CFTR and cerebellar ataxia: Indeed, in mutant mice that lack granule cells or functional PFs, such as weaver, reeler and staggerer as well as X-irradiated mice, the transition from multiple to single CF innervation is defective so that multiple innervation of PCs by CFs persists into the adult stage and is associated with ataxia and loss of motor coordination (Crepel et al., 1980; Crepel, 1982; Hashimoto and Kano, 2013).