J Neurol (2012) 259:1814–1823 based on prior immunosuppressant therapy, anti-John Cunningham (JC) virus antibody status, and treatment duration [2 years [21]. The antibody status in these patients was unknown. Almost 10% of our patients had received prior immunosuppressive therapy and 21% had received more than 2 years of treatment and none of these had developed PML at the time of data collection, apart from the above-mentioned cases. In conclusion, the present observational study in a large population provides further support for the efﬁcacy of na- talizumab in a clinical practice setting. The sharp decrease in relapse rate in the year following initiation of natalizumab treatment in patients with more severe disease than those included in the pivotal trial was in line with other observa- tional studies performed in different countries, with different methodologies and with different treatment protocols. Acknowledgments The authors would like to thank Biogen Idec Iberia S.L. for ﬁnancial support and Dr. Gregory Morley for editorial assistance. Conﬂicts of interest The corresponding author Oscar Ferna´ndez, Rafael Arroyo, and Guillermo Izquierdo have received honoraria as consultants in advisory boards, and as chairmen or lecturers in meetings, and have also participated in clinical trials and other research projects sponsored by Biogen-Idec, Bayer-Schering, Merck- Serono, Teva, Novartis, and Sanoﬁ-Aventis. Celia Oreja-Guevara has received honoraria for speaking and/or consultancy from Biogen- Idec, Bayer-Schering, Merck-Serono, Teva, Sanoﬁ-Aventis, and Novartis. Xavier Montalban has received speaking honoraria and travel expenses for scientiﬁc meetings, and has been a steering committee member of clinical trials or participated in advisory boards of clinical trials in the past years with Bayer Schering Pharma, Biogen Idec, EMD Merck Serono, Genentech, Genzyme, Novartis, Sanoﬁ- Aventis, Teva Pharmaceuticals, and Almirall. Jose´ Luis Pe´rez declares no conﬂicts of interest. Open Access This article is distributed under the terms of the Creative Commons Attribution License which permits any use, dis- tribution, and reproduction in any medium, provided the original author(s) and the source are credited. Appendix GEXNE Group: authors (hospital) (number of patients included in the study) Montalba´n Gair´ın, X., Tintore´, M. (H. Universitario Vall d0Hebron - CEM-Cat, Barcelona) (110); Ferna´ndez, O´ ., Guerrero M., Leo´n A, Alonso A., Ferna´ndez V., Leyva L. (H. Regional Universitario Carlos Haya, Ma´laga) (96); A´ lvarez Lafuente, R., Arroyo Gonza´lez, R., (H. Cl´ınico San Carlos, Madrid) (90); Gamero, M.A., Garc´ıa Moreno, J.M., Izquierdo Ayuso, G., Navarro Mascarell, G., Pa´ramo Camino, M.D., Ruiz-Pen˜a, J.L. (H. Universitario Virgen Macarena, Sevilla) (88); Pe´rez Lo´pez, J.L. (H. Sierrallana, 1821 Torrelavega) (68); Arbizu Urdia´ın, T. (H. de Bellvitge, Barcelona) (55); Ma´laga, I., Oliva Nacarino, P., Tun˜o´n A´ lvarez, A. (H. General de Asturias, Oviedo) (41); Ayuso Blanco, T., Bujanda Alegr´ıa, M., Lacruz Bescos, F., Sori- ano Herna´ndez, G. (Complejo Hospitalario de Navarra, H. A, Pamplona) (38); Herna´ndez Clares, R., Meca Lallana, J.E. (H. Virgen de La Arrixaca, Murcia) (35); Herna´ndez, M.A. (H. Universitario Ntra. Sra. de la Candelaria, Tene- rife) (32); Aguilar-Amat, M.J., Ferna´ndez Pe´rez, M., Oreja- Guevara, C. (H. Universitario La Paz, Madrid) (31); Ramio´ i Torrenta, L. (H. Universitario Dr. Josep Trueta, Girona) (28); Agu¨era Morales, E., Sa´nchez Lo´pez, F. (H. Univer- sitario Reina Sof´ıa, Co´rdoba) (25); A´ lvarez-Cermen˜o, J.C., Costa-Frossard, L. (H. Ramo´n y Cajal, Madrid) (24); Mu- n˜oz Garc´ıa, M. (H. Xeral-C´ıes, Vigo) (23); Coret Ferrer, F., Navarre´-Gimeno A. (H. Cl´ınico Universitario Valencia, Valencia) (22); Asensio Huerga, A.B., Olascoaga, J. (H. Donostia, San Sebastia´n) (22); de Andre´s Frutos, C., Mart´ınez Gine´s, M.L. (H. General Universitario Gregorio Maran˜o´n, Madrid) (22); Arnal Garc´ıa, C. (H. Virgen de las Nieves, Granada) (22); Milla´n-Pascual, J., Turp´ın Fenoll, L. (Complejo Hospitalario La Mancha - Centro, Alcazar de San Juan) (20); Alarcia, R., Ara, J.R., Sa´nchez-Carteyron, A. (H. Universitario Miguel Servet, Zaragoza) (20); Blanco, Y. Saiz, A. (H. Clinic. IDIBAPS, Barcelona) (19); Pe´rez Sempere, A. (H. General Alicante, Alicante) (18); Padilla Parrado, F. (H. Cl´ınico Universitario Virgen de La Victoria, Ma´laga) (17); Argente, J. H. Universitario Puerta Del Mar, Ca´diz) (16); Arias, M., Dapena, M.D. (H. Cl´ınico Universitario Santiago de Compostela, Santiago de Com- postela) (15); Pe´rez Ruiz, D. (H. Comarcal El Bierzo, Leo´n) (15); Ferias, I., Gracia Gil, J., Rallo Gutie´rrez, B. (H. General de Albacete, Albacete) (15); Carrera, D., Ramos, C. (H. Germans Trias i Pujol, Badalona) (15); Barrero, F.J., Ferna´ndez-Ortega, J.D. (H. San Cecilio, Granada) (15); Yusta Izquierdo, A. (H. Universitario de Guadalajara, Guadalajara) (15); Oterino Dura´n, A. (H. Universitario Marque´s de Valdecilla, Santander) (15); Sua´rez Moro, R. (H. Valle del Nalo´n, Langreo) (14); Ferna´ndez-Bolan˜os Porras, R. (H. Universitario de Valme, Sevilla) (13); Otano, M. (Complejo Hospitalario de Navarra, H. B, Pamplona) (13); Cervello´ , A., Parra Mart´ınez, J. (Consorcio H. Gen- eral Universitario Valencia, Valencia) (12); Fraile, A., Te´llez, N. (H. Cl´ınico Universitario de Valladolid, Valla- dolid) (12); Bonaventura, I. (H. Mutua de Terrassa, Ter- rassa) (12); Bowakim Dib, W., Tola-Arribas, M.A. (H. Universitario R´ıo Hortega, Valladolid) (12); Munteis, E. (H. del Mar, Barcelona) (11); I´n˜iguez, C. (H. Cl´ınico Universitario Lozano Blesa, Zaragoza) (10); Are´s-Luque, A., Villafani-Echazu´, J. (H. de Leo´n, Leo´n) (10); Iglesias, F. (H. General Yagu¨e, Burgos) (10); Marzo, M.E. (H. San Pedro, Logron˜o) (9); Escartin, A., Lo´pez Gonza´lez, M. (H. Santa Creu i Sant Pau, Barcelona) (9); Marco Igual, M. (H. 123