[1] Univ Rochester, Sch Med, Dept Neurol, Rochester, NY USA
[2] Univ Sydney, Sydney Sch Hlth Sci, Sydney, NSW, Australia
[3] Fdn IRCCS Ist Neurol Carlo Besta, Milan, Italy
[4] Univ Penn, Perelman Sch Med, Philadelphia, PA 19104 USA
[5] Univ Iowa, Dept Neurol, Carver Coll Med, Iowa City, IA 52242 USA
[6] UCL, MRC Ctr Neuromuscular Dis, London, England