[1] Univ Calif Davis, Dept Rehabil Med, Sacramento, CA 95817 USA
[2] Childrens Natl Med Ctr, Ctr Genet Med, Washington, DC 20010 USA
[3] Univ Pittsburgh, Dept Neurol, Pittsburgh, PA 15213 USA
[4] Dept Vet Affairs Med Ctr, Neurol Serv, Pittsburgh, PA 15240 USA