The mutant DMPK mRNA with the CUGexp repeats accumulates in the nucleus as a ribonuclear foci folding into ‘RNA hairpins’, sequestering and deregulating RNA-binding proteins (RBP) crucial for alternative cell processing of other genes and/or mRNAs, leading to the complexity of the DM1 phenotype. Here, DMPK is linked to myotonic dystrophy type 1.