[1] Mayo Clin, Dept Hlth Sci Res, Div Epidemiol, Coll Med, Rochester, MN 55905 USA
[2] Mayo Clin, Dept Hlth Sci Res, Div Biostat, Coll Med, Rochester, MN 55905 USA
[3] Mayo Clin, Coll Med, Dept Neurol, Rochester, MN USA
[4] INSERM, U708, Inst Natl Sante & Rech Med, F-75013 Paris, France