MSH3 and myotonic dystrophy type 1: Our evidence that repeat interruptions can positively modulate age at onset in DM1 patients, through stabilizing effect on DMPK expansions in somatic cells, is in line with the results showing that suppression of somatic instability of CAG expansions substantially delayed the onset of symptoms in HD mouse models with deletion of certain repair genes (Ogg1, Msh2 and Msh3) (Wheeler et al., 2003; Dragileva et al., 2009; Budworth et al., 2015).