DMPK and myotonic dystrophy: Based on the toxic RNA gain of function model for myotonic dystrophy, in which disease pathogenesis involves the sequestration of one or more proteins by an expanded rCUG repeat in the 3' untranslated region of the myotonic dystrophy protein kinase (DMPK) gene [91,92], the first view of FXTAS envisioned a similar, direct-RNA mechanism in which proteins would be sequestered by the expanded CGG repeat [19,65,67,69].