From the Departments of Laboratory Medicine and Pathology (J.A.H., T.J.K., S.R.H., V.A.L., S.J.P., C.J.K., A.M.), Neurology (A.S.L.-C., V.A.L., S.J.P., C.J.K., A.M.), and Immunology (V.A.L.), College of Medicine, Mayo Clinic, Rochester, MN; and Euroimmun, AG (L.K., M.S.), Lubeck, Germany.