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Uncini A, Cavallaro T, Fabrizi GM, Manganelli F, Vallat JM. Conduction slowing, conduction block and temporal dispersion in demyelinating, dysmyelinating and axonal neuropathies: Electrophysiology meets pathology. J Peripher Nerv Syst 2024. [PMID: 38600691 DOI: 10.1111/jns.12625] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2024] [Revised: 03/02/2024] [Accepted: 03/28/2024] [Indexed: 04/12/2024]
Abstract
Nerve conduction studies are usually the first diagnostic step in peripheral nerve disorders and their results are the basis for planning further investigations. However, there are some commonplaces in the interpretation of electrodiagnostic findings in peripheral neuropathies that, although useful in the everyday practice, may be misleading: (1) conduction block and abnormal temporal dispersion are distinctive features of acquired demyelinating disorders; (2) hereditary neuropathies are characterized by uniform slowing of conduction velocity; (3) axonal neuropathies are simply diagnosed by reduced amplitude of motor and sensory nerve action potentials with normal or slightly slow conduction velocity. In this review, we reappraise the occurrence of uniform and non-uniform conduction velocity slowing, conduction block and temporal dispersion in demyelinating, dysmyelinating and axonal neuropathies attempting, with a translational approach, a correlation between electrophysiological and pathological features as derived from sensory nerve biopsy in patients and animal models. Additionally, we provide some hints to navigate in this complex field.
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Affiliation(s)
- Antonino Uncini
- Department of Neurosciences, Imaging and Clinical Sciences, University "G. d'Annunzio", Chieti-Pescara, Italy
| | - Tiziana Cavallaro
- Department of Neurosciences, Biomedicine, and Movement Sciences, University of Verona, Verona, Italy
| | - Gian Maria Fabrizi
- Department of Neurosciences, Biomedicine, and Movement Sciences, University of Verona, Verona, Italy
| | - Fiore Manganelli
- Department of Neurosciences, Reproductive Sciences and Odontostomatology, University of Naples "Federico II", Naples, Italy
| | - Jean-Michel Vallat
- Department of Neurology, National Reference Center for "Rare Peripheral Neuropathies", CHU Dupuytren, Limoges, France
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Moss KR, Bopp TS, Johnson AE, Höke A. New evidence for secondary axonal degeneration in demyelinating neuropathies. Neurosci Lett 2021; 744:135595. [PMID: 33359733 PMCID: PMC7852893 DOI: 10.1016/j.neulet.2020.135595] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2020] [Revised: 10/31/2020] [Accepted: 12/19/2020] [Indexed: 12/28/2022]
Abstract
Development of peripheral nervous system (PNS) myelin involves a coordinated series of events between growing axons and the Schwann cell (SC) progenitors that will eventually ensheath them. Myelin sheaths have evolved out of necessity to maintain rapid impulse propagation while accounting for body space constraints. However, myelinating SCs perform additional critical functions that are required to preserve axonal integrity including mitigating energy consumption by establishing the nodal architecture, regulating axon caliber by organizing axonal cytoskeleton networks, providing trophic and potentially metabolic support, possibly supplying genetic translation materials and protecting axons from toxic insults. The intermediate steps between the loss of these functions and the initiation of axon degeneration are unknown but the importance of these processes provides insightful clues. Prevalent demyelinating diseases of the PNS include the inherited neuropathies Charcot-Marie-Tooth Disease, Type 1 (CMT1) and Hereditary Neuropathy with Liability to Pressure Palsies (HNPP) and the inflammatory diseases Acute Inflammatory Demyelinating Polyneuropathy (AIDP) and Chronic Inflammatory Demyelinating Polyneuropathy (CIDP). Secondary axon degeneration is a common feature of demyelinating neuropathies and this process is often correlated with clinical deficits and long-lasting disability in patients. There is abundant electrophysiological and histological evidence for secondary axon degeneration in patients and rodent models of PNS demyelinating diseases. Fully understanding the involvement of secondary axon degeneration in these diseases is essential for expanding our knowledge of disease pathogenesis and prognosis, which will be essential for developing novel therapeutic strategies.
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Affiliation(s)
- Kathryn R Moss
- Department of Neurology, Neuromuscular Division, Johns Hopkins School of Medicine, Baltimore, MD, United States
| | - Taylor S Bopp
- Department of Neurology, Neuromuscular Division, Johns Hopkins School of Medicine, Baltimore, MD, United States
| | - Anna E Johnson
- Department of Neurology, Neuromuscular Division, Johns Hopkins School of Medicine, Baltimore, MD, United States
| | - Ahmet Höke
- Department of Neurology, Neuromuscular Division, Johns Hopkins School of Medicine, Baltimore, MD, United States.
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Taniguchi T, Ando M, Okamoto Y, Yoshimura A, Higuchi Y, Hashiguchi A, Shiga K, Hayashida A, Hatano T, Ishiura H, Mitsui J, Hattori N, Mizuno T, Nakagawa M, Tsuji S, Takashima H. Genetic spectrum of Charcot-Marie-Tooth disease associated with myelin protein zero gene variants in Japan. Clin Genet 2020; 99:359-375. [PMID: 33179255 PMCID: PMC7898366 DOI: 10.1111/cge.13881] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2020] [Revised: 11/04/2020] [Accepted: 11/04/2020] [Indexed: 12/24/2022]
Abstract
We aimed to reveal the genetic features associated with MPZ variants in Japan. From April 2007 to August 2017, 64 patients with 23 reported MPZ variants and 21 patients with 17 novel MPZ variants were investigated retrospectively. Variation in MPZ variants and the pathogenicity of novel variants was examined according to the American College of Medical Genetics standards and guidelines. Age of onset, cranial nerve involvement, serum creatine kinase (CK), and cerebrospinal fluid (CSF) protein were also analyzed. We identified 64 CMT patients with reported MPZ variants. The common variants observed in Japan were different from those observed in other countries. We identified 11 novel pathogenic variants from 13 patients. Six novel MPZ variants in eight patients were classified as likely benign or uncertain significance. Cranial nerve involvement was confirmed in 20 patients. Of 30 patients in whom serum CK levels were evaluated, eight had elevated levels. Most of the patients had age of onset >20 years. In another subset of 30 patients, 18 had elevated CSF protein levels; four of these patients had spinal diseases and two had enlarged nerve root or cauda equina. Our results suggest genetic diversity across patients with MPZ variants.
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Affiliation(s)
- Takaki Taniguchi
- Department of Neurology and Geriatrics, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan
| | - Masahiro Ando
- Department of Neurology and Geriatrics, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan
| | - Yuji Okamoto
- Department of Neurology and Geriatrics, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.,Department of Physical Therapy, School of Health Sciences, Faculty of Medicine, Kagoshima University, Kagoshima, Japan
| | - Akiko Yoshimura
- Department of Neurology and Geriatrics, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan
| | - Yujiro Higuchi
- Department of Neurology and Geriatrics, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan
| | - Akihiro Hashiguchi
- Department of Neurology and Geriatrics, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan
| | - Kensuke Shiga
- Department of Neurology, Matsushita Memorial Hospital, Osaka, Japan.,Department of Neurology, Kyoto prefectural University of Medicine, Kyoto, Japan
| | - Arisa Hayashida
- Department of Neurology, Juntendo University School of Medicine, Tokyo, Japan
| | - Taku Hatano
- Department of Neurology, Juntendo University School of Medicine, Tokyo, Japan
| | - Hiroyuki Ishiura
- Department of Molecular Neurology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
| | - Jun Mitsui
- Department of Molecular Neurology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
| | - Nobutaka Hattori
- Department of Neurology, Juntendo University School of Medicine, Tokyo, Japan
| | - Toshiki Mizuno
- Department of Neurology, Kyoto prefectural University of Medicine, Kyoto, Japan
| | - Masanori Nakagawa
- Department of Neurology, Kyoto prefectural University of Medicine, Kyoto, Japan.,North Medical Center, Kyoto prefectural University of Medicine, Kyoto, Japan
| | - Shoji Tsuji
- Department of Molecular Neurology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan.,Institute of Medical Genomics, International University of Health and Welfare, Chiba, Japan
| | - Hiroshi Takashima
- Department of Neurology and Geriatrics, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan
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CNTNAP1 Mutations and Their Clinical Presentations: New Case Report and Systematic Review. Case Rep Med 2020; 2020:8795607. [PMID: 32328110 PMCID: PMC7174947 DOI: 10.1155/2020/8795607] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2019] [Revised: 03/23/2020] [Accepted: 03/27/2020] [Indexed: 01/11/2023] Open
Abstract
Lethal congenital contracture syndrome type 7 (LCCS7) and congenital hypomyelinating neuropathy type 3 (CHN3) are rare autosomal recessive diseases, characterized by severe neonatal hypotonia, polyhydramnios, arthrogryposis, facial diplegia, and severe motor paralysis, leading to death in early infancy. They are related to mutations in the CNTNAP1 (contactin associated protein 1) gene, playing an important role in myelination. Recent studies have shown that both diseases could present with a wide phenotypic spectrum, with promising survival up to early childhood. We report on a 7-year-old boy from a nonconsanguineous Lebanese family presenting with neonatal hypotonia, respiratory distress, and arthrogryposis. Molecular analysis revealed the presence of a pathogenic variant in the CNTNAP1 gene leading to a premature stop codon: NM_003632.2:c.3361C>T p.(Arg1121∗). A review of the literature is discussed.
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Adult-onset demyelinating neuropathy associated with FBLN5 gene mutation. Clin Neuropathol 2017; 36:171-177. [PMID: 28332470 PMCID: PMC5541264 DOI: 10.5414/np301011] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/29/2017] [Indexed: 11/18/2022] Open
Abstract
Rare forms of autosomal-dominant Charcot-Marie-Tooth disease (AD-CMT) may be associated with mutations in Fibulin-5 (FBLN5) as AD-CMT is genetically heterogeneous. Here, we report the first pathological study of an Asian family. The proband was a 46-year-old man with slowly progressive distal numbness and weakness for 12 years. He had a history of diabetes mellitus for 12 years. His mother was 81 years old and had mild polyneuropathy. His 16-year-old daughter was asymptomatic. The nerve conduction velocities (NCVs) and compound muscular action potential (CMAP) amplitudes were moderately to severely reduced in the proband, and moderately reduced in his daughter and mother. A sensory response could not be elicited in the proband and was moderately to severely decreased in the daughter and mother. Nerve ultrasound indicated a general enlargement of the peripheral nerves in the proband, daughter, and mother. A sural nerve biopsy from the proband demonstrated a pronounced depletion of myelinated fibers, thin myelinated fibers, and onion-bulb formations. A reported heterozygous mutation of c.1117C>T in FBLN5 was identified in the proband, mother, and daughter. These findings confirm a novel subtype of AD-CMT 1 due to a mutation in the FBLN5 gene.
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Werheid F, Azzedine H, Zwerenz E, Bozkurt A, Moeller MJ, Lin L, Mull M, Häusler M, Schulz JB, Weis J, Claeys KG. Underestimated associated features in CMT neuropathies: clinical indicators for the causative gene? Brain Behav 2016; 6:e00451. [PMID: 27088055 PMCID: PMC4782242 DOI: 10.1002/brb3.451] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/17/2015] [Revised: 01/25/2016] [Accepted: 02/02/2016] [Indexed: 12/15/2022] Open
Abstract
INTRODUCTION Charcot-Marie-Tooth neuropathy (CMT) is a genetically heterogeneous group of peripheral neuropathies. In addition to the classical clinical phenotype, additional features can occur. METHODS We studied a wide range of additional features in a cohort of 49 genetically confirmed CMT patients and performed a systematic literature revision. RESULTS Patients harbored a PMP22 gene alteration (n = 28) or a mutation in MPZ (n = 11), GJB1 (n = 4), LITAF (n = 2), MFN2 (n = 2), INF2 (n = 1), NEFL (n = 1). We identified four novel mutations (3 MPZ, 1 GJB1). A total of 88% presented at least one additional feature. In MPZ patients, we detected hypertrophic nerve roots in 3/4 cases that underwent spinal MRI, and pupillary abnormalities in 27%. In our cohort, restless legs syndrome (RLS) was present in 18%. We describe for the first time RLS associated with LITAF or MFN2 and predominant upper limb involvement with LITAF. Cold-induced hand cramps occurred in 10% (PMP22,MPZ,MFN2), and autonomous nervous system involvement in 18% (PMP22,MPZ, LITAF,MFN2). RLS and respiratory insufficiency were mostly associated with severe neuropathy, and pupillary abnormalities with mild to moderate neuropathy. CONCLUSIONS In CMT patients, additional features occur frequently. Some of them might be helpful in orienting genetic diagnosis. Our data broaden the clinical spectrum and genotype-phenotype associations with CMT.
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Affiliation(s)
- Friederike Werheid
- Department of Neurology University Hospital RWTH Aachen Aachen Germany; Institute of Neuropathology University Hospital RWTH Aachen Aachen Germany
| | - Hamid Azzedine
- Institute of Neuropathology University Hospital RWTH Aachen Aachen Germany
| | - Eva Zwerenz
- Department of Neurology University Hospital RWTH Aachen Aachen Germany; Institute of Neuropathology University Hospital RWTH Aachen Aachen Germany
| | - Ahmet Bozkurt
- Department of Plastic and Reconstructive Surgery Hand Surgery-Burn Center University Hospital RWTH Aachen Aachen Germany; Department of Plastic & Aesthetic, Reconstructive & Hand Surgery Center for Reconstructive Microsurgery and Peripheral Nerve Surgery (ZEMPEN) Agaplesion Markus Hospital Frankfurt am Main Germany
| | - Marcus J Moeller
- Section Immunology and Nephrology Department of Internal Medicine University Hospital RWTH Aachen Aachen Germany
| | - Lilian Lin
- Department of Neurology University Hospital RWTH Aachen Aachen Germany; Institute of Neuropathology University Hospital RWTH Aachen Aachen Germany
| | - Michael Mull
- Department of Neuroradiology University Hospital RWTH Aachen Aachen Germany
| | - Martin Häusler
- Division of Neuropediatrics and Social Pediatrics Department of Pediatrics University Hospital RWTH Aachen Aachen Germany
| | - Jörg B Schulz
- Department of Neurology University Hospital RWTH Aachen Aachen Germany; JARA - Translational Brain Medicine Aachen Germany
| | - Joachim Weis
- Institute of Neuropathology University Hospital RWTH Aachen Aachen Germany
| | - Kristl G Claeys
- Department of Neurology University Hospital RWTH Aachen Aachen Germany; Institute of Neuropathology University Hospital RWTH Aachen Aachen Germany; Department of Neurology University Hospitals Leuven and University of Leuven (KU Leuven) Leuven Belgium
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7
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Sanmaneechai O, Feely S, Scherer SS, Herrmann DN, Burns J, Muntoni F, Li J, Siskind CE, Day JW, Laura M, Sumner CJ, Lloyd TE, Ramchandren S, Shy RR, Grider T, Bacon C, Finkel RS, Yum SW, Moroni I, Piscosquito G, Pareyson D, Reilly MM, Shy ME. Genotype-phenotype characteristics and baseline natural history of heritable neuropathies caused by mutations in the MPZ gene. Brain 2015; 138:3180-92. [PMID: 26310628 DOI: 10.1093/brain/awv241] [Citation(s) in RCA: 67] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2015] [Accepted: 06/30/2015] [Indexed: 11/14/2022] Open
Abstract
We aimed to characterize genotype-phenotype correlations and establish baseline clinical data for peripheral neuropathies caused by mutations in the myelin protein zero (MPZ) gene. MPZ mutations are the second leading cause of Charcot-Marie-Tooth disease type 1. Recent research makes clinical trials for patients with MPZ mutations a realistic possibility. However, the clinical severity varies with different mutations and natural history data on progression is sparse. We present cross-sectional data to begin to define the phenotypic spectrum and clinical baseline of patients with these mutations. A cohort of patients with MPZ gene mutations was identified in 13 centres of the Inherited Neuropathies Consortium - Rare Disease Clinical Research Consortium (INC-RDCRC) between 2009 and 2012 and at Wayne State University between 1996 and 2009. Patient phenotypes were quantified by the Charcot-Marie-Tooth disease neuropathy score version 1 or 2 and the Charcot-Marie-Tooth disease paediatric scale outcome instruments. Genetic testing was performed in all patients and/or in first- or second-degree relatives to document mutation in MPZ gene indicating diagnosis of Charcot-Marie-Tooth disease type 1B. There were 103 patients from 71 families with 47 different MPZ mutations with a mean age of 40 years (range 3-84 years). Patients and mutations were separated into infantile, childhood and adult-onset groups. The infantile onset group had higher Charcot-Marie-Tooth disease neuropathy score version 1 or 2 and slower nerve conductions than the other groups, and severity increased with age. Twenty-three patients had no family history of Charcot-Marie-Tooth disease. Sixty-one patients wore foot/ankle orthoses, 19 required walking assistance or support, and 10 required wheelchairs. There was hearing loss in 21 and scoliosis in 17. Forty-two patients did not begin walking until after 15 months of age. Half of the infantile onset patients then required ambulation aids or wheelchairs for ambulation. Our results demonstrate that virtually all MPZ mutations are associated with specific phenotypes. Early onset (infantile and childhood) phenotypes likely represent developmentally impaired myelination, whereas the adult-onset phenotype reflects axonal degeneration without antecedent demyelination. Data from this cohort of patients will provide the baseline data necessary for clinical trials of patients with Charcot-Marie-Tooth disease caused by MPZ gene mutations.
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Affiliation(s)
- Oranee Sanmaneechai
- 1 Department of Neurology, University of Iowa Hospitals and Clinics, Iowa, IA, USA 2 Division of Neurology, Department of Pediatrics, Faculty of Medicine, Siriraj Hospital, Mahidol University, Bangkok, Thailand
| | - Shawna Feely
- 1 Department of Neurology, University of Iowa Hospitals and Clinics, Iowa, IA, USA
| | - Steven S Scherer
- 3 The Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - David N Herrmann
- 4 Department of Neurology, University of Rochester Medical Center, Rochester, NY, USA
| | - Joshua Burns
- 5 Arthritis and Musculoskeletal Research Group, University of Sydney / Paediatric Gait Analysis Service of NSW, Children's Hospital at Westmead, Sydney / Neuromuscular Research Group, Murdoch Childrens Research Institute, Melbourne, Australia
| | - Francesco Muntoni
- 6 University College London Institute of Child Health and Great Ormond Street Hospital, London, UK
| | - Jun Li
- 7 Department of Neurology, Vanderbilt University, Nashville, TN, USA
| | - Carly E Siskind
- 8 Department of Neurology, Stanford University, Stanford, CA, USA
| | - John W Day
- 8 Department of Neurology, Stanford University, Stanford, CA, USA
| | - Matilde Laura
- 9 MRC Centre for Neuromuscular Diseases, University College London Institute of Neurology, London, UK
| | - Charlotte J Sumner
- 10 Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Thomas E Lloyd
- 10 Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | | | - Rosemary R Shy
- 1 Department of Neurology, University of Iowa Hospitals and Clinics, Iowa, IA, USA
| | - Tiffany Grider
- 1 Department of Neurology, University of Iowa Hospitals and Clinics, Iowa, IA, USA
| | - Chelsea Bacon
- 1 Department of Neurology, University of Iowa Hospitals and Clinics, Iowa, IA, USA
| | | | - Sabrina W Yum
- 3 The Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA 13 Neuromuscular Program, Children's Hospital of Philadelphia, Philadelphia, PA, USA
| | - Isabella Moroni
- 14 Departments of Child Neurology, IRCCS Foundation, Carlo Besta Neurological Institute, Milan, Italy
| | - Giuseppe Piscosquito
- 15 Departments of Clinical Neurosciences, IRCCS Foundation, Carlo Besta Neurological Institute, Milan, Italy
| | - Davide Pareyson
- 15 Departments of Clinical Neurosciences, IRCCS Foundation, Carlo Besta Neurological Institute, Milan, Italy
| | - Mary M Reilly
- 9 MRC Centre for Neuromuscular Diseases, University College London Institute of Neurology, London, UK
| | - Michael E Shy
- 1 Department of Neurology, University of Iowa Hospitals and Clinics, Iowa, IA, USA
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Abstract
BACKGROUND Charcot-Marie-Tooth disease (CMT) is the most common inherited disorder of the peripheral nervous system. The frequency of different CMT genotypes has been estimated in clinic populations, but prevalence data from the general population is lacking. Point mutations in the mitofusin 2 (MFN2) gene has been identified exclusively in Charcot-Marie-Tooth disease type 2 (CMT2), and in a single family with intermediate CMT. MFN2 point mutations are probably the most common cause of CMT2. The CMT phenotype caused by mutation in the myelin protein zero (MPZ) gene varies considerably, from early onset and severe forms to late onset and milder forms. The mechanism is not well understood. The myelin protein zero (P(0) ) mediates adhesion in the spiral wraps of the Schwann cell's myelin sheath. X-linked Charcot-Marie Tooth disease (CMTX) is caused by mutations in the connexin32 (cx32) gene that encodes a polypeptide which is arranged in hexameric array and form gap junctions. AIMS Estimate prevalence of CMT. Estimate frequency of Peripheral Myelin Protein 22 (PMP22) duplication and point mutations, insertions and deletions in Cx32, Early growth response 2 (EGR2), MFN2, MPZ, PMP22 and Small integral membrane protein of lysosome/late endosome (SIMPLE) genes. Description of novel mutations in Cx32, MFN2 and MPZ. Description of de novo mutations in MFN2. MATERIAL AND METHODS Our population based genetic epidemiological survey included persons with CMT residing in eastern Akershus County, Norway. The participants were interviewed and examined by one geneticist/neurologist, and classified clinically, neurophysiologically and genetically. Two-hundred and thirty-two consecutive unselected and unrelated CMT families with available DNA from all regions in Norway were included in the MFN2 study. We screened for point mutations in the MFN2 gene. We describe four novel mutations, two in the connexin32 gene and two in the MPZ gene. RESULTS A total of 245 affected from 116 CMT families from the general population of eastern Akershus county were included in the genetic epidemiological survey. In the general population 1 per 1214 persons (95% CI 1062-1366) has CMT. Charcot-Marie-Tooth disease type 1 (CMT1), CMT2 and intermediate CMT were found in 48.2%, 49.4% and 2.4% of the families, respectively. A mutation in the investigated genes was found in 27.2% of the CMT families and in 28.6% of the affected. The prevalence of the PMP22 duplication and mutations in the Cx32, MPZ and MFN2 genes was found in 13.6%, 6.2%, 1.2%, 6.2% of the families, and in 19.6%, 4.8%, 1.1%, 3.2% of the affected, respectively. None of the families had point mutations, insertions or deletions in the EGR2, PMP22 or SIMPLE genes. Four known and three novel mitofusin 2 (MFN2) point mutations in 8 unrelated Norwegian CMT families were identified. The novel point mutations were not found in 100 healthy controls. This corresponds to 3.4% (8/232) of CMT families having point mutations in MFN2. The phenotypes were compatible with CMT1 in two families, CMT2 in four families, intermediate CMT in one family and distal hereditary motor neuronopathy (dHMN) in one family. A point mutation in the MFN2 gene was found in 2.3% of CMT1, 5.5% of CMT2, 12.5% of intermediate CMT and 6.7% of dHMN families. Two novel missense mutations in the MPZ gene were identified. Family 1 had a c.368G>A (Gly123Asp) transition while family 2 and 3 had a c.103G>A (Asp35Asn) transition. The affected in family 1 had early onset and severe symptoms compatible with Dejerine-Sottas syndrome (DSS), while affected in family 2 and 3 had late onset, milder symptoms and axonal neuropathy compatible with CMT2. Two novel connexin32 mutations that cause early onset X-linked CMT were identified. Family 1 had a deletion c.225delG (R75fsX83) which causes a frameshift and premature stop codon at position 247 while family 2 had a c.536G>A (Cys179Tyr) transition which causes a change of the highly conserved cysteine residue, i.e. disruption of at least one of three disulfide bridges. The mean age at onset was in the first decade and the nerve conduction velocities were in the intermediate range. DISCUSSION Charcot-Marie-Tooth disease is the most common inherited neuropathy. At present 47 hereditary neuropathy genes are known, and an examination of all known genes would probably only identify mutations in approximately 50% of those with CMT. Thus, it is likely that at least 30-50 CMT genes are yet to be identified. The identified known and novel point mutations in the MFN2 gene expand the clinical spectrum from CMT2 and intermediate CMT to also include possibly CMT1 and the dHMN phenotypes. Thus, genetic analyses of the MFN2 gene should not be restricted to persons with CMT2. The phenotypic variation caused by different missense mutations in the MPZ gene is likely caused by different conformational changes of the MPZ protein which affects the functional tetramers. Severe changes of the MPZ protein cause dysfunctional tetramers and predominantly uncompacted myelin, i.e. the severe phenotypes congenital hypomyelinating neuropathy and DSS, while milder changes cause the phenotypes CMT1 and CMT2. The two novel mutations in the connexin32 gene are more severe than the majority of previously described mutations possibly due to the severe structural change of the gap junction they encode. CONCLUSION Charcot-Marie-Tooth disease is the most common inherited disorder of the peripheral nervous system with an estimated prevalence of 1 in 1214. CMT1 and CMT2 are equally frequent in the general population. The prevalence of PMP22 duplication and of mutations in Cx32, MPZ and MFN2 is 19.6%, 4.8%, 1.1% and 3.2%, respectively. The ratio of probable de novo mutations in CMT families was estimated to be 22.7%. Genotype- phenotype correlations for seven novel mutations in the genes Cx32 (2), MFN2 (3) and MPZ (2) are described. Two novel phenotypes were ascribed to the MFN2 gene, however further studies are needed to confirm that MFN2 mutations can cause CMT1 and dHMN.
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Affiliation(s)
- G J Braathen
- Head and Neck Research Group, Research Centre, Akershus University Hospital, Lørenskog, Norway.
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9
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Myelin protein zero Val102fs mutation manifesting with isolated spinal root hypertrophy. Neuromuscul Disord 2009; 19:849-52. [DOI: 10.1016/j.nmd.2009.09.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2009] [Revised: 08/14/2009] [Accepted: 09/08/2009] [Indexed: 11/19/2022]
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10
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Plotkowski ML, Kim S, Phillips ML, Partridge AW, Deber CM, Bowie JU. Transmembrane domain of myelin protein zero can form dimers: possible implications for myelin construction. Biochemistry 2007; 46:12164-73. [PMID: 17915947 DOI: 10.1021/bi701066h] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Myelin protein zero (MPZ) is the major integral membrane protein of peripheral nerve myelin in higher vertebrates, mediating homoadhesion of the multiple, spiraling wraps of the myelin sheath. Previous studies have shown that full-length MPZ can form dimers and tetramers, and biochemical studies on the extracellular domain (ECD) indicate that it can form a tetramer, albeit very weakly. On the basis of cross-linking studies and equilibrium sedimentation of a transmembrane (TM) domain peptide (MPZ-TM), we find that the MPZ-TM can form homodimers. We further characterized the dimer by measuring the effects of alanine and leucine substitutions on the ability of the TM to dimerize in Escherichia coli membranes. Our results indicate that the primary packing interface for the MPZ TM homodimer is a glycine zipper (GxxxGxxxG) motif. We also find that the G134R mutation, which lies within the glycine zipper packing interface and causes Charcot-Marie-Tooth disease type 1B, severely inhibits dimerization, suggesting that dimerization of the TM domain may be important for the normal functioning of MPZ. By combining our new results with prior work, we suggest a new model for an MPZ lattice that may form during the construction of myelin.
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Affiliation(s)
- Megan L Plotkowski
- Department of Chemistry and Biochemistry, Molecular Biology Institute, and University of California at Los Angeles, USA
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11
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Meekins GD, Weiss MD. Electrodiagnostic Studies in a Murine Model of Demyelinating Charcot-Marie-Tooth Disease. Phys Med Rehabil Clin N Am 2005; 16:967-79, ix. [PMID: 16214054 DOI: 10.1016/j.pmr.2005.08.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Affiliation(s)
- Gregg D Meekins
- Department of Neurology, University of Washington School of Medicine, Box 356115, 1959 NE Pacific Street, Seattle, WA 98195, USA
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