Patients from each research site, with definite PM, DM or IBM, will be asked by their own consultants (Principal Investigator) to give 20 mls of blood via venepuncture for genetic and antibody analysis. The PI will also complete a clinical/laboratory proforma, for each patient, regarding their disease characteristics, to allow subsequent confirmation that patients' disease is indeed definite, and this proforma and the blood sample will be sent to CIGMR. All of the genetic analyses, will take place at CIGMR, but storage of clinical details and certain patient identifiers will be stored at SRFT on a password protected NHS tust computer.