The present invention provides chimeric polypeptides comprising myotubularin 1 (MTM1) polypeptides and an internalising moiety, wherein, the moiety can be an antibody, and is preferably monoclonal antibody 3E10, a functional variant or a fragment thereof. One aspect of the present invention provides compositions comprising these chimeric polypeptides together with a pharmaceutically acceptable carrier, and optionally, a further therapeutic agent. Another aspect of the present invention provides methods of treating Myotubular Myopathy comprising administering the polypeptides or compositions comprising the polypeptides to a subject in need.
