NTRK3 and cerebellar ataxia: Mice deficient in NT-3, its tyrosine kinase receptor, TrkC, or in TrkC-positive neuron-specific transcription factor Runx3 display severe ataxia associated with the absence of muscle spindles, and loss of proprioceptive neurons in dorsal root ganglia (DRGs) or their axons (Ernfors et al. 1994; Klein et al. 1994; Tessarollo et al. 1994; Fariñas et al. 1996; Liebl et al. 1997; Inoue et al. 2002; Levanon et al. 2002).