1. Departments of Molecular Medicine and Surgery (S.Bj., S.Be.), SE-171 76 Stockholm, Sweden;
2. Clinical Epidemiology Unit, Department of Medicine (A.S., J.F.L, P.B.), Karolinska Institutet, SE-171 76 Stockholm, Sweden;
3. Department of Paediatrics, (J.F.L.), Örebro University Hospital, SE-701 85 Örebro, Sweden;
4. Department of Medical Sciences (O.K., S.Be.), Uppsala University, SE-751 85 Uppsala, Sweden