Though autoimmune cerebellar ataxia is more common in mGluR1 encephalitis (10), a 29-year-old man with bilateral horizontal nystagmus, ataxia after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination, was reported with mGluR5 antibodies in the cerebrospinal fluid and serum, with abnormal signals in the splenium of the corpus callosum rather than cerebellum (7). The gene discussed is GRM1; the disease is Horizontal nystagmus.