GRM1 and cerebellar ataxia: Missense mutations in GRM1 were identified in two different families with an adult-onset degenerative disorder primarily causing cerebellar ataxia with some cortical involvement causing spasticity: c.2375A>G (p.Tyr792Cys) in family 1 and c.785A>G (p.Tyr262Cys) in family 2 (Figures 1A and 1B).