To better understand the endocytic degradative pathway in DM1 HFs, we first characterized the endosomes through the detection of the early endosomal antigen-1 (EEA1), a RAB5-effector that binds phosphatidylinositol-3 phosphate [PI(3)P] via its FYVE domain [31]. This evidence concerns the gene RAB5A and myotonic dystrophy type 1.