or null mutations in the ionotropic glutamate receptor gene GRID2 (MIM: 602368)33, 34, 35, 36, 37 all showed evidence of developmental delay and intellectual deficit in addition to cerebellar ataxia, similar to the individual carrying a de novo GRM1 nonsense frameshift mutation described here, albeit to a larger extent. Here, GRM1 is linked to cerebellar ataxia.