DMPK and myotonic dystrophy type 1: DM1 is viewed as an RNA gain of function disorder, wherein a CTG expansion in the 3′ untranslated region of the myotonic dystrophy protein kinase (DMPK) gene causes the accumulation of expanded transcripts as intranuclear RNA foci, which sequester a number of splicing factors, resulting in loss of function and downstream deregulation of the alternative splicing of several genes [1].