ATXN8OS and myotonic dystrophy type 1: The first dominant noncoding repeat expansion disorders described were myotonic dystrophy type 1 (DM1) and spinocerebellar type 8 (SCA8), caused by CTG expansions in the 3′UTRs of DMPK (dystrophia myotonica protein kinase, MIM #605377) [56] and ATXN8OS (ATXN8 Opposite Strand LncRNA, MIM #603680) [50], respectively (Table 1).