RYR1 and myotonic dystrophy type 1: However, using RNA isolated from cultured myoblasts expressing CAG200 or CUG200 transcripts, we observed that splicing of the ryanodine receptor 1 (Ryr1), which is altered in DM1 [56], was shifted from an adult form to a neonatal form when the cells were induced to differentiate (unpublished data).