In 2-month old Ryr1AG/+ muscle, we observed ultrastructural hallmarks of RyR1-associated myopathies (Boncompagni et al., 2009, 2010), including z-line streaming (white arrows in Figure 1J: Table 2), sarcomeric degeneration, irregularly shaped mitochondria, core-like structures (white arrow in Figure 1K), and swelling of the t-tubules (Figure 1L) as well as internalized nuclei (9.8 ± 4.9 per 100 myofibers vs none detected in wild-type). This evidence concerns the gene RYR1 and myopathy.