased by 0.130 L (26.3%) and forced vital capacity by 0.148 L (27.6%)]. The respiratory disturbance index decreased in the four patients who underwent polysomnography. A mean overall 51% decrease in urinary glycosaminoglycan excretion indicated a satisfactory biochemical response. ERT was well tolerated by all patients. This treatment is thus beneficial and appears to be safe for treatment of MPS VI in Taiwanese patients.

Validation of keratan sulfate level in mucopolysaccharidosis type IVA by liquid chromatography-tandem mass spectrometry

Mucopolysaccharidosis type IVA (MPS IVA, Morquio A disease), a progressive lysosomal storage disease, causes skeletal chondrodysplasia through excessive storage of keratan sulfate (KS). KS is synthesized mainly in cartilage and released to the circulation. The excess storage of KS disrupts cartilage, consequently releasing more KS into circulation, which is a critical biomarker for MPS IVA. Thus, assessment of KS level provides a potential screening strategy and determines clinical course and efficacy of therapies. We have recently developed a tandem mass spectrometry liquid chromatography [LC/MS/MS] method to assay KS levels in blood. Forty-nine blood specimens from patients with MPS IVA [severe (n = 33), attenuated (n = 11) and undefined (n = 5)] were analyzed for comparison of blood KS concentration with that of healthy subjects and for correlation with clinical severity. Plasma samples were digested by keratanase II to obtain disaccharides of KS. Digested samples were assayed by LC/MS/MS. We found that blood KS levels (0.4-26 µg/ml) in MPS IVA patients were significantly higher than those in age-matched controls (0.67-4.6 µg/ml; P < 0.0001). It was found that blood KS level varied with age and clinical severity in the patients. Blood KS levels in MPS IVA peaked between 2 years and 5 years of age (mean 11.4 µg/ml). Blood KS levels in severe MPS IVA (mean 7.3 µg/ml) were higher than in the attenuated form (mean 2.1 µg/ml) (P = 0.012). We also found elevated blood KS levels in other types of MPS. These findings indicate that the new KS assay for blood is suitable for early diagnosis and longitudinal assessment of disease severity in MPS IVA.

[Dyggve-Melchior-Clausen syndrome, diagnostic difficulty due to it similarity to Morquio disease]

INTRODUCTION

Dyggve-Melchior-Clausen syndrome (DMCS) is a rare autosomal recessive disorder produced by mutations in the Dymeclin gene recently identified. It is characterized by the association of a progressive spondylo-epi-metaphyseal dysplasia and mental retardation ranging from mild to severe. The clinical and radiological similarities at the onset of the condition with the Morquio disease may hinder its diagnosis and no biochemical abnormality that causes it has been described as of yet.

CLINICAL CASE

An eight-year-old girl had progressive postnatal dwarfism. Platyspondyly and dysplasic epiphyses and metaphyses with biochemical studies that resembled those of Morquio's disease; however the presence of specific radiological features and mental retardation led to the diagnosis of DMCS. A missense Dym mutation in homozygosis was identified.

CONCLUSION

This entity should be known as it may be easily confused with Morquio disease. Radiological appearance of the iliac crests are very pathognomonic of DMCS. Identification of Dym gene is an important step towards the prenatal diagnosis.

[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.

Morquio's syndrome: severe aortic regurgitation and late pulmonary autograft failure

A 44-year-old woman underwent a Ross procedure for severe aortic regurgitation at the age of 32 years. She had been diagnosed in childhood with spondyloepiphyseal dysplasia and a bicuspid aortic valve. At surgery, a tricuspid aortic valve with chondroid metaplasia and fibrosis was reported. Biochemical and genetic evaluation in this patient confirmed the diagnosis of mucopolysaccharidosis IV type B (MPS IV), otherwise known as Morquio's syndrome. This autosomal-recessive inherited syndrome is characterized by the accumulation of keratin sulfate in connective tissue and various other organs. Cardiac (notably valvular) involvement has been well described in the literature. To the authors' knowledge, this is the first reported case of valve replacement or Ross procedure for this condition. This woman presented 12 years after her initial valve surgery with progressive dyspnea. Echocardiographic examination revealed severe pulmonic autograft regurgitation without a dilated aortic root, together with severe stenosis of the pulmonary homograft. It is postulated that the underlying metabolic abnormality may have led to progressive pulmonary autograft failure and to accelerated dysfunction and stenosis of the pulmonary homograft. It is likely that a mechanical prosthesis would have been a better therapeutic option if the preoperative diagnosis of MPS IV had been made.

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.

An adult with Morquio syndrome

We report a case of a 25-year-old male who came to endocrine clinic to get medical certificate so as to claim as the shortest man of the world. He was evaluated for short stature and eventually diagnosed with type-IV mucopolysaccharidosis (MPS) or Morquio syndrome.

Development of an assay for the detection of mucopolysaccharidosis type VI patients using dried blood-spots

BACKGROUND

Mucopolysaccharidosis type VI (MPS VI) is a lysosomal storage disorder (LSD), which is caused by a deficiency in the enzyme N-acetylgalactosamine 4-sulfatase (4-sulfatase). MPS VI is characterized by severe skeletal abnormalities, somatic tissue pathology and early death. Treatment possibilities include bone marrow transplantation (BMT) and enzyme replacement therapy (ERT; currently in phase III clinical trial). Early diagnosis of MPS VI will allow treatment before the onset of irreversible pathology.

METHODS

Sensitive immune assays have been developed to detect 4-sulfatase protein and activity in normal control and MPS VI blood-spots.

RESULTS

Dried blood-spots from MPS VI patients contained no detectable 4-sulfatase protein and activity, compared to 3.5-21 microg/L of 4-sulfatase protein and 291-1298 nmol/min/L of activity for normal human controls. In this evaluation study, the assay was sensitive and 100% specific, allowing reliable detection of individuals with MPS VI.

CONCLUSIONS

The assays reported here have the potential to detect MPS VI patients using dried blood-spots.

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.

Development and testing of new screening method for keratan sulfate in mucopolysaccharidosis IVA

Mucopolysaccharidosis IVA (MPS IVA), a progressive lysosomal storage disease, causes skeletal dysplasia through excessive storage of keratan sulfate (KS). We developed an ELISA-sandwich assay that used a MAb specific to KS. Forty-five blood and 59 urine specimens from MPS IVA patients (ages 1-65 y) were analyzed to determine whether KS concentration is a suitable marker for early diagnosis and longitudinal assessment of disease severity. Blood specimens were obtained from patients categorized as phenotypically severe (n = 36) and milder (n = 9). Urine specimens were also analyzed from patients categorized as severe (n = 56) and milder (n = 12), respectively. Blood KS levels (101-1525 ng/mL) in MPS IVA patients were two to eight times higher than those in age-matched controls (15-323 ng/mL). It was found that blood KS level varied with age and clinical severity. Blood KS levels in both MPS IVA and controls peaked between 5 and 10 y of age (mean, 776 versus 234 ng/mL, respectively). Blood levels in severe MPS IVA were 1.5 times higher than in the milder form. In contrast to blood, urine KS levels in both MPS IVA and controls peaked between 1 and 5 y (15.3 versus 0.26 mg/g creatinine), and thereafter declined with age. Urine KS level also varied with age and clinical severity, and the severe MPS IVA phenotype was associated with 6.7 times greater urine KS excretion than the milder one. These findings indicate that the new assay for blood or urine KS may be suitable for early diagnosis and longitudinal assessment of disease severity in MPS IVA.

MPS screening methods, the Berry spot and acid turbidity tests, cause a high incidence of false-negative results in sanfilippo and morquio syndromes

Because of differences in the types and quantities of glycosaminoglycans (GAGs) in various mucopolysaccharidoses (MPSs), MPS screening tests, including the Berry spot and acid turbidity tests, are not specific or sensitive enough for the preliminary diagnosis of MPS. A false-negative result is common. We analyzed urine samples collected from 492 patients who were examined for inborn errors of metabolism using the Berry spot and acid turbidity (qualitative and quantitative) tests. Of those, 48 MPS patients (seven with MPS I, 17 with MPS II, nine with MPS III, 11 with MPS IV, and four with MPS VI) underwent preliminary differentiation between MPS types by two-dimensional electrophoresis (2D-EP), and were confirmed by enzymatic assay. Approximately 21.0% and 7.1% of the 492 samples showed positive reactions in the Berry spot and acid turbidity tests, respectively. Of these, a total of 35 samples with MPS types I, II, and VI showed strong positive reactions in both tests. Five patients with Sanfilippo (MPS III) and six patients with Morquio (IV) syndromes showed false-negative results in both tests. In our study, approximately 13.8% (68 in 492 samples) samples showed a positive reaction in the Berry spot test but a negative one in the acid turbidity test, for unknown reasons. The Berry spot and acid turbidity tests are used extensively for the preliminary diagnosis of MPS in Asia; however, the possibility of a misdiagnosis of MPS type III and IV with both tests should be kept in mind. For accurate diagnosis and confirmation of MPS, the 2D-EP method and enzymatic assay are recommended. They provide high sensitivity, specificity, and efficiency in diagnosing MPS.

[Dyggve-Melchior-Clausen syndrome: differential diagnosis of mucopolysaccharidosis type IV or Morquio disease]

Dyggve-Melchior-Clausen syndrome (DMCS) is an autosomal recessive skeletal dysplasia. Clinical and radiological similarities with Morquio's syndrome can initially lead wrongly to this diagnosis.

CASE REPORT

A nine-year-old boy had mental retardation and progressive postnatal dwarfism. Platyspondyly and dysplastic epiphyses and metaphyses resembled those of Morquio's disease; however, clinical and radiological data led to the diagnosis of DMCS.

CONCLUSION

Clinical and paraclinical features allowing the differentiation of Morquio's syndrome and DMCS are discussed. Initial clinical presentation may be similar, but the intellectual prognosis is different.

Dental findings in Morquio syndrome (mucopolysaccharidoses type IVa)

Morquio syndrome is a disorder of mucopolysaccharide metabolism with specific skeletal features. The clinical and radiographic appearance of the teeth resembles hypoplastic amelogenesis imperfecta with thin enamel of normal radiodensity. The dental practitioner has a part to play in collaboration with medical colleagues in the recognition and diagnosis of this condition.

[Late diagnosis of Morquio syndrome. Clinical histopathological findings in a rare mucopolysaccharidosis]

BACKGROUND

The Morquio syndrome is a rare autosomal-recessive mucopolysaccharidosis. The Morquio syndrome is characterized by a reduced activity of N-acetylgalactosamine-6-sulfate-sulfatase (type A), or beta-galactosidase (type B). This deficiency leads to a lysosomal storage disease with accumulation of keratan sulfate und chondroitin-6-sulfate in connective tissue, skeletal system und teeth. Consequently, abnormalities of the skeletal system, aortic valvular disease and dental abnormalities occur. Ophthalmologically, diffuse corneal opacification and alterations of the trabecular meshwork--occasionally leading to glaucoma--can be found.

CASE REPORT

A 44-year-old woman asked for perforating corneal transplantation because of corneal clouding on both eyes. Besides, she suffered from dwarfism of unclear reason. The diffuse corneal clouding and the dwarfism suggested a systemic-metabolic disease. Thus, further radiologic and medical investigation was started.

RESULTS

Radiologically, a kyphoscoliosis, a pectus carinatum, a luxation of both hips, and a gonarthrosis were recognized. Fibroblast culture of a skin biopsy showed reduced activity of N-acetyl-galactosamine-6-sulfate-sulfatase. This was the proof of Morquio syndrome type A. The explanted corneal button showed granules of acid mucopolysaccharides. Those were in the epithelial and endothelial cells and in the corneal stroma.

CONCLUSIONS

To our knowledge, a Morquio syndrome has never been diagnosed with an adult and only after the ophthalmologist gave a hint. This can only be explained by the comparative mild expression of the disease in this patient. Diagnosis of Morquio syndrome is important because the frequent odontoid hypoplasia can lead to a deadly atlanto-axial instability, if not treated.

First-trimester diagnosis of Morquio disease type A

Since the introduction in 1990 of a novel fluorogenic substrate for galactose-6-sulphate sulphatase we have used this substrate for prospective prenatal diagnosis in 10 pregnancies at risk for Morquio disease type A. Chorionic villi were analysed in five cases. The results indicated an affected fetus in one pregnancy which represents the first case of first-trimester diagnosis of this disorder; heterozygosity was demonstrated in two cases. Following amniocentesis, two affected fetuses and one heterozygote were diagnosed. The results of the present prospective prenatal analyses confirm our previous retrospective studies and demonstrate the reliability and convenience of the 4-methylumbelliferyl substrate.

Morquio's syndrome. A case report and review of clinical findings

Morquio's syndrome is a genetic disorder caused by the lack of the enzyme responsible for the breakdown of the mucopolysaccharide keratin sulfate. The resulting buildup of keratin sulfate causes a specific pattern of abnormalities, including short stature, spinal deformity, cardiac abnormalities, corneal opacities, deafness and dental abnormalities. The specific dental findings in the patient described here are as follows: the posterior teeth were tapered and had pointed. cusps; the maxillary anterior teeth were spaced and flared, and on radiographs, the enamel was less than 25 percent of normal thickness but of normal radiodensity. Despite these findings, the patient exhibited a low rate of caries. This paper is a review of medical and dental findings in the Morquio's patient and how this may affect dental management.