MTM1 mutation associated with X-linked myotubular myopathy in Labrador Retrievers.

Abstract

Mutations in the MTM1 gene encoding myotubularin cause X-linked myotubular myopathy (XLMTM), a well-defined subtype of human centronuclear myopathy. Seven male Labrador Retrievers, age 14-26 wk, were clinically evaluated for generalized weakness and muscle atrophy. Muscle biopsies showed variability in fiber size, centrally placed nuclei resembling fetal myotubes, and subsarcolemmal ringed and central dense areas highlighted with mitochondrial specific reactions. Ultrastructural studies confirmed the centrally located nuclei, abnormal perinuclear structure, and mitochondrial accumulations. Wild-type triads were infrequent, with most exhibiting an abnormal orientation of T tubules. MTM1 gene sequencing revealed a unique exon 7 variant in all seven affected males, causing a nonconservative missense change, p.N155K, which haplotype data suggest derives from a recent founder in the local population. Analysis of a worldwide panel of 237 unaffected Labrador Retrievers and 59 additional control dogs from 25 other breeds failed to identify this variant, supporting it as the pathogenic mutation. Myotubularin protein levels and localization were abnormal in muscles from affected dogs, and expression of GFP-MTM1 p.N155K in COS-1 cells showed that the mutant protein was sequestered in proteasomes, where it was presumably misfolded and prematurely degraded. These data demonstrate that XLMTM in Labrador Retrievers is a faithful genetic model of the human condition.

• Authors: Alan H Beggs, Johann Böhm, Elizabeth Snead, Marek Kozlowski, Marie Maurer, Katie Minor, Martin K Childers, Susan M Taylor, Christophe Hitte, James R Mickelson, Ling T Guo, Andrew P Mizisin, Anna Buj-Bello, Laurent Tiret, Jocelyn Laporte, G Diane Shelton
• Journal: Proceedings of the National Academy of Sciences of the United States of America (Proc Natl Acad Sci U S A) Vol. 107 Issue 33 Pg. 14697-702 (Aug 17 2010) ISSN: 1091-6490 [Electronic] United States
• PMID: 20682747 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• Green Fluorescent Proteins
• Protein Tyrosine Phosphatases, Non-Receptor
• myotubularin

Topics

• Amino Acid Sequence
• Animals
• Base Sequence
• COS Cells
• Chlorocebus aethiops
• Dog Diseases (genetics, pathology)
• Dogs
• Female
• Fluorescent Antibody Technique, Indirect
• Genetic Diseases, X-Linked (genetics, pathology)
• Genotype
• Green Fluorescent Proteins (genetics, metabolism)
• Haplotypes
• Humans
• Male
• Mice
• Mice, Knockout
• Microscopy, Electron
• Molecular Sequence Data
• Muscle, Skeletal (metabolism, pathology, ultrastructure)
• Mutation
• Myopathies, Structural, Congenital (genetics, pathology, veterinary)
• Pedigree
• Protein Tyrosine Phosphatases, Non-Receptor (genetics, metabolism)
• Sequence Homology, Amino Acid