About 20 years ago, while studies following the discovery of the DM1 peculiar mutation concentrated mainly on CTG metabolism and direct consequences on neighboring genes, identification of the CCTG expansion in DM2 (in the CNBP gene on chromosome 3) helped to provide important milestones to understand how a single mutation can affect so many tissues with such high variability (Liquori et al., 2001). Here, CNBP is linked to myotonic dystrophy type 1.