Mice homozygous for a null mutation of the metabotropic glutamate receptor-subtype 1 (mGluR1) gene18 and spinocerebellar ataxia type 1 (SCA1) model mice19 have functional impairments of mGluR signaling throughout the cerebellum; both types of mice display poor performance in rotarod tests. Here, GRM1 is linked to spinocerebellar ataxia type 1.