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"Necklace" fibers, a new histological marker of late-onset MTM1-related centronuclear myopathy.

Journal article
Authors Jorge A Bevilacqua
Marc Bitoun
Valérie Biancalana
Anders Oldfors
Gisela Stoltenburg
Kristl G Claeys
Emmanuelle Lacène
Guy Brochier
Linda Manéré
Pascal Laforêt
Bruno Eymard
Pascale Guicheney
Michel Fardeau
Norma Beatriz Romero
Published in Acta neuropathologica
Volume 117
Issue 3
Pages 283-91
ISSN 1432-0533
Publication year 2009
Published at Institute of Biomedicine, Department of Pathology
Pages 283-91
Language en
Links dx.doi.org/10.1007/s00401-008-0472-...
Keywords Adolescent, Adult, Age of Onset, Biopsy, Female, Humans, Immunohistochemistry, Magnetic Resonance Imaging, Male, Microscopy, Electron, Middle Aged, Muscle Fibers, Skeletal, metabolism, pathology, ultrastructure, Muscle, Skeletal, pathology, ultrastructure, Mutation, Myofibrils, ultrastructure, Myopathies, Structural, Congenital, genetics, metabolism, pathology, Polymerase Chain Reaction, Protein Tyrosine Phosphatases, Non-Receptor, genetics, metabolism
Subject categories Cell and Molecular Biology

Abstract

Mutations in the gene encoding the phosphoinositide phosphatase myotubularin 1 protein (MTM1) are usually associated with severe neonatal X-linked myotubular myopathy (XLMTM). However, mutations in MTM1 have also been recognized as the underlying cause of "atypical" forms of XLMTM in newborn boys, female infants, female manifesting carriers and adult men. We reviewed systematically the biopsies of a cohort of patients with an unclassified form of centronuclear myopathy (CNM) and identified four patients presenting a peculiar histological alteration in some muscle fibers that resembled a necklace ("necklace fibers"). We analyzed further the clinical and morphological features and performed a screening of the genes involved in CNM. Muscle biopsies in all four patients demonstrated 4-20% of fibers with internalized nuclei aligned in a basophilic ring (necklace) at 3 microm beneath the sarcolemma. Ultrastructurally, such necklaces consisted of myofibrils of smaller diameter, in oblique orientation, surrounded by mitochondria, sarcoplasmic reticulum and glycogen granules. In the four patients (three women and one man), myopathy developed in early childhood but was slowly progressive. All had mutations in the MTM1 gene. Two mutations have previously been reported (p.E404K and p.R241Q), while two are novel; a c.205_206delinsAACT frameshift change in exon 4 and a c.1234A>G mutation in exon 11 leading to an abnormal splicing and the deletion of nine amino acids in the catalytic domain of MTM1. Necklace fibers were seen neither in DNM2- or BIN1-related CNM nor in males with classical XLMTM. The presence of necklace fibers is useful as a marker to direct genetic analysis to MTM1 in CNM.

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