Studies of Great Danes with Inherited Myopathy (also called "Central Core Myopathy"), which results in debilitating muscle weakness and wasting, exercise intolerance, and collapse, have identified a defect in the BIN1 gene. This gene encodes for a protein called amphiphysin 2, which plays a critical role in maintaining the ability of muscles to respond to the nerve signals that result in muscle contraction. (You can read more about it here.)
Bohm et al 2013 Altered splicing of the BIN1 muscle-specific exon in humans and dogs with highly progressive centronuclear myopathy. PLoS Genet 9(6): e1003430. doi:10.1371/journal.pgen.1003430 (pdf)
Bohm et al 2013 Altered splicing of the BIN1 muscle-specific exon in humans and dogs with highly progressive centronuclear myopathy. PLoS Genet 9(6): e1003430. doi:10.1371/journal.pgen.1003430 (pdf)