GAD1 and stiff-person syndrome: Solimena et al., 1988, Lohmann et al., 2000 identified SPS as a distinct autoimmune disease, and over 70 % of SPS cases are associated with the presence of serum anti-glutamic acid decarboxylase (GAD) antibodies (anti-GAD antibodies) (Lee et al., 2019)—a marker first proposed for inclusion in SPS diagnostic criteria by Gordon et al. (1967).