Pathological changes in muscle biopsies were consistent with a myotubular myopathy and a missense mutation, p.(N155K), was identified in exon 7 of canine MTM1. Here we describe, compare, and contrast the clinical presentation, histopathology, muscle ultrastructure, and a second independent mutation of MTM1 in a family of Rottweiler dogs from Australia. This evidence concerns the gene MTM1 and centronuclear myopathy.