1. From the Department of Neurosurgery (M. Korja), Helsinki University Central Hospital, Helsinki, Finland; the Department of Public Health (K.S., M. Koskenvuo, J.K.), University of Helsinki, Helsinki, Finland; the Department of Epidemiology and Public Health (P.M.), Queen’s University Belfast, Belfast, UK; the Division of Cardiovascular Epidemiology (S.Z., U.d.F.), Institute of Environmental Medicine, Karolinska Institute, Stockholm, Sweden; the Danish Twin Registry (A.S., K.C.), Institute of Public...