MBNL1 and myotonic dystrophy type 1: As previous studies have shown marked sequestration of MBNL1 in CUG foci both in skeletal muscle and heart cells (35,36), it has been hypothesized that MBNL1 depletion occurring as a consequence of aberrant sequestration, is a key mechanism that underlies the functional inactivation of MBNL1 in DM1.