CELF1 and myotonic dystrophy: There have been 2 genetically distinct forms of myotonic dystrophy identified (type 1 is due to a trinucleotide repeat expansion of the DMPK gene on chromosome 19, and type 2 is associated with a 4-nucleotide repeat in the ZNF9 gene on chromosome 3).26,27 These mutations interfere with RNA-binding proteins, leading to increased levels of CUGBP1/Elav-like family member 1 (CELF1) and decreased levels of muscleblind-like proteins (MBNLs), which are sequestered in ribonuclear foci.