As shown in animal studies (Aiba et al., 1994; Ichise et al., 2000; Notartomaso et al., 2013; Sillevis Smitt et al., 2000), the reduction in cerebellar mGluR1 availability was recently confirmed to possibly be associated with the development of cerebellar ataxia in human patients using PET imaging of mGluR1 (Ishibashi et al., 2016; Ishibashi et al., 2017). This evidence concerns the gene GRM1 and cerebellar ataxia.