In the brains of patients with DM1, mutant DMPK RNA accumulates extensively as nuclear RNA foci, sequestering RNA-binding proteins such as MBNL proteins and affecting their function, which leads to splicing defects in a variety of pre-mRNAs and misexpression of different protein isoforms (43, 44). The gene discussed is DMPK; the disease is myotonic dystrophy type 1.