[1] Univ Southern Calif, Keck Sch Med, Dept Neurol, Los Angeles, CA 90007 USA
[2] Stanford Univ, Dept Epidemiol & Populat Hlth, Stanford, CA 94305 USA
[3] Stanford Univ, Dept Neurol & Neurol Sci, Stanford, CA 94305 USA
[4] Stanford Univ, Dept Neurol & Neurol Sci, Sch Med, Stanford, CA 94305 USA