MAPT and myotonic dystrophy type 1: More specifically, expanded CTG repeats in the non-coding regions of the DMPK gene lead to the accumulation of mutated RNA in the nucleus, where the resulting nuclear foci sequester RNA-binding proteins and disrupt RNA metabolism and splicing.2 Simultaneously, myotonic dystrophy Type 1 is also a tauopathy characterized by the accumulation of neurofibrillary tangles in the brain.2 The progression of age-related brain volume loss in myotonic dystrophy Type 1 is presumed to be associated with the gradual accumulation of mutated RNA and tau over time.