[1] Univ London Imperial Coll Sci Technol & Med, Dubowitz Neuromuscular Unit, London, England
[2] MRC, Muscle Cell Biol Grp, London, England
[3] Royal Free Hosp, Ctr Rheumatol, London NW3 2QG, England
[4] Harefield Hosp, Harefield UB9 6JH, Middx, England