Authors: Emma J. Dogterom, Margreet A. E. M. Wagenmakers, Martina Wilke, Serwet Demirdas, Nicole M. Muschol, Sandra Pohl, Jan C. van der Meijden, Dimitris Rizopoulos, Ans T. van der Ploeg & Esmée Oussoren

Published: June, 2021

Abstract

Purpose: Mucolipidosis (ML) II, MLIII alpha/beta, and MLIII gamma are rare autosomal recessive lysosomal storage disorders. Data on the natural course of the diseases are scarce. These data are important for counseling, therapies development, and improvement of outcome. The aim of this study is to gain knowledge on the natural history of ML by obtaining data on survival, symptom onset, presenting symptoms, diagnosis, and pathogenic variants associated with the MLII or MLIII phenotype.

Methods: A systematic review on all published MLII and MLIII cases between 1968 and August 2019 was performed.

Results: Three hundred one articles provided data on 843 patients. Median age at diagnosis: 0.7 for MLII and 9.0 years for MLIII. Median survival: 5.0 for MLII and 62.0 years for MLIIIII. Median age of death: 1.8 for MLII and 33.0 years for MLIII. Most frequent causes of death in all ML were pulmonary and/or cardiac complications. Pathogenic variants were described in 388 patients (GNPTAB: 571, GNPTG 179).

Conclusion: This review provides unique insights into the natural history of MLII and MLIII, with a clear genotype–phenotype correlation with the most frequent pathogenic variant c.3503_3504del in MLII and in MLIII alpha/beta c.22A>G for GNPTAB. All pathogenic GNPTG variants resulted in MLIII gamma.

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Authors: Shaukat A Khan, Saori C Tomatsu

Published: September, 2020

Abstract: Mucolipidosis II and III (ML II/III) are caused by a deficiency of uridine-diphosphate N-acetylglucosamine: lysosomal-enzyme-N-acetylglucosamine-1-phosphotransferase (GlcNAc-1-phosphotransferase, EC2.7.8.17), which tags lysosomal enzymes with a mannose 6-phosphate (M6P) marker for transport to the lysosome. The process is performed by a sequential two-step process: first, GlcNAc-1-phosphotransferase catalyzes the transfer of GlcNAc-1-phosphate to the selected mannose residues on lysosomal enzymes in the cis-Golgi network. The second step removes GlcNAc from lysosomal enzymes by N-acetylglucosamine-1-phosphodiester α-N-acetylglucosaminidase (uncovering enzyme) and exposes the mannose 6-phosphate (M6P) residues in the trans-Golgi network, in which the enzymes are targeted to the lysosomes by M6Preceptors. A deficiency of GlcNAc-1-phosphotransferase causes the hypersecretion of lysosomal enzymes out of cells, resulting in a shortage of multiple lysosomal enzymes within lysosomes. Due to a lack of GlcNAc-1-phosphotransferase, the accumulation of cholesterol, phospholipids, glycosaminoglycans (GAGs), and other undegraded substrates occurs in the lysosomes. Clinically, ML II and ML III exhibit quite similar manifestations to mucopolysaccharidoses (MPSs), including specific skeletal deformities known as dysostosis multiplex and gingival hyperplasia. The life expectancy is less than 10 years in the severe type, and there is no definitive treatment for this disease. In this review, we have described the updated diagnosis and therapy on ML II/III.

Keywords: I-cell disease, inclusion body, lysosome enzyme transport, lysosomal storage disorders, mannose 6-phosphate, glycosaminoglycans

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Authors: Çiğdem Seher KASAPKARA, Meltem AKÇABOY, Fehime KARA EROĞLU, and Betül Emine DERİNKUYU

Published: March, 2018

Abstract: Mucolipidoses are metabolic disorders with autosomal recessive inheritance caused by deficiency of N-acetylglucosamine- 1-phosphotransferase leading to accumulation of glycosaminoglycans and sphingolipids intracellularly. The differential diagnosis of mucolipidosis II or III is based on the age of onset, clinical findings and degree of severity. In this article, we present four pediatric patients with mucolipidosis III or pseudo-Hurler polydystrophy who admitted to our hospital with joint stiffness. They were from consanguineous families with characteristic radiographic findings. The joints were painless and the rheumatologic evaluation and inflammation markers were negative. Mucolipidosis is a rare disease in pediatric patients to remember in differential diagnosis of joint stiffness.

Keywords: Differential diagnosis; joint stiffness; mucolipidosis; pediatric rheumatology

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Authors: Sheela Nampoothiri, Nursel H Elcioglu, Suleyman S Koca, Dhanya Yesodharan, Chandrababu Kk, Vinod Krishnan 5th, Meenakshi Bhat, Mohandas Nair K, Natasha Radhakrishnan, Mahesh Kappanayil, Jayesh J Sheth, Sandra Alves, Francisca Coutinho, Michael J Friez, Richard M Pauli, Sheila Unger, Andrea Superti-Furga, Jules G Leroy, Sara S Cathey

Published: January, 2019

Abstract: Mucolipidosis-IIIγ (ML-IIIγ) is a recessively inherited slowly progressive skeletal dysplasia caused by mutations in GNPTG. We report the genetic and clinical findings in the largest cohort with ML-IIIγ so far: 18 affected individuals from 12 families including 12 patients from India, five from Turkey, and one from the USA. With consanguinity confirmed in eight of 12 families, molecular characterization showed that all affected patients had homozygous pathogenic GNPTG genotypes, underscoring the rarity of the disorder. Unlike ML-IIIαβ, which present with a broader spectrum of severity, the ML-III γ phenotype is milder, with onset in early school age, but nonetheless thus far considered phenotypically not differentiable from ML-IIIαβ. Evaluation of this cohort has yielded phenotypic findings including hypertrophy of the forearms and restricted supination as clues for ML-IIIγ, facilitating an earlier correct choice of genotype screening. Early identification of this disorder may help in offering a timely intervention for the relief of carpal tunnel syndrome, monitoring and surgery for cardiac valve involvement, and evaluation of the need for joint replacement. As this condition may be confused with rheumatoid arthritis, confirmation of diagnosis will prevent inappropriate use of immunosuppressants and disease-modifying agents.

Authors: C. Robinson, N. Baker, J. Noble, A. King, G. David, D. Sillence, P. Hofman, T. Cundy

Published: November, 2002

Abstract

Summary: Mucolipidosis type III (ML III; McKusick 252600) is a rare lysosomal storage disease in which skeletal involvement is prominent, in particular the destruction of vertebral bodies and the femoral heads. We describe studies in two siblings with ML III that suggest the presence of a distinct metabolic bone disorder. Biochemical indices of bone turnover were increased, and transiliac bone biopsy demonstrated both trabecular osteopenia and marked subperiosteal bone resorption. Intravenous pamidronate treatment given monthly for a year was well tolerated and produced dramatic clinical effects, with reduction in bone pain and improvements in mobility, despite incomplete suppression of bone resorption as assessed by biochemical, radiographic and histological criteria. Bisphosphonate therapy may have an important role in the management of bone pain in ML III, as it does in the related lysosomal disorder of Gaucher disease

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Authors: Luise Sophie Ammer, Nicole Maria Muschol, René Santer, Annika Lang, Sandra Rafaela Breyer, Phillip Brenya Sasu, Martin Petzoldt, and Thorsten Dohrmann

Published: June, 2022

Abstract: Mucolipidosis (ML) type II, intermediate, and III are lysosomal storage disorders with progressive multiorgan manifestations predisposing patients to a high risk of perioperative morbidity. The aims of the study were to systematically assess disease manifestations relevant to anaesthesia as well as anaesthesia-related complications. This retrospective study includes ML patients who underwent anaesthesia in two centres between 2008 and 2022. We reviewed patients’ demographics, medical history, disease manifestations, as well as procedure- and outcome-related data. A total of 12 patients (7 MLII, 2 ML intermediate, 3 MLIII) underwent 44 anaesthesia procedures (per patient: median 3, range 1–11). The median age was 3.3 years (range 0.1–19.1). At least one complication occurred in 27.3% of the anaesthesia procedures. The vast majority of complications (94%) occurred in children with MLII and ML intermediate. A predicted difficult airway was found in 100% and 80% of the MLII and ML intermediate patients, respectively. Accordingly, most complications (59%) occurred during the induction of anaesthesia. Altogether, respiratory complications were the most frequent (18%), followed by difficult airway management (14%). The risk for anaesthesia-related complications is alarmingly high in patients with ML, particularly in those with MLII and ML intermediate. Multidisciplinary risk–benefit analysis and thoughtful anaesthesia planning are crucial in these patients.

Keywords: mucolipidosis, ML, MLII, disease manifestations, symptoms, morbidity, anaesthesia, airway, perioperative complications, surgery

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Authors: Hua Li, Wang-Sik Lee, Xiang Feng, Lin Bai, Benjamin C Jennings, Lin Liu, Balraj Doray, William M Canfield, Stuart Kornfeld, Huilin Li

Published: March, 2022

Abstract: Vertebrates use the mannose 6-phosphate (M6P)-recognition system to deliver lysosomal hydrolases to lysosomes. Key to this pathway is N-acetylglucosamine (GlcNAc)-1-phosphotransferase (PTase) that selectively adds GlcNAc-phosphate (P) to man-nose residues of hydrolases. Human PTase is an α2β2γ2 heterohexamer with a catalytic core and several peripheral domains that recognize and bind substrates. Here we report a cryo-EM structure of the catalytic core of human PTase and the identification of a hockey stick-like motif that controls activation of the enzyme. Movement of this motif out of the catalytic pocket is associated with a rearrangement of part of the peripheral domains that unblocks hydrolase glycan access to the catalytic site, thereby activating PTase. We propose that PTase fluctuates between inactive and active states in solution, and selective substrate binding of a lysosomal hydrolase through its protein-binding determinant to PTase locks the enzyme in the active state to permit glycan phosphorylation. This mechanism would help ensure that only N-linked glycans of lysosomal enzymes are phosphorylated.

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Authors: Giorgia Di Lorenzo, Lena M. Westermann, Timur A. Yorgan, Julian Stürznickel, Nataniel F. Ludwig, Luise S. Ammer, Anke Baranowsky, Shiva Ahmadi, Elham Pourbarkhordariesfandabadi, Sandra R. Breyer, Tim N. Board, Anne Foster, Jean Mercer, Karen Tylee, Renata Voltolini Velho, Michaela Schweizer, Thomas Renné, Thomas Braulke, Dévora N. Randon, Fernanda Sperb-Ludwig, Louise Lapagesse de Camargo Pinto, Carolina Araujo Moreno, Denise P. Cavalcanti, Michael Amling, Kerstin Kutsche, Dominic Winter, Nicole M. Muschol, Ida V. D. Schwartz, Tim Rolvien, Tatyana Danyukova, Thorsten Schinke & Sandra Pohl

Published: August, 2021

Abstract

Purpose: Pathogenic variants in GNPTAB and GNPTG, encoding different subunits of GlcNAc-1-phosphotransferase, cause mucolipidosis (ML) II, MLIII alpha/beta, and MLIII gamma. This study aimed to investigate the cellular and molecular bases underlying skeletal abnormalities in patients with MLII and MLIII.

Methods: We analyzed bone biopsies from patients with MLIII alpha/beta or MLIII gamma by undecalcified histology and histomorphometry. The skeletal status of Gnptgko and Gnptab-deficient mice was determined and complemented by biochemical analysis of primary Gnptgko bone cells. The clinical relevance of the mouse data was underscored by systematic urinary collagen crosslinks quantification in patients with MLII, MLIII alpha/beta, and MLIII gamma.

Results: The analysis of iliac crest biopsies revealed that bone remodeling is impaired in patients with GNPTAB-associated MLIII alpha/beta but not with GNPTG-associated MLIII gamma. Opposed to Gnptab-deficient mice, skeletal remodeling is not affected in Gnptgko mice. Most importantly, patients with variants in GNPTAB but not in GNPTG exhibited increased bone resorption.

Conclusion: The gene-specific impact on bone remodeling in human individuals and in mice proposes distinct molecular functions of the GlcNAc-1-phosphotransferase subunits in bone cells. We therefore appeal for the necessity to classify MLIII based on genetic in addition to clinical criteria to ensure appropriate therapy.

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Authors: Luise Sophie Ammer, Sandra Pohl, Sandra Rafaela Breyer, Charlotte Aries, Jonas Denecke, Anna Perez, Martin Petzoldt, Johanna Schrum, Ingo Müller, and Nicole Maria Muschol

Published: January, 2021

Abstract

Background: Mucolipidosis type II (MLII) is an ultra-rare lysosomal storage disorder caused by defective lysosomal enzyme trafficking. Clinical hallmarks are craniofacial dysmorphia, cardiorespiratory dysfunction, hepatosplenomegaly, skeletal deformities and neurocognitive retardation. Death usually occurs in the first decade of life and no cure exists. Hematopoietic stem cell transplantation (HSCT) has been performed in few MLII patients, but comprehensive follow-up data are extremely scarce.

Methods: MLII diagnosis was confirmed in a female three-month-old patient with the mutations c.2213C > A and c.2220_2221dup in the GNPTAB gene. At nine months of age, the patient received HSCT from a 9/10 human leukocyte antigen (HLA)-matched unrelated donor.

Results: HSCT resulted in a sustained reduction of lysosomal storage und bone metabolism markers. At six years of age, the patient showed normal cardiac function, partial respiratory insufficiency and moderate hepatomegaly, whereas skeletal manifestations had progressed. However, the patient could walk and maintained an overall good quality of life. Neurocognitive testing revealed a developmental quotient of 36%. The patient died at 6.6 years of age following a human metapneumovirus (hMPV) pneumonia.

Conclusions: The exact benefit remains unclear as current literature vastly lacks comparable data on MLII natural history patients. In order to evaluate experimental therapies, in-depth prospective studies and registries of untreated MLII patients are indispensable.

Keywords: Mucolipidosis type II, I-cell disease, Lysosomal storage disorder, Hematopoietic stem cell transplantation, Bone marrow cell transplantation, Treatment, Cognitive function, Life quality

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Authors: Noor U Ain, Niaz Muhammad, Mehdi Dianatpour, Marta Baroncelli, Muddassar Iqbal, Mohammad A F Fard, Ihtisham Bukhari, Sufian Ahmed, Massoumeh Hajipour, Zahra Tabatabaie, Hamidreza Foroutan, Ola Nilsson, Mohammad A Faghihi, Outi Makitie, Sadaf Naz

Published: November, 2020

Abstract: Skeletal dysplasias are a heterogeneous group of disorders ranging from mild to lethal skeletal defects. We investigated two unrelated families with individuals presenting with a severe skeletal disorder. In family NMD02, affected individuals had a dysostosis multiplex-like skeletal dysplasia and severe short stature (<-8.5 SD). They manifested increasingly coarse facial features, protruding abdomens, and progressive skeletal changes, reminiscent of mucopolysaccharidosis. The patients gradually lost mobility and the two oldest affected individuals died in their twenties. The affected child in family ID01 had coarse facial features and severe skeletal dysplasia with clinical features similar to mucopolysaccharidosis. She had short stature, craniosynostosis, kyphoscoliosis, and hip-joint subluxation. She died at the age of 5 years. Whole-exome sequencing identified two homozygous variants c.133C>T; p.(Arg45Trp) and c.215dupA; p.(Tyr72Ter), respectively, in the two families, affecting an evolutionary conserved gene TMEM251 (NM_001098621.1). Immunofluorescence and confocal studies using human osteosarcoma cells indicated that TMEM251 is localized to the Golgi complex. However, p.Arg45Trp mutant TMEM251 protein was targeted less efficiently and the localization was punctate. Tmem251 knockdown by small interfering RNA induced dedifferentiation of rat primary chondrocytes. Our work implicates TMEM251 in the pathogenesis of a novel disorder and suggests its potential function in chondrocyte differentiation.

Keywords: Facial dysmorphology; Golgi; Iran; Pakistan; mucolipidosis; mucopolysaccharidosis.

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Published: October, 2020

A research team at the Greenwood Genetic Center (GGC) has successfully used small molecules to restore normal heart and valve development in an animal model for Mucolipidosis II (ML II), a rare genetic disorder. Progressive heart disease is commonly associated with ML II. The study is reported in this month's JCI Insight.

The small molecules included the cathepsin protease K inhibitor, odanacatib, and an inhibitor of TGFß growth factor signaling. Cathepsin proteases have been associated with later-onset heart disease including atherosclerosis, cardiac hypertrophy, and valvular stenosis, but their role in congenital heart defects has been unclear. The current study offers new insight into how mislocalizing proteases like cathepsin K alter embryonic heart development in a zebrafish model of ML II.

“Mutations in GNPTAB, the gene responsible for ML II, alter the localization and increase the activity of cathepsin proteases. This disturbs growth factor signaling and disrupts heart and valve development in our GNPTAB deficient zebrafish embryos. By inhibiting this process, normal cardiac development was restored. This finding highlights the potential of small molecules and validates the need for further studies into their efficacy."

Heather Flanagan-Steet, PhD, Director of the Hazel and Bill Allin

Aquaculture Facility and Director of Functional Studies at GGC

Flanagan-Steet noted that she hopes the current work with ML II zebrafish will provide the basis to move one step closer to a treatment.

Source: Greenwood Genetic Center

Journal reference:

Lu, P., et al. (2020) Inappropriate cathepsin K secretion promotes its enzymatic activation driving heart and valve malformation. Journal of Clinical Investigation Insight. doi.org/10.1172/jci.insight.133019.

Authors: Luise Sophie Ammer, Esmeralda Oussoren, Nicole Maria Muschol, Sandra Pohl, Maria Estela Rubio-Gozalbo, René Santer, Ralf Stuecker, Eik Vettorazzi, and Sandra Rafaela Breyer

Published: March, 2020

Abstract: Mucolipidosis type II (MLII) is a rare lysosomal storage disorder caused by defective trafficking of lysosomal enzymes. Severe skeletal manifestations are a hallmark of the disease including hip dysplasia. This study aims to describe hip morphology and the natural course of hip pathologies in MLII by systematic evaluation of plain radiographs, ultrasounds and magnetic resonance imaging (MRI). An international two-centered study was performed by retrospective chart review. All MLII patients with at least one pelvic radiograph were included. A total of 16 patients were followed over a mean of 3.5 years (range 0.2–10.7 years). Typical age-dependent radiographic signs identified were femoral cloaking (7/16), rickets/hyperparathyroidism-like changes (6/16) and constrictions of the supra-acetabular part of the os ilium (16/16) and the femoral neck (7/16). The course of acetabular and migration indexes (AI, MI) significantly increased in female patients. However, in the overall group, there was no relevant progression of acetabular dysplasia with a mean AI of 23.0 (range 5°–41°) and 23.7° (range 5°–40°) at the first and last assessments, respectively. Better knowledge on hip morphology in MLII could lead to earlier diagnosis, improved clinical management and enables assessment of effects of upcoming therapies on the skeletal system.

Keywords: mucolipidosis type II, MLII, ML intermediate, I-cell disease, hip, hip dysplasia, hip dislocation, cloaking, femoral bowing, ultrasound

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Authors: Thomas Braulke 1, Jan E Carette 2, Wilhelm Palm 3

Abstract

Lysosomes degrade and recycle macromolecules that are delivered through the biosynthetic, endocytic, and autophagic routes. Hydrolysis of the different classes of macromolecules is catalyzed by about 70 soluble enzymes that are transported from the Golgi apparatus to lysosomes in a mannose 6-phosphate (M6P)-dependent process. The molecular machinery that generates M6P tags for receptor-mediated targeting of lysosomal enzymes was thought to be understood in detail. However, recent studies on the M6P pathway have identified a previously uncharacterized core component, yielded structural insights in known components, and uncovered functions in various human diseases. Here we review molecular mechanisms of lysosomal enzyme trafficking and discuss its relevance for rare lysosomal disorders, cancer, and viral infection.

Keywords: LYSET; cancer metabolism; lysosomal enzymes; lysosomal storage disorders; mannose 6-phosphate pathway; viral infections.

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Authors: Lin Liu, Wang-Sik Lee, Balraj Doray, and Stuart Kornfeld

Published: June, 2017

Abstract: Several lysosomal enzymes currently used for enzyme replacement therapy in patients with lysosomal storage diseases contain very low levels of mannose 6-phosphate, limiting their uptake via mannose 6-phosphate receptors on the surface of the deficient cells. These enzymes are produced at high levels by mammalian cells and depend on endogenous GlcNAc-1-phosphotransferase α/β precursor to phosphorylate the mannose residues on their glycan chains. We show that co-expression of an engineered truncated GlcNAc-1-phosphotransferase α/β precursor and the lysosomal enzyme of interest in the producing cells resulted in markedly increased phosphorylation and cellular uptake of the secreted lysosomal enzyme. This method also results in the production of highly phosphorylated acid β-glucocerebrosidase, a lysosomal enzyme that normally has just trace amounts of this modification.

Keywords: GlcNAc-1-phosphotransferase, lysosomal enzyme, lysosomal storage disorders, mannose 6-phosphate, enzyme replacement therapy

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Authors: Eline van Meel and Stuart Kornfeld

Published: June, 2017

Abstract: The lysosomal storage disorder mucolipidosis III γ is caused by defects in the γ subunit of UDP-GlcNAc:lysosomal enzyme N-acetylglucosamine-1-phosphotransferase, the enzyme that tags lysosomal enzymes with the mannose 6-phosphate lysosomal targeting signal. In patients with this disorder, most of the newly synthesized lysosomal enzymes are secreted rather than being sorted to lysosomes, resulting in increased levels of these enzymes in the plasma. Several missense mutations in GNPTG, the gene encoding the γ subunit, have been reported in mucolipidosis III γ patients. However, in most cases the impact of these mutations on γ subunit function has remained unclear. Here we report that the variants c.316G>A (p.G106S), c.376G>A (p.G126S) and c.425G>A (p.C142Y) cause misfolding of the γ subunit, while another variant, c.857C>T (p.T286M), does not appear to alter γ subunit function. The misfolded γ subunits were retained in the ER and failed to rescue the lysosomal targeting of lysosomal acid glycosidases.

Keywords: GlcNAc-1-phosphotransferase, GNPTG, misfolding, mucolipidosis III γ

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Authors: Troy C. Lund, Sara S. Cathey, Weston P. Miller, Mary Eapen, Martin Andreansky, Christopher C. Dvorak, Jeffrey H. Davis, Jignesh D. Dalal, Steven M. Devine, Gretchen M. Eames, William S. Ferguson, Roger H. Giller, Wensheng Joanne Kurtzberg, Robert Krance, Emmanuel Katsanis, Victor A. Lewis, Indira Sahdev, and Paul J. Orchard

Published: November, 2014

Abstract: Mucolipidosis type II (MLII), or I-Cell Disease, is a rare, but severe disorder affecting localization of enzymes to the lysosome, generally resulting in death before the 10th birthday. Although hematopoietic stem cell transplant (HSCT) has been used to successfully treat some lysosomal storage diseases, there have been only two case reports in the use of HSCT to treat MLII. For the first time, we describe the combined international experience in the use of HSCT for MLII in 22 patients. Although 95% of the patients engrafted, the overall survival was low with only 6 patients (27%) alive at last follow-up. The most common cause of death post-transplant was cardiovascular complications, most likely due to disease progression. Survivors were globally delayed in development, and often required complex medical support such as gastrostomy tubes for nutrition, and tracheostomy with mechanical ventilation. Although HSCT has demonstrated efficacy in treating some lysosomal storage disorders, the neurologic outcome and survival for patents with MLII were poor. Therefore new medical and cellular therapies should be sought for these patients.

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Authors: Marko Fonović, Boris Turk

Published: January, 2014

Abstract: Since their discovery, cysteine cathepsins were generally considered to be involved mainly in the nonspecific bulk protein degradation that takes place within the lysosomes. However, it has become clear that their proteolytical activity can also influence various specific pathological processes such as cancer, arthritis, and atherosclerosis. Furthermore, their localization was found not to be limited strictly to the lysosomes. In the light of those findings, it is not surprising that cysteine cathepsins are currently considered as highly relevant clinical targets. Moreover, recent development of proteomic-based methods for identification of novel physiological substrates of proteases provides a major opportunity also in the field of cysteine cathepsins. In this review, we will therefore present cysteine cathepsin roles in disease progression and discuss their potential relevance as prognostic and diagnostic biomarkers

Keywords: Biomarker; Cancer; Cathepsin; Cysteine protease; Proteolysis.

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Authors: Jules G Leroy, David Sillence, Tim Wood, Jarrod Barnes, Robert Roger Lebel, Michael J Friez, Roger E Stevenson, Richard Steet, and Sara S Cathey

Published: September, 2013

Abstract: Mucolipidosis (ML) II and ML IIIα/β are allelic autosomal recessive metabolic disorders due to mutations in GNPTAB. The gene encodes the enzyme UDP-GlcNAc-1-phosphotransferase (GNPT), which is critical to proper trafficking of lysosomal acid hydrolases. The ML phenotypic spectrum is dichotomous. Criteria set for defining ML II and ML IIIα/β are inclusive for all but the few patients with phenotypes that span the archetypes. Clinical and biochemical findings of the ‘intermediate' ML in eight patients with the c.10A>C missense mutation in GNPTAB are presented to define this intermediate ML and provide a broader insight into ML pathogenesis. Extensive clinical information, including radiographic examinations at various ages, was obtained from a detailed study of all patients. GNPTAB was sequenced in probands and parents. GNPT activity was measured and cathepsin D sorting assays were performed in fibroblasts. Intermediate ML patients who share the c.10A>C/p.K4Q mutation in GNPTAB demonstrate a distinct, consistent phenotype similar to ML II in physical and radiographic features and to ML IIIα/β in psychomotor development and life expectancy. GNPT activity is reduced to 7–12% but the majority of newly synthesized cathepsin D remains intracellular. The GNPTAB c.10A>C/p.K4Q missense allele results in an intermediate ML II/III with distinct clinical and biochemical characteristics. This delineation strengthens the utility of the discontinuous genotype–phenotype correlation in ML II and ML IIIα/β and prompts additional studies on the tissue-specific pathogenesis in GNPT-deficient ML.

Keywords: mucolipidosis, phosphotransferase, storage disease, GNPTAB

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Authors: Aaron C. Petrey, Heather Flanagan-Steet, Steven Johnson, Xiang Fan, Mitche De la Rosa, Mark E. Haskins, Alison V. Nairn, Kelley W. Moremen, and Richard Steet

Published: March, 2012

Summary: The severe pediatric disorder mucolipidosis II (ML-II; also known as I-cell disease) is caused by defects in mannose 6-phosphate (Man-6-P) biosynthesis. Patients with ML-II exhibit multiple developmental defects, including skeletal, craniofacial and joint abnormalities. To date, the molecular mechanisms that underlie these clinical manifestations are poorly understood. Taking advantage of a zebrafish model of ML-II, we previously showed that the cartilage morphogenesis defects in this model are associated with altered chondrocyte differentiation and excessive deposition of type II collagen, indicating that aspects of development that rely on proper extracellular matrix homeostasis are sensitive to decreases in Man-6-P biosynthesis. To further investigate the molecular bases for the cartilage phenotypes, we analyzed the transcript abundance of several genes in chondrocyte-enriched cell populations isolated from wild-type and ML-II zebrafish embryos. Increased levels of cathepsin and matrix metalloproteinase (MMP) transcripts were noted in ML-II cell populations. This increase in transcript abundance corresponded with elevated and sustained activity of several cathepsins (K, L and S) and MMP-13 during early development. Unlike MMP-13, for which higher levels of protein were detected, the sustained activity of cathepsin K at later stages seemed to result from its abnormal processing and activation. Inhibition of cathepsin K activity by pharmacological or genetic means not only reduced the activity of this enzyme but led to a broad reduction in additional protease activity, significant correction of the cartilage morphogenesis phenotype and reduced type II collagen staining in ML-II embryos. Our findings suggest a central role for excessive cathepsin K activity in the developmental aspects of ML-II cartilage pathogenesis and highlight the utility of the zebrafish system to address the biochemical underpinnings of metabolic disease.

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Authors: Grace David-Vizcarra, Julie Briody, Jenny Ault, Michael Fietz, Janice Fletcher, Ravi Savarirayan, Meredith Wilson, Jim McGill, Matthew Edwards, Craig Munns, Melanie Alcausin, Sarah Cathey, and David Sillence

Published: June, 2010

Abstract

Aim: To assess the natural history and impact of the secondary bone disease observed in patients with Mucolipidosis II and III.

Methods: Affected children and adults were ascertained from clinical genetics units around Australia and New Zealand and the National Lysosomal Diseases Research Unit in Adelaide. The study encompassed all patients ascertained between 1975 and 2005. Data focussing on biochemical parameters at diagnosis, and longitudinal radiographic findings were sought for each patient. Where feasible, patients underwent clinical review and examination. Examinations included skeletal survey, bone densitometry, and measurement of serum and urine markers of bone metabolism. Functional assessment was performed using the Pediatric Evaluation and Disability Inventory (PEDI).

Results: 25 patients with ML II and III were ascertained over a 30-year period. Serum calcium (median 2.35 mmol/L range 2.16–2.64) and phosphate (median 1.51 mmol/L range 1.17–1.72) were normal but five patients had mild elevation of alkaline phosphatase. Serum osteocalcin and urine deoxypyridinoline/creatinine were elevated. Two radiological patterns were observed (i) transient neonatal hyperparathyroidism in infants with ML II and (ii) progressive osteodystrophy in patients with ML II/III and ML III. Molecular Genetic analysis of mutations in the αβsubunit of the UDP-N-acetylglucosamine:lysosomal enzyme N-acetylglucosaminyl-1-phosphotransferase gene in 9 subjects correlated with the phenotypic severity.

Conclusion: ML is characterised by a progressive bone and mineral disorder which we describe as the Osteodystrophy of Mucolipidosis. The clinical and radiographic features of this osteodystrophy are consistent with a syndrome of “Pseudohyperparathyroidism”. Much of the progressive skeletal and joint pathology is attributable to this bone disorder.

Keywords: Mucolipidosis, hyperparathyroidism, pseudohyperparathyroidism, osteoporosis

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Authors: Sara S. Cathey, Jules G. Leroy, Tim Wood, Karisa Eaves, Richard J. Simensen, Mariko Kudo, Roger E. Stevenson, and Michael J. Friez

Published: January, 2010

Abstract

Objectives: Mucolipidoses II and III alpha/beta (ML II and ML III) are lysosomal disorders in which the essential mannose-6-phosphate recognition marker is not synthesized onto lysosomal hydrolases and other glycoproteins. The disorders are caused by mutations in GNPTAB, which encodes two of three subunits of the heterohexameric enzyme, N-acetylglucosamine-1-phosphotransferase. Clinical, biochemical, and molecular findings in 61 probands (63 patients) are presented in order to provide a broad perspective of these mucolipidoses.

Methods: GNPTAB was sequenced in all probands and/or parents. Activity of several lysosomal enzymes was measured in plasma, and GlcNac-1-phosphotransferase was assayed in leukocytes. Thirty-six patients were studied in detail, allowing extensive clinical data to be abstracted.

Results: ML II correlates with near total absence of phosphotransferase activity resulting from homozygosity or compound heterozygosity for frameshift or nonsense mutations. Craniofacial and orthopedic manifestations are evident at birth, skeletal findings become more obvious within the first year, and growth is severely impaired. Speech, ambulation, and cognitive function are impaired. ML III retains a low level of phosphotransferase activity due to at least one missense or splice site mutation. The phenotype is milder with minimal delays in milestones, the appearance of facial coarsening by early school age, and slowing of growth after age four years.

Conclusions: Fifty-one pathogenic changes in GNPTAB are presented, including 42 novel mutations. Ample clinical information improves criteria for delineation of ML II and ML III. Phenotype-genotype correlations suggested in more general terms in earlier reports on smaller groups of patients are specified and extended.

Keywords: mucolipidosis, I-cell disease, pseudoHurler polydystrophy, dysostosis multiplex, lysosomal disease

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Authors: Sara S. Cathey, Mariko Kudo, Stephan Tiede, Annick Raas-Rothschild, Thomas Braulke, Michael Beck, Harold A Taylor, William M Canfield, Jules G Leroy, Elizabeth F Neufeld, Victor A McKusick

Published: February, 2008

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Authors: Stephan Tiede, Michael Cantz, Jürgen Spranger, Thomas Braulke

Published: July, 2006

Abstract: Mucolipidosis type II (ML II; I-cell disease) and mucolipidosis III (ML III; pseudo Hurler polydystrophy) are autosomal recessively inherited disorders caused by a defective N-acetylglucosamine 1-phosphotransferase (phosphotransferase). The formation of mannose 6-phosphate markers in soluble lysosomal enzymes is impeded leading to their increased excretion into the serum, to cellular deficiency of multiple hydrolases, and lysosomal storage of non-digested material. Phosphotransferase deficiency is caused by mutations in GNPTA and GNPTG encoding phosphotransferase subunits. Here we report on an adolescent with progressive joint contractions and other signs of mucolipidosis II who survived to the age of 14 years. Impaired trafficking of lysosomal enzymes cathepsin D and -hexosaminidase in metabolically labeled fibroblasts was documented. Mutations in the GNPTG gene and alterations in the GNPTG mRNA level were not detected. A different electrophoretic mobility of the 97 kDa GNPTG dimer suggested posttranslational modification abrogating the compartmentalization of GNPTG in the Golgi apparatus. A nucleotide substitution in the GNPTA gene (c.3707A>T) was identified altering the predicted C-terminal transmembrane anchor of the phosphotransferase subunit. The data demonstrate that defective GNPTA not only impairs lysosomal enzyme targeting but also the availability of intact GNPTG required for phosphotransferase activity and assembly of subunits. © 2006 Wiley-Liss, Inc.

Keywords: mucolipidosis type II; phosphotransferase; GNPTA; GNPTAB; GNPTG; cathepsin D; lysosomal storage disorders

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Authors: Stephan Tiede, Nicole Muschol, Gert Reutter, Michael Cantz, Kurt Ullrich, Thomas Braulke

Published: August, 2005

Abstract

Mucolipidosis type III (ML III, pseudo-Hurler polydystrophy), an autosomal recessive inherited disorder of lysosomal enzyme targeting is due to a defective N-acetylglucosamine 1-phosphotransferase (phosphotransferase) activity and leads to the impaired formation of mannose 6-phosphate markers in soluble lysosomal enzymes followed by their increased excretion into the serum. Mutations in the phosphotransferase γ subunit gene (GNPTAG) have been reported to be responsible for ML III. Here we report on a 14-year-old adolescent with a mild clinical phenotype of ML III. He presented with progressive joint stiffness and swelling. Urinary oligosaccharide and mucopolysaccharide excretion was normal. Lysosomal enzyme activities were significantly elevated in the serum and decreased in cultured fibroblasts. Impaired trafficking of the lysosomal protease cathepsin D (CtsD) was confirmed by metabolic labeling of the patient's fibroblasts. Neither mutations in the GNPTAG gene nor alterations in the GNPTAG mRNA level were detected whereas the steady state concentration of the 97 kDa GNPTAG dimer was reduced. Most importantly, the patient is homozygous for a pathogenic nucleotide substitution and a polymorphism in the phosphotransferase α/β subunit gene (GNPTA). The data indicate that defects in genes other than GNPTAG can be linked to ML III contributing to the variability of the phenotype. © 2005 Wiley-Liss, Inc.

Keywords: mucolipidosis type III; phos-photransferase;pseudo-Hurlerpolydystrophy; cathepsin D; lyso-somal storage disorders

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Authors: A Raas-Rothschild, R Bargal, O Goldman, E Ben-Asher, J Groener, A Toutain, E Stemmer, Z Ben-Neriah, H Flusser, F Beemer, M Penttinen, T Olender, A Rein, G Bach, and M Zeigler

Published: April, 2004

Abstract:

First described by Maroteaux and Lamy in 1966,1 mucolipidosis III (ML III) or pseudo-Hurler polydystrophy (MIM 252600; Online Mendelian Inheritance in Man (OMIM), McKusick-Nathans Institute for Genetic Medicine, Johns Hopkins University (Baltimore, MD) and National Center for Biotechnology Information, National Library of Medicine (Bethesda, MD), 2000; http://www.ncbi.nlm.nih.gov/omim/) is a rare autosomal recessive condition resembling Hurler syndrome with no organomegaly or mucopolysacchariduria.

Clinical manifestations are variable and progress into adulthood. Bone involvement is slowly progressive and bone pain and disability due to destruction of hip joints are the most frequent and debilitating symptoms. Clinical symptoms include stiffness of the fingers and shoulders, claw hand deformity, short stature, and scoliosis. Mild coarsening of the face with corneal clouding, mild retinopathy, astigmatism, and cardiac valve involvement have also been reported. The radiological findings include moderate to severe dysostosis multiplex with vertebral changes.

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Authors: Junghan Song, Dong Soon Lee, Han Ik Cho, Jin Q. Kim, and Tae-Joon Cho

Published: October, 2003

Abstract:

We performed a biochemical study on the patient with mucolipidosis III (ML-III, pseudo-Hurler polydystrophy) in Korea. Confluent fibroblasts from the patient and from normal controls were cultured for 4, 12, 24, 48, and 72 hr, respectively. Lysosomal enzyme activities in culture media after different incubation times and in plasma, leuko-cytes, and fibroblasts were determined. Most of the leukocyte lysosomal enzymes were within normal limits or slightly lowered; however, plasma lysosomal enzyme activities such as those of hexosaminidase and arylsulfatase A were markedly increased. Numerous phase-dense inclusions were present in the cytoplasm of cultured fibroblasts. Lysosomal enzyme activities of fibroblasts were markedly decreased except for beta-glucosidase. The rates of increase of the lysosomal enzyme activities with incubation time were greater in the culture medium of the patient than in normal control, whereas no difference in the beta-glucosidase activity of the culture media of the patient and the control was found. This study describes the first case of ML-III in Korea, with its typical biochemical characteristics, i.e., a problem with targeting and transporting of lysosomal enzymes which results in a marked increase in plasma lysosomal enzyme activities and a high ratio of extracellular to intracellular lysosomal enzyme activities in cultured fibroblasts.

Keywords: Mucolipidoses; Pseudo hurler polydystrophy; Fibroblasts

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Authors: Sperb-Ludwig F, Ludwig NF, Rizowy GM, Velho RV, Schwartz IVD

Genetics and Molecular Biology, 04 Dec 2023, 46(3 Suppl 1):e20230117

Abstract

Mucolipidosis II and III (MLII and MLIII) are autosomal recessive diseases caused by pathogenic variants in GNPTAB and GNPTG genes that lead to defects in GlcNAc-1-phosphotransferase. This enzyme adds mannose 6-phosphate residues to lysosomal hydrolases, which allows enzymes to enter lysosomes. Defective GlcNAc-1-phosphotransferase causes substrate accumulation and inflammation. These diseases have no treatment, and we hypothesized that the use of substrate reduction therapy and immunomodulation may be beneficial at the cell level and as a future therapeutic approach. Fibroblasts from two patients with MLIII alpha/beta and 2 patients with MLIII gamma as well as from one healthy control were treated with 10 µM miglustat, 20 µM genistein, and 20 µM thalidomide independently. ELISA assay and confocal immunofluorescence microscopy were used to evaluate the presence of heparan sulfate (HS) and the impact on substrate accumulation. ELISA assay showed HS reduction in all patients with the different treatments used (p=0.05). HS reduction was also observed by immunofluorescence microscopy. Our study produced encouraging results, since the reduction in substrate accumulation, even partial, may offer benefits to the phenotype of patients with inborn errors of metabolism.

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