Antibody-mediated autoimmunity in symptom-based disorders: position statement and proceedings from an international workshop by Mountford, R, Adler, BL, Andersson, D, Bashford-Rogers, R, Berwick, R, Bevan, S, Caro, X, Chung, TH, Clark, JD, Dawes, JM, Dong, X, Helyes, Z, Kingery, W, van Middendorp, JJ, Neiland, H, Maurer, M, Scheibenbogen, C, Schmack, K, Schreiner, T, Svensson, CI, Tékus, V, Goebel, A