Article Abstract

Muscle pathology, limb strength, walking gait, respiratory function and neurological impairment establish disease progression in the p.N155K canine model of X-linked myotubular myopathy

Authors: Melissa A. Goddard, David L. Mack, Stefan M. Czerniecki, Valerie E. Kelly, Jessica M. Snyder, Robert W. Grange, Michael W. Lawlor, Barbara K. Smith, Alan H. Beggs, Martin K. Childers


Background: Loss-of-function mutations in the myotubularin (MTM1) gene cause X-linked myotubular myopathy (XLMTM), a fatal, inherited pediatric disease that affects the entire skeletal musculature. Labrador retriever dogs carrying an MTM1 missense mutation exhibit strongly reduced synthesis of myotubularin, the founder member of a lipid phosphatase required for normal skeletal muscle function. The resulting canine phenotype resembles that of human patients with comparably severe mutations, and survival does not normally exceed 4 months.
Methods: We studied MTM1 mutant dogs (n=7) and their age-matched control littermates (n=6) between the ages of 10 and 25 weeks. Investigators blinded to the animal identities sequentially measured limb muscle pathology, fore- and hind limb strength, walking gait, respiratory function and neurological impairment.
Results: MTM1-mutant puppies display centrally-nucleated myofibers of reduced size and disrupted sarcotubular architecture progressing until the end of life, an average of 17 weeks. In-life measures of fore- and hind limb strength establish the rate at which XLMTM muscles weaken, and their corresponding decrease in gait velocity and stride length. Pulmonary function tests in affected dogs reveal a right-shifted relationship between peak inspiratory flow (PIF) and inspiratory time (TI); neurological assessments indicate that affected puppies as young as 10 weeks show early signs of neurological impairment (neurological severity score, NSS =8.6±0.9) with progressive decline (NSS =5.6±1.7 at 17 weeks-of-age).
Conclusions: Our findings document the rate of disease progression in a large animal model of XLMTM and lay a foundation for preclinical studies.