[1] Univ Oslo, Inst Clin Med, Oslo, Norway
[2] Oslo Univ Hosp, Res & Commun Unit Musculoskeletal Hlth, Oslo, Norway
[3] Lund Univ, Fac Med, Dept Clin Sci Lund, Orthopaed,Clin Epidemiol Unit, Lund, Sweden
[4] Diakonhjemmet Hosp, Oslo, Norway
[5] Norwegian Univ Sci & Technol, NTNU, Dept Publ Hlthand Nursing, KG Jebsen Ctr Genet Epidemiol, Trondheim, Norway
[6] Oslo Univ Hosp, Dept Neurol, Oslo, Norway
[7] NTNU, Dept Publ Hlth & Nursing, KG Jebsen Ctr Genet Epidemiol, Trondheim, Norway