To determine the contribution of CUGBP1REP to cognitive dysfunction in CDM1 and DM1, we began behavioral analysis of S302A-CUGBP1 KI mice, in which CUGBP1 was un-phosphorylatable at S302 by the GSK3β-CDK4 pathway [26]. This evidence concerns the gene GSK3B and myotonic dystrophy type 1.