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Anton E Tjust, Adam Danielsson, Peter M Andersen, Fatima Pedrosa Domellof; Loss of myofibers containing MyHC Slow tonic in extraocular muscles of terminal ALS patients with bulbar onset. Invest. Ophthalmol. Vis. Sci. 2016;57(12):No Pagination Specified.
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© ARVO (1962-2015); The Authors (2016-present)
The extraocular muscles (EOMs) are relatively spared even in terminal amyotrophic lateral sclerosis (ALS) although there is substantial variability in the extent of pathological changes. Here, we investigated the EOMs of terminal ALS patients for changes in the content of myofibers containing myosin heavy chain (MyHC) slow-tonic, as these are innervated by a subset of motor neurons with other cell surface markers and a different anatomical position compared to motor neurons innervating other myofibers.
Immunofluorescence was used to study the proportion of MyHC slow-tonic myofibers in cross-sections of the medial rectus in 7 ALS cases with spinal onset, 9 ALS cases with bulbar onset, and 6 healthy controls. A minimum of 1400 myofibers were classified in the orbital and global layers, respectively.
One-way ANOVA with Sidak post-hoc correction showed that the percentage of MyHC slow-tonic myofibers in relation to total myofibers was significantly decreased in the global layer of bulbar onset ALS patients (10,5±2,5%) compared to patients with spinal onset (p<0,048 – 13,8±2,7%) and healthy controls (p<0,022 –14,4±2,0%). Morphologically, the bulbar onset cases seemed to exhibit a considerable number of atrophic MyHC slow-tonic myofibers. Quantitative investigation of the cross-sectional area of MyHC slow-tonic myofibers is currently underway.
These data suggest a higher susceptibility to ALS in a subgroup of muscle fibers in the EOMs. The next step will be to investigate the oculomotor nuclei of these ALS cases and compare them with oculomotor nuclei of donors not suffering from ALS, in order to better understand whether the present findings reflect loss of a particular subpopulation of motor neurons or fiber-specific susceptibility.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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