GAD1 and stiff-person syndrome: Although the truncated GAD isoforms retain enzyme activity [13] and retain antibody reactivity not only with the sera from TID patients [23], [24], but also with SPS sera [unpublished data], a major linear epitope in SPS has been described within the first 22 amino acids of the N-terminus of GAD65 [27], [35], a region lacking in the GAD65 used in this study.