[1] Penn State Univ, Dept Neurol, Hershey Med Ctr, Hershey, PA 17033 USA
[2] Med Univ South Carolina, Dept Neurol, Charleston, SC 29425 USA
[3] Univ Cape Town, Cape Town, South Africa
[4] South African Med Res Council, Cape Town, South Africa
[5] Penn State Coll Med, Dept Publ Hlth Sci, Hershey, PA USA