These two forms of the disease differ at the genetic level, with DM1 stemming from an expanded CTG triplet in the DMPK gene on chromosome 19 and DM2 resulting from an expansion of a CCTG tetramer in the CNBP gene, also known as ZNF9, in chromosome 3 (1, 2). The gene discussed is CNBP; the disease is myotonic dystrophy type 1.