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ß2008 Wiley-Liss, Inc. American Journal of Medical Genetics Part A 146A:512– 513 (2008)
Research Letter
Molecular Order in Mucolipidosis
II and III Nomenclature
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,
and Victor A. McKusick
Greenwood Genetic Center, Greenwood, South Carolina
Genzyme Corporation, Oklahoma City, Oklahoma
Schleswig-Holstein University Hospital, Lu¨beck, Germany
Department of Human Genetics, Hadassah Hebrew University Hospital, Jerusalem, Israel
Department of Biochemistry, Children’s Hospital, University of Hamburg, Hamburg, Germany
Children’s Hospital, University of Mainz, Mainz, Germany
Department of Biological Chemistry, David Geffen School of Medicine at UCLA, Los Angeles, California
McKusick-Nathans Institute of Genetic Medicine, The Johns Hopkins Hospital, Baltimore, Maryland
Received 8 November 2007; Accepted 9 November 2007
How to cite this article: Cathey SS, Kudo M, Tiede S, Raas-Rothschild A, Braulke T, Beck M, Taylor HA,
Canfield WM, Leroy JG, Neufeld EF, McKusick VA. 2008. Molecular order in mucolipidosis
II and III nomenclature. Am J Med Genet Part A 146A:512– 513.
To the Editor:
The Second International Conference on Glyco-
protein and Related Storage Diseases was held on
July 26–27, 2007 in Ann Arbor, Michigan. It was
organized by the group known as the International
Advocate for Glycoprotein Storage Diseases. Pro-
gress reports on pathogenesis, molecular genetics,
and therapy were presented by clinicians and
scientists active in the field of these rare lysosomal
disorders. We present a proposal initiated at the
meeting, regarding the nomenclature of mucolipi-
dosis (ML) II and ML III. The proposed naming
system incorporates the recently acquired knowl-
edge of the molecular etiology of these conditions.
ML II (I-cell disease, OMIM # 252500) [Leroy et al.,
1971] and ML III (pseudo-Hurler polydystrophy,
OMIM # 252600) [Maroteaux and Lamy, 1966]
are considered to be allelic disorders due to defi-
cient UDP-N-acetylglucosamine: lysosomal hydrolase
N-acetyl-1-phosphotransferase (IUBMB #
[Hasilik et al., 1981; Reitman et al., 1981], commonly
termed UDP-GlcNAc 1-phosphotransferase (GlcNAc-
PT). The enzyme catalyzes the initial step in the
synthesis of the mannose 6-phosphate (M6P) recogni-
tion marker that is crucial for targeting nascent
hydrolases to lysosomes [Kaplan et al., 1977; Hasilik
and Neufeld, 1980]. Because its function is failing in
ML II and ML III patients, the lysosomal enzymes lack
the M6P marker and cannot bind to M6P receptors.
The acid hydrolases cannot enter lysosomes and are
released instead into the intercellular space and body
fluids. Intracellular inclusions, identified as swollen
lysosomes filled with undigested macrocompounds,
are seen in ML II and ML III patients. Excessive urinary
excretionof oligosaccharides is observed consistently
in both disorders, and ML II and ML III have been
grouped among the oligosaccharidoses, also termed
glycoproteinoses. Complete loss of GlcNAc-PT acti-
vity causes the clinically severe ML II, which is
apparent from early infancy or even prenatally.
Residual enzyme activity is detected in patients with
ML III, with onset of symptoms in childhood and
slower progression.
The GlcNAc-PT has been purified and charac-
terized as a hexameric (a2b2g2) protein, a 540-KDa
complex of disulfide linked homodimers [Bao et al.,
1996]. Both the aand the bsubunits are encoded
as a single ab polypeptide by the GNPTAB gene
comprising 21 exons and assigned to chromosome
12q23.3 [Kudo et al., 2005; Tiede et al., 2005]. The
subunits acquire molecular maturity following post-
translational proteolysis of the initial gene product
and encompass the catalytic center in the GlcNAc-PT
enzyme complex. Mutations in the GNPTAB gene
(OMIM # 607840) cause ML II and ML IIIA [Paik et al.,
2005; Tiede et al., 2005; Kudo et al., 2006; Cathey
*Correspondence to: Sara S. Cathey, Greenwood Genetic Center, 101
Gregor Mendel Circle, Greenwood, SC 29646. E-mail:
DOI 10.1002/ajmg.a.32193
et al., 2007]. Mutations in the GNPTG gene (OMIM #
607838) that encodes the gsubunit of the GlcNAc-PT
protein complex were rst identied in a large Druze
family in the Middle-East with a variant form of ML III,
termed ML IIIC (OMIM # 252605). GNPTG is located
at chromosome 16p13.3 [Raas-Rothschild et al.,
2000]. The original designations ML III ‘‘A’’ and ML
III ‘‘C’’ refer to the results of in vitro complementation
studies in heterokaryons obtained by fusion of
broblast strains derived from ML II and ML III
patients with broblasts derived from other ML
patients or from individuals with other lysosomal
storage diseases with single enzyme deciencies
[Honey et al., 1982; Shows et al., 1982]. These
experiments ultimately identied the three comple-
mentation groups A, B, and C. All ML II patients
were assigned to group A. Group B was the label
assigned to only a single cell strain that show-
ed complementation with all other strains. The
clinical characterization of the patient designated
group B was never completed. No published patients
have subsequently been assigned to the B comple-
mentation group. ML III patients were considered
to belong to either complementation group A or C.
Because the molecular characterization of the ML III
patients proved to be congruent with the earlier
complementation results, the designations, ML II, ML
IIIA, and ML IIIC were adopted [OMIM, 2007].
It is now appreciated that all ML II patients and the
larger group of ML III patients (ML IIIA) are either
homozygotes or compound heterozygotes for muta-
tions in the GNPTAB gene. The location of the
mutations within the asubunit or the bsubunit
appears to be of less importance in determining
the phenotype than the nature of the mutations
themselves [Cathey et al., 2007]. The second,
smaller group of patients with ML III (ML IIIC) are
homozygotes or compound heterozygotes for muta-
tions in the GNPTG gene [Raas-Rothschild et al.,
2000]. Although the complementation studies led to
accurate predictions that these conditions are caused
by different genes, the designations A and C can
now be replaced by more descriptive terms. The
proposed changes are summarized in Table I.
These name changes have been prompted by
the knowledge of the molecular causes of these
rare disorders. The reclassication is relevant to
clinicians and patients, as GNPTG (gamma) muta-
tions appear to predict a milder phenotype and better
prognosis than do GNPTAB (alpha/beta) mutations.
As clinicians and scientists with special interest in ML
II and ML III, we believe that this new nosology
succinctly summarizes our understating of the
clinical, biochemical, and now, molecular, hetero-
geneity of ML II and III.
Bao M, Booth JL, Elmendorf BJ, Caneld WM. 1996. Bovine UDP-N-
acetylglucosamine: Lysosomal enzyme N-acetylglucosamine-
1-phosphotransferase. I. Purication and subunit structure. J Biol
Chem 271:3143731445.
Cathey S, Friez M, Wood T, Eaves K, Leroy J. 2007. Exploring
mucolipidosis II and III. Mol Genet Metab 90:240.
Hasilik A, Neufeld EF. 1980. Biosynthesis of lysosomal enzyme
in broblasts. Phosphorylation of mannose residues. J Biol
Chem 255:49464950.
Hasilik A, Waheed A, von Figura K. 1981. Enzymatic phosphory-
lation of lysosomal enzymes in the presence of UDP-N-
acetylglucosamine. Absence of the activity in I-cell broblasts.
Biochem Biophys Res Commun 98:761767.
Honey NK, Mueller OT, Little LE, Miller AL, Shows TB. 1982.
Mucolipidosis III is genetically heterogeneous. Proc Natl Acad
Sci USA 79:74207424.
Kaplan A, Achord DT, Sly WS. 1977. Phosphohexosyl compo-
nents of a lysosomal enzyme are recognized by pinocytosis
receptors on human broblasts. Proc Natl Acad Sci USA 74:
Kudo M, Bao M, DSouza A, Ying F, Pan H, Roe BA, Caneld WM.
2005. The a- and b-subunits of the human UPD-N-acetylglu-
cosamine: Lysosomal enzyme N-acetylglucosamine-1-phos-
photransferase are encoded by a single cDNA. J Biol Chem
Kudo M, Brem MS, Caneld WM. 2006. Mucolipidosis II (I-cell
disease) and mucolipidosis IIIA (classical pseudo-Hurler
polydystrophy) are caused by mutations in the GlcNAc-
phosphotransferase a/b-subunits precursor gene. Am J Hum
Genet 78:451463.
Leroy JG, Spranger JW, Feingold M, Opitz JM, Crocker AC. 1971.
I-cell disease: A clinical picture. J Pediatr 79:360365.
Maroteaux P, Lamy M. 1966. La pseudopolydystrophie de Hurler.
Presse Me
´d 74:28892892.
OMIM. 2007. Online Mendelian Inheritance in Man. http://
Paik KH, Song SM, Ki CS, Hu H-W, Kim JS, Min KH, Chang SH,
Yoo EJ, Lee IJ, Kwan EK, Han SJ, Jin D-K. 2005. Identication
of mutations in the GNPTA (MGC4170) gene coding for
GlcNAc-phosphotransferase a/bsubunits in Korean patients
with mucolipidosis Type II or Type IIIA. Hum Mut 26:308
Raas-Rothschild A, Cormier-Daire V, Bao M, Genin E, Salomon R,
Brewer K, Zeigler M, Mandel H, Toth S, Roe B, Munnich A,
Caneld WM. 2000. Molecular basis of variant pseudo-Hurler
polydystrophy (mucolipidosis IIIC). J Clin Invest 105:673
Reitman ML, Varki A, Kornfeld S. 1981. Fibroblasts from patients
with I-cell disease and pseudo-Hurler polydystrophy are
decient in uridine 5-diphosphate N-acetylglucosamine:
Glycoprotein N-acetylglucosaminylphosphotransferase acti-
vity. J Clin Invest 67:15741579.
Shows TB, Mueller OT, Honey NK, Wright CE, Miller AL. 1982.
Genetic heterogeneity of I-Cell disease is demonstrated by
complementation of lysosomal enzyme processing mutants.
Am J Med Genet 12:343353.
Tiede S, Storch S, Lu¨bke T, Henrissat B, Bargal R, Raas-Rothschild
A, Braulke T. 2005. Mucolipidosis II is caused by mutations in
GNPTA encoding the a/bGlcNAc-1-phosphotransferase. Nat
Med 11:11091112.
TABLE I. Revised Classication of Mucolipidosis II and III
I-cell disease ML II ML II alpha/beta
PseudoHurler polydystrophy ML IIIA ML III alpha/beta
ML III variant ML IIIC ML III gamma
American Journal of Medical Genetics Part A: DOI 10.1002/ajmg.a
... Although the clinical onset and manifestations are highly variable in affected individuals, MLIII has been classified as an attenuated form of MLII and is characterized by a later onset and slower disease progression. Moreover, the identification of the disease causing genes in 2000 and 2005 [7,8] allowed classifying ML into three different types of diseases [12]. According to this revised classification, the severe MLII disease (MIM 252500) is caused by complete inactivation of GlcNAc-1-phosphotransferase due to biallelic variants in GNPTAB. ...
... Thereafter, according to the clinical phenotype and the obtained genetic data, patients were classified as MLIII gamma (patients 1 to 7), MLIII alpha/ beta (patients [8][9][10][11][12][13][14], or MLII (patients [15][16][17] (Table S1). All 17 individuals were characterized by growth retardation and skeletal abnormalities, which were more pronounced in patients with MLII. ...
... Hence, our results have clearly confirmed, that MLIII alpha/beta and MLIII gamma are not only genetically but also phenotypically different. Although the genetic bases of both diseases are easily detectable, the clinical entities remain hardly discernible as patients present with similar signs, symptoms, and clinical course and radiographically with congruent dysostosis multiplex [10,12]. This issue has been recently addressed [36] and deserves more studies in the future. ...
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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 Gnptg ko and Gnptab -deficient mice was determined and complemented by biochemical analysis of primary Gnptg ko 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 Gnptg ko 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.
... таблицу). В 2008 г. в связи с пересмотром номенклатуры были внесены коррективы в названия типов МЛ [8]. ...
... По данным лабораторного обследования выявлено повышение уровня суммарной КФК до 254 Ед/л (при нор-ме 25-140), повышение КФК-МВ до 11,6 Ед/л (при норме до 3,4), увеличение уровня ЛДГ -315 Ед/л (при норме 91-225), мочевой кислоты -374 мкмоль/л (при норме 140-210), АСТ -57 Ед/л (при норме менее 42), снижение сывороточного железа -4 мкмоль/л (при норме 7,[2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]9). Проведено исследование мочи на экскрецию ГАГ -содержание ГАГ в моче в пределах референсных значений. ...
Background. Type II mucolipidosis (I-cell disease, ICD) is one of the lysosomal storage diseases. It is very rare disease; the literature describes only few cases with confirmed diagnosis of mucolipidosis. Cardiovascular changes in children with such pathology are even less often. Clinical case description. The article describes the clinical case of type II mucolipidosis alongside with cardiovascular pathology — valvular heart apparatus defect with abdominal aortic hypoplasia and reversible myocardial dysfunction on the therapy of chronic heart failure (CHF). The patient has coarse face, gingival hyperplasia, macroglossia, dysostosis multiplex, diffuse muscular hypotonia, and mass of subcutaneous tissue. Arterial hypertension, heart cavities dilatation, left ventricular (LV) walls hypertrophy, and data of CT aortography let us to diagnosis abdominal aortic hypoplasia. Conclusion. Cardiovascular malformation in patients with mucolipidosis leads to severe, life-threatening conditions development. Untimely diagnosis can worsen the course of disease. Multidisciplinary approach is needed for the patient management.
... In patients with MLs, the molecules accumulate in the brain, visceral organs, and muscle tissue as well as in the bone, causing mental retardation, skeletal deformities, and poor function of vital organs such as the liver, spleen, heart, and lungs. There are four types of ML which are classified according to the enzyme(s) that is deficient or mutated: sialidosis (ML I), ML type II, initially called "inclusion cell disease or I-cell disease [3]", now known as ML II alpha/beta (α/β) [4], ML type III (previously known as pseudo-Hurler polydystrophy, [5]), later as ML IIIA and ML IIIC, and now known as ML III α/β and ML III gamma (γ), respectively [4], and ML IV. In this review, we will focus on ML II α/β and ML III α/β in more detail and will refer them as ML II and ML III, respectively. ...
... In patients with MLs, the molecules accumulate in the brain, visceral organs, and muscle tissue as well as in the bone, causing mental retardation, skeletal deformities, and poor function of vital organs such as the liver, spleen, heart, and lungs. There are four types of ML which are classified according to the enzyme(s) that is deficient or mutated: sialidosis (ML I), ML type II, initially called "inclusion cell disease or I-cell disease [3]", now known as ML II alpha/beta (α/β) [4], ML type III (previously known as pseudo-Hurler polydystrophy, [5]), later as ML IIIA and ML IIIC, and now known as ML III α/β and ML III gamma (γ), respectively [4], and ML IV. In this review, we will focus on ML II α/β and ML III α/β in more detail and will refer them as ML II and ML III, respectively. ...
Full-text available
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.
... McKusick, an early proponent of the Human Genome Project (McKusick, 1971b;McKusick, 1991a), was an author on the paper by Venter et al. (his most frequently cited paper with more than 8000 citations) ( Table 2) (Venter et al., 2001). Accompanying the paper in Science was a viewpoint (Peltonen & McKusick, 2001) (Cathey et al., 2008). ...
Victor McKusick's contributions to the field of medical genetics are legendary and include his contributions as a mentor, as creator of Mendelian Inheritance in Man (now Online Mendelian Inheritance in Man [OMIM®]), and as a leader in the field of medical genetics. McKusick's full bibliography includes 772 publications. Here we review the 453 papers authored by McKusick and indexed in PubMed, from his earliest paper published in the New England Journal of Medicine in 1949 to his last paper published in American Journal of Medical Genetics Part A in 2008. This review of his bibliography chronicles McKusick's evolution from an internist and cardiologist with an interest in genetics to an esteemed leader in the growing field of medical genetics. Review of his bibliography also provides a historical perspective of the development of the discipline of medical genetics. This field came into its own during his lifetime, transitioning from the study of interesting cases and families used to codify basic medical genetics principles to an accredited medical specialty that is expected to transform healthcare. Along the way, he helped to unite the fields of medical and human genetics to focus on mapping the human genome, culminating in completion of the Human Genome Project. This review confirms the critical role played by Victor McKusick as the founding father of medical genetics.
... Compared to MLII, the disease progression is slower and life expectancy is longer. ML III gamma (MIM #252605) is caused only by pathogenic variants in the GNPTG gene and presents as the milder disease, with joints and bone symptoms and average life expectancy [1,4,5]. ...
Full-text available
Methodology: a retrospective study that included 32 unrelated Brazilian patients with a clinical and genetic diagnosis of Mucolipidosis II/III alpha/beta. The regional frequency of the altered alleles was determined. Results: The patients were from all regions of Brazil. The most prevalent variants were c.3503_3504del, associated with the severe form of the disease, and c.1208T>C, associated with the milder form. Variant c.3503_3504del is the most frequently found in the Midwest, Northeast, and Southeast regions of Brazil. In the South, 42.8% of the alleles present the c.1196C>T variant. Conclusions: From the perspective of all patients diagnosed with Mucolipidosis II/III in Brazil, it is possible to conclude that different regions present allelic frequencies of specific pathogenic variants, which can be explained by the occurrence of a founding effect or high inbreeding rates.
... 11 The contemporary nomenclature for classification of ML II and III was established at the Second International Conference on Glycoprotein and Related Storage Diseases and incorporates current molecular and biochemical knowledge, designating which subunit of the gene is mutated (Table). 7,10 The UDP-G1cNAc 1-phosphotransferase is a heterohexamer consisting of 3 subunits: 2 a, 2 b, and 2 g subunits. It is a product of 2 separate, unlinked genes: GNPTAB, on chromosome 12q23.3, ...
We report findings from an autopsy of a 45-year-old woman with the rare lysosomal storage disease mucolipidosis type III α/β. Her disease manifested most notably as multiple bone and cartilage problems with tracheal and bronchial malacia. Principal autopsy findings included gross abnormalities in bone and cartilage with corresponding microscopic cytoplasmic lysosomal granules. These cytoplasmic granules were also seen in histologic preparations of the brain, myocardium, heart valves, and fibroblasts of the liver and skin by light and electron microscopy. By electron microscopy there were scattered, diffuse vesicular cytoplasmic granules in neurons and glia and an increase in lysosomal structures with fine electron lucent granularity in the above tissue types. Our findings help elaborate current understanding of this disease and differentiate it from the mucopolysaccharidoses and related disorders. To our knowledge, this is the first report to document pathologic findings in a patient with mucolipidosis type III α/β by autopsy.
... MLIII can be caused by mutations in either GNPTAB or GNPTG, the latter encoding the γ-subunit of the hexameric (α 2 β 2 γ 2 ) GlcNAc-1-phosphotransferase complex (Bao et al., 1996;Raas-Rothschild et al., 2000;Tiede et al., 2005). Based on the affected gene, MLIII is accordingly classified into MLIII alpha/beta (MIM #252600) and MLIII gamma (MIM #252605) (Cathey et al., 2008). In contrast to MLII, in which the activity of GlcNAc-1-phosphotransferase is completely abolished, GlcNAc-1phosphotransferase displays residual activity in individuals with MLIII alpha/beta and MLIII gamma, which might explain variable clinical presentation among these patients (Velho et al., 2019). ...
Full-text available
Mucolipidosis type III (MLIII) gamma is a rare inherited lysosomal storage disorder caused by mutations in GNPTG encoding the γ-subunit of GlcNAc-1-phosphotransferase, the key enzyme ensuring proper intracellular location of multiple lysosomal enzymes. Patients with MLIII gamma typically present with osteoarthritis and joint stiffness, suggesting cartilage involvement. Using Gnptg ko mice as a model of the human disease, we showed that missorting of a number of lysosomal enzymes is associated with intracellular accumulation of chondroitin sulfate in Gnptg ko chondrocytes and their impaired differentiation, as well as with an altered microstructure of the cartilage extracellular matrix (ECM). We also demonstrated distinct functional and structural properties of the Achilles tendons isolated from Gnptg ko and Gnptab ki mice, the latter displaying a more severe phenotype resembling mucolipidosis type II (MLII) in humans. Together with comparative analyses of joint mobility in MLII and MLIII patients, these findings provide a basis for better understanding of the molecular reasons leading to joint pathology in these patients. Our data suggest that lack of GlcNAc-1-phosphotransferase activity due to defects in the γ-subunit causes structural changes within the ECM of connective and mechanosensitive tissues, such as cartilage and tendon, and eventually results in functional joint abnormalities typically observed in MLIII gamma patients. This idea was supported by a deficit of the limb motor function in Gnptg ko mice challenged on a Rotarod under fatigue-associated conditions, suggesting that the impaired motor performance of Gnptg ko mice was caused by fatigue and/or pain at the joint.
... Null GNPTAB mutations result in a severe storage disease that is often diagnosed in infancy or prenatally. Death due to cardio-pulmonary disease is common in the first decade, and early clinical findings include dysostosis multiplex, growth failure, marked developmental delay, and generalized hypotonia [50][51][52]. ...
Full-text available
The glycoprotein disorders are a group of lysosomal storage diseases (α-mannosidosis, aspartylglucosaminuria, β-mannosidosis, fucosidosis, galactosialidosis, sialidosis, mucolipidosis II, mucolipidosis III, and Schindler Disease) characterized by specific lysosomal enzyme defects and resultant buildup of undegraded glycoprotein substrates. This buildup causes a multitude of abnormalities in patients including skeletal dysplasia, inflammation, ocular abnormalities, liver and spleen enlargement, myoclonus, ataxia, psychomotor delay, and mild to severe neurodegeneration. Pharmacological treatment options exist through enzyme replacement therapy (ERT) for a few, but therapies for this group of disorders is largely lacking. Hematopoietic cell transplant (HCT) has been explored as a potential therapeutic option for many of these disorders, as HCT introduces functional enzyme-producing cells into the bone marrow and blood along with the engraftment of healthy donor cells in the central nervous system (presumably as brain macrophages or a type of microglial cell). The outcome of HCT varies widely by disease type. We report our institutional experience with HCT as well as a review of the literature to better understand HCT and outcomes for the glycoprotein disorders.
Lipids play a critical role in the structure and function of mammalian cells, which acquire lipids both by endocytosis of exogenous material and intracellular biosynthesis. This chapter reviews the molecular and genetic bases, diagnosis, and available treatment for the lipoprotein‐associated disorders, the disorders of biosynthesis and lysosomal catabolism of glycosphingolipids, the lysosomal breakdown and transport of cholesteryl esters, and the neuronal ceroid lipofuscinoses (NCLs). Glycosphingolipids are transported to the lysosomes along with other membrane components by endocytosis, autophagy, and phagocytosis. The chapter presents the molecular basis, genotype/phenotype correlation, post‐ and prenatal diagnosis, and therapy of the individual lysosomal storage diseases resulting from defects in the catabolism or processing of sphingolipids and cholesterol esters. The NCLs, also collectively known as Batten disease, encompass a group of more than a dozen genetically distinct, severe, progressive, degenerative disorders characterized by the accumulation of autofluorescent ceroid lipopigments in neural and peripheral tissues.
The rapid emergence and integration of effective therapies for many of the mucopolysaccharidoses (MPSs) has fueled a resurgence in the establishment of strategies leading to early diagnosis, including newborn screening and prenatal diagnosis as well as delineation of the precise pathogenic mechanisms underlying disease symptoms and natural history. The insights gained from the success of enzyme replacement strategies in altering somatic disease in the MPSs has led to the recent development and evaluation of alternative therapies for the MPSs, including those that specifically target the central nervous system as well as gene‐based therapeutics. The emergence of molecular genetic techniques, including chromosome microarray analysis, Sanger sequencing, and next‐generation sequencing methodologies providing accurate, single‐gene, gene‐panel, whole‐exome, and whole‐genome sequencing, has largely replaced enzymatic‐based prenatal diagnosis for the MPSs. Prior to the elucidation of the biochemical and molecular bases of MPS I, Scheie syndrome was initially thought to represent a distinct disorder and was termed MPS V.
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Human beta-glucuronidase (beta-D-glucuronide glucuronosohydrolase, EC, like many other glycoprotein lysosomal hydrolases, is specifically taken up from the culture medium by human fibroblasts. Prior work has indicated that the enzyme exhibits charge heterogeneity and that "high-uptake" forms, i.e., those rapidly internalized by human fibroblasts, are more acidic than slowly internalized forms. Here we present two lines of evidence that the acidic group required for the high-uptake property of certain forms of the enzyme is a phosphate on, or in proximity to, a D-mannose-type carbohydrate. The first line of evidence was obtained from analysis of inhibition of enzyme pinocytosis by yeast mannans, phosphorylated sugars, and sugars. Mannans that contained phosphate were more potent inhibitors than those that did not contain phosphate. D-Mannose 6-phosphate was a more potent inhibitor than either D-mannose 1 phosphate or 2-deoxy-D-glucose 6-phosphate. D-Mannose and certain related sugars were weak pinocytosis inhibitors, while 2- and 4-epimers of mannose were noninhibitory. Competitive inhibition was demonstrated and the apparent Kis estimated for the following compounds: Saccharomyces cerevisiae mannan from mutant X2180-mnnl, 3 X 10(-6) M; mannan from wild-type S. cerebisiae, 3 X 10(-5) M; D-mannose 6-phosphate, 6 X 10(-5) M; L-fucose, 4 X 10(-2) M; and D-mannose, 6 X 10(-2) M. The second line of evidence comes from the observation that alkaline phosphatase [orthophosphoric-monoester phosphohydrolase (alkaline optimum), EC] treatment of human platelet beta-glucuronidase abolished its "high-uptake" activity, without diminishing its catalytic activity, and converted some forms of the heterogeneous enzyme to less acidic forms.
UDP-N-acetylglucosamine:lysosomal-enzyme N-acetylglucosamine-1-phosphotransferase (GlcNAc-phosphotransferase) catalyzes the initial step in the synthesis of the mannose 6-phosphate determinant required for efficient intracellular targeting of newly synthesized lysosomal hydrolases to the lysosome, The enzyme was partially purified similar to 30,000-fold by chromatography of solubilized membrane proteins from lactating bovine mammary glands on DEAE-Sepharose, reactive green 19-agarose, and Superose 6, The partially purified enzyme was used to generate a panel of murine monoclonal antibodies, The anti-GlcNAc-phosphotransferase monoclonal antibody PT18 was coupled to a solid support and used to immunopurify the enzyme similar to 480,000-fold to apparent homogeneity with an overall yield of 29%, The purified enzyme has a specific activity of 10-12 mu mol of GlcNAc phosphate transferred per h/mg using 100 mM alpha-methylmannoside as acceptor. The subunit structure of the enzyme was determined using a combination of analytical gel filtration chromatography, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and amino-terminal sequencing. The data indicate that bovine GlcNAc-phosphotransferase is a 540,000-Da complex composed of disulfide-linked homodimers of 166,000- and 51,000-Da subunits and two identical, noncovalently associated 56,000-Da subunits.
Eight patients are presented who have a particular type of “Hurler”-like bodyconfiguration, severe skeletal dysplasia, severe psychomotor retardation, and normal urinary excretion of acid mucopolysaccharides, constituting in the sum a new entity, here designated as “I-cell” disease (or mucolipidosis II). The condition is evident from birth, with gradual accentuation of clinical features, complicated by respiratory infections, and with a fatal outcome. Familial occurrence in two instances and parental consanguinity in one, make autosomal recessive mode of inheritance most likely. Fibroblasts of these patients show an abundance of special cytoplasmic inclusions (“I cells”), have numerous deficiencies in lysosomal hydrolases, and contain excessive amounts of lipids and mucopolysaccharides. Results obtained on analysis of liver and brain specimens have less notable abnormalities. The pathogenesis of this new syndrome remains unknown. It must be differentiated especially from the Hurler's disease, GM1-gangliosidosis type 1, and lipomucopolysaccharidosis.
Newly synthesized acid hydrolases, destined for transport to lysosomes, acquire a phosphomannosyl targeting signal by the transfer of N-acetylglucosamine 1-phosphate from uridine 5'-diphosphate (UDP)-N-acetylglucosamine to a mannose residue of the acid hydrolase followed by removal of the outer, phosphodiester-linked N-acetylglucosamine to expose 6-phosphomannose. This study demonstrates that fibroblasts from patients with the lysosomal enzyme storage diseases, I-cell disease (mucolipidosis II) and pseudo-Hurler polydystrophy (mucolipidosis III), are severely deficient in UDP-N-acetylglucosamine:glycoprotein N-acetylglucosaminylphosphotransferase, the first enzyme of the sequence. The N-acetylglucosaminylphosphotransferase activity (assayed using endogenous acceptors) in cultures from six normal subjects ranged from 0.67 to 1.46 pmol N-acetylglucosamine-1-phosphate transferred/mg protein per h, whereas five pseudo-Hurler polydystrophy and five I-cell disease cultures transferred less than 0.02 pmol/mg protein per h. The activity in five other pseudo-Hurler cultures ranged from 0.02 to 0.27 pmol transferred/mg protein per h. The activity of alpha-N-acetylglucosaminyl phosphodiesterase, the enzyme responsible for phosphomonoester exposure, is normal or elevated in cultured fibroblasts from both I-cell disease and pseudo-Hurler polydystrophy patients. The deficiency of UDP-N-acetylglucosamine:glycoprotein N-acetylglucosaminylphosphotransferase explains the biochemical abnormalities previously observed in I-cell disease and pseudo-Hurler polydystrophy.
I-cell disease (mucolipidosis II) is a fatal childhood disorder affecting the expression of multiple lysosomal acid hydrolases. The disorder is characterized by clinical and biochemical heterogeneity which may reflect different mutants with a similar phenotype. Genetic complementation studies demonstrating genetic heterogeneity within this disorder are described utilizing cultured fibroblasts from 11 different patients. Fibroblasts from I-cell disease (ICD) and from five different lysosomal storage diseases with single structural gene enzyme deficiencies were fused in different combinations, and fractions enriched for multinucleated heterokaryons were isolated and tested for acid hydrolase activity and electrophoretic mobility. In fusions of ICD fibroblasts and various single lysosomal enzyme-deficient fibroblasts, the activity of the deficient enzyme and of the other ICD hydrolases were restored, demonstrating that ICD is not a lysosomal enzyme structural gene defect and that the ICD defect, and not just the single enzyme deficiency, is corrected. In fusions involving only I-cell fibroblasts, at least two complementation groups were identified by the recovery of activities of all lysosomal enzymes tested in heterokaryons. These results demonstrate the existence of genetic heterogeneity within the disorder and suggest that different mutations can result in the I-cell clinical and biochemical phenotype. The data support an altered post-translational processing of lysosomal enzymes as the cause of ICD and suggest that at least two genes participate in this pathway.
Recent finding of α-N-acetylglucosamine(1)phospho(6)mannose diesters in lysosomal enzymes suggested that formation of mannose 6-phosphate residues involves transfer of N-acetylglucosamine 1-phosphate to mannose. Using dephosphorylated β-hexosaminidase as acceptor and [β-32P]UDP-N-acetylglucosamine as donor for the phosphate group, phosphorylation of β-hexosaminidase by microsomes from rat liver, human placenta and human skin fibroblasts was achieved. The reaction was not affected by tunicamycin. Acid hydrolysis released mannose 6-[32P]phosphate from the phosphorylated β-hexosaminidase. Our results suggest that lysosomal enzymes are phosphorylated by transfer of N-acetylglucosamine 1-phosphate from UDP-N-acetylglucosamine. The transferase activity was deficient in fibroblasts from patients affected with l-cell disease. This deficiency is proposed to be the primary enzyme defect in l-cell disease.
Mucolipidosis III (ML III), or pseudo-Hurler polydystrophy, is an inherited childhood disorder characterized biochemically by low activities and abnormal electrophoretic patterns of multiple lysosomal enzymes in fibroblasts. The primary deficiency of ML III has been proposed to be in UDP-N-acetylglucosamine:lysosomal enzyme N-acetylglucosamine-1-phosphotransferase. However, variation in this enzyme and in other biochemical properties of different ML III lines has been observed. Therefore, we investigated genetic heterogeneity within the disorder by complementation analysis. Heterokaryon cell fractions were generated by fusing together ML III fibroblast lines. When pairs of cells complemented, correction of lysosomal enzyme activities and electrophoretic patterns was observed. Twelve fibroblast lines from 10 sibships were analyzed and three distinct complementation groups were characterized. One complementation group represents the classical ML III disorder. A single cell line identifies a second complementation group. The cell lines comprising a third complementation group have a number of biochemical characteristics different from classical ML III and may represent a genetically distinct disorder.