GAD2 and viral encephalitis: This multi‐center retrospective study enrolled 390 participants: 222 definite AE patients (comprising four subtypes: LGI1‐AE, NMDAR‐AE, GABAB‐AE, GAD65‐AE), 122 age‐ and sex‐matched healthy controls, and 33 age‐ and sex‐matched antibody‐negative AE patients along with 13 age‐ and sex‐matched viral encephalitis patients, both serving as disease controls.