GRM1 and aceruloplasminemia: Mutations in the mGluR1 gene itself also cause spinocerebellar ataxia, irrespective of whether these mutations are gain or loss of function mutations (Watson et al., 2017) and autoantibodies against mGluR1 are a common cause of autoimmune or paraneoplastic cerebellar ataxia (Joubert and Honnorat, 2019).