myotonic dystrophies
Etiology
myotonic dystrophy type 1 (Steinert disease) is caused by mutation in the dystrophia myotonica protein kinase gene (DMPK) (MIM.605377) at 19q13.2-q13.3.
myotonic dystrophy type 2 (Ricker syndrome) is caused by by expansion of a CCTG repeat in intron 1 of the zinc finger protein-9 gene (ZNF9) (MIM.116955) at 3q13.3-q24.