1. Department of Clinical Biochemistry, University of Cambridge, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QR, U.K.
2. Jerry Lewis Muscle Research Centre, Hammersmith Hospital, Ducane Road, London W12 OHS, U.K.
3. Department of Medical Biochemistry, University of Wales College of Medicine, Heath Park, Cardiff CF4 4XN, U.K.