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Patterson K, Chong JX, Chung DD, Lisch W, Karp CL, Dreisler E, Lockington D, Rohrbach JM, Garczarczyk-Asim D, Müller T, Tuft SJ, Skalicka P, Wilnai Y, Samra NN, Ibrahim A, Mandel H, Davidson AE, Liskova P, Aldave AJ, Bamshad MJ, Janecke AR. Lisch Epithelial Corneal Dystrophy Is Caused by Heterozygous Loss-of-Function Variants in MCOLN1. Am J Ophthalmol 2024; 258:183-195. [PMID: 37972748 DOI: 10.1016/j.ajo.2023.10.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2023] [Revised: 10/19/2023] [Accepted: 10/20/2023] [Indexed: 11/19/2023]
Abstract
PURPOSE To report the genetic etiology of Lisch epithelial corneal dystrophy (LECD). DESIGN Multicenter cohort study. METHODS A discovery cohort of 27 individuals with LECD from 17 families, including 7 affected members from the original LECD family, 6 patients from 2 new families and 14 simplex cases, was recruited. A cohort of 6 individuals carrying a pathogenic MCOLN1 (mucolipin 1) variant was reviewed for signs of LECD. Next-generation sequencing or targeted Sanger sequencing were used in all patients to identify pathogenic or likely pathogenic variants and penetrance of variants. RESULTS Nine rare heterozygous MCOLN1 variants were identified in 23 of 27 affected individuals from 13 families. The truncating nature of 7 variants and functional testing of 1 missense variant indicated that they result in MCOLN1 haploinsufficiency. Importantly, in the homozygous and compound-heterozygous state, 4 of 9 LECD-associated variants cause the rare lysosomal storage disorder mucolipidosis IV (MLIV). Autosomal recessive MLIV is a systemic disease and comprises neurodegeneration as well as corneal opacity of infantile-onset with epithelial autofluorescent lysosomal inclusions. However, the 6 parents of 3 patients with MLIV confirmed to carry pathogenic MCOLN1 variants did not have the LECD phenotype, suggesting MCOLN1 haploinsufficiency may be associated with reduced penetrance and variable expressivity. CONCLUSIONS MCOLN1 haploinsufficiency is the major cause of LECD. Based on the overlapping clinical features of corneal epithelial cells with autofluorescent inclusions reported in both LECD and MLIV, it is concluded that some carriers of MCOLN1 haploinsufficiency-causing variants present with LECD.
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Affiliation(s)
- Karynne Patterson
- From the Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA (K.P., M.J.B.)
| | - Jessica X Chong
- Department of Pediatrics and Brotman-Baty Institute for Precision Medicine, University of Washington, Seattle, WA 98195, USA (J.X.C.)
| | - Doug D Chung
- Department of Ophthalmology, Stein Eye Institute, David Geffen School of Medicine, UCLA, Los Angeles, CA 90095, USA (D.D.C., A.J.A.)
| | - Walter Lisch
- Department of Ophthalmology, University Medical Center of the Johannes Gutenberg- University Mainz, 55131 Mainz, Germany (W.L.)
| | - Carol L Karp
- Department of Ophthalmology, Bascom Palmer Eye Institute, University of Miami Miller, School of Medicine, Miami, USA (C.L.K.)
| | - Erling Dreisler
- Independent scholar, N.Jespersensvej 3, DK-2000 Copenhagen, Frederiksberg, Denmark (E.D.)
| | - David Lockington
- Tennent Institute of Ophthalmology, NHS Greater Glasgow and Clyde, Gartnavel General Hospital, 1053 Great Western Road, Glasgow, G12 0YN, UK (D.L.)
| | - Jens M Rohrbach
- Universitäts-Augenklinik, Elfriede-Aulhorn-Str. 7, 72076, Tübingen, Deutschland (J.M.R.)
| | - Dorota Garczarczyk-Asim
- Department of Pediatrics I, Medical University of Innsbruck, 6020 Innsbruck, Austria (D.G.-A., T.M., A.R.J.)
| | - Thomas Müller
- Department of Pediatrics I, Medical University of Innsbruck, 6020 Innsbruck, Austria (D.G.-A., T.M., A.R.J.)
| | - Stephen J Tuft
- Moorfields eye hospital NHS foundation trust, London, UK (S.J.T.); UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK (A.E.D.)
| | - Pavlina Skalicka
- Department of Ophthalmology, First Faculty of Medicine, Charles University and General University Hospital in Prague, Prague, Czech Republic (P.S., P.L.)
| | - Yael Wilnai
- Genetic Institute, Tel Aviv Sourasky Medical Center, Tel Aviv 6423906, Israel (Y.W.)
| | - Nadra Naser Samra
- Genetic Unit, Sieff hospital, Bar Ilan University Faculty of Medicine, Safed, Israel (N.N.S.)
| | - Ali Ibrahim
- Ophthalmology unit, Maccabi and Clalit Health Services, Magdal Shams Medical center, Golan Heights, Israel (A.I.)
| | - Hanna Mandel
- Pediatric Metabolic Clinic, Sieff hospital, Bar Ilan University Faculty of Medicine, Safed, Israel (H.M.)
| | - Alice E Davidson
- UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK (A.E.D.)
| | - Petra Liskova
- Department of Ophthalmology, First Faculty of Medicine, Charles University and General University Hospital in Prague, Prague, Czech Republic (P.S., P.L.); Department of Paediatrics and Inherited Metabolic Disorders, First Faculty of Medicine, Charles University and General University Hospital in Prague, Prague, Czech Republic (P.S.,P.L.)
| | - Anthony J Aldave
- Department of Ophthalmology, Stein Eye Institute, David Geffen School of Medicine, UCLA, Los Angeles, CA 90095, USA (D.D.C., A.J.A.)
| | - Michael J Bamshad
- From the Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA (K.P., M.J.B.); Department of Pediatrics and Brotman-Baty Institute for Precision Medicine, University of Washington, Seattle, WA 98195, USA (J.X.C.)
| | - Andreas R Janecke
- Department of Pediatrics I, Medical University of Innsbruck, 6020 Innsbruck, Austria (D.G.-A., T.M., A.R.J.); Division of Human Genetics, Medical University of Innsbruck, 6020 Innsbruck, Austria (A.R.J.).
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Gibson D, Brar V, Li R, Kalra A, Goodwin A, Couser N. The High Association of Ophthalmic Manifestations in Individuals With Mucolipidosis Type IV. J Pediatr Ophthalmol Strabismus 2022; 59:332-337. [PMID: 35192386 DOI: 10.3928/01913913-20211206-03] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PURPOSE To present a case report of mucolipidosis type IV (ML4) and review the literature for all of the ophthalmic abnormalities associated with this disease. METHODS A systematic review of the literature using PubMed/Medline was conducted, and with the addition of the current case report, the eye and ocular adnexa findings of 93 patients with ML4 are summarized. RESULTS The most common ophthalmic findings reported among the 93 patients included corneal clouding (90.3%), strabismus (58.1%), optic nerve pallor (52.2%), retinal dystrophy/pigmentary changes (50.5%), and retinal vascular attenuation (38.9%). Other less commonly reported findings included nystagmus, photophobia, ocular pain, excessive lacrimation, ptosis, and cataracts. CONCLUSIONS The ophthalmic findings discussed in the current case report and literature review serve as indicators for ML4. Early diagnosis of ML4 is important in forming a multidisciplinary management plan, genetic counseling strategy, and maximizing the visual development of affected individuals. [J Pediatr Ophthalmol Strabimus. 2022;59(5):332-337.].
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Hoogmartens C, Rickmann A, Bocqué C, Szurman P, Boden KT. [Late onset visual loss due to retinal atrophy in atypical mucolipidosis type IV]. Ophthalmologe 2021; 119:90-92. [PMID: 33502543 DOI: 10.1007/s00347-021-01322-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2020] [Accepted: 01/08/2021] [Indexed: 11/30/2022]
Affiliation(s)
- Caroline Hoogmartens
- Augenklinik Sulzbach, Knappschaftsklinikum Saar, An der Klinik 10, 66280, Sulzbach/Saar, Deutschland.
| | - Annekatrin Rickmann
- Augenklinik Sulzbach, Knappschaftsklinikum Saar, An der Klinik 10, 66280, Sulzbach/Saar, Deutschland
| | - Catheline Bocqué
- Augenklinik Sulzbach, Knappschaftsklinikum Saar, An der Klinik 10, 66280, Sulzbach/Saar, Deutschland
| | - Peter Szurman
- Augenklinik Sulzbach, Knappschaftsklinikum Saar, An der Klinik 10, 66280, Sulzbach/Saar, Deutschland
| | - Karl Thomas Boden
- Augenklinik Sulzbach, Knappschaftsklinikum Saar, An der Klinik 10, 66280, Sulzbach/Saar, Deutschland
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Jezela-Stanek A, Ciara E, Stepien KM. Neuropathophysiology, Genetic Profile, and Clinical Manifestation of Mucolipidosis IV-A Review and Case Series. Int J Mol Sci 2020; 21:ijms21124564. [PMID: 32604955 PMCID: PMC7348969 DOI: 10.3390/ijms21124564] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2020] [Revised: 06/21/2020] [Accepted: 06/23/2020] [Indexed: 12/23/2022] Open
Abstract
Mucolipidosis type IV (MLIV) is an ultra-rare lysosomal storage disorder caused by biallelic mutations in MCOLN1 gene encoding the transient receptor potential channel mucolipin-1. So far, 35 pathogenic or likely pathogenic MLIV-related variants have been described. Clinical manifestations include severe intellectual disability, speech deficit, progressive visual impairment leading to blindness, and myopathy. The severity of the condition may vary, including less severe psychomotor delay and/or ocular findings. As no striking recognizable facial dysmorphism, skeletal anomalies, organomegaly, or lysosomal enzyme abnormalities in serum are common features of MLIV, the clinical diagnosis may be significantly improved because of characteristic ophthalmological anomalies. This review aims to outline the pathophysiology and genetic defects of this condition with a focus on the genotype–phenotype correlation amongst cases published in the literature. The authors will present their own clinical observations and long-term outcomes in adult MLIV cases.
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Affiliation(s)
- Aleksandra Jezela-Stanek
- Department of Genetics and Clinical Immunology, National Institute of Tuberculosis and Lung Diseases, 01-138 Warsaw, Poland;
| | - Elżbieta Ciara
- Department of Medical Genetics, The Children’s Memorial Heath Institute, 04-730 Warsaw, Poland;
| | - Karolina M. Stepien
- Adult Inherited Metabolic Diseases, Salford Royal NHS Foundation Trust, Salford M6 8HD, UK
- Correspondence:
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Boudewyn LC, Walkley SU. Current concepts in the neuropathogenesis of mucolipidosis type IV. J Neurochem 2019; 148:669-689. [PMID: 29770442 PMCID: PMC6239999 DOI: 10.1111/jnc.14462] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2018] [Revised: 04/29/2018] [Accepted: 05/02/2018] [Indexed: 12/11/2022]
Abstract
Mucolipidosis type IV (MLIV) is an autosomal recessive, lysosomal storage disorder causing progressively severe intellectual disability, motor and speech deficits, retinal degeneration often culminating in blindness, and systemic disease causing a shortened lifespan. MLIV results from mutations in the gene MCOLN1 encoding the transient receptor potential channel mucolipin-1. It is an ultra-rare disease and is currently known to affect just over 100 diagnosed individuals. The last decade has provided a wealth of research focused on understanding the role of the enigmatic mucolipin-1 protein in cell and brain function and how its absence causes disease. This review explores our current understanding of the mucolipin-1 protein in relation to neuropathogenesis in MLIV and describes recent findings implicating mucolipin-1's important role in mechanistic target of rapamycin and TFEB (transcription factor EB) signaling feedback loops as well as in the function of the greater endosomal/lysosomal system. In addition to addressing the vital role of mucolipin-1 in the brain, we also report new data on the question of whether haploinsufficiency as would be anticipated in MCOLN1 heterozygotes is associated with any evidence of neuron dysfunction or disease. Greater insights into the role of mucolipin-1 in the nervous system can be expected to shed light not only on MLIV disease but also on numerous processes governing normal brain function. This article is part of the Special Issue "Lysosomal Storage Disorders".
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Affiliation(s)
- Lauren C. Boudewyn
- Dominick P. Purpura Department of Neuroscience, Rose F. Kennedy Intellectual and Developmental Disabilities Research Center, Albert Einstein College of Medicine, Bronx, New York
| | - Steven U. Walkley
- Dominick P. Purpura Department of Neuroscience, Rose F. Kennedy Intellectual and Developmental Disabilities Research Center, Albert Einstein College of Medicine, Bronx, New York
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The role of TRPMLs in endolysosomal trafficking and function. Cell Calcium 2014; 58:48-56. [PMID: 25465891 DOI: 10.1016/j.ceca.2014.10.008] [Citation(s) in RCA: 140] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Revised: 10/15/2014] [Accepted: 10/17/2014] [Indexed: 12/24/2022]
Abstract
Members of the Transient Receptor Potential-Mucolipin (TRPML) constitute a family of evolutionarily conserved cation channels that function predominantly in endolysosomal vesicles. Whereas loss-of-function mutations in human TRPML1 were first identified as being causative for the lysosomal storage disease, Mucolipidosis type IV, most mammals also express two other TRPML isoforms called TRPML2 and TRPML3. All three mammalian TRPMLs as well as TRPML related genes in other species including Caenorhabditis elegans and Drosophila exhibit overlapping functional and biophysical properties. The functions of TRPML proteins include roles in vesicular trafficking and biogenesis, maintenance of neuronal development, function, and viability, and regulation of intracellular and organellar ionic homeostasis. Biophysically, TRPML channels are non-selective cation channels exhibiting variable permeability to a host of cations including Na(+), Ca(2+), Fe(2+), and Zn(2+), and are activated by a phosphoinositide species, PI(3,5)P2, that is mostly found in endolysosomal membranes. Here, we review the functional and biophysical properties of these enigmatic cation channels, which represent the most ancient and archetypical TRP channels.
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Wakabayashi K, Gustafson AM, Sidransky E, Goldin E. Mucolipidosis type IV: an update. Mol Genet Metab 2011; 104:206-13. [PMID: 21763169 PMCID: PMC3205274 DOI: 10.1016/j.ymgme.2011.06.006] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/20/2011] [Revised: 06/09/2011] [Accepted: 06/09/2011] [Indexed: 11/28/2022]
Abstract
Mucolipidosis type IV (MLIV) is a neurodevelopmental as well as neurodegenerative disorder with severe psychomotor developmental delay, progressive visual impairment, and achlorydria. It is characterized by the presence of lysosomal inclusions in many cell types in patients. MLIV is an autosomal recessive disease caused by mutations in MCOLN1, which encodes for mucolipin-1, a member of the transient receptor potential (TRP) cation channel family. Although approximately 70-80% of patients identified are Ashkenazi Jewish, MLIV is a pan-ethnic disorder. Importantly, while MLIV is thought to be a rare disease, its frequency may be greater than currently appreciated, for its common presentation as a cerebral palsy-like encephalopathy can lead to misdiagnosis. Moreover, patients with milder variants are often not recognized as having MLIV. This review provides an update on the ethnic distribution, clinical manifestations, laboratory findings, methods of diagnosis, molecular genetics, differential diagnosis, and treatment of patients with MLIV. An enhanced awareness of the manifestations of this disorder may help to elucidate the true frequency and range of symptoms associated with MLIV, providing insight into the pathogenesis of this multi-system disease.
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Affiliation(s)
| | | | - Ellen Sidransky
- Section on Molecular Neurogenetics, Medical Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Building 35, Room 1A213, 35 Convent Dr., MSC 3708, Bethesda, MD 20892-3708
| | - Ehud Goldin
- Section on Molecular Neurogenetics, Medical Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Building 35, Room 1A213, 35 Convent Dr., MSC 3708, Bethesda, MD 20892-3708
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Abstract
MLIV (mucolipidosis type IV) is a neurodegenerative lysosomal storage disorder caused by mutations in MCOLN1, a gene that encodes TRPML1 (mucolipin-1), a member of the TRPML (transient receptor potential mucolipin) cation channels. Two additional homologues are TRPML2 and TRPML3 comprising the TRPML subgroup in the TRP superfamily. The three proteins play apparently key roles along the endocytosis process, and thus their cellular localization varies among the different group members. Thus TRPML1 is localized exclusively to late endosomes and lysosomes, TRPML2 is primarily located in the recycling clathrin-independent GPI (glycosylphosphatidylinositol)-anchored proteins and early endosomes, and TRPML3 is primarily located in early endosomes. Apparently, all three proteins' main physiological function underlies Ca2+ channelling, regulating the endocytosis process. Recent findings also indicate that the three TRPML proteins form heteromeric complexes at least in some of their cellular content. The physiological role of these complexes in lysosomal function remains to be elucidated, as well as their effect on the pathophysiology of MLIV. Another open question is whether any one of the TRPMLs bears additional function in channel activity
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Goldin E, Caruso RC, Benko W, Kaneski CR, Stahl S, Schiffmann R. Isolated ocular disease is associated with decreased mucolipin-1 channel conductance. Invest Ophthalmol Vis Sci 2008; 49:3134-42. [PMID: 18326692 DOI: 10.1167/iovs.07-1649] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE To evaluate a 15-year-old boy with MLIV (mucolipidosis type IV) and clinical abnormalities restricted to the eye who also had achlorhydria with elevated blood gastrin levels. METHODS In addition to a detailed neuro-ophthalmic and electrophysiological assessment, his mutant mucolipin-1 was experimentally expressed in liposomes and its channel properties studied in vitro. RESULTS The patient was a compound heterzygote for c.920delT and c.1615delG. Detailed neuro-ophthalmic examination including electroretinography showed him to have a typical retinal dystrophy predominantly affecting rod and bipolar cell function. In vitro expression of MCOLN1 in liposomes showed that the c.1615delG mutated channel had significantly reduced conductance compared with wild-type mucolipin-1, whereas the inhibitory effect of low pH and amiloride remained intact. CONCLUSIONS These findings suggest that reduced channel conductance is relatively well tolerated by the brain during development, whereas retinal cells and stomach parietal cells require normal protein function. MLIV should be considered in patients with retinal dystrophy of unknown cause and screened for using blood gastrin levels.
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Affiliation(s)
- Ehud Goldin
- Molecular Neurogenetics Section, Medical Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland, USA
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Zeevi DA, Frumkin A, Bach G. TRPML and lysosomal function. Biochim Biophys Acta Mol Basis Dis 2007; 1772:851-8. [PMID: 17306511 DOI: 10.1016/j.bbadis.2007.01.004] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2006] [Revised: 01/10/2007] [Accepted: 01/10/2007] [Indexed: 11/28/2022]
Abstract
Mucolipin 1 (MLN1), also known as TRPML1, is a member of the mucolipin family. The mucolipins are the only lysosomal proteins within the TRP superfamily. Mutations in the gene coding for TRPML1 result in a lysosomal storage disorder (LSD). This review summarizes the current knowledge related to this protein and the rest of the mucolipin family.
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Affiliation(s)
- David A Zeevi
- Department of Human Genetics, Hadassah Hebrew University Hospital, Jerusalem, Israel
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Ro LS, Chen CM, Chang HS, Lyu RK, Wu YR, Hsu WC, Lee-Chen GJ. Contribution of clinical screening to carrier detection in a large Chinese family with fabry disease due to a novel alpha-galactosidase A gene deletion. Eur J Neurol 2007; 14:493-7. [PMID: 17437606 DOI: 10.1111/j.1468-1331.2006.01611.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Diagnosis of heterozygous Fabry patients is difficult because of its variable clinical manifestations and overlapping serum alpha-galactosidase A (AGA) activity between carriers and non-carriers. We tried to facilitate diagnosis of heterozygous Fabry patients by detailed clinical examination. We analyzed clinical presentations, biochemical, electrophysiological and genetic characteristics of 16 patients with Fabry disease in a large Chinese family. Male patients demonstrated significantly higher pain scores, poorer renal function, and higher frequency of hypohidrosis and corpora angiokeratomas than female patients. Interestingly, all the males and females had corneal verticilata by slit lamp examination. However, there was no association of serum AGA activity with renal function or pain symptom scores. The results indicated that detailed ocular and neurological examination might provide an alternative way of detecting heterozygous patients. We also report a novel large deletion spanning across the joint of Alu repetitive elements in introns 1 and 2 with resultant exon 2 deletion in a Chinese family with Fabry disease.
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Affiliation(s)
- L-S Ro
- Department of Neurology, Chang Gung Memorial Hospital and University, Taipei, Taiwan
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Dobrovolny R, Liskova P, Ledvinova J, Poupetova H, Asfaw B, Filipec M, Jirsova K, Kraus J, Elleder M. Mucolipidosis IV: report of a case with ocular restricted phenotype caused by leaky splice mutation. Am J Ophthalmol 2007; 143:663-71. [PMID: 17239335 DOI: 10.1016/j.ajo.2006.11.049] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2006] [Revised: 11/22/2006] [Accepted: 11/22/2006] [Indexed: 11/28/2022]
Abstract
PURPOSE To confirm and define a molecular basis for a case of mucolipidosis type IV (ML IV) with an extremely atypical phenotype pattern. DESIGN Observational case report of a patient with ML IV with disease progression restricted to ocular symptoms. METHODS Complete ophthalmologic and neurologic examination. Ultrastructural examination of white blood cells, skin, conjunctiva, and corneal epithelium. The MCOLN1 gene was sequenced from cDNA and the proportion of splicing variants were assessed by quantitative allele-specific polymerase chain reaction. RESULTS Absence of any neurological abnormalities. Retinal pathologic features were the main cause of visual disability: low visual acuity and cloudy corneas since 2 years of age, progressive decrease in visual acuity since the age of 9 years. Ultrastructural examination showed storage lysosomes filled with either concentric membranes or lucent precipitate in corneal and conjunctive epithelia and in vascular endothelium. Cultured fibroblasts were free of any autofluorescence. Sequencing of the MCOLN1 gene identified compound heterozygosity for D362Y and A-->T transition leading to the creation of a novel donor splicing site and a 4-bp deletion from exon 13 at the mRNA level. Both normal and pathologic splice forms were detected in skin fibroblasts and leukocytes, with the normal form being more abundant. CONCLUSIONS The case of this patient with ML IV is unique and is characterized by a curious lack of generalized symptoms. In this patient, the disorder was limited to the eyes and appeared without the usual psychomotor deterioration. The resulting phenotype is the mildest seen to date.
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Affiliation(s)
- Robert Dobrovolny
- Institute of Inherited Metabolic Diseases, First Medical Faculty and General Faculty Hospital, Charles University, Prague, Czech Republic
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Bach G. Mucolipin 1: endocytosis and cation channel--a review. Pflugers Arch 2004; 451:313-7. [PMID: 15570434 DOI: 10.1007/s00424-004-1361-7] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2004] [Accepted: 10/05/2004] [Indexed: 11/26/2022]
Abstract
Mucolipidosis type IV (MLIV) is a neurodegenerative, recessive, lysosomal storage disorder characterized by psychomotor retardation and visual impairment due to various ophthalmologic abnormalities. MLIV is found in relatively high frequency in the Ashkenazi Jewish population. The disease is caused by mutations in the gene MCOLN1, which encodes the protein mucolipin 1 (MLN1), a member of the mucolipins family. MLN1 is a non-specific cation channel, and its putative structure attributes it to the TRP superfamily; thus, the gene is also referred as TRPML1. Over 16 MLIV-causing mutations, including two founder mutations in the Ashkenazi population, have been identified hitherto. Atypical increased lysosomal storage in MLIV is present in the cells of all patients. This accumulation is caused by an abnormal endocytosis process of the membrane components to late endosomes to the lysosomes, resulting in an apparent block in the traffic process in pre-lysosomal vacuoles with intraluminal pH of >5.0. MLN1 was localized in cultured cells to late endosomes and lysosomes. The exact function of this cation channel in the late stages of lysosomal maintenance is currently under study.
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Affiliation(s)
- Gideon Bach
- Department of Human Genetics, Hadassah Hebrew University Hospital, 91120 Jerusalem, Israel.
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Abstract
Mucolipidosis type IV (MLIV) is a neurodegenerative lysosomal storage disorder characterized by psychomotor retardation and ophthalmological abnormalities, including corneal opacities, retinal degeneration, and strabismus. Severely affected as well as milder patients have been described. Over 80% of the MLIV patients are Ashkenazi Jews; the estimated heterozygote frequency in this population is 1/100. The disease is classified as a mucolipidosis due to the simultaneous lysosomal storage of lipids together with water-soluble substances. A broad spectrum of lipids and acid mucopolysaccharides were identified as the storage substances. Kinetic studies demonstrated that this heterogeneous storage stems from an abnormal endocytosis process in cells from MLIV patients of membrane components from late endosomes to the lysosomes and/or delayed efflux to the Golgi apparatus. The MLIV gene was mapped to chromosome 19p13.2--13.3 where a novel gene, MCOLN1, with MLIV-causing mutations, was identified. Two mutations were found among 95% of the Ashkenazi MLIV alleles, including an intronic acceptor splice-site mutation in 72% of the alleles and a partial gene deletion in 23%. Each of these mutations was associated with a defined haplotype in this chromosomal region. Other mutations were mostly identified in single, Ashkenazi and non-Ashkanazi patients, including missense, nonsense nucleotide deletions, and insertions. All mutations but one were identified in patients exhibiting the severe phenotype, an in-frame amino acid deletion was identified in a mild patient. MCOLN1 encodes a 580 aa protein, mucolipin 1, which is a member of a new protein family of unknown function at present, the mucolipins. Mucolipin 1 is a membrane protein with 6 transmembrane domains, a serine lipase, and nuclear localization signal motives. The protein shows homology to a group of calcium channels of the TRP/TRPL family. The involvement of this protein in the endocytosis process of membrane components is currently studied. A population screening operation among the Ashkenazi population for the detection of heterozygotes has been started in Israel as a prevention program.
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Affiliation(s)
- G Bach
- Department of Human Genetics, Hadassah Hebrew University Hospital, Jerusalem 91120, Israel.
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Abstract
We investigated 16 patients with Fabry's disease (eight hemizygous men and eight heterozygous women) in one family. We used constant current perception threshold (CPT) testing, which evaluated three major sensory nerve fiber populations, to assess subjective complaints of pain and paresthesias. We also examined clinical and biochemical features and compared the values of CPTs and nerve conduction studies (NCS) in detecting the sensory neuropathy. Our results showed that CPT testing at low frequencies (5 and 250 Hz) was significantly more sensitive than at a higher frequency (2 kHz) and NCS in detecting sensory neuropathy in patients with Fabry's disease. However, there was no correlation between CPT testing and clinical symptom scores, duration of disease, creatinine clearance (Ccr) values or alpha-galactosidase A (AGA) activities in either hemizygous or heterozygous patients. Hemizygous patients clinically demonstrated more severe symptom scores, poorer renal function, and higher prevalence of hypohidrosis and corpora angiokeratomas than did heterozygous patients, which indicates that detailed clinical examinations can differentiate the clinical status of hemizygous men from heterozygous women. There were no associations between the biochemical levels of serum AGA activity and renal function (Ccr values) or the symptom scores (grading of acroparesthesia), indicating that biochemical parameters do not predict clinical severity.
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Affiliation(s)
- L S Ro
- Department of Neurology, Chang Gung Memorial Hospital, and Chang Gung University, 199 Tung Hwa North Road, Taipei, Taiwan 10591.
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