Chitotriosidase as biomarker for early stage amyotrophic lateral sclerosis: a multicenter study by Steinacker, P, Feneberg, E, Halbgebauer, S, Witzel, S, Verde, F, Oeckl, P, Van Damme, P, Gaur, N, Gray, E, Grosskreutz, J, Jardel, CG, Kachanov, M, Kuhle, J, Lamari, F, Maceski, A, del Mar Amador, M, Mayer, B, Morelli, C, Petri, S, Poesen, K, Raaphorst, J, Salachas, F, Silani, V, Turner, M, Verbeek, MM, Volk, AE, Weishaupt, JH, Weydt, P, Ludolph, AC, Otto, M