Here we report that smaug, a gene not previously known to be implicated in DM1, is a powerful suppressor of CUG-induced myopathy when overexpressed in Drosophila. We show that human SMAUG1 protein (a.k.a SAMD4A) interacts with CUGBP1 and decreases its abnormally high steady-state levels in DM1 nuclei. Here, SAMD4A is linked to myotonic dystrophy type 1.