[1] UNIV PENN, SCH MED, DEPT NEUROL, PHILADELPHIA, PA 19104 USA
[2] UNIV MILAN, DINO FERRARI CTR NEUROMUSCULAR DIS, DEPT NEUROL, I-20122 MILAN, ITALY
[3] CHILDRENS HOSP, DEPT NEUROL, PHILADELPHIA, PA 19104 USA
[4] CHILDRENS HOSP, DEPT OBSTET & GYNECOL, PHILADELPHIA, PA 19104 USA
[5] CHILDRENS HOSP, SCH MED, PHILADELPHIA, PA 19104 USA