ITPR1 and spinocerebellar ataxia type 15/16: Insufficient levels of IP3R1 remarkably disrupt Purkinje neuron function, as observed in ataxia (SCA15 van de Leemput et al., 2007; Hara et al., 2008; Iwaki et al., 2008; Di Gregorio et al., 2010; Novak et al., 2010a,b; Marelli et al., 2011).