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

Division of Genetics and Program in Genomics, The Manton Center for Orphan Disease Research at Children's Hospital Boston and Harvard Medical School, Boston, MA 02115, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 08/2010; 107(33):14697-702. DOI: 10.1073/pnas.1003677107
Source: PubMed


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.

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    • "Clinically, there was severe muscle atrophy. Histologically there were numerous small centrally-nucleated myofibres, resembling myotubes, necklace myofibres, abnormal localization of RYR1 and DHPR and diminished and disturbed T tubule structures (Beggs et al., 2010). Thus in both non-mammalian and mammalian models (small and large) the pathophysiology of MTM1-related disease is remarkably similar and consistent with functionally important abnormalities of triadic structure with consequences on excitation-contraction coupling. "
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    ABSTRACT: The congenital myopathies are a diverse group of genetic skeletal muscle diseases, which typically present at birth or in early infancy. There are multiple modes of inheritance and degrees of severity (ranging from foetal akinesia, through lethality in the newborn period to milder early and later onset cases). Classically, the congenital myopathies are defined by skeletal muscle dysfunction and a non-dystrophic muscle biopsy with the presence of one or more characteristic histological features. However, mutations in multiple different genes can cause the same pathology and mutations in the same gene can cause multiple different pathologies. This is becoming ever more apparent now that, with the increasing use of next generation sequencing, a genetic diagnosis is achieved for a greater number of patients. Thus, considerable genetic and pathological overlap is emerging, blurring the classically established boundaries. At the same time, some of the pathophysiological concepts underlying the congenital myopathies are moving into sharper focus. Here we explore whether our emerging understanding of disease pathogenesis and underlying pathophysiological mechanisms, rather than a strictly gene-centric approach, will provide grounds for a different and perhaps complementary grouping of the congenital myopathies, that at the same time could help instil the development of shared potential therapeutic approaches. Stemming from recent advances in the congenital myopathy field, five key pathophysiology themes have emerged: defects in (i) sarcolemmal and intracellular membrane remodelling and excitation-contraction coupling; (ii) mitochondrial distribution and function; (iii) myofibrillar force generation; (iv) atrophy; and (v) autophagy. Based on numerous emerging lines of evidence from recent studies in cell lines and patient tissues, mouse models and zebrafish highlighting these unifying pathophysiological themes, here we review the congenital myopathies in relation to these emerging pathophysiological concepts, highlighting both areas of overlap between established entities, as well as areas of distinction within single gene disorders. Published by Oxford University Press on behalf of the Guarantors of Brain 2014. This work is written by US Government employees and is in the public domain in the US.
    Brain 12/2014; 138(2). DOI:10.1093/brain/awu368 · 9.20 Impact Factor
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    • "Use and care of animals followed principles outlined in the National Institutes of Health Guide for the Care and Use of Laboratory Animals. Affected XLMTM dogs from two litters were identified just after birth by Taqman genotyping assay, as previously described [12]. XLMTM dogs (N = 3) and their true littermate controls (N = 3) were then assessed at 4–5 time points, beginning at 10 weeks and continuing through 17 weeks for litter A and 15 weeks for litter B. The cranial tibialis muscle of the left hind limb of affected dogs was injected at 10 weeks of age with AAV8-cMTM1 (4 × 10 11 viral genomes) diluted in 1 mL lactated Ringer's solution, as described previously [10]. "
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    ABSTRACT: X-linked myotubular myopathy (XLMTM) is a fatal pediatric disease where affected boys display profound weakness of the skeletal muscles. Possible therapies are under development but robust outcome measures in animal models are required for effective translation to human patients. We established a naturally-occurring canine model, where XLMTM dogs display clinical symptoms similar to those observed in humans. The aim of this study was to determine potential endpoints for the assessment of future treatments in this model. Video-based gait analysis was selected, as it is a well-established method of assessing limb function in neuromuscular disease and measures have been correlated to the patient's quality of life. XLMTM dogs (N=3) and their true littermate wild type controls (N=3) were assessed at 4-5 time points, beginning at 10weeks and continuing through 17weeks. Motion capture and an instrumented carpet were used separately to evaluate spatiotemporal and kinematic changes over time. XLMTM dogs walk more slowly and with shorter stride lengths than wild type dogs, and these differences became greater over time. However, there was no clear difference in angular measures between affected and unaffected dogs. These data demonstrate that spatiotemporal parameters capture functional changes in gait in an XLMTM canine model and support their utility in future therapeutic trials.
    Journal of the Neurological Sciences 08/2014; 346(1-2). DOI:10.1016/j.jns.2014.08.032 · 2.47 Impact Factor
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    • "We have identified a novel canine CMS in a family of Labrador Retrievers. Affected littermates exhibited signs clinically distinct from neuromuscular disorders previously characterized in the breed: exercise-induced collapse (EIC) [14], centronuclear myopathy (CNM) [15], and myotubular myopathy [16]. "
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    PLoS ONE 08/2014; 9(8):e106425. DOI:10.1371/journal.pone.0106425 · 3.23 Impact Factor
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