In parallel, analyses of Mbnl1 mutant mice (Dixon et al., 2015) and evidence that misregulation of MBNL1-splice target gene SCN5A encoding a cardiac sodium channel leads to cardiac arrhythmia and conduction delay (Freyermuth et al., 2016), indicate that Mbnl1 contributes to DM1 heart phenotypes. The gene discussed is MBNL1; the disease is cardiac arrhythmia.