[1] Harvard Univ, Sch Med, Massachusetts Gen Hosp, Neurol Clin Trials Unit, Charlestown, MA 02129 USA
[2] Harvard Univ, Sch Med, Massachusetts Gen Hosp, Dept Neurol, Charlestown, MA 02129 USA
[3] Harvard Univ, Sch Med, Massachusetts Gen Hosp, Biostat Ctr,Dept Med, Charlestown, MA 02129 USA
[4] Harvard Univ, Sch Med, Massachusetts Gen Hosp, Day Neuromuscular Res Lab, Charlestown, MA 02129 USA