GRM1 and Ataxia: Mutations in several genes with known functions related to calcium homeostasis cause monogenetic forms of ataxia, including those encoding the P type voltage-gated Ca2+ channel (Zhuchenko et al., 1997), mGluR1 (Guergueltcheva et al., 2012), the type 1 IP3R (van de Leemput et al., 2007), the type 3 Ca2+ ATPase (Zanni et al., 2012; Calì et al., 2015), and possibly TRPC3 (Fogel et al., 2015).